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Effect of Screw Length on Bioabsorbable Interference Screw Fixation in a Tibial Bone Tunnel
Abstract
Initial tibial fixation strength is the weak link after anterior cruciate ligament reconstruction with a quadrupled hamstring tendon graft fixed with bioabsorbable interference screws. The purpose of this study was to determine the biomechanical differences between 28-mm and tapered 35-mm interference screws for tibial fixation of a soft tissue graft in 16 young cadaveric tibias. Failure mode, displacement before failure, and ultimate failure load were tested with a testing machine aligned with the tibial tunnel to simulate a worst-case scenario. The mode of failure was graft slippage past the screw in all but one of the specimens. The mean maximum load at failure of the 28-mm screw was 594.9 +/- 141.0 N, with mean displacement at failure of 10.97 +/- 2.20 mm. The mean maximum load at failure of the 35-mm screw was 824.9 +/- 124.3 N, with a mean displacement to failure of 14.38 +/- 2.15 mm. The 38% difference in mean maximal load at failure was significant. Important variables in hamstring tendon graft fixation within a bone tunnel include bone mineral density, dilatation, gap size, screw placement, and screw width and length. Attention to these variables will help to provide secure graft fixation during biologic incorporation throughout the rehabilitation period.
... 3,4 Several authors have reported research pertaining to the primary fixation strength of the tendon grafts. [5][6][7] It was reported that the initial fixation strength of the tendon graft depended on the contact area of the IS and the tendon graft and the diameter of IS. [8][9][10][11] Stalder et al. 4 showed that the pullout force was increased with a short IS, because better graft fixation was achieved when the tip of the IS did not extend past the end of the tendon graft. However, to the best of our knowledge, there have been no reports focusing on the positional relationship between the IS and the tendon graft and the effect of the pullout direction of the tendon graft. ...
... The initial fixation strength of the tendon graft depends on the IS size and the relationship between the IS length and the tendon graft. [8][9][10][11] Regarding the length of the screw, it has been reported that the use of a longer screw resulted in higher maximum pullout loads. 8,9 On the other hand, Stalder et al. 4 showed that the pullout strength is increased with a short IS because a short IS can be caught on the tendon graft edge when a tendon graft longer than the IS is used. ...
... [8][9][10][11] Regarding the length of the screw, it has been reported that the use of a longer screw resulted in higher maximum pullout loads. 8,9 On the other hand, Stalder et al. 4 showed that the pullout strength is increased with a short IS because a short IS can be caught on the tendon graft edge when a tendon graft longer than the IS is used. ...
Purpose::
To reveal the effects of the positional and length relationships between the interference screws (ISs) and the tendon graft in the bone tunnel on the fixation strength in ligament reconstruction.
Methods::
We compared three IS positions on the anterior (the Anterior group) or posterior (the Posterior group) or side (the Side group) of the tendon graft in relation to the pullout direction. The tendon graft was pulled at 0°, 30°, 60°, and 90° to the bone tunnel, and the maximum pullout load at each angle was compared among the groups. We also investigated the relationship between the length of the tendon graft and the length of the IS in the bone tunnel. The direction of the pullout force was the same as that of the Anterior group, and the maximum load was compared between groups in which the tendon graft was longer or shorter than the IS.
Results::
The maximum loads of the Anterior group were significantly greater than those of the Posterior and Side groups at the traction angles of 30° and 60°, respectively. An IS shorter than the tendon graft was found to provide significantly superior fixation strength compared to an IS longer than the tendon graft.
Conclusions::
Better fixation strength was achieved when the IS was placed on the side of the anchorage tunnel on which the tendon graft was loaded and the IS was shorter than the tendon graft.
... In plate-screw systems, the bond strength between the screw and the bone influences stability. Screw type, dimensions, thread width, insertion length, insertion angle, plate type, and bone properties are all important for the pull-out strength of the screw [10], [11]. Studies on pull-out strength of plate-screw system screw scan determine success of treatment [12]. ...
... In this case, it is seen that higher force is needed for the screw to pull-out. Moreover, angled placement of the screws increases the rigidity of the fixation by increasing the area in contact with the cortical bone [10]. ...
Different types of plates are available to allow insertion of screws for internal fixation of long bone fractures. The aim of the study was to determine the effect of the insertion of screws at different angles on a long bone to the pull-out strength. Using 3D printed bone models, we tested the pull-out strength of screws in long bones at insertion angles between 0 and 40° with both finite element analysis and on printed models experimentally and compared the results. Test samples and cortical screws used were modeled with SolidWorks software and analyzed with Ansys software. As the screw insertion angle increases, the pull-out forces on the test specimens increase from 61.14 ± 3.5 N at 0° to 273 ± 6.8 N at 40° with an exception of a small drop between 15 and 20° from 235.4 ± 6.2 to 233 ± 6.9 N. Both methods showed an increase in the pull-out strength of screws as the insertion angle increases. This might be applicable in the clinical practice of bone fixation. Further studies on plate and screw fixation are needed to complement the findings.
... Regarding the time-dependent viscoelastic behavior of soft tissue grafts, a 24-hour postfixation measurement would be a reasonable amount. 54 The effects of different screw diameters 7,24,28,33,38,39,50,60 and lengths 5,19,20,24,49,52,53,60 on tibial ACL fixation have been evaluated, with controversial results, but only at time zero and without analysis of the postfixation resting period. Thus, little is known about the influence of these parameters during the first 24 hours after fixation, which is a critical phase. ...
... Directly after preconditioning, the looped end of each graft was placed through the bone tunnel with 30 mm protruding from the proximal aperture of the tunnel. Therefore, the 6-cm hamstring graft was divided into an intra-articular portion of 30 mm and a tibial tunnel portion of 30 mm. 8,49,65 The looped part of the graft was attached to a shackle bolt and connected to the force sensor. Intra-articularly, the graft was positioned at the angle of the physiological anteromedial bundle of the ACL (47.9 sagittal, 73.8 coronal to tibial level) ( Figure 2). ...
Background
Tibial-sided graft fixation is thought to be critical for the success of anterior cruciate ligament (ACL) reconstruction. Nevertheless, little is known about the graft force after fixation during the first 24 hours after surgery or the influence of screw diameter and length during this time.
Purpose
To investigate the force, over the course of 24 hours, in soft tissue grafts secured with a tibial interference screw and to evaluate the effect of different screw diameters (7, 8, and 9 mm) and lengths (25 and 30 mm) on the force in these grafts.
Study Design
Controlled laboratory study.
Methods
Quadruple-strand flexor tendon grafts were fixed with bioabsorbable interference screws in 60 porcine tibiae. Grafts were pretensioned at 80 N over 10 minutes, and screws were inserted outside-in while a preload force of 80 N was applied. Different screw lengths (25 and 30 mm) and diameters (7, 8, and 9 mm), resulting in 6 groups with 10 specimens each, were tested. After release of the preload, graft force was recorded over 24 hours.
Results
A significant decrease in graft force progressed in all groups over the 24-hour period. In total, a median loss of 75 N (IQR, 68-79 N) compared with the initial loading force was observed. Compared with the loading force of 80 N, this corresponded to a median loss of 91%. No significant differences in the remaining graft force could be found among the 6 different screw length and diameter groups after 10 minutes, 100 minutes, or 24 hours.
Conclusion
Graft force in soft tissue grafts secured with a tibial interference screw decreased substantially over the first 24 hours after fixation. Neither the screw diameter nor the screw length affected the decrease in graft force. This raises substantial questions regarding the remaining fixation strength in vivo.
Clinical Relevance
It should not be expected that ACL reconstruction can mechanically restabilize an injured knee as would an intact ACL. Reconstructed knees should be protected from mechanical overload in the early postoperative period.
... Another element to consider is the screw itself. Selby et al. [19] showed that the length of the screw was fundamentally important to the graft's fixation. In their study with cadaver tibial bones from young subjects, they reported a pullout strength ranging from 594 N to 824 N depending on the screw length. ...
... The other factor contributing to the lower values in our study may be the screw itself (30 mm). As mentioned previously, Selby et al. [19] pointed out the mechanical benefit of longer screws, with 35-mm long screws being preferred. ...
Introduction:
The best fixation method for an anterior cruciate ligament (ACL) graft is debated. The tibial fixation of tendon grafts is the principal weak point for mechanical and anatomical reasons. Preserving the tibial insertion for hamstring grafts during ACL reconstruction make provide a mechanical benefit. The aim of this study was to compare the strength at the tibial tunnel of a hamstring graft with intact tibial insertion without a screw, to that of a graft with intact tibial insertion and screw fixation, and to that of a free graft with screw fixation. We hypothesized that preserving the graft's tibial insertion increases the maximum resistance of the tibial fixation relative to a free graft.
Materials and methods:
Five pairs of knees (10 specimens) from frozen human donors were used. The tendons of the semitendinosus and gracilis were prepared as a four-strand graft while preserving their tibial insertion. The graft was passed through the tibial tunnel using standard instrumentation and the usual landmarks. Three conditions were tested: group 1 - graft with intact tibial insertion without interference screw; group 2 - graft with intact tibial insertion and interference screw; group 3 - knees from group 1 in which the tendons were detached (free graft) after the first test and fixed with an interference screw in the tibial tunnel. The screw diameter was chosen based on the graft diameter. The specimens were tested in traction using a materials testing system (Instron® 8500 PLUS) in the axis of the tunnel. The main outcome measure was the maximum load at failure (N). The secondary outcome measure was the stiffness. The groups were compared using the Friedman test and the Nemenyi post-hoc test with a 5% threshold.
Results:
The load at failure was 33% higher in group 1 than group 3 (89.2N vs. 67.2N, p>0.05). The load at failure of group 2 was 25% higher than group 1 (111.2N vs. 89.2N, p>0.05) and 65% higher than group 3 (111.2N vs. 67.2N p=0.005). There were no differences in stiffness between groups 1 and 2 (p=1).
Discussion:
Our hypothesis was confirmed-preserving the tibial insertion of hamstring tendons intended for ACL reconstruction increases the maximum load to failure at the tibial tunnel. Under these experimental conditions it seems that adding a screw increases the pullout strength of the graft by +25% in absolute terms; however this difference was not statistically significant.
Level of evidence:
III, controlled laboratory study.
... 19 However, there is controversy over the effects of screw length on graft fixation strength. 13,16,19 The objective of this second part of our study was to evaluate the strength of fixation of six different devices in the fixation of quadrupled hamstring tendon graft to the tibia by using both single-cycle load-to-failure and cyclicloading testing. ...
... Concerns regarding the adequacy of strength of fixation of interference screws in securing soft tissue grafts into the biomechanically more demanding tibial bone tunnel led to the introduction of longer screws. To date, there are two studies showing improved strength of fixation of the soft tissue graft in the tibia with increased screw length, 13,18 whereas, in the study by Stadelmeier et al., 16 no extra benefit was found by increasing the screw length from 20 to 40 mm. ...
