Knee Joint Biomechanics after Anterior Cruciate Ligament Reconstruction
Anterior cruciate ligament (ACL) is an important stabilizer of the knee joint. After ACL rupture, the knee joint has difficulty maintaining its stability; thus the patient often has to receive an ACL-reconstructive surgery to regain the knee joint functions. Unfortunately, traditional transtibial surgical techniques could not fully restore the normal knee joint kinematics during daily activities. Moreover, a higher rate of osteoarthritis was found from the ACL-reconstructed knees compared to the knees without a history of ACL-injuries. The reason for the increased risk of knee osteoarthritis is still unclear, and the pathologies due to abnormal knee joint kinematics remain controversial. The dissertation was to delineate the knee joint motion and loading after ACL-reconstruction. Thirty patients who received ACL-reconstructive surgeries using the traditional transtibial technique and 14 using the recently developed anteromedial portal technique were recruited from the same center (OrthoCarolina). Twenty healthy subjects without history of knee injuries were recruited as the control group. Human motion data and ground reaction force data were collected during level walking and downstairs pivoting using an optical motion capture system. Three-dimensional (3D) knee joint motions were determined from redundant markers using an optimization approach. The 3D knee joint moments and forces were calculated from motion data, ground reaction data by using an inverse dynamics model of the lower extremity. A finite element model was created, and the distributions of stress/strain within articular cartilage under physiological loading were estimated. The results from two groups of patients using different reconstruction techniques were compared.In the transtibial group, excessive internal tibial rotation (2º on average during stance phase), varus rotation and anterior femur translation (swing phase) were observed in the ACL-reconstructed knees when compared to the control group during level walking. The 3D knee joint motion following ACL-reconstruction was found to be influenced by the leg dominance. The motion and load in the uninjured contralateral knee were also affected. During downstairs pivoting, the normal varus rotation and adduction moment were not fully restored by the transtibial technique. Overall, the anteromedial portal technique improved the postsurgical knee joint kinematics by reducing the offsets in the internal tibial rotation, varus rotation and anterior femur translation during level walking. It also improved the adduction moment during downstairs pivoting. At the same time, the anteromedial portal technique may cause a flexion/extension deficit during the stance phase of walking. Results of finite element analysis demonstrated higher pressures within the medial femoral cartilage during the stance phase of walking; it also demonstrated that there is an increased knee joint laxity after ACL-reconstruction. The anteromedial portal technique was overall better than the traditional transtibial technique in respect to postsurgical knee joint compressive loading and contact pressure. The study provides evidence of the possibility by using anatomical single-bundle ACL-reconstruction technique to fight the knee joint osteoarthritis after ligament injury.