An Anatomical Study of the Human Spinal Column

Since the work of Schmorl" in 1927, there has been growing interest in the study of the various degenerative changes associated with the aging process in the spinal column, especially in the intervertebral discs. The earlv developmental anatomy of the spinal column has received special attention in the attempt to explain some of these degenerative changes. This paper deals with a study of these changes in unselected cadavers. The developmental anatomy of the vertebral column has been described by several investigators.",4'16 The notochordal origin of the nucleus pulposus of the intervertebral disc, and the progressive decrease in its mucoid content during fetal life have been outlined by Keyes and Compere.' The nucleus pulposus is variously described as being large and situated somewhat posterior to the center of the disc,' or it is said to vary widely in size and position." Progressive degenerative changes occur in the intervertebral disc throughout life.'"' From the eighteenth to the seventieth year the water content of the nucleus pulposus falls from about 80 per cent to between 70 and 75 per cent." The relative avascularity of the intervertebral disc is an important factor in the production of degenerative changes, but the nature of the meager vascular supply is controversial.8'9',' -6,' Defects left in the cartilage plates of the vertebral bodies by atrophied pre-pubertal blood vessels may explain the formation of Schmorl's nodules.' Schmorl" found nuclear prolapses into the vertebral centra in 38 per cent of his routine autopsies, with a slightly higher incidence in males, and in the middle-age groups. Lumbar Schmorl's nodules have been reported in from 9.3 to 20 per cent of cadavers in various series.7'1 A brownish discoloration termed "brown degeneration" has been described in the intervertebral discs, the etiology and nature of which are not definitely known.1"' "Fissuring" is another change described in senile intervertebral discs.1' Posterior herniations of the nucleus pulposus through the annulus fibrosus are usually lateral to the posterior longitudinal ligament and may compress the spinal nerves against the vertebral pedicles or articular processes.10 In the cervical region, however, herniations may lie close enough to the midline to produce compression of the spinal cord. Andrae' found posterior herniations in 15.2 per cent of 368 spinal columns, with the greatest number in the lower dorsal and lumbar regions. Lumbar herniations posteriorly have been described in 5.3 to 16 per cent of various series of cadavers,7"' and anterior herniations in 6 per cent.7 Horwitz' found fifty instances of bulging of the annular fibers without actual herniation of the nucleus pulposus. Artificial puncture of the annulus fibrosus has produced herniations in rabbits1' and human cadavers.' Horwitz' noted one instance of posterior herniation and three of ossification of the intervertebral disc in the cervical region of fifty cadavers; however, other degenerative