Effects of current and discontinued estrogen replacement therapy on hip structural geometry: The study of osteoporotic fractures

It is assumed that estrogen influences bone strength and risk of fractures by affecting bone mineral density (BMD). However, estrogen may influence th e mechanical strength of bones by altering the structural geometry in ways that may not be apparent in the density. Repeated dual energy X-ray absorpt iometry (DXA) hip scan data were analyzed for bone density and structural g eometry in elderly women participating in the Study of Osteoporotic Fractur es (SOF). Scans were studied with a hip structural analysis program for the effects of estrogen replacement therapy (ERT) on BMD and structural geomet ry. Of the 3964 women with ERT-use data, 588 used ERT at both the start and end of the similar to3.5-year study, 1203 had past use which was discontin ued by clinic visit 4, and 2163 women had never used ERT. All groups lost B MD at the femoral neck, but the reduced BMD among users of ERT was entirely due to subperiosteal expansion and not bone loss, whereas both bone loss a nd expansion occurred in past or nonusers. BMD increased 0.8%/year at the f emoral shaft among ERT users but decreased 0.8%/year among nonusers. Sectio n moduli increased at both the neck and shaft among ERT users but remained unchanged in past and nonusers. Current, but not past, use of estrogen ther apy in elderly women seems to increase mechanical strength of the proximal femur by improving its geometric properties. These effects are not evident from changes in femoral neck BMD.