Before an exploration of the lowest two lumbar interspaces is abandoned as noncontributory, serious consideration should be given to an extended exposure by hemilaminectomy, facetectomy, or undermining foraminotomy. An ample exposure of the spinal canal is a necessary preliminary, and it has several advantages in itself

1. The spinal nerve can be clearly seen before retraction, and if it lies in a contracted space or if it is severely compressed or held taut by a large herniation, the means by which it may be released and retracted without undue damage will become apparent.

2. The extradural veins can be seen and it may be possible to retract the nerve and the dura medially without rupturing these vessels. One of the common causes of unsatisfactory results in disc surgery is the bleeding which inevitably follows tearing of the extradural veins. When this bleeding is severe, adequate exploration becomes almost impossible. Exploratory attempts under this handicap have led to damage of the exposed spinal nerve, laceration of the dura, and even to damage to the intrathecal roots.

3. The disc is disclosed to direct inspection and even to palpation. In some instances we have been able to palpate a mid-line protrusion through the dura.

4. Even if the exposure of the spinal canal does not show direct evidence of a disc herniation, then the clear visibility of the spinal nerve, the disc, and the lateral recess opening may indicate, by evidence found in the spinal canal, the direction in which an extended exposure should be carried out. Such evidence might be:

1. Pathological condition of the nerve root such as injection, oedema, scarring, or enlargement of the nerve root; or evidence of nerve-root adherence indicated by poor retractability or tension of the root; or angulation of the nerve root on retraction.

2. A contracted lateral recess, that is, the upward projecting articular process approximating the anterior structures.

3. Evidence of herniation into the foraminal canal or inadequacy of the canal, determined by probing or by calibration.

4. A positive tap test. (Mention of the tap test logically belongs here even though its evidence is usually noted before the spinal canal is entered.)

In Case 1, the clue to the herniation of the fifth lumbar disc in the lateral recess was the angulation of the first sacral nerve on retraction. In Case 5, the clue to the dissecting herniation of the fourth lumbar disc was the discovery of the injection of the fifth lumbar nerve; the dissecting herniation was then disclosed by hemilaminectomy. In Case 2, compressions of the fifth lumbar nerve in the contracted lateral recess was suspected when it was seen that the articular process of the sacrum was practically in contact with the body of the fifth lumbar vertebra, and that the first sacral nerve was placed too far medially to be affected.