Biomechanical Comparison Between Double-Row Repair and Soft Tissue Tenodesis for Treatment of Proximal Rectus Femoris Avulsions.

Background: Some patients with proximal rectus femoris (PRF) avulsions require surgical treatment after failed nonoperative treatment. There is no consensus on the superiority of suture anchor repair with the suture-bridge repair (SBR) technique versus tenodesis repair (TR) for PRF avulsions. Purpose: To compare the failure load and elongation at failure between SBR and TR and to compare the stiffness of these 2 repair techniques versus the native state. Study Design: Controlled laboratory study. Methods: Seven pairs of human cadaveric hemipelvises were dissected to the PRF and sartorius origins. Each specimen underwent preconditioning followed by a distraction test to determine the stiffness of the native specimen. One specimen of each pair received one of the repair methods (SBR or TR), while the other specimen in the pair received the other repair technique. After repair, each specimen underwent preconditioning followed by a pull to failure. The failure load, elongation at failure, stiffness, mode of failure, and stiffness as a percentage of the native state were determined for each repair. Results: The SBR group exhibited a stronger failure load (223 ± 51 N vs 153 ± 32 N for the TR group; P = .0116) and significantly higher stiffness as a percentage from the native state (70.4% ± 19% vs 33.8% ± 15.5% for the TR group; P = .0085). While the stiffness of the repair state in the SBR group (41.5 ± 9.4 N/mm) was not significantly different from that of the native state (66.2 ± 36 N/mm), the stiffness of the repair state in the TR group (20.3 ± 7.5 N/mm) was significantly lower compared with that of the native state (65.4 ± 22.1 N/mm; P < .001) and repair state in the SBR group (41.5 ± 9.4 N/mm; P = .02). The SBR group primarily failed at the repair site (71%), and the TR group primarily failed at the suture-sartorius interface (43%) and at the muscle (29%). Conclusion: SBR and TR specimens were significantly weaker than the native tendon. The stiffness of the SBR was equivalent to that of the native tendon, while TR was significantly less stiff than the native tendon. The SBR was superior to TR in terms of failure load, stiffness, and percentage stiffness from the native state. Clinical Relevance: SBR may be a better surgical option than TR to optimize failure load and stiffness for PRF avulsions.

Biomechanical Comparison of Proximal Hamstring Reconstruction Using Distal Hamstring Graft Versus Fascia Lata Graft for Treatment of Chronic Hamstring Injury.

BACKGROUND: Surgical reconstruction using autografts is often required in treating chronic proximal hamstring injuries where the hamstring has retracted >5 cm. There is a paucity of evidence that evaluates reconstructive procedures using the 2 most popular autografts, distal hamstring and fascia lata. PURPOSE: To (1) compare failure load and elongation at failure between the proximal hamstring tendon reconstruction with distal hamstring and fascia lata grafts and (2) compare the stiffness between these reconstructions and the native state. STUDY DESIGN: Controlled laboratory study. METHODS: Seven pairs of human cadaveric hemipelvises (mean age, 60.4 ± 5.0 years; 6 male, 1 female) with no evidence of previous injury or abnormality were dissected to the proximal hamstring origin. Through use of a dynamic tensile testing system, each specimen underwent preconditioning followed by a distraction test to determine the native specimen stiffness. Each pair of specimens was assigned to undergo proximal hamstring reconstruction with distal hamstring and reconstruction with fascia lata. Each specimen then underwent preconditioning followed by pull to failure. The failure load, elongation at failure, mode of failure, and stiffness were determined for each repair. RESULTS: The distal hamstring group exhibited a greater failure load (mean, 334 ± 108 N; P = .031) and higher stiffness (mean, 47.6 ± 16.0 N/mm; P = .009) compared with the fascia lata group (mean, 179 ± 78 N and 23.0 ± 11.2 N/mm, respectively). Although the stiffness of the repair state in the distal hamstring group (mean, 61.4 ± 13.4 N/mm) was not significantly different from that of the native state (mean, 47.6 ± 16.0 N/mm), the stiffness of the repair state in the fascia lata group (mean, 23.0 ± 11.2 N/mm) was significantly lower than that of the native state (mean, 60.1 ± 17.7 N/mm) (P < .0001). The elongation at failure of the distal hamstring graft group (mean, 33.0 ± 6.6 mm) was not significantly different from that of the fascia lata graft group (mean, 29.2 ± 14.9 mm) (P = .58). The most common modes of failure for the distal hamstring group (29% each) were at the repair site, at the graft-muscle interface, and at the muscle, while the most common modes of failure for the fascia lata graft were at the tendon-graft interface. CONCLUSION: The distal hamstring group achieved higher failure load and stiffness than the fascia lata group, and stiffness of the distal hamstring group was not significantly different from that of the native tendon. Elongation at failure was not different between repair techniques. Although distal hamstring graft failure predominantly occurred in 3 distinct locations, failure of the fascia lata repair occurred predominantly at the tendon-graft interface. These cadaveric results suggest that it may be more clinically appropriate to use distal hamstring versus fascia lata for proximal hamstring reconstruction. CLINICAL RELEVANCE: Our time-zero study suggests that the proximal hamstring reconstruction with distal hamstring could be the preferred surgical treatment for chronic hamstring injury over reconstruction with fascia lata. The failure load of reconstruction with distal hamstring was inferior to that of primary suture anchor, suggesting that rehabilitation after reconstruction should not be more aggressive than the standard postoperative rehabilitation protocol for acute repair.

