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MR imaging and metallic implants for anterior cruciate ligament reconstruction: Assessment of ferromagnetism and artifact
Abstract
Magnetic resonance (MR) imaging is contraindicated for patients with certain ferromagnetic implants, primarily because of potential risks related to movement or dislodgment of the devices. An additional problem with metallic implants is the potential image distortion that may affect the interpretation of the MR study. Since MR imaging is frequently useful for the evaluation of postoperative anterior cruciate ligament (ACL) reconstruction, the ferromagnetic qualities and artifacts associated with MR imaging were determined for five metallic orthopedic implants commonly used for this surgery. Only the Perfix interference screw displayed a substantial deflection force and caused extensive signal loss. Images of the knee of one patient with two Perfix screws in place were not interpretable because of the image distortion caused by these implants. Therefore, alternative nonferromagnetic implants should be considered for reconstruction of the ACL.
... Bioabsorbable interference screws may offer many advantages over their metal counterparts, including the decreased risk for graft laceration, decreased stress protection, undistorted postsurgical MRI, no need for hardware removal, and lack of corrosion (Black 1988, Shellock et al. 1992, Safran and Harner 1996, Jacobs et al. 1998, Suh et al. 1998, Brown and Carson 1999. The increased popularity of the ACL reconstruction surgery has also increased the number of ACL revisions (Jaureguito andPaulos 1996, Safran andHarner 1996). ...
... Along with the popularity of ACL reconstruction surgery, the number of ACL revisions also increased dramatically (Jaureguito and Paulos 1996, Safran and Harner 1996, Allen et al. 2003. As the retained metal screws may severely complicate the revision ACL surgery and disturb MRI (Shellock et al. 1992, Suh et al. 1998, there was an apparent benefit associated with the use of fixation implants made of bioabsorbable material, but their suitability had to be properly validated. ...
... Complications related to metal screws such as pain, graft injury at time of insertion, magnetic resonance imaging (MRI) incompatibility, need for a second operation for screw removal, and technical challenges with revision surgery have been reported. 11,25,29 These reports led to the development and popularization of bioabsorbable interference screws. ...
Background
Interference screw fixation using bioabsorbable implants has become the most common form of tibial-sided graft fixation in anterior cruciate ligament reconstruction (ACLR). Complications related to implant use in the pediatric and adolescent population have not been well studied.
Purpose/Hypothesis
The purpose of this study was to retrospectively analyze the complications associated with tibial bioabsorbable interference screw use in adolescents after ACLR. We hypothesized that complication rates would be low (<5%) and that different screw types would have similar complication rates and clinical outcomes.
Study Design
Case series; Level of evidence, 4.
Methods
Included in this study were patients aged ≤18 years who underwent ACLR with a bioabsorbable tibial interference screw between 2000 and 2011 at a single institution. The subpopulation with screw-related symptoms or complications were identified through chart review. The following 2 outcomes were considered: screw-related symptoms and secondary surgery related to the screw. Multivariable logistic regression was used for adjusted analysis of any screw-related problem.
Results
There were 925 ACLR procedures in 858 patients (mean age, 15.7 years; range, 10-18 years) who met inclusion criteria. The median follow-up period was 32.0 months. Of the 925 knees, 89 (9.6%) developed a screw-related problem. In 44 (4.8%) cases, no surgery was required; in 45 (4.9%) cases, surgery for a screw-related problem occurred at a median of 24 months postoperatively. The most common surgical indication was pain at the tibial screw site (42/45, 93%), followed by intra-articular screw issues (3/45, 7%). In adjusted analysis, ACLR procedure performed by a “low-volume” ACL surgeon was the only significant predictor identified. After screw removal surgery, 25 of 27 (93%) patients with at least 12 months of follow-up had complete resolution of screw site symptoms, 18 of 23 (78%) evaluable patients returned to sports, while 8 of 27 (30%) patients underwent additional surgeries, 7 of which were unrelated to the screw procedure.
Conclusion
The rate of clinical sequelae from bioabsorbable tibial interference screws was surprisingly high, with symptoms arising after approximately 1 of 10 ACLRs in adolescents. Reoperation for these symptoms was performed in approximately 5% of the knees in the study, at a median 2 years postoperatively. Most patients were able to return to sports after screw removal surgery.
... It is embedded in bone, so it has sufficient force to prevent movement. On the other hand, it causes significant signal distortion during MRI of the knee (Shellock, 1992). Big concern is also heating, due to good conductivity of materials, especially in external fixation systems. ...
... Similar rates of infection in the both groups suggest that bioabsorbable PLLA pins can be used in fixation of the chevron osteotomy for treatment of hallux valgus deformity, instead of metallic K-wires. A potential complication with using bioabsorbable materials is occasional breakage [55,56]. In this study, bioabsorbable pin failure by a motor vehicle accident and a fall from height caused loss of fixation of the osteotomy site in 2 patients (2 feet, 3.2%) at 4-8 weeks requiring ...
... Metallic implant with BPTB graft was appraised as a paragon or ideal model in ACL reconstructive surgery due to its high stiffness and superior fixation strength [34]. However, due to the increased risk of graft laceration, high stress exposure, need for implant removal and corrosion imposed by metallic fixation, development of various bioabsorbable interference screws were made to overcome the shortcomings [53][54][55][56][57] that include poly (glycolide-co-trimethylene carbonate) (PGA TMC), poly (DL-lactide) (PDLLA), PLDLA with calcium phosphate, poly (DL-lactide-co-glycolide) (PLDLG), poly (Llactide D-lactide) (PLDLA), poly (lactide carbonate) (PLC) screws, and poly (L-lactide) (PLLA) [36]. Bioabsorbable PLLA screw that shows an extended degradation time has been widely and most frequently used for the applications of bioabsorbable implants [58].A study in [59] claimed that the use of bioabsorbable screw demonstrates comparable biomechanical performance with metallic screw during high failure loads. ...
... Metal implants have many disadvantages such as erosion, allogenic response, bone atrophy, Dovepress Dovepress 6626 Dai et al MRI interference, and requirements for removal surgery. [4][5][6][7] Using a bioabsorbable implant is one approach to eliminate the need for implant removal after fracture fixation. The ideal bioabsorbable implants can be completely resorbed after surgery. ...
Objective
To evaluate the internal fixation effect of nano-calcium-deficient hydroxyapatite/poly-amino acid (n-CDHA/PAA) composite screws in the intraarticular fracture model.
Materials and methods
A total of 35 New Zealand White rabbits were used in a bilateral femoral intercondylar fracture model and randomly divided into two groups. n-CDHA/PAA screws were used in the experimental group, and medical metal screws were used in the control group. The fracture condition, range of motion, and the screw push-out strength were assessed, and an arthroscopic examination of knee joint was performed at 4, 8, and 12 weeks after surgery. The biodegradation of the n-CDHA/PAA screws in vivo was tested through weighing, and changes in screw structure were assessed by X-ray diffraction at 12 weeks after surgery.
Results
The general situation of all animals was good and showed no incision infection and dehiscence after surgery. X-ray scanning showed that significant callus growth was present in both groups at 4 weeks after surgery, and there was no significant difference (P>0.05) in the Lane-Sandhu score between the experimental and control groups at all time points after surgery. There were no statistically significant differences (P>0.05) in the range of motion and Oswestry Arthroscopy Score of arthroscopic examination of the knee joints between the two groups. The screw push-out strength of the control group was stronger than that of the experimental group at 4 weeks after surgery (P<0.05), but after that, there was no significant difference between the groups (P>0.05). The degradation tests showed that the n-CDHA/PAA screws degraded gradually after implantation, and the weight loss rate was approximately 16% at 12 weeks after surgery. The X-ray diffraction results showed that the crystal structure of the outer surface of the n-CDHA/PAA screw has changed at 12 weeks after surgery.
Conclusion
The n-CDHA/PAA screw is an effective and safe implant as a potential internal fixation device for an intercondylar fracture of the femur, and its internal fixation effect was similar to that of medical metal screw.
... 3 Metallic interference screws are complicated by damage to the graft or sutures, disruption of magnetic resonance imaging (MRI), and the need for their removal during any subsequent revision surgeries. 4,5 Bioabsorbable interference screws were developed as an alternative to metallic screws and have been shown to have equivalent fixation strength and clinical results. [6][7][8] The advantages of bioabsorbable versus metallic screws include increased compatibility with MRI, no need for removal during revisions, and decreased likelihood of injuring the graft upon insertion. ...
