Pull-out strength of four tibial fixation devices used in anterior cruciate ligament reconstruction

In reconstructions of the anterior cruciate ligament (ACL), tibial fixation can be the weak point in the assembly during the early postoperative period. The present study sought to compare pull-out strength between four tibial fixation systems used in ACL reconstruction. The study hypothesis was that all four devices show ≥450N pull-out strength with comparable biomechanical breakage characteristics. An experimental study used a mechanical model to perform axial traction on a synthetic ligament (polypropylene cord folded in four) implanted in an artificial tibia (Sawbones Proximal Tibia # 1116-2: model: normal anatomy; solid foam; size: medium) using four tibial fixation systems: Ligafix® interference screw (SBM™); Bio-Intrafix® (Mitek™); Translig® (SBM™); RIGIDfix® (SBM™). For each system, four models were tested using an Instron 5566® traction machine, allowing 100mm/min stretching up to breakage. Study parameters comprised: pull-out strength, maximal whole assembly slippage, stiffness at breaking point, and type of break. Mean pull-out strength was 450±24N (range, 421–488N) for Ligafix®, 415±60N (327–454N) for Bio-Intrafix®, 539±66N (449–636N) for RigidFix and 1067±211N (736–1301N) for Translig®, and was significantly greater for Translig® than for the other devices (p=0.02), which did not significantly differ from one another. The expected maximal load of 450N was reached in 100% of cases with Translig® and RIGIDfix® and in 50% of cases with Bio-Intrafix® and Ligafix®. There were no significant differences regarding stiffness. Ligafix® showed significantly less slippage than the others (p=0.006), with breakage caused by the ligament sliding between bone and implant. In this in-vitro study, the Translig® fixation device showed better pull-out strength than the other three devices tested. Comparative laboratory study. Level II.