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Adapted from ref. 20 with kind permission from Elsevier Science Ireland Ltd., Bay 15K, Shannon Industrial Estate, Co. Clare, Ireland.

Adapted from ref. 20 with kind permission from Elsevier Science Ireland Ltd., Bay 15K, Shannon Industrial Estate, Co. Clare, Ireland.

Fig. 2-15. PA and lateral DXA lumbar spine images acquired on the Hologic QDR-4500. The arrow seen in (A) indicates the faint outline of the calcified aorta that is easily seen on the lateral study in (B). Case courtesy of Hologic Inc., Bedford, MA.

Effect of Facet Sclerosis on BMD. Unlike aortic calcification, facet sclerosis can have a profound effect on the measured BMD in the AP or PA projection. In the study by Drinka et al. (25) noted earlier, 113 elderly men were evaluated with standard AP and lateral lumbar spine films and DPA of the lumbar spine. A grading system for facet sclerosis was developed with a grade of 0 indicating no sclerosis and a grade of 3 indicating marked sclerosis. As shown in Table 2-7, grade 1 sclerosis had no significant effect on the BMD. Grades 2 and 3, however, markedly increased the BMD at the vertebral levels at which the facet sclerosis was found. Figure 2-17 is a PA spine BMD study in which facet sclerosis is suggested at L3 by the appearance of the image. The BMD values at L3 and L4 are also markedly higher than expected based on the values at L1 and L2. The plain film of this patient shown in Fig. 2-18 confirms facet sclerosis at the lower lumbar levels.

Fig. 2-16. A DXA PA and lateral lumbar spine study acquired on the Hologic QDR-4500. These are the analyzed studies for the images shown in Fig. 2-15. Case courtesy of Hologic Inc., Bedford, MA.

Fig. 2-17. A DXA PA lumbar spine study acquired on the GE Lunar DPX. There is a marked increase in the BMD between L2 and L3, which is maintained at L4. The image faintly suggests sclerosis in the region of the facet joints at L3 and L4. This is more dramatically seen in the plain film of this patient shown in Fig. 2-18.

Fig. 2-17. A DXA PA lumbar spine study acquired on the GE Lunar DPX. There is a marked increase in the BMD between L2 and L3, which is maintained at L4. The image faintly suggests sclerosis in the region of the facet joints at L3 and L4. This is more dramatically seen in the plain film of this patient shown in Fig. 2-18.

The Vertebral Rotation and PA Lumbar Spine Bone Density

Rotation of the vertebral bodies is often a component of idiopathic scoliosis, although it is not frequently seen in adult-onset degenerative scoliosis. To study the effect of vertebral body rotation on bone density measured in the lumbar spine with DXA, Girardi and colleagues (27) utilized a cadaveric spine with intact soft tissue. The spine, which spanned the ninth thoracic vertebra to the sacrum, was mounted at both ends in the neutral midline position. Calibration markings on the mounts allowed for the spine to be rotated in 10° increments to a maximum of 60° in either direction. The bone density of L1 through L4 was measured with DXA in duplicate in the neutral position and at each 10° increment in both directions.

Table 2-7 The Increase in BMD from Facet Sclerosis

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