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Biodegradable Interference Screw Fixation Exhibits Pull-Out Force and Stiffness Similar to Titanium Screws
Abstract
Recently, increased interest in biodegradable interference screws for bone-tendon-bone graft fixation has led to numerous screws becoming available. The implants are made from different polymers and have different designs, which might influence their mechanical properties. Several studies have reported a wide range of mechanical results for these screws using different biomechanical models. The aim of the present study is to compare reliable biomechanical data for six different biodegradable interference screws, consisting of five different polymers, with a conventional titanium screw in a standardized model. Seventy proximal calf tibias were used to determine maximal pull-out force, stiffness of fixation, and insertion torque for interference screw fixation of bone-tendon-bone grafts. Additionally, maximal torque at failure was determined. Data were analyzed with respect to aspects of screw design, such as drive and thread shape. Five of the six biodegradable screws provided initial pull-out force and stiffness of fixation comparable with that of a conventional titanium screw. Torque at failure can be greatly increased by adapting the drive design to the mechanical properties of the polymeric raw material. A correlation between pull-out force and thread height indicates that fixation rigidity depends on screw design, even in a biodegradable implant.
... ± 66.5 N, and elongation of 5.1 ± 0.5 mm vs. 5.1 ± 0.4 mm, comparable to the results of the present study [15]. Further studies compared different biodegradable IFS to titanium IFS, with no significant differences between biodegradable and titanium implants, regarding both biomechanical primary stability, as well as clinical outcome [9,14,29,46]. Exemplary, Weiler et al. compared six different biodegradable IFS to a titanium IFS, finding mean load to failure values ranging from 439.2 to 830.2 N for the biodegradable implants, compared to 821.6 ± 129.8 N for the titanium implant [46]. These results, although not directly comparable due to differences in biomechanical testing and experimental setup, are similar to the findings of the present study, which reported load to failure of 683.9 ± 116.5 N for the tested Mg-IFS. ...
... Further studies compared different biodegradable IFS to titanium IFS, with no significant differences between biodegradable and titanium implants, regarding both biomechanical primary stability, as well as clinical outcome [9,14,29,46]. Exemplary, Weiler et al. compared six different biodegradable IFS to a titanium IFS, finding mean load to failure values ranging from 439.2 to 830.2 N for the biodegradable implants, compared to 821.6 ± 129.8 N for the titanium implant [46]. These results, although not directly comparable due to differences in biomechanical testing and experimental setup, are similar to the findings of the present study, which reported load to failure of 683.9 ± 116.5 N for the tested Mg-IFS. ...
... A Bc-IFS was used as control group in the present study, to compare Mg-IFS to another biodegradable implant. Biodegradable IFS were shown to provide comparable fixation strength, in comparison to titanium IFS [14,46]. The IFS utilized in this study have different geometries, most prominently different thread shapes and thread pitches, which could have possibly influenced the biomechanical properties of the screws. ...
Purpose
Biodegradable interference screws (IFS) can be manufactured from different biomaterials. Magnesium was previously shown to possess osteoinductive properties, making it a promising material to promote graft-bone healing in anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to compare IFS made from magnesium to a contemporary biocomposite IFS.
Methods
In a porcine model of ACL reconstruction, deep porcine flexor tendons were trimmed to a diameter of 8 mm, sutured in Krackow technique, and fixed with either 8 × 30 mm biocomposite IFS (Bc-IFS) or 8 × 30 mm magnesium IFS (Mg-IFS) in an 8 mm diameter bone tunnel in porcine tibiae. Cyclic loading for 1000 cycles from 0 to 250 N was applied, followed by load to failure testing. Elongation, load to failure and stiffness of the tested constructs was determined.
Results
After 1000 cycles at 250 N, elongation was 4.8 mm ± 1.5 in the Bc-IFS group, and 4.9 mm ± 1.5 in the Mg-IFS group. Load to failure was 649.5 N ± 174.3 in the Bc-IFS group, and 683.8 N ± 116.5 in the Mg-IFS group. Stiffness was 125.3 N/mm ± 21.9 in the Bc-IFS group, and 122.5 N/mm ± 20.3 in the Mg-IFS group. No significant differences regarding elongation, load to failure and stiffness between Bc-IFS and Mg-IFS were observed.
Conclusion
Magnesium IFS show comparable biomechanical primary stability in comparison to biocomposite IFS and may therefore be an alternative to contemporary biodegradable IFS.
... Three materials are commonly employed for IS testing: polyurethane foam blocks, a Sawbones tibia model, and human cadaveric knees 3,4,[19][20][21][22] . In addition, for the tibia model, the tunnel of 65° in the coronal and sagittal plane is a practical tibia tunnel range of 52°-75° and 64°-80° in the coronal and sagittal plane, respectively [26][27][28] . ...
... After the dynamic test, the cadaveric tibiae pull-out force was slightly higher than the initial cadaver pull-out test. This is congruent with other studies 28 : the IS retains the same fixation ability after 1000 cyclic loads. The ACL graft force was estimated in situ between 30 and 450 N, with 150 N sufficient to undertake daily activities such as walking 28 . ...
... This is congruent with other studies 28 : the IS retains the same fixation ability after 1000 cyclic loads. The ACL graft force was estimated in situ between 30 and 450 N, with 150 N sufficient to undertake daily activities such as walking 28 . This initial fixation value may vary between studies according to the experimental setup, from 200 N to more than 1000 N 4,25,30 . ...
Tears of the anterior cruciate ligament (ACL) negatively impact the stability and kinematics of the knee. Interference screws (ISs) are used for graft fixation in ACL reconstruction and provide sufficient fixation strength to withstand the patients' activities during the graft-to-bone integration process. Magnesium is a novel material used to manufacture IS given its strength and bioabsorbability. In previous studies, the selected magnesium IS design showed a better fixation performance in comparison to the conventional IS design due to its shape design and surface condition. In this study, bioabsorbable magnesium ISs were tested for their insertion (insertion torque and a number of turns to implement the IS) and fixation performance (pull-out and dynamic test). To obtain a reliable initial assessment of IS performance, ISs were implanted in 15 per cubic foot (PCF) Sawbones polyurethane foam blocks, Sawbones biomechanical tibia models with 17 PCF foam cores, and human cadaveric tibiae. Porcine tendons were used in the foam block pull-out test, and nylon ropes were used in all other test setups to prevent influences of the ligament graft material itself. In the pull-out test, the graft was subjected to tensile stress at a rate of 6 mm/min. For the dynamic test, 1000 cycles between 0 and 200 N were performed, followed by a final pull-out test. After each test, the tunnel widening pattern was observed by measuring the aspect ratio of the tunnel at the insertion site. The insertion torque lies within the normal insertion torque of the ISs as well as the average ligament tension before the insertion. In the foam block setup, the nylon rope showed a higher pull-out force than the porcine tendon. The comparison of each setup using nylon rope for both pull-out and pull-out after the dynamic test showed no significant difference between the foam block and cadaver setup. However, all tibia model setup shows unexpectedly high pull-out force due to the influence of its cortical layer. There were no statistically significant differences in tunnel widening between foam block-porcine tendon and foam block-nylon rope constructs. The pull-out resistance of magnesium ISs falls within the typical ACL tension range during daily activities. Even though the test results of the magnesium ISs are different in each bone material, the magnesium IS shows adequate fixation ability and workability during insertion without material failure.
... However, the actual degradation after implantation of these screws was slow, inconsistent, and often incomplete even after two years [6]. In addition, problems with screw breakage during insertion can be frequent [7,8]. Efforts have been made to understand screw-graft performance under postoperative conditions. ...
... Weiler et al compared six bioabsorbable polymer IFSs of similar size with differing drive designs. These authors found that resistance to breakage during insertion was highly dependent on the drive design; specifically, the drive diameter and drive shape [7,8,[14][15][16][17]. Unfortunately, material properties of the screws were not altered as part of the analysis. ...
... A 2 Nm torque was applied to the inner surface of the drive of the screw. This torque is within the range of published insertion torques reported for ACL IFSs [8,[23][24][25]. The maximum von Mises stress and maximum shear stress were recorded for each model as well as the stress distribution within the drive design. ...
Background/objective:
In anterior cruciate ligament reconstruction, a tendon graft, anchored by interference screws (IFSs), is frequently used as a replacement for the damaged ligament. Generally, IFSs are classified as being either metallic or polymeric. Metallic screws have sharp threads that lacerate the graft, preventing solid fixation. These constructs are difficult to image and can limit bone--screw integration because of the higher stiffness of the screw. Polymeric materials are often a better match to bone's material properties, but lack the strength needed to hold grafts in place. Magnesium (Mg) is a material of great promise for orthopaedic applications. Mg has mechanical properties similar to bone, ability to be seen on magnetic resonance imagings, and promotes bone healing. However, questions still remain regarding the strength of Mg-based screws. Previous ex vivo animal experiments found stripping of the screw drive when the full torque was applied to Mg screws during surgery, preventing full insertion and poor graft fixation. The similar design of the Mg screw led to questions regarding the relationship between material properties and design, and the ultimate impact on mechanical behaviour. Thus, the objective of this study was to analyze the stresses in the screw head, a key factor in the stripping mechanism of IFS, then use that information to improve screw design, for this material.
Methods:
Using finite element analysis, a comparison study of six drive designs (hexagonal, quadrangle, torx, trigonal, trilobe, and turbine) was performed. This was followed by a parametric analysis to determine appropriate drive depth and drive width.
Results:
It was observed that with a typical torque (2 Nm) used for screw insertion during anterior cruciate ligament reconstruction, the maximum von Mises and shear stress values were concentrated in the corners or turns of the drive, which could lead to stripping if the values were greater than the yield stress of Mg (193 MPa). With a four-time increase in drive depth to be fully driven and a 30% greater drive width, these maximum stress values were significantly decreased by more than 75%.
Conclusion:
It was concluded that improving the design of a Mg-based screw may increase surgical success rates, by decreasing device failure at insertion.
The translational potential of this article:
The results of this work have the potential to improve designs of degradable IFSs, allowing for greater torque to be applied and thus greater screw fixation between host bone and the graft. Such a fixation will allow greater integration, better patient healing, and ultimately improved patient outcomes.
... Screws are often used for ACL surgery, dental implants, fracture fixation, and early intervention chondral repair implants. They offer high levels of implant stability, with high pull-out loads (around 1,000 N), 5,6 and by changing the thread, can be optimized for different bone densities. 7 However, because screws must be rotated about their own axis to achieve fixation, they are of no use for non-axisymmetric/multiple fixation features. ...
... [12][13][14][15] However, they provide lower initial fixation strength than screws (only around 50-150 N of pull-out force, an order of magnitude less than a screw equivalent). 5,6,9,16,17 A technology that is able to provide screw-strength fixation, while allowing nonaxisymmetric/multiple fixation features could therefore enable new/improved orthopaedic treatments. Improvements in implant fixation could come from additive manufacturing (AM) technology which has influenced a number of fields ranging from aerospace to sports equipment to orthopaedics as it offers engineers new design freedoms. ...
... The level of pull out achieved by the barbed fixation in both synthetic and human bone (mean AE S.D. of 773 AE 61 N and 1124 AE 146 N, respectively) is of the same magnitude as that measured for a variety of bone screws in synthetic (Fig. 11) 5,7,17,40 and cadaveric bone. 6,17 It greatly exceeds current additive manufactured knee replacement designs which have peg fixation of only 100 N; 16 applying the technology to such Figure 10. Push-in force comparison for optimum the barbed fixation design and the tapered press-fit pegs with their optimum interference in synthetic bone (N ¼ 4 per design). ...
Additive manufacturing offers exciting new possibilities for improving long-term metallic implant fixation in bone through enabling open porous structures for bony ingrowth. The aim of this research was to investigate how the technology could also improve initial fixation, a precursor to successful long-term fixation. A new barbed fixation mechanism, relying on flexible struts was proposed and manufactured as a push-fit peg. The technology was optimised using a synthetic bone model and compared with conventional press-fit peg controls tested over a range of interference fits. Optimum designs, achieving maximum pull-out force, were subsequently tested in a cadaveric femoral condyle model. The barbed fixation surface provided more than double the pull-out force for less than a third of the insertion force compared to the best performing conventional press-fit peg (p<0.001). Indeed, it provided screw-strength pull out from a push-fit device (1,124 ± 146 N). This step change in implant fixation potential offers new capabilities for low profile, minimally invasive implant design, whilst providing new options to simplify surgery, allowing for one-piece push-fit components with high levels of initial stability. This article is protected by copyright. All rights reserved
... Desirable outcome can be gained in a suitable combination of higher fixation of screw in adjacent bone and providing sufficient pressure on graft while avoiding graft laceration (Daneshvarhashjin et al., 2021). In 1998, Weiler et al. commented on the stability of interference screw fixation and concluded that the thread depth is more important than thread diameter (Weiler et al., 1998). However, in their study, screws with different thread diameters were used, making the comparison difficult (Weiler et al., 1998). ...
... In 1998, Weiler et al. commented on the stability of interference screw fixation and concluded that the thread depth is more important than thread diameter (Weiler et al., 1998). However, in their study, screws with different thread diameters were used, making the comparison difficult (Weiler et al., 1998). On the other hand, Garcés et al. investigated the effect of pitch on fixation strength and they did not find a significant difference between interference screws performance with a pitch of 2.5 and 5 mm (Garcés et al., 2019). ...