Current treatment options for cartilage injuries are limited. The goals of this study are to create a biodegradable polymer scaffold with the capabilities of sustaining chondrocyte growth and proliferation, enable cell-to-cell communication and tissue regeneration through large pores, and assess the biological augmentation of the scaffold capabilities using platelet lysate (PL). We synthesized biodegradable polycaprolactone fumarate (PCLF) scaffolds to allow cell-cell communication through large interconnected pores. Molds were printed using a three-dimensional printer and scaffolds synthesized through UV crosslinking. Culture medium included alpha modified Eagle's media with either 10% fetal bovine serum (FBS) or 5% PL, a mixture of platelet release products, after being seeded onto scaffolds through a dynamic bioreactor. Assays included cellular proliferation (MTS), toxicity and viability (live/dead immunostaining), differentiation (glycosaminoglycan [GAG], alkaline phosphatase [ALP], and total collagen), and immunostaining for chondrogenic markers collagen II and Sox 9 (with collagen I as a negative control). The large interconnected pores (500 and 750??m) enable cell-to-cell communication and cellular infiltration into the scaffolds, as the cells remained viable and proliferated for 2 weeks. Chondrocytes cultured in PL showed increased rates of proliferation when compared with FBS. The chondrogenic markers GAG and total collagen contents increased over 2 weeks at each time point, whereas the osteogenic marker ALP did not significantly change. Immunostaining at 2 and 4 weeks for the expression of chondrogenic markers Collagen II and Sox 9 was increased when compared with control human fibroblasts. These results show that the PCLF polymer scaffold enables chondrocytes to attach, proliferate, and retain their chondrogenic phenotypes, demonstrating potential in chondrocyte engineering and cartilage regeneration.
... [3] Metallic interference screws are complicated by damage to the graft or sutures, disruption of magnetic resonance imaging (MRI), and the need for their removal during any subsequent revision surgeries. [4,5] Bioabsorbable interference screws were developed as an alternative to metallic screws and have been shown to have equivalent fixation strength and clinical results. [6][7][8] The advantages of bioabsorbable versus metallic screws include increased compatibility with magnetic resonance imaging (MRI), no need for removal during revisions, and decreased likelihood of injuring the graft upon insertion. ...
Anterior cruciate ligament (ACL) ruptures reconstructed with tendon grafts are commonly fixed with bioabsorbable implants, which are frequently complicated by incomplete bone filling upon degradation. Bone regeneration after ACL reconstruction could be enhanced by utilizing tissue engineering techniques and three-dimensional (3D) printing to create a porous bioabsorbable scaffold with delayed delivery of recombinant-human bone morphogenetic protein 2 (rhBMP-2). The first aim of this study was to design a 3D PPF porous scaffold that maintained suitable pull-out strength for future testing in a rabbit ACL reconstruction model. Our second aim was to determine the release kinetics of rhBMP-2 from PPF scaffolds that utilized both calcium-phosphate coatings and growth factor delivery on microspheres, both of which have been shown to decrease the initial burst release of rhBMP-2 and increase bone regeneration. To determine the degree of scaffold porosity that maintained suitable pull-out strength, tapered scaffolds were fabricated with increasing porosity (0%, 20%, 35%, and 44%) and pull-out testing was performed in a cadaveric rabbit ACL reconstruction model. Scaffolds were coated with carbonate hydroxyapatite (synthetic bone mineral, SBM) and radiolabeled rhBMP-2 was delivered in four different experimental groups: Poly(lactic-co-glycolic acid) PLGA microspheres only, microspheres and collagen (50:50), collagen only, and saline solution only. rhBMP-2 release was measured at day one, two, four, eight, sixteen, and thirty-two. The microsphere delivery groups had a smaller burst release and released a smaller percentage of rhBMP-2 over the 32 days than the collagen and saline only groups. In conclusion, a porous bioabsorbable scaffold with suitable strength for a rabbit ACL reconstruction was developed. Combining a synthetic bone mineral coating with microspheres had an additive effect, decreasing the initial burst release and cumulative release of rhBMP-2. Future studies need to evaluate this scaffold's fixation strength and bone filling capabilities in vivo compared to traditional bioabsorbable implants.
... Aperture fixation by bioabsorbable or titanium interference screws during HT ACLR is a well-established technique that allows accelerated rehabilitation. 3,4,11,16,20 Although metallic interference screws and bioabsorbable screws have been shown to have the same fixation strength, 13 metallic screws have been associated with graft damage, 24 they hinder subsequent magnetic resonance imaging (MRI) examination because of their ferromagnetic qualities and artifacts, 21 and they potentially need to be removed in revision surgery or high tibial osteotomy. To overcome these disadvantages, different designs of bioabsorbable screws have been introduced and are becoming increasingly popular. ...
Longer-term results of bioabsorbable screws for anterior cruciate ligament reconstruction (ACLR) have been reported, but results are specific to the exact screw material and design. Titanium and poly-L-lactic acid with hydroxyapatite (PLLA-HA) screw outcomes have been compared only to 2 years.
The purpose of this study was to compare the clinical and radiologic outcomes of the PLLA-HA screw versus titanium screw for hamstring tendon ACLR over a 5-year follow-up period. The hypothesis was that there are no differences in clinical scores or tunnel widening between the PLLA-HA and the titanium screws and that the PLLA-HA screw as seen on magnetic resonance imaging (MRI) should show high-grade resorption and ossification response over 5 years.
Randomized controlled trial; Level of evidence, 1.
A total of 40 patients undergoing ACLR were randomized to receive either a PLLA-HA screw (PLLA-HA group) or a titanium screw (titanium group) for ACL fixation. Blinded evaluation was performed at 2 and 5 years with the International Knee Documentation Committee and Lysholm knee score, KT-1000 arthrometer, single-legged hop test, and MRI to evaluate tunnel and screw volumes, periscrew ossification, graft integration, and cyst formation.
There was no difference in any clinical outcome measure at 2- or 5-year follow-up between the 2 groups. At 2 years, the femoral tunnel in the PLLA-HA group was smaller than that in the titanium group (P = .02); at 5 years, there was no difference. At 2 years, the femoral PLLA-HA screw was a mean 76% of its original volume, and by 5 years, it was 36%. At 2 years, the tibial PLLA-HA screw mean volume was 68% of its original volume, and by 5 years, it was 46%. At 5 years in the PLLA-HA group, 88% of femoral tunnels and 56% of tibial tunnels demonstrated a significant ossification response. There was no increase in cyst formation in the PLLA-HA group and no screw breakages.
There were equivalent clinical results between the PLLA-HA and titanium groups at 2- and 5-year follow-ups. The PLLA-HA screw was not associated with increased tunnel widening or cyst formation when compared with the titanium screw. The PLLA-HA screw demonstrated progressive screw resorption and gradual but incomplete ossification over 5 years.
© 2015 The Author(s).
... However, metal artifact is not uncommon in MR images of patients' knees following ACL reconstruction. 14,33 The problem could be minimized in part with the use of non-metallic fixation screws and flushing the joint to flush residual debris prior to closure. It was assumed the MR parameters (volume and median SI) used to directly predict ex vivo biomechanical properties of the graft in an animal model 3,4 would directly translate to a human clinical population. ...
Clinical, functional, and patient-oriented outcomes are commonly used to evaluate the efficacy of treatments after anterior cruciate ligament (ACL) injury; however, these evaluation techniques do not directly measure the biomechanical changes that occur with healing.
To determine if the magnetic resonance (MR) image-derived parameters of graft volume and signal intensity (SI), which have been used to predict the biomechanical (ie, structural) properties of the graft in animal models, correlate with commonly used clinical (anteroposterior [AP] knee laxity), functional (1-legged hop), and patient-oriented outcome measures (Knee Injury and Osteoarthritis Outcome Score [KOOS]) in patients 3 and 5 years after ACL reconstruction.
Cohort study (diagnosis); Level of evidence, 3.
Based on a subset of participants enrolled in an ongoing ACL reconstruction clinical trial, AP knee laxity, 1-legged hop test, and KOOS were assessed at 3- and 5-year follow-up. Three-dimensional, T1-weighted MR images were collected at each visit. Both the volume and median SI of the healing graft were determined and used as predictors in a multiple regression linear model to predict the traditional outcome measures.
Graft volume combined with median SI in a multiple linear regression model predicted 1-legged hop test at both the 3- and 5-year follow-up visits (R (2) = 0.40, P = .008 and R (2) = 0.62, P = .003, respectively). Similar results were found at the 5-year follow-up for the KOOS quality of life (R (2) = 0.49, P = .012), sport/function (R (2) = 0.37, P = .048), pain (R (2) = 0.46, P = .017), and symptoms (R (2) = 0.45, P = .021) subscores, although these variables were not significant at 3 years. The multiple linear regression model for AP knee laxity at 5-year follow-up approached significance (R (2) = 0.36, P = .088).
The MR parameters (volume and median SI) used to predict ex vivo biomechanical properties of the graft in an animal model have the ability to predict clinical or in vivo outcome measures in patients at 3- and 5-year follow-up.
Results from this study may enhance clinical evaluation of graft health by relating the MR parameters of volume and median SI to traditional outcome measures and could potentially aid researchers in determining the appropriate timing for athletes to return to sport.
© 2014 The Author(s).
... The use of biologic materials avoids the use of metals that distort future magnetic resonance imaging of the reconstructed knee. 3 The major advantage of bioabsorbable interference screws is revision ligament reconstruction surgery. Retained metal screws may be problematic at the time of revision. ...
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.
Background
All-suture anchors (ASAs) are noted to cause various bone reactions when used in upper limb surgery but clinical implications are unknown.
Methods
88 shoulders and 151 elbows with a mean follow-up of 47.1 ± 17.7 months were invited for follow-up including clinical examination, questionnaires and radiographs. The anchor drill holes were radiographically assessed.
