Are animal models useful for studying human disc disorders/degeneration?

Abstract

Intervertebral disc (IVD) degeneration is an often investigated pathophysiological condition because of its implication in causing low back pain. As human material for such studies is difficult to obtain because of ethical and government regulatory restriction, animal tissue, organs and in vivo models have often been used for this purpose. However, there are many differences in cell population, tissue composition, disc and spine anatomy, development, physiology and mechanical properties, between animal species and human. Both naturally occurring and induced degenerative changes may differ significantly from those seen in humans. This paper reviews the many animal models developed for the study of IVD degeneration aetiopathogenesis and treatments thereof. In particular, the limitations and relevance of these models to the human condition are examined, and some general consensus guidelines are presented. Although animal models are invaluable to increase our understanding of disc biology, because of the differences between species, care must be taken when used to study human disc degeneration and much more effort is needed to facilitate research on human disc material.

Fig. 1

Cells of the intervertebral disc differ in morphology according to the region of origin, age and species: a Annulus fibrosus cells (bovine disc); b Notochordal cells (bovine disc); c Nucleus pulposus cells (human disc)

Fig. 2

Growth plates (asterisks) occur within the vertebral bodies of many species, e.g. a sheep, unlike in the (b) human where they are restricted to the base of the cartilage endplate (CEP), interfacing between the disc and vertebral body

Fig. 3

Relative sizes of discs in different species. From left to right: human lumbar, L4–L5; bovine tail, C1–C2; sheep thoracic, T11–T12; rat lumbar and tail (arrows show the intervertebral disc location)

Fig. 4

Median range of motion (ROM) in degree in left plus right axial rotation for each single segment of the calf, sheep, pig and kangaroo spine compared to the human (human data from White and Panjabi [160])