Growth and development of the human intervertebral disc

Abstract

The object of this study is to compare the growth and development of a lumbar intervertebral disc with those in the thoracic and cervical regions from embryonic life to childhood. Particular attention is paid to changes during and following the establishment of the secondary curvatures of the vertebral column. Current knowledge of development of the intervertebral disc is reviewed.Postmortem material from 67 cases and a large series of radiographs are used in histological and mensural studies. The vertical dimensions of the 'total disc' (which includes the cartilage plates), its parts, and the vertebral body above the disc are measured in each region at every age. Notochordal remnants in vertebrae and discs are used as 'natural markers' from which horizontal dimensions are measured in the median plane to give an indication of growth anteriorly and posteriorly from the position of the notochord.Notochordal cells appear to multiply during foetal life and infancy, playing an important role in growth and extension of the notochordal nucleus pulposus up to about three years, but they degenerate and disappear from about three to seven years.As the notochordal nucleus pulposus grows rapidly in V volume, principally by increase in its macoid matrix (notably in lumbar discs), the anulus fibrosus and cartilage plates bounding it become thinner. Associated with thinning of the cartilage plates, vertical growth of the central part of the 'total disc' slows down during the first two postnatal years.As secondary cervical and lumbar curvatures are established, the cervical and lumbar notochordal nuclei pulposi respectively move to more anterior and central positions, but the thoracic notochordal nucleus pulposus remains posteriorly situated. From two years onwards, the central parts of lumbar discs grow rapidly in height though the heights of the central parts of thoracic discs remain almost unchanged. The central situation of the lumbar nucleus pulposus in childhood, and the rapid increase in height of the central part of the lumbar 'total disc' from two to seven years are associated with corresponding changes in the shape of the cephalic and caudal end surfaces of lumbar vertebral bodies from convexity to concavity.During the same period (about two to seven years) there is an increase in the rate of antero- posterior growth of the lumbar vertebral column without any increase in its lateral growth rate.The present investigation throws further light on the work of Houston and Zaleski (1967) who demonstrate a relationship between 'activity' and vertebral body shape, and suggests that the rate of anteroposterior growth of the lumbar vertebral column, the vi the rate of vertical growth of lumbar vertebrae and 'total discs', and their changes in shape during childhood, all depend to some extent on the assumption of the normal erect posture.