Although the anterior cruciate ligament (ACL) reconstruction using interference screw is a well-accepted surgical procedure, patients still suffer graft failure in the initial rehabilitation phase. Graft fixation stability of a newly designed anatomical hybrid thread tapered interference screw (AHTTIS) was compared with a conventional standard one (CSIS) by conducting in-vitro mechanical tests. According to the CSIS manufacturer’s instruction, eight tapered bone tunnels, matching AHTTIS geometry, and eight straight cylindrical tunnels were drilled in artificial bone blocks. Bovine tendon grafts were fixed using AHTTIS and CSIS in their corresponding bone tunnels. Each graft was subjected to a pre-load, a dynamic cyclic sinusoidal tensile load, and a tensile pullout load. Aggregate graft displacement relative to the bone tunnel under dynamic cyclic load, load corresponding to a 3mm displacement; load and displacement at yield and ultimate failure of the graft; and graft-bone-screw stiffness resulted from pullout tests were recorded. There were no significant differences between recorded parameters of the two groups, except the graft displacements relative to the bone tunnel at ultimate failure load (8.35±3.03mm versus 5.28±1.37mm) and at the yield point (7.73±3.02mm versus 4.59±1.25mm) (P <0.05), which were both significantly greater for the AHTTIS group. Considering all tests were made in the worst-case scenario of fixation of an interference screw, i.e., the employed synthetic bone just mimicked cancellous bone, graft fixation with the AHTTIS is practical. However, in the case of employing high strain rate loads on AHTTIS, further considerations are needed to reduce the side effect of slippage of the graft.
... 9,[14][15][16]18,20,21 Arthroscopic biceps tenotomy has been proposed for patients with chronic and significant shoulder pain in the presence of a massive irreparable rotator cuff tear, leading to complete resolution of pain. 19 Because we were familiar with the technique of interference screw fixation for hamstring anterior cruciate ligament reconstruction, [25][26][27] we developed a personal technique for biceps tenodesis using bioabsorb able interference screws. This technique has been used routinely in open surgery since 1996, and since 1997 has been used under arthroscopic control. ...
... success for hamstring anterior cruciate ligament reconstruction of the knee. [25][26][27] We have used interference screw fixation for biceps tenodesis in open surgery since 1996 and developed the arthroscopic technique in 1997. 28,29 The technique of arthroscopic biceps tenodesis is simple: after biceps tenotomy, the bicipital groove is open under arthroscopic control; the tendon is exteriorized and doubled on a suture; the biceps tendon is then pulled into a humeral socket (7 or 8 mm ϫ 25 mm) drilled at the top of the bicipital groove; the fixation is done using a bioabsorbable interference screw, 1 mm larger than the humeral socket (8 or 9 mm ϫ 25 mm). ...
Owing to the multiple possibilities of pathology of the tendon itself and its pulley system, the long head of the biceps is often a cause of shoulder pain. Surgical treatment for disorders of the long head of the biceps is limited to removal of the intra-articular portion of the tendon, with either tenotomy or tenodesis. Biceps tenodesis with or without rotator cuff repair, is a common and well-accepted open surgical procedure. Previous authors have described biceps tenodesis under arthroscopic control, either using isolated sutures (Habermeyer) or sutures with anchors (Snyder, Gartsman). Because of familiarity and success with the technique of interference screw fixation for hamstring anterior cruciate ligament (ACL) reconstruction grafts in a bone tunnel, a similar technique was developed for use in both open and arthroscopic tenodeses of the biceps.
... These problems led to the development of bioabsorbable screws which provide similar fi xation strength to that of metal interference screws. Many clinical reports compare bioabsorbable and metallic interference screws and show similar results in clinical performance like range of motion, knee effusion, and activity level [6][7][8][9][10][11][12][13] . In addition to lactic acid copolymers, a combination of PLA and PGA is an effective alternative in developing orthopedic implants. ...
... The literature includes a large number of biomechanical studies related to the screws for ACL reconstruction, focused on establishing relationships between various factors/parameters such as bone mineral density, bone block size, divergence angles between screw and bone plug, interference screw diameter, shape, thread and length, gap between tunnel and bone block, etc., and fi xation strength, pullout strength, or insertion torque [ 13,[36][37][38][39][40][41][42][43][44][45][46][47][48] . ...
The current development of bioresorbable materials provided the support for improvement of the clinical performance of the interference screws used during knee-ligament reconstruction. In general, commercially available biodegradable interference screws used in clinical practice are chemically based on degradable, but now a trend to use biodegradable composite materials using the same synthetic biodegradable polymers as matrix reinforced with biodegradable ceramics could be observed. Hydroxyapatite or tricalcium phosphate are used as ceramics in order to reduce the foreign body reaction and increase osteoconduction and mechanical properties of the biodegradable composite materials. In our study several new design features of an innovative interference screw were proposed in order to ameliorate press-fit fixation without damaging the graft based on clinical experience, retrieval analysis of some failed screw, and finite element simulation. We proposed a self-tapping screw with conical shape and three cutting flutes at the distal end and cylindrical shape at the proximal end. The clinical performance of an interference screw is assured by the combination between the clinical technique, screw design, and biodegradable composite material properties, which guarantees the integrity of the screw during insertion, the tissue regrowth, and the stability of fixation.
... A justificativa para o uso dos parafusos bioabsorvíveis é que permitem o crescimento do tecido hospedeiro na medida com que o parafuso se degrada, não apresentam grandes riscos de laceração do enxerto e são mais vantajosos nos exames de ressonância magnética, pois não distorcem a imagem facilitando cirurgias de revisão (Weiler A., et al., 1998). Além disso proporcionam uma fixação inicial segura comparável com a dos parafusos metálicos. ...
... Um dos paradigmas da classe médica para o do uso de parafusos bioabsorvíveis na cirurgia de reconstrução ligamentar é sua fragilidade quando comparado aos parafusos de ligas metálicas de Titânio (Weiler A., et al., 1998). ...
Resumo. O parafuso de interferência é o dispositivo de fixação mais usados em cirurgias de reconstrução ligamentar de joelho. O material mais usado para a fabricação destes dispositivos são as ligas de Titânio. Contudo os polímeros bioabsorvíveis estão sendo cada vez mais utilizados nesta aplicação, devido suas vantagens relacionadas a biocompatibilidade, bioabsorção, integração do enxerto/osso e facilidade na revisão cirúrgica. O presente estudo tem por objetivo o desenvolvimento de um parafuso de interferência bioabsorvível fabricado através do processo de injeção em dois polímeros bioabsorvíveis: PLDL(Poli L-D-ácido lático) e um compósito de PLDL+30% TCP (β Trifosfato de Cálcio). Após a definição dos materiais foram fabricadas amostras do parafuso nos dois materiais e foram realizados testes mecânicos. Em adição foi executado teste de degradação in vitro, durante um período de 180 dias, onde foi avaliada a perda de massa dos implantes, resistência mecânica e queda da viscosidade inerente. Pode-se observar que a degradação molecular do implante teve como consequência a queda na resistência mecânica do parafuso, de forma lenta e gradual, sendo que o material compósito (PLDL + TCP) apresentou um processo de degradação mais acentuado do que o material PLDL. Além disso, pode-se concluir que o parafuso apresenta resistência mecânica adequada e segura, uma vez que o torque máximo de ruptura do parafuso foi quase 120% maior do que o torque de inserção, no material PLDL e 227% no compósito. Palavras-chave: Polímeros bioabsorvíveis, PLLA, β-TCP, parafuso de interferência.
... Study by Weiler etal. 18 has shown that the maximum pull-out force and stiffness of fixation for biodegradable screws is comparable to titanium screw, with the screw design having a bearing on the fixation rigidity. Tests for evaluating the torsional strength showed four different modes of failure like shearing of screw at the interface, radial screw driver failure at the screw driver hole, failure of the screw to screw-driver hole interface and failure of the screw driver shaft 16 . ...
... [26] Metallic screws are stronger than bioresorbable screws, but bioresorbable screws showed enough strength against physiological bone for bone fracture fixation. [24,[27][28][29] The flexural and tensile properties of fiber-reinforced composites depended on VF, fiber properties, and orientation. In contrast, the shear properties are more related to the matrix. ...
Background
Metal screws are commonly used for fracture fixations. However, the high modulus of elasticity relative to bones and releasing metallic ions by the metal screw needed a second surgery to remove the implant after the healing period. Furthermore, the removal of metal screws following the healing of the bone is a serious problem that can lead to refracture due to the presence of holes in the screw. Bioresorbable screws can overcome most of the problems associated with metallic screws which motivated research on manufacturing nonmetallic screws.
Methods
In this study, three-layer poly L-lactic acid/bioactive glass composite screws were manufactured according to functionally graded material theory, by the forging process. All of the physical and chemical parameters in the manufacturing stages from making composite layers to the forging process were optimized to obtain suitable mechanical properties and durability off the screw in load-bearing positions.
Results
The tri-layer composite screw with unidirectional, ±20° angled, and random fibers orientation from core to shell shows a flexural load of 661.5 ± 20.3 (N) with a decrease about 31% after 4-week degradation. Furthermore, its pull-out force was 1.8 ± 0.1 (N) which is considerably more than the degradable polymeric screws. Moreover, the integrity of the composite screws was maintained during the degradation process.
Conclusions
By optimizing the manufacturing process and composition of the composite and crystallinity, mechanical properties (flexural, torsion, and pull-out) were improved and making it a perfect candidate for load-bearing applications in orthopedic implants. Improving the fiber/matrix interface through the use of a coupling agent was also considered to preserve the initial mechanical properties. The manufactured screw is sufficiently robust enough to replace metals for orthopedic load-bearing applications.
... For the graft fixation, Katabi and his colleagues [7], particularly in the 4SHS group, discovered that femoral fixation by EndoButton offers excellent resistance to rupture but poses a problem due to the reduction in rigidity of this assembly, resulting in knee laxity, whereas the use of an interference screw allows for a more rigid anatomical fixation with significant knee stabilization. Ishibashi et al. [8], Guirea et al. [9], and Weiler et al. [10] all reported the same finding. Nonetheless, at the tibial level, the quality of the screw fixation was unsatisfactory, necessitating the inclusion of a second means of fixation, particularly a staple, in 25% of the instances. ...
In this study, we looked at the clinical outcomes of individuals who had a symptomatic torn anterior cruciate ligament and had their anterior cruciate ligament repaired using a four-strand hamstring (4SHS) tendon autograft at least two years later. This is a retrospective study of 34 cases of anterior cruciate ligament arthroscopic reconstruction using the four-strand hamstring graft, collected from Traumatology and Orthopedics at Cheikh Khalifa Hospital in Casablanca, Morocco between January 2017 and January 2021. Different surgeons performed the operations. Physical findings and functional scores were recorded before the follow-up physical examination and surgery; thus, knee radiographs have been evaluated. A six-month rehabilitation program was devised following surgery. The average age of the patients was 30 years, with a male predominance of 94%. Thirty patients (88%) reported negative pivot shift tests and the Lachman test. The average Lysholm score enhanced from 59.3 before surgery to 85.29 at the time of the assessment. Three patients (8.82%) with a positive pivot shift test had no background of extra knee damage. In comparison to the appearance on the preoperative radiographs, no proof of progressive degenerative deterioration was found on the follow-up radiographs. All of the patients, however, had tunnel extension. The tibial tunnel grew on average by 18%, while the femoral tunnel grew on average by 30%. In 88% of patients assessed at least two years after surgery, ligamentoplasty of the anterior cruciate ligament using the four-strand hamstring graft eradicated anterior tibial subluxation. The failure rate was overall 10%. The functional knee scores had greatly improved at the time of the follow-up.
... Figure 1 displays examples of bioabsorbable interference srews that were compared in the work performed by Costi et al. [10], where authors evaluate the torque resistance of screws with different geometries (length, diameter, and drive geometry). Another study by Weiler et al. [12] analyzed six bioabsorbable interference screws with different geometries and materials and compared them with a titanium interference screw. This study also confirms that the drive geometry influences the torque resistance of the screws and their failure modes. ...
In this work, the design and development of a bioabsorbable interference screw used in Anterior Cruciate Ligament (ACL) reconstruction is proposed. This interference screw is perforated along its length with holes that have an elliptical geometry to allow a calcium triphosphate-based bone cement to be introduced. Several screw geometries, with different thread geometries, different pitch, different drive geometries and different hole geometries, were created using a 3D CAD modeling software and analyzed using a finite element analysis (FEA) program to assess which geometry provides the most favorable mechanical performance to the implant. Selected screw geometries were produced using fused filament fabrication (FFF) and insertion tests were performed. During insertion, screws were tested in holes with variable diameters, and the maximum torque achieved in each test was recorded. Tests show that most failures started in the areas close to one of the holes of the implant. In the future, results should be improved to allow FFF bioabsorbable interference screws to be a solution that promotes early rehabilitation during ACL reconstruction.
... Scaffolds for bone tissue regeneration have been developed with controlled porosity to enhance cell infiltration and supply of nutrients that stimulated the bone remodeling and repair [16,17]. Presence of interconnected pores in bone scaffolds have shown enhanced vascularization of the ingrown tissue and infiltration of cells to grow into desired physical form minimizing the recovery time [18][19][20]. Average pore size of 250-300 μm supported cellular infiltration and capillary formation thereby promoting osseous growth whereas pores < 100 μm favor hypoxic induced cartilage formation [21]. ...
... Previous investigations on qCT BMD analysis mainly focused on predicting tibial interference screw fixation strength or evaluating effects of graft preconditioning on graft tension. [24][25][26][27] Weiler et al. 40 did use qCT to identify a location with adequate BMD (800 mg/cm 3 ) within the bovine tibia to conduct fixation strength testing. Unfortunately, there were no further descriptions of the technique used for BMD assessment in that study, nor in a variety of subsequent biomechanical investigations of ACL graft fixation strength from the same authors, limiting the reproducibility of this method by others. ...
