Abstract
1. The clinical features in nineteen patients with structural defects of the pars interarticularis are compared with the findings in twenty-two patients with degenerative changes in the lumbar spine, and are shown to be essentially the same.
2. It is suggested that both structural defects and degenerative changes give rise to mechanical instability of the lumbar spine. This puts an increased load on the posterior vertebral soft tissues and gives rise to a characteristic picture, the features of which are described.
3. The signs and symptoms of root compression may be superimposed on this picture, and when this is the case, decompression of the nerve roots should be undertaken in addition to spinal fusion, which is suggested as the logical treatment.
4. After fusion, with decompression when indicated, 50 per cent of the patients were completely relieved of their symptoms and 87 per cent derived worthwhile benefit.
