Posterior-Anterior and Lateral Dual-Energy X-Ray Absorptiometry for the Assessment of Vertebral Osteoporosis and Bone Loss Among Older Men

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Abstract
Lateral spine dual‐energy x‐ray absorptiometry (DXA) selectively measures the trabecular‐rich vertebral bodies without the contributions of the cortical‐rich posterior elements of the spine and is less affected by spinal degenerative disease than posterior‐anterior DXA. We tested whether lateral DXA detects vertebral osteoporosis more often and is more sensitive to age‐related bone loss than posterior‐anterior DXA in 193 healthy, community‐dwelling men aged 51–81 years (mean ± SD; 67 ± 8 years). All men had supine lateral, posterior‐anterior, and proximal femur DXA scans on a Hologic QDR 2000 densitometer. A subset (n = 102) had repeat scans after 4 years to determine annualized rates of change in bone mineral density (BMD). Age was inversely and significantly associated with BMD in the midlateral (r = −0.27) and lateral (r = −0.24) but not posterior‐anterior (r = 0.04) projections. Midlateral (−1.43 ± 3.48% per year; p = 0.0001), lateral (−0.27 ± 1.68% per year; p = 0.12), and hip (−0.19 ± 1.02% per year; p = 0.06) BMD decreased, whereas posterior‐anterior BMD increased (0.73 ± 1.11% per year; p = 0.0001) during follow‐up. When compared with normal values in 43 men aged 21–42 years, mean T scores were significantly lower with lateral (−1.47 ± 1.32) and midlateral (−1.57 ± 1.36) than posterior‐anterior (−0.12 ± 1.30; p < 0.0001) DXA. Only 2.6% of the older men were considered osteoporotic (T score ≤ −2.5) at the posterior‐anterior spine, whereas 11.0% were osteoporotic at the femoral neck, 22.5% at the lateral spine, and 24.6% were osteoporotic at the midlateral spine. We conclude that supine lateral DXA identifies considerably more men as osteoporotic and is more sensitive to age‐related bone loss than posterior‐anterior DXA. Spinal osteoporosis may represent a substantially greater health problem among older men than previously recognized.