Background: Tibial fixation is more problematic than femoral fixation in anterior cruciate ligament reconstruction. Hypothesis: There is no difference in initial fixation strength among hamstring tendon graft tibial fixation devices. Study Design: Randomized experimental study. Methods: Each of six devices used to fix 120 quadrupled human semitendinosus-gracilis tendon grafts into porcine tibiae was tested 10 times with a single-cycle load-to-failure test and 10 times with a 1500-cycle loading test. Specimens surviving cyclic loading were subjected to a single-cycle load-to-failure test. Results: Intrafix (1332 N) was the strongest in the single-cycle load-to-failure test, followed by WasherLoc (975 N), tandem spiked washer (769 N), SmartScrew ACL (665 N), BioScrew (612 N), and SoftSilk (471 N). After cyclic-loading tests, Intrafix showed the lowest residual displacement (1.5 mm) and was also strongest (1309 N) in the single-cycle load-to-failure test after the cyclic-loading test, followed by WasherLoc (3.2 mm; 917 N). Conclusion: The Intrafix provided clearly superior strength in the fixation of hamstring tendon grafts to the tibial drill hole. Clinical Relevance: Some caution may be warranted when using the implants that showed increased residual displacement, especially if aggressive rehabilitation is to be used. Preconditioning of the hamstring tendon graft-implant complex before tibial fixation is needed. (C) 2003 American Orthopaedic Society for Sports Medicine.
... Many different tissue sources have been used to evaluate ACL graft fixation, including human, porcine, bovine and ovine. Human knees are the most commonly used for evaluation of ACL graft fixation devices (Kurosaka et al. 1987, Shapiro et al. 1992, Matthews et al. 1993, Butler et al. 1994, Kohn and Rose 1994, Steiner et al. 1994, Kao et al. 1995, Johnson et al. 1996, Caborn et al. 1997, Rowden et al. 1997, Aune et al. 1998, Caborn et al. 1998, Dalldorf et al. 1998, Matthews et al. 1998, Stapelton et al. 1998, Höher et al. 1999, Magen et al. 1999, Seitz et al. 1999, Stadelmaier et al. 1999, Brand et al. 2000a, Brand et al. 2000b, Shino and Pflaster 2000, Nagarkatti et al. 2001, Rittmeister et al. 2001, Selby et al. 2001, Honl et al. 2002, Rittmeister et al. 2002, Scheffler et al. 2002, Starch et al. 2003, Steenlage et al. 2002, Nurmi et al. 2003, Aydin et al. 2004, Kocabey et al. 2004, Nurmi et al. 2004a, Nurmi et al. 2004c). Obviously it would be optimal to use human cadaver tissue from young and healthy donors in evaluating the structural properties of ACL graft fixation, but since human tissues are difficult to obtain in the required extent, animal tissues have been used widely in biomechanical experiments. ...
... Many factors contribute to the strength of the initial fixation of the soft tissue graft including the density of the bone, the insertion torque of the screw and the diameter, length, design and material of the screw (Weiler et al. 1998a, Brand et al. 2000b, Weiler et al. 2000. Weiler et al. (2000) and Selby et al. (2001) found that the strength of the fixation of the soft tissue graft improves with increase in the length of the screw, but the opposite has also been described (Stadelmeier et al. 1999, Harvey et al. 2003. Weiler et al. (2000) also found that increasing the screw diameter improves the fixation strength. ...
... There were no gross abnormalities in terms of laxity, flexion contracture, or alignment, and no patient required a support to walk. At the end of 1 year, the Lysholm score improved on average by 33 group (P Ͻ .001). The clinical results continued to be the same or improved further until the mean follow-up period of 22 months was reached (range, 19 to 32 months). ...
... On the tibial side, an interference screw is commonly used as a fixation method, and bioabsorbable screws have been shown to reduce the tunnel widening of hamstring grafts. 32 Selby et al. 33 showed a significant difference in the load to failure of hamstring grafts based on interference screw length. The failure load of the 28-mm screw was 594 N, whereas it was 825 N for the 35-mm screw. ...
We prospectively sought to compare the incidence and properties of tunnel widening in patients undergoing anterior cruciate ligament reconstruction with quadrupled hamstring graft by use of either EndoButton CL (Smith & Nephew Endoscopy, Andover, MA) or Transfix (Arthrex, Naples, FL) on the femoral side with a bioabsorbable interference screw in the tibial tunnel by computed tomography scan.
We included 34 patients in the study and randomized them into 2 groups--EndoButton and Transfix groups. An anteromedial portal technique was used to create the femoral tunnels in the EndoButton group, whereas a transtibial technique was used in the Transfix group. A bioabsorbable screw was used on the tibial side in both groups. Thirty patients completed the study protocol, and assessment was done at regular intervals until 12 months of follow-up was reached. The patients underwent computed tomography scans at 2 weeks, 3 months, and 6 months postoperatively. The diameters of the tunnels were measured perpendicular to the long axis of the tunnels on oblique coronal and oblique sagittal planes at 3 levels: aperture, midway, and suspension point. We performed functional scoring with the International Knee Documentation Committee 2000 Subjective Knee Evaluation score and Lysholm score.
Femoral tunnel widening at the aperture and at midway was significantly greater in the EndoButton group compared with the Transfix group. A decrease in the loop length in the EndoButton group was associated with lesser tunnel widening, although this was not found to be statistically significant with the numbers available. A trend toward decreased tunnel widening at the aperture on the tibial side was observed when the tip of the screw was 10 to 15 mm away from the aperture.
Femoral tunnel widening was significantly less in the Transfix group compared with the EndoButton group.
Level II, prospective comparative study.
... Regardless of fixation of a bone plug or soft-tissue graft, interference screw geometry has strength and stiffness implications. Investigating tibial fixation of a soft-tissue graft in a bone tunnel in young cadaveric knees, a 35-mm screw was found to have significantly improved strength and stiffness over a 28-mm length screw [44]. Some investigators have suggested increasing screw length provides a greater improvement in fixation of soft-tissue grafts over increasing screw diameter; whereas in bone plugs, increasing screw diameter provides a greater improvement over increasing screw length. ...
... Insertion torque may be altered by increasing screw diameter, decreasing gap size, and performing tunnel dilation. Underdrilling by 2 mm and dilating the final 2-mm diameter compresses the adjacent cancellous bone, increasing the relative bone mineral density and compressive stiffness, with subsequent increased fixation strength [44,52]. ...
Reconstruction of the anterior cruciate ligament is a frequently performed procedure that has had outstanding results. Outcomes are dependent upon an early postoperative physical therapy program that stresses early motion. Early rehabilitation demands rigid intraoperative mechanical fixation of the graft since therapy begins before biologic incorporation of the graft in the bone tunnels. Regardless of the graft substitute chosen, many methods of fixation are available. The best fixation technique depends on several factors, including graft choice and surgeon comfort. The figures are not documented in this paper. We review current methods available for graft fixation in anterior cruciate ligament surgery.
... Studies have shown that increasing the length of the screw for ligamentous tissue stabilization in the hole created in the leg bone increases the average maximum shear force and the average final tensile force [38]. It has also been observed that even the length of the interference screw has a greater effect on increasing the strength of ligamentous tissue stabilization than its diameter. ...
The present study introduced and mechanically tested an alternative method for graft preparation for ACL reconstruction surgery. The designed method aims to offer a replacement for conventional suturing, which reduces the chance of graft rupture and gradually increases the fixation strength.
Six prototypes were introduced for the fixation. A Product Design Specification chart was developed to select the most suitable prototype. the characteristics presented in the chart were determined based on mechanical limitations and medical requirements stated by the consulting surgeons and available in the literature. Variants of the selected prototype were designed, modeled, and subjected to in-vitro experiments to validate the study. A set of experiments was performed. Five bovine tendon samples were harvested and trimmed into identical sizes. Samples were passed through two endo buttons and looped in a manner that both ends share a common surface. Two custom straps were later applied around the graft. A three-stage mechanical test was performed, a cyclical preload of 10 to 50 N, 10 cycles, and 0.1 Hz. The major pullout test with a cyclical load of 50 to 200 N, 1 Hz for 200 cycles, and a pullout force with a loading rate of 20 mm/min determining the ultimate strength of the fixation.
No failure occurred on the overall structure during the cyclic stages. Also, no failure associated with tendon tissue damage was recorded. All samples experienced a fixation failure during the final pull-out test. The mean values for ultimate strength, cyclic elongation, and Average cyclic Stiffness were 287.66 ± 11.84 N, 2.08 ± 0.15 mm, and 14.52 ± 1.09 kN/mm respectively.
The results indicate that using the proposed strapping method not only reduces any chance of tendon tearing but also presents acceptable major mechanical properties in comparison with the conventional suturing method. The study showed that the new design was mechanically sound.
Keywords: Orthopedics, ACL Reconstruction, Mechanical Testing, Experimental, Mechanical Design.
... The association between implant length and ultimate load is intuitive, however, it could not be confirmed consistently. Testing 28 mm vs. 35 mm tapered screws in sixteen anatomic specimens of tibiae (mean donor age: 38.5 years) revealed significantly higher ultimate loads in the longer screw (595 vs. 825 N, respectively) (Selby et al., 2001). In contrast, a 25 mm and 40 mm interference screw, tested in fourteen tibia specimens (62.6 years) showed similar mean ultimate loads (both 336 N) (Stadelmaier et al., 1999). ...
The purpose of this study was to compare the biomechanical stability, especially graft slippage of an allograft screw and a conventional interference screw for tibial implant fixation in ACL reconstruction. Twenty-four paired human proximal tibia specimens underwent ACL reconstruction, with the graft in one specimen of each pair fixed using the allograft screw and the other using the conventional interference screw. Specimens were subjected to cyclic tensile loading until failure. The two fixation methods did not show any statistical difference in load at graft slippage (p = 0.241) or estimated mean survival until slippage onset (p = 0.061). The ultimate load and the estimated mean survival until failure were higher for the interference screw (p = 0.04, and p = 0.018, respectively). Graft displacement at ultimate load reached values of up to 7.2 (interference screw) and 11.3 mm (allograft screw). The allograft screw for implant fixation in ACL reconstruction demonstrated comparable behavior in terms of graft slippage to the interference screw but underperformed in terms of ultimate load. However, the ultimate load, occurring at progressive graft slippage, may not be considered a direct indicator of clinical failure.
