Importance of lateral spine view in DEXA bone densitometry

Bone Mineral Density (BMD) measurement is a very useful technique in the assessment of risks of fracture in suspected cases of osteoporosis. The procedure is routinely carried out in antero-posterior (AP) view of the spine and the hip. But very often discordant results have been reported using the above cited views. Bone mineral concentration (BMC) obtained in the AP view of spine appears higher than that obtained in the hip views. The present study was conducted to establish the importance of lateral view of spine. The lateral view would provide better scope to draw the ROI perfectly thereby resulting in more precise measurement of BMC. In a prospective study a total of 60 consecutive patients (48F, 12M) were evaluated for bone densitometric measurements. The age of the patients ranged from 35-80 years with a mean age of 59 years. None of the patients received ooestrogen, biphosphonates or steroid therapy. Bone densities of the hip and lumbar spine were measured with a Norland XR 36 bone densitometer equipment. The Tscore, which measures the difference between patient's BMD and young-normal, was computed and age-matched Z-score were calculated. X-ray correlation was also done in most of the cases. Analyses of the values obtained over femoral neck revealed 30 cases with osteoporosis and 23 cases with osteopaenia. While on the other hand analyses of AP spine views revealed osteoporosis in 20 and osteopaenia in 30 patients. Hence, it became evident that significant number of patients who were actually suffering from osteoporosis were in fact interpreted as osteopaenic (P<0.05) in the spinal examinations. When the lateral views of the spine were analysed the bone mineral concentrations matched more closely with femoral neck values (P>0.05). Significant differences (P>0.05) in the values of BMC in the same vertebra measured in AP and lateral views were also observed in this study. Based on the results of this study it was concluded that the lateral view of the spine is an important factor in the accurate measurement of BMC. This view excludes the posterior element of the vertebra as well as the aorta anteriorly, where high incidence of calcified atherosclerotic plaques is present. Since AP view cannot exclude these areas from the region of interest, the BMC values obtained using this view are falsely higher than the actual value. It is therefore recommend that a lateral view of the spine should be included in the determination of BMC as a matter of routine in day to day clinical practice of bone densitometry. (author)