Optimal graft fixation--the effect of gap size and screw size on bone plug fixation in ACL reconstruction

In reconstruction of the anterior cruciate ligament (ACL), using central one-third patellar tendon graft, an early weak link is the bone plug junction. To study this, we carried out experiments to determine the relationship between gap size, screw size, and pullout force of patellar bone plugs inserted in the femur of the porcine model. Forty-nine porcine knees were obtained. Holes 11 mm in diameter were drilled in the intercondylar notch of the femur. Bone plugs fashioned from the patella were made to fit the holes with gap sizes of 1, 2, 3, or 4 mm. The bone plugs were inserted into the holes in the femur and secured by means of 20-mm-long screws (either 7- or 9-mm diameter). The bone plugs were then pulled out using a tensile testing machine and the pullout force was measured. The results suggest that a 7-mm (or a 9-mm) diameter screw can be used for gaps of 1 and 2 mm, and a 9-mm diameter screw should be used for gaps of 3 and 4 mm.