Spondylolisthesis refers to the forward displacement, or slippage, of a vertebra from its normal position. Upon diagnosis, the degree of slippage is determined radiographically. Slippage is measured in terms of grades: Grade I: 0-25%, Grade II: 26-50%, Grade III: 51-75%, Grade IV: 76-100%, Grade V, over 100% and called spondyloptosis). The cause of isthmic spondylolisthesis are fibrous defects (healed or unhealed stress fractures surrounded by fibrous tissue) in the vertebra which allow forward slippage of the vertebra over time. These defects occur in an area of the vertebra called the pars interarticularis which is a narrow area (an isthmus) of bone between the upper and lower articular processes. A defect in the pars interarticularis represents a condition known as spondylolysis. may or may not result in spondylolisthesis. The pars defect is commonly bilateral, occurring on both sides of the vertebra. The stress fracture(s) separates the anterior aspects of the vertebra from its neural arch; cycles of healing and repeat fracture occur which can lengthen the pars interarticularis itself or the fracture, allowing further displacement of the affected vertebra with increased spinal instability.
The defect usually occurs during childhood, but symptoms and vertebral slippage may not be diagnosed until middle-age; progressive slippage is precipitated by ongoing degeneration of the intervertebral disc, a consequence of aging.The pars defect is commonly found in children who participate in sports involving hyperextension, such as gymnastics or pole vaulting.
Symptoms from spondylolisthesis are uncommon or rarely severe enough in children and adolescents to seek medical attention. With children, an abnormal posture and gait (a type of waddle from reduced hip flexion and subsequent tight hamstring muscles) may be the only suggestive signs if significant slippage has occurred. Spasm of muscles along the spine on bending forward is common and may, over time, impact on spinal curvature. However, strenuous physical or sport activity may provoke low back, buttock, and leg pain in children with spondylolisthesis. Numbness, tingling, and weakness in the lower extremity may also be apparent in more advanced cases. Symptoms include back pain as well as leg pain (numbness, tingling, weakness). Pain is the main complaint in adults. The severity of symptoms and physical findings often correlate with the degree of slippage of the affected vertebrae (see grades above).
Standard radiographic examination (anterior, lateral, and oblique views) of the lumbosacral spine is performed to make the diagnosis, the lateral X-ray view being considered key to observing if slippage has occurred). On oblique views, the pars defect and fracture can be observed.
Rest or restricted activity usually decreases the symptoms in low grade spondylolisthesis. Nonoperative treatment is similar to that of degenerative spondylolisthesis (see above). As symptoms improve, activities can be reintroduced. Acute pars defects caused by trauma can be treated with a brace or cast. Complete healing of stress fractures (stable union of bone) may not occur with nonoperative treatment; however, patient symptoms may still improve.¾Recurrent symptoms in spite of significant attempts at relief with nonoperative treatment are an indication for surgical intervention.
Surgery consists of an operation to restore spinal stability by fusing the affected vertebrae with bone graft (arthrodesis), applying internal or external fixation devices to halt further forward slippage and, in some cases, by returning the displaced vertebra to normal anatomic alignment (reduction). Reduction adds to surgical risk and the complication of postoperative nerve injury (usually foot drop). Postoperative bracing (with or without reduction) may be recommended, particularly for persons with high grade slips (late Grade II and Grade III, see above). Strenuous activities or contact sports are not permitted for as long as one year postsurgery. In very advanced cases where slippage is greater than 50% (Grade III), some further slippage may occur, even with a solid fusion by strict radiologic criteria.
With progression of the vertebral slippage, compensating mechanisms affect posture, bending, and walking. For example, as the L5 or L4 vertebra moves forward, the center of gravity of the body is also moved forward and the lumbar spine above the defect shifts into a forced extension, moving the upper region of the spine backward and impacting the normal lordotic (concave) and kyphotic (convex) curves. Pelvic and trunk deformities may occur in advanced stages of spondylolisthesis where the grade of slippage is high (late Grade II and Grade III, see grades above). Scoliosis and spondylolisthesis may occur in the same person. Advanced spondylolisthesis can become incapacitating without surgical intervention.