... Some previous in-vitro biomechanical studies investigated the effect of interference screw's length, diameter, material properties, and different manufacturer designs on critical clinical outcomes (such as displacement and strength of the fixed graft), as well as its mode of failure, through applying cycling loading, and loading grafts to failure [3,[22][23][24][25][26][27][28]. Investigations on the effect of bone tunnel-interference screw diameter ratio implied that the use of a small diameter screw may cause graft slippage from the bone tunnel, and a larger screw diameter may damage the graft [12]. ...
Background
Superior biomechanical performance of tapered interference screws, compared with non-tapered screws, with reference to the anterior cruciate ligament (ACL) reconstruction process, has been reported in the literature. However, the effect of tapered interference screw’s body slope on the initial stability of ACL is poorly understood. Thus, the main goal of this study was to investigate the effect of the interference screw’s body slope on the initial stability of the reconstructed ACL.
Methods
Based on the best screw-bone tunnel diameter ratios in non-tapered screws, two different tapered interference screws were designed and fabricated. The diameters of both screws were equal to bone tunnel diameter in one-third of their length from screw tip, then they were gradually increased by 1mm, in the lower slope (LSTIS), and 2 mm, in the higher slope (HSTIS) screws. To simulate the ACL reconstruction, sixteen soft tissue grafts were fixed, using HSTIS and LSTIS, in synthetic bone blocks. Through applying sub-failure cyclic incremental tensile load, graft-bone-screw construct’s stiffness and graft laxity in each cycle, also through applying subsequent step of loading graft to the failure, maximum load to failure, and graft’s mode of failure were determined. Accordingly, the performance of the fabricated interference screws was compared with each other.
Results
HSTIS provides a greater graft-bone-screw construct stiffness, and a lower graft laxity, compared to LSTIS. Moreover, transverse rupture of graft fibers for LSTIS, and necking of graft in the HSTIS group were the major types of grafts’ failure.
Conclusions
HSTIS better replicates the intact ACL’s behavior, compared to LSTIS, by causing less damage in graft’s fibers; reducing graft laxity; and increasing fixation stability. Nonetheless, finding the optimal slope remains as an unknown and can be the subject of future studies.
... Previous in-vitro biomechanical studies throughout applying cycling loading, as well as loading grafts to failure, investigated the effect of interference screw's length, diameter, material and different manufacturer designs on critical clinical outcomes, such as displacement and strength of the xed graft, and its mode of failure [3,[22][23][24][25][26][27][28]. Investigation on the effect of bone tunnel-interference screw diameter ratio implies that use of a small diameter screw may cause graft slippage from bone tunnel, and larger screw diameter may damage graft [12]. ...
Background
Superior biomechanical performance of tapered interference screws, in regard to reconstruction of anterior cruciate ligament (ACL), compared with non-tapered screws, has been reported in the literature. However, the effect of tapered interference screw’s body slope on the initial stability of ACL is not studied yet. Thus, the main goal of this study was to investigate the effects of interference screw's body slope on the initial stability of the reconstructed ACL.
Methods
Based on the best screw-bone tunnel diameter ratios in non-tapered screws, two different tapered interference screw were designed and fabricated. The diameters of both screws were considered to be equal to bone tunnel diameter in one third of their length from screw tip, then they were gradually increased by 1mm, in the lower slope (LSTIS), and 2 mm, in the higher slope (HSTIS) screws. To simulate the ACL reconstruction, sixteen soft tissue grafts were fixed, using HSTIS and LSTIS, in synthetic bone blocks. Through applying sub-failure cyclic incremental tensile load, graft-bone-screw construct's stiffness and graft laxity in each cycle, and through applying subsequent step of loading graft to the failure, maximum load to failure, and graft’s mode of failure were determined. Accordingly, performance of the fabricated interference screws were compared with each other.
Results
HSTIS, compared to LSTIS, provides a greater graft-bone-screw construct stiffness, and a lower graft laxity. Moreover, transverse rupture of graft fibers for LSTIS, and necking of graft in HSTIS group were the major types of grafts' failure.
Conclusion
HSTIS compared to LSTIS, by causing less damage in graft's fibers; reducing graft laxity; and increasing fixation stability, better replicates the intact ACL's behavior.
... While several studies over the past decades that have compared metallic and bioabsorbable screws in ACL reconstruction have demonstrated similar initial fixation strengths 76,77 , there remain relatively few studies that critically compare specific biomechanical properties among commercially available bioabsorbable interference screws. Furthermore, the majority of studies examining the differences in fixation biomechanics have focused primarily on interference screws that have been placed in the tibial bone tunnel 78,79 . As such, the improvement in biomechanical properties of commercially available bioabsorbable screws that result from variable screw diameter, in addition to newer implant designs and materials 80,81 and screw shapes 82 , that contributes to successful graft fixation following BPTB ACL reconstruction remains unknown and merits additional investigation. ...
» Anterior cruciate ligament (ACL) reconstruction is a commonly performed orthopaedic procedure with numerous reconstructive graft and fixation options. Interference screws have become one of the most commonly utilized methods of securing ACL grafts such as bone-patellar tendon-bone (BPTB) autografts.
» The composition of interference screws has undergone substantial evolution over the past several decades, and numerous advantages and disadvantages are associated with each design.
» The composition, geometry, and insertional torque of interference screws have important implications for screw biomechanics and may ultimately influence the strength, stability of graft fixation, and biologic healing in ACL reconstruction.
» This article reviews the development and biomechanical properties of interference screws while examining outcomes, complications, and gaps in knowledge that are associated with the use of femoral interference screws during BPTB ACL reconstruction.
... 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. ...
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.
... Additionally, there is the potential for harvest utilizing a single incision, thereby minimizing wound complication potential. 3,4,11,25,26 Although there have been a few studies evaluating the biomechanical properties of FHL tendon transfer utilizing an interference screw system, analogous investigations have been performed in other tendon transfers 21 establishing optimum screw length, 27 pilot hole size, 19,23 and screw size. 19 Manufacturer guidelines for interference screw systems advocate the use of a terminal 2.0 suture whipstitch presumably to both augment and tension the tendon prior to fixation. ...
Introduction:
Flexor hallucis longus (FHL) tendon transfer to the calcaneus is commonly used in the surgical treatment of chronic Achilles tendinopathy. This study assesses the integrity of FHL tendon biotenodesis screw fixation with respect to 2 variables: incorporation of a terminal whipstitch and tunnel depth.
Materials and methods:
A total of 60 fresh-frozen cadaver FHL tendons and 28 calcanei were harvested for analysis in 4 sets of fixation constructs; 14 whipstitched tendons were compared against their nonwhipstitched paired tendon via pull-out strength load testing, and 16 tendon pairs were randomized for fixation in either a full-depth tunnel (bicortical) or a 25-mm partial tunnel (unicortical). All comparisons were carried out in native bone and synthetic models.
Results:
Whipstitched tendons demonstrated significantly stronger mean clinical load (253.68 vs 177.24 N, P = .008) and maximum load to failure (294.31N vs 194.57 N, P = .001) compared with the nonwhipstitched tendons in synthetic bone. There were no statistical differences in mean clinical load (200.96 vs 228.31 N, P = .63) and maximum load to failure (192.69 vs 217.74 N, P = .73) between full and partial tunnel groups. There were no significant differences found in trials carried out in cadaveric bone.
Conclusion:
Use of a terminal whipstitch achieves greater fixation strength in FHL tendon biotenodesis transfers. Complete and partial tunnel constructs are equivocal in their pull-out strength. Data produced in a homogeneous bone substitute model demonstrate the biomechanical superiority of the whipstitch as well as the noninferiority of the partial tunnel technique.
Levels of evidence:
Level IIb.
... In a comparative study, Walton [ 12 ] demonstrate that absorbable interference screws of 28 mm or 35 mm provide similar or even better fi xation than metallic screws. Selby et al. [ 67 ] demonstrated that it is easier to place the insertion torque force near the articular line with long screws, making the graft less prone to failure mechanisms as the "windshield" effect. ...
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.
... The maximum pull-out force for the fixation will need to exceed 450 N, the maximum force incurred over the course of rehabilitation [78,87]. Initial fixations currently used with autografts and allografts are not completely rigid but rather have a stiffness averaging between 40 N/mm and 60 N/mm [39,73,[87][88][89]. If the device is to be secured with a suspensory-type fixation only, the stiffness and shape of the device tunnel segment should be such that tunnel motion and widening are not detrimental to function [90]. ...
Anterior cruciate ligament (ACL) tearing is a common knee injury often requiring reconstruction with an autograft or an allograft. A prosthetic ligament replacement with off-the-shelf availability could potentially provide significant advantages over the current options for both patients and surgeons. Limitations of previous prosthetics include lack of biocompatibility and susceptibility to fatigue, creep, and failure of bony incorporation. This paper describes design considerations and possible improvements for the next generation prosthetic ACL. Design controls, as mandated by the FDA, are a systematic set of practices within the design and development process used to ensure that a new medical device meets the needs of the intended users. The specified requirements, called the design inputs, for a prosthetic ACL are discussed pertaining to material and structural properties, resistance to creep and fatigue, ability to support secure initial fixation, biocompatibility, and long-term osseointegration. Design innovations to satisfy the design inputs are discussed with regards to material selection, textile pattern, bone tunnel features, and short term fixation. A risk analysis is presented along with descriptions of proposed testing. Design control methodology and tissue engineering may be used to develop a next generation prosthetic ligament, solving multiple problems, simultaneously, on a holistic level, providing major improvements over earlier devices and current treatment options.
... There are multiple factors reported to improve tibial intratunnel biomechanical fixation: ensuring tunnel diameter is within 0.5 mm of the graft size, 29 increasing screw length, 14,27,34,35 using a screw diameter sized according to the tunnel size, 14,34,35 and concentric placement of the screw in the tunnel. 28 Combination devices, which incorporate an interference screw with a sheath, attempt at improving fixation characteristics by increasing radial force and compression on the graft against the tunnel wall. ...
... Previous studies have shown that a decreased BMD negatively affects the pullout strength of tibia-sided graft fixation, [22][23][24] and Nyland et al. 23 recommended backup fixation in cases in which an initial interference screw is inadequate. Lee et al. 25 compared interference screws and interference screws with backup PushLock (PL) (Arthrex, Naples, FL) fixation and found that supplemental fixation had twice the pullout strength compared with interference screws alone. ...
The purpose of this study was to compare anterior cruciate ligament (ACL) fixation using a bioabsorbable interference screw (BIS) and a supplemental low-profile suture anchor (PushLock 4.5-mm polyetheretherketone anchor; Arthrex, Naples, FL) with a standard BIS fixation to determine if fixation methods were dependent on tibial bone mineral density (BMD).
Ten matched pairs of fresh-frozen human female knee specimens (20 total) were harvested with specimen ages ranging from 40 to 65 years. The BMD for each specimen was determined with a dual-energy x-ray absorptiometry scanner. The specimens were divided into 2 groups, 1 with a BIS and the other with a BIS plus a PushLock. Tibial-sided ACL fixation with hamstring tendon grafts was performed on all the specimens. Then, load to failure and stiffness were biomechanically tested.
