Prospective assessment of thoracic kyphosis in postmenopausal women with osteoporosis

Abstract

We attempt to assess quantitatively thoracic kyphosis and its influence on incident fractures and quality of life over three years in postmenopausal women with osteoporosis and the effect of strontium ranelate on thoracic kyphosis progression. This study was performed on women with postmenopausal osteoporosis from the Spinal Osteoporosis Therapeutic Intervention (SOTI) and Treatment of Peripheral Osteoporosis (TROPOS) studies. Vertebral fractures were assessed on lateral thoracic radiographs performed at baseline and at three years according to standardized procedure. Kyphosis index (KI, %), was defined as the percentage ratio between the maximum depth of thoracic curvature and the height measured from the T4 to the T12 vertebrae. Baseline characteristics of the 3218 patients (1594 strontium ranelate, 1624 placebo) were mean age 73.3 years, spine bone mineral density (BMD) T-score (L2-4) -3.1, femoral neck T-score -3.0, and KI 25.4%. In the placebo group, patients with the highest baseline KI experienced significantly more vertebral fractures than those with medium KIs [relative risk (RR) = 1.53; 95% confidence interval (CI) 1.19-1.96, p < .001) or the lowest KIs (RR = 1.70, 95%CI 1.32-2.21, p < .001), even after adjusting for the presence of prevalent fractures, age, body mass index (BMI), and BMD. There was no difference in the risk of nonvertebral fractures according to baseline KI. Three-year changes in quality-of-life physical scores reflected significantly better status for patients in the lowest tertile of KI compared with those in the highest at baseline. Over three years, the KI increased for all patients, indicating worsening of thoracic kyphosis, whatever the presence of prevalent or incident vertebral fractures. This KI progression was lower in the strontium ranelate group than in the placebo group. Thoracic kyphosis is a risk factor for vertebral fractures over three years and influences physical capacity changes in postmenopausal women with osteoporosis. Thoracic kyphosis progression over three years is lower in a subgroup of strontium ranelate-treated patients compared with placebo-treated patients.