Spondylolisthesis describes a condition of a forward slippage of one vertebra over another, which may or may not be associated with demonstrable instability. The vertebrae of the spine are stacked one on top of the other and held in place by ligaments, muscles, joints, and discs. The healthy spine is flexible and moves in many planes, including flexion, extension, and rotation.
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There are five types of spondylolisthesis (congenital/dysplastic, isthmic, degenerative, traumatic, and pathological). Congenital or dysplastic spondylolisthesis is a defect in the posterior part of L5 or S1, and the abnormal orientation of the bones permits forward slippage of one vertebra on another. It is a rare condition and is frequently associated with neurologic involvement. The severity of subluxation is graded as follows: Grade I is 0% to 25%, Grade II is 26% to 50%, Grade III is 51% to 75%, and Grade IV is more than 75% of vertebral slippage as evidenced on x-ray (Devereaux).
The most common type of spondylolisthesis is isthmic or spondylolytic spondylolisthesis. Spondylolysis, which is generally a stress fracture in the posterior part of the vertebra, called the pars interarticularis, is present in this type of spondylolisthesis. Spondylolysis is the most common cause of spondylolisthesis. Isthmic spondylolisthesis most commonly occurs in the lumbar region, at the level between the fifth lumbar vertebra and the first sacral vertebra (L5-S1 level).
Degenerative spondylolisthesis is an acquired condition related to chronic degenerative disc disease and the associated changes that may lead to segmental instability The pars interarticularis is not affected in degenerative spondylolisthesis. The degeneration of intervertebral discs (degenerative disc disease) results in narrowing of the disc space, which allows the supporting structures to become lax and can lead to segmental instability, most common at L4-L5. The facet joints are also affected: the result is persistent slippage (subluxation) of the facet joints with decreased resistance to forward slippage of one vertebra on another. The slippage is limited by the structures at the back of the spine that are still intact. Degenerative spondylolisthesis is more common in women and occurs most often at L4-5.
Spondylolisthesis can also be caused by a traumatic fracture (traumatic spondylolisthesis) of the posterior elements of the vertebra, by destruction of the posterior aspect of the spine through tumor, infection, or osteoporosis (pathological spondylolisthesis), and by spinal surgery (postsurgical spondylolisthesis).
Risk: Individuals at risk for spondylolisthesis include those who have spondylolysis and those with an abnormal forward curvature of the lumbar spine (lordosis). The risk is increased in individuals who engage in contact sports (football, volleyball, or soccer), certain kinds of gymnastics, or weight lifting. Individuals with radiographic osteoarthritis and postmenopausal women with osteoporosis are also at greater risk of developing spondylolisthesis.
Spondylolytic (isthmic) spondylolisthesis is most common in white males (Froese). Women are more likely to progress to a higher degree of slippage than men (Froese).
Degenerative spondylolisthesis is three times more common in blacks than whites and usually occurs after the age of 40 (Irani). It is more common in females than males by 5 to 1 (Froese).
Congenital spondylolisthesis is twice as common in females as in males, and symptom onset is usually during adolescence (Irani).
Incidence and Prevalence: In the US, the incidence of isthmic spondylolysis is 6% to 7%, with 11.3% of cases occurring at the L4-L5 level, and 82% occurring at the L5-S1 level (Froese).
The prevalence of degenerative spondylolisthesis is 5.8% in men and 9.1% in women (Vokshoor).
The prevalence of spondylolisthesis in osteoporotic women is 28.4%, with 12% occurring at the L3-L4 level, 73% occurring at the L4-L5 level, and 28% occurring at the L5-S1 level (Nizard).
The incidence of postoperative spondylolisthesis is 11% to 14% at the vertebral level above the fused segments (Nizard).