Utility of Talus Osteochondral Allograft Augmentation for Varying Hill-Sachs Lesion Sizes: A Cadaveric Study.

Background: Humeral head reconstruction with fresh osteochondral allografts (OCA) serves as a potential treatment option for anatomic reconstruction. More specifically, talus OCA is a promising graft source because of its high congruency with a dense cartilaginous surface. Purpose: To analyze the surface geometry of the talus OCA plug augmentation for the management of shoulder instability with varying sizes of Hill-Sachs lesions (HSLs). Study Design: Controlled laboratory study. Methods: Seven fresh-frozen cadaveric shoulders were tested in this study. The humeral heads were analyzed using actual patients' computed tomography scans. Surface laser scan analysis was performed on 7 testing states: (1) native state; (2) small HSL; (3) talus OCA augmentation for small HSL; (4) medium HSL; (5) talus OCA augmentation for medium HSL; (6) large HSL; and (7) talus OCA augmentation for large HSL. OCA plugs were harvested from the talus allograft and placed in the most medial and superior aspect of each HSL lesion. Surface congruency was calculated as the mean absolute error and the root mean squared error in the distance. A 1-way repeated-measures analysis of variance was performed to evaluate the effects of the difference in the HSL size and associated talus OCA plugs on surface congruency and the HSL surface area. Results: The surface area analysis of the humeral head with the large (1469 ± 75 mm2), medium (1391 ± 81 mm2), and small (1230 ± 54 mm2) HSLs exhibited significantly higher surface areas than the native state (1007 ± 88 mm2; P < .001 for all sizes). The native state exhibited significantly lower surface areas as compared with after talus OCA augmentation for large HSLs (1235 ± 63 mm2; P < .001) but not for small or medium HSLs. Talus OCA augmentation yielded improved surface areas and congruency after treatment in small, medium, and large HSLs (P < .001). Conclusion: Talus OCA plug augmentation restored surface area and congruency across all tested HSLs, and the surface area was best improved with the most common HSLs-small and medium. Clinical Relevance: Talus OCA plugs may provide a viable option for restoring congruity of the shoulder in patients with recurrent anterior glenohumeral instability and an HSL.

Increased Posterior Tibial Slope Increases Force on the Posterior Medial Meniscus Root.

