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The attachment locations of anterior cruciate ligament (ACL) grafts during reconstruction have been reported to influence knee joint function. However, there are controversial opinions on femoral ACL attachment locations for restoring normal knee kinematics. The knee stability and ACL force by different ACL attachment locations could be predicted using the musculoskeletal model simulation. The objectives of this study are to develop a detailed musculoskeletal knee model and to quantify the effect of ACL graft attachment locations on knee kinematics and graft force. Five normal subjects walked at a self-selected speed, and motion data were captured. A detailed knee model including 14 ligaments was developed for dynamics simulation using cadaveric specimen data, which were previously published and are open to public access. The ACL bundles of the model were removed and replaced with ACL grafts to develop anatomical and isometric ACL-reconstructed knee models; the femoral anatomical footprint and isometric locations were used, respectively. After the knee models were embedded in a full-body template model from the AnyBody Managed Model Repository, the full-body musculoskeletal model was simulated using the measured gait data. The isometric reconstruction model had significantly large anterior translation and internal rotation than the intact and anatomical reconstruction model. The average differences between the isometric reconstruction and intact models were 4.5 mm and 3.0° for tibial anterior translation and internal rotation, respectively. The ACL tensional force in the isometric reconstruction model was significantly lower than that in the intact model. Anatomical reconstruction could closely restore the normal knee kinematics.

Chronic occupational lower limb injuries such as osteoarthritis require an understanding of mechanical loading conditions in joints during occupational activities. We aimed to develop a human musculoskeletal model and to estimate knee contact force and ground reaction force (GRF) simultaneously during walking and squatting. GRF and joint kinematics were obtained from a subject with electronic total knee replacement during walking and squatting. Force reaction elements were embedded in the knee and foot of a full-body musculoskeletal model. The joint kinematics and ground vertical force were applied to the musculoskeletal model to estimate ground shear force and knee contact force using an inverse dynamics-based optimization. Ground shear force and knee contact force could be estimated simultaneously with root mean square (RMS) error less than 1.6% body weight (BW) and 35% BW, respectively. Simultaneous estimations could be accurately conducted but the RMS error for the knee contact force increased by approximately 10% BW.