Effect of Interference Screw Fixation on ACL Graft Tensile Strength

Tibial-sided fixation of soft tissue grafts in anterior cruciate ligament (ACL) reconstruction has often been identified as the weak link in the fixation construct, with interference screws being a commonly used technique. A significant concern surrounding the use of interference screws for soft tissue fixation is graft laceration and the possibility of loss of pull-out strength and slippage. The act of interference screw insertion for soft tissue graft fixation in ACL reconstruction alters the biomechanical properties of the graft. Two groups of 12 porcine knees (24 total) were utilized for the tibial-sided fixation of porcine flexor digitorum tendons using single-insertion interference screws, in a model of soft tissue ACL reconstruction. Two different screw types were used for comparison. Following screw insertion, the grafts were dissected free and underwent biomechanical testing in tension to failure. Control flexor digitorum tendons underwent the same biomechanical testing for comparison. Control soft tissue grafts exhibited significantly higher yield load, ultimate load, and stiffness (p < 0.001) in comparison to both groups of treated grafts, without evidence of significant macroscopic damage. Single insertion of interference screws for soft tissue graft fixation in ACL reconstruction weakens the biomechanical properties of the graft itself.