BACKGROUND: Posterior medial meniscus root (PMMR) tears have been associated with increased posterior tibial slope, but this has not been fully evaluated biomechanically. In addition, the effects of knee flexion and rotation on the PMMR are not well understood biomechanically because of technological testing limitations. A novel multiaxial force sensor has made it possible to elucidate answers to these questions. PURPOSE: (1) To determine if increased posterior tibial slope results in increased posterior shear force and compression on the PMMR, (2) to evaluate how knee flexion angle affects PMMR forces, and (3) to assess how internal and external rotation affects force at the PMMR. STUDY DESIGN: Controlled laboratory study. METHODS: Ten fresh-frozen cadaveric knees were tested in all combinations of 3 posterior tibial slopes and 4 flexion angles. A multiaxial force sensor was connected to the PMMR and installed below the posterior tibial plateau maintaining anatomic position. The specimen underwent a 500-N compression load followed by a 5-N·m internal torque and a 5-N·m external torque. The magnitude and direction of the forces acting on the PMMR were measured. RESULTS: Under joint compression, an increased tibial slope significantly reduced the tension on the PMMR between 5° and 10° (from 13.5 N to 6.4 N), after which it transitioned to a significant increase in PMMR compression, reaching 7.6 N at 15°. Under internal torque, increased tibial slope resulted in 4.7 N of posterior shear at 5° significantly changed to 2.0 N of anterior shear at 10° and then 8.2 N of anterior shear at 15°. Under external torque, increased tibial slope significantly decreased PMMR compression (5°: 8.9 N; 10°: 4.3 N; 15°: 1.1 N). Under joint compression, increased flexion angle significantly increased medial shear forces of the PMMR (0°, 3.8 N; 30°, 6.2 N; 60°, 7.3 N; 90°, 8.4 N). Under internal torque, 90° of flexion significantly increased PMMR tension from 2.3 N to 7.5 N. Under external torque, 30° of flexion significantly increased PMMR compression from 4.7 N to 12.2 N. CONCLUSION: An increased posterior tibial slope affects compression and anterior shear forces at the PMMR. An increased flexion angle affects compression, tension, and medial shear forces at the PMMR. CLINICAL RELEVANCE: The increase in compression and posterior shear force when the knee is loaded in compression may place the PMMR under increased stress and risk potential failure after repair. This study provides clinicians with information to create safer protocols and improve repair techniques to minimize the forces experienced at the PMMR.

Meniscotibial Ligament Insufficiency Increases Force on the Posterior Medial Meniscus Root.

BACKGROUND: Posterior medial meniscus root (PMMR) tears are a challenge to assess and treat. However, the forces sustained at the PMMR are yet to be fully characterized. In addition, it has been shown that meniscotibial ligament (MTL) injuries happen before PMMR tears, suggesting that insufficiency of the MTL results in a change of forces acting on the PMMR. PURPOSE/HYPOTHESIS: The purpose of this study was to evaluate the 3-dimensional forces acting on the PMMR in the intact, MTL cut, and MTL tenodesis states. It was hypothesized that the MTL cut state would increase medial shear forces seen at the PMMR, whereas the medial shear force in the MTL tenodesis state would return PMMR forces to that of the intact state. STUDY DESIGN: Controlled laboratory study. METHODS: Ten fresh-frozen cadaveric knees were tested in 3 states (intact, MTL cut, and tenodesis). A 3-axis load cell was installed below the posterior tibial plateau and attached to the enthesis of the PMMR. The specimen was mounted to a load frame that applied an axial load, an internal torque, and an external torque. The amount of compression-tension, mediolateral shear force, and anteroposterior shear force acting on the PMMR was measured. RESULTS: When the joint was loaded in compression, the MTL cut state significantly increased compression of the PMMR (P = .0368). The tenodesis state did not significantly restore forces of the PMMR (P = .008). When the joint was loaded in external torque, the MTL cut state significantly increased compression (P < .0001) and significantly decreased anterior shear on the PMMR (P = .0003). The tenodesis state did not significantly restore forces on the PMMR to the intact state (P < .0001). Increased flexion angle significantly increased medial shear forces of the PMMR when the joint was loaded in compression (P < .007 at every angle). CONCLUSION: When evaluated biomechanically, MTL insufficiency resulted in increased compressive force at the PMMR. A single-anchor centralization procedure did not restore PMMR forces to that of the intact state. Increased knee flexion angle resulted in increased medial shear force on the PMMR. CLINICAL RELEVANCE: The findings in this study provide clinicians information on PMMR forces when the MTL is disrupted. These data can aid in the decision-making for adding an MTL repair to augment PMMR repairs.

Biomechanical Analysis of Meniscotibial Ligament Tenodesis to Treat Meniscal Extrusion in the Setting of Posterior Medial Meniscus Root Repair.

