Essentially spondylolysis is a break in the posterior elements of a vertebra. It usually occurs in the lowermost lumbar vertebra and specifically in that part of the vertebra termed the ‘pars interarticularis’; that is, the portion of the bone which lies between the upper and lower facet joints at the back of the vertebra. 

The condition is a relatively common cause for pain in the lower back, most frequently occurring in adolescents. It is usually associated with an  injury such as a fall, a motor accident, or while playing sport, such as gymnastics, which causes a sudden, forced hyper-extension of the spine .

As this occurs the lowermost process of the vertebra above is driven into the pars interarticulares of the vertebra below, causing it to break. In the normal course of events this fracture heals. In some, however, it does not, giving rise to a ‘non-union’ of the bone. Non-unions typically are painful.

Typically the pain starts during adolescence or young adulthood but occasionally it does not manifest until later life when degenerate changes occur as a result of the spondylolysis. The pain can be quite severe and is aggravated by activity. This, in a young active individual is particularly distressing.

The general measures to control backache i.e. analgesics, rest, lumbar supports, strengthening exercises to the back and weight loss often serve to relieve the pain. If, however, the pain persists at an unacceptable level the only other recourse is surgery.

In aim of surgery is to reconstruct the lost bridge of bone at the back of the vertebra and for this a small bone graft is needed. This is usually obtained from the back of the pelvis during the operation.

Bone graft, in itself, may not cause the break in the bone to heal as there is too much movement in this region. Any new tissue formed is likely to be broken down again. It is thus necessary to stabilize the region and protect the bone graft while it heals with some internal support.

      If the gap in the bone is not too wide a couple of small hooks are usually sufficient to hold the bone together while it heals. However if the gap is great, or if the vertebra has moved forward as it sometimes does (spondylolisthesis), a more substantial form of fixation is required and this usually takes the form of screws into the vertebrae held together with rods.

The possible complications for surgery are the same as those outlined in Degeneration of the spine but, all going well, the results of surgery for spondylolysis are usually rewarding. Most, if not all, pain is often relieved and the affected individual generally finds that he (or she) can lead a much more active life.