Results
At final follow up, mean DASH was 12.9 ± 13.8 and mean VAS 2.2 ± 2.4 in the shoulder population. In the elbow group mean MEPS was 91.8 ± 12.7 and mean VAS 1.5 ± 1.9. Implant-specific complications were seen in 10 elbow cases but none in the shoulder group. The mean diameter of the 1.4 mm all-suture anchor drill hole was enlarged to 2.5 ± 1.4 mm in the shoulder group and to 2.9 ± 1.0 mm in the elbow group. 50% of the 1.4 mm anchor drill holes showed abnormal morphology but these morphologic changes did not correlate with clinical outcome, complications or reoperation rate.
Discussion
Satisfying clinical outcomes are found in upper limb surgery using ASAs. Various bone changes are seen after implantation of an ASA, but these are not clinically relevant. Long-term consecutive follow-up data is required.
Upgradation is still in need for the clinically applied interference screws in anterior cruciate ligament reconstruction for more reliable fixation. Silk fibroin bulk materials offer a promising opportunity for this application except lacking osteoinductivity to some extent. Here we report a novel silk-based bulk material with high content of hydroxyapatite-silk fibroin (HA-SF) hybrid particles, which is prepared via a dual-network hydrogel. This composite bulk material possesses a compression modulus of 3.2 GPa, comparable to that of the natural compact bone, and presents satisfactory cytocompatibility and osteoinductivity in vitro when combined with the HA-SF nanoparticles particularly. This composite bulk material shaped into interference screws exhibits remarkable biomechanical properties and significant new-bone ingrowth in the host bone tunnel in a rabbit anterior cruciate ligament reconstruction (ACLR) model at 4 weeks and 12 weeks post-operatively. Moreover, considering that this "hydrogel method" allows the material to be formed in a mold, avoiding complicated post fabrication, it is a potential candidate for clinical translation.
Introduction:
Fatty degeneration of the gluteal muscles on metal artefact reduction sequence (MARS) MRI has been shown to correlate with poor functional outcomes, particularly in patients with total hip arthroplasty (THA). Standardized, reliable classification systems that permit assessment of fatty gluteal infiltration are needed for clinical decision making. This study aimed to compare the reproducibility and accuracy of commonly used MRI classification systems for fatty gluteal atrophy in THA patients.
Methods:
MARS magnetic resonance images of 82 patients with unilateral THA were analysed by three independent trained observers. The readers evaluated fatty degeneration of the gluteus minimus, gluteus medius, and gluteus maximus according to 3 widely used classification systems: Goutallier, Quartile, and Bal and Lowe. Interobserver and intraobserver repeatability were determined using the weighted Kappa test. Quantitative evaluation of the proportion of intramuscular fat based on MR signal intensities was obtained and represented the gold standard.
Results:
Mean interobserver agreement for the Quartile classification system (0.93) was higher compared with Goutallier classification system (0.87) and the Bal and Lowe classification system (0.83; range 0.79-0.88; p = 0.04). Intraobserver repeatability was significantly higher for the Quartile classification system (weighted kappa 0.91, 0.89, 0.85) compared with the Bal and Lowe classification system (weighted kappa 0.83, 0.77, 0.75; p < 0.01) and Goutallier classification system (weighted kappa 0.83, 0.77, 0.75; p = 0.04). Agreement with the gold standard measurements was significantly higher in the Quartile classification system (0.88, 0.84, 0.81) compared with the Goutallier classification system (0.80, 0.77, 0.78; p = 0.02) and Bal and Lowe classification system (0.76, 0.74, 0.73; p < 0.01).
Discussion:
This study directly compared three clinically used MRI classification systems for fatty gluteal muscle atrophy in THA patients. Our findings demonstrate that although all three classification systems demonstrate good reproducibility and accuracy, the Quartile classification system is superior to the others in terms of intraobserver reliability and accuracy to quantify fatty gluteal degeneration in THA patients.
Background
The purpose of this study was to investigate postoperative tunnel widening after rectangular tunnel bone–patellar-tendon–bone graft anterior cruciate ligament reconstruction using newer-generation bioabsorbable interference screws.
Methods
Forty-six patients who had undergone primary rectangular tunnel bone–patellar-tendon–bone graft anterior cruciate ligament reconstruction using MILAGRO bioabsorbable interference screws (DePuy Synthes, Warsaw, IN, USA) for femoral fixation and for whom computed tomography was performed at two weeks and one year postoperatively were included in this prospective study. To assess the tunnel widening, the cross-sectional area of the femoral tunnel aperture (compared between two weeks and one year postoperatively) was assessed using computed tomography. Cyst formation, postoperative screw breakage, screw migration, and graft migration were also evaluated using computed tomography one year postoperatively.
Results
Mean tunnel widening was 1.9%, and the cross-sectional area of the femoral tunnel aperture was not significantly different between two weeks and one year postoperatively. Postoperative cyst formation, screw breakage, screw migration, and graft migration were not observed in any patient.
Conclusions
After rectangular tunnel bone–patellar-tendon–bone graft anterior cruciate ligament reconstruction using bioabsorbable interference screws for femoral fixation, tunnel widening was not observed via computed tomography analysis at two weeks and one year postoperatively.
» 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.
Objectives
To compare the rate of initial fixation failure and clinical outcomes in anterior cruciate ligament reconstruction (ACL-R) surgery with a rectangular tunnel bone-patellar tendon-bone (RT-BTB) graft (RT-BTB ACL-R) using metallic interference screws (M-IFSs) and bioabsorbable interference screws (B-IFSs) for femoral fixation.
Methods
Data were prospectively collected from patients undergoing RT-BTB ACL-R and CT within 2 weeks after surgery. Femoral fixation was performed using M-IFSs (M-IFS group) or B-IFSs (B-IFS group). Screw selections were historically controlled. The following parameters were intraoperatively assessed: IFS breakage and initial fixation failure examined by movement of the graft pulled with maximum manual force. Posterior wall breakage was assessed using CT. Lysholm Score, the 2000 International Knee Documentation Committee Knee Examination Form and the KT-2000 arthrometer was evaluated as the clinical outcome measures.
Results
The study included 116 patients. Of these, 26 were included in the M-IFS group and 92 in the B-IFS group. The rate of IFS breakage was not significantly different between the M-IFS and B-IFS groups (0.0% vs 2.2%). The rate of initial fixation failure was not significantly different between the M-IFS and B-IFS groups (3.8% vs 5.6%). Logistic regression analysis revealed that only posterior wall breakage predicted initial fixation failure (p=0.02). No significant difference of the clinical outcomes was observed between the M-IFS and B-IFS groups.
Conclusion
Initial fixation failure or clinical outcomes is not different between M-IFS and B-IFS use for femoral fixation in RT-BTB ACL-R.
Level of evidence
Prospective study using historical controls, level IV.
A case of anterior cruciate ligament (ACL) reconstruction with meniscal repair in an osteogenesis imperfecta patient is reported. A 24-year-old female with osteogenesis imperfecta type 1a suffered from a valgus extension injury resulting in tear of ACL and medial meniscus. She underwent an arthroscopic-assisted ACL reconstruction and medial meniscus repair. Meniscal tear at the menisco-capsular junction of the posterior horn of medial meniscus was repaired with three absorbable sutures via inside-out technique. ACL reconstruction was then performed with a bone-patellar tendon-bone allograft. The patient was followed up for 1 year with intact ACL grafts and healed medial meniscus. This case report showed that successful ACL reconstruction and meniscal repair is possible in an osteogenesis imperfecta patient.
Objectives:
To report the safety and clinical outcomes of placing current MRI components inside and outside the MRI bore during MRI scans.
Design:
Retrospective case series.
Setting:
Four trauma centers (three Level I, one Level II), from January 2005 to January 2015 PATIENTS:: All patients who had MRI scans with external fixators in place either inside our outside the MRI bore.
Intervention:
MRI scan of patients with external fixator in place.
Main outcome measurements:
Adverse events were defined as catastrophic pullout of the external fixator during the MRI scan, thermal injury to the skin, severe field distortions precluding the intended imaging, alterations of the magnetic field or visible structural damage to the magnet casing.
Results:
Thirty-eight patients with 44 external fixators were identified who had an MRI with the fixator inside or outside the MRI bore. Twelve patients with 13 external fixators had an MRI with the external fixator inside the MRI bore. Twenty-seven patients with 32 external fixators had an MRI with the external fixator outside the MRI bore. There were no adverse events.
Conclusions:
While no universal guidelines exist, there are circumstances in which obtaining MRI scans of patients with external fixators can be safe. This is the first clinical series with the primary outcome of safety when placing modern external components both inside and outside an MRI bore during a scan.
Introduction
The Anterior cruciate ligament (ACL) is the most commonly injured ligament around the knee and is best reconstructed with a biological graft. For ideal graft fixation, there should be sufficient initial strength to avoid failure of fixation and sufficient stiffness to restore the stability of the knee and to avoid gradual loosening in the post-operative period.
When considering fixation of Bone Patellar Tendon Bone (BPTB) grafts to the tibia, the interference screw is considered to be the gold standard. As an alternative, we have used of staples and stainless steel (SS) wire to anchor the BPTB graft to the tibia and femur. The aim of this study was to assess the biomechanical efficacy of this fixation technique for anchoring the BPTB graft to the proximal tibia. We used a bovine model to compare three fixation techniques −interference screw, braided polyester sutures tied to a screw post and SS wire tied to a staple.