Purpose
To develop a standardized method for tibial tunnel volumetric bone mineral density (BMD) analysis with quantitative computed tomography (qCT) using cadaveric specimens to provide validation of this technique on a healthy control population and to determine whether osteopenia occurs following an anterior cruciate ligament (ACL) injury.
Methods: qCT was used to develop a volumetric BMD (mg/cm³) measurement technique throughout the region of a standard tibial tunnel. This method was applied to 90 lower extremities, including 10 matched cadaveric knees, 10 matched healthy knees, 25 ACL-injured knees, and 25 contralateral ACL-uninjured knees. The mean total and segmental (proximal, middle, and distal) tibial tunnel BMD were analyzed.
Results
The mean entire tibial tunnel BMD measured 165.8 ± 30.5 mg/cm³ (cadaver), 255.9 ± 28.2 mg/cm³ (healthy control), 290.3 ± 36.4 mg/cm³ (ACL-injured), and 300.1 ± 35.1 (ACL-uninjured). Segmental tibial tunnel BMD demonstrated distal one-third segments as the greatest areas of BMD, followed by proximal one-third, and middle one-third for all cohorts with all pairwise comparisons (P < .001). The mean BMD was significantly greater in the uninjured extremity compared with the injured extremity in the entire tunnel (290.3 vs 300.1; P < .001), proximal (271.2 vs 279.1; P = .002), middle (167.6 vs 179.6; P < .001), and distal segments (432.7 vs 441.7; P = .004) at an average of 8 weeks following ACL injury.
Conclusions
A standardized method to quantitatively measure the volumetric BMD within the region of a standard tibial tunnel for ACL reconstruction was successfully developed and validated. Significant osteopenia of the injured knee occurs following ACL injury when compared with the contralateral uninjured knee. This observation has potential clinical implications for ACL graft tibial fixation and healing.
Level of Evidence
Descriptive diagnostic study, Level III.
... Most biomechanical tests have shown that metallic or bioabsorbable interference screws provide sufficient fixation strength [28][29][30]. However, the insertion of interference screws during ACL reconstruction significantly leaded to graft laceration. ...
Background
Interference screw is commonly used for graft fixation in anterior cruciate ligament (ACL) reconstruction. However, previous studies had reported that the insertion of interference screws significantly caused graft laceration. The purposes of this study were to (1) quantitatively evaluate the graft laceration from one single insertion of PEEK interference screws; and (2) determine whether different types of sutures reduced the graft laceration after one single insertion of interference screws in ACL reconstruction.
Methods
The in-vitro ACL reconstruction model was created using porcine tibias and bovine extensor digitorum tendons of bovine hind limbs. The ends of grafts were sutured using three different sutures, including the bioabsorbable, Ethibond and ultra-high molecular weight polyethylene (UHMWPE) sutures. Poly-ether-ether-ketone (PEEK) interference screws were used for tibial fixation. This study was divided into five groups (n = 10 in each group): the non-fixed group, the non-sutured group, the absorbable suture group, the Ethibond suture group and the UHMWPE suture group. Biomechanical tests were performed using the mode of pull-to-failure loading tests at 10 mm/min. Tensile stiffness (newtons per millimeter), energy absorbed to failure (in joules) and ultimate load (newtons) were recorded for analysis.
Results
All prepared tendons and bone specimens showed similar characteristics (length, weight, and pre-tension of the tendons, tibial bone mineral density) among all groups (P > 0.05). The biomechanical tests demonstrated that PEEK interference screws significantly caused the graft laceration (P < 0.05). However, all sutures (the bioabsorbable, Ethibond and UHMWPE sutures) did not reduce the graft laceration in ACL reconstruction (P > 0.05).
Conclusions
Our biomechanical study suggested that the ultimate failure load of grafts was reduced of approximately 25 % after one single insertion of a PEEK interference screw in ACL reconstruction. Suturing the ends of the grafts using different sutures (absorbable, Ethibond and UHMWPE sutures) did not decrease the graft laceration caused by interference screws.
... Scaffolds for bone tissue regeneration have been developed with controlled porosity to enhance cell infiltration and supply of nutrients that stimulated the bone remodeling and repair [16,17]. Presence of interconnected pores in bone scaffolds have shown enhanced vascularization of the ingrown tissue and infiltration of cells to grow into desired physical form minimizing the recovery time [18][19][20]. Average pore size of 250-300 μm supported cellular infiltration and capillary formation thereby promoting osseous growth whereas pores < 100 μm favor hypoxic induced cartilage formation [21]. ...
Advent of additive manufacturing in biomedical field has nurtured fabrication of complex, customizable and reproducible orthopaedic implants. Layer-by-layer deposition of biodegradable polymer employed in development of porous orthopaedic screws promises gradual dissolution and complete metabolic resorption thereby overcoming the limitations of conventional metallic screws. In the present study, screws with different pore sizes (916 × 918 μm to 254 × 146 μm) were 3D printed at 200 μm layer height by varying printing parameters such as print speed, fill density and travel speed to augment the bone ingrowth. Micro-CT analysis and scanning electron micrographs of screws with 45% fill density confirmed porous interconnections (40.1%) and optimal pore size (259 × 207 × 200 μm) without compromising the mechanical strength (24.58 ± 1.36 MPa). Due to the open pore structure, the 3D printed screws showed increased weight gain due to the deposition of calcium when incubated in simulated body fluid. Osteoblast-like cells attached on screw and infiltrated into the pores over 14 days of in vitro culture. Further, the screws also supported greater human mesenchymal stem cell adhesion, proliferation and mineralized matrix synthesis over a period of 21 days in vitro culture as compared to non-porous screws. These porous screws showed significantly increased vascularization in a rat subcutaneous implantation as compared to control screws. Porous screws produced by additive manufacturing may promote better osteointegration due to enhanced mineralization and vascularization.
... The Mg-6Zn-0.5Sr rods with 5 mm in diameter were used for the fabrication of specially designed hollow interference screw that was similar to commercially available screw for human applications [39]. Prior to animal surgery, the Mg-6Zn-0.5Sr ...
Peri-tunnel bone loss after anterior cruciate ligament (ACL) reconstruction is often observed clinically, which may detrimentally affect tendon graft integration with surrounding bone tissue. Biodegradable magnesium (Mg) based fixators in terms of interference screws may be suitable for fixation of the tendon graft due to their favorable effects on promotion of new bone formation. However, the poor mechanical strength of Mg is still one of the major challenges for its clinical applications. The addition of alloying elements into Mg is one of the strategies to improve their mechanical properties. Here, we prepared magnesium (Mg)-(4 and 6 wt%) zinc (Zn)-(0.2, 0.5, 1 and 2 wt%) strontium(Sr) alloys and tested their potential for attenuating peri-tunnel bone loss in ACL reconstruction. The optimal (6 wt%) Zn and (0.5 wt%) Sr contents were screened with respect to the microstructures, mechanical properties and corrosion behavior of these alloys. As compared to pure Mg, Mg-6Zn-0.5Sr rods and screws showed significantly higher torque and torsional stiffness in both numerical and experimental analysis. The in vitro cyto-compatibility of Mg-6Zn-0.5Sr alloy was assessed with MTT test and fluorescence assay. The Mg-6Zn-0.5Sr interference screw was designed for fixation of the tendon graft to the femoral tunnel in a rabbit model of ACL reconstruction, with a commercially available poly-lactide (PLA) screw for comparison. In vivo high resolution peripheral quantitative computed tomography (HR-pQCT) scanning was performed to measure the degradation behavior of Mg-6Zn-0.5Sr interference screws and peri-tunnel bone quality at 0, 6, 12 and 16 weeks post-surgically. Mg-6Zn-0.5Sr interference screw was completely degraded within 12 weeks after surgery. The peri-tunnel bone loss was significantly attenuated in the Mg-6Zn-0.5Sr group when compared to the PLA group. Importantly, the bony ingrowth rapidly filled the cavity left by the complete degradation of Mg-6Zn-0.5Sr screws at 16 weeks. In histological analysis, more bone formation was observed in peri-tunnel region in the Mg-6Zn-0.5Sr group in comparison to the PLA group at 6 and 16 weeks after surgery. The femur-tendon graft-tibia complex was harvested at the end of week 6 and 16 post-operation for tensile testing. The maximum load to failure was significantly improved in the Mg-6Zn-0.5Sr group at week 16 post-operation. Therefore, our results indicate the potential clinical application of MgZnSr based interference screws in ACL reconstruction.
... "Bioscrews" were designed with the goal of creating a screw that is radiologically friendly, able to provide strong fixation until the graft incorporates, and then fully undergo resorbtion to be replaced by bone. Although most studies have shown that "bioscrews" are associated with good clinical outcomes, which may be equivalent to metal screws, [2][3][4][5][6][7][8][9][10][11][12] there is also evidence that these screws are not readily absorbed by the body, nor replaced with bone. 2,[13][14][15][16] The literature is scattered with reported complications and adverse events, including cyst formation, sterile abscess formation, inflammatory reaction, breakage, intraarticular migration, transcutaneous migration, tunnel widening, and osteolysis. ...
Bioresorbable screws have been widely adopted for graft fixation in knee anterior cruciate ligament (ACL) reconstruction on the promise of screw resorbtion and replacement by bone. When considering the value of bioresorbable screws, it is imperative to understand that the “A” in PGA and PLA, the base ingredient of all bioscrews, is for Acid. All resorb by a process of hydrolysis; the speed and extent of resorbtion is determined by both the acidity of the screw and the environment in which it is placed. Regrettably, the promise of reliable, predictable screw resorbtion and replacement by bone remains elusive, despite the addition of “osteoconductive” materials. For the most part, bioresorbables are associated with good clinical outcomes for ACL reconstruction; they are not “dangerous,” just disappointing with respect to bony replacement. We propose that nonresorbing inert plastics such as PEEK (polyether ether ketone) may be better suited for the purpose of graft fixation devices for ACL reconstruction.
... A wide variety of screw sizes are available from each producer. [10] Advantages of bioscrews aren't any need for removal, no metal related complications, radiologically transparent, patient acceptability more. Disadvantages of bioabsorbable screws are choric aseptic synovitis, tunnel widening, intra operative screw breakage, more expensive. ...
... In order to ensure a good graft fixation, different extracortical (e.g. sutures, suspension devices, cross pins [1,5,6]), intercortical (interference screws) [7][8][9][10], and combined systems [5] were evolved. The main disadvantages of the extracortical fixation for soft-tissue grafts are the decreased stiffness due to the linkage material and the increased tunnel motion [11], which could interfere with the healing process. ...
Background:
Rupture of the anterior cruciate ligament (ACL) is one of the most common injuries of the knee. Common techniques for ACL reconstruction require a graft fixation using interference screws. Nowadays, these interference screws are normally made of titanium or polymer/ceramic composites. The main challenge of application of a fixation device made entirely of bioactive ceramic is in relation to the low strength of such materials. The purpose of this study was to evaluate a novel geometry for a fixation device made of pure hydroxyapatite for ACL reconstructions that can overcome some problems of the titanium and the polymer/ceramic screws.
Methods:
Finite Element Analysis was used for optimization of the stress distribution in conventional interference screw geometry. For experimental evaluation of the new fixation device, ex vivo tests were performed.
Results:
The innovative screw-like fixation device is characterized by multiple threads with a large thread pitch. The novel design enabled the insertion of the screw into the bone without the application of an external torque or a screwdriver. In turn, it also allowed for the use of low-strength and high-bioactivity materials, like hydroxyapatite. Ex vivo tests showed that the novel screw can sustain pull-out forces up to 476 N, which is comparable to that of the commercially available BioComposite™ interference screws (Arthrex Inc., Germany), as a reference.
Conclusions:
In summary, the novel screw design is a promising strategy to develop all-ceramic fixation devices for ACL reconstructions, which may eliminate some drawbacks of the current interference screws.
... Entre ellas destacan la rotura del implante, fracturas en la zona de inserción, osteolisis, formación de quistes, reacción de partes blandas e inclusión del implante en la superficie articular. 1,6,19,20 . ...
Background: We report a series of cases that presented as pretibial cyst, swelling and pain following anterior cruciate ligament (ACL) reconstruction using bioabsorble fixation devices (HA-PLLA). Methods: All ACL reconstructions were done between 2008 and 2014 reviewed retropectively to identify complications related to bioabsorbable fixation devices. During this period of 6 years, 620 ACL reconstructions were performed using the bioabsorbable screw (HA-PLLA) for tibial fixation of the quadrupled hamstring autograft. Results: Nine patients (1,45%) with mean age of 29,8 (19-44) years, presented in the post-operative period, pretibial pain, cyst and swelling in tibial screw site. All of them had normal inflammatory markers.All of these patients underwent surgical debridement, which revealed remnants of screw and reactive material. There was evidence of infection
in 4 intraoperative specimen cultures. Histopathology revealed detritic birefringent remains in macrophages
cytoplasm. Removal of screw debris and curettage of the tunnel resulted in complete recovery of all patients in our series.
Conclusions: Pretibial cyst as an adverse biological response should be considered as a posible complication in ACL reconstruction. We report a 1,45% of pre-tibial reaction in patients undergoing ACL reconstruction with bio-absorbable (HAPLLA) interference screw fixation for the proximal tibia.
... An initial concern with bioabsorbable screws was their inferior mechanical strength compared with metallic implants. [20] However, biomechanical tests of these screws have revealed sufficient pull-out strength, [21] and reports have indicated that bioabsorbable interference screws made of polylactic acid have an advantage over those made of surgical steel or titanium, including less laceration of the graft, no interference with MRI examination, and no interference with subsequent knee surgery. [9] Complications associated with the use of bioabsorbable screws are uncommon. ...
