The index of radiographic area (IRA): a new approach to estimating the severity of vertebral deformity.

To assess the overall severity of vertebral deformity for an individual, we developed the index of radiographic area (IRA), a computerized method for analyzing vertebral dimensions from lateral radiographs of the spine. Six coordinates for each vertebral body are recorded in a computer by means of a digitizer. A computer program identifies all abnormal vertebrae, computes the radiographic area of the remaining normal vertebrae, and then estimates the expected normal radiographic area for the abnormal vertebrae in that individual. Differences between the expected and observed radiographic area of all abnormal vertebrae are summed to produce the IRA score. The score correlated well with the quantitative score of vertebral deformity of an experienced radiologist (r = 0.85), and with the vertebral bone density by quantitative computed tomography (QCT) (r = 0.66). The IRA is a practical, standardized method for quantitating the overall severity of vertebral deformity in individuals who have vertebral fractures. Its reproducibility for longitudinal studies and clinical trials needs further study.