Three-dimensional observation of collagen framework of lumbar intervertebral discs.

Lumbar intervertebral discs obtained from rats, dogs and humans were examined by scanning electron microscopy. The nucleus pulposus was constructed of a loose network of fine fibrils and formed lamellated membranes in the peripheral areas. The annulus fibrosus was composed of concentric lamellae of fibrous bundles that ran uniformly in each lamella and crossed over to the bundles of adjoining lamellae. The lamellae were made of fine fibrils measuring 0.1-0.2 mu in diameter, corresponding to matured collagen fibrils. The cartilage plate consisted of a close meshwork of collagen fibrils which interconnected with the annular fibrils. From these results, it was concluded that the intervertebral disc was well developed for shock absorption at the light microscopic and ultrastructural levels. In specimens treated with chymotrypsin, the extra-fibrillar substances were easily digested in the nucleus, as well as in the annulus. The intervertebral disc may thus be easily affected by chemical agents.