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

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.