The intervertebral ligaments as a source of segmental pain.

Steindler and Luck (1938) noted that localised lesions in the territory of the posterior primary divisions of the spinal nerves were capable of causing pain which radiated not only in this region but also in that of the anterior primary divisions. Kellgmen (1939) and Lewis and Kellgren (1939) injected hypertonic saline in the mid-line of the back and caused pain of segmental distribution which they claimed was due to stimulation of the interspinous ligaments. In consequence, Kellgren (1941, 1942) stressed the importance of lesions of the posterior intervertebral ligaments as a cause of low back pain and sciatica. Indeed, he claimed (1941) that ' ' in most patients suffering from so-called sciatica the pain is referred from a ligamentous or muscular lesion in the region of the hips or lumbosacral spine. " Study of the experimental work upon which this statement is based leads at once to certain criticisms of the technique employed, and of the inferences drawn. In the first place, the interspinous ligaments are mid-line structures connecting adjacent spinous processes. They are thin and membranous. Frazer (1940) states that they are " best developed in the lumbar region and only represented higher up by a fibrous or ameolar web. " It follows that accurate insertion of a needle into an interspinous ligament is difficult, and that to achieve it the point of the needle must lie exactly in the mid-line. Moreover, in any situation other than the lumbar region, there can be no guarantee that the injected fluid will be confined within the ligament. Keligren (1939) did not even attempt to inject fluid in the mid-line. He stated that the injecting needle was introduced " exactly in the mid-line and passed through the supraspinous ligament. It is then moved slightly to one side until the tough intemspinous ligament is felt with the needle point. At this moment the subject feels a unilateral pain, and the saline is injected. " Similarly, Lewis and Kellgren state that the needle is inserted until ' ' at a depth of about 1 to 3 cm. , the deep ligament is encountered. Carrying the needle a half-centimetre to one side of the mid-line usually gives a little pmelimillary pain that is felt unilaterally. The injection of 03 c.c. of 6 per cent. saline (or less) is made at once. .. ' ' In no case was the position of the needle point ascertained …