Dual-energy X-ray absorptiometry overestimates bone mineral density of the lumbar spine in persons with spinal cord injury

Abstract

Background: Bone mineral density (BMD) of the lumbar spine (L-spine) has been reported to be normal or increased in persons with chronic spinal cord injury (SCI).

Objective: To determine BMD of the L-spine by dual-energy X-ray absorptiometry (DXA) and quantitative computerized tomography (qCT) in men with chronic SCI compared with able-bodied controls.

Design: Cross-sectional, comparative study.

Setting: Clinical research unit, Veterans Affairs Medical Center, Bronx, NY, USA and Kessler Institute of Rehabilitation, West Orange, NJ, USA.

Methods: Measurements of the L-spine were made in 20 men with SCI and compared with 15 able-bodied controls. The DXA images were acquired on a GE Lunar DPX-IQ. The qCT images of the L-spine were acquired on a Picker Q series computerized tomographic scanner.

Results: The mean ages for the SCI and control groups were 44+/-13 vs 42+/-9 years, and the duration of injury of the group with SCI was 14+/-11 years. There were no significant differences between the SCI and control groups for L-spine DXA BMD (1.391+/-0.210 vs 1.315+/-0.178 g/m(2)) or for L-spine DXA T-score (1.471+/-1.794 vs 0.782+/-1.481). L-spine qCT BMD was significantly lower in the SCI compared with the control group (1.296+/-0.416 vs 1.572+/-0.382 g/m(2), P=0.05); the T-score approached significance (-1.838+/-1.366 vs -0.963+/-1.227, P=0.059). Subjects with moderate degenerative joint disease (DJD) had significantly higher T-scores by DXA than those without or with mild DJD.

Conclusion: Individuals with SCI who have moderate to severe DJD may have bone loss of the L-spine that may be underestimated by DXA, reducing awareness of the risk of fracture.