Slipped vertebra. Coloured X-ray of the lower spine (yellow, down centre) of an 82 year old woman with a slipped vertebra. Bones, such as in the ribcage (upper frame) and pelvis (lower frame) are yellow. The fifth lumbar vertebra (L5) is the bone which articulates with the pelvis. The bone above it (L4) has slipped both sideways and forwards (not seen). There has also been wedge collapse of L5's upper surface, causing it and L4 to become compressed. This condition is caused by a lack of bone tissue (osteopaenia), most likely due to osteoporosis. Osteoporosis is most common in elderly women due to their low hormone levels.