Tunnel Widening after Anterior Cruciate Ligament Reconstruction

Abstract

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 <. 05) and hypertrophy of the graft throughout the remodeling process. The histologic evaluation of the bone tunnel walls demonstrated an increase of bone volume in animals with tunnel enlargement. No statistically significant correlation could be found between the number of osteoclasts and the presence of tunnel widening. Conclusion In this large animal model of anterior cruciate ligament reconstruction, animals with significant tunnel widening did not suffer increased anteroposterior translation. Tunnel widening was associated with a high stiffness of the graft, graft hypertrophy, and an increase in bone volume of the tunnel wall. Clinical Relevance The present data correspond to the current opinion in humans that tunnel widening is not associated with knee instability. Further research is needed to understand the role of graft stiffness, graft hypertrophy, and the increase in bone volume in this phenomenon.