Introduction
The use of bioabsorbable interference screws has become popular for treatment of avulsion fractures of the posterior cruciate ligament (PCL). Complications are uncommon. We report a case of severe chondral damage caused by the early breakage of an absorbable screw head after fixation of an avulsion fracture of the tibial attachment of the PCL. The patient felt a sudden locking of the knee when getting off a car at 4 months after the PCL surgery. MRI revealed intraarticular migration of the head of the interference screw. During revision surgery, the broken part was removed without incident, and severe cartilage damage was observed. The patient experienced a complete resolution of symptoms at the 6-month follow-up.
Conclusion
MRI examination is recommended in case of sudden locking of the knee for patients undergoing PCL fixation with bioabsorbable interference screws. Surgical treatment should be performed immediately when screw breakage was confirmed.
... Despite many advantages of the bioabsorbable implant, it may have disadvantages such as lower strength, high screw breakage rate, and foreign body reaction to the implant. 34,35 PLA is believed to have slower degradation than polyglycolic acid (PGA) and therefore less inflammation by 1%, 7 and PLA screws are also reported to have less late foreign body reaction, 10,27 50% of which happens 3 years after the operation. 16 In our study, this also happened in approximately 1% (1 of 115 patients) at the 38-month follow-up (Table 5). ...
Background:
Scarf osteotomy has been used in hallux valgus surgery due to its large fixation surface for screws and low postoperative complications. However, screws may cause skin irritation from their head, which may require an additional surgical procedure to remove.
Methods:
This study included 115 patients (106 females and 9 males, 115 feet) who underwent hallux valgus correction with a scarf osteotomy using bioabsorbable screws between September 2010 and September 2012. Preoperative and postoperative 1-month and 1-year radiographic measurements, including intermetatarsal angle (IMA), hallux valgus angle (HVA), distal metatarsal articular angle (DMAA), proximal phalangeal articular angle (PPAA), and lateral translational distance (LTD), were obtained. American Orthopedic Foot & Ankle Society (AOFAS) hallux/forefoot scores were used for patient satisfaction.
Results:
Preoperative mean values of HVA, IMA, and PPA of 32.8 degrees, 14.6 degrees, and 7.52 degrees, respectively, improved to 10.7 degrees, 6.0 degrees, and 4.6 degrees, respectively at 1-year follow up (P < .05). The difference in LTD between the 1-month and 1-year follow-up was not statistically significant. AOFAS hallux/forefoot score improved from 69.1 to 96.1 at the 1-year follow up (P < .001). Complete screw absorption was not seen radiographically. Sixteen feet had complications reported. One patient complained of skin irritation over a small protrusion of the screw, and another patient had a foreign body reaction. There were 3 patients with neurologic injury from a popliteal block and 3 patients with dorsal cutaneous nerve symptoms. Four feet had metatarsal fracture during surgery.
Conclusion:
We found the scarf osteotomy using bioabsorbable screws to have satisfactory clinical and radiographic results with a low complication rate.
Level of evidence:
Level IV, case series.
... The main advantages of using absorbable materials are the reduction of stress shielding, removal operations that are no longer required, and the risks of long term complications that are reduced (Bleach et al., 2002). Weiler et al. (1998) demonstrated that the biodegradable material somehow enhanced the strength of fixation of interference screws over that of their metal counterparts. Because the current study used a simple type of the tested samples, further studies will be required to evaluate real types of the fracture fixation devices such as screws and pins for the clinical relevance of these findings. ...
To achieve the excellent mechanical properties of biodegradable materials used for cortical bone graft substitutes and fracture fixation devices remains a challenge. To this end, the biomimetic calcium silicate/gelatin/chitosan oligosaccharide composite implants were developed, with an aim at achieving high strength, controlled degradation, and superior osteogenic activity. The work focused on the effect of gelatin on mechanical properties of the composites under four different kinds of mechanical stresses including compression, tensile, bending, and impact. The evaluation of in vitro degradability and fatigue at two simulated body fluid (SBF) of pH 7.4 and 5.0 were also performed, which the pH 5.0 condition was to simulate clinical conditions caused by bacterial induced local metabolic acidosis or tissue inflammation. In addition, human mesenchymal stem cells (hMSCs) were sued to examine osteogenic activity. Experimental results showed that the appropriate amount of gelatin positively contributed to failure enhancement in compressive and impact modes. The 10 wt% gelatin-containing composite exhibits the maximum value of the compressive strength (166.1 MPa), which is within the reported compressive strength for cortical bone. The stability of the bone implants was apparently affected by the in vitro fatigue, but not by the initial pH environments (7.4 or 5.0). The gelatin not only greatly enhanced the degradation of the composite when soaked in the dynamic SBF solution, but effectively promoted attachment, proliferation, differentiation, and formation of mineralization of hMSCs. The 10 wt%-gelatin composite with high initial strength may be a potential implant candidate for cortical bone repair and fracture fixation applications.
An anterior cruciate ligament (ACL) reconstruction is a common treatment for patients with ACL rupture that aims to regain pre-injury knee stability and kinematics. During the ACL reconstruction, one method to fix the graft is the use of an interference screw (IS). The IS should provide initial stability and secure the graft during the healing period. In recent years, magnesium has emerged as an alternative material to permanent metal and polymer ISs. In addition, differences in designs, such as the shape of the IS, can influence the fixation performance of the IS. Therefore, in this biomechanical experiment, two different screw designs with two ligament materials were compared in an insertion and a pull-out test at a rate of 1 mm/s. The screw designs were a conventional polymer screw and a magnesium screw. Porcine tendon and nylon rope were used as ligament materials. All tests were performed in polyurethane foam blocks with 15 PCF density (Synbone AG, Switzerland). As a result, both screw designs required an insertion torque of less than 3 Nm. There was a significant difference between the porcine and nylon rope in pull-out tests for each screw design. The magnesium screw had the highest pull-out force at 412.14 ± 50.00 N for porcine tendon and 707.38 ± 21.81 N for nylon rope. There were no significant differences in tunnel widening (narrow–wide ratio) between each ligament material. The magnesium screw showed the lowest narrow–wide tunnel ratio, implying a better ability to compress the graft to the tunnel. In conclusion, a more optimized magnesium IS design resulted in better graft fixation and an improved ACL reconstruction outcome.
Background
To determine the ideal fixation technique for an ACL reconstruction with a hamstring graft, multiple studies have been undertaken to define the initial biomechanical properties of tibial fixation.
Purpose
The aim of this study was to compare the biomechanical properties of tibial fixation methods by creating single or hybrid systems.
Methods
Bovine tibias and forefoot digital extensor tendons were prepared with four different tibial anterior cruciate ligament fixation methods and compared biomechanically. Fixation materials included polyethylene Ultrabraid high-strength sutures, Biosure interference screws (Smith and Nephew, Memphis, TN, USA), staples (Smith and Nephew, Richards Regular Fixation Staples without Spikes, Memphis, TN, USA), and knotless suture anchors (Multifix-S PEEK) (Smith and Nephew, Memphis, TN, USA). Four groups (n = 5 specimens) were established – group I: single fixation with interference screws; group II: single fixation with knotless anchors; group III: hybrid fixation with interference screws and staples; group IV: hybrid fixation with interference screws and knotless anchors. Each specimen underwent evaluations for cyclic displacement, cyclic stiffness, initial loading strength, ultimate failure load, pull-out displacement, and pull-out stiffness.
Results
All specimens completed cyclic loading and load-to-failure. The cyclic displacement in group II, which had a single fixation, indicated significantly greater elongation compared with the other groups (P = 0.002). The hybrid systems were more rigid than the single systems in terms of cyclic stiffness, and no statistically significant difference was observed between the hybrid systems (P = 0.461). Group IV was significantly superior in terms of the ultimate failure load (P = 0.004). No statistically significant differences were noted between the groups for pull-out displacement or pull-out stiffness.
Conclusion
Single fixation with bioscrews as an in-tunnel tibia fixation method was as successful as hybrid systems. Multifix-S PEEK knotless suture anchors, which can be combined with bioscrews, can be a superior fixation alternative due to its flexibility and ultimate failure load values.
Recently, anatomic reconstruction procedures for chronic lateral ankle instability (CLAI) using arthroscopic and percutaneous minimally invasive technique has been described with the goal of improving clinical outcomes of open non-MIS techniques. In this chapter we describe the history of reconstruction for CLAI and a new anatomical reconstruction of the lateral ankle ligament (AntiRoLL) MIS techniques.
With the development of medical technology and materials science, the structure optimization method of bioabsorbable materials for implantable medical devices becomes more and more important, and the absorbable interface screw is the most representative device in implantable medical devices. Based on the previous parametric design method for the loading and structural characteristics of the interface screw, this paper assembled the interface screw and cancellous bone with the tunnel hole and simulated the graft fixation after cruciate ligaments surgery. In this study, through the finite element method, the mechanical properties of interface screws with different structural parameters obtained by parametric design were comprehensively evaluated from the aspects of stress and strain energy density.
Background
Strength of graft fixation is the weakest link in anterior cruciate ligament reconstruction.
Hypothesis
There is no difference in initial fixation strength between different hamstring tendon graft femoral fixation devices.
Study Design
Randomized experimental study.
Methods
Each of six devices was used in the fixation of 10 quadrupled human semitendinosus-gracilis tendon grafts in tunnels drilled in porcine femora and tested 10 times with a single-cycle load-to-failure test at a rate of 50 mm/min and 10 times with a 1500-cycle loading test between 50 and 200 N at one cycle every 2 seconds. The specimens that survived the cyclic loading were subjected to a single-cycle load-to-failure test.
Results
The Bone Mulch Screw (1112 N) was strongest in the single-cycle load-to-failure test, followed by EndoButton CL (1086 N), RigidFix (868 N), SmartScrew ACL (794 N), BioScrew (589 N), and RCI screw (546 N). It also showed the lowest residual displacement (2.2 mm) and was strongest in the single-cycle load-to-failure test after cyclic loading.
Conclusions
The Bone Mulch Screw was superior to all other devices.
Clinical Relevance
Caution may be warranted in employing aggressive rehabilitation after reconstruction with these devices. Preconditioning of the graft-implant complex before fixation is important.
Titanium dioxide (TiO2) nanomaterials have attracted much interest in life science and biological fields because of their excellent photocatalytic activity and good biocompatibility. However, owing to wide band-gap, photocatalysis of TiO2 can be only triggered by UV light. The limited transparent depth of UV light and the generated reactive oxygen species (ROS) cause inflammation response of skin tissue, thus posing two major challenges in the photocatalytic application of TiO2-based materials in drug delivery and other biotechnology fields. Here, we propose an upconversion-related strategy to enable the photocatalytic activity of TiO2 nanotubes in near-infrared (NIR) light and apply the system as controllable drug delivery platform. More importantly, the ROS-induced cytotoxicity and the preleaching of payload are significantly reduced on the as-proposed amphiphilic TiO2 nanotubes. The hydrophobic monolayers are served as a “cap” to provide protection for ROS-induced inflammation and long-term storability. This amphiphilic drug delivery system broadens the potential applications of TiO2-based nanomaterials in biomedicine.
Anterior cruciate ligament (ACL) plays a crucial role stabilizing the knee joint while connecting tibia to femur. Lack of proper treatment of injured ACL can lead to meniscus tear and osteoarthritis. Interference screws secure the graft tissue for superior integration of graft on host tissue during autograft fixation. Metal interference screws come with various disadvantages like mechanical load mismatch, graft laceration, secondary surgical removal and hindrance during MRI and CT post-operative scan. Though biodegradable polymeric screws provide various advantages their clinical outcomes reveal unprecedented complications for long term use of such screws. This review highlights polymer and composite screw currently available for surgical fixations and associated adverse reactions with the proposed mechanism for tunnel enlargement, effusion, osteolysis in ligament repairs. The need for suitable material engineering for development of orthopedic screws for successful rigid fixation has been highlighted in this review.
Purpose: Most interference screws (IFS) for anterior cruciate ligament (ACL) reconstruction are manufactured from traditional materials like titanium. The advent of degradable metals (i.e. magnesium (Mg) alloys) has shown great promise for numerous orthopedic applications, including IFS for ACL replacement. Questions surrounding the mechanical integrity of degradable Mg alloys, as well as the impact of design changes on behavior, are still unanswered. The purpose of this research was to determine the impact of thread shape, diameter and screw taper on pullout strength of Mg-based IFS. Methods: Four different thread shapes were modeled, and analyzed, using finite element analysis. It was hypothesized that the thread shape, diameter and taper of the screw would significantly impact the pullout performance of the screw. Results: A buttress design resulted in the highest reaction (pullout) force (1247N) providing the greatest hold. Conclusion: Results of this study indicate that design factors impact pullout force and suggest thread shape, taper, and major diameter having the greatest impact.
Purpose:
This study aimed to identify the difference in postoperative perianchor bone reactions in different groups of patients who underwent rotator cuff tear repairs with all-suture-, bioabsorbable screw-, and PEEK (polyether ether ketone)-type suture anchors. Furthermore, the rate of rotator cuff retear and its association with perianchor bone reactions based on the different anchors used were investigated. Moreover, their impact on the clinical outcome of patients was examined.
Methods:
The study included 213 patients who underwent arthroscopic single-row repair and were divided into 3 groups according to the suture anchor used: all-suture (n = 137), biodegradable (n = 36), and PEEK (n = 40) anchor groups. The clinical outcomes and magnetic resonance imaging findings were evaluated at a mean follow-up of 9.6 months. The perianchor bone reaction at the anchor site was categorized according to grades. Patients were classified based on repair integrity into the healed and retear groups with Sugaya type I to III and Sugaya type IV to V, respectively.
