Basic concepts of femoral neck anteversion: comparison of two definitions.

Femoral neck anteversion is determined by the neck, shaft and knee axes. It is commonly assumed that the neck axis is a straight line connecting the centre of the femoral head, the centre of the femoral neck and the axis of the femoral shaft. However, the line through the centre of the femoral head and neck crosses anterior to the axis of the femoral shaft. A distinction has therefore to be made between two principal different definitions of anteversion, denoted ANTEV 1 and ANTEV 2 in this paper, depending on the precise definition of the neck axis. Previous studies have indicated substantial differences between these definitions. The present study, using precise measuring methods, shows that the definitions have a systematic but small spread of differences. The large individual variation previously found between the two definitions is therefore caused mainly by the measuring methods and to a lesser extent by real anatomical variations.