Gap formation following primary repair of the anterior cruciate ligament: A biomechanical evaluation

Background: Historically, inconsistent and unpredictable results of open primary anterior cruciate ligament (ACL) repair were reported. Recently, however, good results of arthroscopic primary ACL repair of proximal tears have been reported. Purpose of this study was to assess the direct postoperative gap formation and maximum failure load following simulated knee motion after primary ACL repair.

Methods: Six matched-paired human cadaveric knees (mean age: 52years, range: 48 to 56years) were used. After primary proximal ACL repair with either suture button fixation or suture anchor fixation, knees were cycled five, 50 and 100 times with a simulated active quadriceps force. Gap formation between the femoral wall and ligament was measured using a digital caliper and maximum failure load was tested.

Results: Gap formation after five, 50 and 100cycles of the knee were 0.30mm (±0.23), 0.75mm (±0.55) and 0.97mm (±0.70), respectively, with no significant differences between both fixation techniques. The overall maximum failure load was 243N (±143) with no difference between both techniques. Most common failure mode was slipping of suture from the fixation.

Conclusion: Following proximal ACL repair, gap formation of approximately one millimeter was measured after repetitious knee cycling with mean maximum failure load of 243N. These findings are likely to be sufficient for careful early active range of motion (ROM) when extrapolating from other available studies. Future studies with second-look arthroscopy are necessary to assess the gap formation and healing in patients treated with primary repair.