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This study reports on detailed analyses of retrieved, annealed crosslinked liners. Twelve crosslinked liners (Crossfire, Stryker Orthopaedics, Mahwah, NJ) of the same Omnifit design were retrieved at revision surgery by one institution after an average 1.9 years (0.02 to 4.8 years) in vivo. In each case, the revision surgery was performed for reasons unrelated to wear. The mechanical properties and extent of oxidation of all inserts were characterized using a standard small punch test and measurement of the oxidation index. Results indicated that there was no association between implantation time and either mechanical properties or extent of oxidation for the inserts near the worn bearing surface. Slight variation in properties was observed as a function of sampling location, with the properties near the unworn surface displaying the greatest relative variability. We conclude that the variability in polyethylene properties observed in this small study was not clinically significant for these short term-implanted, annealed crosslinked liners.

There are few good surgical options that allow for continued spinal growth in patients with early-onset scoliosis. The ''Shilla'' is a growth guidance system that does not require repeated surgical lengthenings. The Shilla system guides growth at the ends of dual rods with the apex of the curve corrected, fused, and fixed to the rods. The growth occurs through the extraperiosteally implanted pedicle screws that slide along the rods at either end of the construct. We implanted 11 2-month-old immature goats with the dual rod system and euthanized all 11 goats 6 months postoperatively. We evaluated plain radiographs, regular computed tomography, microcomputed tomography, physical and histologic examinations, and a microscopic wear analysis. All of the goat spines grew with the implants in place; growth occurred in both the thoracic and lumbar ends of the rods for a total average of 48 mm. None of the implants failed, although we observed minor wear at the rod/screw interface. Growth guidance with the Shilla rod system allowed for continued growth in this goat model.

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