Quantitative computed tomography in the evaluation of spinal osteoporosis following spinal cord injury

Disuse osteoporosis occurs in the lower extremities of patients with spinal cord injury (SCI). However, spinal osteoporosis is not usually observed in these patients. We investigated lumbar spine bone mineral density (BMD) in SCI patients using single energy quantitative computed tomography (QCT) an d dual-energy X-ray absorptiometry (DXA). Our study population consisted of 64 patients with long-standing SCI. Spine BMD (g/cm(3)) was assessed by QC T at four vertebrae ranging from T11 to L4 with single midvertebral CT slic es 1 cm thick parallel to the vertebral end-plates. Confounding variables a ffecting normal trabecular bone pattern, such as compression fractures, sur gical hardware or fat replacement, were excluded. For a subset of 29 patien ts, DXA values of the spine and femoral neck were also measured, and QCT an d DX4 Z-scores were compared On the average, the 64 SCI patients had Z-scor es 2.0 +/- 1.2 below those of age matched controls. In the subset of 29 pat ients with both QCT and DXA measurements, the QCT and DXA Z-scores were 2.4 +/- 1.1 below and 1.3 +/- 2.3 above the mean, respectively (p < 0.0001). O ur results indicate that QCT reveals osteoporosis of the spine after SCI, i n contrast to DXA. We postulate that QCT is more valuable for evaluating sp inal osteoporosis following SCI than DXA and thus recommend QCT for spinal BMD studies in SCI.