Vertebral morphometry reference data by X-ray absorptiometry (MXA) in Iranian women

The anterior, medial, and posterior heights and the A/P and M/P ratios of the spine (T5-L4) in 41 normal premenopausal Iranian women were determined using an imaging densitometer (Expert XL) and dual energy X-ray absorptiometry (DXA) method. All the women were healthy (age 20-39 years, and height 149-171 cm), without any signs of vertebral fractures, and with normal bone mineral density (BMD) of the spine and femoral neck (T-score>-1.5). The vertebral heights were normalized using the Expert XL software, and the average vertebral height for the L2-L4 vertebrae was taken to minimize the effect of variation of body size among the subjects. The Z-score for all vertebral heights (T5-L4) averaged -0.68, with the A/P and M/P ratios coming to +0.34 and +0.49, respectively. It showed the normalization procedure not to correct the differences of vertebral heights in Iranian women. The average of the three heights (H (avg)) correlated fairly well with the stature of the subject (r=0.47, p<0.05), but no correlation was found between H (avg) and subject age (p>0.05). The lower vertebral heights in older women in comparison with the younger women (0.4 mm) obtained in our study can be attributed to the relatively shorter stature of older women (mean 154 vs 159 cm for younger women, p<0.05). It was concluded that the normalization procedure used in the software does not equally apply to Iranian women due to their having different heights than those of American and northern European women, from whom the reference data for the Expert XL software have been gathered. The reference values thus obtained are therefore not accurate for our population group and a separate study with a bigger and more varied sample group is needed for obtaining more definitive results.