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The article presents a study which described the paucity of an objective recorded data delineating the pattern of weightbearing distribution within the prosthetic socket of patients with transtibial amputation. The researchers analyzed the information obtained from finite element analysis computer models. The experimental model accurately recorded loading within a transtibial prosthetic socket consistent with the previously reported finite element analysis computer models.

Abstract: Two variations of crescentic shelf osteotomies have been described for the treatment of moderate to severe hallux abductovalgus: a short arm and a long arm. This study tested the hypothesis that the short-arm osteotomy will have a greater moment to failure and angular stiffness than the long arm. Eighteen first metatarsal specimens were dissected from 9 matched pairs of fresh frozen cadaveric specimens. One metatarsal from each pair received a short-arm osteotomy, whereas the other received a long-arm osteotomy. Each osteotomy was fixed with 2 screws. The short arm was fixed with 1 oblique screw and 1 dorsal-to-plantar screw. The long arm was fixed with 2 dorsal-to-plantar screws: 1 at the proximal aspect and 1 at the distal aspect of the shelf. Each specimen was loaded in a materials testing machine to measure moment to failure and angular stiffness. The base of the first metatarsal was potted and load applied to the plantar aspect of the metatarsal head at a constant rate until failure of the osteotomy. The mean maximum moment to failure of the short arm was significantly greater than the long arm (2.04 ± 0.96 Newton meter [Nm] vs. 1.48 ± 0.67 Nm, P = .03). The mean angular stiffness was significantly greater for short arm versus long arm (23.8 ± 19.11 Nm/radian vs. 0.98 ± 9.08 Nm/radian, P = .01). We report statistically significant data supporting the short-arm crescentic shelf osteotomy to have a greater moment to failure and angular stiffness compared with the long-arm crescentic shelf osteotomy. [Copyright &y& Elsevier]

Abstract: Background: Total disc replacement (TDR) and total facet replacement (TFR) have been the focus of recent kinematics evaluations. Yet their concurrent function as a total joint replacement of the lumbar spine''s 3-joint complex has not been comprehensively reported. This study evaluated the effect of a TFR specifically designed to replace the natural facets and supplement the function with the natural disc and with TDR. The ability to replace degenerated facets to complement a pre-existing or simultaneously implanted TDR may allow surgeons to completely address degenerative pathologies of the 3-joint complex of the lumbar spine. We hypothesized that TFR would reproduce the biomechanical function of the natural facets when implanted in conjunction with TDR. Methods: Lumbar spines (L1-5, 51.3 ± 14.2 years, N = 6) were tested sequentially as follows: (1) intact, (2) after TDR implantation, and (3) after TFR implantation in conjunction with TDR, all at L3-4. Specimens were tested in flexion-extension (+ 8 Nm to − 6 Nm), lateral bending (± 6 Nm), and axial rotation (± 5 Nm). A 400 N compressive follower preload was applied during flexion-extension tests. Three-dimensional segmental motion was recorded and analyzed using analysis of variance in Systat (Systat Software Inc., Chicago, Illinois) and multiple comparisons with Bonferroni correction. Results: The TDR implantation (TDR + natural facets) allowed similar lateral bending (P = .66), but it generally increased flexion-extension (P = .06) and axial rotation (P < .05) range of motion (ROM) at the implanted level compared to intact. The TFR + TDR (following replacement of the natural facets with TFR) decreased ROM to levels similar to intact in lateral bending (P = .70) and axial rotation (P = .23). The TFR + TDR flexion-extension ROM was reduced in comparison to intact and TDR + natural facets (P < .05). Conclusions: The TFR with TDR was able to restore stability to the lumbar segment after bilateral facetectomy, while allowing near-normal motions in all planes. [Copyright &y& Elsevier]

Abstract: Background: Facet arthroplasty is a motion restoring procedure. It is normally suggested as an alternative to rigid fixation after destabilizing decompression procedures in the posterior lumbar spine. While previous studies have reported successful results in reproducing normal spine kinematics after facet replacement at L4-5 and L3-4, there are no data on the viability of facet replacement at the lumbosacral joint. The anatomy of posterior elements and the resulting kinematics at L5-S1 are distinctly different from those at superior levels, making the task of facet replacement at the lumbosacral level challenging. This study evaluated the kinematics of facet replacement at L5-S1. Methods: Six human cadaveric lumbar spines (L1-S1, 46.7±13.0 years) were tested in the following sequence: (1) intact (L1-S1), (2) complete laminectomy and bilateral facetectomy at L5-S1, and (3) implantation of TFAS-LS (Lumbosacral Total Facet Arthroplasty System, Archus Orthopedics, Redmond, Washington) at L5-S1 using pedicle screws. Specimens were tested in flexion (8Nm), extension (6Nm), lateral bending (LB,±6Nm), and axial rotation (AR,±5Nm). The level of significance was α=.017 after Bonferroni correction for three comparisons: (1) intact vs. destabilized, (2) destabilized vs. reconstructed, and (3) intact vs. reconstructed. Results: Laminectomy-facetectomy at L5-S1 increased the L5-S1 angular range of motion (ROM) in all directions. Flexion-extension (F-E) ROM increased from 15.3±2.9 to 18.7±3.5 degrees (P <.017), LB from 8.2±1.8 to 9.3±1.6 degrees (P <.017), and AR from 3.7±2.0 to 5.9±1.8 degrees (P <.017). The facet arthroplasty system decreased ROM compared to the laminectomy-facetectomy condition in all tested directions (P <.017). The facet arthroplasty system restored the L5-S1 ROM to its intact levels in LB and AR (P >.017). F-E ROM after the facet arthroplasty system implantation was smaller than the intact value (10.1±2.2 vs. 15.3±2.9 degrees, P <.017). The load-displacement curves after the facet arthroplasty system implantation at L5-S1 were sigmoidal, and quality of motion measures were similar to intact, demonstrating graded resistance to angular motion in F-E, LB and AR. Conclusions: The facet arthroplasty system was able to restore stability to the lumbosacral segment after complete laminectomy and bilateral facetectomy, while also allowing near-normal kinematics in all planes. While F-E ROM after the facet arthroplasty system implantation was smaller than the intact value, it was within the physiologic norms for L5-S1. These results are consistent with previous studies of facet arthroplasty at L3-L4 and L4-L5 and demonstrate that TFAS technology can be adapted to the lumbosacral joint with functionality comparable to its application in superior lumbar levels. [Copyright &y& Elsevier]

Although the biomechanics of the coracoacromial arch and coracoacromial ligament (CAL) morphology are well studied, to our knowledge, the biomechanics of the coracoacromial arch after CAL resection and medial reattachment have not yet been studied. The purpose of this report is to examine the biomechanical consequences of coracoacromial arch alteration and subsequent reconstruction in cadaveric specimens. Anterosuperior humeral head translation was measured after the application of an anterosuperior 150-N load under 5 sequential scenarios: (1) intact CAL, (2) subperiosteal CAL release, (3) standard acromioplasty, (4) CAL reconstruction, and (5) modified Neer acromioplasty. A significant decrease in anterosuperior migration was found after CAL reconstruction compared with both anterior acromioplasty (P = .038) and modified Neer acromioplasty (P = .01). Thus, in patients with massive rotator cuff tears, reconstruction of the CAL may provide the necessary stabilizing force to prevent excessive anterosuperior translation and possible humeral head escape from the coracoacromial arch. [Copyright &y& Elsevier]