1. In this series of posterior onlay grafting with fresh autogenous bone and without internal fixation, in the treatment of non-infective structural lesions in the lumbo-sacral area, 71 per cent of the patients were relieved of their symptoms, but bony fusion was obtained in only 60 per cent.

2. It is probable that with this technique twelve weeks' immobilisation in a plaster bed is required.

3. Some failures are ascribed to the use of an insufficient quantity of bone or to poor apposition of the graft to its bed.

4. It is evident that the more vertebrae one attempts to fuse the more difficult it is to succeed. When the diseased area is successfully fused but an unnecessarily long graft has been used, a pseudarthrosis above the level of the pre-operative pathology may be the cause of persisting backache. For these reasons we believe that one should not attempt to graft more vertebrae than is necessary to stabilise the local lesion.

5. The complication rate, particularly from deep vein thrombosis, was high. This major complication could perhaps be overcome by using banked bone.

6. The indications for the operation are assessed as follows. It should be done for low back pain only when there is a definite diagnosis and a limited extent of structural pathology; one can then expect excellent results when successful fusion is achieved and also an appreciably high proportion of satisfied patients even when bony fusion has not been obtained, presumably because there is a fibrous union strong enough to stabilise the affected spine.

It is inadvisable to undertake lumbar-lumbo-sacral fusion for intervertebral disc degeneration when there are more than three adjacent vertebrae involved, and in any case operation should be confined to the indicated extent.