REVERSAL OF VERTEBRAL DEFORMITIES IN OSTEOPOROSIS - MEASUREMENT ERROROR REBOUND

Digitized morphometry of vertebral bodies on lateral spine films is us ed to identify and quantify vertebral deformities or fractures. One pr oblem associated with this method is the phenomenon of ''disappearing fractures,'' which results from the apparent increase in vertebral bod y heights of previously deformed vertebrae on subsequent radiographs. These have been considered biologically implausible and therefore a re sult of measurement error. Measurement error is unlikely to be unidire ctional, so that a proportion of fractures identified by morphometry i s also the result of measurement error. Since some vertebral deformiti es are real events, some disappearances of deformities detected by mor phometry may be real events. In this report, we examine the data from our clinical trial of sodium fluoride in spinal osteoporosis to assess critically the plausibility of two hypotheses: (1) The ''rebound'' ph enomenon results from measurement error. If this is the case, then som e fractures of the same magnitude as the rebound must also represent m easurement error. (2) Some deformed vertebrae in fact rebound toward t heir original shape and size, displaying an elastic response to deform ation. If this occurs, then some vertebral deformities are transient e vents, not true fractures. We conclude that the variability inherent i n morphometric data obtained from serial spine x-rays results in both disappearing fractures and a high false positive fracture rate. The us e of more stringent criteria for defining significant deformities, or true fractures, will minimize these problems. We cannot exclude the se cond hypothesis, that some vertebral deformities may be transient even ts, but this needs further study.