The effect of soft‐tissue graft fixation in anterior cruciate ligament reconstruction on graft‐tunnel motion under anterior tibial loading

Abstract

PURPOSE: To compare the motion of an anterior cruciate ligament (ACL) replacement graft within the femoral bone tunnel (graft- tunnel motion) when a soft-tissue graft is secured either by a titanium button and polyester tape (EndoButton fixation; Acufex, Smith & Nephew, Mansfield, MA) or by a biodegradable interference screw (Biointerference fixation; Endo-fix; Acufex, Smith & Nephew) An additional purpose was to evaluate the effect of the graft-tunnel motion on the kinematics of ACL-reconstructed knees and in situ force of the ACL replacement graft. TYPE OF STUDY: Biomechanical experiment using an in vitro animal model. METHODS: ACL reconstruction with a flexor tendon autograft was performed in 8 cadaveric knees of skeletally mature goats. The knee kinematics and the in situ force in the ACL replacement graft in response to anterior tibial loads were evaluated using the robotic/universal force-moment sensor testing system. The longitudinal and transverse graft-tunnel motion during anterior tibial loading was determined based on radiographic measurements parallel and perpendicular to the femoral bone tunnel, respectively. RESULTS: In response to an anterior tibial load of 100 N, the longitudinal graft-tunnel motion for EndoButton fixation and Biointerference fixation was 0.8 +/- 0.4 mm and 0.2 +/- 0.1 mm, respectively (P <.05), whereas the transverse graft-tunnel motion was 0.5 +/- 0.2 mm and 0.1 +/- 0.1 mm, respectively (P <.05). Furthermore, the anterior tibial translation for EndoButton fixation (5.3 +/- 1.2 mm) was also significantly larger than that for Biointerference fixation (4.2 +/- 0.9 mm) (P <.05). With both fixations, however, no significant difference between the in situ forces in the ACL replacement graft and that in the intact ACL could be detected. CONCLUSIONS: EndoButton fixation of a soft-tissue graft via an elastic material resulted in significantly larger graft-tunnel motion, and consequently, greater anterior knee laxity compared with more rigid fixation using an interference screw closer to the intra-articular entrance of the bone tunnel. In terms of force distribution, the ACL replacement graft in both fixations still functioned as a primary restraint to an anterior tibial load close to the intact ACL.