Correlation between vertebral body rotation and two-dimensional vertebral bone density measurement

The aim of this study was to determine the effect of vertebral rotation, as seen in idiopathic scoliosis. on bone mineral density determination for th e lumbar spine. Bone mineral content, biplanar vertebral segment area and c alculated bone mineral density of each vertebra from L1 to L4 were obtained for a human cadaveric specimen. The average density for the entire L1-L4 s egment was also recorded. This was done with the spine in the midline posit ion as well as in rotation up to a maximum of 60 degrees either side of the midline. The spine was rotated in each direction using 10 increments and t wo bone density readings were done at each rotation interval. The measured biplanar vertebral segment area increased with increasing rotation from 0 t o 50 but decreased after 50 degrees of rotation (r=0.73. p <0.001). The bon e mineral density was significantly negatively correlated with the degree o f rotation (r = -0.92, p <0.001). The decrease in measured bone mineral den sity was nearly 20% when the lumbar spine was rotated from neutral to 60. T his study demonstrates that degree of spinal rotation influences apparent b one mineral density by increasing the apparent vertebral segment area. The measurement change may be as high as 20%. This fact should be considered wh en investigating scoliotic patients with vertebral segment rotation.