Grafted Tendon Healing in Tibial Tunnel Is Inferior to Healing in Femoral Tunnel After Anterior Cruciate Ligament Reconstruction: A Histomorphometric Study in Rabbits

Abstract

This study aimed to test whether graft healing in the tibial tunnel was inferior to that in the femoral tunnel after anterior cruciate ligament (ACL) reconstruction in rabbits. Surgical reconstruction by use of the digital extensor tendon in the bone tunnel was performed in 18 rabbits. The rabbits were killed at weeks 2, 6, and 12 postoperatively, with 6 at each time point, for histologic examination. The transiently formed cartilaginous interface was gradually mineralized during re-establishment of direct tendon-to-bone integration, which was observed significantly less in the tibial tunnel than in the femoral tunnel (P < .05). The cell density of the graft was significantly lower in the tibial tunnel than that in the femoral tunnel at weeks 2 and 6 postoperatively (P < .05 for both). An increase in the immature type III collagen content was accompanied by a decrease in graft collagen fiber organization, with healing over time in both the femoral and tibial tunnels. The collagen fiber organization of the graft was significantly poorer in the tibial tunnel than that in the femoral tunnel at week 12 after surgery (P < .05). Grafted tendon healing in the tibial tunnel was inferior to that in the femoral tunnel at the tendon-to-bone interface and with regard to the grafted tendon within the bone tunnel after ACL reconstruction in rabbits. Future biopsy study is desirable to test whether this observation was valid clinically, which might provide a scientific basis for therapeutic targets to improve the outcome of ACL surgery.