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Values are in g/cm2. Adapted with permission of the publisher from ref. 25.

Values are in g/cm2. Adapted with permission of the publisher from ref. 25.

Fig. 2-18. A lateral lumbar spine X ray of the patient whose bone density study is shown in Fig. 2-17. The arrows indicate sclerotic regions in the posterior elements.

The vertebral segment area increased with increasing rotation up to 50° in either direction from midline and then decreased between 50° and 60°. The BMC remained relatively constant throughout rotation except at the extreme of 60° on either side of the midline, at which point it decreased. Because BMD is determined by dividing the BMC by area, the increasing area with rotation resulted in BMD decreasing with rotation to either side of the midline. From neutral to 60°, the decrease in BMD was almost 20%. In clinical practice then, rotation of the spine for any reason, should be expected to cause an apparent decrease in bone density when measured with DXA.

Fig. 2-19. A DXA PA lumbar spine study acquired on the Lunar DPX. The image suggests increased density at L3 and L4, but there is also a linear vertical lucency over L4. The BMD values are markedly increased at L3 and L4. This patient had previously undergone an L3-L4, L4-L5 interbody fusion and laminectomy at L4. Although the laminectomy alone would decrease the BMD at L4, the fusion mass has increased the BMD at L3 and L4 dramatically.

Fig. 2-19. A DXA PA lumbar spine study acquired on the Lunar DPX. The image suggests increased density at L3 and L4, but there is also a linear vertical lucency over L4. The BMD values are markedly increased at L3 and L4. This patient had previously undergone an L3-L4, L4-L5 interbody fusion and laminectomy at L4. Although the laminectomy alone would decrease the BMD at L4, the fusion mass has increased the BMD at L3 and L4 dramatically.

Other Causes of Artifacts in PA and AP Lumbar Spine Studies

Potential causes of apparent increases in the BMD in the AP or PA lumbar spine have been identified by Stutzman et al. (28). These include pancreatic calcifications, renal stones, gall stones, contrast agents, and ingested calcium tablets in addition to osteophytes, aortic calcification, and fractures. Figures 2-19, 2-20, and 2-21 illustrate other structural changes in the spine that will affect the BMD measured in the PA projection.

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