Pitfalls in the Measurement of Bone Mineral Density by Dual Energy X-ray Absorptiometry

STUDY DESIGN: Fifty-three human thoracic and lumbar vertebrae were analyzed by dual energy x-ray absorptiomety to obtain projectional (g/cm2) and volumetric (g/cm3) bone mineral density. OBJECTIVES: To determine the effect of volume on the measurement of bone mineral density by DEXA. SUMMARY OF BACKGROUND DATA: Despite the widespread use of dual energy x-ray absorptiomety to measure bone mineral density expressed as grams per projectional unit area (g/cm2), the effect of volume has been ignored in many published biomechanical studies. METHODS: Projectional bone mineral density (g/cm2) of fifty-three human vertebrae was obtained by dual energy x-ray absorptiometry measurement. This was compared to bone mineral density expressed as grams per unit volume. RESULTS: Many specimens with near equal projectional bone mineral density were demonstrated to have significantly different true densities when measured by dual energy x-ray absorptiomety in grams per unit volume. The difference in true bone mineral density for these specimens ranged from 24.1% to 139%. CONCLUSION: The effect of volume on bone mineral density data based on projectional areas can cause very significant perturbations of the data in biomechanical studies.