Delta screw versus retroscrew tibial fixation for ACL reconstruction

Purpose The purpose of this study is to determine whether the RetroScrew tibial fixation system offers a biomechanical advantage over the Delta screw for anterior cruciate ligament (ACL) reconstruction in cadaveric tibias with low bone mineral density (BMD). Methods Ten matched pairs of osteoporotic cadaveric tibiae underwent simulated ACL reconstruction using quadrupled hamstring grafts with one of the two tibial fixation constructs. Group 1 was fixed with the Delta screw (DS; 35-mm antegrade biointerference screw), and group 2 was fixed with the RetroScrew system (RSS; 20-mm retrograde and 17-mm antegrade biointerference screws). Each construct was cyclically loaded (50-200 N, 1 Hz, 500 cycles) and subsequently loaded to failure (20 mm/s). Results All specimens were osteoporotic without significant segmental (proximal, middle, and distal) BMD differences between groups by quantitative computed tomography (P = n.s.). A trend was noted for more construct failures due to graft slippage in the DS group (n = 3) over the RSS group (n = 1). There were no significant differences in cyclic displacement (P = n.s.), maximum cyclic stiffness (P = n.s.), maximum load at failure (P = n.s.), or pullout stiffness (P = n.s.) between groups. Conclusions In an osteoporotic cadaveric model, there was no significant biomechanical advantage of the Retro- Screw system versus the Delta screw for tibial fixation in soft tissue graft ACL reconstruction. However, a trend toward lower graft fixation failure to cyclic loading was noted with the RetroScrew system.