Predicting the position of the femoral head center.

To find an accurate method to predict the position of the normal head center in severely deformed hips without a contralateral reference, we studied the relationships between the head center and dimensions of the normal proximal femur using cadaveric specimens. From a large anatomic collection, 32 cadaveric femora with neck-shaft angles ranging from 115 to 146 were selected. The two parameters with the greatest correlation with the height of the femoral head were the height of the neck isthmus (r = .932) and the lowest point of neck saddle (r = .790). Medial head offset was most strongly correlated with the offset of the neck isthmus (r = .945) and the distance from the medullary axis to the outer borders of the medial cortex at the +30% level (r = .861). As a rule of thumb, the height of the head center can be predicted as the height of the midpoint of the neck isthmus plus 10 mm or as the height of the neck saddle with an accuracy of +/-5.1 mm and +/-8.3 mm. The offset of the head center can be predicted as the offset of the midpoint of the neck isthmus plus 15 mm or as the distance from the medullary axis to the medial cortex at the +30% level plus 15 mm with an accuracy of +/-4.6 mm and +/-6.3 mm.