One- and two-incision anterior cruciate ligament reconstruction: A biomechanical comparison including the effect of simulated closed-chain exercise

The purpose of this study was to evaluate the effect of simulated closed-chain exercise on anterior translation in the anterior cruciate ligament (ACL) reconstructed knee comparing patellar tendon grafts secured with endoscopic and two-incision techniques. ACL reconstructions, were performed on five matched pairs of fresh frozen cadaver lower extremities. One of each pair had endoscopic (inside-out) placement of the femoral interference screw and other had outside-in femoral screw placement. A model for closed-chain exercise was developed to simulate half squat exercises using a custom apparatus on the Material Testing machine with a 356 N (80 lb) axial load and 40 N (9 lb) static hamstring force. Knee motion from near full extension to 60°flexion was achieved by varying the quadricep force. One thousand squats were performed, and KT-1000 arthometry was done before and after cycling each specimen. The femur-graft-tibia constructs were then stressed to failure. Closed-chain cycling resulted in no significant change in anterior translation in either group. The mean maximum load to failure of the femur-graft-tibia construct was 340.4N in the one-incision group and 434.2 N in the two-incision group. P = .048 was considered statistically significant. Anterior translation did not increase after 1,000 simulated half knee bends in either the one- or two-incision groups. Shallow knee bends are an important part of aggressive rehabilitation programs, and our data support the position that these closed-chain exercises do not deleteriously affect the graft. Though the maximum strength to failure differed significantly between the one- and two-incision groups, both techniques offered sufficient strength to withstand an aggressive simulated rehabilitation protocol.