A measurement of the extent of a plane through, that is, perpendicular to the axis of, a lumbar vertebra, any of the individual bones forming the portion of the spinal column (the protective bony corridor through which the spinal cord passes) between the thoracic vertebrae in the chest region and the sacrum in the hip region. The area includes any or all of the bone elements present at the level of the cross-sectional plane, including cortical bone, trabecular bone and/or marrow.