Search

Purpose: To compare the biomechanics of a transosseous equivalent (TOE) repair using medial and lateral anchors with tape to a transosseous knotless (TOK) tape repair with only laterally placed intraosseous anchors., Methods: One of 2 different repairs were performed on 8 paired specimens: (1) transosseous equivalent (TOE) tape repair or (2) transosseous knotless (TOK) tape repair. Specimens were mounted on a materials testing machine and loaded in uniaxial tension to measure cyclic construct gap formation, followed by failure testing. Paired t tests were used to compare gapping, ultimate stiffness, and failure loads. Fisher exact test was used to compare modes of failure (soft tissue failure vs construct failure)., Results: Peak cyclic gapping, failure stiffness, and ultimate failure loads did not differ between TOE and TOK repairs (P = .140 for gapping, P = .106 for stiffness, and P = .672 for peak failure loads). All TOK repairs failed via soft tissue failure medial to the medial suture line, with no construct failures. TOE repairs failed more often through construct failure (anchor migration or suture-bone interface cut through) than TOK repairs (P = .026)., Conclusion: TOK repairs only failed through soft tissue whereas TOE repairs failed through both soft tissue and the repair construct. Despite 50% fewer suture anchors in the TOK repairs than the TOE repairs, cyclic gapping and ultimate stiffness and failure loads were not significantly different., Clinical Relevance: The transosseous knotless construct presented is a 2-anchor construct that is equivalent in biomechanical function to a traditional 4-anchor construct, reducing anchor load in the tuberosity., (Copyright © 2017 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Background: Many decompression procedures involve complete or partial facetectomy. Spinal fusion usually stabilizes the motion segment after complete facetectomies. However, problems with fusion, such as adjacent-level degeneration, have increased interest in motion- preservation technologies. Facet arthroplasty may become an important posterior motion-preservation device, but its biomechanical literature is sparse., Methods: We conducted an in vitro investigation and finite element study to compare the biomechanical effects of an artificial facet system to the intact spine. In the in vitro study, we tested human osteo-ligamentous segments (L3-S1) in intact, injured, and artificial facet-repaired conditions. For the finite element study, we used a 3-dimensional ligamentous L3-S1 segment model. We simulated destabilization in the intact model by removing the facets across the L4-L5 functional unit, then repaired it with appropriately sized facet implants and compared the ranges of motion, facet loads, disc pressures, and device loads. We also analyzed a finite element model with a rigid posterior pedicle-rod fixation system. We subjected the cadaveric specimens and the models to 400 N of follower load plus a 10 Nm moment in extension, flexion, bending, and rotation. We used a novel technique to apply the follower load in the finite element models such that preload induced minimal vertebral rotation during the range of motion., Results: The predicted ranges of motion for the intact and implanted models were consistent with cadaver data. After destabilization and facet replacement, the artificial facet system restored motion in all loading modes to intact values. The implant facet loads were similar to intact facet loads in extension and axial rotation, but less in lateral bending. The intradiscal pressure at the implanted level for the facet replacement device was similar to the intact pressure, whereas with the rigid system the intradiscal pressure was up to 70% less than the intact pressure. The maximum von-Mises stress predicted in the facet replacement construct was 85 MPa in extension at the bone-pedicle screw interface, compared with 174 MPa in the rigid system. Contact stresses at implant mating surfaces were minimal., Conclusions: The artificial facet system replicated natural facet kinematics. The cadaveric ranges of motion and the predicted finite element-based data indicated that the implant can "restore" the normal function of the segment after artificial facet replacement., Clinical Relevance: Compared to rigid posterior pedicle-rod fixation, the artificial facet system restored the intact mechanics at the implanted level and may prevent adjacent-level degeneration.