Proximal femoral fracture. Range of hip motion as a predictor of fracture type.

A cadaveric study has shown that the femoral neck impinges on the posterior part of the acetabulum at an average of 54.5° external rotation and that an intracapsular fracture can be reproduced by an impact load onto the greater trochanter with the hip in external rotation. A clinical study of hip rotation of the contralateral uninjured hip in 100 patients after proximal femoral fracture was done to compare the degree of external rotation between extracapsular and intracapsular fracture. The mean value for intracapsular fracture was 62.1° and for extracapsular fracture was 48.9°. A retrieval study of the femoral head and neck from patients undergoing hip hemiarthroplasty for intracapsular fracture showed a consistent pattern of fracture with posterior comminution suggesting neck impingement. Previous work has suggested that an intracapsular fracture occurs during a fall when external hip rotation thrusts the femoral neck against the posterior margin of the acetabulum. The current investigation would support this hypothesis and suggests that the natural degree of external hip rotation is a predictor of fracture type.