Spine research in companion animals

Abstract

The present thesis consists of two parts. Part I consists of Chapters 3, 4, 5, 6 and 7. The aim of these chapters was to increase the knowledge of three spinal disorders (i.e., diffuse idiopathic skeletal hyperostosis (DISH), spondylosis deformans, and degenerative disc disease (DDD) due to intervertebral disc (IVD) degeneration) of companion animals, and to determine if these animals may serve as translational spontaneous disease models for humans. In Part II of this thesis, consisting of Chapters 8, 9 and 10 the canine model was used to study the feasibility to close the annular defect with a glue and to evaluate the performance of a nucleus pulposus prosthesis in an ex vivo canine model. The hypotheses of this thesis were: 1. Dogs may serve as optimum longitudinal spontaneous disease models for human intervertebral disc degeneration (IVDD) and DDD; 2. Dogs and cats may serve as a research population for DISH and spondylosis; 3. Dogs may serve as an optimal test population for new treatments for degenerative disc disease in man; 4. It is feasible to permanently close an annular defect with a glue; 5. A hydrogel nucleus pulposus prosthesis with a softness gradient to replace the degenerated nucleus pulposus is a surgical alternative for patients with DDD. The findings described in chapters 3-7 of this thesis indicated that hypotheses 1, 2, and 3 stating that companion animals are valuable animal models for spinal research, may be accepted with some limitations. The annular closing technique described in chapter 8, in its current composition, proved to be inadequate to close an annular defect. The NPP in its current form and in combination with the used annular closing technique as evaluated in chapters 9 and 10, was not found to be a feasible treatment option for DDD. Hypotheses 4 and 5 are therefore rejected. In conclusion, IVD degeneration, DDD, DISH, and spondylosis are prevalent spinal disorders in both humans and companion animals. There are many similarities between humans and companion animals for these spinal disorders. Companion animals are therefore valuable animal models in spinal research but species-related differences may limit the way the results are translated to humans. Especially when the availability of proper human vertebral material is lacking, canine spines may be used to assess the feasibility of surgical techniques for DDD. The annular closing technique and the hydrogel NPP described in this thesis are in their current forms inadequate DDD treatment options.