Radiological, Morphological, Histological and Biochemical Changes of Lumbar Discs in an Animal Model of Disc Degeneration Suitable for Evaluating the Potential Regenerative Capacity of Novel Biological Agents.

Abstract

Circumferential tears of the Annulus Fibrosus (AF) are frequently observed pathological features of degenerate lumbar discs and have been associated with vascular propagation and the generation of low back pain. In order to evaluate the potential of novel biological agents to repair annular defects and arrest disc degeneration we required an animal model that would permit injection of cells or their cryoprotectant into adjacent lumbar discs of the same animal. Three lumbar discs (L2/3, L3/4 and L4/5) of 6 sheep were subjected to a peripheral lateral annular surgical incision. The adjacent uninjured lumbar L1/2 and L5/6 discs served as uninjured controls. After three months the spines were radiographed and disc height indices (DHI) calculated and Pfirrmann disc degeneration scores determined from MRI spinal images. Isolated lumbar discs were analysed morphologically, histologically and biochemically using published procedures. Disc height index measurements of injured discs revealed an average decrease of 23.67% relative to baseline values (p<0.0001). The corresponding MRI Pfirrmann degeneration scores were significantly higher than non-injured control discs (p<0.05), as were their morphology scores (p<0.005). The sulphated - glycosaminoglycan content, of the Nucleus Pulposus (NP) and injured side of the AF of lumbar discs, were significantly lower than control discs (p<0.05 and p<0.0005) respectively. Conversely, the DNA levels of the injured side of the AF were higher than the uninjured side (p<0.05). The histological scores showed higher degenerative changes in injured than in control discs (p<0.005). For all parameters monitored in this study no statistical differences were observed between the three injured lumbar discs confirming their uniform response to injury. This study therefore confirmed the suitability of this large animal model for evaluating the potential of biologicals to reconstitute degenerate ovine lumbar discs relative to their carriers/cryoprotectant.