MORPHOMETRIC X-RAY ABSORPTIOMETRY - REFERENCE DATA FOR VERTEBRAL DIMENSIONS

Vertebral fractures are a common and important consequence of osteopor osis and are often identified via morphometric analysis of conventiona l lateral spine radiographs (morphometric radiography or MRX). A new m ethod of performing vertebral morphometry using images acquired on dua l-energy X-ray absorptiometry (DXA) scanners (morphometric X-ray absor ptiometry or MXA) has recently been developed, In this study, we deriv e reference data for vertebral heights and height ratios using MXA sca ns as the data source and compare the results with previously publishe d MRX studies, One thousand and nineteen Caucasian women (mean age 63 years, range 33-86) were recruited, An MXA scan, covering 13 vertebrae from L4 to T4, was acquired for each subject on one of four DXA syste ms located at three centers in the U.K. Analysis of variance found sta tistically significant but relatively small differences among centers, machines, and scan anodes, and therefore data were pooled for referen ce range calculations, Three vertebral heights (anterior, mid, and pos terior) were measured and four ratios (wedge, mid-wedge, and two crush ) calculated, These data sets were trimmed using an iterative algorith m to remove extreme values assumed to represent deformed vertebrae, th en mean and SD values were calculated using the remaining data, When t he data were split by age, a small but statistically significant decre ase in vertebral height between the sixth and eighth decades was found , but this was not replicated for the vertebral height ratios, Marked differences were observed between MXA data and MRX, but were comparabl e to those between different MRX studies, These may result from differ ences in image quality and point placement protocols, population diffe rences, differences in radiographic technique, and differences in the derivation of a group of ''normal'' vertebrae, This study suggests tha t reference data of vertebral dimensions should be specific to the tec hnique which uses those data as a reference, i.e., MXA.