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 ablebodied 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 ¼ 0.05); the T-score approached significance (À1.838 ± 1.366 vs À0.963 ± 1.227, P ¼ 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.

Perioperative complications associated with spine surgery in patients with established spinal cord injury

“…These reports question the method used for testing BMD, showing that the standard method of testing may be misleading. The studies have revealed that the standard posteroanterior dual-energy X-ray absorptiometry overestimates BMD, whereas lateral dual-energy X-ray absorptiometry and quantitative computed tomography scans are more reliable indicators of osteoporosis in SCI patients [28][29][30]. These more recent findings seem to confirm declining bone densities in the axial skeleton that is certainly consistent with the clinical course in some of the patients from our experience.…”

“…The theory is that the sustained weight bearing on the spine in the sitting position helps to maintain the bone density [21,22,27]. However, recent reports have challenged the notion that the axial skeleton is spared loss of BMD in SCI patients [28][29][30]. These reports question the method used for testing BMD, showing that the standard method of testing may be misleading.…”

Reduced Bone Density and Vertebral Fractures in Smokers. Men and COPD Patients at Increased Risk

“…CT has the advantage of measuring trabecular bone and avoids the overestimation of BMD by DXA due to degenerative spine disease and increased tissue density (39,40). QCT may be a better predictor of fracture risk than DXA, which is more commonly used in clinical practice (41,42).…”

Influences of nutrition and adiposity on bone mineral density in individuals with chronic spinal cord injury: A cross-sectional, observational study

“…LS preservation is evident in the comparable LS BMD of non-SCI controls. Alternatively, DXA has been found to overestimate the LS BMD in SCI due to confounding osteophytes or heterotrophic ossification (Bauman et al, 2009), and may mask bone loss following injury.…”