Relation between increase in length of hip axis in older women between 1950s and 1990s and increase in age specific rates of hip fracture.

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 fractures during those years. Retrospective assessment of anteroposterior x ray films of the pelvis. Radiology department of a rheumatology hospital, New Zealand. Two cohorts of women aged > 60 (mean 70) who were x rayed on the same apparatus in either the 1950s or the 1990s. Length of hip axis (distance from the medial 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 femoral neck (see figure). 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 more recent x ray films, indicating that these findings are not due to an unrecognised change in radiographic technique. An increase 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 the increase in the age adjusted rate of hip fractures during those years.