Postnatal histogenesis of the cartilage plate of the spinal column: electron microscopic observations.

The cartilage plate in the vertebral columns in mice, from birth to 45 weeks of age, were examined by light and electron microscopy. At the day of birth, the intermediate part of the vertebral body consisted of bone, and its cranial and caudal parts were composed of thick cartilage. The cartilage was divided into an outer and an inner zone, according to the shape and arrangement of chondrocytes. In the deep portion of the outer zone, calcification developed from one week, and ossification appeared at eight weeks of age. The matrix in the superficial layer of the outer zone remained metachromatic during the development of the vertebral body. The inner zone of the cartilage showed columnar arrangements of chondrocytes and a metachromatic matrix like cartilaginous growth plates in long bones. Thus, vertebral bodies show development similar to that of long bones. The findings suggest that histogenetically the cartilage plate belongs to the vertebral body but not to the intervertebral disc and that age-related changes in the cartilage plate are concerned with age-related degenerative changes of the nucleus pulposus.