Study Design. Controlled laboratory study. Objective. The aim was to compare motions at the upper instrumented vertebra (UIV) and supra-adjacent level (UIV+1) between two fixation techniques in thoracic posterior spinal fusion constructs. We hypothesized there would be greater motion at UIV+1 after cyclic loading across all constructs and bilateral pedicle screws (BPSs) with posterior ligamentous compromise would demonstrate the greatest UIV+1 range of motion. Summary of Background Data. Proximal junctional kyphosis is a well-recognized complication following long thoracolumbar posterior spinal fusion, however, its mechanism is poorly understood. Materials and Methods. Twenty-seven thoracic functional spine units were randomly divided into three UIV fixation groups (n=9): (1) BPS, (2) bilateral transverse process hooks (TPHs), and (3) BPS with compromise of the posterior elements between UIV and UIV+1 (BPS-C). Specimens were tested on a servohydraulic materials testing system in native state, following instrumentation, and after cyclic loading. functional spine units were loaded in flexion-extension (FE), lateral bending, and axial rotation. Results. After cyclic testing, the TPH group had a mean 29.4% increase in FE range of motion at UIV+1 versus 76.6% in the BPS group (P<0.05). The BPS-C group showed an increased FE of 49.9% and 62.19% with sectioning of the facet joints and interspinous ligament respectively prior to cyclic testing. Conclusion. BPSs at the UIV led to greater motion at UIV+1 compared to bilateral TPH after cyclic loading. This is likely due to the increased rigidity of BPS compared to TPH leading to a “softer” transition between the TPH construct and native anatomy at the supra-adjacent level. Facet capsule compromise led to a 49.9% increase in UIV+1 motion, underscoring the importance of preserving the posterior ligamentous complex. Clinical studies that account for fusion rates are warranted to determine if constructs with a “soft transition” result in less proximal junctional kyphosis in vivo.
Background: Current techniques for ulnar collateral ligament (UCL) reconstruction do not reproduce the anatomic ulnar footprint of the UCL. The purpose of this study was to describe a novel UCL reconstruction technique that utilizes proximal-to-distal ulnar bone tunnels to better re-create the anatomy of the UCL and to compare the biomechanical profile at time zero among this technique, the native UCL, and the traditional docking technique. Hypothesis: The biomechanical profile of the anatomic technique is similar to the native UCL and traditional docking technique. Study Design: Controlled laboratory study. Methods: Ten matched cadaveric elbows were potted with the forearm in neutral rotation. The palmaris longus tendon graft was harvested, and bones were sectioned 14 cm proximal and distal to the elbow joint. Specimen testing included (1) native UCL testing performed at 90° of flexion with 0.5 N·m of valgus moment preload, (2) cyclic loading from 0.5 to 5 N·m of valgus moment for 1000 cycles at 1 Hz, and (3) load to failure at 0.2 mm/s. Elbows then underwent UCL reconstruction with 1 elbow of each pair receiving the classic docking technique using either anatomic (proximal to distal) or traditional (anterior to posterior) tunnel locations. Specimen testing was then repeated as described. Results: There were no differences in maximum load at failure between the anatomic and traditional tunnel location techniques (mean ± SD, 34.90 ± 10.65 vs 37.28 ± 14.26 N·m; P = .644) or when including the native UCL (45.83 ± 17.03 N·m; P = .099). Additionally, there were no differences in valgus angle after 1000 cycles across the anatomic technique (4.58°± 1.47°), traditional technique (4.08°± 1.28°), and native UCL (4.07°± 1.99°). The anatomic group and the native UCL had similar valgus angles at failure (24.13°± 5.86° vs 20.13°± 5.70°; P = .083), while the traditional group had a higher valgus angle at failure when compared with the native UCL (24.88°± 6.18° vs 19.44°± 5.86°; P = .015). Conclusion: In this cadaveric model, UCL reconstruction with the docking technique utilizing proximal-to-distal ulnar tunnels better restored the ulnar footprint while providing valgus stability comparable with reconstruction with the docking technique using traditional anterior-to-posterior ulnar tunnel locations. These results suggest that utilization of the anatomic tunnel location in UCL reconstruction has similar biomechanical properties to the traditional method at the time of initial fixation (ie, not accounting for healing after reconstruction in vivo) while keeping the ulnar tunnels farther from the ulnar nerve. Further studies are warranted to determine if an anatomically based UCL reconstruction results in differing outcomes than traditional reconstruction techniques. Clinical Relevance: Current UCL reconstruction techniques do not accurately re-create the ulnar UCL footprint. The UCL is a dynamic constraint to valgus loads at the elbow, and a more anatomic reconstruction may afford more natural joint kinematics. This more anatomic technique performs similarly to the traditional docking technique at time zero, and the results of this study may offer a starting point for future in vivo studies.
