Illustrating the effect of subject-specific muscle insertions on joint and muscle mechanics in a shoulder joint model

Subject-specific shoulder joint models can be used as clinical tools in pre-surgery planning as well as post-surgery rehabilitation domains. We performed a comparison of muscle mechanics between shoulder joint models that have generic and subject-specific muscle insertions. Ten healthy cadaveric shoulder scans were used in this study. Subject-specific muscle origins and insertions were determined on scapula and humerus using a statistical shape model (SSM)-based prediction algorithm. Simulations were performed using Newcastle Shoulder Model (NSM) and joint mechanics were determined. For simulated abduction and scapular plane elevation motions, significant differences were found in joint contact forces, muscle forces and moment arms. Subject-specific insertions revealed a change in the muscle force balance strategies which can be an important factor during pre-surgical planning as well as post-surgical rehabilitation.