Vertebral morphometric X-ray absorptiometry (MXA): relationship with bone mineral density in perimenopausal women

To evaluate the relationship between vertebral morphometry and vertebral bone mineral density (BMD) in a population of perimenopausal women.

We studied 120 healthy women (mean age (S.D.) 53.4 (8.3) years) referred for baseline bone densitometry around the menopause. Morphometric X-ray absorptiometry (MXA) was performed using a Hologic QDR 4500 A apparatus and assessed the anterior, mid and posterior heights of the third lumbar vertebra (L3). The anterior to posterior height ratio (AH/PH index) and the mid to posterior height ratio (MH/PH index) were calculated. Simultaneously, BMD of L3 was measured as antero-posterior dual energy X-ray BMD (AP-BMD DXA) and as lateral DXA BMD (L-BMD DXA). Subsequently, BMD of L3 was measured using single energy quantitative computed tomography, with a Siemens Somatom device (BMD QCT).

The AH/PH index ranged from 0.840 to 1.150, with a mean of 0.995, the MH/PH index 0.880-0.980, with a mean of 0.937. The AH/PH index showed significant correlation with either L-BMD DXA (r = 0.54, P < 0.001) or BMD-QCT (r = 0.50, P < 0.001) but not with AP-BMD DXA (r = 0.05). Using an AH/PH index threshold of 0.97 we categorized the subjects into 42 women (group A) with an AH/PH index < 0.97 and 78 women (group B) with an AH/PH index greater than or equal to 0.97. BMD values were found to be lower in group A than in group B. The difference was not significant with AP-BMD DXA (1011.5 (155.7)) versus 988.5 (193.5) mg/cm2, P = 0.47) but reached high significance (P < 0.0001) with L-BMD DXA (797.2 (166.8) versus 462.9 (131.1) mg/cm2) and with BMD QCT (135.5 (24.8) versus 83.6 (18.3) mg/cm3).

These results suggest that the AH/PH index of L3, assessed using MXA, shows some degree of correlation with BMD in perimenopausal women.