Introduction

Anterior cruciate ligament (ACL) repair has historically led to high failure rates. However, new research suggests that adding structural support may increase the success rate. The aims of this study were: 1) to investigate the influence of STA on ACL repair and 2) to determine the best STA fixation angle. It was hypothesized that 1) STA will reduce knee laxity as compared the ACL repair alone and 2) ACL repair with STA fixed at 20° of knee flexion would be better than fixation at full extension.

Methods

With institutional approval, 14 fresh-frozen human cadaveric knees were tested using a 6 degrees-of-freedom robotic testing system. Knees were tested under two loadings: 1) 89 N anterior tibial load; 2) a simulated pivot-shift (sPS) with combined rotatory 7 N-m valgus with 5 N-m internal torques. The testing states were: 1) ACL Intact, 2) ACL Cut, 3) ACL Repair, 4) ACL Repair with STA fixed at 0° of knee flexion (ACL Repair + 0 STA), and 5) ACL Repair with STA fixed at 20° of knee flexion (ACL Repair + 20 STA). For the ACL Cut state, a type I ACL tear (proximal avulsion tear) was simulated by cutting the ACL off from the femoral footprint. For the ACL Repair state, two sutures were passed through and around the ACL in a luggage tag configuration, then passed into the femoral bone tunnel and fixed at the femoral cortex with an adjustable length suspensory fixation button. For the STA, a suture tape was attached to the button loop and fixed on the tibial side with a knotless suture anchor at either 0 or 20 degrees (this order was randomized). Repeated measures ANOVA followed by post hoc analysis with Bonferroni correction was performed to determine differences in knee laxity between the states. A p value of < 0.05 (prior to Bonferroni correction) was considered significant.

Results

Under anterior tibial loading the anterior tibial translation (ATT) after ACL Repair only was significantly different from intact ACL for was significantly different at all knee flexion angles except 90 º knee flexion. ACL Repair + 0 STA was only statistically different from the intact ACL state at 0º, 15ºand 30º. ACL Repair + 20 STA restored the ATT closest to ACL intact, with differences only occurring at 15º and 30º. Coupled ATT under simulated pivot-shift loading, showed significant differences between the ACL Repair and the ACL Intact states at all knee flexion angles. Comparing Coupled ATT between ACL Repair + 0 STA and ACL Repair only, statistical differences were seen at 0º and 15º and between ACL Repair +20 STA and ACL Repair at 30º knee flexion.

Conclusion

This cadaveric study suggests that in the proximal ruptured ACL knee, repair only cannot restore the knee stability. ACL repair with STA fixed at 20° of knee flexion best restored knee laxity to the native, intact state. These results suggest that ACL repair with STA fixed at 20° ought to be considered for acute, femoral sided ACL tears.