Spondylolisthesis
Spondylolisthesis occurs most commonly in the lower part of the spine. The term literally means ‘slippage of the vertebra’ as this is what occurs. One of the lumbar vertebrae slips forward over the one below. Usually the degree of slippage is small but there are various degrees of movement and, in rare cases, the upper vertebra can slip right off.
The posterior elements of the vertebrae, conceptually, form a ‘hook’. For a vertebra to move forward there must be a break in this ‘hook’ and there are several possible causes for this to occur. In some instances there is a definite break in the posterior portion of the upper vertebra, a spondylolysis. In other instances the posterior elements become elongated, usually in association with some form of bone disease. In other instances it is the ‘facet joints’ at the back of the spine which become extremely worn in degenerative conditions of the spine and this allows the upper vertebra to move forward.
This slippage, if minor, may cause no discernable problem. Greater degrees of forward slippage will cause the lumbar spine to bend backward in order to compensate for the displacement; that is there will be an increased ‘lordosis’ of the lumbar spine.
Small degrees of slippage are generally not painful but, as the degree of slippage increases, it may be associated with some discomfort due to the movement. As the vertebra moves forward it can cause some pressure on the nerve roots at this level leading to pain radiating down one or both the legs. Spondylolisthesis due to degenerative back disease is painful as a direct result of the arthritis in the small joints of the back.
The aim of surgery, if indicated, is twofold. The first is to prevent further slippage of the vertebra, preferably with reconstitution of the ‘hook’. The second is to reduce the slippage if this is indicated and if it is possible.
The procedure is usually performed from the back. Screws are inserted into the posterior elements of the vertebra and connected with a rod. In some instances a cage is also inserted between the vertebral bodies in the front. The purposes of these implants is to stabilise the vertebrae until the bone graft, which is applied at the time of the operation, has consolidated.
The hospital stay for the operation is usually only a few days but it is necessary to protect the back with a lumbar support for about six weeks. After this time movements of the spine are encouraged.
The general risks of surgery in this region apply. It must be pointed out that smoking has been shown to reduce the healing of the bone graft. Nevertheless the operation is usually successful and significantly reduces the pain in the region. It also often improves the appearance of the back.
