Bone spavin is a common disease of horses and frequently associated with lameness.
Bone spavin is osteoarthritis or osteitis of the hock joint, usually the distal intertarsal and tarsometatarsal articulations, and occasionally the proximal intertarsal joint. This differentiates it from bog spavin which involves the joint capsule and articular cartilage.
Lesions involve degenerative joint disease, particularly on the craniomedial aspect of the hock with periarticular new bone proliferation, which eventually leads to ankylosis. Although bone spavin usually causes lameness, this may be obscured if the lesions are bilateral.
Theories advanced to explain this condition include faulty hock conformation, excessive concussion, and mineral imbalance. All breeds can be affected, but it is most prevalent in Standardbreds and Quarter Horses.
The lame horse tends to drag the toe. The forward flight of the hoof is shortened, and hock action is decreased. The lameness sometimes is continuous because the bone lesions involve the articular surfaces. The heel may become elongated. Standardbreds develop soreness in the gluteal musculature (so-called trochanteric bursitis, Trochanteric Bursitis) secondary to spavin. In advanced cases, the bony proliferation may be visible on the distal craniomedial aspect of the hock (seat of spavin). When standing, the horse may rest the toe on the ground with the heel slightly raised. The lameness often disappears with exercise and returns after rest. The spavin test (ie, trotting after limb flexion for ~60 sec) may be a useful aid to diagnosis but is not specific for this condition or even this joint. In so-called occult spavin, there are no visible or radiographic exostoses. Local anesthesia of the individual tarsal joints is necessary to localize the exact site of pain responsible for the lameness.
The disease is self-limiting, ending with spontaneous ankylosis of the affected joint(s) and a return to soundness. In the early stages, intra-articular injection of corticosteroids or sodium hyaluronate (or both) may be beneficial. NSAID (eg, phenylbutazone) eliminate or reduce the clinical signs. Working the horse after this treatment is aimed at accelerating ankylosis and resolution of lameness. Surgical arthrodesis is another means of accelerating ankylosis of the affected joint. Cunean tenotomy is commonly used but of questionable value by itself. Deep-point firing used to be advocated for hastening ankylosis, but it is very doubtful that it has any beneficial effect beyond encouraging rest. Corrective shoeing by raising the heels and rolling the toe may help but is unlikely to eliminate lameness on its own.