Spondylolisthesis is a malalignment of the vertebrae in which one vertebra slips forwards or backwards over the vertebra below it. There are six different types of spondylolisthesis: traumatic, iatrogenic, congenital, degenerative, pathologic, and isthmic. This type of structural abnormality of the spine can be found in all regions (i.e. cervical, thoracic, and lumbar), but most frequently occurs in the lumbar spine.
Type I: Congenital/Dysplastic
Congenital spondylolisthesis, also known as dysplastic spondylolisthesis, is an abnormality present at birth. The slip in this type of spondylolisthesis is a defect in the facet joints which connect spinal vertebrae. This occurs in the lower joints at L5 (inferior joint), the upper joints at S1 (superior joints), or at both joints and cause a gradual slip of the L5 vertebrae over time. This type of spondylolisthesis is rare compared to the other types.
Type II: Isthmic
Isthmic spondylolisthesis is the most common type of spondylolisthesis and is divided into three separate subtypes, but all have a defect at the same location in the spine. In isthmic spondylolisthesis there is a defect, typically a fracture, of the pars interarticularis, the bone that connects the upper and lower facet joints. This fracture prevents the affected vertebra from staying in line with the other vertebrae, allowing it to slide forward. The L5-S1 level is most frequently affected by isthmic spondylolisthesis.
Type III: Degenerative
Degenerative spondylolisthesis is a slip from arthritis within the spine. Degenerative changes or arthritis is common in aging individuals. Once the joints in the spine begin to wear, they have difficulty keeping the spine in line and a vertebra slips forward. This occurs most frequently in the lumbar spine, but can happen in the cervical spine as well.
Type IV: Traumatic
Traumatic spondylolisthesis is a slip due to an event that places a large amount of force on the spine. This high force results in damage to the neural arch, which is the ring of bone that surrounds the spinal cord. The fracture of the neural arch causes a sliding forward of the vertebrae. Both the cervical and lumbar spine may be affected, but this is an uncommon type of spondylolisthesis.
Type V: Pathologic
Pathologic spondylolisthesis is a slip from weakness within the bones, such as tumors, types of cancers, and bone disease. This weakening causes destruction of the posterior (backside) portion of the vertebrae, such as the neural arch, which surrounds the spinal cord. Just like the traumatic type, pathologic spondylolisthesis is a rare type.
Type VI: Iatrogenic
Iatrogenic spondylolisthesis is a slip caused directly from a prior spine surgery that involved decompression of the spine without stabilization. During decompression procedure a small amount of bone is removed to release pressure on the spinal cord and/or the nerves that branch off. The removal of too much bone during this procedure can cause the vertebral body to slip. In general, this is avoided using a stabilization surgery when a large portion of bone needs to be removed.
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