What it is
Spondylolisthesis occurs when a vertebra slips forward relative to the vertebra below it. The degree of slip ranges from mild (grade I: less than 25% displacement) to severe (grade IV/V: more than 75%). Most cases in adults are either:
- Degenerative spondylolisthesis — caused by disc degeneration and facet joint arthritis allowing the vertebra to slide forward. Common at L4-5 in older adults.
- Isthmic spondylolisthesis — caused by a defect or stress fracture in the pars interarticularis (a small bony bridge on the posterior vertebra). More common at L5-S1 and often detected in adolescent athletes.
When it causes symptoms
Many people with mild spondylolisthesis have no symptoms. Symptoms arise when the slip is significant enough to narrow the spinal canal (causing stenosis and leg symptoms) or destabilize the segment enough to produce mechanical back pain.
Treatment
Conservative management — physical therapy, activity modification, and injections — is appropriate for most patients with mild to moderate slips and manageable symptoms. Surgery is considered when:
- Neurological symptoms (leg weakness, numbness, bowel or bladder changes) are present
- Conservative treatment over an adequate trial has not provided sufficient relief
- The slip is severe or progressing
Surgical treatment typically involves decompression (to relieve nerve compression) and fusion (to stabilize the segment and prevent further slippage). The exact technique depends on the grade of slip, level, and patient anatomy.