The elastic fiber and elastin in the human yellow ligament and intervertebral disk were studied histologically and biochemically The elastic fiber in the human intervertebral disk, which until now had not been clearly identified microscopically, was observed clearly We found the distribution of the elastic fiber in the intervertebral disk to be very sparse and irregular, and its diameter was small, being about one-tenth of that found in the yellow ligament. The elastin contents of the yellow ligament and intervertebral disk were 46 7 % ยฑ 0 9 % and 1 7 % ยฑ 0 2 % respectively (mean ยฑ SE) of the total dry weight.
The amino acid composition of elastin in the yellow ligament is similar to that of other tissue, as reported in the literature; however, that found in the intervertebral disk is significantly different It would appear, therefore, that the elastin in the intervertebral disk is of a different type from that found elsewhere.
Little is known about the elastic fiber and elastin of the intervertebral disk, although there have been some reports on the elastic fiber of the yellow ligament l 8-11, 15, 18 l The presence of elastic fiber in the intervertebral disk has long been suspected, but attempts to identify it with a light microscope were not successful until the reports by Watanabe l 16 l and Johnson et al l 5 l Buckwalter et al l 2 l observed its presence in the annulus fibrosus and the nucleus pulposus using an electron microscope.