08/26/2026
Distal Tarsitis
Brian S. Burks, DVM
Diplomate of the American Board of Veterinary Practitioners®
394 Fox Road
Apollo, PA 15613
(724) 727-3481
www.foxrunequine.com
Osteoarthritis is the most disorder of the hock (tarsus). There are several forms: Distal arthritis (bone spavin), the talocalcaneal joint (high spavin) and bog spavin when there is distention of the tibiotarsal joint. The term comes from old high German meaning sparrow, as affected horses may lift the limb similar to that of a sparrow or sparrow hawk.
Distal tarsitis, often referred to as "bone spavin", is the most common cause of clinical lameness associated with the tarsus (or hock) in horses. Distal tarsitis is an osteoarthritis and periostitis of the distal intertarsal, tarsometatarsal, and occasionally the proximal intertarsal joints.
The tarsus is homologous to the human heel. The tarsus consists of 5 joints: the tibiotarsal joint, the proximal intertarsal joint, the distal intertarsal joint, and the tarsometatarsal joint. There is also a talocalcaneal joint contained within the tibiotarsal joint. There are 10 bones: The upper row includes the calcaneus and the talus. The middle row includes the central tarsal bone, fused first and second tarsla bones and the thrid and fourth tarsal bones. The metatarsal region includes the first, second, and third metatarsal bones. The second and fourth are also known as the splint bones.
During movement, the tibiotarsal joint performs approximately 98% of the motion of the tarsus. The proximal intertarsal joint, just below the tibiotarsal joint, performs approximately 2% of the motion. The lowest two joints, the distal intertarsal and tarsometatarsal joints, move very little. In fact, if the horse did not have these joints- if there was solid bone across the distal tarsus- no unsoundness or alteration in gait could be detected.
Several types of bone spavin have been described:
Jack Spavin is a term used to describe the presence of unusually large osseous lesion(s).
High Spavin denotes osseous pathology higher (more proximal) in the joint than is typical.
Occult Spavin does not produce any significant bony projections (exostoses) associated with the distal tarsal joints. This term, therefore, is used to define clinical evidence of arthritis/ pain rather than the presence of visible bony abnormalities.
Juvenile Spavin is used to describe the occurrence of bone spavin in young horses (less than 3 years of age). This form of bone spavin occurs before the animal has done much work. While osteochondrosis (developmental orthopedic disease) is the most common cause of juvenile spavin, cuboidal bone distortion in premature or dysmature foals has also been implicated in some cases. Like other forms of spavin, juvenile spavin may occur in the presence or absence of clinical pain and/or lameness.
Dressage horses, western horses, pulling horses, Standardbreds, and Thoroughbreds are all prone to spavin, which is associated with the type of athletic activity. Icelandic horses may develop distal tarsitis, related to a mismatch of rider and the horse at the gaits in which these horses are used. The rack is a fast four-beat gait during which the hind limbs are placed very far forward, and this extreme gait is associated with the development of arthritis. Poor conformation is also a factor: bowlegged and sickle-hock conformation results in abnormal loading of the cuboidal bones and leads to OA.
Although the distal tarsal joints are not essential to normal locomotion of the horse, they are prone to instability. Chronic joint instability results in the development of joint inflammation (i.e. synovitis). Repeated compression and rotation of the tarsal bones and excessive tension on the attachment of the major dorsal ligaments have been implicated as causes of distal tarsitis. Factors which can affect the development of distal tarsitis include the horse's age, weight, breed, job description, frequency of work, intensity of work, and conformation.
Distal tarsitis may be caused from chronic compression of joint cartilage from the tarsal bones. This causes cartilage erosion, exposing the subchondral bone, which proliferates and crosses the joint spaces. Eventually this may lead to bone on bone, which is quite painful.
Uneven loading may lead to distal tarsitis. Like most joints, the distal tarsal joints are designed to bear weight uniformly from one side to the other. Medial (inside) - to lateral (outside) imbalance causes uneven loading across the articular surface(s). Excessive compression (of cartilage) is experienced along one side of the joint and excessive tension of the joint capsule and collateral ligaments is experienced along the other side. This inherently causes instability, which in turn triggers excessive bone production and proliferation along the margins of the joint; unstable joints tend to grow extra bone along their edges to try and stabilize themselves.
Conformational abnormalities which may increase the horse's chances of developing distal tarsitis include:
• Straight pelvic limbs
• Sickle hocks
• Cow hocks
Poor trimming or shoeing can also contribute to bone spavin, especially if distal limb balance is affected.
Certain activities may also contribute to abnormal, uneven, repeated and/or excessive loading of the lower hock joints, and therefore bone spavin. Such disciplines can impose excessive forces on the distal hock joints in the form of flexion (dressage), shearing stress (jumping), sudden stopping (reining), rotation (western events) or concussion (Standardbred racing).
