There are five types of spondylolisthesis, categorized based on the etiology:
Type I, congenital: caused by agenesis of superior articular facet
Type II, isthmic: caused by a defect in the pars interarticularis (spondylolysis)
Type III, degenerative: caused by articular degeneration as occurs in conjunction with osteoarthritis
Type IV, traumatic: caused by fracture, dislocation, or other injury
Type V, pathologic: caused by infection, cancer, or other bony abnormalities
Spondylolisthesis usually involves the L3-L4, L4-L5, or most commonly the L5-S1 vertebrae.
Types II (isthmic) and III (degenerative) are the most common.
Type II often occurs in adolescents or young adults who are athletes and who have had only minimal trauma; the cause is a weakening of lumbar posterior elements by a defect in the pars interarticularis (spondylolysis). In most younger patients, the defect results from an overuse injury or stress fracture.
Type III (degenerative) can occur in patients who are > 60 and have osteoarthritis; this form is six times more common in women than men.
Anterolisthesis requires bilateral defects.
Spondylolisthesis is graded according to the percentage of vertebral body length that one vertebra subluxes over the adjacent vertebra:
Spondylolisthesis is evident on plain lumbar x-rays. The lateral view is usually used for grading. Flexion and extension views may be done to check for increased angulation or forward movement.
Mild to moderate spondylolisthesis (anterolisthesis of ≤ 50%), particularly in the young, may cause little or no pain. Spondylolisthesis can predispose to later development of foraminal stenosis. Spondylolisthesis is generally stable over time (ie, permanent and limited in degree).
Treatment of spondylolisthesis is usually symptomatic. Physical therapy with lumbar stabilization exercises may be helpful.