Materials and methods
Fifteen fresh bovine knees specimens were used for the study. The patella was fixed to a load cell and the construct was pre-tensioned to 40N to allow for creep of the tendon. The BPTB graft was fixed to the tibia using the three fixation techniques − the interference screw, polyester suture tied to a post, and SS wire anchored to a staple. After fixation, the graft was subjected to a single load to failure test, and the forces generated were recorded. The ultimate failure load (the pullout strength), stiffness, and mode of failure were noted.
Results
In the single load-to-failure biomechanical testing, the ultimate failure load and stiffness for Staple with SS wire were 726.40N and 61.9N/mm respectively. For the screw post and polyester suture, it was 733.20N and 53.22N/mm, and for Interference screw − 594.00N and 79.50 N/mm respectively. There was no statistically significant difference in the stiffness or ultimate failure load between the three fixation techniques. The graft fixation using interference screws failed at the bone- tunnel interface by slippage of the bone block from the tunnel in all 5 specimens. In all 5 of the specimens fixed with polyester suture and the screw post, the fixation failed when the polyester suture snapped. When the SS wire and staple construct was stressed, the graft failed as the SS wire cut through the graft in 4 specimens, and in the fifth construct, the knot over the staple unraveled as the load was applied.
Conclusion
The biomechanical properties of BPTB graft fixation with SS wire tied to a staple is similar to that of other fixation devices like the interference screw and suture post. This technique provides a simple, yet effective fixation for the graft − but needs further clinical assessment.
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.
Absorbable (poly 1-lactic acid) interference screws were used to fix an autologous patellar tendon graft in 21 anterior cruciate ligament reconstructions. The results were evaluated clinically with the IKDC form and a KT 1000 arthrometer. CT and MRI were also carried out 3, 6 and 12 months after surgery. At follow-up after two years, the subjective assessments were normal in 5 cases, nearly normal in 12 and abnormal in 4. No cases of infection nor clinically evident reactive synovitis were observed. CT after 1 year showed that the bone plugs were completely incorporated in the bone tunnels. The gap between the screw and the plug was completely-filled with bone and there was a reactive bone layer around the screw. There was no evidence of lysis at the absorbable implant site. The screws had retained their shape and there were slight signs of resorption along their outer and inner surfaces. MRI provided a more meaningful picture of the position of the tunnels and the intra-articular part of the graft. CT, on the other hand, proved superior through its better demonstration of bone plug incorporation, the bone-screw interface and screw absorption.
Purpose: The purpose of this study is to evaluate the short-term clinical outcome of the capsulolabral repair using absorbable suture anchor in traumatic anterior instability of shoulder. Materials and Methods: From June 2000 to September 2001, 15 shoulders with recurrent anterior instability were operated with arthroscopic Bankart repair using absorbable suture-anchor 'PANALOK' (Mitek, westwood, MA), and were followed up over 1 year (average; 13 months). The mean age was 23-years. There were fourteen males and one female. The mean duration from the initial symptoms to the operation was 24 months. Associated pathologies were Hill-Sachs defect in 12 cases, SLAP in 6 cases, and partial rotator cuff tear in 2 cases. The results were evaluated by patien's satisfaction, Modified Rowe Score in regard to joint stability, mobility, pain and function in comparison with the preoperative ones, and other complications. Results: At the last follow-up, the total Rowe Score increased from 38 points to 92 points. There were no recurrence and 14 patients among 15 patients gained pre-operative level of sports activity and no other complications. Conclusion: Effective capsulolabral repair could be obtained by the absorbable anchoring without any untoward complications. This procedure is simple and safe one and this system can be a good substitute for the metallic anchor.
This chapter discusses a variety of titanium (Ti) applications. The CpTi and Ti-based alloys are usually used as fixtures for dental implantation. When these metals are used as restoratives for anterior teeth, the metal prostheses are covered with esthetic materials, such as porcelain or resin. The denture bases are presently manufactured mainly by a casting process of Co-Cr or Ni- Cr alloys. The Ti-6Al-4V alloy is a biocompatible metal with both high strength and low density, and is considered to be the best material for denture bases. It has superplastic properties at high temperatures, forming very simple processes by argon pressure at 800–900°C. When constructing removable dentures— the implant supported prostheses, the resin-bonded bridges, and the interfacial bond between metal and acrylic resin are completely reliable. Numerous investigations such as—the surface treatments of the alloys by macro-, micromechanical-, chemical methods, or by the addition of chemical bonding agents to acrylic, are shown to enhance retention.
Anterior cruciate ligament (ACL) revision reconstructions are likely to increase as the number of primary ACL reconstructions increases. Poor prior tunnel locations and tunnel expansion can complicate fixation of the graft in a revision setting, and thus the surgeon must be familiar with multiple different fixation methods, their advantages, disadvantages, and potential complications. This chapter reviews the various fixation types that can be used with soft tissue-to-bone or bone-to-bone fixation, the biomechanical properties of several common fixation devices, and offers technical advice for hardware removal and graft fixation in the setting of nearby prior tunnels or tunnel expansion. © Springer Science+Business Media New York 2014. All rights are reserved.
Over the last years the use of bioabsorbable materials in orthopaedic surgery has increased exponentially. One of the first surgical interventions to take benefit from these absorbable materials was the reconstructive surgery for the anterior cruciate ligament (ACL) of the knee, meaning the use of interference screws for the primary fixation of the ligament graft. The aim of this paper is to present the main types of screws of this kind, used in current practice, the preferred manufacturing materials and to evaluate the standard implantation procedures in terms of the stability they ensure to the ligament graft.
Die Magnetresonanztomografie ist zur nicht invasiven Einschätzung der Transplantat-integrität einer vorderen Kreuzbandersatzplastik in der postoperativen Phase hilfreich. Bei klinischen Studien wurde die MRT zur Beobachtung des Transplantatremodelings eingesetzt, jedoch in keinem Fall die Signalintensität mit biomechanischen Befunden korreliert. In der vorliegenden Studie wurde erstmals das quantitative MR-Signal in Form eines Signal/Noise-Quotienten mit biomechanischen Parametern über zwei Jahre am Langzeit Tiermodell verglichen und miteinander korreliert. 29 Schafe wurden einer Rekonstruktion des vorderen Kreuzbandes mit autologem Achillessehnen-Split-Transplantat unterzogen und nach 6, 12, 24, 52 und 104 Wochen geopfert. Vor Opferung wurden die Kniegelenke aller Tiere sowohl nativ, als auch mit Kontrastmittel (Gadolinium-Diethylentriaminpentaessigsäure) MR-tomografisch (1,5 Tesla, T1-Wichtung, 2 mm Schichtdicke, sagital/schräge Orientierung) untersucht. Anschließend wurden die Hinterläufe explantiert und biomechanisch getestet. Der Signal/Noise-Quotient wurde berechnet und die Daten mit der Versagenslast, der Reißfestigkeit und der Steifigkeit des Transplantates korreliert. In der frühen Phase des Transplantatremodelings konnte ein Anstieg der Signalintensität bei gleichzeitiger Abnahme der biomechanischen Eigenschaften beobachtet werden. Im weiteren Verlauf nahm die Signalintensität wieder ab und respektive die biomechanischen Kenndaten zu. In der Korrelationsanalyse zeigte sich ein signifikanter negativ linearer Zusammenhang zwischen den Signal/Noise-Quotienten und allen biomechanischen Parametern. Die Korrelationen mit Kontrastmittelunterstützung waren im Allgemeinen grösser. Schlussfolgernd kann gesagt werden, dass das quantitative MR-Signal ein nützliches Hilfsmittel ist, den Prozess des Transplantatremodelings nicht-invasiv zu verfolgen. Die Ergebnisse sind für das Verständnis der beeinflussenden Faktoren des Transplantatremodelings auch für den Menschen ausgesprochen nutzbringend. In Hinblick auf mögliche Unterschiede zwischen dem Tiermodell und dem Menschen stellen die hier präsentierten Daten eine wissenschaftliche Grundlage dar, das Remodeling beim Menschen weiter nicht invasiv zu untersuchen
Einleitung: Aufgrund der hohen Inzidenz der vorderen Kreuzbandverletzungen und der damit einhergehenden funktionellen Einschränkung besteht ein anhaltendes Interesse an der Verbesserung bestehender und Entwicklung neuer, besserer Techniken zur Rekonstruktion dieser Bandstruktur des Kniegelenkes. In dieser Studie wurde der Einfluss des Verankerungsniveaus (anatomisch vs. extrakortikal) und der Verankerungsart (direkt vs. indirekt) auf das mechanische Verhalten von drei exemplarischen, in der Klinik häufig angewandten Rekonstruktionstechniken, untersucht. Material & Methoden: An insgesamt 24 Kniegelenken humaner Spender mittleren Alters (40 Jahre) wurden drei Rekonstruktionstechniken (n=8 pro Gruppe) des VKB durchgeführt. Als Transplantat wurden jeweils humane Hamstringsehnen verwendet: 1.) HADBIO: anatomische und direkte Verankerung mit biodegradierbaren Interferenzschrauben, 2.) HADTIT: semi-anatomische und direkte Verankerung mit Titanschrauben, 3.) HEIButton: extrakortikale, indirekte Verankerung mit Faden-Button Verbindung. Alle rekonstruierten Kniegelenke wurden einer zyklischen, inkremental zunehmenden Belastung bis zum Versagen unterzogen. Es wurden die Parameter Konstruktsteifigkeit, absorbierte Energie, Transplantatauslenkung und Laxizitätszunahme bei Belastungen von 200, 300, 400 N, sowie die maximale Steifigkeit und Versagenskraft bestimmt. Ergebnis: Die anatomische und direkte Transplantatverankerung mit biodegradierbarer Interferenzschraube zeigt die vorteilhaftesten mechanischen Eigenschaften, während die extrakortikale und indirekte Verankerung die niedrigsten mechanischen Eigenschaften aufwies. Die tibiale Verankerungsseite ist bei Interferenzschraubenverankerung der Schwachpunkt, während die Fadenverbindungen bei der extrakortikalen Verankerungstechnik die Schwachstelle darstellten. Auch bei anatomischer und direkter Transplantatfixation findet ein nicht zu vernachlässigender permanenter Verankerungsverlust bei vergleichsweise geringer Versagenskraft statt, der vor allem auf der tibialen Verankerungsseite zu beobachten ist. Diskussion: Eine anatomische und direkte Transplantatverankerung ist von mechanischem Vorteil. Allerdings hängt die Konstruktsteifigkeit auch in erheblichem Maße vom Fixationsobjekt ab. Extrakortikale Fixationstechniken, die eine indirekte Faden-Knoten-Transplantatverbindung erfordern, unterliegen einer erheblichen nicht-reversiblen Lockerung unter zyklischer Belastung und sollten durch direkte Verankerungstechniken ersetzt werden. Aufgrund der permanenten Laxizitätszunahme auch in der anatomischen und direkten Interferenzschraubenverankerung, vor allem der tibialen Seite, sollte über Sicherungsverankerungen, so genannten Hybridfixationen nachgedacht werden, um die mechanischen Vorteile dieser Rekonstruktionsart voll zum Tragen bringen zu können.