Horses with distal tarsitis usually exhibit a gradual onset of pelvic limb lameness, most apparent during the trot and may be characterized by a hypermetric "stabby" pelvic limb flight pattern. Horses will commonly pull the pelvic limbs underneath their body and "stab" them to the outside as the foot strikes the ground surface. There is also a snapping quality to the tarsus when moving. Although lameness is frequently bilateral, horses will favor the more affected limb during exercise. A "hip hike" or a “hip drop” (pelvic excursion) is sometimes apparent, particularly when the horse is trotting with the affected limb to the inside of a circle. Lameness may worsen following a period of rest. Affected horses usually exhibit stiffness when first starting to exercise but can often warm up and improve their gait. Some horses will drag the hind toes, leading to squared off hooves or shoes.
Many affected horses will show a lack of impulsion, an inability to engage the hindquarters and to push forward from behind. When jumping, the horse may knock rails with the hind limbs, take off early or avoid the jump altogether due to pain during takeoff. Such horses will also find hill work difficult, going down the incline, which forces the horse to stabilize its weight entirely on the tarsal joints. Collection is difficult for affected horses, and they cannot maintain canter, have poor ex*****on of transitions, or a failure to sit and collect for upper level movements.
Horses with tarsal pain will shift their weight at rest, pointing one hind leg forward. They become resistant to the farrier, pulling away, leaning heavily, or reacting negatively to flexion and holding a limb up for trimming. There may be secondary back soreness from overcompensation for primary tarsal pain. Often, there is localized heat, pain, and swelling around the lower tarsal joints. It is possible to have proximolateral thoracic limb suspensory desmitis as a result of chronic overloading of the thoracic limbs
In chronic cases, firm enlargement on the inside of the hock may become visible; the swelling represents excessive proliferation of bone associated with the distal tarsal joints. Horses with moderate to severe tarsitis will usually exhibit a positive Churchill's Hock Test, a procedure which is performed during the passive lameness evaluation. A positive response to this test is manifested by pelvic limb abduction. Pelvic limb flexion ("spavin testing") during active lameness evaluation is an accurate and widely used detector of distal tarsitis. Pelvic limb flexion prior to trotting may exacerbate the lameness.
Since these abnormalities are often secondary to distal tarsitis, successful treatment of the tarsitis alone frequently results in resolution of these problems. Horses that exhibit one or more of the above mentioned clinical signs should be evaluated for the presence of distal tarsitis as a potential primary cause.
Distal tarsitis is a clinical diagnosis; demonstration of pain in distal tarsal joints is diagnostic. Pain is demonstrated upon clinical examination, lameness characteristics, response to Churchill's Hock Test and hock flexion, and response to intra-articular anesthesia. There is little appreciable effusion/distention of the lower hock joints, as this is prevented by the flexor retinaculum.
Radiographs are frequently used to assess the presence and severity of distal tarsitis. It is important to note, however, that joint inflammation (synovitis) is invisible on a radiograph, which provides only structural information. Since the tarsus is a low-motion area, radiographic changes and the presence of distal tarsitis do not always correlate. Nuclear scintigraphy (bone scan) is a more accurate assessor of the presence of distal tarsal inflammation since it provides physiologic information. This diagnostic modality has proved to be very useful in the identification of distal tarsitis.
There are several ways to treat distal tarsitis. The first involves the reduction and possibly the elimination of inflammation within the distal tarsal joints. This is achieved by the use of systemic and/or intra-articular anti-inflammatory therapy. Reduction of inflammation (arthritis/synovitis) results in improved comfort. Intra-articular therapy usually involves the use of steroids, which are extremely effective at reducing local inflammation and pain. This approach also involves an attempt to maintain normal synovial integrity within the distal tarsal joints. Systemic medications such as Adequan®, Legend®, Cosequin®, etc. are designed to improve synovial function and general joint comfort in the horse. Clinicians at Fox Run Equine Center also use intra-articular hyaluronan therapy, in combination with steroids to enhance the effect of the treatment locally.
Another form of distal tarsal therapy involves fusion of the distal intertarsal and tarsometatarsal joints. This can be accomplished surgically or by the use of a chemical agent which is infused into the distal tarsal joints. Since these joints have almost no motion, their fusion results in minimal alteration in the horse's gait. By eliminating the joint instability, inflammation and pain are also eliminated. This approach is generally reserved for those horses that have proved to be refractory to anti-inflammatory treatment and have advanced osseous changes associated with the distal tarsal joints.
Other methods of treatment include extracorporeal shock wave therapy (ECSWT) and bisphosphonate therapy. The former is a sound wave directed at the bone to stimulate bone healing by osteoblastic activity. These cells make new bone, which then leads to a more stable joint. The latter therapy is with medications such as Tildren or OsPhos. These drugs target osteoclasts which break down bone during normal bone remodeling. By preventing bone from being resorbed, the joint damage is considerably slowed and other methods of treatment used concurrently may work better than without a bisphosphonate drug.
A final method of treating arthritis is by using non-steroidal anti-inflammatory medication. These include phenylbutazone, Banamine, and Equioxx. This type of medication will decrease inflammation, and therefore destruction, of the joint. It is important to recognize that despite the several treatment modalities mentioned here, there is no ‘cure’ for arthritis in most cases. Complete fusion of the distal tarsal joints of the horse may result in a clinical ‘cure’.
