RELATION BETWEEN INCREASE IN LENGTH OF HIP AXIS IN OLDER WOMEN BETWEEN 1950S AND 1990S AND INCREASE IN AGE-SPECIFIC RATES OF HIP FRACTURE

Objective-To determine whether length of hip axis in elderly women has increased over the past 40 years and, if so, whether the increase may have contributed to the increase in the age adjusted rate of hip frac tures during those years. Design-Retrospective assessment of anteropos terior x ray films of the pelvis. Setting-Radiology department of a rh eumatology hospital, New Zealand. Patients-Two cohorts of women aged > 60 (mean 70) who were x rayed on the same apparatus in either the 1950 s or the 1990s. Main outcome-length of hip axis (distance from the med ial aspect of the pelvis to the lateral aspect of the femur along the axis of the femoral neck), length of femoral neck (length of hip axis excluding the femoral head and more medial structures), and width of f emoral neck (see figure). Results-Both the mean length of the hip axis and the mean length of the femoral neck were significantly greater in the women whose x ray films were taken in the 1990s than in those in the 1950s (124.0 mm (SE 1) v 130.5 (1), P=0.0002; 79.4 (1) v 84.9 (1), P<0.0001, respectively). The width of the femoral neck did not change , and the lengths expressed as ratios to width were greater in the mor e recent x ray films, indicating that these findings are not due to an unrecognised change in radiographic technique. Conclusions-An increas e in the length of the hip axis in elderly women in New Zealand during the past 40 years has occurred which is large enough to account for t he increase in the age adjusted rate of hip fractures during those yea rs.