Defining incident vertebral deformity: A prospective comparison of severalapproaches

Vertebral deformities are common and important outcomes in clinical trials and epidemiologic studies of osteoporosis. While several different methods for defining new deformities have been proposed, it is not clear which is b est. We used data from serial spine radiographs obtained an average of 3.7 years apart in 7238 women age greater than or equal to 65 years from the St udy of Osteoporotic Fractures to compare several approaches to defining new deformities by morphometry including a fixed percentage reduction in any v ertebral height (FIXED%), a change in a summary spinal deformity index, a c hange in a vertebra from no prevalent deformity at baseline to a deformity at follow-up, as well as several variations of these methods. We compared r esults of each definition with several clinical correlates, including heigh t loss, back pain, age, baseline bone mineral density, and the presence of a baseline deformity. We also estimated the sample size required for a clin ical trial using various cut points. At a given level of incidence, all met hods had similar relationships with each of the correlates. Given that simi larity, the FIXED% method was simplest and needed no reference data. Using the FIXED% method, a 20-25% vertebral height reduction criterion for deform ity maximized the power for a clinical trial. We conclude that all of the m orphometric approaches to defining incident deformities have similar relati onships to clinical correlates of vertebral deformity, but that use of a fi xed percentage reduction in vertebral height is the simplest and most pract ical. For the FIXED% method, a 20-25% reduction in vertebral height minimiz es the sample size required for clinical trials and epidemiologic studies.