Drill wobble - effect on femoral tunnel aperture during anterior cruciate ligament reconstruction

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.

The drill wobble effect: oversizing the femoral tunnel during ACL reconstruction

OBJECTIVES

In ACL reconstruction, autologous tendon graft can be attached to the femur, within a boney tunnel, using an Endobutton device. The ultimate aim being to achieve biological fixation and incorporation into the bone. Accurate bone tunnel diameter to match the tendon graft is vital to biologic incorporation and strength. The common technique of in sequence passing a guide wire, a cannulated 4.5 mm Endobutton drill, then a cannulated femoral socket drill causes the guidewire to lose cortical fixation and stability before the femoral socket drill is passed. The Objective of this study is to analyze this common technique of femoral socket creation and determine if it results in unintentionally oversizing the femoral socket due to femoral socket drill-wobble over a destabilised guide wire.

METHODS

12 cadaveric femoral pairs equally divided between two groups underwent femoral socket creation in one of the two following sequences. Group 1: Guidewire, 4.5 mm endobutton drill, 8 mm femoral socket drill. Group 2: Guidewire, 8 mm femoral socket drill, 4.5 mm endobutton drill. The created femoral tunnels apertures and calibres were measured and then compared for accuracy between the two groups.

RESULTS

Passing the 4.5 mm drill before the 8 mm socket drill results in oversized tunnel apertures and calibres when compared to passing an 8 mm socket drill after the 4.5 mm drill has been passed (p<0.0001).

CONCLUSION

To most precisely create an 8 mm femoral socket in ACL reconstruction, the 8 mm femoral socket reamer followed by the 4.5 mm should be passed over the guide wire to prevent guide wire destabilization and drill-wobble.