Expenditures in musculoskeletal injuries and diseases are projected to continuously increase due to the aging population and the change of lifestyles. The development of effective biomaterials and novel devices for musculoskeletal applications are one of the most important tasks of biomedical research. This chapter will introduce hard and soft tissues in the human musculoskeletal system. The physiochemical and mechanical properties of natural bone and ligaments will be reviewed so as to design novel biomaterials and devices to repair or regenerate these tissues. Biomaterials, including metals, ceramics and polymers, used for the repair and regeneration of bone and ligament tissues will be discussed. Recent research efforts and renewed interests in developing resorbable metallic biomaterials such as magnesium (Mg) alloys for orthopedic and craniofacial applications will be highlighted. Lastly, growing clinical interests in the development of responsive biosensors for orthopedic/craniofacial applications will be discussed.
The second edition of Bioscience and Bioengineering of Titanium Materials is an essential resource for anyone researching titanium in its fundamental aspects and in medical/dental applications. The book organizes and processes the findings from over 2,000 published articles and studies into a coherent and easily accessible volume, deftly weaving together older and newer technologies to give a clear overview. Bridging the gap between medical/dental and engineering/technology areas, the book covers material classification, fabrication and modification, as well as applications and biological reactions to titanium implants. The author, with extensive work in academics and industry, helps medical practitioners and students answer many practical questions, including: What is titanium? What type of titanium materials should I use in this case? How can I fabricate my design using titanium? Are there any alternative materials or methods? In the second edition, macro-, micro-, and nano-texturing of titanium surfaces, tissue engineering-related materials including scaffolds, and functionally graded materials and structures are extensively included and analyzed.
Purpose: We compared the results of arthroscopic Bankart repair using metal and biodegradable anchor fixation. Materials & Methods: We reviewed 26 patients with anterior shoulder instability treated by arthroscopic Bankart repair from October, 2006, to March, 2007, 15 patients with metal anchors and 11 patients with biodegradable anchors. The average age was 27.4 years old (range: 17~55) and mean follow-up was 14 months (range: 12~17 months). Functional outcome was evaluated using the Korean Shoulder Score for Instability (KSSI), Rowe's Bankart Grading scale (RBGS), ASES score, and UCLA scores. Results: In the metal-anchor group, the improvements of mean KSSI, ASES, UCLA score, and RBGS were 20.6, 24.0, 4.0, and 45.5, respectively. In the biodegradable anchor group, improvements of mean KSSI, ASES, UCLA score, and RBGS were 21.0, 23.6, 4.6, and 48.9. The improvements in final outcomes were not significantly different (p>.05). One metal problem and one traumatic redislocation occurred in the metal group. Conclusion: Both techniques produced satisfactory outcomes in the treatment of traumatic anterior instability. The biodegradable anchor group could also avoid problems with metal anchors.
The focus of this study was to fabricate and investigate the mechanical behavior of porous poly(para-phenylene) (PPP) for potential use as a load-bearing orthopedic biomaterial. PPPs are known to have exceptional mechanical properties due to their aromatic backbone; however, the manufacturing and properties of PPP porous structures have not been previously investigated. Tailored porous structures with either small (150-250µm) or large (420-500µm) pore sizes were manufactured using a powder-sintering/salt-leaching technique. Porosities were systematically varied using 50 to 90vol%. Micro-computed tomography (µCT) and scanning electron microscopy (SEM) were used to verify an open-cell structure and investigate pore morphology of the scaffolds. Uniaxial mechanical behavior of solid and porous PPP samples was characterized through tensile and compressive testing. Both modulus and strength decreased with increasing porosity and matched well with foam theory. Porous scaffolds showed a significant decrease in strain-to-failure (<4%) under tensile loading and experienced linear elasticity, plastic deformation, and densification under compressive loading. Over the size ranges tested, pore size did not significantly influence the mechanical behavior of the scaffolds on a consistent basis. These results are discussed in regards to use of porous PPP for orthopedic applications and a prototype porous interbody fusion cage is presented.
We report the case of a patient with a painful subcutaneous nodule, measuring 13 mm × 17 mm, at the pretibial graft aperture site, which presented two years after a successful anterior cruciate ligament reconstruction with an autologous hamstring graft. A bioabsorbable poly-L-lactide interference screw was used for graft fixation at the tibial aperture. The patient underwent surgical excision of the lesion and curettage at the tunnel aperture. Grossly, extruded fragments of the screw and a thick pseudocapsule of surrounding tissue were excised. There was no communication between the tunnel aperture and the knee joint. The graft was also intact. Histological analysis revealed fragments of the bioabsorbable material in association with fibrous and granulomatous chronic inflammatory cells. This was consistent with a foreign body reaction. The patient subsequently recovered and resumed preinjury level of activity. To the best of our knowledge, this is the first report describing a nodular granulomatous type reaction to foreign bioabsorbable poly-L-lactide screw material subsequent to an anterior cruciate reconstruction surgery.
The possibility of synthesizing bulk catalysts by means of mechanochemical activation (MCA), the basis for wasteless technologies for the production of catalysts with particle sizes less than 10 μm, is demonstrated. The precursors of Ni-Mo catalysts for hydrogenation processes are synthesized by MCA. The chemical and phase composition and specific surface area of mechanically activated composites with Ni: Mo atomic ratio = 1.0 and 1.4 are studied by DTA, XRD, TPR, and low-temperature adsorption. It is established that during the simultaneous MCA of Ni- and Mo-containing salts, solid-state reactions yield complex X-ray amorphous compounds that after calcination at 520°C form nickel molybdates composed almost entirely of highly active modified β-NiMoO4, the sulfidation of which produces MoS2 and Ni3S2 phases. Comparative testing of sulfide catalysts (i.e., bulk (Ni: Mo = 1.4) and industrial supported) in model reactions of the conversion of 1-methylnaphthalene and dibenzothiophene was performed at a temperature of 350°C, a pressure of 3.5 MPa, a feedstock hourly space velocity of 2 h−1, and a hydrogen/feedstock ratio of 600. Based on the composition of the 1-methylnaphthalene and dibenzothiophene conversion products while using industrial and bulk catalysts, it is concluded that the bulk catalyst exhibits higher hydrogenating activity.
Biodegradable implants are increasingly used in the field of operative sports medicine. Today, a tremendous variety of implants such as interference screws, staples, sutures, tacks, suture anchors, and devices for meniscal repair are available. These implants consist of different biodegradable polymers that have substantially different raw material characteristics such as in vivo degradation, host-tissue response, and osseous replacement. Because these devices have become the standard implant for several operative procedures, it is essential to understand their biological base. The purpose of this report is to provide a comprehensive insight into biodegradable implant biology for a better understanding of the advantages and risks associated with using these implants in the field of operative sports medicine. In particular, in vivo degradation, biocompatibility, and the osseous replacement of the implants are discussed. A standardized classification system to document and treat possible adverse tissue reactions is given, with special regard to extra-articular and intra-articular soft-tissue response and to osteolytic lesions. Key Words: Biodegradable implants—Clinical application—Sports medicine—Biocompatibility—In vivo degradation.
