A biomechanical comparison of initial fixation strength of 3 different methods of anterior cruciate ligament soft tissue graft tibial fixation: resistance to monotonic and cyclic loading

BACKGROUND: Tibial fixation of soft tissue grafts continues to be problematic in the early postoperative period after anterior cruciate ligament reconstruction. HYPOTHESIS: No differences exist for resistance to slippage of soft tissue grafts fixed with CentraLoc, Intrafix, or 35-mm bioabsorbable interference screws. STUDY DESIGN: Controlled laboratory study. METHODS: Bovine tibia and hoof extensor tendons were divided into 3 matched groups with 12 tibia and 12 extensor tendons in each group. Within each group, 6 specimens underwent monotonic loading to failure (1 mm/s), and 6 underwent cyclic loading (10,000 cycles, 125-325 N, 1 Hz). RESULTS: No statistically significant differences were noted in mean load to failure or stiffness. The mean load to failure (and stiffness) for the 3 types of fixation were as follows: bioabsorbable interference screw, 631.6 +/- 130.1 N (88.17 +/- 6.79 N/mm); Intrafix, 644.3 +/- 195.2 N (81.65 +/- 16.5 N/mm); and CentraLoc, 791.1 +/- 72.7 N (77.89 +/- 7.07 N/mm). The slippage rates under cyclic loading for the 3 types of fixation were bioabsorbable interference screw, 0.336 +/- 0.074 microm/cycle; Intrafix, 27.2 +/- 31.6 microm/cycle; and CentraLoc, 0.0355 +/- 0.0046 microm/cycle. In this model, CentraLoc proved statistically superior in resistance to cyclic loading compared with the bioabsorbable interference screw (P < .05) and Intrafix (P < .0001). The bioabsorbable interference screw proved statistically superior to Intrafix in resistance to cyclic loading (P < .05). CONCLUSIONS: In this bovine model, CentraLoc and bioabsorbable interference screws provided superior resistance to cyclic loading compared with Intrafix. CLINICAL RELEVANCE: CentraLoc and bioabsorbable interference screws showed superior resistance to cyclic loading, which may indicate an increased resistance to clinical failure.