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Fig. 2-3. The lumbar spine in the posterior view. (A) Intact vertebrae. (B) The transverse processes have been removed. (C) The vertebral bodies have been removed, leaving only the posterior elements. (Adapted from McMinn RMH, Hutchings RT, Pegington J, and Abrahams PH. [1993] Colour Atlas of Human Anatomy, 3rd edition, p. 83. By permission of the publisher Mosby.)

Fig. 2-3. The lumbar spine in the posterior view. (A) Intact vertebrae. (B) The transverse processes have been removed. (C) The vertebral bodies have been removed, leaving only the posterior elements. (Adapted from McMinn RMH, Hutchings RT, Pegington J, and Abrahams PH. [1993] Colour Atlas of Human Anatomy, 3rd edition, p. 83. By permission of the publisher Mosby.)

Transverse Process Tumor

Fig. 2-4. A DXA PA spine study acquired on the Lunar DPX. The shapes of the vertebrae in this image are primarily created by the posterior elements. The shapes in this study are classic. The expected increase in BMC and area is also seen from L1 to L4. The increase in BMD from L1 to L3, with a decline from L3 to L4, is also typical.

Shape Lumbar Vertebrae Dexa
Fig. 2-5. A graphic illustration of the characteristic shapes of the lumbar vertebrae as seen on a DXA PA spine study.

The transverse processes are eliminated from the scan field and the vertebral bodies are not well seen because they are both behind and equally or less dense than the posterior elements. In a study of 34 lumbar vertebrae taken from 10 individuals, aged 61 to 88, the average mineral content of the posterior elements was 47% of the mineral content of the entire vertebra (11).

The unique shapes of the posterior elements of the various lumbar vertebrae can be used as an aid in identifying the lumbar vertebrae. The posterior elements of L1, L2, and L3 have a U- or Y-shaped appearance. L4 can be described as looking like a block H or X. L5 has the appearance of a block I on its side. Figure 2-5 is a graphic illustration of these shapes. Compare these shapes to the actual posterior elements seen in Fig. 2-3C and the DXA lumbar spine study shown in Fig. 2-4. Although the transverse processes are generally not seen on a spine bone density study, the processes at L3 will sometimes be partially visible because this vertebra tends to have the largest transverse processes. This fact can also be helpful in lumbar vertebral identification. Figures 2-6A and 2-6B are the spine image only from the study shown in Fig. 2-4. In Fig. 2-6B, the shapes of the posterior elements have been outlined for emphasis.

On PA or AP DXA lumbar spine studies, L1 through L4 are quantified. Although L5 can be seen, it is not usually quantified because of potential interference from the pelvis. In fact, even if labeled on the scan, some software programs will not analyze L5 unless it is deliberately mislabeled L4. L1 frequently has the lowest BMC and BMD of the first four lumbar vertebrae. In a study of 148 normal women aged 50 to 60, Peel et al. (12) found that the BMC increased between L1-L2, L2-3, and L3-4 although the increase between L3-4 was roughly half that seen at the other levels as shown in Table 2-2. BMD increased between L1-2 and L2-3 but showed no significant change between L3-4. The average change between L3-4 was actually a decline of0.004 g/cm2. The largest increase in BMD occurred between L1-2. The apparent discrepancies in the magnitude of the change in BMC and BMD between the vertebrae are the result of the progressive increase in area of the vertebrae from L1 to L4. The DXA PA lumbar spine study shown in Fig. 2-4 illustrates the progressive increase in BMC and area from L1 to L4 and the expected pattern of change in BMD between the vertebral levels.

Studies from both Peel et al. (12) and Bornstein and Peterson (13) suggest that the majority of individuals have five lumbar vertebrae with the lowest set of ribs on T12.

Abnormal Bone Density Lumbar
Fig. 2-6. (A) A DXA PA spine image acquired on the Lunar DPX. This is the spine image from the study shown in Fig. 2-4, with the intervertebral disk markers and bone-edge markers removed for clarity. (B) The shapes have been outlined for emphasis.

Table 2-2

Incremental Change in BMC and BMD Between Adjacent Vertebrae in 148 Normal Women Ages 50-60 as Measured by DXA

Table 2-2

Incremental Change in BMC and BMD Between Adjacent Vertebrae in 148 Normal Women Ages 50-60 as Measured by DXA

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