Intervertebral disc degeneration in the dog. Part 1: Anatomy and physiology of the intervertebral disc and characteristics of intervertebral disc degeneration

Abstract

Intervertebral disc (IVD) degeneration is common in dogs and can give rise to a number of diseases, such as IVD herniation, cervical spondylomyelopathy, and degenerative lumbosacral stenosis. Although there have been many reports and reviews on the clinical aspects of canine IVD disease, few reports have discussed and reviewed the process of IVD degeneration. In this first part of a two-part review, the anatomy, physiology, histopathology, and biochemical and biomechanical characteristics of the healthy and degenerated IVD are described. In Part 2, the aspects of IVD degeneration in chondrodystrophic and non-chondrodystrophic dog breeds are discussed in depth.

Introduction

The canine spine consists of 7 cervical, 13 thoracic, 7 lumbar, 3 (fused) sacral, and a variable number of coccygeal vertebrae (Hansen, 1952, Dyce et al., 2010). The vertebral bodies of C2-S1 and all coccygeal vertebrae are interconnected by an intervertebral disc (IVD) (Dyce et al., 2010). The IVD is composed of a central nucleus pulposus (NP), an outer annulus fibrosus (AF), the transition zone (TZ), and cartilaginous endplates (EPs) (Fig. 1).

Degeneration of the IVD is a common phenomenon in dogs and can lead to disease (Brisson, 2010, da Costa et al., 2006, Meij and Bergknut, 2010). IVD degeneration is known to predispose dogs to Hansen type I cervical and thoracolumbar disc herniation (Hansen, 1952) and Hansen type II disc herniation diseases, such as degenerative lumbosacral stenosis (DLSS) (Meij and Bergknut, 2010) and cervical spondylomyelopathy (CSM) (da Costa et al., 2006). However, IVD degeneration is also a common incidental finding in dogs without clinical signs of disease (Hansen, 1952, da Costa et al., 2006, De Decker et al., 2010).

The first case report of IVD degenerative disease in a dog was published in 1881 and involved a Dachshund with sudden onset of hind limb paralysis (Janson, 1881, cited by Hansen, 1952); the mass that compressed the spinal cord was described as a ‘chondroma located only to the epidural space’. Shortly afterwards, in 1896, a more comprehensive study was published on ‘enchondrosis intervertebralis’ (Dexler, 1896, cited by Hansen, 1952), a reactive inflammation in the epidural space, but it would take another 40 years before that disease was correctly described in the veterinary literature as the herniation of NP material into the spinal canal, causing compression of the spinal cord (Tillmanns, 1939).

Pioneering studies of IVD degeneration in dogs were performed during the 1950s by the Swedish veterinarians Hansen and Olsson, in particular the study that led to the thesis by Hans-Jörgen Hansen in 1952 (Fig. 2) (Hansen, 1951, Hansen, 1952, Hansen, 1959, Olsson, 1951, Olsson and Hansen, 1952). Since their studies, numerous publications have described the clinical aspects of IVD degenerative diseases, but few have revisited the fundamental aspects of IVD degeneration (Braund et al., 1975, Braund et al., 1976, Ghosh et al., 1975, Ghosh et al., 1976a, Ghosh et al., 1976b, Ghosh et al., 1977a, Ghosh et al., 1977b, Cole et al., 1985, Cole et al., 1986, Gillett et al., 1988, Royal et al., 2009, Johnson et al., 2010). The aim of this two-part review was to summarize current literature on canine IVD degeneration. In this first part, the anatomy, physiology, histopathology, and biochemical and biomechanical characteristics of the healthy and degenerated IVD are described. In Part 2, aspects of IVD degeneration in chondrodystrophic and non-chondrodystrophic dog breeds are discussed (Smolders et al., 2013).