The relative contributions of menopause and aging to postmenopausal reduction in intervertebral disk height.

AIM: To evaluate, in a population of normal women, the effects of aging and menopause on the height of intervertebral discs by measuring the intervertebral disk space, between the 12th thoracic and 4th lumbar vertebrae, by dual-energy X-ray absorptiometry (DXA). MATERIALS AND METHODS: The study was conducted on 2455 consecutive women attending our Department, from whom 464 normal women were selected. The measurement was validated utilizing a spine phantom. RESULTS: The phantom mean intervertebral disk space was 0.44 cm, with a coefficient of variation of 1.4%. The coefficients of variation in premenopausal, early postmenopausal and elderly women were 2.2, 2.0 and 6.0%, respectively. Values of intervertebral disk space were stable from age 20 to 50 years, thereafter showing a significant (p < 0.05) decrease, negatively correlated with both age and years since menopause (p < 0.0001). In postmenopausal women younger than 60 years, a correlation (p = 0.042) was evident between intervertebral disk space and years since menopause, but no correlation was evident with age. In women over 60 years, no correlations were found between intervertebral disk space and either age or years since menopause. In three groups of age-matched women (47.5 +/- 1.5 years, n = 39 in each group), intervertebral disk space was significantly (p < 0.0001) lower in postmenopausal than in both premenopausal and perimenopausal women. CONCLUSION: The DXA measurement of intervertebral disk space is precise. After menopause, intervertebral disk space shows a progressive decrease that almost entirely occurs in the first 5 - 10 years since menopause, suggesting that the estrogen decrease may rapidly change connective tissue metabolism in the intervertebral disks.