Anterior cruciate ligament reconstruction with patellar tendon. An ex vivo study of wear-related damage and failure at the femoral tunnel.

Patellar tendon grafts used in the reconstruction of the anterior cruciate ligament may be subjected to thousands of knee flexion-extension cycles during the early postoperative period. The purpose of this study was to model experimentally the patellar tendon graft wear-related damage and failure at the femoral tunnel during simulated knee motion of 0 degrees to 112 degrees of flexion at 1 cycle/sec. To evaluate the effects of 2 different femoral tunnel orientations, tunnel chamfering, and 3 different graft loads on graft survival, 25 calf femurs and patellar tendons were used. All 5 specimens with a "straight-line" femoral tunnel and an applied load of 5 pounds (22.3 N) survived greater than 125,000 cycles. All 5 of the 5-pound unchamfered transverse tunnel grafts failed at an average of 19,869 cycles, but chamfering transverse tunnels resulted in the survival of 4 of 5 specimens. Decreasing the load to 2 pounds (8.9 N) for transverse unchamfered tunnels increased survival to 1 of 5, and cycles to failure to 75,132. If patellar tendon grafts used to reconstruct the anterior cruciate ligament are subjected to large numbers of flexion-extension cycles, the risk of wear-related damage and early failure may be decreased by straight-line femoral tunnel orientation, by chamfering of more transverse tunnels, or by avoiding large graft preloads.