The aim of this study is to predict the shape and orientation of the femoral growth plate under specific loading conditions. Mechanical loads affect not only the mechanical properties of long bones but also the rate and the direction of their growth. Subsequently, loading influences the shape and ultimate functionality of these bones and their corresponding joints. Mechanical stress is a key factor in local regulation of the growth plate, which is responsible for longitudinal growth via endochondral ossification. Bone deformities of femur occur in children who experience abnormal loading on their bones during daily activities, such as in developmental dysplasia of the hip, cerebral palsy, or femoroacetabular impingement. Here we propose that the growth plate aligns in a direction that minimizes shear stress on its surface.

An algorithm was developed to determine orientation of the resulting growth plate under various loading conditions. The geometry of the femur was created from medical images of a 7-year-old. The algorithm determined a surface along the principle stress directions, for which in-plane shear stress was minimized. A parametric study was performed considering various application angles of the hip contact force. The anatomical reference values were measured in the models and compared with clinical data. It was shown that the growth plate orientation changed significantly for 15 degrees changes in anterior/posterior and laterally/medially placement of the joint load. This has implications for understanding changes in proximal femoral bone morphology in conditions such as anteversion, coxa valga/vara, and cam morphology, which are caused by altered growth.