COMPARISON OF PULLOUT STRENGTH FOR 7-MILLIMETER AND 9-MILLIMETER DIAMETER INTERFERENCE SCREW SIZE AS USED IN ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

This study compares biomechanical properties of 7- and 9-mm diameter s crews providing interference fixation in anterior cruciate ligament re construction. Sixteen pairs of fresh-frozen bovine knees were evaluate d. Uniaxial load to failure was performed at a deformation rate of 30 mm/s along the mechanical axis of the ligament graft with the knees se cured at 45 degrees of flexion in a custom jig, A video analyzer was u sed to measure ligament strain and bone-to-bone deformation. Ultimate force, deformation, and failure mode were recorded and compared. The 7 -mm screws provided 98% yield strength, and 95% ultimate force compare d with the 9-mm screws. The average femoral pullout strength was 1161 +/- 93 N in the 7-mm group and 1198 +/- 142 N in the 9-mm group, Failu re mode was similar in both groups. Clinically, the usage of 7-mm scre ws may reduce iatrogenic injuries to the patellar tendon graft compare d with larger screws. This study shows that the biomechanical advantag es of 9-mm screws compared with 7-mm screws are minimal.