The BIS-plus-PushLock specimens had a significantly higher mean yield load compared with specimens with the BIS alone (702 N v 517 N, P = .047). However, in samples with lower bone density, there was no statistically significant difference in failure loads between fixation techniques (P = .8566 at BMD of 0.5 g/cm(2)). As the bone density of the samples increased, the failure loads increased for both techniques (P < .0001 for PushLock and P = .0057 for BIS). This BMD-associated increase was greater for the PushLock (P = .0148), resulting in a statistically significant difference in failure load at the upper range tested (P = .0293 at BMD of 0.9 g/cm(2)).
Supplemental fixation of ACL reconstructions with a PushLock is beneficial in persons with a normal BMD of the proximal tibia, but at a lower BMD, there was no difference in our study.
Individuals with normal BMDs may benefit from this supplemental fixation. However, caution should be used in postmenopausal women or individuals with chronic ACL injuries when using this fixation strategy.
... Increased screw length for tibial tunnel hamstring fixation exhibited increased mean maximal load at failure and mean pullout force. 6,12 Greater screw length has been shown to be more important than increasing screw diameter in a calf tibial hamstring model. 6 Some authors recommend underdrilling and sequentially dilating the tibial tunnel during preparation to improve grafttunnel fit. 10 In general, the screw and tunnel diameter should be equal. ...
The purpose of this article is to discuss the bioabsorbable interference screws currently available for graft fixation in anterior cruciate ligament reconstruction. A brief review of the literature regarding the use of bioabsorbable interference screws is included. The screw design, insertion technique, graft options, and various manufactured sizes for each screw are addressed. Relevant screw characteristics to consider include availability of guidewire, tap, and tunnel notching devices to ease insertion.
... Each sample was loaded in tension and tested to failure at a displacement rate of 20 mm/minute. 15 The data were collected at 500 Hz. After 500 cycles, the ultimate load to failure testing was commenced. ...
The objective of the study was to compare the load to failure between a retro screw (RS) and a standard interference screw (IS) for tibial-sided anterior cruciate ligament (ACL) fixation. We used 20 bovine tibia and extensor tendons for the study. A group of 10 specimens underwent IS fixation while the other 10 underwent RS fixation. Within each group, five specimens had graft suture in contact (interdigitating) with the screw threads. All specimens were tested on the MTS 858 Mini Bionix II (MTS Systems, Shakopee, MN). There was no statistically significant difference between the RS and IS with respect to peak load to failure. IS with suture interdigitation failed at an average of 520 N (range: 358 to 793 N), while the RS with suture interdigitation failed at 613 N (range: 438 to 1089 N). The IS without suture interdigitation failed at 654 N and the RS without suture interdigitation at 531 N. Specimens with a whipstitch in contact with the screw did not demonstrate higher pull out strength. The RS fixation strength appears to equal the IS. Graft suture contact with screw threads does not increase fixation strength. Based on this study, using a RS for tibial ACL soft tissue graft fixation is feasible and provides equal fixation strength compared with the standard IS.
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.
Résumé
Introduction
Le moyen de fixation d’un transplant de reconstruction du ligament croisé antérieur (LCA) est débattu. La fixation tibiale des greffes tendineuses constitue la faiblesse principale pour des raisons mécaniques et anatomiques. La ligamentoplastie aux ischio-jambiers (STG) pédiculés pourrait avoir un intérêt mécanique. L’objectif du travail était de comparer la résistance maximale de la fixation tibiale d’une plastie STG pédiculée non fixée par vis, à celle d’une plastie pédiculée fixée par vis d’interférence et à celle d’une plastie non pédiculée. L’hypothèse était que le caractère pédiculé de la greffe augmentait la résistance maximale de la fixation tibiale par rapport au transplant libre.
Matériel et méthodes
Cinq paires de genoux appariés (10 genoux) de cadavres humains congelés étaient étudiés. Les tendons du semi-tendineux et du gracile étaient préparés en une greffe à 4 brins pédiculée au tibia. Le transplant était passé au travers du tunnel tibial en utilisant l’ancillaire et les repères habituels. 3 groupes étaient créés. Groupe 1 : transplant pédiculé non fixé par vis d’interférence. Groupe 2 : transplant pédiculé, fixé par une vis d’interférence. Groupe 3 : constitué des genoux du groupe 1 dont le greffon était détaché (transplant libre) après le premier test et fixé par une vis d’interférence dans le tunnel. Le diamètre de la vis était calibré au transplant. Le test de traction était réalisé sur machine hydraulique (Instrom 8500), dans l’axe du tunnel. Le critère de jugement principal était la charge maximale à la rupture. Le critère secondaire était la mesure de la rigidité. La comparaison des groupes était réalisée par un test de Friedman et par la méthode de Nemenyi au seuil de 5 %.
Résultats
La charge à la rupture du groupe 1 était augmentée de 33 % par rapport à celle du groupe 3 (89,2 N vs 67,2 N p > 0,05) Celle du groupe 2 était augmentée de 25 % par rapport à celle du groupe 1 (111,2 N vs 89,2 N, p > 0,05) et de 65 % par rapport à celle du groupe 3 (111,2 N vs 67,2 N p = 0,005). Il n’apparaissait pas de différence de rigidité entre le groupe 1 et 2 (p = 1).
Discussion
L’hypothèse était confirmée : la conservation de l’insertion anatomique tibiale des tendons ischio-jambiers augmente la charge maximale à la rupture du transplant. Dans les conditions d’expérimentation il semble que l’adjonction d’une vis augmente la tenue mécanique de la plastie pédiculée (+25 % en valeur absolue), mais la différence n’est pas significative.
Niveau de preuve
III, étude de laboratoire contrôlée.
The aim of this study was to determine if the type of reamer used in tibial tunnel creation during anterior cruciate ligament (ACL) reconstruction influences the dimensions of the tunnel's outer aperture. Tibial tunnels were created in tibial saw bones by reaming over a guidewire using an 8 mm acorn or fluted reamer in an antegrade manner. Reaming was aimed either in line with the guidewire, or with 10-degree inferior/superior deviation in relation to the wire. The shape and size of the outer aperture of the tibial tunnel were compared between the two reamers. When using the acorn reamer, a 10-degree deviation in relation to the guidewire resulted in minimal change in outer aperture length (mean 13.6 vs. 15.6 mm, p = 0.11) and width (11.6 vs. 11.1 mm, p = 0.51). However, when using the fluted reamer, although the aperture width showed no substantial change with reamer/guidewire deviation (11.4 vs. 11.2 mm, p = 0.71), the mean length almost doubled (14.7 vs. 28.1 mm, p = 0.002). The use of a fluted reamer when reaming the tibial tunnel creates a distal aperture which is inconsistently sized, larger, and of oblong shape compared with an acorn-shaped reamer. This should be taken in consideration when using a fluted reamer for creating the tibial tunnel in ACL reconstruction.
» The method of graft fixation in anterior cruciate ligament (ACL) reconstruction is important for initial stability. The tibial fixation site is reported to be the weakest point in ACL reconstructions.
» Tibial fixation techniques include aperture fixation (intra-tunnel), suspensory fixation (extra-tunnel), and hybrid tibial fixation.
» Although biomechanical data have demonstrated superior pull-out strength and resistance to cyclic loading with certain tibial fixation devices, the available clinical data have overall demonstrated no significant differences in patient outcomes and failure rates among methods.
» Further work is necessary to determine which technique optimizes biologic maturation and incorporation of the graft within the tibial tunnel.
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.
Quadrupled hamstring tendon is one of the most commonly used ligamentous substitutes in anterior cruciate ligament reconstruction. We describe a case of a young athlete who sustained a rerupture of a semitendinosus-gracilis autograft fixed with biodegradable screws 2 years after primary surgery. Radiologic, arthroscopic, histologic, and electromicroscopic investigation showed tendon-to-bone healing of the soft tissue graft and partial degradation of the interference screws.
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.
Anterior cruciate ligament (ACL) graft fixation has been considered for many years the weakest link of the ACL reconstruction. Graft fixation should be secure, by achieving structural properties of the native ligament, and should provide graft stability until bone–tendon healing has occurred. Several different fixation devices are available for bone–tendon–bone and soft tissue grafts. Controversy still exists regarding the best fixation according to the surgical technique and the graft. The aim of this chapter is to give an overview of the available fixation devices, separately for bone–tendon–bone and soft tissue grafts, in order to clarify differences between them in terms of biomechanical properties and clinical results. This is hoped to be helpful to specifically tailor each reconstruction to patients’ and surgeons’ requirements.
Objective: The aim of the present study was to develop the experimental methodology for the biomechanical analysis of the anterior cruciate ligament reconstruction. Material and method: An ACL reconstruction was performed on 16 porcine knees. The graft used was the pig doubled lateral extensor of toes (DLET). Three different femoral fixation devices were tested and classified according to their fixation mechanism: compression, expansion and cortical-cancellous suspension. A fixation device was developed in order to analyze the unfavorable load case. All GFC were subjected to a load-to-failure test. Failure load, elongation and stiffness were calculated for each device. Results: Regarding stiffness and failure load, cortical-cancellous suspension and expansion, both with the double graft technique, showed the highest mean values. Compression and expansion, both with the single graft technique, showed worse results. Conclusions: Failure always took place in the graft, and thus was impossible to compare correctly the different fixation devices behavior.
This paper, describes the biomedical testing of an Anterior Cruciate Ligament (ACL) reconstruction using an interference screw fixation on the bovine and porcine tissues. The harvesting procedure, experimental setup, mechanical testing, and evaluation of the tendon graft interference screw fixation are all presented throughout this study. A guideline has also been introduced to evaluate the basic mechanical properties of the bone components and the tendon graft.
The aim of this study was to evaluate at time-zero four tibial fixations on four major criteria: the elongation and cyclic stiffness of the hamstring graft construct under cyclic loading, the yield load and pullout stiffness under load at failure. Four fixation systems were tested: the Delta screw, the WasherLoc, the TightRope Reverse and the tape locking screw on 32 tibiae of adult pigs using 32 pairs of human semitendinosus and gracilis tendons. Two tests were performed: cyclic tests using loads at 70-220 N, to measure the elongation at the end of the cycles, followed by load-to-failure testing to measure the yield load and the cyclic stiffness. The mean elongation was 1.23 mm for the TLS, 3.81 mm for the Delta, 3.59 mm for the WasherLoc and 3.91 mm for the TightRope. The mean yield loads and SD were 1,015 ± 129 N for the TLS, 844 ± 394 N for the Delta, 511 ± 95 N for the WasherLoc and 567 ± 112 N for the TightRope. The results showed the significant superiority of TLS and Delta over WasherLoc and tibial TightRope in regard to yield load. The results showed the significant superiority of TLS over the other fixations in regard to slippage. The TLS system and the Delta screw provide a better quality of primary fixation to the tibia, but further in vitro studies are needed.
