Spondylolisthesis is officially categorized into five different types by the Wiltse classification system: Dysplastic, Isthmic, Degenerative, Traumatic, and Pathologic.
Dysplastic spondylolisthesis is a true congenital spondylolisthesis that occurs because of malformation of the lumbosacral junction with small, incompetent facet joints. Dysplastic spondylolisthesis is very rare, but tends to progress rapidly, and is often associated with more severe neurological deficits. It is difficult to treat because the posterior elements and transverse processes tend to be poorly developed, leaving little surface area for a posterolateral fusion.
Isthmic spondylolisthesis is the most common form of spondylolisthesis. Isthmic spondylolisthesis (also called spondylolytic spondylolisthesis) is a common condition with a reported prevalence of 5%-7% in the U.S. population. Fredrickson, et al. demonstrated that the spondylolytic defect is usually acquired between the ages of 6 and 16 years, and that the slip often occurs shortly thereafter. Once the slip has occurred, it rarely continues to progress, although one study did find an association between disc desiccation and slip progression during middle age. It is thought that the vast majority of isthmic slips do not become symptomatic, but the incidence of symptoms is unknown. One very long-term prospective study by Fredrickson, et al. that followed a cohort of 22 patients from the development of their slip into middle age, reported that many of the patients experienced occasional back pain, but so does the vast majority of people without isthmic spondylolisthesis. One patient did undergo spinal fusion at the slipped level, but the study could not verify if the isthmic slip was the indication for surgery. Roughly 90% of isthmic slips are low-grade(less than 50% slip) and 10% are high-grade (greater than 50% slip).
The most common grading system for spondylolisthesis is the Meyerding grading system for severity of slip. The system categorizes severity based upon measurements on lateral X-ray of the distance from the posterior edge of the superior vertebral body to the posterior edge of the adjacent inferior vertebral body. This distance is then reported as a percentage of the total superior vertebral body length:
- Grade 1 is 0–25%
- Grade 2 is 25–50%
- Grade 3 is 50–75%
- Grade 4 is 75–100%
- Over 100% is Spondyloptosis, when the vertebra completely falls off the supporting vertabra.
Degenerative spondylolisthesis is a disease of the older adult that develops as a result of facet arthritis and facet remodeling. As the facets remodel, they take on a more sagittal orientation, allowing a mild slip to occur. These slips are very common: a study of osteoporosis found a 30% incidence among Caucasian women older than 65 years and a 60% incidence among African-American women older than 65 years. Most slips are asymptomatic but can worsen the symptoms of neurogenic claudication when associated with lumbar spinal stenosis. Degenerative spondylolisthesis with spinal stenosis is one of the most common indications for spine surgery among older adults, and current evidence suggests that patients have much better success rates and more clinical benefit with decompression and fusion than with decompression alone.
Traumatic spondylolisthesis is very rare and may be associated with acute fracture of the inferior facets or pars interarticularis. It is treated in the same manner as are other spinal fractures, and there are only a handful of case reports on this type.
Pathologic spondylolisthesis is the last type and is also very rare. This type can occur following damage to the posterior elements from metastases or metabolic bone disease. These slips have been reported in cases of Paget’s disease of bone, tuberculosis, giant-cell tumors, and tumor metastases.
Further Reading
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