punctate deposits in the outer annulus, diffuse deposits in the transitional zone or inner annulus fibrosus with occasional deposits in the nucleus, or large deposits in the transitional zone extending variably into the nucleus. Their maximal incidence was in the lower lumbar discs (L4/5-L6/7) with no calcification seen in the lumbosacral or lower thoracic discs. All deposits were hydroxyapatite with large crystallite sizes (800–1300 angstrom) compared to cortical bone (300–600 angstrom). No type X-collagen, osteopontin or osteonectin, were detected in calcific deposits although positive staining for bone sialoprotein was evident. Calcified discs had less proteoglycan of smaller hydrodynamic size than non-calcified discs.
Calcification of a thoracic intervertebral disc (IVD) with prolapse and root syndromes/spinal cord compression in humans are well-documented entities. The mineral phases have been identified. Similar pathology occurs very rarely in children. It is also seen in dogs, especially the short-legged, chondrodystrophoid (CD) breeds, which are prone to disc degeneration, and in older sheep. The latter exhibit some morphological CD features. This study is based on radiological/histological/electron microscopic/x-ray diffraction studies of human operative specimens and post-mortem adult animal tissues The transitional zone (TZ), the interface between the nucleus pulposus and the annulus fibrosus, is the area of the IVD most sensitive in children and adults to the events which lead to dystrophic calcification. The TZ is the “growth plate” of the IVD and the site of maximal proteoglycan and protein synthesis. Giant hydroxyapatite crystallites are the dominant mineral phase in the human (children and adults) and canine pathology. Nucleation occurs in degraded matrix. The new observation of the type and distribution of calcification in the elderly ovine IVD suggests this animal is a suitable model for further research into the enigmatic phenomenon of so-called dystrophic IVD calcification.
We have used a sheep model of intervertebral disc degeneration to monitor the presence and organisation of nerves in the disc as degeneration progresses. This model has been used to study morphological and bio-chemical changes of the disc as it degenerates, in addition to associated alterations in end-plate vascularity and vertebral bone remodelling. One aspect of this model which has not been studied to date is how the innervation of the disc may change with the onset of degeneration. This is the object of the present study.