Purpose:
The purpose of this study was to evaluate the effects of screw position and compaction of the bone tunnel on the strength of the flexor tendon graft after fixation using interference screws.
Methods:
Forty fresh-frozen porcine tibias were used for this study. The digital flexor tendons were folded into a quadrupled graft measuring 9 mm in diameter. In the extraction-drilling group, tibial bone tunnels were drilled with a conventional cannulated 9-mm drill bit in a single step. In the compaction-drilling group, bone tunnels were drilled using a cannulated 7-mm drill bit and were expanded to a final diameter of 9 mm in 0.5-mm increments by placement of dilators with increasing diameter. The grafts were fixed using 9 × 30-mm titanium screws in central and eccentric positions. Specimens underwent a cyclic-loading test, and the surviving specimens were then loaded until failure.
Results:
Graft displacement after 1,500 loading cycles occurred significantly more often in the extraction-drilling group with eccentric screw placement than in the groups of extraction-drilling (P < .05) and compaction-drilling (P < .01) with central screw placement. There were no statistically significant differences for the maximum screw insertion torque, maximum load at failure, or stiffness among the 4 groups. One strand of the quadrupled tendon grafts showed partial injury during screw insertion in 3 (30%) and 4 (40%) of 10 specimens of the extraction-drilling and compaction-drilling groups with central screw placement, respectively.
Conclusions:
Central screw placement significantly decreased the displacement of the tendon graft in comparison with eccentric screw placement in the extraction-drilling condition. Compaction of the bone tunnel walls by serial dilation in a central screw position did not increase the strength of interference screw fixation of a soft tissue graft.
Clinical relevance:
When using the extraction method and fixing the graft in an eccentric position, it is advisable to provide additional fixation outside the tunnel to prevent slippage of the graft.
Objective: To analyse the biomechanical behaviour of different femoral fixation systems employed in the reconstruction of the anterior cruciate ligament (ACL) using a static load. Material and method: ACL reconstruction of 33 pig femurs. A high resistance braided cord was used as graft, with the aim of eliminating variability and premature fractures. Nine devices were analysed: Biosteon, Biocryl and Softsilk (compression); Biosteon Cross-Pin and Cross-Pin ACL (cortical-cancellous suspension); Endobutton and XO Button (cortical suspension); staple (cortical compression); Rigidfix (transverse fixation). Static resistance failure tests were performed, calculating the linear rigidity, failure load, and elongation of that load. The bone was sectioned to observe the failure mode. Results: The staple showed a higher load failure (1,173.7 ± 220.0. N), but with a greater elongation (58.8 ± 13.2. mm). Of the rest of the fixations, the most resistant were Cross-Pin ACL (1,054.6 ± 150.8. N) and Endobutton (1,018.6 ± 230.1. N), with the former having greater rigidity (43.5 ± 7.1. N/mm). Discussion: Cortical suspension fixations seem to be very affected by the geometry of the bone in the cortical support surface, while those of the cortical-cancellous suspension produced a better load distribution. Compression and transverse fixations changed their mechanical properties due to using a synthetic graft. Conclusions: Taking into account the behaviour shown by the model studied, cortical-cancellous suspension fixation was shown to be a very good option, on having a balanced load distribution on the bone and not very aggressive.
Anterior cruciate ligament (ACL) injury is one of the most common sports injuries of
the knee. ACL reconstruction has become, standard orthopaedic practice worldwide
with an estimated 175,000 reconstructions per year in the United States.6 The ACL
remains the most frequently studied ligament in orthopaedic research. Hundreds of
papers are published each year related to the ACL. However, the treatment options
and techniques are still developing and increasing, indicating the difficulties in the
treatment of this central knee ligament.
Objective
To analyse the biomechanical behaviour of different femoral fixation systems employed in the reconstruction of the anterior cruciate ligament (ACL) using a static load.
Background:
The tibial fixation site has been reported to be the weakest point in anterior cruciate ligament (ACL) reconstructions. Numerous interference screws and combination screw and sheath devices are available for soft tissue fixation, and a biomechanical comparison of these devices is necessary.
Hypothesis:
Combination screw and sheath devices would provide superior soft tissue fixation properties compared with interference screws in a porcine model.
Study design:
Controlled laboratory study.
Methods:
Eight different intratunnel tibial soft tissue fixation devices were biomechanically tested in a porcine model with bovine tendons, with 10 specimens per group. The soft tissue fixation devices included 3 interference screws-the Bio-Interference Screw, BIOSURE PK, and RCI Screw-and 5 combination screw and sheath devices (combination devices)-the AperFix II, BIOSURE SYNC, ExoShape, GraftBolt, and INTRAFIX. The specimens were subjected to cyclic (1000 cycles, 50-250 N, 0.5 Hz) and pull-to-failure loading (50 mm/min) with a dynamic tensile testing machine. Ultimate failure load (N), cyclic displacement (mm), pull-out stiffness (N/mm), displacement at failure (mm), load at 3 mm displacement (N), and mechanism of failure were recorded.
Results:
The ultimate failure loads were highest for the GraftBolt (1136 ± 115.6 N), followed by the INTRAFIX (1127 ± 155.0 N), AperFix II (1122 ± 182.9 N), BIOSURE PK (990.8 ± 182.1 N), Bio-Interference Screw (973.3 ± 95.82 N), BIOSURE SYNC (829.5 ± 172.4 N), RCI Screw (817.7 ± 113.9 N), and ExoShape (814.7 ± 178.8 N). The AperFix II, GraftBolt, and INTRAFIX devices were significantly stronger than the BIOSURE SYNC, RCI Screw, and ExoShape. Although the 3 strongest devices were combination screw and sheath devices, no significant differences were observed between the ultimate failure strengths of the screw and combination devices when compared as groups. The least amount of cyclic displacement after 1000 cycles was observed for the GraftBolt (1.38 ± 0.27 mm), followed by the AperFix II (1.58 ± 0.21 mm), Bio-Interference Screw (1.61 ± 0.22 mm), INTRAFIX (1.63 ± 0.15 mm), ExoShape (1.68 ± 0.30 mm), BIOSURE PK (1.72 ± 0.29 mm), BIOSURE SYNC (1.92 ± 0.59 mm), and RCI Screw (1.97 ± 0.39 mm). The GraftBolt allowed significantly less displacement than did the BIOSURE SYNC and RCI Screw. Similarly, no significant differences were observed between the cyclic displacements of the screws and combination devices when compared as groups.
Conclusion:
The combination screw and sheath devices did not provide superior soft tissue fixation properties compared with the interference screws alone in a porcine model. Although the highest ultimate failure loads and least amounts of cyclic displacement were observed for combination devices, group comparisons of screw and combination devices did not result in any significant differences for ultimate failure load and cyclic displacement.
Clinical relevance:
It is important to consider that these results represent device performance in an in vitro animal model and are not directly transferrable to an in vivo clinical situation. The combination of a sheath and screw did not consistently result in improved fixation characteristics compared with interference screw fixation.
Failure after anterior cruciate ligament reconstruction is a potentially devastating event that affects a predominantly young and active population. This review article provides a comprehensive analysis of the potential causes of failure, including graft failure, loss of motion, extensor mechanism dysfunction, osteoarthritis, and infection. The etiology of graft failure is discussed in detail with a particular emphasis on failure after anatomic anterior cruciate ligament reconstruction.
Reconstruction of the anterior cruciate ligament is a frequently performed procedure that has had outstanding results. Outcomes are dependent upon an early postoperative physical therapy program that stresses early motion. Early rehabilitation demands rigid intraoperative mechanical fixation of the graft since therapy begins before biologic incorporation of the graft in the bone tunnels. Regardless of the graft substitute chosen, many methods of fixation are available. The best fixation technique depends on several factors, including graft choice and surgeon comfort. The figures are not documented in this paper. We review current methods available for graft fixation in anterior cruciate ligament surgery.
To compare clinical outcomes of tibial fixation between a biodegradable interference screw only and a biodegradable interference screw supplemented by a post-tie using a washer screw in single-bundle anterior cruciate ligament (ACL) reconstruction with 2-strand free tendon Achilles allograft in active young men.
A prospective study was performed in 80 subjects who underwent single-bundle ACL reconstruction. A 2-strand free tendon Achilles allograft fixed with an EndoButton (Smith & Nephew, Andover, MA) in the femoral tunnel and with a Bio-Interference screw (Arthrex, Naples, FL) in the tibial tunnel was used in group I. Supplementary fixation was performed with a post-tie using a washer screw in group II. The Lachman test, pivot-shift test, International Knee Documentation Committee classification, Lysholm score, range of knee motion, and side-to-side difference were evaluated preoperatively and at the last follow-up. The Tegner activity scale was evaluated before injury and at the last follow-up. The 1-leg hop test was assessed at the last follow-up.
Of the patients, 36 in group I and 35 in group II could be followed up for at least 2 years. At the last follow-up, 7 patients in group I and 1 in group II showed a 2+ or 3+ on the Lachman test (P = .027). The mean side-to-side difference was 2.9 ± 2.3 mm in group I and 1.4 ± 1.6 mm in group II at the last follow-up (P = .002). The other clinical outcomes were not significantly different between the 2 groups.
Supplementary tibial fixation with a post-tie in ACL reconstruction using 2-strand free tendon Achilles allograft was more effective than a biodegradable interference screw only in restoration of the anterior stability of the tibia.
Level II, randomized controlled trial.
For the successful transplantation or transposition of ligaments and tendons, fixation techniques are very important. As most
postsurgical rehabilitation protocols emphasize immediate full range of motion and early return to function, fixation must
provide adequate strength and stiffness during the early postoperative period. Table 1 lists mechanical properties (failure
load, ultimate strength, stiffness, and elastic modulus) of ligament, tendon, or deep fascia of different species. Ideally,
fixation strength should meet or exceed the requirements for normal activity on ligaments or tendons. In addition, fixation
should not interfere with healing and must be biocompatible for long-term use or easily removable (1). Large animals (goats, dogs, sheep, pigs, and monkeys) are common species for studies of ligament and tendon fixation. Large
bone volume of these animals is the most important factor for the facilitation of bone instrumentation (fixations with screws
or implants). Selected animal models from the literature to evaluate ligament or tendon fixation to bone are listed in Table
2.
Background:
In anterior cruciate ligament (ACL) reconstruction, an interference device achieves soft-tissue graft fixation by radially compressing the graft against the bone.
Purpose:
The objective of this study was to measure the radial force generated by different interference devices and evaluate the effect of this radial force on the pullout strength of graft-device constructs.
