A biomechanical comparison of the Delta screw and RetroScrew tibial fixation on initial intra-articular graft tension

Purpose: The purpose of this study is to determine the effect of bioabsorbable interference screw (BIS) tibial fixation with the Delta screw (antegrade) and RetroScrew (retrograde) on initial (time zero) intra-articular graft tension in soft tissue anterior cruciate ligament (ACL) reconstruction in a cadaveric model. Methods: Ten matched pairs of cadaveric tibias received one of two tibial fixation constructs using quadrupled hamstring grafts, Delta screw (antegrade) or the RetroScrew (retrograde). Each specimen was mounted to the materials testing device with the displacement force vector in line with the tibial tunnel. The construct was pre-tensioned (10-30 N, 0.1 Hz, 10 cycles), a baseline tension of 25 N was introduced, and the change in intra-articular graft tension before and after screw insertion was recorded. Results: Segmental (proximal, middle, distal) BMD was utilized to assess BMD using quantitative computed tomography (qCT). The Delta screw had a higher maximum insertion torque (P = 0.03) and exhibited a larger increase in intra-articular graft tension as compared to the RetroScrew (38.3 ± 17.9 N, 7.6 N ± 14.4, P = 0.004), respectively. There were no significant correlations between intra-articular graft tension increase to maximum insertion torque (P = NS) or corresponding segmental BMD (P = NS). Conclusions: Delta screw tibial fixation (antegrade) in soft tissue ACL reconstruction significantly increases the initial intra-articular graft tension as compared to RetroScrew screw fixation (retrograde) in this cadaveric model. Delta screw (antegrade) tibial fixation may increase initial quadrupled hamstring graft intra-articular tension with currently accepted insertion techniques.