Histological Features of the Degenerating Intervertebral Disc in a Goat Disc-Injury Model

Study Design. An in vivo study to develop a goat large-animal model for intervertebral disc (IVD) degeneration. Objective. To determine an optimal method for inducing goat IVD degeneration suitable for testing disc regeneration therapies. Summary of Background Data. Although rodent, rabbit, and other small animal studies are useful, the narrow dimensions of IVDs in these species limit studies requiring injection of a relevant volume of therapeutics or implantation of engineered tissue constructs. For this study, the goat was selected because the size and shape of their IVDs are comparable with those of adult humans. Methods. A minimally invasive approach that did not cause significant morbidity or mortality to adult goats (n = 6) was used. Under fluoroscopic guidance, goat lumbar IVDs were injured with a 4.5-mm drill bit or #15 or #10 surgical blades. Two months postinjury, the goats were killed and their IVDs with adjacent end plates were isolated, decalcified, and stained. Results. A numerical histologic scale to categorize the degree of goat IVD degeneration was developed on the basis of the histologic features of rabbit IVDs previously described by Masuda et al, goat IVDs described by Hoogendoorn et al, and human IVDs described by Boos et al. The interrater agreement of our scoring system was assessed (weighted kappa value = 0.6646). Mann-Whitney U tests were used to compare the injured IVDs with uninjured control. A 4.5-mm drill bit inserted to a 15-mm depth resulted in a significantly higher histologic score than uninjured controls (P = 0.01). Injury with a #15 or #10 blade did not result in increased histologic scores compared with uninjured controls. Conclusion. A comparison of the various injuries inflicted showed that the use of a 4.5-mm drill bit resulted in the most significant histologic changes.