Study design:
Controlled laboratory study.
Methods:
A resultant force (F(R)) was used as a representative measure of the total radial force generated. Bovine tendons were fixated in either synthetic bone or porcine tibia using one of following devices: (1) RCI titanium screw, (2) PEEK screw, (3) IntraFix sheath-and-screw device, and (4) ExoShape sheath-and-insert device. F(R) was measured while each device was inserted into synthetic bone mounted on a test machine (n=5 for each device). In a subsequent test series, graft-device constructs were loaded to failure at 50mm/min. The pullout strength was measured as the ultimate load before failure (n=10 for each device).
Results:
The F(R) values generated during insertion into synthetic bone were 777 ± 86N, 865 ± 140N, 1313 ± 198N, and 1780 ± 255N for the RCI screw, PEEK screw, IntraFix, and ExoShape, respectively. The pullout strengths in synthetic bone for the RCI screw, PEEK screw, IntraFix and ExoShape were 883 ± 125N, 716 ± 249N, 1147 ± 142N, and 1233 ± 190N, respectively.
Conclusions:
These results suggest that the F(R) generated during interference fixation affects the pullout strength with sheath-based devices providing superior F(R) compared with interference screws. The use of synthetic bone was validated by comparing the pullout strengths to those when tested in porcine tibia.
Clinical relevance:
These results could be valuable to a surgeon when determining the best fixation device to use in the clinical setting.
The purpose of this study is to determine whether the RetroScrew tibial fixation system offers a biomechanical advantage over the Delta screw for anterior cruciate ligament (ACL) reconstruction in cadaveric tibias with low bone mineral density (BMD).
Ten matched pairs of osteoporotic cadaveric tibiae underwent simulated ACL reconstruction using quadrupled hamstring grafts with one of the two tibial fixation constructs. Group 1 was fixed with the Delta screw (DS; 35-mm antegrade biointerference screw), and group 2 was fixed with the RetroScrew system (RSS; 20-mm retrograde and 17-mm antegrade biointerference screws). Each construct was cyclically loaded (50-200 N, 1 Hz, 500 cycles) and subsequently loaded to failure (20 mm/s).
All specimens were osteoporotic without significant segmental (proximal, middle, and distal) BMD differences between groups by quantitative computed tomography (P = n.s.). A trend was noted for more construct failures due to graft slippage in the DS group (n = 3) over the RSS group (n = 1). There were no significant differences in cyclic displacement (P = n.s.), maximum cyclic stiffness (P = n.s.), maximum load at failure (P = n.s.), or pullout stiffness (P = n.s.) between groups.
In an osteoporotic cadaveric model, there was no significant biomechanical advantage of the RetroScrew system versus the Delta screw for tibial fixation in soft tissue graft ACL reconstruction. However, a trend toward lower graft fixation failure to cyclic loading was noted with the RetroScrew system.
The purpose of this study is to determine the effect of bioabsorbable interference screw (BIS) tibial fixation with the Delta screw (antegrade) and RetroScrew (retrograde) on initial (time zero) intra-articular graft tension in soft tissue anterior cruciate ligament (ACL) reconstruction in a cadaveric model.
Ten matched pairs of cadaveric tibias received one of two tibial fixation constructs using quadrupled hamstring grafts, Delta screw (antegrade) or the RetroScrew (retrograde). Each specimen was mounted to the materials testing device with the displacement force vector in line with the tibial tunnel. The construct was pre-tensioned (10-30 N, 0.1 Hz, 10 cycles), a baseline tension of 25 N was introduced, and the change in intra-articular graft tension before and after screw insertion was recorded.
Segmental (proximal, middle, distal) BMD was utilized to assess BMD using quantitative computed tomography (qCT). The Delta screw had a higher maximum insertion torque (P = 0.03) and exhibited a larger increase in intra-articular graft tension as compared to the RetroScrew (38.3 ± 17.9 N, 7.6 N ± 14.4, P = 0.004), respectively. There were no significant correlations between intra-articular graft tension increase to maximum insertion torque (P = NS) or corresponding segmental BMD (P = NS).
Delta screw tibial fixation (antegrade) in soft tissue ACL reconstruction significantly increases the initial intra-articular graft tension as compared to RetroScrew screw fixation (retrograde) in this cadaveric model. Delta screw (antegrade) tibial fixation may increase initial quadrupled hamstring graft intra-articular tension with currently accepted insertion techniques.
This study assessed the effect of unilateral strength training at 80% one repetition maximum and of detraining on bone mineral density (BMD, g/cm-2) and bone mineral content (sigma BMC, g) in young women. Twelve female physiotherapy students trained their left limb by leg press an average of four times per week for 1 year followed by 3 months of detraining. Twelve students served as controls. Repeated bone measurements were performed by dual energy X-ray absorptiometry of the lumbar spine, femoral neck, distal femur, patella, proximal tibia, and calcaneus. The training increased the muscle strength of the trained limb, and the BMD of the same limb showed a nonsignificant but systematic increase in distal femur, patella, and proximal tibia, and in sigma BMC of the five measured limb sites (considered an index of the total osteogenic effectiveness of the training). Simultaneously, the muscle strength increased in the untrained limb as an evidence of cross-training effect. A corresponding small but systematic increase was also seen in BMD of this limb as well as in sigma BMC. After the cessation of training, leg extension strength was retained but BMD and sigma BMC of the trained and untrained limbs declined towards baseline values in 3 months. The BMD and sigma BMC values in the control group showed an increasing tendency during the follow-up but the changes were less than 1%. The differences of the changes in BMD and sigma BMC between the left and right limb in the control group, as well as between the same limb in the training and control groups were nonsignificant.(ABSTRACT TRUNCATED AT 250 WORDS)
The initial fixation strengths of two spiked-washer designs were evaluated using human femurs and fascia lata tissue. Fascia lata was attached to the femur using the fixation devices, and then each femur-washer-fascia lata complex was loaded in tension to failure. Load-elongation curves were recorded, the initial failure load, initial failure displacement, stiffness, ultimate load, and ultimate displacement were determined for each test, and failure modes were recorded. Results indicated that the 6-spike design provided superior initial fixation strength in the 19-mm diameter size. This washer design was then compared with two commercially available fixation devices: the spiked AO washer and soft tissue fixation plate. Fixation provided by the prototypal washer design was not different in most instances from that provided by the AO fixation devices. Based on these results, important design characteristics for soft tissue spiked washers are identified and discussed.
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.
Deficiency of the anterior cruciate ligament (ACL) is a common disorder which can lead to changes in lifestyle. We followed 59 patients who had had arthroscopic reconstruction of the ACL using a central-third patellar-tendon autograft for seven years to assess the long-term effectiveness of recent advances in reconstruction of the ACL. The standard criteria for evaluation of the International Knee Documentation Committee, the Lysholm knee score and measurements using the KT 1000 arthrometer all showed satisfactory results. Deterioration in the clinical performance after seven years was associated with osteoarthritic changes and correlated with chronic ligament injuries and meniscectomy, There were three traumatic and three spontaneous ruptures. We believe that the procedure can be successful, but remain concerned about failure of the graft and osteoarthritis. The results raise questions about the best time to operate and suggest that early surgery may reduce the risk of osteoarthritis.
Arthroscopic reconstruction of the anterior cruciate ligament-deficient knee using the middle third of the patellar tendon is an effective treatment for acute or chronic anterior cruciate ligament insufficiency. The strength of this bone-ligament-bone graft is superior to virtually all other autogenous tissue utilized. We report the complication of avulsion of one half of the remaining patellar tendon from the tibia associated with patellar fracture in the early postoperative period.
Eighty consecutive patients with chronic laxity due to a torn ACL underwent arthroscopically assisted recon struction with either autogenous patellar tendon or doubled semitendinosus and gracilis tendons. Recon structions were performed on a one-to-one alternating basis. Preoperatively, no significant differences be tween the two groups were noted with respect to age, sex, level of activity, and degree of laxity (chi square analysis). A standard rehabilitation regimen was used for all patients after surgery including immediate pas sive knee extension, early stationary cycling, protected weightbearing for 6 weeks, avoidance of resisted ter minal knee extension until 6 months, and return to activity at 10 to 12 months postoperatively.
Seventy-two patients were evaluated at a minimum of 24 months postoperatively (range, 24 to 40 months). No significant differences were noted between groups with respect to subjective complaints, functional level, or objective laxity evaluation, including KT-1000 meas urements. Seventeen of 72 patients (24%) experienced anterior knee pain after ACL reconstruction. Overall, 46 of 72 patients (64%) returned to their preinjury level of activity. Mean KT-1000 scores were 1.6 ± 1.4 mm for the patellar tendon group and 1.9 ± 1.3 mm for the semitendinosus and gracilis tendons group.
This study did find a statistically significant weakness in peak hamstrings torque at 60 deg/sec when recon struction was performed with double-looped semiten dinosus and gracilis tendons.
Obesity is associated with increases in fat-free mass (FFM) and organ sizes, in addition to body fat (BF). Several studies show increased bone mass in extreme obesity, but data are conflicting (Steiniche et al., 1986).
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.
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)
In vivo forces in the anterior cruciate ligament (ACL) were measured in three adult goats during quiet standing and during gait (walking or trotting). A modified pressure transducer (MPT) was implanted within the anteromedial band of the ligament to make direct measurements of ACL force. One or two days following implantation, measurements were made of ACL force, knee joint flexion angle, ground reaction forces, and speed of locomotion. MPT calibration was performed in vitro using anteroposterior displacement tests at six flexion angles. The ACL was loaded during quiet standing (30-61 N) and during the stance phase of gait. Peak ACL forces were achieved within the first 40% of stance, with magnitudes ranging from 63 to 124 N during walking and from 102 to 150 N during trotting. The average ACL force during the stance phase ranged from 34 to 68 N while walking and from 46 to 69 N while trotting. The partial correlations between peak ACL force and speed, and between average ACL force and speed, were both statistically different from zero (p < 0.01). ACL forces dropped to zero during the swing phase in all trials. ACL forces were less than 15 N throughout swing in two of the animals, both of which did not extend their knees during gait beyond 20 degrees from full extension. In the animal which did show knee extension beyond 40 degrees (20 degrees from full extension), ACL loading occurred during late swing. The magnitude of the peak ACL force during late swing was significantly correlated with the extent of knee extension in this animal.