Results:
No statistically significant differences in Constant scores and retear rates were observed between the groups (P = .934 and P = .548, respectively). Magnetic resonance imaging showed that the total number of perianchor cysts formed postoperatively was 23 (10.8% [23 of 213 patients]). Moreover, the proportions of perianchor cysts were 8.8%, 16.7%, and 12.5% in the all-suture-type, bioabsorbable-, and PEEK-type anchor groups, respectively (P = .485). In the retear group, the incidence rate was significantly increased with higher grades of perianchor bone reaction (P = .001). The tear size and perianchor bone reaction were found to be independent factors that affected the incidence of retear.
Conclusions:
Perianchor cyst formation was observed in 10.8% of cases after the use of suture anchors for arthroscopic rotator cuff repair. No significant differences were observed among all-suture-type, bioabsorbable-type, and PEEK-type anchors in terms of visual analog scale and Constant scores, retear rates, and perianchor bone reactions. However, the retear rate was associated with a greater perianchor cystic reaction and larger tear size.
Level of evidence:
Level III, retrospective comparative trial.
Objective
To evaluate the effectiveness of Scarf osteotomy combined with Akin osteotomy in the treatment of moderate to severe hallux valgus with absorbable screws or metal screws fixation by clinical and radiological data.
Methods
Between March 2014 and May 2016, the Scarf osteotomy combined with Akin osteotomy was used to treat 62 patients (83 feet) with moderate to severe hallux valgus. Twenty-five patients (35 feet) were fixed by absorbable screws (group A) and 37 patients (48 feet) were fixed by metal screws (group B). The difference in gender, age, affected side, etiology, severity, disease duration, preoperative hallux valgus angle (HVA) and first-second intermetatarsal angle (1-2IMA) measured in weight-bearing anteroposterior X-ray film, preoperative American Orthopaedic Foot and Ankle Society (AOFAS) scores and visual analogue scale (VAS) scores between 2 groups ( P>0.05). The complications and healing time of 2 groups were recorded and compared. At last follow-up, the AOFAS and VAS scores, and HVA, 1-2IMA measured by weight-bearing anteroposterior X-ray film were used to evaluate the effectiveness.
Results
All incisions healed by first intention and no incision-related complication occurred in the two groups after operation. Both groups were followed up, the follow-up time in group A was 12-36 months (mean, 24.4 months) and in group B was 14-38 months (mean, 25.7 months). In group A, 1 foot was complicated with hallux varus, 2 feet had mild stiffness, 1 foot appeared metastatic metatarsal pain, and in group B was 2, 3, 2 feet, respectively. There was no recurrence of hallux valgus in both groups. The difference in the incidence of complications between the two groups after the first operation was not significant ( χ ²=0.275, P=0.843). The removal rate of internal fixator in group B was 89.2% (33 cases) during the second operation, among which 3 cases had screw slip and 1 case had screw fracture. And 10.8% (4 cases) refused the second removal operation due to their age. Postoperative X-ray films showed that both groups had good healing at the osteotomy site, and there was no significant difference in healing time between the two groups ( t=1.633, P=0.285). At last follow-up, the AOFAS score, VAS score, HVA, and 1-2IMA were significantly improved in the two groups when compared with preoperative ones ( P<0.05); but no significant difference was found between the two groups ( P>0.05).
Conclusion
The effectiveness of Scarf osteotomy combined with Akin osteotomy in the treatment of moderate to severe hallux valgus is significant, with few complications. Compared with being fixed by metal screws, being fixed by absorbable screws has the same effectiveness, but can avoid the risk of second operation to remove the internal fixator.
There has been a growing interest in the use of bioabsorbable polymers in interference screws for knee ligament reconstruction surgeries. This interest is driven by virtue of the relevant properties exhibited by these polymers. Among such essential properties include excellent biocompatibility and bioabsorption, good integration between graft/bone, in addition to the ease they offer when it comes to surgical revision. This article seeks to report the results obtained from the study aimed at the development of a bioabsorbable interference screw produced by the injection molding process with two distinct polymeric materials: PLDL poly(L,DL‐Lactic acid) and a composite PLDL + 30 wt% TCP (β‐tricalcium phosphate). Finite element analysis (FEA) was used for the development of the screw design. The mechanical strength of the screws was evaluated, where the maximum torque to break was found to surpass the insertion torque by 136% in PLDL material and by 190% in PLDL+TCP. The mean values of pullout force obtained for PLDL and PLDL+TCP were 1635 N and 809 N, respectively. An in vitro degradation test performed over a period of 180 days helped to assess the mechanical behavior during degradation and facilitated the comparison of the screws based on specific application requirements. The composite material (PLDL+TCP) exhibited a faster degradation process, with 88% loss of mechanical resistance following 180 days of degradation compared with 55% observed in the PLDL material. The results show that the addition of bioactive ceramic TCP contributed toward raising the initial mechanical resistance and acceleration during the process of degradation. POLYM. COMPOS., 2018.
Background:
This biomechanical cadaveric in vitro study aimed to evaluate and compare the dynamic elongation behavior and ultimate failure strength of tibial adjustable-length loop cortical button versus interference screw fixation in quadriceps tendon-based anterior cruciate ligament reconstruction.
Methods:
Sixteen human quadriceps tendons were harvested and fixed into porcine tibiae using either biodegradable interference screw (n = 8) or adjustable loop device (n = 8) fixation. An acrylic block was utilized for femoral adjustable loop device fixation for both groups. All constructs were precycled for 10 times at 0.5 Hz and manually retensioned before tested in position and force control mode each for 1000 cycles at 0.75 Hz according to in vitro loading conditions replicating the in vivo ACL environment. Subsequently, an ultimate failure test at 50 mm/min was performed with mode of failure noted.
Findings:
Tibial IS fixation showed no statistically significant differences in the initial (-0.46 vs. -0.47 mm; P = 0.9780), dynamic (2.18 mm vs. 2.89 mm; P = 0,0661), and total elongation (1.72 mm vs. 2.42 mm; P = 0,0997) compared to adjustable loop device fixation. The tibial button fixation revealed an increased ultimate failure load (743.3 N vs. 606.3 N; P = 0.0027), while stiffness was decreased in comparison to screw fixation (133.2 N/mm vs. 153.5 N/mm; P = 0,0045).
Interpretation:
Anterior cruciate ligament reconstruction for quadriceps tendon graft using a tibial adjustable-length loop cortical button provides for comparable dynamic stabilization of the knee with increased ultimate failure load at decreased stiffness compared to screw fixation.
Objectives
To compare the rate of initial fixation failure and clinical outcomes in anterior cruciate ligament reconstruction (ACL-R) surgery with a rectangular tunnel bone-patellar tendon-bone (RT-BTB) graft (RT-BTB ACL-R) using metallic interference screws (M-IFSs) and bioabsorbable interference screws (B-IFSs) for femoral fixation.
Methods
Data were prospectively collected from patients undergoing RT-BTB ACL-R and CT within 2 weeks after surgery. Femoral fixation was performed using M-IFSs (M-IFS group) or B-IFSs (B-IFS group). Screw selections were historically controlled. The following parameters were intraoperatively assessed: IFS breakage and initial fixation failure examined by movement of the graft pulled with maximum manual force. Posterior wall breakage was assessed using CT. Lysholm Score, the 2000 International Knee Documentation Committee Knee Examination Form and the KT-2000 arthrometer was evaluated as the clinical outcome measures.
Results
The study included 116 patients. Of these, 26 were included in the M-IFS group and 92 in the B-IFS group. The rate of IFS breakage was not significantly different between the M-IFS and B-IFS groups (0.0% vs 2.2%). The rate of initial fixation failure was not significantly different between the M-IFS and B-IFS groups (3.8% vs 5.6%). Logistic regression analysis revealed that only posterior wall breakage predicted initial fixation failure (p=0.02). No significant difference of the clinical outcomes was observed between the M-IFS and B-IFS groups.
Conclusion
Initial fixation failure or clinical outcomes is not different between M-IFS and B-IFS use for femoral fixation in RT-BTB ACL-R.
Level of evidence
Prospective study using historical controls, level IV.
Anatomic ACL reconstruction depends on adequate time-zero graft fixation to allow for graft incorporation and subsequent knee stability. Biomechanical testing has demonstrated significant differences between fixation devices and excellent clinical results have been reported using a wide variety of fixation devices and techniques. This chapter explores a number of these factors and their relevance in obtaining ideal ACL intratunnel fixation.
Statement of significance:
How to promote tendon-bone junction healing is one of the major challenging issues for satisfactory clinical outcomes in patients after ACL reconstruction. The improvement of bony ingrowth into the tendon graft-bone interface can enhance the tendon graft osteointegration. In this study, we applied Mg based interference screws to fix the tendon graft in rabbits and found the use of Mg screws could accelerate and significantly increase mineralized matrix formation at the tendon-bone interface in animals when compared to those with Ti screws. We elucidated the mechanism behind the favorable effects of Mg screws on the graft healing in both in vitro and in vivo studies from multiscale technologies. The optimized interface structure and function in Mg group may be ascribed to the improved cell migration capability, enhanced cell adhesion strength and promoted osteogenic differentiation ability of BMSCs under the stimuli of Mg ions degraded from implanted Mg screws. Our findings may help us broaden our thinking in the application potential of Mg interference screws in future clinical trials.
Background: We report a series of cases that presented as pre-tibial cyst, swelling and pain following anterior cruciate ligament (ACL) reconstruction using bioabsorble fixation devices (HA-PLLA). Methods: All ACL reconstructions were done between 2008 and 2014 reviewed retropectively to identify complications related to bioabsorbable fixa-tion devices. During this period of 6 years, 620 ACL reconstructions were performed using the bioab-sorbable screw (HA-PLLA) for tibial fixation of the quadrupled hamstring autograft. Results: Nine patients (1,45%) with mean age of 29,8 (19-44) years, presented in the post-operative period, pre-tibial pain, cyst and swelling in tib-ial screw site. All of them had normal inflammatory
Tears of the anterior cruciate ligament are common in¬juries. Today the incidence is 1 injury per 1000 people per year [102]. It occurs typically during sports due to a external rotation valgus movement of the flexed weight bearing knee e.g. during skiing or football. An overextension mechanism is also possible.
Objective: To compare clinical outcome of bioabsorbable interference screws (BS) with metal Interference screws (MS) for restruction of anterior cruciate ligament (ACL). Methods: The electronic databases (PubMed, EMbase, Cochrane Central Register of Controlled Trials, CBM, CNKI, and VIP) were searched in order to retrieve randomized controlled trials (RCTs) about comparing BS with MS for restruction of ACL. In addition, reference lists from original studies and review articles were handsearched. The Jadad's scale and Cochrane collaboration's RevMan 5.0 software were used for assessing trial methodological quality and data analyses. Results: Eleven RCTs were included. There were 935 participants that met inclusion criteria in all studies. Results of Meta-analyses showed the MS group had a higher Lysholm score. However, no significant differences were found in Lanchman Test, IKDC Data and KT1000 result between patients treated by BS and by MS. Conclusion: Bioabsorbable interference screws provide equivalent clinical outcomes compared with metal interference screws. However, further confirmation is required because of varieties of types and complex compositions.
The understanding and treatment of anterior cruciate ligament (ACL) ruptures has advanced significantly in the modern era. Risk factors for injury, including female gender, anatomic variations, and landing mechanics, are now better understood. Evaluation of anatomy and the biomechanical function of the ACL have defined contemporary reconstruction techniques. Randomized studies with clinical outcome measures evaluating graft type, fixation methods, and tunnel position are now available to guide surgeons in their operative technique and decision making. A new frontier in anatomic ACL reconstruction is grounded in clinical evidence that offers patients restored kinematics, increased knee stability and more predictable return to sport.
Screws are one of the major implants in orthopaedic surgery. For the application of the Anterior-Cruciate-Ligament (ACL) reconstruction so called interference screws are used. These screws normally consist of biodegradable polylactid or polyglycolid acids but some studies found foreign-body reactions like fistulization or persistent secretion in up to 23%. Processed cortical bone seems to be an adequate implant material for orthopaedic surgery. Bone as an implant material has the advantage to be resorbed and replaced by new own bone tissue. However, the biomechanical and osteoinductive properties of bone can easily be harmed by exceeding a critical temperature for a certain time. By using the AWIJ as the manufacturing tool this can be avoided. Furthermore it is possible to drill, cut, turn and thread bone material with this non-contact tool. In this study some fundamental investigations to manufacture screws made of cortical bone will be presented. The cutting process of inner contours with a wrench size of 2.5 mm will be focused.
We compared the strength of fixation of a biodegradable screw with that of two metal screws in a bone-patellar-tendon-bone (BPTB) graft in the bovine knee. We used 33 fresh BPTB specimens with a circular tibial bone plug of 9 mm in diameter which were anchored in a tibial metaphyseal bone tunnel with either an interference screw (n = 11), an AO cancellous screw (n = 11) or a fibrillated, self-reinforced biodegradable poly-L-lactide screw (n = 11). The mean force to failure (+/- SD) in the three groups was 1358 +/- 348 N, 1081 +/- 331 N and 1211 +/- 362 N, respectively. There was no significant difference in the groups with regard to the linear load or the elastic moduli of the fixation. We conclude that the biodegradable screw is as good as either of the two metal screws in the fixation of a BPTB graft in the bovine knee and can be recommended for ACL reconstruction using this type of graft.
