Reliability and accuracy of vertebral fracture assessment with densitometry compared to radiography in clinical practice

Abstract

Absorptiometry of the thoraco-lumbar spine at the time of bone densitometry to detect vertebral deformities consistent with fracture is now available. The performance of absorptiometry in clinical practice compared to radiography has not been fully established, especially in the presence of osteoarthritis or scoliosis. Our first objective was to compare absorptiometry to radiography for detection of vertebral deformity in elderly women who were referred for bone densitometry with or without scoliosis or disc space osteoarthritis excluded. Our second objective was to assess the effect of osteoarthritis and scoliosis on the inter-rater reliability of both technologies. The study group comprised two hundred five women age 65 and older referred for bone densitometry in a large multispecialty group practice. Lateral and antero-posterior (AP) absorptiometry images and lateral spine radiographs were obtained on all participants. The vertebrae on all images were evaluated for vertebral deformity by two observers according to the Genant semiquantitative criteria who were blinded to each other's readings. Disc spaces were evaluated on radiographs for osteoarthritis. Absorptiometry AP images were evaluated for scoliosis. In the absence of scoliosis, the sensitivity and specificity of absorptiometry for persons with one or more radiographic grade 2-3 deformities (>25% reduction of vertebral height) for the two readers were 87-93% and 93-95%, respectively. The inter-rater reliability of absorptiometry improved in the absence of moderate or severe disc space osteoarthritis. A strategy of absorptiometry with follow-up radiography only in those with scoliosis or apparent grade 2 deformity accurately identifies those with prevalent grade 2 or 3 deformity on radiography (accuracy 0.98 and kappa 0.86 for reader 1; accuracy 0.99 and kappa 0.92 for reader 2). Lateral and AP absorptiometry imaging of the spine with selective follow-up radiography accurately identifies elderly women with vertebral deformity consistent with moderate or severe fracture, but extra caution is necessary when evaluating vertebrae in the presence of adjacent disc space osteoarthritis.