Purpose: The purpose of this prospective study was to review, using expanded clinical-assessment tools, the long-term results of the local effects of a bioabsorbable interference screw (copolymer 85/15 D,L lactide/glycolide) in anterior cruciate ligament (ACL) reconstruction. Type of Study: This prospective study was initiated in May 1993. The inclusion criteria for patient selection included rupture of the ACL in athletic patients without involvement of the collateral ligaments, arthroscopic ACL reconstruction using middle third of the ligamentum patella, and magnetic resonance imaging (MRI) and plain radiographic examinations of the knee joint during follow-up. Materials: Between May 1993 and October 1994, 32 patients were enlisted in the study; 48 patients did not fit the inclusion criteria. There were 25 men 7 women. The average age was 29.1 years (range, 19 to 50 years). There were 21 right knees and 11 left knees. The follow-up examinations were performed by an independent examiner. There were 28 patients available for follow-up at a medium of 5.2 years (range, 4.1 to 6.4 years). The evaluation included various testing systems (i.e., OAK, IKDC, Lysholm) as well as MRI and plain radiographic studies to investigate the longevity of the implant and potential adverse effects of this new bioabsorbable material. Results: The clinical results were good. The OAK score (Orthopädische Arbeitsgruppe Knie) showed 93% excellent and good results, and 7% fair results. The IKDC and Lysholm scores were 92% and 96% good and excellent results, respectively. MRI showed bone remodeling and new bone formations at the site of the implant in the femoral as well as in the tibial bone tunnel at follow-up. No cystic or osteolytic changes where seen on MRI or plain radiographs. Conclusions: This study showed the correlation between histology and MRI: there was minimal surgical-site edema, minimal reaction to this material, and complete replacement by new bone formation of the previous site of this implant. At 5 years, this bioabsorbable interference screw appeared clinically safe and effective for fixation of bone blocks during ACL reconstruction and MRI showed complete absorption and replacement with new bone.
The goal of this study was to fabricate and mechanically characterize a high-strength porous polymer scaffold for potential use as an orthopedic device. Poly(para-phenylene) (PPP) is an excellent candidate due to its exceptional strength and stiffness and relative inertness, but has never been explicitly investigated for use as a biomedical device. PPP has strength values 3 to 10 times higher and an elastic modulus nearly an order of magnitude higher than traditional polymers such as poly(methyl methacrylate) (PMMA), polycaprolactone (PCL), ultra-high molecular weight polyethylene (UHMWPE), and polyurethane (PU) and is significantly stronger and stiffer than polyetheretherketone (PEEK). By utilizing PPP we can overcome the mechanical limitations of traditional porous polymeric scaffolds since the outstanding stiffness of PPP allows for a highly porous structure appropriate for osteointegration that can match the stiffness of bone (100-250 MPa), while maintaining suitable mechanical properties for soft-tissue fixation. Porous samples were manufactured by powder sintering followed by particle leaching. The pore volume fraction was systematically varied from 5080 vol% for a pore sizes from150-500 µm, as indicated by previous studies for optimal osteointegration. The tensile modulus of the porous samples was compared to the rule of mixtures, and closely matches foam theory up to 70 vol%. The experimental modulus for 70 vol% porous samples matches the stiffness of bone and contains pore sizes optimal for osteointegration.
Injury of the anterior cruciate ligament (ACL) can lead to knee instability associated with damage to other knee structures and the increased risk of osteoarthritis. Thus, surgeons have turned to the use of autografts as ACL replacements to restore knee function and expedite the patient's return to sports, as well as avoid the long-term complications associated with chronic knee instability. However, retrospective and prospective clinical studies conducted at short- and long-term follow-up have revealed that 15% to 25% of patients have less than satisfactory results. Whereas there can be numerous factors that contribute to this outcome, biomechanical studies have helped to gain a new perspective of the complex function of the ACL that these replacement grafts failed to restore. In this article, the readers are provided with a brief review of the experimental methodology used to evaluate the biomechanical properties and function of the ACL and its replacements. Specifically, the use of tensile tests to measure the structural properties of the graft tissue and graft-fixations constructs is described. Tensile testing has allowed for comparison of different graft materials, fixation methods, as well as provided insight into changes in mechanical behavior of the graft construct throughout graft remodeling and incorporation. A unique testing system utilizing a six degrees of freedom robotic manipulator and universal force-moment sensor (UFS) has been developed such that the knee measurements can be made in a non-contact fashion while allowing a series of experiments to be performed on the same knee. Using this robotic/UFS testing system, it has been possible to quantitatively assess the crucial roles of the ACL and their respective bundles in maintaining normal knee stability, especially under rotatory loading. The effects of several variables for reconstruction (graft selection, femoral tunnel positioning, anatomic “double bundle” reconstruction, and initial graft tension) on knee kinematics are then reviewed. To close, directions for future research that could potentially further improve the outcome of reconstructions are provided.
Artifact reduction is fundamental to the daily clinical application of magnetic resonance (MR) imaging. Imaging of the postoperative patient may be difficult because of surgically introduced materials that result in artifacts. The authors tested some commonly used types of surgical suture for MR susceptibility artifact with various imaging sequences. Ten different suture types were studied. Suture was immersed in vegetable oil in separate plastic test tubes. The sutures were also studied embedded in meat. All samples were studied with T1-weighted and T2-weighted spin-echo, STIR (short-inversion-time inversion-recovery), and two-dimensional and three-dimensional gradient-echo sequences. Silk suture produced the most artifact.
The purpose of our study was to asacsa Futomagneh. hating. ad artifactr, associated with vabcular access ports exposed to a 1.5-T MR system. Tweaty-cight different vabcular access port. were evaluated in thb investlgation. Fmmagnetism was determined by using two previouely de techniques. Temperature changes were measured immediately before and after performing a pulse sequence on the vascular access port6 for 80 min at a speciflc absorption rate of 3.1 W/kg. Artifacts were assessed h aesoclation with the use of a fht CRASS pulse sequence. None of the vascular access ports displayed ferromnlpletim. Heating was 0.2°or less. The prerence of adhcts varied. depending on the component materials. The Lack of fcrromagnetiam and negligible heating indicates that MR imaging performed at 1.6 T or lees may be conducted dely in patients with any of the vascular access port. tested. None of the associated artifacts produced by the vascdar access port. is comddercd to paw a rubsttantial problem for MR imaging.
Although long-term results in cruciate ligament surgery are continuously improving, we are still confronted with a certain rate of surgical failures and an increasing number of revision procedures. Despite a tremendous effort towards experimental and clinical research in the field of anterior and posterior cruciate ligament surgery over the past decades, there is still a strong need to further improve results. Therefore, the goal of the present paper is to introduce and discuss new developments in the rapidly changing field of cruciate ligament surgery, in order to give the clinician a base for discussion to include these developments in their daily clinical work. The present paper focuses on current developments and future perspectives such as biodegradable implants, new aspects in graft selection, double-bundle posterior cruciate ligament reconstruction, possibilities of biological intervention with growth factors, and the new technology of robotics and navigation.
Anterior cruciate ligament (ACL) reconstruction using autologous hamstring tendons are being performed more frequently and satisfactory results have been reported. Advantages such as low donor site morbidity and ease of harvest as well as disadvantages like low initial construct stiffness have been described. Recently, it has been demonstrated that graft fixation close to the original ACL insertion sites increases anterior knee stability and graft isometry. Hamstring tendon fixation techniques using interference screws offer this possibility. To reduce the risk of graft laceration, a round threaded titanium interference screw (RCI) was developed. To improve initial fixation strength, fixation techniques for hamstring tendons with separate or attached tibial bone plugs were introduced. However, data on fixation strength do not yet exist. With respect to the proposed advantages of biodegradable implants, like undistorted magnetic resonance imaging, uncompromised revision surgery and a decreased potential of graft laceration during screw insertion, we performed pullout tests of round threaded biodegradable and round threaded titanium interference screw fixation of semitendinosus (ST) grafts with and without distally attached tibial bone plugs. Data were compared with bone-tendon-bone (BTB) graft fixation using biodegradable and conventional titanium interference screws.
We used 56 proximal calf tibiae to compare maximum pullout force, screw insertion torque, and stiffness of fixation for biodegradable direct ST tendon and bone plug fixation (group I: without bone plug, group II: with bone plug) versus titanium interference screw fixation (group III: without bone plug, group IV: with bone plug). A round threaded biodegradable poly-(D, L-lactide) (Sysorb) and a round threaded titanium interference screw (RCI) were used. As a control calf bone-tendon-bone (BTB) grafts fixed with either poly-(D, L-lactide) (group V) or conventional titanium (group VI) interference screws were used. ST tendons were harvested either with or without their distally attached tibial bone plugs from human cadavers and were folded to a three-stranded graft. Specimen were loaded in a material testing machine with the applied load parallel to the long axis of the bone tunnel.
Maximum pullout force of ST bone plug (group III: 717 N ± 90, group IV: 602 N ± 117) fixation was significantly higher than that of direct tendon (group I: 507 N ± 93, group III: 419 N ± 77) fixation. Maximum pullout force of biodegradable screw ST fixation was higher than that of titanium screw fixation in both settings. There was no significant difference in pullout force between biodegradable (713 N ± 210) and titanium (822 N ± 130) BTB graft fixation or between ST fixation with bone plug and biodegradable screw with BTB fixation.
