Effect of varying angles on the pullout strength of interference screw fixation

Arthroscopically assisted reconstruction of the anterior cruciate ligament-deficient knee using a bone-patellar tendon-bone graft is a new and evolving technique. One technically demanding aspect involves the placement under arthroscopic visualization of the femoral interference screw. The effect on pullout strength of changing the angle of the interference screw from 0 degree to 10 degrees, 20 degrees, or 30 degrees with respect to the bone plug was examined. The mean pullout strengths were 621 +/- 82, 594 +/- 48, 508 +/- 66, and 485 +/- 62 N, respectively. We concluded that there was no significant difference in the tensile strength provided by interference screw fixation for angles up to 10 degrees, but that there was a significant (p = 0.0010) weakening of fixation for screw angles > or = 20 degrees.