Parekh, Amit

» Bearing materials that are used in total hip arthroplasty have undergone major developments in structure and durability since the 1960s. » Osteolysis and aseptic loosening associated with ultra-high molecular weight polyethylene had been a major concern; this led to the development of the first generation of highly cross-linked polyethylene (HXLPE), which was followed by a second generation of HXLPE. » The second generation of HXLPE was introduced with the aim of providing oxidative stability while maintaining high wear resistance. » Oxidative stabilization methods include mechanical deformation and annealing, incorporation of antioxidant-containing materials, high-pressure crystallization after melting, and polyethylene surface-grafting with a biocompatible polymer. » Results of clinical studies with ≤5 years of follow-up have shown that second-generation HXLPE acetabular liners are superior to any of the previous generation with regard to wear rates; however, additional studies are needed to compare second-generation materials among each other.

Purpose To investigate the biomechanical effects of superior capsule reconstruction with subacromial allograft spacer on superior humeral head translation and subacromial contact pressure. Methods Eight cadaveric shoulder specimens were tested in 4 conditions: (1) intact rotator cuff, (2) supraspinatus tear and superior capsule excision, (3) superior capsule reconstruction with human dermal allograft, and (4) superior capsule reconstruction with subacromial resurfacing using human dermal allograft. In each condition, specimens were tested at 0, 30, 60, and 90° of shoulder abduction in balanced and unbalanced loaded states for subacromial contact pressure and superior humeral head translation. Statistical comparisons were made using a repeated‐measures analysis of variance test, followed by a Tukey post hoc test for pairwise comparisons. A P value <.05 was set as statistically significant. Results Superior humeral head translation and subacromial contact pressure were increased after irreparable rotator cuff tear ( P = .001). There was no significant difference between superior capsule reconstruction and intact cuff in regard to superior humeral head translation and subacromial contact pressure at all abduction angles. Superior capsule reconstruction with subacromial resurfacing decreased superior humeral head translation relative to intact (0°, P = .004; 30°, P = .02; 60°, P = .08; 90°, P = .01), superior capsule reconstruction (0°, P = .001; 30°, P = .003; 60°, P = .019; 90°, P = .001), and cuff‐deficient states ( P = .001). Superior capsule reconstruction with subacromial resurfacing resulted in nonsignificant increases in subacromial contact pressure relative to intact cuff at 0 to 90° abduction angles. Conclusions Superior capsule reconstruction with subacromial resurfacing using human dermal allograft results in decreased superior humeral head translation relative to superior capsule reconstruction with human dermal allograft only, while increasing subacromial contact pressure. Clinical Relevance Superior capsule reconstruction with subacromial resurfacing using human dermal allograft reduces superior humeral head translation while increasing subacromial contact pressure in a cadaveric model.