RESUMO
PURPOSE: Adjustable cortical fixation has gained popularity recently for ACL reconstruction; however, one concern with these types of devices is the potential for laxity occurring post-operatively. An indicator of clinical laxity is cyclic displacement during bench-top mechanical testing. The hypothesis was that the cyclic displacement and maximum strength of different adjustable buttons currently on the market would vary depending on their mechanism of fixation. METHODS: Three devices were studied: Biomet's ToggleLoc with ZipLoop Technology (ZL), Arthrex's TightRope RT (TR), and DePuy Mitek's RIGIDLOOP Adjustable (RLA). Each was tested in isolation on a servohydraulic test machine. The implants were pre-conditioned from 5 to 67 N for 10 cycles and then tested from 50 to 250 N for 1000 cycles at 1 Hz. Following cyclic loading, a load to failure test was conducted at a rate of 20 mm/min. Total displacement was calculated from the 1st to the 1000th cycle, and ultimate strength and failure mode were recorded. RESULTS: Results showed that the RLA had significantly lower displacement versus both the TR (p = 0.012) and the ZL (p < 0.001). The TR also showed significantly lower displacement than the ZL (p < 0.001). The RLA and the ZL were both significantly stronger than the TR (p < 0.001). CONCLUSIONS: Both the RLA and TR showed clinically acceptable amounts of cyclic displacement and maximum strength. The clinical relevance of this study is that cyclic displacement results from bench-top tests may correlate with post-operative laxity, which ideally should be kept to a minimum.
