Variations in hip shape in individuals entering early old age

Purpose: Hip shape has been shown to vary in osteoarthritis and osteoporosis but there is little evidence for associations with other markers of health and disease. The purpose of this pilot study was to characterise hip shape in a sample of early old-age adults from the Medical Research Council National Survey of Health and Development (NSHD) and explore how it varies with anthropometric measures, bone mineral density (BMD) and sex. Methods: Using a pilot sample of 200 individuals in the NSHD birth cohort, all born in a single week in 1946, data included height, weight, body mass index (BMI), and hip bone mineral density (BMD) acquired at 60–64 years. Hip shape was described using a 68 point template on dual energy absorptiometry (DXA) images. Points were entered into a statistical shape model using the Shape software (University of Aberdeen), which identified the mean hip shape and independent modes of variation in the shape, using principal components analysis. Modes scores quantified as the deviation from the mean shape (mean = 0). The first 15 modes (M1-M15) described 86.8% of the total variation of shape within the model, in decreasing order. Modes 1–15 were included in further analysis. Modes scores were tested for normality using the Shapiro-Wilk test and the Mann-Whitney test was used to compare the median difference between males and females. Spearman’s rank correlation was used to investigate the association between potential predictive factors and shape modes. Results: The sample consisted of 90 males and 110 females with a median age of 63.6 (62.8–64.2) years and median BMI of 27.3 (24.5–30.5) kg/m2. Males were significantly taller and heavier than women. In this sample there were significant differences between the sexes in 6 of the 15 analysed modes. Comparisons of hip shape between males and females revealed a significant difference with males having a higher M1 (P=0.017) and M4 (P=0.004) scores, both of which were associated with flattening of the femoral head and presence of osteophytes, and lower M9 scores reflecting flattening of the femoral head and neck (P<0.0001; Fig. 1). M11 scores were associated with increased acetabular coverage and higher in females (P=0.0137). Associations between shape and height, weight, BMI and BMD varied greatly between men and women. In the hip, M1 was negatively correlated with height and BMD in women, but not men, whilst M9 was positively correlated with height and BMD in men, but not women. Modes 15 was correlated with weight and BMI in men. The only mode which showed significant correlations in both sexes was M5, though this was positively correlated with weight and BMI in women and Total hip BMD in men. Modes 9, 11 and 12 were all correlated with BMD in men. Conclusions: In this sample of adults entering early old-age, sex differences were observed in the width of the femoral neck, femoral neck/head curvature and migration of the femoral head. Correlations between hip shape, BMD and body size varied by sex. Greater BMD was associated with a more compact hip shape in women and being a taller man was associated with changes in the curvature of the femoral head and neck. Opens large image Figure 1 Difference in hip shape with positive (solid line) or negative (broken line) two standard deviation changes in mode score in modes 1, 4 & 9.