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 results of intraarticular anterior cruciate ligament reconstruction with either the patellar tendon or the semitendinosus and gracilis tendons (four strands) were prospectively compared in a consecutive series of 60 patients with chronic injuries. A single surgeon performed arthroscopically assisted reconstructions in an alternating sequence. Preoperative and operative data revealed no significant differences between the two groups. After 28 months of followup there were no significant differences in the incidence of symptoms, and recurrent giving way was present in only one knee with semitendinosus and gracilis tendon graft. Return to sport participation was more frequent in the patellar tendon group (80% versus 43%, P < 0.01). A minor extension loss (< or = 3 degrees) was more frequent in the patellar tendon group (47% versus 3%, P < 0.001). Other differences between the two groups were not significant. KT-2000 arthrometer side-to-side difference of anterior displacement > 5 mm at 30 pounds was present in 13% of the knees with patellar tendon grafts and in 20% of those with semitendinosus and gracilis; a patellofemoral crepitation developed in 17% and 3% of the two groups, respectively. Based on these data we routinely use patellar tendon grafts. Semitendinosus and gracilis tendons are preferred in selected cases: older patients, patients with preexisting patellofemoral problems, and those with failed patellar tendon grafts.
Our study evaluated tendon-to-bone healing in a dog model. Twenty adult mongrel dogs had a transplantation of the long digital extensor tendon into a 4.8-millimeter drill-hole in the proximal tibial metaphysis. Four dogs were killed at each of five time-periods (two, four, eight, twelve, and twenty-six weeks after the transplantation), and the histological and biomechanical characteristics of the tendon-bone interface were evaluated. Serial histological analysis revealed progressive reestablishment of collagen-fiber continuity between the bone and the tendon. A layer of cellular, fibrous tissue was noted between the tendon and the bone, along the length of the bone tunnel; this layer progressively matured and reorganized during the healing process. The collagen fibers that attached the tendon to the bone resembled Sharpey fibers. High-resolution radiographs showed remodeling of the trabecular bone that surrounded the tendon. At the two, four, and eight-week time-periods, all specimens had failed by pull-out of the tendon from the bone tunnel. The strength of the interface was noted to have significantly and progressively increased between the second and the twelfth week after the transplantation. At the twelve and twenty-six-week time-periods, all specimens had failed by pull-out of the tendon from the clamp or by mid-substance rupture of the tendon. The progressive increase in strength was correlated with the degree of bone ingrowth, mineralization, and maturation of the healing tissue, noted histologically.
We present a retrospective report of 50 patients (31 autograft and 19 allograft patients) who underwent arthroscopic bone-patellar tendon-bone anterior cruciate ligament (ACL) reconstructions between August 1988 and September 1990. All patients were followed for a minimum of 2 years. The purpose of this study was to analyze each group regarding hospital stay, swelling, thigh atrophy, laxity, strength, endurance, range of motion, patellofemoral symptoms, and complications. We found no statistical difference between autograft or allograft ACL reconstructions with regard to perioperative morbidity.
The effects of closure of the peritendineum and bone grafting of the patellar defect after harvest of the bone-tendon-bone patellar tendon autograft was investigated prospectively in two groups of 25 patients. Anterior cruciate ligament (ACL) reconstruction was performed with minimally invasive techniques either arthroscopically or via mini-arthrotomy. Patellar height, size of bony and tendon defects, and overall result were followed up for 2 years postoperatively. The results showed that closure of the peritendineum enhances healing of the patellar tendon defect and restores a normal appearance of the tendon within 2 years. We have stopped bone grafting the patellar defect with cancellous bone because of the risk of formation of painful spurs at the inferior pole of the patella which occurred in 36% of patients.
To distinguish between morbidity caused by harvesting semitendinosus and gracilis tendons and morbidity associated with anterior cruciate ligament reconstruction surgery, we performed a prospective randomized study using 65 patients who underwent anterior cruciate ligament reconstruction using these tendons. The patients underwent either contralateral (N = 34) or ipsilateral (N = 31) graft harvest. For the nonoperated knees in the ipsilateral harvest group, isometric and isokinetic strength of the quadriceps and hamstring muscles increased to approximately 120% of the preoperative value at 12 months after surgery. Compared with these knees, the tendon harvest did not affect quadriceps muscle strength at all. However, harvest did decrease hamstring muscles strength for 9 months after surgery. The graft harvest in the knees with anterior cruciate ligament reconstruction also did not significantly affect quadriceps muscle strength, but it did significantly decrease hamstring muscles strength only at 1 month. Activity-related soreness at the donor site was rarely restricting and resolved by 3 months. This study demonstrated that the semitendinosus and gracilis tendon graft is a reasonable choice to minimize the donor site morbidity in ligament reconstruction using autografts.
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.
Retrospective clinical and radiographic evaluation was performed on 41 patients seen at the Salzburg General Hospital Department of Traumatology on average 2 years following ACL reconstruction. In 26 patients (61%) clinical examination revealed pain trigger points over the donor site of the midthird patellar tendon and in the patellofemoral joint. Functional pain during kneeling activities was observed in 19 patients (46%). Objective measurement of the length of the patellar tendon in bilateral radiographs demonstrated exactly equal patellar tendon length in both knees in 11 patients (27%). The radiographs showed tendon shortening following harvesting of the midthird patellar tendon by 1-3 mm in 7 patients (17%), by 4-6 mm in 16 (39%), and by 6-9 mm in 7 (17%). Average length change in the patellar tendon on the donor side was -3 mm, representing a patellar tendon shortening of 9.8%. On the basis of the OAK score, however, good and very good results were recorded in 33 patients (80%). On the whole, these good overall results were compromised only be patellar tendon defect morbidity. In addition to the local scarring problems at the donor site, shortening of the patellar tendon was observed with changes to patella position and interference with the mechanics of the patellofemoral joint. Tendon shortening can be explained on the basis of cicatricial contraction in the process of autorepair to the tendon defect. The problems affecting the patellofemoral joint are inherent in the therapy and must be treated as a negative factor. In the case of patients whose work requires mainly a kneeling position and those who make significant functional demands of the extension system of the knee, a critical assessment is required of the use of the midthird patellar tendon for anterior cruciate ligament reconstruction.
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.
The initial biomechanical properties of semitendinosus and patellar tendon autografts and their fixation strengths were investigated. Twenty fresh cadaveric knees from donors under 42 years of age were used in the study. After removing all soft tissues other than the anterior cruciate ligament, we determined the ultimate tensile strength (2195 +/- 427 N) and stiffness (306 +/- 80 N/mm) of the anterior cruciate ligament in nine knees. In six knees, anterior cruciate ligaments were reconstructed using an autologous patellar tendon graft with proximal and distal interference fit screws; this resulted in an ultimate tensile strength of 416 +/- 66 N. Five knees were reconstructed with quadruple-stranded (double-looped) semitendinosus tendons fixed proximally by a titanium button and braided tape and distally by tibial post screw. This resulted in an ultimate tensile strength of 612 +/- 73 N, which was significantly higher than the strength in the patellar tendon group. Graft stiffness did not differ between the groups and was 47 +/- 19 N/mm (N = 11). This study demonstrates that the reconstructed knees had only 20% to 30% of the ultimate tensile strength of the normal anterior cruciate ligament. In summary, the semitendinosus reconstruction using a button for proximal fixation is, at the time of surgery, approximately 50% stronger than patellar tendon reconstructions with similar stiffness.
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.
The purpose of this study was to examine the relationship between body weight and composition, muscular strength, physical activity, and bone mineral density (BMD) in eumenorrheic college-aged women.
BMD and bone mineral content (BMC) of the total body, and BMD of the lumbar spine (L2-L4) and femoral neck (via dual energy x-ray absorptiometry), as well as body composition and muscular strength, were measured in 60 college-aged women. The women were divided into three groups: 1) low body weight athletes involved in weight-bearing, collegiate sports (N = 20), 2) matched low body weight and sedentary (N = 20), and 3) average body weight and sedentary (N = 20). All groups were matched for height, age, and age at menarche.
The athletes had significantly greater (P < 0.05) (mean +/- SD) total body BMD (1.164 +/- 0.06 g x cm[-2]), L2-L4 BMD (1.240 +/- 0.13 g x cm[-2]), femoral neck BMD (1.144 +/- 0.13 g x cm[-2]) and total body BMC (2.44 +/- 0.30 kg) than the low body weight, sedentary (LWS) group, but were only greater than the average body weight sedentary group (AWS) for femoral neck BMD. Significant correlations were found between lean body mass (LBM) and all BMD variables (P < 0.001). A significant correlation (P < 0.01) was found between fat mass and all BMD variables in the sedentary subjects alone (N = 40), but with inclusion of the athletes (N = 60), none of the correlations between fat mass and BMD were significant. Arm and leg strength isometric torque values corrected for muscle + bone cross-sectional area (M + B CSA) were not significantly different between the athletes and LWS group, but the athletes were greater (P < 0.05) than the AWS group for both arm and leg strength/M + B CSA. No significant, site-specific correlations were found between strength/M + B and BMD.
In summary, the athletes had significantly greater BMD, BMC, and LBM than the LWS group and, except for a greater femoral neck BMD, similar BMD, BMC, and LBM as the AWS group. These results suggest that LBM and weight-bearing exercise both enhance BMD in eumenorrheic young adult women.
Although semitendinosus-gracilis (SG) grafts for anterior cruciate ligament reconstruction have many potential benefits, effective fixation remains a challenge. This study assessed differences between the maximum pullout forces needed to detach a quadrupled SG graft from a femoral tunnel when secured by either a metal or a bioabsorbable interference screw. Sixteen paired fresh frozen quadrupled SG autografts (x, 8.4 mm; range, 7-10 mm) from 8 donors were anchored into cadaveric femoral tunnels by either a 7-mm metal or a 7-mm bioabsorbable screw after bone mineral density (BMD) assessment and before undergoing a longitudinal 20 mm/min traction force. Statistical analysis compared BMD (gm/cm2), insertional torque (N-m), and maximum load at pullout (N) between screw types. Insertional torques (.28-1.21, N-m range) did not correlate (P>.05) to BMD or maximum load at pullout (x +/- S.D.) 242 +/- 90.7 N (metal screw) and 341.1 +/- 162.9 N (bioabsorbable screw). Differences did not exist between the maximum load at pullout for bioabsorbable or metal screw fixation (P = .16). Careful graft preparation, sizing, and matched tunnel placement enables interference fit and fixation capable of reliably withstanding the low-level rehabilitation loads to which the graft is exposed until bony ingrowth occurs.
This study evaluates the effect of submaximal cyclical loads on the tendinous portion of the central 10 mm of the patellar tendon compared with doubled semitendinosus and gracilis tendons. Six fresh-frozen cadaveric knee specimens were used for the study. There was no significant difference between the cross-sectional areas of a 10-mm patellar tendon and four strands of hamstring tendon (looped semitendinosus and gracilis) from the same specimen. The mean cross-sectional area was 44.4 mm2 for the patellar tendon and 47.5 mm2 for the four strands of hamstring. The specimens were cyclically loaded for 1000 cycles from 0 to 300 N at a rate of 1 Hz; the materials testing machine was set on load control. There were no significant differences in the strain, stress, or modulus between the 10-mm patellar tendon and four strands of hamstring tendon after 1000 cycles of loading to 300 N. These data substantiate the excellent clinical results obtained with either graft source and support the use of either graft source for ACL reconstruction.
