Diagnosis of Distal Tarsal Osteoarthritis in Horses

The distal tarsal joints (i.e., distal intertarsal, tarsometatarsal) in horses are complicated anatomic structures that are thought to absorb the torsional and shear forces applied to the limb during movement. Osteoarthritis (OA) of the distal tarsal joints is a common cause of hindlimb lameness in performance horses and is usually referred to as bone spavin. Three clinical syndromes have been associated with distal tarsal OA in horses: (1) tarsitis in standardbreds and other performance horses, (2) juvenile distal tarsal OA, and (3) adult-onset distal tarsal OA. Tarsitis is used to describe lameness attributable to the periarticular soft tissues of the distal tarsus. Juvenile distal tarsal OA is often associated with malformation of the tarsal cuboidal bones. Adult-onset distal tarsal OA usually develops as a result of repetitive joint trauma associated with prolonged use and exercise. Western performance horses and horses that are required to jump or pull a cart are commonly affected. Diagnosis is based on a combination of historical and clinical findings, lameness examination, and radiographic abnormalities within the distal tarsal joints. However, lack of abnormal physical examination findings in the remainder of the limb together with a positive full-limb flexion test often suggests a distal tarsal problem in horses prone to this condition. Radiographic findings consistent with distal tarsal OA include periarticular osteophytes or enthesiophytes, joint space irregularity and/or narrowing, and subchondral bone sclerosis and/or lysis within one or both distal tarsal joints.

Three clinical syndromes have been associated with distal tarsal osteoarthritis (OA) in horses:

• Tarsitis has been used in the past to specifically describe lameness attributed to periarticular soft tissues of the distal tarsus in standardbred racehorses. However, tarsitis can occur in other performance horses, most notably the western performance horse. Horses with tarsitis have pain and lameness originating from the distal tarsus (as determined by physical examination and diagnostic local anesthesia) but have no radiographic abnormalities consistent with distal tarsal OA. Whether horses with tarsitis