Prediction of the femoral neck-shaft angle from the length of the femoral neck.

A total of 171 adult South Indian femora, devoid of gross pathology, are used to measure the neck-shaft angle, length of the neck, intertrochanteric apical axis length, maximum vertical diameter of the head, kinematic radius, and maximum femoral length. The neck-shaft angle ranges from 120 degrees to 136 degrees with a mean of 126.7 degrees and no significant side difference. The angle significantly and positively correlates with neck length, intertrochanteric apical axis length, kinematic radius, and minimum femoral length (P < 0.001) but not with the vertical diameter of the head. Regression equations for the neck-shaft angle against the correlated parameters are derived but only that against the length of the neck is strongly significant. From those correlations, 1) the neck-shaft angle can be estimated from a proximal femoral fragment, and 2) the required size of the length of the neck can be determined to design prostheses for the restoration of normal neck-shaft angle. Further, any estimated defective angle can be of help for forensic identification of an individual with pathological changes leading to an abnormal gait.