Context: Little is known of associations between hip geometry and skeletal regulators. This is important because geometry is both a determinant of hip function and resistance to fracture.

Objective: We aimed to determine the effects of sex hormone status and other candidate regulators on hip geometry and strength.

Subjects and Methods: A random sample of 351 women aged 67-79 had 2 to 4 hip DXA scans performed over 8-years of follow up. Hip structural analysis (HSA) software was used to measure subperiosteal diameter (PD) and d-lat (the distance from the center of mass to the lateral cortical margin) on three 5 mm thick cross-sectional regions: narrow neck (NN); intertrochanter (IT); and shaft (S). Section modulus (Z), BMD (g/cm²), and an index of bone mineral content (CSA) were calculated as estimators of bone strength. Serum analytes measured at baseline included: sex hormone binding globulin (SHBG), estradiol (E2), parathyroid hormone (PTH), creatinine, albumin, vitamin D metabolites, Glu- and Gla- osteocalcin (OC). A linear mixed model was used to model associations with predictor variables, including testing whether the predictors significantly modified the effect of aging.

Results: Aging was associated with increasing PD and d-lat and higher baseline SHBG significantly modified this effect, in the case of PD increasing the rates of change at the NN region by 19% for SHBG level 2 SD higher than population mean (P = 0.026). Higher baseline creatinine was independently associated with faster increase in PD and d-lat with aging (P < 0.041). Z declined faster with ageing if baseline PTH was higher and higher albumin had a contrary effect. Z was positively associated with free E2 and inversely associated with SHBG and Glu-osteocalcin.

Conclusion: These results show large effects of SHBG on the regulation of proximal femur expansion and bending resistance, probably acting as a surrogate for low bio-available estrogen. Potentially important effects for fracture resistance in old age were also revealed for parathyroid hormone, markers related to renal function and the nutritional markers albumin and under-carboxylated osteocalcin.