A Closer Look at Equine Joint Inflammation

A healthy joint in the limb of a horse provides a frictionless system and facilitates movement with ease. Each joint depends on the function of each of its components to serve this purpose in an equine athlete. Bone articular cartilage synovial fluid synovial membrane fibrous joint capsule and ligamentous structures make up these components. 
Subchondral bone provides contour and stability to the articular cartilage which constitutes the joint surface. In conjunction with the synovial fluid it is the articular cartilage that allows for frictionless movement and it is typically the state of the cartilage that is used to determine joint health. Articular cartilage does not have a blood supply and as such it depends on the synovial fluid in the joint to provide its nutrition. About one to twelve percent of the cartilage is made up of chondrocyte cells and the remainder is an extracellular matrix composed of collagens which provide structure proteoglycans which provide resistance to compression and water. Proteoglycans are a combination of protein and glycosaminoglycans such as chondroitin4sulfate.

The synovial fluid in a joint is produced by the synovial membrane which lines the joint cavity. This synovial membrane also clears unwanted particles from the joint and secretes proteins that contribute to joint health such as hyaluronan and lubricin. The fibrous joint capsule surrounds the synovial membrane and is supported by the periarticular ligaments.
The volume of the space in the joint varies with the location and because of the elastic nature of the joint capsule it can change depending on level of exercise and disease. Horses working at a higher level often will have synovial effusion an increased amount of fluid in the joint in certain joints such as the fetlock and hock without signs of disease being present. When a joint moves and pressure is applied to the surface of the cartilage fluid is squeezed from the surface of the cartilage and creates a wedge of fluid that separates the surfaces.
Osteoarthritis refers to a disorder of movable joints characterized by degeneration and loss of articular cartilage. It may result from a response of the joint components to exercise to repetitive trauma or to a single injury. In a young horse with normal healthy cartilage osteoarthritis is predominantly trauma related. It can result from overuse repeated cycles of athletic trauma fractures that involve the joint ligamentous injury and loss of stability of the joint or remodelling and microfractures of