1. The usual methods of posterior arthrodesis of the lumbo-sacral joint are not satisfactory in cases in which laminectomy has been performed.

2. Estimation of fusion by mobility radiographs is unreliable and cannot distinguish between fibrous ankylosis and bony fusion.

3. Bone grafts inserted from behind between the vertebral bodies almost invariably fail to become incorporated.

4. Intertransverse arthrodesis has given promising results and is probably the best method available at present.

1. A detailed analysis of the anatomy of spondylolisthesis reveals many causes of serious interference with the nerve roots.

2. These anatomical findings can be correlated with the symptoms.

3. In association with spondylolisthesis, cases of disc prolapse, tuberculosis, and a cauda equina lesion are described.

4. Adequate decompression of the affected nerve root is essential in all cases with sciatica. The operative procedure is described.

5. The problem of arthrodesis will be discussed fully in a separate paper.