A defect in a vertebra in the lower back, typically the last vertebra at the bottom of the spine, an area called the lumbar spine. The defective area of this vertebra is the bony ring that protects the spinal cord and connects the vertebral bone to the facet joints at the top and bottom of each vertebra. In spondylolysis, the back part of the vertebra and the facet joints are connected only by soft tissue. It is believed that this can be caused by an incompletely healed stress fracture of the vertebra affected. There is usually a lump of hardened tissue in the area where the stress fracture did not completely heal. This tissue may press on the nerve roots at the bottom of the spine, causing pain that extends down into the legs. The condition first appears in childhood and is common among young football players, gymnasts, and ballet dancers.
A spinal condition where the arch of the fifth lumbar vertebra, or less commonly the fourth, is made up of soft fibrous tissue instead of regular bone. This makes the arch vulnerable to damage, particularly under stress, and could lead to the onset of spondylolisthesis. Typically, the condition presents no symptoms.