BIOMECHANICAL EVALUATION OF INTERFERENCE SCREW FIXATION IN A BOVINE PATELLAR BONE TENDON BONE AUTOGRAFT COMPLEX FOR ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION

A bovine model was developed for biomechanical evaluation of anterior cruciate ligament (ACL) reconstruction using patellar bone-tendon-bone (b-t-b) autograft to examine the differences in time zero fixation me chanical properties of different interference screw lengths and diamet ers. The surgical technique of interference screw fixation of the b-t- b complex performed clinically was reproduced in a controlled animal m odel. The femur-patellar tendon graft-tibia complex was tested with an terior displacement of the tibia in 30-degrees of knee flexion to allo w examination of the femoral and tibial fixation properties simultaneo usly. The statistical model concurrently explored differences between screw length and diameter while accounting for variations between graf t properties. No statistically significant differences were found betw een the 7- and 9-mm screws with respect to peak load or energy to fail ure when using a 10-mm triangular graft in a 10-mm tunnel. The 7- and 9-mm screws were superior to the 5.5-mm screws with respect to these s ame parameters. Based on our results, the 7-mm interference screws can be used with equal confidence as the 9-mm screw, and the 20-mm length can be similarly exchanged for 30-mm length for patellar b-t-h graft fixation.