Posterior-anterior and lateral dual-energy x-ray absorptiometry for the assessment of vertebral osteoporosis and bone loss among older men

Lateral spine dual-energy x-ray absorptiometry (DXA) selectively measures t he trabecular-rich vertebral bodies without the contributions of the cortic al-rich posterior elements of the spine and is less affected by spinal dege nerative disease than posterior-anterior DXA, We tested whether lateral DXA detects vertebral osteoporosis more often and is more sensitive to age-rel ated bone loss than posterior-anterior DXA in 193 healthy, community-dwelli ng men aged 51-81 years (mean +/- SD; 67 +/- 8 years). All men had supine l ateral, posterior-anterior, and proximal femur DXA scans on a Hologic QDR 2 000 densitometer, A subset (n = 102) had repeat scans after 4 years to dete rmine annualized rates of change in bone mineral density (BMD), Age was inv ersely 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 decr eased, 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 age d 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 osteopor otic (T score less than or equal to -2.5) at the posterior-anterior spine, whereas 11.0% were osteoporotic at the femoral neck, 22.5% at the lateral s pine, 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, Spina l osteoporosis may represent a substantially greater health problem among o lder men than previously recognized.