The fixation strength of a novel ACL soft-tissue graft fixation device compared with conventional interference screws: a biomechanical study in vitro

Anterior cruciate ligament reconstruction using autologous hamstring tendons is an established surgical procedure but some grafts fail due to poor fixation. This study compared the fixation of a new ACL graft fixation device (the EZ KneeSpan) to conventional soft-tissue threaded titanium interference screws (IS). The EZ device was designed to provide secure fixation while avoiding soft-tissue graft damage associated with use of an IS. Eight paired fresh-frozen cadaveric human knees and bovine digital extensor tendons were used. Two tunnels were placed in each tibia and femur, and grafts were fixed using the EZ device and the IS in each bone. Cyclic tensile loading and pull-out testing measured graft slippage (mm) and ultimate strength (N) of the fixation. The results were compared using the non-parametric Wilcoxon signed-rank test. Graft slippage after cyclic loading was significantly lower in the EZ group at 2.4 ± 0.1 mm versus 9.5 ± 6.2 mm for the IS group in the femur and 3.3 ± 1.4 mm versus 17.7 ± 13.6 mm in the tibia. The mean ultimate load for the femoral EZ group was significantly higher than the IS group (769 ± 223 N versus 468 ± 60 N), but they did not differ significantly in the tibia (518 ± 48 N versus 546 ± 139 N). Our results indicate that with the EZ device the initial fixation of cyclically loaded hamstring grafts could be superior to that with an IS. The EZ KneeSpan device also had similar tibial and higher femoral ultimate fixation strength than an IS.