Degenerative joint disease is actually several progressive disorders that result in a deterioration of some of the anatomical structures within the coffin joint.
There is a deterioration of the articular cartilage, changes within the bony structures and changes within the soft tissues involved with the joint. When the articular cartilage deteriorates, it splits into fragments similar to the effects that a jackhammer has on a smooth concrete surface.
Changes occur within the bone that result in microfractures and areas of deterioration called cysts. The joint capsule, synovial membranes and a number of associated tendons and ligaments become inflamed. When the synovial membranes are inflamed, this condition is termed synovitis. The fluid within the joint has abnormal characteristics and is excessive. The term osteoarthritis is synonymous with degenerative joint disease (DJD).
DJD in the horse can be divided into four categories: