This condition is defined as the shifting or displacement of one vertebrae over another vertebrae. It can either occur with a shift in a forward fashion, called anterolisthesis or backward fashion, retrolisthesis. The result is typically a gradual deformity that can result in narrowing of the canal that houses the spinal cord and may result in pain. The condition is often classified based on the degree of slippage or shifing, graded as I – IV.

There are five major types of spondylolisthesis:

Type I – dysplastic spondylolisthesis is a result of a congenital defect at the L5 facets resulting in gradual slippage of the L5 vertebrae.

Type II – isthmic or spondylolytic is a lesion in the isthmus or pars interarticularis. This category can be divided into three subtypes.

Type IIA These typically are a result of micro-fractures and are also termed a stress fracture
Type IIB Also a micro stress fracture, but the injured area fills in with bone

Type IIC – this is caused by an acute fracture of the pars

Type III – degenerative process involving the facet joint that allow the movement or slippage of the vertebral bodies. This is typically seen in the older population and does not involve a pars defect

Type IV involves acute traumatic fracture of the pedicle, lamina or facet (not the pars interarticularis). A fracture resulting in slippage of the spine

Type V results in structural weakness due to a disease such as a tumor.
The most common symptom of spondylolisthesis is back pain. Many times a patient can develop a defect as a child or young adult and not suffer from symptoms until adulthood. Symptoms can also include leg pain as the slippage results in pressure on the nerves that exit the spine.

Spondylolisthesis is typically diagnosed with x-rays and is best seen on a side view of the spine. The patient may be required to perform x-rays in flexion and extension to assess the stability of the spine, but may also need more specialized tests such as a Bone Scan or CT scan. These tests will reveal the pars defect and the position of the vertebral bodies of the spine Spondylolisthesis is graded according to the amount of slippage or movement of the vertebral bodies.

Grade I – the upper vertebra has slipped forward less than 25 percent of the total width of the vertebral body
Grade II – the slip is between 25 and 50 percent
Grade III – the slip is between 50 and 75 percent
Grade IV – the slip is more than 75 percent
Grade V – the upper vertebral body has slid all the way forward off the front of the lower vertebral body

The conservative, non-surgical treatment for spondylolysis or spondylolisthesis is most commonly rest, followed by core strengthening with physical therapy, anti-inflammatory medications and possibly short term bracing.

Surgical repair the defect in the pars intra-articularis is indicated only after non-operative measures have failed to relieve symptoms. In younger patients, surgery may be used to directly repair the pars defect; in older patients or in those with some degree of instability, a fusion may be required. If a Grade III spondylolisthesis is present then a fusion may be required to stop further slippage and provide relief from the associated symptoms of instability and nerve root irritation. This involves the fusion of the abnormal vertebral bodies together to prevent further slippage, but is not performed to realign the spine so no slippage is present because it risks injury to the nerves.