A pain in the neck: Articular process joint osteochondrosis and intervertebral disc degeneration in warmblood horses

Cervical vertebral stenotic myelopathy (CVM) is a well-known syndrome in horses in which compression of the spinal cord and nerves in the neck leads to nervous signs. In warmblood horses, osteoarthrosis of the articular process joints is the most common underlying pathology resulting in CVM. The cause for the osteoarthrosis is unknown. In this thesis, first the possible role of osteochondrosis, a defect in the development of bone, in the development of articular process joint arthrosis is explored. Non-clinical osteochondrosis was found to be common, however without preference for the predilection site of osteoarthrosis. Therefore osteochondrosis does not seem a likely main cause. Yet, a significant variation in the shape of the articular surfaces of the process joints was seen and some of these shapes were correlated with the presence of osteochondrosis. Next, the possible role of intervertebral disc degeneration (IVDD) in the development of articular process joint osteoarthrosis was explored, because a correlation between the two is seen in dogs and people. Equine IVDD has been considered clinically insignificant even though research confirming this has not been published. In contrast to literature, we found that the intervertebral disc of horses does have a nucleus pulposus and that IVDD is common with a predilection site concurrent with that of osteoarthrosis. Biochemical changes, important for biomechanical characteristics, associated with equine IVDD differed from those in dogs and people. However, the changes that were found, have in human discs and in equine tendons been associated with stiffness, loss of strength and brittleness. It is likely that these biomechanical changes are also present in the degenerated equine intervertebral disc. This could lead to changes in loading of the articular process joints and therefore it is possible that equine IVDD can lead to articular process joint osteoarthrosis and CVM .