This study assessed the tensile properties of hamstring and patellar tendon anterior cruciate ligament reconstructions in older cadaveric knees (age range, 48 to 79 years). Mechanical testing to failure was conducted by translating the tibia anteriorly at 1 mm/sec with the knee in 20 degrees of flexion. The strongest gracilis-semitendinosus graft fixation technique (103% of intact anterior cruciate ligament) had the tendons doubled and secured with soft tissue washers (P < 0.01). However, all reconstructions using gracilis-semitendinosus grafts were significantly less stiff than the intact anterior cruciate ligament specimens regardless of fixation technique (P < 0.01). The highest strength patellar tendon graft fixation technique (84% of intact anterior cruciate ligament) was obtained with a combination interference screw and suture technique. The difference in stiffness between a patellar tendon graft and an intact anterior cruciate ligament was not significant when interference screws were placed at both ends of the graft (P > 0.05). Both types of grafts failed most often on the tibial side. With appropriate fixation, both grafts approximated the intact anterior cruciate ligament in strength, but only patellar tendon grafts secured with interference screws were comparable in stiffness.
Twenty-seven paired human cadaveric knee specimens were used to determine the effect of surgical technique and various interference screw parameters on the pullout strength of patellar tendon femoral bone blocks. The study compared the fixation strength of endoscopically inserted and conventional "rear-entry" screws of different diameters and lengths. In all tests the most frequent mode of failure was bone block pullout from the interference screw. There was no significant difference in fixation strength between 9-mm diameter screws inserted through a conventional rear-entry technique and 7-mm diameter screws inserted through an endoscopic technique. There was no significant effect of screw length on fixation strength. The pullout force for 20-mm long screws increased on average 120% when 7-mm diameter screws were compared with 5.5-mm diameter screws. There was no significant effect of increased screw core diameter on fixation strength. There was a weak positive correlation (r2 = 0.45) between screw insertion torque and pullout force. Our measured mean pullout force for the 7-mm endoscopically inserted screws of 362 +/- 198 N represents 20.1% of the failure load of the normal young adult anterior cruciate ligament. Our data indicate that properly inserted 7-mm diameter endoscopic interference screws can provide fixation strengths of patellar tendon anterior cruciate ligament grafts equivalent to those of conventional 9-mm diameter rear-entry, outside-in screws.
Schrauben werden entweder als Zugschrauben zur stabilen Fixation von Knochenfragmenten oder aber zur Befestigung von Platten oder ähnlichen Vorrichtungen am Knochen verwendet.
In vivo and in vitro degradation of high molecular weight poly(L-lactide) used for internal bone fixation has been investigated. Within 3 months as-polymerized, microporous PLLA (M-v = 6.8–9.5 sx 105) exhibited a massive strength-loss (gsb = 68–75 MPatogsb = 4 MPa) and decrease of M-v (90–95%). At week 39, the first signs of resorption were evident (mass-loss 5 wt%). Except for dynamically loaded bone plates no differences between In vivo and in vitro degradation of PLLA were observed. The increase of crystallinity of PLLA upon degradation (up to 83%) is likely to be attributed to recrystallizaton of tie-chain segments. A more ductile PLLA exhibiting a lower rate of degradation was prepared by extraction of low molecular weight compounds with ethyl acetate.
An entire range of screw sizes and types from one manufacturer (Synthes, Switzerland) along with two experimental sizes were tested in bovine cancellous bone to measure torque of insertion, screwdriver pressure, axial compression generated by the screw, screw breaking strength and efficacy of various head types. The results showed a gradual increase in strength as diameter increased. Maximal axial compression peaked at 5.0 mm. The hexagonal shaped imbus head proved superior to the Phillips type.
Although arthroscopic Bankart repair has become an accepted surgical stabilization technique for anterior shoulder instability, the failure rate remains unacceptably high. Little information is available concerning healing of the Bankart repair. The purpose of this article is to clarify this issue by analyzing a cohort of 15 patients who underwent a “second-look” artroscopy to evaluate and treat pain or recurrent instability following arthroscopic Bankart repair with the Suretac device (Acufex Microsurgical, Mansfield, MA). “Second-look” arthroscopy was performed at an average of 9 months following the index surgical procedure. The reasons for this second surgery were recurrent instability in 7, pain in 6, and pain and stiffness in 2. In the 7 patients with recurrent instability, the Bankart repair was found to be completely healed in 3 (43%), partially healed in 1 (14%), and had recurred in 3 (43%); however, 6 of 7 were observed to have lax capsular tissue. In 4 of these cases, retrospective review of the index surgical procedure showed that a technical error had been made during the repair. Two cases had biopsy of the repair site on “second-look” at 6 to 8 months, and this showed residual polyglyconate polymer debris surrounded by a histiocytic infiltrate. In the remaining 8 cases with stable shoulders, the Bankart repair had completely healed in 5 cases (62.5%) and partially healed in 3 cases (37.5%). The higher failure rate with this approach compared with open approaches appears to result from improper patient selection and errors in surgical technique. There is some question concerning healing strength of the Bankart repair, although complete healing of the Bankart does not seem to be a prerequisite for shoulder stability. Success of the procedure might be expected to improve by selecting only patients with unidirectional, post-traumatic, anterior instabilit who are found to have a discrete Bankart lesion and well-developed ligamentous tissue.
Purpose:
To compare bioabsorbable screw (BS) against metal screw (MS) primarily on adverse effects and secondarily on clinical outcomes after single-bundle primary anterior cruciate ligament reconstruction.
Methods:
Electronic searches were performed using search strategies meeting the mentioned purposes. Retrieved articles were selected for randomised controlled trials (RCTs) reporting at least 1-year follow-up. Potential studies were selected under inclusion and exclusion criteria. Risk of biases and data extraction was completed by two review authors. Discrepancies were resolved through discussion. Mean difference and risk ratio with 95 % confidence interval (CI) were used for continuous and binary outcomes, respectively. Heterogeneity was assessed using I (2). Pooled treatment effects with 95 % CI were estimated using the fixed- or random-effect model where appropriate.
Results:
Eleven RCTs with 878 randomly allocated patients were included, and 711 patients (81 %) with eligible follow-up time up to 8 years were analysed. Comparing with the MS group, BS group using medial hamstring graft showed evidence of larger tunnel widening on the femoral side measured from radiographs or magnetic resonance imaging, though data could not be pooled because diverse measurement methods had been used. Significantly higher rates of effusion and screw breakage, and fewer cases of complete tunnel healing were reported in the BS group. Nevertheless, functional and clinical results were not deteriorated by the presence of these adverse effects for both short- and longer-term follow-ups.
Conclusion:
This is the first systematic review focusing on adverse effects of the BS, such as larger tunnel widening and higher rates of other complications. With these effects, routine use of the BS should be balanced with the advantages claimed. Cost-effectiveness is another issue, and well-designed RCTs are needed to better validate the implication.
Bioabsorbable implants have been advocated for use in repair of a torn glenoid labrum to correct shoulder instability. These implants have been thought to be safe and to have little toxicity, antigenicity, or adverse side effects. However, similar implants have been shown to cause nonspecific granulomatous reactions when implanted into bone or soft tissues in studies in both animals and human beings. This article reports the adverse effects of these implants in six shoulders of five patients who had repair of a damaged glenoid labrum. All patients reported increasing pain and loss of shoulder motion after insertion of these devices. All required a further arthroscopic lavage and debridement to reduce the inlracapsular synovitis. Granulomatous reactions were identified histologically in all cases. No long-term side effects were encountered, and all patients recovered satisfactorily.
Magnetic resonance (MR) imaging is contraindicated for patients with certain ferromagnetic implants, primarily because of potential risks related to movement or dislodgment of the devices. An additional problem with metallic implants is the potential image distortion that may affect the interpretation of the MR study. Since MR imaging is frequently useful for the evaluation of postoperative anterior cruciate ligament (ACL) reconstruction, the ferromagnetic qualities and artifacts associated with MR imaging were determined for five metallic orthopedic implants commonly used for this surgery. Only the Perfix interference screw displayed a substantial deflection force and caused extensive signal loss. Images of the knee of one patient with two Perfix screws in place were not interpretable because of the image distortion caused by these implants. Therefore, alternative nonferromagnetic implants should be considered for reconstruction of the ACL.
To overcome many of the complications after ACL reconstruction (prolonged knee stiffness, limitation of complete extension, delay in strength recovery, anterior knee pain), yet still maintain knee stability, we developed a rehabilitation protocol that emphasizes full knee extension on the first postoperative day and immediate weightbearing according to the patient's tolerance. Of 800 patients who underwent intraarticular ACL patellar tendon-bone graft reconstruction, performed by the same surgeon, the last 450 patients have followed the accelerated rehabilitation schedule as outlined in the protocol. A longer than 2 year followup is recorded for 73 of the patients in the accelerated rehabilitation group. On the 1st postoperative day, we encouraged these patients to walk with full weightbearing and full knee extension. By the 2nd postoperative week, the patients with a 100° range of motion participated in a guided exercise and strengthening program. By the 4th week, patients were permitted unlimited activities of daily living and were allowed to return to light sports activities as early as the 8th week if the Cybex strength scores of the involved extremity exceeded 70% of the scores of the noninvolved extremity and the patient had completed a sport-specific functional/agility program. The patient database was compiled from frequent clinical examinations, periodic knee questionnaires, and objective information, such as range of motion measurements, KT-1000 values, and Cybex strength scores. A series of graft biopsies obtained at various times have revealed no adverse histologic reaction. The evidence indicates that in this population, the accelerated rehabilitation program has been more effective than our initial program in reducing limitations of motion (particularly knee extension) and loss of strength while maintaining stability and preventing anterior knee pain.
Great difficulty is encountered in choosing screws for internal fixation, for screws differ in material, geometry, dimension, and in insertion technique. Recently claims have been made that self-tapping screws cause necrosis of bone and result in fibrous tissue formation, with loss of holding power. This investigation was undertaken to study the healing of bone about screws inserted for a period of 3 months. Self tapping and non-self tapping screws were employed. The Vitallium screws not only differed in dimension, but also in configuration of the thread, with the smaller of the self-tapping screws exhibiting a "V" thread in distinction to the buttress thread of the larger screw. The histologic data were correlated with the holding power of the screws as obtained by means of a push out test, performed with the aid of an Instrom testing machine. The largest screw tested, the 4.5 mm non-self tapping stainless steel AO screw (Type 1), provided the greatest safety factor to push out loading over the period tested in the unloaded system. The self tapping and non-self tapping screws of similar material and size were found to maintain comparable holding power at all intervals tested in vivo in the unloaded system. No histological differentiation could be made with regard to both death or tissue reaction around the implant, between the stainless steel or cobalt chromium alloy materials, nor between the self tapping and non-self tapping insertion methods.
Biodegradable rods made of polyglycolide (Dexon, Biofix) or lactide-glycolide copolymer (Vicryl) have been used for the past 5 years for internal fixation of a variety of fractures and osteotomies (Böstman et al. 1989, 1990b). Experience from using such rods for fixation of intraarticular osteochondral lesions seems to be less extensive. We report a case of severe synovial reaction to biodegradable rods used for fixation of osteochondritis dissecans of the knee and discuss possible reasons for the increased risk of foreign-body reactions when these rods are used intraarticularly.
In a prospective trial, biodegradable polyglycolic acid rods were compared with Kirschner wires for fixation of wrist fractures (Frykman types I, II, V and VI). Fifteen patients were randomly assigned to each treatment group. There was no significant difference between the groups with regard to age, sex ratio and fracture type. Kapandji's pinning technique was used in all cases. There were no significant differences in the results obtained in both groups at final follow-up. At three months and six months the functional results of the Kirschner-wire group were, however, significantly better (p < 0.05), due to numerous transient complications from foreign-body reactions to the polyglycolic acid rods. The use of polyglycolic acid rods is therefore not recommended for the fixation of distal radial fractures.
The authors report an in vitro biomechanical evaluation of a biodegradable material that might be used for the reinforcement of surgical screws in fractures involving severely osteoporotic bone. The material is a particulate composite with a matrix phase consisting of a hydrolyzable prepolymer, polypropylene fumarate (PPF), crosslinked with methacrylate monomer, and a particulate phase consisting of tricalcium phosphate and calcium carbonate. Pullout force and stripping load of cancellous screws were determined along with screw pullout force before and after reinforcement with either polymethylmethacrylate (PMMA) or PPF composite. Pullout force was moderately correlated (R2 = 0.59) with apparent density by a power law relationship of the form 0.065p1.37-1.77. Stripping load was strongly correlated (R2 = 0.91) with apparent density by a power law of the form 0.13p1.35-93.8. Mean pullout force before and after reinforcement with PMMA was 382 +/- 100 N (mean +/- standard deviation) and 879 +/- 315 N, respectively. Mean pullout force before and after reinforcement with PPF composite was 571 +/- 294 N and 829 +/- 354 N, respectively. Although the increase in pullout force with cement reinforcement was highly significant in both cases, the magnitude of the increase did not depend on the type of cement. Thus PPF seems to provide reinforcement that is equivalent to that provided by PMMA.
