Estimating lumbar bone mineral density from routine radiographs of the lumbar spine.

To evaluate the information content of lateral lumbar films with respect to bone mineral content, we compared reading criteria with values obtained by quantitative computed tomography (CT) of L1 at baseline and after 5 years. The highest correlations with mineral content were found for the criteria "overall assessment of the vertebra", "vertebral bone density versus soft tissue", and "amount of trabeculations". These three reading criteria yielded higher correlations with CT scores in subjects with lower body mass index. Changes in mineral content over the 5-year period could not be read adequately, the average difference representing only a loss of about 10% in the study subjects. We conclude that a rough estimate of bone density can be obtained from lateral radiographs which, in the presence of eventual risk factors for osteoporosis, may serve as an additional indication to timely bone densitometry with methods which allow precise short-term follow-up measurements.