To determine whether HRT modifies the:
(1) prevalence of OA in peri-menopausal and post-menopausal women.
(2) disease progression in peri-menopausal and post-menopausal women with established OA.

If a beneficial effect is found, to determine whether there is:
(1) an optimum duration of exposure to HRT and
(2) whether there is an age group where exposure to HRT has a maximal effect.