Effects of Tunnel Dilation and Interference Screw Position on the Biomechanical Properties of Tendon Graft Fixation for Anterior Cruciate Ligament Reconstruction

Purpose: The purpose of this study was to evaluate the effects of screw position and compaction of the bone tunnel on the strength of the flexor tendon graft after fixation using interference screws. Methods: Forty fresh-frozen porcine tibias were used for this study. The digital flexor tendons were folded into a quadrupled graft measuring 9 mm in diameter. In the extraction-drilling group, tibial bone tunnels were drilled with a conventional cannulated 9-mm drill bit in a single step. In the compaction-drilling group, bone tunnels were drilled using a cannulated 7-mm drill bit and were expanded to a final diameter of 9 mm in 0.5-mm increments by placement of dilators with increasing diameter. The grafts were fixed using 9 x 30-mm titanium screws in central and eccentric positions. Specimens underwent a cyclic-loading test, and the surviving specimens were then loaded until failure. Results: Graft displacement after 1,500 loading cycles occurred significantly more often in the extraction-drilling group with eccentric screw placement than in the groups of extraction-drilling (P < .05) and compaction-drilling (P < .01) with central screw placement. There were no statistically significant differences for the maximum screw insertion torque, maximum load at failure, or stiffness among the 4 groups. One strand of the quadrupled tendon grafts showed partial injury during screw insertion in 3 (30%) and 4 (40%) of 10 specimens of the extraction-drilling and compaction-drilling groups with central screw placement, respectively. Conclusions: Central screw placement significantly decreased the displacement of the tendon graft in comparison with eccentric screw placement in the extraction-drilling condition. Compaction of the bone tunnel walls by serial dilation in a central screw position did not increase the strength of interference screw fixation of a soft tissue graft.