Geometric measurements of the proximal femur in UK women: Secular increase between the late 1950s and early 1990s

The aim of this study was to determine whether hip axis or femoral length has increased in women in the United Kingdom between the late 1950s and early 1990s. Such an observation would be of interest as it might explain the rise in age-specific incidence of hip fracture observed during these years. We studied two sets of antero-posterior pelvic radiographs of women aged 55-69 years taken during the course of population-based studies in the UK, one in 1958-60 and the other in 1989-91. One observer (S.G.) recorded the following measurements at the right hip: hip axis length (HAL), femoral length (FL) and femoral width (FW). Two summary ratios, HAL/FW and FL/FW were calculated to allow for differences in radiographic technique. HAL, FL and FW were greater in the 1989-91 films compared with those taken in 1958-60. Both HAL and FL expressed as a ratio to FW were also greater in the later films. FL/FW increased by 4.5% (p<0.05); HAL/FW increased by 2.3%, though this was not statistically significant. We conclude that there has been a small apparent change in geometric measurements of the hip during the past 36 years. Cautious extrapolation suggests that such a change may explain up to one third of the increase in incidence of hip fracture observed during this period.