Tunnel Widening after Anterior Cruciate Ligament Reconstruction: An Experimental Study in Sheep

Background A common clinical concern after anterior cruciate ligament reconstruction is the expansion of the bone tunnels as seen radiographically. The etiology and clinical relevance of this phenomenon remain unclear. Hypothesis Tunnel widening results in an increased anteroposterior translation, and there are specific histologic changes due to osteoclastic bone resorption associated with this phenomenon. Study Design Controlled laboratory study. Methods Thirty sheep (age, 4 months) underwent an anterior cruciate ligament reconstruction using a soft tissue graft. Graft fixation was achieved using the EndoButton and Suture Washer. Six animals each were sacrificed at 0, 3, 6, 12, and 24 weeks after surgery. Each anterior cruciate ligament–reconstructed knee was examined by computed tomography. Anteroposterior translation was determined using a universal force-moment sensor robot. The bone surrounding the tunnel was evaluated histologically. Results The prevalence of tunnel enlargement on the femoral side was 77.3%. Animals with tunnel widening did not demonstrate increased anteroposterior translation. Widening of the femoral tunnel was significantly associated with a higher stiffness of the graft (P