Bone · Lumbar spine

Fourth lumbar vertebra

The fourth lumbar vertebra sits second from the bottom of the lower back. It is a standard reference point: a line drawn between the highest points of the two iliac crests crosses the spine at about this level, which is how clinicians count the lumbar vertebrae by hand. The L4 nerve root leaves the spine just below it and travels down the front of the thigh towards the inner shin.