Bone mass and structure at the hip in men and women over the age of 60 years

Bone mass and structure at the proximal femur are important predictors of h ip fracture. The aims of this study were to compare in a large sample of el derly men and women the precision of measurements of bone mass and structur e at multiple sites at the proximal femur, to examine their interrelationsh ips, to establish their relationships with age and body size, and to examin e criteria for defining geometric and architectural variables in bone struc ture. Women (n = 336) and men (n = 141) over the age of 60 years were studi ed cross-sectionally. Bone mineral density (BMD) and content (BMC) at the p roximal femur were measured in duplicate by dual-energy X-ray absorptiometr y (DXA). Shaft and total upper femur (hip) sites in addition to femoral nec k, Ward's triangle and trochanter were measured. Structural variables, meas ured from radiographs and from DXA images, including cortical thickness at calcar femorale, lateral cortex and mid-femur, width of the femur and medul la, Singh grade, hip and femoral axis length, femoral head and neck width a nd the center of mass of the femoral neck. BMD and BMC had high reproducibi lity and there were significant differences in reproducibility across sites . Among sites, total upper femur and shaft had the highest reproducibility. Duplicate measurements substantially improved reliability of the measureme nt and are recommended when the value is close to a diagnostic level or whe n it will be used to establish rates of change. Reproducibility of structur al variables was also high except for the lateral cortex, center of mass an d Singh grade. Variance due to measurement error did not change with either age or gender. Women were significantly different from men, after controll ing for differences in body size, in all variables except Singh grade and m edulla width. BMD and BMC were negatively related to age and positively to body size. Structural variables examined in relation to age and body size f ell into two categories. The first comprised variables that were not age-re lated but were body-size-related, suggesting that they could be classified as geometric variables. The second comprised variables that were both body- size-related and age-related, suggesting that they could be classified as a rchitectural variables. Using these criteria, calcar and lateral cortex wer e architectural variables, whereas shaft width, hip and femoral axis length , femoral head and neck width, and center of mass were geometric in both me n and women. In women, shaft cortex width and medulla width were age-relate d, whereas in men they were not. Singh grade showed no consistent pattern w ith age or body size in women and men.