What is "ringbone"

Ringbone \Ring"bone`\, n. (Far.) A morbid growth or deposit of bony matter between or on the small pastern and the great pastern bones.
--J. H. Walsh.

n. osteoarthritis affecting any of several bones of a horse's foot

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 (Rogers and Waldron, 1995: 34-35).

Ringbone can be classified by its location, with "high ringbone" occurring on the lower part of the large pastern bone or the upper part of the small pastern bone. "Low ringbone" occurs on the lower part of the small pastern bone or the upper part of the coffin bone. 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 bump on the coronet of the horse.