Objectives: Recent studies have stressed the important role of the deltoid ligament in maintaining global ankle stability. However, controversy remains around whether deltoid ligament repair is necessary in addition to syndesmotic repair when addressing injuries that disrupt both the syndesmosis and deltoid ligament. The purpose of this study was to measure differences in tibiotalar joint contact pressures and tibio-talar torsional stability in the presence of deltoid ligament injury, syndesmotic injury, and after their respective repairs using a cadaveric model. Our hypotheseis were 1) injury to the syndesmoosis and deltoid would increase contact pressures and decrease torsional stability, 2) repaired injuries would restore biomechanics to near native state, and 3)that there would be similar tibiotalar contact pressures and torsional stability with syndesmosis repair alone compared to syndesmosis and deltoid ligament repair. Methods: Twelve fresh-frozen human cadaveric lower extremity specimens with intact ankle joints were randomized and tested under a series of conditions: 1) intact syndesmosis and deltoid, 2) sectioning of syndesmosis or deltoid, 3) sectioning of both the syndesmosis and deltoid, 4) repair of syndesmosis or deltoid, 5) repair of both the syndesmosis and deltoid. In one group, the syndesmosis was sectioned and repaired first and in the other the deltoid was sectioned and repaired first. The syndesmosis was repaired with a single high-tensile strength suture mechanism (TightRope, Arthrex), and deltoid ligament repairs were performed with a single suture anchor (FiberTak, Arthrex). Specimens were tested under each condition with 800 N axial compression load, followed by cyclic torsional preconditioning of 5 Nm internal tibial torque (i.e., external foot rotation) at a rate of 2.5 Nm/s, and then a single rotation test of 7.5 Nm internal tibial torque at 1 Nm/s under 800 N axial compression load on a servohydraulic mechanical testing system. Contact pressures within the tibiotalar joint were measured with a digitized pressure sensor film (Tekscan, Boston MA), and coronal plane motion about the tibia was measured in angular displacement. Results: There was no significant difference in peak contact pressures between conditions except when the comparing an isolated deltoid ligament injury to a combined deltoid and syndesmosis injury (4.43±1.33MPa vs 2.67±0.45MPa, p=0.038). Total contact area was less following syndesmosis repair in isolation (609.55±312.37mm2) and combined syndesmosis and deltoid repair (598.28±181.47mm2) compared to all other conditions (p<0.001). There was also a decrease in total contact area compared to native state when the deltoid was repaired in isolation (951.51±72.79mm2 vs 888.72±105.74mm2, p=0.027). The mean external rotation angle was greater when the syndesmosis (15.67±5.39°), deltoid (13.21±3.28°), and both injuries combined (16.59±4.01°) compared to native state (8.55±2.02°), however these values did not achieve statistical significance. Additionally, There was no statistically significant difference in external rotation angle between isolated syndesmosis, isolated deltoid, or combined repairs. Conclusions: These findings demonstrate that ankle contact pressures and torsional stability do not differ significantly when a deltoid ligament repair is performed in conjunction with a syndesmosis repair for a purely ligamentous injury. However, the change in contact area following syndesmosis repair may play a role in the development of post-traumatic arthritis. This finding reinforces the importance of striving for an anatomic syndesmotic reduction, and care should be taken not to over-reduce the syndesmosis during repair.
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