Pullout force of hamstring tendon interference screw fixation can be improved by using a biodegradable implant. In addition, initial pullout force can be greatly improved by harvesting the hamstring tendon graft with its distally attached tibial bone plug. This may be important, especially in improving tibial graft fixation. This study encourages further research in tendon-bone healing with direct interference screw fixation to confirm the potential of this advanced method.
Trotz verbesserter Operationsmethoden bei einer vorderen Kreuzbandplastik kommt es immer noch zum Versagen der Primroperation, wodurch Revisionseingriffe notwendig werden. Eine exakte properative Analyse, warum es zum Versagen der Primroperation kam, sowie die genaue Planung des Revisionseingriffs sind wesentliche Voraussetzungen fr einen Behandlungserfolg.Vor allem die Beurteilung von Knochendefekten (durch Kanalerweiterung, resorbierbare Materialien etc.) ist wesentlich. Eine erweiterte bildgebende Diagnostik ist deshalb unbedingt angezeigt, sollte die alleinige Rntgendiagnostik Zweifel offen lassen.Die MRT bietet eine ideale Ergnzung bzgl. intraartikulrer Pathologie, whrend die CT bzgl. der Darstellung der Tunnelmorphologie (Platzierung und Ausdehnung) Vorteile bietet. Im Einzelfall mssen Vor- und Nachteile deshalb abgewogen werden. Gelegentlich kann eine Operationsplanung die Verwendung aller diagnostischen Mglichkeiten notwendig machen.Failures of ACL reconstruction still occur despite improved arthroscopic methods. The reasons for failures must be evaluated carefully prior to revision surgery. Therefore imaging of tunnel placement and bone defects is essential for successful clinical outcome. Plain radiographs may be sufficient in some revision cases, but MRI and CT scans are important if tunnel morphology or bone loss cannot be adequately recognized. MRI has an advantage for imaging of intrarticular pathology, whereas CT is preferable to evaluate bony architecture. In selected cases preoperative planning of revision ACL surgery has to include all three diagnostic modalities.
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.
The aim of the study was to assess the hard tissue response of a composite hydroxyapatite/poly L-lactic acid (HA/PLLA) interference screw for anterior cruciate ligament (ACL) reconstruction compared to a standard PLLA screw. Twelve skeletally mature rams underwent unilateral ACL reconstruction using an autologous bone-patellar tendon graft. Each animal received either two test HA/PLLA interference screws or two control PLLA interference screws. Animals were sacrificed at 6 and 12 months post-implantation and the operated knees excised. Undecalcified sections of the screw and surrounding tissues were cut from resin embedded samples and stained; sections were approximately parallel to the longitudinal axis of the screws. A quantitative assessment of bone formation between each screw type (PLLA vs. HA/PLLA) and adjacent tissue in both the tibia and femur was undertaken using automated image analysis (KS400, Zeiss, UK). The inflammatory response of each screw type was assessed by histological evaluation. New bone formation along the perimeter of the screw threads was statistically significantly higher with the HA/PLLA than the PLLA alone. The inflammatory response as assessed semi-quantitatively by histologically determining the number of inflammatory cells present in the tissue adjacent to the implant, was higher for PLLA than HA/PLLA. Significantly increased new bone formation and decreased inflammatory cells were observed in vivo with the composite screw in comparison with the standard polymer. A novel HA/PLLA composite biomaterial in the form of an interference screw demonstrated an improved hard-tissue response compared to PLLA in a large animal ACL reconstruction. This study determined the differences in the tissue response between PLLA and a composite material of HA/PLLA. The improved tissue related outcomes observed in vivo, may be of benefit clinically in ACL reconstruction.
Magnetic resonance imaging (MRI) examinations were reviewed in 10 postsurgical patients with metallic implants in the abdomen or pelvis. MRI scans in these patients were free of the streak artifacts commonly encountered in computed tomography. This represents a significant advantage in diagnostic imaging in postsurgical patients, and it suggests that MRI may be a valuable technique in the postoperative assessment of patients with extensive abdominal surgical clips or metallic prostheses.
The following are policies, guidelines, and recommendations from the Safety Committee of the Society for Magnetic Resonance Imaging (SMRI) concerning various issues related to magnetic resonance (MR) imaging safety and patient management. These policies, guidelines, and recommendations were developed to provide standardized and consistent information for use by health practitioners involved in clinical MR imaging.
MR imaging is contraindicated for patients with certain ferromagnetic implants because of potential risks related to movement or dislodgement. This is especially true for metallic implants located in sensitive areas of the body, such as those placed in and around the ear. Therefore, the ferromagnetic qualities of 35 different metallic otologic implants were assessed by placing them individually on a millimeter scale in a plastic petri dish that was slowly moved into the center of a 1.5-T MR imaging system. None of the metallic otologic implants moved during this procedure. The results demonstrate that each of these implants are made from nonferromagnetic materials and do not pose a risk to patients undergoing high-field-strength MR imaging. These data effectively expand the list of metallic implants that appear to be safe for MR imaging.
Fifty magnetic resonance (MR) imaging examinations were performed in 37 patients after arthroscopic anterior cruciate ligament (ACL) reconstruction with patellar bone-tendon-tibial bone autografts. T1-weighted sagittal and axial images were obtained. In 34 patients with clinically stable ACL autografts, 43 of 47 MR examinations demonstrated a well-defined, intact ACL autograft. All three patients with ACL laxity failed to demonstrate a well-defined autograft, for an overall correlation between MR imaging and clinical examination results of 92%. Of the 12 patients who underwent second-look arthroscopy, 100% correlation was present between MR imaging and arthroscopic results. As in the nonreconstructed knee, buckling of the posterior cruciate ligament was suggestive of ACL laxity. MR imaging also documented optimum placement of bone tunnels in the femur and tibia. MR imaging has proved to be an excellent noninvasive imaging modality for evaluating ACL reconstruction, while also providing ancillary information about the postoperative knee.
A prospective, observational study was performed to document the serial changes in the magnetic resonance signal of devascularized, hamstring ACL autografts dur ing the 1 st year of implantation.
Twenty-one ACL deficient knees (14 chronic, 7 acute) were reconstructed. Instability developed in five knees within the first 6 months of graft implantation (24%). Magnetic resonance examinations were performed at 1, 6, 12, 24, 36, and >48 weeks postoperatively (rep etition time 1500, echo delay time = 50). A total of 104 scans were reviewed (average, five per knee). The ACL graft was divided into four unequal size zones for analysis. The proximal, middle, and distal thirds of the intraarticular portion of the graft and the portion of the graft within the tibial tunnel were independently an alyzed. The magnetic resonance signal in each portion of the graft was graded on a scale with (I) being a normal signal, (II) >50% of the total volume of the graft having a normal signal, (III) <50% of the graft having a normal signal, and (IV) 100% of the graft having an increased signal.
The increased magnetic resonance signal of the ACL graft was observed to be regionalized and confined to the distal two-thirds of the intraarticular portion of the graft. The portion of the graft exiting the femoral tunnel and within the tibial tunnel retained a normal magnetic resonance signal. The increases in magnetic resonance graft signal were time-dependent, became well estab lished by 3 months, and remained unchanged at 1 year. The clinical outcome could not be predicted based on the magnetic resonance signal of the graft.
Almost all reported measurements of the attractive force exerted on metallic implants in magnetic fields of magnetic resonance imagers have been obtained at the portal. This study was done to determine whether the maximum force on an implant is at the portal. Horizontal attractive forces on needles were measured along the axis of the bore at various distances from the portal of a 0.3-T vertical-field magnet and 0.5- and 1.5-T solenoid magnets. Upward vertical forces along the top of the bore were also measured. The horizontal forces 40 cm in from the portals of the 0.5- and 1.5-T magnets were 70%-80% greater than the horizontal forces at the portal. The upward vertical force at the top of the 0.3-T magnet bore, 63 cm in from the portal, was 20 times the horizontal force at the portal and was twice the maximum force measured in the 0.5-T magnet. The maximum force was not at the portal.
Certain ferromagnetic metallic implants, materials, and devices are regarded as contraindications for magnetic resonance imaging, primarily because of the risks associated with their movement or dislodgment. More than 40 publications have reported the ferromagnetic qualities of 261 different metallic objects (aneurysm and hemostatic clips, 32; carotid artery vascular clamps, five; dental devices or materials, 16; heart valve prostheses, 29; intravascular coils, filters, and stents, 14; ocular implants, 12; orthopedic implants, materials, and devices, 15; otologic implants, 56; pellets and bullets, 23; penile implants, nine; vascular access ports, 33; and miscellaneous, 17) on the basis of measurements of deflection forces or attraction during exposure to static magnetic fields at strengths of 0.147-4.7 T. The results of these studies are listed with respect to the specific object tested, the material used to construct the object (if known), whether or not the object was deflected or moved during exposure to the static magnetic field, and the highest static magnetic field strength used for testing the object.
