The reproducibility of the iliac crest as a marker of lumbar spine level.

The postero-anterior lumbar spine X rays of 163 patients undergoing investigation for back pain were reviewed and the spinal level marking the intersection of a line joining the iliac crests was determined. This point coincided with the L4 spinous process or the L4-5 interspace in 78.6% of patients but was as high as the L3-4 interspace in 3.7% of cases. Reliance on this landmark might lead to more cranial placement of epidural or spinal needles than was intended and this may increase the risk of spinal cord damage.