Effect of femoral tunnel angle on tunnel enlargement in anterior cruciate ligament reconstructions

Introduction: The aims of this study were to explore whether the angle of the femoral tunnel had effect on the contact pressure of the graft in the femoral tunnel and to find the best femoral tunnel with the aim of minimizing bone tunnel enlargement after anterior cruciate ligament (ACL) reconstruction. Materials and methods: A three-dimensional (3D) finite element (FE) model of a healthy human knee which comprised proximal tibia, distal femur, ligaments, menisci and articular cartilages was developed. Besides, five FE models of femoral tunnels which were 10°, 20°, 25°, 30° and 40° relative to the midcoronal plane respectively and each FE model of tibial tunnel and Ligament Advanced Reinforcement System (LARS) were constructed. A load of 40N was applied to the quadriceps and each load of 10N was applied to the biceps femoris and semitendinosus tendons of the FE model. The contact pressures of the simulated graft in the femoral tunnel wall were measured at 0°, 30°, 60°, 90° and 120° of knee flexion. Results: The contact pressure at anterior portion of 40° femoral tunnel was significantly higher than those of 10°, 20°, 25° and 30° femoral tunnels. The contact pressure at posterior portion of 10° femoral tunnel was significantly higher than those of the other four tunnels. The contact pressure at posterior portion of 20° femoral tunnel was higher than that of 25° femoral tunnels. The contact pressure at anterior portion of 30° femoral tunnel was significantly higher than that of 25° femoral tunnel. Conclusion: The results obtained showed that the femoral tunnel angle had noticeable effect on the contact pressure in the femoral tunnel which could lead to femoral tunnel enlargement and the 25° femoral tunnel was the best femoral tunnel minimizing the femoral tunnel enlargement after ACL reconstruction.