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

Introduction: 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.

Hypothesis: The study hypothesis was that all four devices show ≥450N pull-out strength with comparable biomechanical breakage characteristics.

Material And Methods: 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.

Results: 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.

Discussion: In this in-vitro study, the Translig fixation device showed better pull-out strength than the other three devices tested.

Type Of Study And Level Of Evidence: Comparative laboratory study. Level II.