Bone · Lumbar spine

Fifth lumbar vertebra

The fifth lumbar vertebra is the last of the mobile spine, sitting on the sloping top of the sacrum. It is a transition point: everything above it moves, everything below it is fused into the pelvis, and because the surface it sits on is tilted, it has to resist a forward-sliding force as well as a downward one. Thick iliolumbar ligaments tie its side processes to the rim of the pelvis to help hold it there. The L5 nerve root emerges just below it and runs down to the outer shin and the top of the foot.