Three femoral fixation devices for anterior cruciate ligament reconstruction: comparison of fixation on the lateral cortex versus the anterior cortex.

Purpose: To evaluate the biomechanical properties of 3 anterior cruciate ligament (ACL) reconstruction femoral fixation devices in a porcine model with implantation on both the lateral femoral cortex and the anterior femoral cortex.

Methods: ACL reconstructions with an 8-mm porcine tendon graft were performed on 48 porcine femurs with the EndoButton CL (Smith & Nephew, Andover, MA), ToggleLoc with ZipLoop technology (Biomet Sports Medicine, Warsaw, IN), or EZLoc (Biomet Sports Medicine). In 8 specimens for each implant, the femoral tunnel was drilled from the 10:30 surgical position out the lateral cortex. In another 8 specimens for each implant, the tunnel was drilled from the 10:30 position to a standardized anterior femoral surface. Cyclic testing was performed on an MTS testing machine (MTS, Eden Prairie, MN) from 50 N to 450 N for 2,000 cycles, followed by load-to-failure testing in specimens that survived. The cortical thickness and location of the implant exit were recorded.

Results: In the lateral femur group, 0 of the EZLoc devices, 2 of the ToggleLoc devices, and 3 of the EndoButtons completed cyclic testing. In the anterior femur group, 1 of the EZLoc devices, 5 of the ToggleLoc devices, and 5 of the EndoButtons completed cyclic testing (P = .012). In the anterior femur group, the ToggleLoc exhibited higher 2,000-cycle elongation (5.46 +/- 1 mm) than the EndoButton (3.55 +/- 0.6 mm) (P = .005). The EndoButton showed a higher first failure load (1,190.9 +/- 150.0 N) than the ToggleLoc (912.6 +/- 82.4 N) (P = .007). The anterior cortex (1.4 mm) was thinner than the lateral cortex (1.7 mm) (P = .0002).

Conclusions: The EndoButton provided the strongest ACL femoral fixation with significantly less graft-implant elongation and significantly higher failure loads. It was also shown in a porcine model that implants on the anterior cortical surface perform better than those on the lateral surface. Increased cortical thickness, in the range tested, was not associated with improved implant performance in the porcine model.

Clinical Relevance: The EndoButton provided the best ACL femoral fixation of the devices tested.