Central versus peripheral tibial screw placement in hamstring anterior cruciate ligament reconstruction: in vitro biomechanics.

Purpose: To determine whether a cone-shaped interference screw positioned centrally during tibial fixation in hamstring anterior cruciate ligament (ACL) reconstruction was equal to or better than a peripheral position in terms of stiffness, yield load, ultimate load, and mode of failure.

Type Of Study: Randomized matched-pair biomechanical pullout study.

Methods: One of each of 7 matched pairs of human cadaveric tendon in porcine tibia with titanium cone-shaped screws were randomly allocated to either the peripheral or central group. Bone tunnels were drilled 45 degrees to the long axis of the tibia, akin to standard ACL reconstruction. Tunnel diameter was matched to tendon diameter and a screw 1 mm larger than tunnel diameter was inserted. A Universal Materials Testing Machine (Hounsfield Testing Equipment, Horsham, PA) was used to pull in the line of the tendon. Tendons were inspected after construct disassembly.

Results: The central screw configuration showed significantly higher stiffness (P = .0085), yield load (P = .0135), and ultimate load (P = .0075). The mode of failure in the peripheral screw position was slippage at the screw-tendon interface in all cases. In the central group, 87.5% of cases had a breakage in the tendon and 12.5% had slippage at the tendon-bone interface.

Conclusions: Central interference screw fixation of soft-tissue ACL reconstruction offers superior fixation strength and stiffness in single pullout mode when compared with peripheral interference screw fixation. Failure in the central group was mostly by tendon breakage, suggesting that a larger difference may be exhibited by the central over the peripheral fixation than demonstrated in this study.

Clinical Relevance: Central interference screw fixation compared with peripheral fixation may allow greater confidence in early rehabilitation and reduced clinical failure rates in the long term.