BACKGROUND: Meniscal extrusion often persists after a medial meniscus root repair. If the meniscus is extruded, the function of the meniscus as a load-sharing device and secondary knee stabilizer is compromised. HYPOTHESIS: It was hypothesized that repairing the meniscotibial ligament (MTL) would decrease meniscal extrusion in the settings of both an isolated MTL tear and a repaired medial meniscus root while also improving medial compartment contact mechanics. STUDY DESIGN: Controlled laboratory study. METHODS: Ten fresh-frozen cadaveric knees (mean age, 50.5 years) were tested in 5 conditions: intact, MTL deficiency, MTL deficiency + posterior medial meniscus root deficiency, MTL deficiency + posterior medial meniscus root repair, and MTL tenodesis + posterior medial meniscus root repair. Specimens were mounted to a load frame that applied a 1000-N axial load. Joint contact pressures were measured using thin pressure sensors, and the peak and mean pressures were analyzed. Ultrasound was used to measure meniscal extrusion. RESULTS: The MTL tear in isolation resulted in significant meniscal extrusion compared with the intact state (P = 0.035) without a detectable difference in medial compartment pressures. The addition of a root tear to the MTL tear state resulted in significantly more extrusion (P = 0.001) and significant increases in medial compartment pressure (P = .030) compared to the MTL tear state. Root repair alone restored extrusion, mean contact pressure, and peak contact pressure back to the intact state (P > .05). CONCLUSION: This study showed that MTL disruption led to increased meniscal extrusion in a cadaveric model. Unlike the root tear state, MTL disruption did not change contact mechanics. Furthermore, root repair alone was sufficient in restoring intact biomechanics and extrusion. CLINICAL RELEVANCE: This study may help clinicians understand the origin of medial meniscus root tears and aid in the decision-making process for whether to add an MTL tenodesis in the setting of root repair.

Direct measurement of three-dimensional forces at the medial meniscal root: A validation study.

The posterior medial meniscal root (PMMR) experiences variable and multiaxial forces during loading. Current methods to measure these forces are limited and fail to adequately characterize the loads in all three dimensions at the root. Our novel technique resolved these limitations with the installation of a 3-axis sensing construct that we hypothesized would not affect contact mechanics, would not impart extraneous loads onto the PMMR, would accurately measure forces, and would not deflect under joint loads. Six cadaveric specimens were dissected to the joint capsule and a sagittal-plane, femoral condyle osteotomy was performed to gain access to the root. The load sensor was placed below the PMMR and was validated across four tests. The contact mechanics test demonstrated a contact area precision of 44 mm2 and a contact pressure precision of 5.0 MPa between the pre-installation and post-installation states. The tibial displacement test indicated an average bone plug displacement of < 1 mm in all directions. The load validation test exhibited average precision values of 0.7 N in compression, 0.5 N in tension, 0.3 N in anterior-posterior shear, and 0.3 N in medial-lateral shear load. The bone plug deflection test confirmed < 2 mm of displacement in any direction when placed under a load. This is the first study to successfully validate a technique for measuring both magnitude and direction of forces experienced at the PMMR. This validated method has applications for improving surgical repair techniques and developing safer rehabilitation and postoperative protocols that decrease root loads.

Anterior to Posterior Bone Plug Suture Tunnels Provide Optimal Biomechanics for Bone-Patellar Tendon-Bone Anterior Cruciate Ligament Graft.

Purpose: To evaluate different bone-patellar tendon-bone (BPTB) plug suture configurations for pull through strength, stiffness, and elongation at failure in a biomechanical model of suspensory fixation. Methods: Forty nonpaired, fresh-frozen human cadaveric BPTB allografts with an average age of 65.6 years were tested. Tensile testing was performed with the use of a custom-designed fixture mounted in a dynamic tensile testing machine. A preload of 90 N was applied to the graft and held for 5 minutes. Following this, a tensile load-to-failure test was performed. The ultimate failure load, elongation at failure, and mode of failure were recorded, and the resulting load-elongation curve was documented. Results: The drill tunnel through the cortical surface (anterior to posterior) was found to be significantly stronger than the drill tunnel through the cancellous surface (medial to lateral). There were no significant differences found when comparing the strength of the suture augmentation through the tendon and the drill tunnel alone (P = .13 among cancellous groups, P = .09 among cortical groups). The cortical drill tunnel with suture augmentation through the tendon showed significantly greater elongation values (13.7 ± 3.2) at failure when compared with either the cancellous or cortical drill tunnel only test groups (P = .0003 compared with cancellous alone, P = .009 when compared with cortical alone). Conclusions: The BPTB suture configuration with an anterior to posterior-directed suture tunnel without a suture through tendon augmentation provides the optimal strength and stiffness while minimizing graft elongation after fixation in a biomechanical model. This configuration is best for preventing suture pull through and failure when passing sutures through the BPTB plug. Clinical Relevance: This study biomechanically evaluates the optimal suture configuration in the proximal bone plug for suspensory fixation in the setting of BPTB grafts.

