Differential effect of long-term oestrogen therapy on trabecular and cortical bone

The effect of long-term oestrogen therapy has been assessed in 40 oophorectomised women. Twenty-one of the women had received mestranol (mean 26 micrograms/day) and 19 received placebo tablets for a mean duration of 14 yr. A newly developed gamma-ray computed tomography (CT) scanner was used to measure trabecular and cortical bone separately in the distal radius. Bone density in the lumbar spine was measured using dual photon absorptiometry (DPA). Prevention against bone loss was demonstrated at all sites for the mestranol treated group (P less than 0.01). The deficit of radial trabecular bone (27%) was greater than that for radical cortical bone (14%). The deficit for the spine was intermediate (20%). One-year follow-up radial measurements showed a significant 1.2% increase (P less than 0.01) in cortical bone for the treated group. The DPA measurement was found to be best correlated (r = 0.80) with a mixed trabecular and cortical bone parameter in the radius. We conclude that the degree of bone loss at any site is dependent on the proportion of trabecular bone present.