Knee joint model for anterior cruciate ligament reconstruction

Tearing of the anterior cruciate ligament (ACL) is a common knee injury, and is frequently treated through ACL reconstruction. However, sequelae such as tunnel enlargement and tibia fracture have been reported. The creation of bone tunnels or implantation of interference devices may interrupt the normal loading transmission and potentially contribute to long-term sequelae. This chapter aims to (1) develop a three-dimensional finite element (FE) model of the human knee joint with ACL reconstructions; (2) quantify the change of strain energy density (SED) distribution induced by the tunnel creation and interference screw; and (3) investigate the influence of screw material on the SED changes in the tibia. The bone SED distribution was derived from the validated FE model under compressive loading. The numerical results confirmed that the bone SED distribution and stress orientation changed after surgery. These changes occurred around the bone tunnel, and could produce abnormal bone remodeling. The consequential bone resorption and micro-damage may serve as a predisposing factor for tunnel enlargement and osteoarthritis. The material property of the screw could also influence the postoperative SED distribution in the tibia. On the premise of achieving sufficient fixation strength, using a screw with a modulus similar to the bone could decrease the risk of stress shielding. These findings together with histology factors could help us to understand the pathomechanism of the sequelae, and help to improve surgical techniques.