We developed a three-dimensional finite element model of the shoulder glenohumeral joint after shoulder arthroplasty including humerus shaft, scapular, scapular cartilage and eight muscles, while each of the muscles was simulated with 50 spring elements. To reduce the element number and improve the analytical precision, we used mixed tetrahedral and hexahedral elements in the model. We then used the model to calculate the biomechanics of the shoulder glenohumeral joint after hemiarthroplasty during humeral external rotation. Results showed that the maximum joint reaction force was 374.72 N and the maximum contact stress was 6.573 MPa together with the contact areas at 40° external rotation. These might be one of the reasons for prosthetic disarticulation, and would provide theoretical bases to prosthetic design.
We developed a three-dimensional finite element model of development dysplasia of hip (DDH) of a patient. And then we performed virtual Bernese periacetabular osteotomy (PAO) by rotating the acetabular bone with different angle so as to increase femoral head coverage and distribute the contact pressure over the cartilage surface. Using finite element analysis method, we analyzed contact area, contact pressure, and von Mises stress in the acetabular cartilage to determine the effect of various rotation angle. We also built a normal hip joint model. Compared to the normal hip joint model, the DDH models showed stress concentration in the acetabular edge, and higher stress values. Compared to the DDH models, the post-PAO models showed decreases in the maximum values of von Mises stress and contact pressure while we increased the contact area. An optimal position could be achieved for the acetabulum that maximizes the contact area while minimizing the contact pressure and von Mises stress in the acetabular cartilage. These would provide theoretical bases to pre-operative planning.