An investigation of spinal bone mineral density measured laterally: a normal range for UK women.

A UK normal range for 250 volunteers was established for bone mineral density (BMD) of the lumbar spine (L2-L4) measured laterally in the decubitus position. Two software defined regions of interest ("Body" and "Mid") within the vertebral body were analysed throughout. As expected, a negative correlation of BMD with age was found for Body (r = -0.55, p < 0.001) and Mid (r = -0.56, p < 0.001). The age related bone loss from young to old (20-80 years) was 40% in L3 (Body) and 45% in L3 (Mid). In 22% of the cases only L3 could be measured owing to the influence of rib over L2 and interference of the iliac crest over L4. Age related normal ranges (+/- 2 standard deviations) for the three lumbar vertebra L2, L3, L4 for young normals (age 19-39 years) were found to be 0.54 to 1.02, 0.49 to 1.05 and 0.5 to 1.14 g cm-2 respectively for the Body region and 0.49 to 0.97, 0.45 to 1.01 and 0.45 to 1.13 g cm-2 respectively for the Mid region. These ranges can now be used as reference values for patients with suspected osteoporosis and possibly for future fracture prediction. The in vivo precision in 19 volunteers was found to be 4.2% and 5.6% on Body and Mid respectively. The short term (less than 1 week) in vitro precision was 3.1% and 2.7% respectively. From these data it appears that there is a greater measured age related drop in BMD in the vertebral body (measured laterally) than in the entire vertebra (measured anterior-posteriorly) indicating that the lateral measurement may prove to be more sensitive in predicting fracture. The precision of these results indicates that lateral measurements of the spine are not yet useful for monitoring individuals over short term periods and are less useful for studying the effects of drug treatment than the more traditional anterior-posterior measurement of the spine and femur.