In Part 1 of this study, the forces and torques exerted on metallic spine implants by a 0.3-T magnetic field were evaluated using a cantilever system sensitive to forces as low as 250 mg and torques as low as 4 g/cm. Results indicated that the 0.3-T magnification field did not cause forces or torques that could be measured within this range. It is concluded that patients with spine implants may safely undergo magnetic resonance scanning. In Part 2, the magnetic resonance scans from 33 patients (61 studies) then were reviewed to determine which, if any, parameters could be adjusted to minimize artifact. Magnetic power, slice thickness, plane of scan, and pulse sequence were considered. Plane of scan was found to be the most significant parameter in achieving useful studies, with the sagittal plane being the preferred orientation. Scans of patients who had posterior wiring were more likely to be useful, while scans of patients with spinal rods usually showed a large amount of artifact.
To find out whether MR imaging is contraindicated in patients with metallic implants or can be a routine diagnostic procedure, MR investigations in 18 patients with 22 Charnley-Müller total hip prostheses were performed on a 0.5 T Gyroscan S 5, Philips. No adverse reactions during or post MR investigation were encountered. The imaging of the soft tissue was superior to CT and showed less distortion. The diagnosis of loosening, by detection of demarcation lines at the interfaces was at its best in the distal part of the femoral stem prosthesis and was poor in the acetabular component and in the upper part of the stem prosthesis due to artifacts.
Ferromagnetic metallic implants and materials are regarded as contraindications for MR imaging because of the potential risks associated with their movement or displacement. To date, 14 published articles have evaluated the ferromagnetic qualities of 127 different metallic implants and other materials, including aneurysm and hemostatic clips (32); dental implants and materials (five); intravascular coils, filters, and stents (13); ear implants (14); prosthetic heart valves (29); orthopedic implants and materials (eight); penile implants (nine); and miscellaneous metallic implants and materials (17). All of these materials were evaluated by measuring the deflection forces induced by static magnetic fields at strengths ranging from 0.147 to 4.7 T. This article is a compilation of the results of these studies; it lists all 127 of the materials tested, indicates whether they were found to be deflected by the static magnetic fields, and gives the highest static magnetic field strength at which they were evaluated. Of the metallic implants tested, 66 were nonferromagnetic, and 29 exhibited only minimal deflection relative to their in vivo applications (i.e., the deflection forces were thought to be insufficient to move or dislodge the implant or material in situ). The authors of these studies concluded that patients with these particular metallic implants or materials (95/127, 75%) can be examined safely by MR imaging with scanners having static magnetic field strengths up to and including those used for the specific evaluations. Patients with other ferromagnetic materials or implants may also undergo MR imaging safely; however, both careful consideration of the factors that influence the deflection of metallic implants and prudent clinical judgment are required before patients who have these objects are examined via MR imaging.
Ferromagnetic biomedical implants are considered a contraindication for MR imaging primarily because of the potential hazards associated with their movement or dislodgment. Many metallic biomedical implants are composed of nonferromagnetic materials and do not present a danger to patients during MR imaging. Therefore, to evaluate the ferromagnetic qualities of 36 different metallic biomedical implants (four aneurysm clips, six hemostatic clips, four dental implants, seven prosthetic heart valves, eight orthopedic prostheses, one artificial urinary sphincter, three contraceptive diaphragms, and three cerebral ventricular shunt tube connectors) not previously evaluated with a high-field-strength MR system, we measured deflection forces at the portal of the magnet of a 1.5-T MR system. Fourteen of the 36 metallic biomedical implants were determined to be ferromagnetic as indicated by their deflection in the static magnetic field. However, only the four aneurysm clips (Drake, Mayfield, McFadden, and Sundt-Kees) had sufficient ferromagnetism to warrant exclusion of patients with these implants from imaging with a 1.5-T MR system because of the possibility of movement or displacement. The calculated deflection forces for these aneurysm clips were comparable with previously reported values of certain aneurysm clips that have been designated to present a risk for patients undergoing MR imaging. Patients with 32 of 36 metallic biomedical implants tested can be safely imaged with high-field-strength MR systems.
Experiments were conducted in which various intravascular filters, stents, and coils were imaged using magnetic resonance (MR) spin-echo technique at 0.35 T. These devices were also evaluated for ferromagnetism (at 0.35, 1.5, and 4.7 T), magnetic torque (at 0.35 and 1.5 T), and magnetically induced migration within a plastic tube (at 0.35 and 1.5 T for the Greenfield filter [GF]). The stainless-steel GF was evaluated in vitro for its propensity to perforate canine inferior venae cavae (IVC). Magnetic force and torque at 1.5 T did not dislodge the GF or result in perforation of canine IVC by the GF. Beta-3 titanium alloy (used in a new percutaneous version of the GF) is apparently one of the best-suited metals for use with MR imaging because of its lack of ferromagnetism (up to 4.7 T) and absence of MR imaging artifacts (at 0.35 T). Devices composed of Elgiloy (Mobin-Uddin filter), nitinol, and MP32-N (Amplatz filter) alloys all created mild artifacts. Devices fashioned from 304 and 316L (GF and Palmaz stent) stainless-steel alloys created severe "black-hole" artifacts, with the 304 alloy devices also showing marked image distortion. Generally, the greater the ferromagnetism of a device, the greater its magnetic susceptibility artifact.
Many types of artifacts may occur in magnetic resonance imaging. These artifacts may be related to extrinsic factors such as patient motion or metallic artifacts; they may be due specifically to the MR system such as power gradient drop off and chemical shift artifacts; they may occur as a consequence of general image processing techniques, as in the case of truncation artifacts and aliasing. Change in patient position, pulse sequence, or other imaging variables may improve some artifacts. Although reduction of some artifacts may require a service engineer, the radiologist has the responsibility to recognize MR imaging problems. The radiologist's knowledge of MR imaging artifacts is important to the continued maintenance of high image quality and is essential if one is to avoid confusing artifactual appearances with pathology.
To evaluate the safety of magnetic resonance (MR) imaging of prosthetic heart valves, nine different synthetic and tissue valves were studied ex vivo. Deflection was measured in 0.35-tesla (T) and 1.5-T superconducting magnets and at the edge of the bore of a 2.35-T electromagnet in field gradients of 5, 1.1, and 6.3 mT/cm, respectively. No valve deflected in the 0.35-T magnet; six synthetic valves deflected 0.25 degrees-3 degrees in the 1.5-T magnet; all valves deflected 1 degree-27 degrees at the edge of the 2.35-T magnet. Each valve was then submerged in a vial of water and the temperature was measured immediately before and after each of two spin-echo imaging sequences in the two superconducting magnets. No significant temperature rise followed exposure in either magnet. Image distortion varied from negligible to severe in both imagers; magnitude of distortion paralleled magnitude of deflection. These data suggest that patients with present-day prosthetic heart valves can be safely imaged in present-day MR imagers and that prosthesis-induced artifacts will not interfere with interpretation in most instances.
Forces and torques, due to a 0.3 Tesla magnetic field were evaluated on ten hip prostheses and ten hemostat clips. Measurements were performed with an instrument utilizing the movement of a laser beam caused by the deflection of a cantilever. The results indicate effects, if any, to be smaller than the instrument's sensitivity which, at its highest, was 7 mg of force and 125 mg.cm of torque.
A total of 305 magnetic resonance (MR) examinations were performed in 236 patients with metallic implants. Most examinations were performed at 0.3 T. The metallic implants included central nervous system shunting devices, tantalum mesh, surgical wire, skin staples, surgical clips, metallic orthopedic devices, and a few miscellaneous metallic objects. Patients with cardiac pacemakers, electrical implants, prosthetic cardiac valves, and aneurysm clips were excluded from MR examinations. The images were reviewed for evidence of metallic artifact. The conspicuity of artifact was related to the composition, mass, orientation, and position of the metallic object in the body. In most instances, the metallic artifact did not interfere with the interpretation of the image. The patients' records were also reviewed for adverse effects noted by each patient during the MR examination. Only two patients reported discomfort that could possibly have been related to their metallic implants, but in both cases it seemed unlikely that the symptoms were actually related to the imaging process. There were no apparent short-term adverse effects demonstrated in these patients.
The risks to patients with metal surgical implants who are undergoing nuclear magnetic resonance (NMR) imaging and the artifacts caused by such implants were studied. Twenty-one aneurysm and other hemostatic clips and a variety of other materials (e.g., dental amalgam, 14 karat gold) were used. Longitudinal forces and torques were found to be exerted upon 16 of the 21 clips. With five aneurysm clips, forces and torques sufficient to produce risk of hemorrhage from dislocation of the clip from the vessel or aneurysm, or cerebral injury by clip displacement without dislodgement were identified. The induced ferromagnetism was shown to be related to the composition of the alloys from which the clips were manufactured. Clips with 10-14% nickel are evidently without sufficient induced ferromagnetism to cause hazard. The extent of NMR imaging artifacts was greater for materials with measurable ferromagnetic properties, but metals without measurable ferromagnetism in our tests also resulted in significant artifacts. Dental amalgam and 14 karat gold produced no imaging artifacts, but stainless steels in dentures and orthodontic braces produced extensive artifacts in the facial region.
- New
- Pusey
High‐field strength MR imaging and metallic otologic implants
- Shellock FG
High‐field strength MR imaging and metallic bioimplants: an in vitro evaluation of deflection forces and temperature changes induced in large prostheses (abstr)
- Shellock FG