Aging of the thoracic spine: distinction between wedging in osteoarthritis and fracture in osteoporosis--a cross-sectional and longitudinal study.

Thoracic kyphosis is clinically associated with osteoporosis as well as with osteoarthritis. Because misinterpretation of thoracic spine deformities on X-rays may lead to overdiagnosis of vertebral fracture, we studied morphological changes of the thoracic spine in a cross-sectional (n = 89) and longitudinal study (n = 38) in 30 women with established osteoporosis (OP), in 31 women with spinal osteoarthritis (OA), and in 28 normal women. Vertebral deformation was assessed on lateral roentgenograms of the thoracic spine from T-4-T-12. The anterior, middle, and posterior heights were measured using six points corresponding to the four corners of the vertebral body excluding osteophytes and the midpoints of the endplates. For the thoracic T-6-T-9 region, the mean anterior/posterior height ratio was 7.7% in the controls, 13% in osteoarthritis, and 21% in osteoporosis. For the mid-height/posterior height ratio the respective values were 13%, 12%, and 22%. The osteoporosis group differed significantly from the control and osteoarthritis group in anterior and in midheight reduction. The yearly mean anterior height reduction in the osteoarthritis group was 0.7% compared with 1.5% in the osteoporosis group. The mean yearly midheight reduction was, respectively, 0.5% versus 2.9%. The differences between the groups were significant. We conclude that vertebral deformity, in particular wedging, of the thoracic spine is not exclusively characteristic for osteoporosis and that certain vertebral deformities develop by mechanisms other than fracture. Osteoporotic fracture of the thoracic spine is characterized by an exaggerated reduction of the midheight to posterior height in addition to reduction of the anterior to posterior height.(ABSTRACT TRUNCATED AT 250 WORDS)