The body tries to heal the fracture and stabilize the bones. Unfortunately, it fills in the defect with dense fibrous tissue. It's more like a ligament than solid bone. As a result, there is motion at the fracture site when there shouldn't be. This creates a pseudoarthrosis or false joint.

Repetitive mechanical stress or load on the area can cause a spondylolysis to become a spondylolisthesis. In both conditions, low back pain is common. But neurologic signs and symptoms are more likely if the fracture pulls apart or displaces.

Then the upper portion of the bone slides forward. This puts pressure on the spinal cord or spinal nerve roots, causing severe pain, numbness, weakness, and atrophy of the muscles.

A nondisplaced fracture (even with a pseudoarthrosis) can be treated without surgery. Patients with severe back and/or leg pain (sciatica) are more likely to be candidates for operative care. Otherwise, conservative (nonoperative) care is the standard form of treatment.