- The lumbar spines from 105 fresh autopsy cases covering different ages have been examined roentgenologically. All the intervertebral discs have been cut through horizontally and examined macroscopically. In 65 cases all five lumbar discs have been systematically studied histologically. In addition, those of the remaining discs which macroscopically showed changes have been investigated histologically. One series of spines has been cut vertically in a sagittal and frontal direction and has been studied macroscopically and microscopically.
- The annulus fibrosus or, better, lamellosus, since it consists of a lamellar system or fibro-cartilage, was already found distinctly developed in a 7-months-old foetus (25 cm.) and clearly distinguishable from the nucleus pulposus. The annulus assumes its final form and thickness through interstitial and appositional growth from the long ligaments, which are a continuation of the periosteum of the vertebrae and on the intervertebral discs represent a kind of perichondrium.
- Ventrally and dorsally the annulus lamellae show distinct differences in regard to structure and course. VentraIly the ring is broader, the lamellae are more numerous and thicker. Its attachment to the anterior ligament is firmer than in the dorsal aspect. The ventral ligamunt is denser and has thicker fibres than the posterior. Towards the sides the annulus shows approximately the same structure as it does ventrally. The annulus is narrower in the dorsal aspect, and has fewer and thinner lamellae. The structure is not so distinctly marked. The attachment to the thinner posterior ligament is not so firm.
- The annulus in the adult is entirely lacking in blood vessels. Before the epiphyseal nuclei of the vertebral bodies have become ossified, isolated vessels penetrate them from the perichondrium towards the marginal edge. In the adult there are vessels in the outer layer in the long ligament; these are fewer ventrally than dorsally. Dorsally, it may occur that one or two vessels extend to the annulus, hut in that case they never penetrate into the annulus itself.
- In our cases we have not found any nerve fibres in the annulus.
- The annulus becomes metachromatic upon staining with toluidin blue, a fact that indicates that it retains a certain amount of niucopolysaccharides. It is, however, not as strongly metachromatic as the nucleus. The long ligaments do not stain violet and are not metachromatic.
- The most common changes observable in the annulus are concentric cracks or cavities. They frequently occur as early as the fifteenth year and increase as age advances both in extension and in frequency. They must be regarded as physiological phenomena and can only be imagined to acquire pathological significance if the foci become very numerous and large, with the result that the fibrocartilaginous ring becomes weaker. Their occurrence may possibly he due to disturbances of the polysaccharides in the intercellular suhstance of the annulus fihrosus.
- In a large number of cases, chiefly at the ages between 30 and 60, we have found radiating ruptures in the annulus. They are met with most frequently in the posterior part of the lower lumbar discs. If the rupture is complete and extends out towards the long ligament, there grows out from the latter a highly vascular connective tissue into the non-vascular annulus. If the rupture is small and not very extensive, a healing process, an overbridging of the annulus lesion, may set in. A fibrous scar is formed in the annulus, If, however, the rupture is more or less extensive and the disc still retains its elasticity, the ingrowth of connective tissue does not involve the formation of scars in the area in question. We have been able to follow all phases of develop- ment between a very young undifferentiated, connective tissue and a firm ahundantly fibrous connective-tissue scar, which, however, long retains its abundance of vessels.
- The frequency of radiating ruptures is highest in the two lowest lumbar discs, in which they arise far earlier than in the intervertebral discs situated higher up. The occurrence of these ruptures coincides in time wiith those periods during which lumbago and sciatica show the highest clinical frequency and before X-ray photographs can throw any light on the condition of the intervertebral disc.
- For the purposes of discussion the authors present the idea that the appearance of a highly vascular granulation tissue within the intervertehral disc may constitute a new pathological basis for low back pain.