Lumbosacral fusion must be considered in light of the newer concepts developed through surgical treatment of herniated intervertebral discs. Structural faults must be re-evaluated. Stabilization by fusion is still the treatment of choice in lumbosacral instability, irrespective of the spectacular results obtained after removal of the disc without fusion. Pseudarthrosis, especially of the fourth and fifth lumbar segments, has been found frequently after the regular types of fusion, and a special technique is necessary.

The technique described for accurately impacting a mortised transfacet bone block under interlaminal distraction has the following advantages:

1. The period of confinement in bed is increased very little over that required for simple removal of a herniateti disc.

2. The fusion technique adds thirty minutes or less to the time involved in removing a herniated disc.

3. There is a minimum amount of mutilation of the spinal structures.

4. The articular facets are fused, which is of mechanical advantage.

5. The bone block rigidly stabilizes interlaminal motion, immediately after being countersunk into position.

6. Extension of the spine after operation locks the bone grafts firmly into position.