Femoral Shape Analysis by Bi-plane X-ray Photogrammetry : Graphic Display and Calculation of Anteversion Angle and Neck-shaft Angle

Abstract

For the osteotomy on hip joint diseases caused by abnormality of the shape of bones, an accurate 3-dimensional femoral shape must be recognized before operation. It was been reported by the present authors that spinal shape is sufficiently analyzed by a developed system based on bi-plane photogrammetry. This paper describe an application of the system to the femoral shape analysis. The shaft axis, the neck axis, the head center of femur and the radius of the head are reconstructed 3-dimensionally using the vector anlysis of plane and line, and the least square approximation method. The obtained axes and head are graphically displayed on the screen of a personal computer through the perspective transformation. The shape parameters usually used in clinic, such as the anteversion angle and the neck-shaft angle, are also calculated by the present method. Result obtained by this system is compared with that by photographical measurement of exposed femurs, then the present method is reduced to have higher accuracy than Kai's method currently used.