Spinal deformity index (SDI) is a good predictor of incident vertebral fractures

Abstract

The spinal deformity index is a convenient tool to quantify the number and the severity of prevalent vertebral fractures. It is a predictor of the risk of sustaining incident vertebral fracture. This quantification must be taken into account to improve management of patients. Prevalent fractures are strong risk factors for subsequent fractures. The study subjects were women from the placebo groups of two studies of strontium ranelate in postmenopausal osteoporosis (N = 723 and 637 patients, respectively). Three lateral radiographs of the spine were obtained at baseline and annually over 3 years, according to standardized procedures. The semiquantitative visual assessment of each vertebra from T4 to L4 was performed by the same reader throughout the study. A spinal deformity index (SDI) was calculated by summing for each patient the grade of each vertebra from T4 to L4. There was a linear relationship between baseline SDI and the 3-year incidence of vertebral fracture (adjusted R(2) = 0.76). The 3-year incidence of vertebral fractures was different among the tertiles of baseline SDI: 17.3 +/- 3.6%, 25.4 +/- 2.6%, and 47.6 +/- 3.1% from the lowest to the highest, respectively. There was no relationship between SDI and non-vertebral fractures incidence. SDI is a good predictor of incident vertebral fractures. Patients with highest SDI should receive highest priority to treatment.