The spine in the lateral projection – bone dolor lumbar izquierdo density

The effect on BMD measured in the AP or PA dolor lumbar izquierdo projection from aortic calcification, facet sclerosis, osteophytes, and other degenerative changes in the spine can be nullified dolor lumbar izquierdo by quantifying the bone density of the spine in the dolor lumbar izquierdo lateral projection as shown in fig. 2-15B. In addition, the highly cortical posterior elements and a portion of the dolor lumbar izquierdo cortical shell of the vertebral body can be eliminated from dolor lumbar izquierdo the measurement, resulting in a more trabecular measure of bone density in dolor lumbar izquierdo the spine. The measurement is not a 100% trabecular measure as portions of the cortical vertebral body shell dolor lumbar izquierdo will still be included in the measurement. In addition to the elimination of artifact or confounding degenerative dolor lumbar izquierdo changes, the lateral spine BMD measurement is desirable in those circumstances dolor lumbar izquierdo in which a trabecular measure of bone density is indicated dolor lumbar izquierdo and particularly in circumstances in which changes in trabecular bone dolor lumbar izquierdo are being followed over time. The higher metabolic rate of trabecular bone compared to cortical dolor lumbar izquierdo bone should result in a much larger magnitude of change dolor lumbar izquierdo in this more trabecular measure of bone density compared to dolor lumbar izquierdo the mixed cortical-trabecular measure of bone density in the PA spine.

Vertebral identification in the lateral projection can be difficult. The lumbar vertebrae are generally identified by the relative position dolor lumbar izquierdo of the overlapping pelvis and the position of the lowest dolor lumbar izquierdo set of ribs. The position of the pelvis tends to differ however, when the study is performed in the left lateral decubitus dolor lumbar izquierdo position compared to the supine position. Rupich et al. (29) found that the pelvis overlapped L4 in only 15% of individuals when studied in the supine position. Jergas et al. (30) reported a figure of 19.7% for fig. 2-20. A DXA PA spine study acquired on the lunar DPX. The image is unusual at L4, with what appears to be an absence of part of dolor lumbar izquierdo the posterior elements. This was confirmed with plain films. This should decrease the BMD at L4.

Fig. 2-21. A DXA PA spine study acquired on the lunar DPX. The image suggests a marked sclerotic reaction at L4 and dolor lumbar izquierdo L5. There is also a marked increase in the BMD at dolor lumbar izquierdo L4, compared to L3. This sclerotic process was thought to be the result of dolor lumbar izquierdo an episode of childhood discitis. The patient was asymptomatic.

Fig. 2-21. A DXA PA spine study acquired on the lunar DPX. The image suggests a marked sclerotic reaction at L4 and dolor lumbar izquierdo L5. There is also a marked increase in the BMD at dolor lumbar izquierdo L4, compared to L3. This sclerotic process was thought to be the result of dolor lumbar izquierdo an episode of childhood discitis. The patient was asymptomatic.

L4 overlap for individuals studied in the supine position. In DXA studies performed in the left lateral decubitus position, pelvic overlap of L4 occurred in 88% of individuals in the study by peel et al. (12). In the other 12%, the pelvis overlapped L5 in 5% and the L3-4 disc space or L3 itself in 7%. As a consequence, although the position of the pelvis tends to identify L4 dolor lumbar izquierdo in most individuals scanned in the left lateral decubitus position, it also eliminates the ability to accurately measure the BMD dolor lumbar izquierdo at L4 in those individuals. The ribs are less useful than the pelvis in identifying dolor lumbar izquierdo the lumbar vertebrae. Rib overlap of L1 can be expected in the majority dolor lumbar izquierdo of individuals whether they are studied in the supine or dolor lumbar izquierdo left lateral decubitus position (12). This may not be seen, however, in the 12.5% of individuals whose lowest set of ribs in on T11.

Although the location of the pelvis and the presence of dolor lumbar izquierdo rib overlap aid in identification of the vertebrae, they also limit the available vertebrae for analysis. When a lateral spine DXA study is performed in the dolor lumbar izquierdo left lateral decubitus position, L4 cannot be analyzed in

Fig. 2-22. (A) the proximal femur as viewed from the front. The lesser trochanter is behind the shaft of the femur. (B) the proximal femur as viewed from behind. The lesser trochanter is clearly seen to be a posterior dolor lumbar izquierdo structure. (adapted from mcminn RMH, hutchings RT, pegington J, and abrahams PH. [1993] colour atlas of human anatomy, 3rd edition, p. 267-268. By permission of the publisher mosby.)

Fig. 2-22. (A) the proximal femur as viewed from the front. The lesser trochanter is behind the shaft of the femur. (B) the proximal femur as viewed from behind. The lesser trochanter is clearly seen to be a posterior dolor lumbar izquierdo structure. (adapted from mcminn RMH, hutchings RT, pegington J, and abrahams PH. [1993] colour atlas of human anatomy, 3rd edition, p. 267-268. By permission of the publisher mosby.)

The majority of individuals because of pelvic overlap. L1 is generally not analyzed because of rib overlap, regardless of whether the study is performed supine or in dolor lumbar izquierdo the left lateral decubitus position. Rupich et al. (29) also found that rib overlay L2 in 90% of individuals studied in the supine position. It was estimated that rib BMC added 10.4% to the L2 BMC. As a consequence, when lateral DXA studies are performed in the left lateral dolor lumbar izquierdo decubitus position, L3 may be the only vertebra that is not affected dolor lumbar izquierdo by either pelvic or rib overlap. In the supine position, L3 and L4 are generally unaffected. This means that depending on the positioning required by the dolor lumbar izquierdo technique, the value from a single vertebra or from only a dolor lumbar izquierdo two-vertebrae average may have to be used. This is undesirable, although sometimes unavoidable, from the standpoint of statistical accuracy and precision.

If the vertebrae are misidentified in the lateral projection, the effect on BMD can be significant. In the study by peel et al. (12), misidentification of the vertebral levels would have occurred in 12% of individuals in which the pelvis did not overlap L4 dolor lumbar izquierdo in the left lateral decubitus position. If L2 was misidentified as L3, the BMD of L3 was underestimated by an average of dolor lumbar izquierdo 5.7%. When L4 was misidentified as L3, the BMD at L3 was overestimated by an average of dolor lumbar izquierdo 3.1%. Although spine X-rays are rarely justified for the sole purpose of vertebral dolor lumbar izquierdo identification on a DXA study performed in the PA or dolor lumbar izquierdo AP projection, this may occasionally be required for DXA lumbar spine studies dolor lumbar izquierdo performed in the lateral projection. Analysis may be restricted to only one or two vertebrae dolor lumbar izquierdo because of rib and pelvic overlap. This reduces the statistical accuracy and precision of the measurement. Because of this reduction in accuracy, consideration should be given to combining lateral DXA spine studies dolor lumbar izquierdo with bone density assessments of other sites for diagnostic purposes.

RELATED_POSTS