Radiological, Histological and Biochemical Characterization of a Novel Ovine Lumbar Intervertebral Disc Injury Model

Abstract

Introduction Numerous animal models of degenerative disc disease exist. Debate exists as to the ideal animal model and optimal method of inducing degeneration. The ovine lumbar spine is one accepted animal model of degenerative intervertebral disc disease. The goal of this study is to describe and characterize a novel, simple, reproducible ovine disc-injury model utilizing a drill bit inserted into the lumbar intervertebral disc to mimic disc degeneration. Material and Methods Six female sheep underwent pre-operative MRI followed by lumbar intervertebral disc injury at two levels via insertion of a 3.5mm diameter drill bit to a depth of 12 mm via a lateral retroperitoneal approach. Necropsies were performed two months following injury. Lumbar spines were explanted and underwent 9.4T MRI, radiographic imaging, gross morphological, histological and biochemical analysis. Gross morphologic assessment consisted of horizontal section of the intervertebral disc, digital photography of the surfaces. Biochemical analysis was performed for sulphated glycosaminoglycans, type I and type II collagen and DNA. Histological analysis utilized a semiquantitative grading system. Results There was no evidence of disc degeneration on pre-operative MRI. Drill bit injured discs demonstrated increased Pfirrmann degenerative scores relative to controls and pre-operative scores. Injured levels demonstrated significantly greater reductions in Disc Height Index than control levels. Gross morphological assessment similarly revealed significantly higher degenerative morphological scores in injured disc relative to pre-operative scores and controls. On biochemical analysis the annulus fibrosus (AF) at the entry point in injured discs contained less type II collagen and proteoglycans than the AF of non-injured control discs. Histological assessment demonstrated increased degenerative scores in injured disc on semiquantitative scoring. Conclusion These finding demonstrate that the 3.5mm drill bit ovine lumbar intervertebral-disc injury model produced macroscopic, radiological, biochemical and histological changes consistent with disc degeneration.