Correlation of interference screw insertion torque with depth of placement in the tibial tunnel using a quadrupled semitendinosus-gracilis graft in anterior cruciate ligament reconstruction

Abstract

To evaluate the insertion torque of a soft-tissue interference screw in relation to depth of insertion into the tibial tunnel when used for fixation of a quadrupled semitendinosus-gracilis autograft in anterior cruciate ligament reconstruction. Biomechanical cadaver study. Ten quadrupled semitendinosus-gracilis grafts were harvested from fresh-frozen cadaver knees and fixed in donor proximal tibias using 10-mm bioabsorbable interference screws (Arthrex, Naples, FL). A cannulated torque screwdriver was used to measure screw insertion torque at 3 depths in the tibial tunnel: the outer cortex (distal third), the articular surface (proximal third), and between these 2 points (middle third). The mean insertion torques for the distal third, middle third, and proximal third were 8.7, 4.7, and 4.3 in/lb, respectively. The insertion torque was significantly higher at the outer cortex (distal third) than the middle third and proximal third (joint line of the tibial tunnel) ( P < .05). Our results indicate a correlation between insertion torque and depth of placement of bioabsorbable interference screws used for fixation of a semitendinosus-gracilis graft. Lower insertion torque at the articular surface, resulting in lower peak load or pullout strength, may outweigh the proposed benefits of joint-line fixation of a semitendinosus-gracilis graft used for anterior cruciate ligament reconstruction. Studies have suggested that anatomic proximal fixation of ACL grafts in the tibial tunnel produces stability similar to intact knees. The results of our study indicate that lower insertion torque at the articular surface results in lower peak load and pullout strength of the graft, which may outweigh the proposed benefits of joint-line fixation.