Evaluation of Bone Plug and Soft Tissue Anterior Cruciate Ligament Graft Fixation Over Time Using Transverse Femoral Fixation in a Sheep Model

PURPOSE: To evaluate the mechanical role of bone-anterior cruciate ligament (ACL) graft junction in comparison with primary fixation of the graft. TYPE OF STUDY: Ex vivo controlled biomechanical study. METHODS: An ACL reconstruction was performed on 2 groups of 40 sheep each. The ACL graft was patellar tendon in group 1, and free tendon in group 2. Load-to-failure tests were performed at 1, 2, 3, and 6 months. Each group was divided into 2 subgroups: In subgroup A the femoral fixation devices were removed before testing and in subgroup B they were left in place. RESULTS: At 1 month, structural properties of subgroup 2A were significantly lower than other subgroups. Until the third month, structural properties of each subgroup were significantly lower than normal ACL. Grafts always failed at midsubstance, except for subgroup 2A at 1 month, which pulled out of the femoral tunnel. CONCLUSIONS: Bone plug incorporation was stronger than graft strength at 1 month whereas soft tissue tendon incorporation was not stronger than graft until 2 months. At 3 months, both groups failed at approximately 30% of the native ACL strength, and at 6 months, both groups were nearly equal in terms of load to failure and stiffness. CLINICAL RELEVANCE: High fixation strength and stiffness of ACL graft does not allow earlier return to sports activities.