Anterior Cruciate Ligament Reconstruction And Cartilage Contact Forces-A3D Computational Simulation

The anterior cruciate ligament(ACL) originates from a depressed area anterolateral to the anterior tibial spine, inserts on the medial wall of the lateral femoral condyle. It is the primary restraint to the anterior tibial displacement and internal tibial rotation. The exact incidence of anterior cruciate ligament injuries is unknown; however, it has been estimated that 200,000 are torn each year, and 100,000 anterior cruciate ligament reconstructions are done each year in the United State. The classic history of anterior cruciate ligament injury begins with a noncontact deceleration, jumping, or cutting action. The patient often describes the knee as having been hyperextended or popping out of joint and then reducing. A pop was frequently heard or felt. The Lachman test is the most sensitive test for anterior cruciate ligament injuries(95% sensitivity). Increased extrusion relative to the contralateral knee and absence of a firm end point suggest an injury to the anterior cruciate ligament. The pivot shift test and KT- 1000/2000 can assist in the diagnosis while MRI is the most helpful diagnostic radiographic technique. Anterior cruciate ligament reconstruction has been routinely performed to treat patients with a ruptured ACL while numerous studies have reported that contemporary single-bundle ACL reconstruction is efficient to restore knee stability under an anterior tibial load, many recent studies have reported prevalent radiographic osteoarthritis(OA) 10 years after ACL reconstruction. Understanding he causative mechanisms of OA development after ACL reconstruction is critical for improvement of the surgery to prevent long-term joint degeneration. Mechanical factors including abnormal kinematics and consequent abnormal loading within the joint often initiate knee cartilage degeneration. In-vivo patient study also demonstrated that contemporary ACL reconstruction could cause higher cartilage contact deformation compared to the uninjured contralateral side. Several in-vitro cadaveric studies have indicated that single-bundle ACL reconstructions restored knee stability with abnormal graft forces and higher cartilage contact pressure. However, due to the difficulties of experimental measurement technology, the intrinsic biomechanics of the knee after ACL reconstruction, including the graft forces and articular contact forces in response to various external conditions, is still not well understood. Therefore, the objective ofthis study is to investigate the effect of graft position on the biomechanics of the knee after single-bundle ACL reconstruction. This experiment can be divided into three parts:1) The effect of two contemporary surgical techniques(anatomic ACL reconstruction and transtibial technique) on the cartilage contact force after single-bundle ACL reconstruction. Use the 3D computational model to simulate these two techniques. Two fixation angles were simulated for each technique. Biomechanics of the knee was investigated in intact, anterior cruciate ligament deficient and reconstructed conditions when the knee was subjected to 134 N anterior load and400 N quadriceps load. Anterior tibial translation, internal tibial rotation, graft force,medial and lateral cartilage contact forces were calculated. This study suggests that neither the anatomic nor the transtibial reconstruction can consistently restore normal knee biomechanics at different flexion angles. The anatomic reconstruction may better restore anteroposterior stability and contact force with the graft fixed at 0°. The transtibial technique may better restore knee anteroposterior stability and articular contact force with the graft fixed at 30° of flexion.2) The effect of femoral graft position on the knee biomechanics after ACL reconstruction. Use the computational model to simulate anatomic tunnels with both centers located on the center of ACL insertions on the tibia and the femur. We simulated different graft positions by dividing both tunnel surfaces into 4 quadrants.Then we chose the outside one-third points on four dividing lines and the center of both surfaces to represent different graft positions in both tunnels. All grafts were fixed at 30 degree of flexion. Biomechanics of the knee was investigated in intact,anterior cruciate ligament deficient and reconstructed conditions when the knee was subjected to 134 N anterior load and 400 N quadriceps load. Anterior tibial translation,graft forces, medial and lateral cartilage contact forces were calculated. Changing the graft position in the femoral tunnel resulted in different trends of ATT and graft force during flexion under anterior load. Under the quadriceps load, posterior and distal positions resulted in higher cartilage contact force at full extension. The proximal and center positions resulted in similar cartilage contact force as intact knee.3) The effect of tibial graft positioning on cartilage contact forces of the knee after ACL reconstruction. While numerous studies have investigated the effect of femoral graft placement on knee joint biomechanics after ACL reconstruction, fewstudies have reported on the effect of tibial graft placement on knee joint function.The model was used to simulate single-bundle ACL reconstruction. The graft was placed at the center of ACL footprint on the femur, but at three different positions on the tibia –anteromedial, center and posterolateral positions of the ACL footprint.Biomechanics of the knee was investigated in intact, anterior cruciate ligament deficient and reconstructed conditions when the knee was subjected to 134 N anterior load and 800 N quadriceps load. The results demonstrated that the posterior placement of the graft on the tibia resulted in lower graft forces in the anterior-posterior direction but higher forces in the proximal-distal direction compared to other graft locations.Consequently, the contact forces at the medial and lateral compartments were increased.In conclusion, neither anatomic ACL reconstruction nor transtibial technique can restore normal cartilage contact force. Anteroposterior position of the graft on the femur has significant effect on the knee stability, graft force, and cartilage contact force after ACL reconstruction. Under the quadriceps load, the posterior and distal positions results in larger medial and lateral carttilage contact forces at full extension.The center and proximal positions can better restre normal cartilage contact forces at both the medial and the lateral compartment. The tibial graft position could affect the force distribution on different directions. Posterior placement of the graft on the tibia results in larger meidial and lateral cartilage contact force.