thumb|right|200px|Drawing of a ringbone on both pastern and coffin jointsthumb|right|200px|Drawing of a ringbone, advanced stagethumb|right|200px|Drawing of lower leg bone disorders, ringbone in the upper left side
Ringbone is exostosis (bone growth) in the pastern or coffin joint of a horse. In severe cases, the growth can encircle the bones, giving ringbone its name. It has been suggested by some authors that such a colloquial term, whilst commonly used, might be misleading and that it would be better to refer to this condition as osteoarthritis of the inter-phalangeal joints in ungulates
Ringbone can be classified by its location, with "high ringbone" occurring at the level of the pastern joint (proximal interphalangeal joint), and by whether it directly involves the joint or not (articular ringbone, non-articular ringbone). "Low ringbone" occurs at the level of the coffin joint (distal interphalangeal joint). "High ringbone" is easier seen than low ringbone, as low ringbone occurs in the hoof of the horse. However, low ringbone may be seen if it becomes serious, as it creates a bony prominence on the coronet of the horse.
Causes
- Osteoarthritis (the endstage of degenerative joint disease) of the pastern or coffin joint is the primary cause of articular ringbone. Bone is then produced to try to immobilize the joint and to relieve the chronic inflammation of the joint capsule. This process may take years, and lameness will continue until the joint is completely immobilized. Although most cases of arthritis do not form noticeable bone growth, the term "ringbone" is typically still used as a colloquial term.
- Poor shoeing and conformation, such as long-toes with low heels, pigeon toes, splay foot, or unbalanced feet may predispose the horse to ringbone, as they create uneven stress on the pastern and coffin joint, unequal tension on the soft tissues, or worsen the concussion that is absorbed by the pastern area.
Signs
Ringbone usually occurs in the front legs but can also be in the hind legs, and is usually worse in one leg than the other. Ringbone is most often found in mature horses, especially those in intensive training.
Prognosis
The prognosis for continued athletic use is not as good for articular ringbone as it is for non-articular reingbone. Ringbone that is progressing rapidly has a poorer prognosis as well.