Validation of Pre-operative Templating for Total Disc Replacement Surgery.

OBJECTIVES: This was an analytic retrospective observational study. The aims were (1) to validate patient-specific templating process by comparing postoperative range of motion (ROM) with that predicted by the model, (2) to retrospectively determine the ideal implant size, height, configuration, and location to evaluate if the ROM achieved could have been improved, and (3) to correlate postoperative ROM and clinical outcome. BACKGROUND: Previous research revealed that after total disc replacement surgery, 34% of patients with less than 5° of postoperative ROM developed adjacent segment disease. The match between patient anatomy (size, facet orientation, disc height) and implant parameters are likely to affect postoperative ROM and clinical outcomes. METHODS: Seventeen consecutive patients were implanted with 22 ProDisc-L devices between 2008 and 2015. Three-dimensional finite element (FE) models of the implanted segment were constructed from preoperative computed tomography scans and virtually implanted with the ProDisc-L implant. ROM was determined with the endpoints of facet impingement in flexion and implant contact in extension. FE templating was used to determine the optimal implant size and location. ROM was then measured directly from flexion and extension radiographs and compared to predicted ROM. Pre and postoperative Oswestry Disability Index (ODI) data were used to correlate ROM with clinical outcomes. RESULTS: No significant difference was found between the actual and predicted ROM. The computational templating procedure identified an optimal ROM that was significantly greater than actual ROM. The ROM in our cohort could have been improved by an average of 1.2° or 12% had a different implant size or position been used. CONCLUSIONS: FE analyses accurately predicted ROM in this cohort and can facilitate selection of the optimal implant size and location that we believe will increase the chance of achieving clinical success with the application of this technology.

Statistical shape modeling characterizes three-dimensional shape and alignment variability in the lumbar spine.

The mechanics of the lumbar spine are heavily dependent on the underlying anatomy. Anatomical measures are used to assess the progression of pathologies related to low back pain and to screen patients for surgical treatment options. To describe anatomical norms and pathological differences for the population, statistical shape modeling, which uses full three-dimensional representations of bone morphology and relative alignment, can capture intersubject variability and enable comparative evaluations of subject to population. Accordingly, the objective of this study was to develop a comprehensive set of three-dimensional statistical models to characterize anatomical variability in the lumbar spine, by specifically describing the shape of individual vertebrae, and shape and alignment of the entire lumbar spine (L1-S1), with a focus on the L4-L5 and L5-S1 functional spinal units (FSU). Using CT scans for a cohort of 52 patients, lumbar spine geometries were registered to a template to establish correspondence and a principal component analysis identified the primary modes of variation. Scaling was the most prevalent mode of variation for all models. Subsequent modes of the statistical shape models of the individual bones characterized shape variation within the processes. Subsequent modes of variation for the FSU and entire spine models described alignment changes associated with disc height and lordosis. Quantification of anatomical variation in the spine with statistical models can inform implant design and sizing, assist clinicians in diagnosing pathologies, screen patients for treatment options, and support pre-operative planning.

Patient-Specific Templating of Lumbar Total Disk Replacement to Restore Normal Anatomy and Function.

The purpose of this study was to develop a tool to determine optimal placement and size for total disk replacements (TDRs) to improve patient outcomes of pain and function. The authors developed a statistical shape model to determine the anatomical variables that influence the placement, function, and outcome of lumbar TDR. A patient-specific finite element analysis model has been developed that is now used prospectively to identify patients suitable for TDR and to create a surgical template to facilitate implant placement to optimize range of motion and clinical outcomes. Patient factors and surgical techniques that determine success regarding function and pain are discussed in this article.