Design modification of the Van Nes prosthesis: A study of anatomical and prosthetic joint motion

Congenital shortening of the femur (proximal femoral focal deficiency) is a rare condition sometimes treated by knee fusion and foot rotation through 180 degrees (Van Nes rotational osteotomy). This study examined the rotated foot and prosthetic knee joint design to improve function during walking and playing. Two subjects used both hinge-like motion, corresponding to the talocrural axis in normals, and twisted motion about a joint axis approximately 45 degrees from the hinge-like axis, different from the subtalar axis in normals. Hinge-like motion was considered optimal for controlling movements of the prosthetic knee joint. Subjects also reached greater maximum flexion angles using this motion. A mechanical analysis of the prosthetic hinge joint design led to design recommendations, which have laid groundwork for prosthesis design development. A method for prosthesis independent Van Nes functional analysis was developed in this work and insight into rotated ankle joint and prosthetic joint function were contributed.