A biomechanical comparison of initial soft tissue tibial fixation devices

Background: Biomechanical testing of the Intrafix device has not been performed using human tibiae. Hypothesis: The Intrafix device would provide comparable or superior tibial fixation of a quadrupled hamstring tendon graft to a 35-mm-long bioabsorbable interference screw. Study Design: In vitro, biomechanical study. Methods: Eight paired human tibiae and 16 quadrupled hamstring tendon grafts were divided into 2 groups. Each quadrupled hamstring tendon graft was fixed in a tunnel sized to 0.5 mm graft diameter with either an Intrafix device or a screw. Results: Displacement at failure was greater in the Intrafix group (17.3 +/- 4.6 mm versus 10.9 +/- 4.4 mm, P = .002). Load at failure (796 +/- 193 N versus 647 +/- 269 N), stiffness (49.2 +/- 21.9 N/mm versus 64.5 +/- 22 N/mm), and bone mineral density (0.74 +/- 0.15 gm/cm(3) versus 0.74 +/- 0.14 gm/cm(3)) did not display significant differences for the Intrafix device and the screw, respectively (P > .05). Conclusions: Displacement at failure was greater for the Intrafix device. Clinical Relevance: Increased displacement at failure for the Intrafix group suggests slippage from sheath channel deployment. Concentric fixation may not occur when less than optimal tibial bone mineral density increases the difficulty of attaining precise sheath deployment and quadrupled hamstring tendon graft strand alignment.