Understanding the Development of Cam-Type Deformity by FE Analysis of the Immature Proximal Femur

Abstract

Cam impingement appears to be an important factor in the development of early osteoarthritis (OA) of the hip. A Cam is generally diagnosed in young and active adults, already at the age of thirteen. Therefore, it has been suggested that excessive femoral loading during skeletal development might trigger the abnormal morphology. The goal of this research is to understand how the deformity develops. A finite element analysis is conducted to predict the stress distribution in the immature proximal femur under different loading conditions. Furthermore, the influence of the orientation of the epiphyseal plate is studied, as a Cam-type deformity is highly associated with an abnormal epiphyseal extension on the anterosuperior region. Previous studies suggested that octahedral shear stress promotes growth, while hydrostatic compressive stress inhibits growth. These mechanobiological principals are implemented to predict the bone growth rate. The position and the shape of the growth plate, as well as the loading direction highly influence the stress distribution in the proximal femur and growth plate. A medial directed load causes high compression stress in the growth cartilage in the lateral region. Endochondral growth is inhibited, which could result in a deflection of the growth plate, observed in Cam patients as epiphyseal extension. High regional stresses and osteogenic index appear in the epiphysis at the anterosuperior region when a convex growth plate is modeled. These results would support the theory that a Cam-type deformity might not be a result of endochondral growth, but the higher stresses demand local remodeling and apposition. Incorporating dynamic loading and tissue adaptation is needed to further understand how mechanical stimuli effects the epiphyseal growth and to predict morphological changes over time. Once one understands the etiological factors of cam impingement, the disorder can be treated at an early stage and the development into early osteoarthritis might be prevented.