Differences in thoracic kyphosis and in back muscle strength in women with bone loss due to osteoporosis.

STUDY DESIGN Cross-sectional. OBJECTIVES To determine if thoracic kyphosis was different in older women grouped based on their bone mineral density (BMD) and back extensor strength (BES), and to determine if an association between and these variables exist. SUMMARY OF BACKGROUND DATA Changes in kyphosis might be related to back extensor weakness in patients with osteoporosis. Disproportionate weakness in back extensor musculature considerably increases the possibility of deformities in the fragile osteoporotic spine. METHODS A total of 189 female subjects 50 to 80 years of age were grouped by their BMD and additionally by their BES. All were evaluated for thoracic kyphosis, maximal isometric strength of the back extensors, and BMD of the lumbar spine and the hip. RESULTS There was no significant difference in thoracic kyphosis among all groups. Multivariate analyses of BES and BMD showed that only BES might influence thoracic kyphosis (P = 0.02). There was no correlation between BES and BMD. Statistically significant deficit in BES was observed only between the osteoporotic and osteopenic group (P < 0.05). The importance of BES in maintaining posture was observed when the study population was divided according to their BES level. With respect to thoracic kyphosis and BMD values, there were no statistical differences between strong women (BES more than 60 N) and those with medium BES (BES between 60 and 35 N). But the weakest group (BES less then 35 N) had significantly higher (P < 0.05) mean values of thoracic kyphosis in comparison to strong women (BES more than 60 N) and those with medium BES (BES between 60 and 35 N). CONCLUSION The severity of thoracic kyphosis may be influenced especially by changes in BES. Therefore, provision of strong, natural extrinsic support for the spine seems to be important to decrease the incidence of spinal deformity.