Morphometric X-ray absorptiometry and morphometric radiography of the spine: A comparison of analysis precision in normal and osteoporotic subjects

Morphometric techniques, which use conventional lateral spine radiographs t o quantify vertebral body shape (morphometric radiography, MRX), have prove d a useful tool in the identification and evaluation of osteoporotic verteb ral deformities. Recently a new method of acquiring the images required for vertebral morphometry using dual-energy X-ray absorptiometry scanners (mor phometric X-ray absorptiometry, MXA) has been developed. Ln this study we c ompare repeat analysis precision of vertebral height measurement using MXA and MRX. Twenty-four postmenopausal women were recruited (mean age 67 +/- 5 .8 years): 12 normal subjects and 12 with osteoporosis and vertebral deform ities. Each subject had a MXA scan and lateral thoracic and lumbar radiogra phs at a single appointment, which were each analyzed quantitatively in a m asked fashion, using a standard B-point method, twice by one observer and o nce by a second observer. Anterior (Ha), mid (Hm) and posterior (Hp) verteb ral heights were measured and wedge (Ha/Hp) and mid-wedge (Hm/Hp) ratios ca lculated for each vertebral body. Intra- and interobserver precision were c onsistently poorer in MXA compared with MRX in both normal subjects and tho se with vertebral deformities, with MXA CV% generally at least 50% higher t han corresponding values for MRX. For both MXA and MRX interobserver precis ion was clearly poorer than intraobserver precision, a problem associated w ith any morphometric technique. MXA intra- and interobserver precision were significantly poorer for subjects with vertebral deformities compared with those without, with a CV% for deformity subjects up to twice that of norma l subjects. Conversely, MRX showed little or no obvious worsening of intra- or interobserver precision for deformity subjects. Comparison of MXA preci sion in the normal and deformed vertebrae of the deformity subjects demonst rated that the poorer precision in these subjects compared with normal subj ects was the result of increased variability in point placement on the defo rmed vertebrae themselves. However, the precision for normal vertebrae in t hese subjects was also somewhat poorer than the precision in normal subject s. We conclude that MXA precision is generally poorer than that of MRX and that the presence of vertebral deformities has a more pronounced effect on MXA precision than on MRX precision.