[An electron microscopic study on the aging process of the lumbar intervertebral disc].

It is well recognized that the intervertebral disc is composed of a nucleus pulposus, an annulus fibrosus, and a cartilage plate and may play a very important role in spinal stability and kinetics. Degeneration by aging of the lumbar intervertebral disc has been implicated as an important causal factor in the development of low back pain. This study has been undertaken to evaluate the ultrastructural changes of the nucleus pulposus and the annulus fibrosus of the lower lumbar intervertebral disc which has the most pressure from outside. Morphological alteration of the chondrocytes and the collagen fibrils have been carefully investigated. Twenty-eight intervertebral discs were obtained from autopsies in the department of pathology, Nippon Medical School. The subjects ranged from a 27-week old fetus to an 84-year old man. The intervertebral disc between the 4th and 5th lumbar vertebral body was excised and the nucleus pulposus and the annulus fibrosus were isolated. The annulus fibrosus was further sectionalized to anterior inner part, anterior outer part, lateral inner part, lateral outer part, posterior inner part and posterior outer part. Every part was fixed in 2.5% glutaraldehyde, post-osmificated, dehydrated in graded alcohols and embedded in Epok 812. Ultra-thin sections were cut, stained doubly with uranyl acetate and lead citrate and observed by the Hitachi 800 electron microscope. Moreover, the Periodic Acid Methenamine Silver (PAM) stain had been applied for further detailed analysis of collagen fibril. The results obtained were as follows: 1) In the nucleus pulposus, degeneration of chondrocytes was observed from the fetal stage. 2) In the inner part of the annulus fibrosus, degeneration of chondrocytes began from the second decade and progressed rapidly during the third decade. 3) In the outer part of the annulus fibrosus, degeneration of chondrocytes began from the third decade and progressed during the fourth decade. 4) Comparing the anterior, the lateral and the posterior part of an annulus fibrosus, there was no remarkable change among them. 5) In degenerated chondrocytes, the shape of the cell membrane and nucleus was irregular, and the lacunar space was wide, where cell debris and so-called banded structures were present.