This study provides biomechanical support for a new technique of autograft anterior cruciate ligament reconstruction featuring circular bone plugs and endosteal interference fit fixation. Six matched pairs of fresh frozen human knees were utilized. Femoral interference fit pull-out strength was determined from material-testing-machine-generated oscillograph recordings at a strain rate of 100%/s. Circular bone plugs, obtained with a circular oscillating saw, provided 19.9% greater interference fit pull-out strength compared with identically fixed trapezoidal bone plugs. Different geometric defects were compared in three- and four-point bending on an Instron machine with frozen patellae and an artificial bone composite. Circular defects have 107% greater strength than matched trapezoidal patellar defects in three-point bending. In a bone composite, circular defects are 53% stronger than triangular and 25% stronger in four-point bending than trapezoidal defects. A new technique of harvesting bone plugs with endosteal interference fit fixation is described and biomechanically supported. To date, this technique has been performed on over 500 cases clinically without evidence of patellar fracture or fixation failure. This study demonstrates the efficacy of this simple and reproducible technique compared with previously reported procedures.
We report two cases of severe aseptic synovitis of the knee 8 and 13 weeks after biodegradable internal fixation (Biofix rods) of a fracture of the intercondylar eminence. Both knees were treated by surgical revision and synovectomy. Histologic examination revealed a severe foreign-body type of reactive synovitis in the absence of infection. It is not advisable to use Biofix intraarticularly.
Stability of internal fixation by plate and screw depends on the interface of bone and screw threads. Bone-screw thread design was tested in a synthetic bone model to determine maximum bone-screw pullout force. The model was confirmed to provide reproducible results in a clinically relevant range. Consistent material properties were reflected in the relatively small standard deviations in pullout force, which were less than 10% of mean values. As expected, major diameter was an important determinant of pullout force in a roughly linear manner. Pitch was important with a finer thread giving greater purchase. Minor diameter and the ratio of major to minor diameter had a small but significant effect on pullout force. This study was significant for establishing a good bone-screw testing model and suggesting important thread parameters in selecting or manufacturing a bone screw to optimize its holding power.
Arthroscopically assisted bone patellar tendon bone reconstruction of the anterior cruciate ligament (ACL) is becoming an increasingly popular surgical technique. Use of interference screw fixation of the bone plugs within bony tunnels has been shown to improve fixation and pull-out strength. Several potential pitfalls exist which can jeopardize results of the surgical procedure when this form of fixation is used. This article describes the potential pitfalls and suggests methods to avoid them.
Biodegradable polylactide-glycolide copolymer implants for fracture fixation were developed and tested in rabbits. In a prospective clinical study 44 patients with a displaced fracture of the ankle were randomly allocated to two groups; one was treated with conventional metallic implants and the other with the biodegradable implants. There were no differences between the two groups in the early results, but the biodegradable fixation method is advantageous because the removal procedure associated with metallic implants is avoided.
The authors report on the fixation of cartilage-bone fragments via an (absorbable) PDS rod. The study was conducted with 18 rabbit knee joints. Good healing of the fragments was seen over a period of 10 weeks. In vitro examinations of the rod showed satisfactory tearing and bending strength with only slow deterioration of strength due to hydrolysis. On the basis of these studies the authors believe that the rods are suitable for fixing small fragments in accident surgery. Other fields of application are possible and require to be investigated.
Resorbable pins made of solid polydioxanone (PDS) were tested for refixation of osteochondral fragments. In both medial femoral condyles of sheep osteochondral fragments were chiselled and refixed by 3 PDS pins. After 3 months the sheep were sacrificed and healing of the fragments investigated histologically and biomechanically. Fragment dislocation was not seen in any of the cases and the cartilage surface could be described as normal. The strength of the bone healing zone reached 80% of the strength of the normal bone. The contact surface between fragment and subchondral bone showed complete bony healing. Only the border of the cartilage flake was still visible. The PDS pins had not been completely biodegraded after 3 months.
Different surgical methods of graft fixation in ACL reconstruction were examined to determine the effects on mechanical properties of the reconstructed ACL. Ten human cadavers were used in this study. Six different types of grafts were studied. The tendon grafts were removed from each cadaver and fixed to femurs and tibias as ACL substitutes with different surgical fixation methods, leaving femur-reconstructed graft-tibia preparations. The surgical techniques used were staple fixation, tying sutures over buttons, and screw fixation. In the latter, the screws were introduced through femoral and tibial drill holes from the outside in order to achieve interference fit as described by Lambert. Tensile testing demonstrated that the original ACL is significantly stronger than the graft used for reconstruction in linear load, stiffness, and maximum tensile strength. All of the failures of the reconstructed ACL grafts occurred at the fixation site, indicating that the mechanically weak link of the reconstructed graft is located at the fixation site. Among the different methods of fixation, one-third of the patellar tendon secured with a cancellous screw, especially with a custom designed large diameter screw, showed significantly higher values. Although many other factors affect the success of ACL reconstruction, our study indicates that the method of surgical fixation is the major factor influencing the graft's mechanical properties in the immediate postoperative period.
In vivo and in vitro degradation of high molecular weight poly(L-lactide) used for internal bone fixation has been investigated. Within 3 months as-polymerized, microporous PLLA (Mv = 6.8-9.5 X 10(5] exhibited a massive strength-loss (sigma b = 68-75 MPa to sigma b = 4 MPa) and decrease of Mv (90-95%). At week 39, the first signs of resorption were evident (mass-loss 5 wt%). Except for dynamically loaded bone plates no differences between in vivo and in vitro degradation of PLLA were observed. The increase of crystallinity of PLLA upon degradation (up to 83%) is likely to be attributed to recrystallization of tie-chain segments. A more ductile PLLA exhibiting a lower rate of degradation was prepared by extraction of low molecular weight compounds with ethyl acetate.
The function of a surgical bone screw is to clamp together the bone and a bone plate or to fix bone fragments. This is achieved by the generation of a tensile stress along the length of the screw which is derived from the torsional moment introduced into the screw during the screwing process. This work shows that the strength of the commonly available surgical materials, assessed on a combined torque and tensile basis, is in the descending order cold-worked En58J stainless steel>cast Co-Cr-Mo>titanium 160. Core diameter is the major factor determining the strength of a screw in a given material.
For maximum efficiency the highest tensile stress should be generated in a screw by the lowest torsional moment. It can be shown that under adverse circumstances only 5 per cent of the applied torque can be used to induce tension in the screw. By alteration of the method of insertion this value can be raised to about 65 per cent.
The holding power of a screw is shown to be independent of the screw's material, but is dependent on the major diameter of the screw and also on the shearing strength of the bone. For any given level of bone strength there is optimum pilot hole size, which is related to the major diameter of the screw. The sizes of these holes have been determined for a range of screws.
Virtually all types of collagenous tissues have been transferred in and around the knee joint for intra-articular and extra-articular ligament reconstructions. However, the mechanical properties (in particular, strength) of such grafts have not been determined in tissues from young adult donors, where age and disuse-related effects have been excluded. To provide this information, we subjected ligament graft tissues to high-strain-rate failure tests to determine their strength and elongation properties. The results were compared with the mechanical properties of anterior cruciate ligaments from a similar young-adult donor population. The study indicated that some graft tissues used in ligament reconstructions are markedly weak and therefore are at risk for elongation and failure at low forces. Grafts utilizing prepatellar retinacular tissues (as in certain anterior-cruciate reconstructions) and others in which a somewhat narrow width of fascia lata or distal iliotibial tract is utilized are included in this at-risk group. Wider grafts from the iliotibial tract or fascia lata would of course proportionally increase ultimate strength. The semitendinosus and gracilis tendons are stronger, having 70 and 49 per cent, respectively, of the initial strength of anterior cruciate ligaments. The bone-patellar tendon-bone graft (fourteen to fifteen millimeters wide, medial or central portion) was the strongest, with a mean strength of 159 to 168 per cent of that of anterior cruciate ligaments. Patellar tendon-bone units, based on grip-to-grip motions, were found to be three to four times stiffer than similarly gripped anterior cruciate ligaments, while gracilis and semitendinosus tendon preparations had values that were nearly identical to those of anterior cruciate ligaments.(ABSTRACT TRUNCATED AT 250 WORDS)
After diagnosing the anterior cruciate ligament (ACL) rupture by manual and arthroscopic examination with the patient under anesthesia, the decision to augment or substitute depends on the patient's requirements. In a community of athletically motivated patients, a method of strong, durable stabilization is achieved using a pedicled patellar tendon graft with a 90 degrees twist and bone-to-bone fixation. The intercondylar notch is surgically enlarged; holes are drilled from without into the tibia and femur, the graft is harvested with bone plugs at each end, pulled into place, and transfixed with screws. Knee function is tested before closure. After operation, the emphasis is on joint ranging exercises. Quadriceps exercises are not initiated until three months after operation. Participation in a sport is not advised for approximately one year. The patellar tendon graft has all of the advantages of an autologous tissue, either for augmentation or substitution of the ACL. It has strength, durability, and elasticity; it can be transplanted with bone plugs; with the infrapatellar fat pad preserved, it retains its paratendinous vascularity. The method has been employed for five years. No graft failures have occurred, and no patient has reinjured the reconstructed ligament. Not one patient has had to give up the sport that caused the injury due to recurrent instability.
Patients with fractures of the zygomatic bone were treated with high molecular weight poly(L-lactic) acid (PLLA) bone plates and screws. Three years after implantation four patients returned to our department with a swelling at the site of implantation. At the recall of the remaining patients we found an identical type of swelling after the same implantation period. To investigate the nature of the tissue reaction, eight patients were reoperated for the removal of the swelling. The implantation period of the PLLA material varied from 3.3 to 5.7 years. Microscopic evaluation and molecular weight measurements were performed. The excised material showed remnants of degraded PLLA material surrounded by a dense fibrous capsule. Ultrastructural investigation showed crystal-like PLLA material internalized by various cells. The results of this investigation suggest that the PLLA material slowly degrades into particles with a high crystallinity. The intra- and extracellular degradation rate of these particles is very low. After 5.7 years of implantation, these particles were still not fully resorbed.
Suture anchors are being increasingly reported as a means of fixation of torn rotator cuff tendons to bone. The author has developed a mechanical model for the suture anchor-rotator cuff construct based on an analogy to the deadman system used to stabilize a corner fence post. Using this model, one can demonstrate a mechanically favorable angle of insertion of the suture anchor (theta 1) such that the anchor's pullout strength is increased at low angles of theta 1. In addition, the angle that the suture makes with the direction of pull of the rotator cuff (theta 2) has a direct effect on tension in the suture. A low angle of theta 2 minimizes the total tension in the suture, thereby minimizing the chance of suture breakage.
In reconstruction of the anterior cruciate ligament (ACL), using central one-third patellar tendon graft, an early weak link is the bone plug junction. To study this, we carried out experiments to determine the relationship between gap size, screw size, and pullout force of patellar bone plugs inserted in the femur of the porcine model. Forty-nine porcine knees were obtained. Holes 11 mm in diameter were drilled in the intercondylar notch of the femur. Bone plugs fashioned from the patella were made to fit the holes with gap sizes of 1, 2, 3, or 4 mm. The bone plugs were inserted into the holes in the femur and secured by means of 20-mm-long screws (either 7- or 9-mm diameter). The bone plugs were then pulled out using a tensile testing machine and the pullout force was measured. The results suggest that a 7-mm (or a 9-mm) diameter screw can be used for gaps of 1 and 2 mm, and a 9-mm diameter screw should be used for gaps of 3 and 4 mm.
Interference screw fixation is frequently used in anterior cruciate ligament reconstruction with the bone-patellar tendon-bone graft. There have been no data available about the influence of screw diameter and insertion torque on primary stability. We designed a cadaveric study using paired knees to analyze the comparative effectiveness of 20-mm long screws of different diameters (9 mm versus 7 mm) and the significance of torque during screw insertion. Testing to failure was performed in a tensiometer with a crosshead speed of 200 mm/min. After slippage of a bone peg in the 7-mm screw specimens, the experiment was repeated in each specimen with a 9-mm screw fixation. Maximum tensile force was greater at the femoral insertion than at the tibial site. Results of refixations with 9-mm screws were only slightly inferior to the original 9-mm screw fixation specimens. Our results further showed that the torque can be used as a predictor of the stability of the bone block but cannot be used as an indicator for the strength of the reconstruction. The 7-mm screws are not recommended for tibial fixation. Failed 7-mm screw fixations can be replaced by 9-mm screws and refixations were successful in our study model.
The aim of this study was to investigate the effect of phagocytosed poly(L-lactic acid) particles on the morphology and viability of phagocytes, mainly macrophages. Therefore, predegraded poly(L-lactic acid) (P-PLLA) and nontreated PLLA (N-PLLA) particles, both having diameters not exceeding 38 microns, were injected intraperitoneally in mice. P-PLLA particles were obtained by 25 kGy gamma-irradiation of N-PLLA particles. N-PLLA and P-PLLA particles were injected using an 0.3% ethanol/0.9% saline solution intraperitoneally to the mice. We also studied the release of the absorbed ethanol as a possible model for the release of low molecular weight, potentially toxic products. As control, nondegradable polytetrafluoroethylene (PTFE) particles and the carrier solution were used. After 1, 2, 3, 4, 5, and 7 days, the cells of the abdominal cavity were harvested to study the effect of phagocytosis of polymer particles on phagocytic cell morphology and viability. Studies with transmission electron microscopy indicated that, upon injection of particles in the peritoneal cavity, macrophages demonstrated signs of cell damage, cell death, and cell lysis due to phagocytosis of a large amount of P-PLLA particles. The morphology of the cells that had phagocytosed the N-PLLA and PTFE particles did not differ substantially from those of control animals in which only the solution was injected. Also, in the controls, hardly any cell death and no debris was observed. When the PLLA particles were injected as a suspension in a 0.3% ethanol/0.9% saline solution, no difference was observed between N-PLLA and P-PLLA. After phagocytosis, both cause cell damage, sometimes leading to cell death.(ABSTRACT TRUNCATED AT 250 WORDS)
A bovine model was developed for biomechanical evaluation of anterior cruciate ligament (ACL) reconstruction using patellar bone-tendon-bone (b-t-b) autograft to examine the differences in time zero fixation mechanical properties of different interference screw lengths and diameters. The surgical technique of interference screw fixation of the b-t-b complex performed clinically was reproduced in a controlled animal model. The femur-patellar tendon graft-tibia complex was tested with anterior displacement of the tibia in 30 degrees of knee flexion to allow examination of the femoral and tibial fixation properties simultaneously. The statistical model concurrently explored differences between screw length and diameter while accounting for variations between graft properties. No statistically significant differences were found between the 7- and 9-mm screws with respect to peak load or energy to failure when using a 10-mm triangular graft in a 10-mm tunnel. The 7- and 9-mm screws were superior to the 5.5-mm screws with respect to these same parameters. Based on our results, the 7-mm interference screws can be used with equal confidence as the 9-mm screw, and the 20-mm length can be similarly exchanged for 30-mm length for patellar b-t-b graft fixation.
