Bone spavin

Bone spavin is a bony growth within the lower hock joint of horse or cattle. It is caused by osteoarthritis, and the degree of lameness that results can be serious enough to end a horse's competitive career.

Bone spavin is osteoarthritis, or the final phase of degenerative joint disease (DJD), in the lower three hock joints. It usually affects the two lowest joints of the hock (the tarsometatarsal and the distal intertarsal joints), with the third joint, the proximal intertarsal, being the least likely to develop bone spavin. This condition has various types: jack spavin when lesion on the tarsal and carpal bones is large, and high spavin when the pathology occurs higher in the joint than is typical. Conversely, occult spavin does not produce any significant exostoses on the small tarsals, whilst bog spavin and blood spavin do not involve bony changes.

Excessive compression can cause, over time, the cartilage between the upper and lower surfaces of the lower tarsal bones to become compressed and eroded. The joint spaces then become smaller, and new bone growth may occur in the area.

Uneven loading causes excessive compression of the cartilage and bone on one side, and strain in the joint capsule and supporting ligaments on the other side. When the joint is repeatedly overloaded on the edge of its surface, exostoses, or "bone spurs," occur. Strain of the supporting ligaments can cause exostosis around the joint as well.

There are several conformational defects that contribute to bone spavin. Those that cause uneven loading of the hocks, such as sickle hocks and cow hocks, are especially noteworthy. Poor trimming or shoeing can also contribute to bone spavin in any horse, no matter what their conformation.

Certain types of activities may also contribute to uneven or repeated loading of the lower hock joints, and thus bone spavin. These include sports that require a great deal of hock flexion (dressage), stress (jumping), sudden stops or turns (western events, such as reining), or a great deal of concussion (Standardbred racing).

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