THE COMPARATIVE PATHOLOGY OF INTERVERTEBRAL DISC (IVD) CALCIFICATION

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.