This study compares biomechanical properties of 7- and 9-mm diameter screws providing interference fixation in anterior cruciate ligament reconstruction. Sixteen pairs of fresh-frozen bovine knees were evaluated. Uniaxial load to failure was performed at a deformation rate of 30 mm/s along the mechanical axis of the ligament graft with the knees secured at 45 degrees of flexion in a custom jig. A video analyzer was used to measure ligament strain and bone-to-bone deformation. Ultimate force, deformation, and failure mode were recorded and compared. The 7-mm screws provided 98% yield strength, and 95% ultimate force compared with the 9-mm screws. The average femoral pullout strength was 1161 +/- 93 N in the 7-mm group and 1198 +/- 142 N in the 9-mm group. Failure mode was similar in both groups. Clinically, the usage of 7-mm screws may reduce iatrogenic injuries to the patellar tendon graft compared with larger screws. This study shows that the biomechanical advantages of 9-mm screws compared with 7-mm screws are minimal.
A randomized, prospective multicenter comparison was done of a bioabsorbable interference screw (Bioscrew; Linvatec Corp, Largo, FL) made from poly L-lactic acid and a metal interference screw produced by the same company. Assignment was randomized by sealed envelopes. A total of 110 patients underwent arthroscopic patellar tendon autografts. A minimum 12 months follow-up is available on 85 patients (mean 19 months, range 12 to 33) including 42 with Bioscrews and 43 with metal screws. There were 56 male and 29 female patients. The average age was 29 years (16 to 50 years). Tourniquet times and associated surgical findings were similar for the two groups. Postoperative Tegner and Lysholm scores were not statistically different between the two groups. KT tests at 1 year showed an average 20-lb laxity of 1.8 mm for the Bioscrew and 1.2 mm for the metal screw groups. The average 1-year KT maximum manual side-to-side difference was 1.6 mm for Bioscrews and 1.6 mm for metal screws. A pivot shift was absent in 83% of Bioscrews and 90% of metal screws at follow-up. Six of 85 Bioscrews inserted (7%) broke on insertion (all were 7-mm diameter screws at the femoral site). No additional fixation was required in four cases. In two, the broken screw was replaced. No lytic bone changes or tunnel widening were found with any Bioscrew. One metal screw had tibial tunnel widening. No statistical difference was found between the Bioscrew and the metal screw groups. Short-term data support the conclusion that the Bioscrew is a reasonable alternative to metal interference screws.
Foreign-body reaction to polyglycolide (PGA) implants has been described in man. Many animal experiments have verified the mechanical properties of fixation devices made from PGA, but a significant foreign-body reaction has not been described. We studied the effect of PGA rods in 12 sheep with standardized osteochondral fractures of the medial femoral condyle fixed with uncoloured, self-reinforced PGA rods (Biofix). Radiographs were taken at intervals ranging from two weeks to two years, and the sheep were killed at intervals ranging from six to 24 months. All knees were examined histologically.
Eleven of the 12 fractures healed radiologically and histologically. Moderate to severe osteolysis was seen at four to six weeks with maximum changes at 12 weeks in ten animals. Six knees showed fistula-like connections between the implant site and the joint space. Three developed synovitis, one with inflammatory changes involving the whole cartilage and one with destruction of the medial condyle.
Although in our study osteochondral fractures fixed with PGA rods healed reliably, there were frequent, significant foreign-body reactions. Caution is needed when considering the use of PGA fixation devices in vulnerable regions such as the knee.
Lumps and bumps on the extremities and trunk are common presentations to physicians and surgeons. These growths range from benign neoplasms and cystic structures based in the epidermis and dermis to malignant neoplasms arising within the structures below the deep fascia. These soft-tissue lesions are classified according to the direction of differentiation of the mesenchymal tissue (Table I). Most soft-tissue lesions are benign; however, benign and malignant soft-tissue lesions can present in a similar fashion. In addition, the diverse lesions within the classification system and the unfamiliarity of many pathologists with soft-tissue lesions may make the correct diagnosis difficult. The annual incidence of new sarcoma cases in the United States is about 5000. While Enzinger and Weiss11 suggested that there are at least 100 benign soft-tissue tumors for every malignant tumor examined by a pathologist, the incidence of benign lesions is unknown. This heavy preponderance of benign lesions in patients presenting for medical care mandates that any physician who is planning to treat or excise such lesions be familiar with the characteristics of the potentially malignant mass in order to avoid compromising optimum treatment. Sarcomas may occur in the head and neck areas, the trunk, or the extremities. The buttock and thigh are the most common locations of the most frequent soft-tissue sarcomas. As many of these lesions occur in the extremities, the orthopaedist will see many of these patients and be expected to provide an appropriate workup, referral, or definitive treatment. Soft, mobile, well defined subcutaneous masses are usually benign. In general, one should consider any mass below the deep fascia as potentially malignant, particularly if the mass is firm and immobile. Soft-tissue neoplasms are not necessarily painful and may grow to a relatively large size in the buttock, shoulder girdle, or thigh before they are obvious to …
Because of the good initial fixation strength of interference screws used in anterior cruciate ligament reconstruction, metal interference screws have become the standard method for fixation of bone-patellar tendon-bone grafts. To avoid some of the complications with metal screws, a bioabsorbable interference screw was developed. Data on fixation strength in older human cadavers indicate a similar failure strength between bioabsorbable and metal screws. We studied the failure mechanisms, insertion torques, and fixation strengths of absorbable and metal interference screws in cadaveric knees from young and middle-aged donors. With identical gap and screw size, the mean insertion torque for the metal screws (mean, 1.5 N-m; SD, 0.8) was significantly higher than for the absorbable screws (mean, 0.3 N-m; SD, 0.19). The mean failure load for the metal screws (mean 640 N; SD, 201) was also significantly higher than for the absorbable screws (mean, 418 N; SD, 118).
A failure analysis of interference screw fixation was performed to test the hypothesis that bovine and/or elderly human cadavers are appropriate models for bonepatellar tendon-bone anterior cruciate ligament (ACL) reconstruction fixation studies. Failure mode is an important criterion for validating experimental models. The bovine, young human, and elderly human failure loads were 799±261 N, 655±186 N, and 382±118 N, respectively, and the failure modes were 75%, 69%, and 30% tissue failures, respectively. The similarities between the bovine and young human models in failure loads and failure modes indicate that bovine models are appropriate for ACL reconstruction fixation studies. The statistically significant differences between the young human and elderly human models in failure loads and failure modes indicate that elderly human cadavers are not an appropriate model for ACL reconstruction fixation studies. The differences in failure modes are consistent with previous studies using elderly human cadavers in which the predominant failure mode was bone block pullout. The tissue failures observed in the bovine and young human models contradict previous studies suggesting fixation strength is the weakest link in bone-patellar tendon-bone ACL reconstruction. Results of linear regression modeling showed statistically significant correlations between insertion torque and failure load (R
2=0.44,P<0.0001) and interference (defined as the screw outer thread diameter minus the tunnel-bone block gap) and insertion torque (R
2=0.18,P=0.003) when data from all models was combined. Results for the bovine model multiple regression showed a statistically significant regression of insertion torque (linear) and interference (quadritic) versus failure load (R
2=0.56,P=0.02). Regression slopes for screw diameter (P=0.52) and gap size (P=1.00) were not statistically significant. These results indicate that insertion torque and interference are independent predictors of failure load and should be included in future interference screw studies in addition to bone block dimensions, tunnel size, gap size, and screw diameter. Clinicians may consider using insertion torque and interference as indicators of postoperative graft fixation regarding rehabilitation decisions.
The purpose of this laboratory investigation was to determine if there was any difference in the force required to pull out a patellar bone-tendon-bone graft from a femoral bone tunnel when secured by an interference screw of different materials, metal or biodegradable. The tibial end of the bone-tendon-bone graft was placed in the femoral tunnel. A 9-mm metal interference screw was used on the left side, and a 9-mm biodegradable screw was used on the right to secure the graft. Ultimate load to failure was determined by Instron testing. The average load before failure for the graft secured by the metal screw was 436 Newtons and for the biodegradable screw was 565 Newtons. A statistical significance was not demonstrated because there was wide range of loads between donor specimens, probably because of variations in bone density.
Revision anterior cruciate ligament surgery will become more common as the number of primary anterior cruciate ligament reconstructions increases. Also contributing to this increase are those patients who had anterior cruciate ligament reconstruction using synthetic ligaments and other nonanatomic techniques that are no longer used. Preoperative planning is imperative to a successful outcome. This begins with determining the primary, and often times secondary, mechanism of failure for each patient. The determination of the etiology of failure is the first step in a carefully constructed preoperative plan, including the type of revision, skin incision, graft removal, hardware removal, tunnel placement, graft selection, graft fixation, and rehabilitation. The precise preoperative plan should have enough flexibility to accommodate unanticipated findings in the operating room. Rehabilitation protocols must be designed specifically for the revision surgery patient and be flexible enough to accommodate changes based on surgical findings and techniques. Finally, the importance of counseling the patient preoperatively regarding the potential results which, in general, are somewhat less satisfactory than with most primary reconstructions, must be emphasized. However, with proper planning, attention to detail, and adherence to basic principles of anterior cruciate ligament reconstruction, revision anterior cruciate ligament surgery can provide a satisfying solution to difficult knee instability cases.
The objective of this study was to evaluate the fixation strength of a biodegradable interference screw (Arthrex, Naples, FL) compared with press fit fixation and a titanium interference screw in anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone (BPTB) graft. Porcine lower limbs were used. Ultimate failure loads of the biodegradable screw (805.2 N; range 680 to 995 N) did not differ significantly from ultimate failure loads of titanium interference screws (768.6 N; range 544 to 1094 N). Press fit fixation provided significant (P < .01) lower fixation strength (462.5 N; range 80 to 825 N). These results support the conclusion that biodegradable interference screws are a reasonable alternative in terms of primary fixation strength.
The clinical biocompatibility and degradation of bioabsorbable interference screws of different polymer composition is described in this report for six patients who underwent repeat arthroscopy after anterior cruciate ligament (ACL) reconstruction. Bioabsorbable interference screws were used for bone plug fixation of bone--patellar tendon--bone (BPTB) autografts. Poly (L-lactide) (PLLA) interference screws were used in one case, poly (D,L-lactide-co-glycolide) (PDLLA-co-PGA) in two cases and poly (D,L-lactide) (PDLLA) in three cases. The patients either underwent removal of the femoral screw or had a biopsy taken from the screw site during re-arthroscopy. Large fragments of the PLLA screw were still present 20 months postoperatively. In one case, the PDLLA-co-PGA screw was extruded spontaneously from the tibial bone tunnel 3 weeks after the operation. In the second PDLLA-co-PGA screw case, there was no evidence left of the screw material on biopsy 12 months after implantation. The PDLLA screw in one patient was removed 6 weeks after implantation without any signs of degradation. No traces of the PDLLA screws were found in the two other patients, 10 or 14 months postoperatively. There were no clinical signs of foreign-body reactions in all cases.
This investigation compared the maximum load at failure of BioScrew (Linvatec Corp, Largo, FL) and titanium alloy interference screw femoral fixation using a human cadaveric model that approximated the anatomical orientation and physiological strain rate of in vivo bone-patellar tendon-bone (BPTB) graft loading following anterior cruciate ligament reconstruction. Eighteen fresh-frozen human BPTB allografts (10-mm wide, 10-mm thick, 25-mm long bone plugs) with either BioScrew or titanium alloy (Ti 6A14V) screw (7 x 25 mm) fixation were compared for maximum load at failure at a strain rate of 20 mm/minute. Nine cadaver femurs with bone mineral densities of 0.88 +/- 0.18 g/cm2 (anterior/posterior) and 1.3 +/- 0.24 g/cm2 (lateral) received the allografts. No statistical differences were observed in maximum load at failure (P = .95) or failure mode (P = .11) between specimens fixed with either screw type. When biomechanically tested with anatomic orientation and at functionally relevant strain rates, the BioScrew provided maximum load at failure equal to a titanium alloy screw.
Biodegradable implants are increasingly used in orthopedic and trauma surgery. Many different implants consisting of different biodegradable polymers are currently available. Different factors contribute to the biocompatibility of these implants, and local foreign-body reactions remain a matter of concern. Therefore, it is mandatory to document and compare the tissue reactions caused by various biodegradable implants in experimental or clinical studies. We have developed a standardized system of classification based on our previous experimental and clinical observations. Foreign-body reactions are differentiated into osteolysis (0-0 to 0-4), extra-articular (EA-0 to EA-4) and intraarticular (IA-0 to A-4) soft-tissue reactions.