The purpose of this paper is to review scientific evidence that graft tension affects remodelling of the autograft in ligament reconstruction. The in situ freezing model of the patellar tendon, an ideal patellar tendon autograft model, demonstrated that subsequent cellular proliferation following fibroblast necrosis reduces the mechanical properties of the autograft. Stress shielding enhances reduction of the strength in the once-frozen patellar tendon. The strength of the patellar tendon also changes depending on the degree of stress shielding. Transmission electron micrographs revealed that the number of small-diameter fibrils decreases in the stress-shielded tendons compared with non-stress-shielded tendons after in situ freezing. Restressing essentially restores the mechanical properties of patellar tendon autografts even if the strength has been much reduced by complete stress shielding. The effects of restressing may depend on the period of stress shielding applied before restressing. Unphysiologically high tension significantly reduces the mechanical properties of the in situ frozen anterior cruciate ligament (ACL). Therefore, not only stress-deprivation but also stress-enhancement significantly affect the mechanical properties of tendon autografts. Results of in vivo and in vitro studies suggest that cyclic tensile loading may inhibit the deterioration in mechanical strength of the transplanted tendon. Clinically, our prospective randomized study demonstrated that a relatively high initial tension reduces the postoperative anterior laxity of the knee joint after ACL reconstruction using the doubled autogenous hamstring tendons connected in series with polyester tapes, when the tension applied is less than 80 N. Our experimental and clinical results indicate that the initial tension is one of the significant factors that affect the results of ACL reconstruction, although the optimal initial tension for the other graft materials still remains unknown.
The purpose of the study was to compare the hamstring and quadriceps isokinetic results 6 months postoperatively in patients having patellar tendon or hamstring anterior cruciate ligament (ACL) reconstruction. The study group was comprised of 106 randomly selected patients who had ACL reconstruction with either autogenous patellar tendon (PT), semitendinosus (ST), or semitendinosus and gracilis (ST/G). Hamstring and quadriceps isokinetic strength were assessed at 180 degrees/sec and 300 degrees/sec with the results of the operatively treated leg expressed as a percent compared with the nonoperative leg. The mean results for knee extension at 180 degrees/sec were 68.3%, 74.3%, and 78.1%; and at 300 degrees/sec were 70.7%, 76.7%, and 81.7% for PT, ST, and ST/G, respectively. The mean results for knee flexion at 180 degrees/sec were 86.1%, 80.6%, and 81.7%; and at 300 degrees/sec were 77.6%, 79.1%, and 75.6% for PT, ST, and ST/G, respectively. No statistically significant differences were found in regard to knee extension or flexion strength when evaluating the different tissue sources. The results show that selection of autogenous hamstring or PT used for ACL reconstruction should not be based solely on the assumption of the tissue source altering the recovery of quadriceps and/or hamstring strength. In addition, a majority of the patients had not achieved adequate strength to safely partake in unlimited activities at 6 months postoperatively.
The purpose of this study was to measure the effect of bone-patellar tendon-bone autograft harvest for anterior cruciate ligament (ACL) reconstruction on the surface strain of the human patella. Through progressive removal of bone from the patella, three different defect shapes as well as the intact patella were tested in each of seven knees. Maximum principal strain and corresponding principal direction were determined from each of three gages around the defect for the four conditions (intact plus three defect shapes). There were no statistically significant differences in overall average surface strain between any of the defect shapes. Following graft harvest, overall average strain (all three defects combined) increased in the patella both medial (15 percent increase) and lateral (34 percent increase) to the defect, while decreasing in the region directly proximal (22 percent decrease) to the harvest site compared to the intact patella. A statistically significant 7.5 deg shift of principal direction from longitudinal toward a more transverse (lateral-superior to medial-inferior) direction was observed in the medial region when a shallow-dome defect was made. We conclude that removal of a bone block from the anterior, inferior part of the patella induces a significant redistribution of the surface strain. This results in greater local strain adjacent to the upper border of the bone block increasing the risk for patella fracture. This effect may be of importance in various complications known to occur after ACL reconstruction.
Our hypothesis that multiple, equally tensioned strands of hamstring graft used for reconstruction of the anterior cruciate ligament are stronger and stiffer than ten-millimeter patellar ligament grafts was tested biomechanically with use of tendons from cadavera.
In the first part of the study, we measured the strength and stiffness of one, two, and four-strand hamstring grafts, from fresh-frozen cadaveric knees, that had been tensioned equally when clamped. In the second part of the study, we compared four-strand grafts to which tension had been applied by hand and then clamped with similar grafts to which tension had been applied with weights and then clamped. The grafts for the two experiments were obtained from thirty-four paired and ten unpaired knees. We also studied the effects of cooling on the biomechanical properties of grafts by comparing patellar ligament grafts tested at 13 degrees Celsius with those tested at room temperature.
Two equally tensioned gracilis strands had 185 percent of the strength and 210 percent of the stiffness (1550+/-428 newtons and 336+/-141 newtons per millimeter, respectively) of one gracilis strand (837+/- 138 newtons and 160+/-44 newtons per millimeter, respectively). Two equally tensioned semitendinosus strands had 220 percent of the strength and 220 percent of the stiffness (2330+/-452 newtons and 469+/-185 newtons per millimeter, respectively) of one semitendinosus strand (1060+/-227 newtons and 213+/-44 newtons per millimeter, respectively). Four combined strands (two gracilis strands and two semitendinosus strands) that were equally tensioned with weights and clamped had the additive tensile properties of the individual strands. With the numbers available, four combined strands that were manually tensioned and clamped were not found to be significantly stronger or stiffer than two semitendinosus strands that were equally tensioned with weights (p>0.07).
Four combined strands that were equally tensioned with weights and clamped were stronger and stiffer than all ten-millimeter patellar ligament grafts that have been described in previous reports. All strands of a hamstring graft must be equally tensioned for the composite to have its optimum biomechanical properties.
Because of the well recognized donor-site morbidity associated with the use of patellar ligament grafts for reconstruction of the anterior cruciate ligament, multiple-strand hamstring-tendon grafts have become an increasingly popular choice. Our data demonstrate that equally tensioned four-strand hamstring-tendon grafts have initial tensile properties that are higher than those reported for ten-millimeter patellar-ligament grafts; thus, from a biomechanical point of view, they seem to be a reasonable alternative.
We compared the outcome of anterior cruciate ligament reconstruction using hamstring tendon autograft with outcome using patellar tendon autograft at 2 years after surgery. Patients had an isolated anterior cruciate ligament injury and, apart from the grafts, the arthroscopic surgical technique was identical. Prospective assessment was performed on 90 patients with isolated anterior cruciate ligament injury undergoing reconstruction with a patellar tendon autograft; 82 were available for follow-up. The hamstring tendon autograft group consisted of the next 90 consecutive patients fulfilling the same criteria; 85 were available for follow-up. Clinical review included the Lysholm and International Knee Documentation Committee scores, instrumented testing, thigh atrophy, and kneeling pain. These methods revealed no difference between the groups in terms of ligament stability, range of motion, and general symptoms. Thigh atrophy was significantly less in the hamstring tendon group at 1 year after surgery, a difference that had disappeared by 2 years. The KT-1000 arthrometer testing showed a slightly increased mean laxity in the female patients in the hamstring tendon graft group. Kneeling pain after reconstruction with the hamstring tendon autograft was significantly less common than with the patellar tendon autograft, suggesting lower donor-site morbidity with hamstring tendon harvest.
Blunt-threaded interference screws used for fixation of hamstring tendons in anterior cruciate ligament reconstructions provide aperture fixation and may provide a biomechanically more stable graft than a graft fixed further from the articular surface. It is unknown if soft tissue fixation strength using interference screws is affected by screw length. We compared the cyclic and time-zero pull-out forces of 7 x 25 mm and 7 x 40 mm blunt-threaded metal interference screws for hamstring graft tibial fixation in eight paired human cadaveric specimens. A four-stranded autologous hamstring tendon graft was secured by a blunt-threaded interference screw into a proximal tibial tunnel with a diameter corresponding to the graft width. Eight grafts were secured with a 25-mm length screw while the other eight paired grafts were secured with a 40-mm length screw. During cyclic testing, slippage of the graft occurred as the force of pull became greater with each cycle until the graft-screw complex ultimately failed. All grafts failed at the fixation site, with the tendon being pulled past the screw. There were no measurable differences in the mean cyclic failure strength, pull-out strength, or stiffness between the two sizes of screws. Although use of the longer screw would make removal technically easier should revision surgery be necessary, it did not provide stronger fixation strength than the shorter, standard screw as had been postulated.
The purpose of this study was to use current fixation techniques and compare the stiffness and ultimate tensile failure of the tendinous end of the quadriceps tendon (QT) with the bone plug end of the bone-patellar tendon-bone (BPTB) graft using current techniques of fixation. Type of Study: Randomized trial of elderly cadaver knees. Materials and Methods: Tibial and femoral biodegradable interference fixation and femoral EndoButton (Smith & Nephew, Acufex, Mansfield, MA) fixation in bone tunnels with the QT and the BPTB graft were compared by using 10 pairs of elderly cadavers and biomechanical testing. Two groups, fixation at time zero (simulating fixation in the operating room) and testing after 1, 000 loading cycles (simulating patient rehabilitation exercises), were used.
At time zero fixation, stiffness of the soft tissue QT tibial tunnel interference fixation was 59% less stiff than the stiffness of the interference fixation of a BPTB plug in a femoral tunnel (P =.11). The EndoButton femoral fixation resulted in a decrease in stiffness at time zero compared with femoral tunnel interference fixation of the soft tissue QT (P =.03). All groups improved stiffness with cycling the construct to 1,000 cycles.
Placement of the QT tendinous end of the graft in the femoral bone tunnel when using a interference fixation will approximate the stiffness of a bone plug in the tibial bone tunnel with interference fixation. The EndoButton fixation is not as stiff as either of the femoral interference fixation options. The addition of more than 20 loading cycles could remove laxity from the graft fixation-graft cruciate ligament complex and improve its stiffness.
Hamstring and patellar tendon graft response to cyclical loading
- P T Simonian
- Williams
- Rj
- X H Deng
Tendon-healing in a bone tunnel. A biomechanical and histological study in the dog
- S A Rodeo
- Arnoczky
- Sp
- P A Torzilli
Anterior cruciate ligament graft fixation: Comparison of hamstring and patellar tendon grafts
- M E Steiner
- Hecker
- At
- C H Brown