Though lameness problems are more prevalent in the front feet of a horse, the hocks can also be a source of concern. There is a wide range of injuries that can occur to the hocks, and a variety of reasons behind those injuries.
Dr. Terry Swanson of Littleton, Colorado, deals with lame horses nearly every day. On occasion, a horse used for pleasure will contract a problem, but the majority involve horses that are used for speed, cutting, turning and jumping. ?Watch the horses move, and then you will understand why the hocks become such a significant thing,? Dr. Swanson says. ?Pushing off is a major thing in all horses that require speed, going over fences or turning.
?As we breed horses for their speed and other things, hock problems become more significant,? he continues. ?When the competition was not so keen from one horse to the next, or when horses were not competing so strongly, the hocks weren?t such a problem.?
The hock, or tarsus, is made up of several joints acting together. The range of motion of the hock takes place where the tibia and the talus bones meet. The fibular tarsal bone forms the point of the hock, and several other tarsal bones make up the remaining joints.
Two of these bones are in a stacked formation on top of the large metatarsal, or cannon bone. They form the proximal and distal intertarsal and tarsometatarsal joints. Cartilage can be found between the bones.
Lameness in performance horses usually occurs in the bottom two joints, the distal intertarsal and the tarsometatarsal.
?The range of hock problems is from the horse that is not performing quite the way he should or has been, to the horse that is obviously lame with a hock problem,? Dr. Swanson says.
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The result of use-trauma hock problems in the distal intertarsal and tarsometatarsal joints is usually a bone spavin. This type of spavin is a firm swelling of the inside, front corner on the lower half of the hock. On the other hand, a bog spavin is a soft swelling of the front, inside corner, in the upper half of the hock. Extra fluid in the joint capsule is the cause of this swelling. A more specific trauma, such as twisting or wrenching, is normally the cause of a bog spavin.
In young horses, a bog spavin may develop as a result of vitamin or mineral imbalances. Also, if the horse is growing too fast or playing too hard, a bog spavin may occur, Dr. Swanson says. Depending upon the severity, a change in the nutritional pattern may be all that is necessary to eliminate the spavin. Draining the area and or medication will also be required at times, he says.
Another cause of a bog spavin is a fairly common disease called osteochondrosis dissecans, or OCD, Dr. Swanson says. OCD is one form of developmental orthopedic disease, a term coined by an ad hoc committee of veterinarians in 1985. With OCD, a small piece of bone inside the top joint, the tibial tarsal joint, does not attach to its parent bone, ultimately causing lameness. OCD occurs in the development of the horse, after birth, when cartilage is turning to bone. This small piece of bone may sit quietly in the hock until the horse begins to work. Then it may become a significant lameness problem. After stress is put on the leg, extra fluid will enter the hock joint, resulting in a bog spavin.
?Any time you have a bog spavin, you need to have a radiology study to try to determine what the underlying cause is,? he says. Arthroscopy surgery can be performed to remove the small bone, while having minimal cosmetic effects on the horse. If the joint capsule has not been stretched for too long, the joint will shrink down to a normal size after the surgery and once the extra fluid is flushed from the area.
Bone spavin is degenerative and proliferative changes (meaning that a growth appears) that happen in the distal joints, Dr. Swanson says.
?If they are just degenerative changes, you may not notice an outward change in the hock. But if there are any proliferative changes, that is when you notice the thickness developing,? he says.
Horses can also have ligament damage in the hocks, though it is not particularly common, Swanson says. A ligament injury in an older horse is most likely due to specific trauma, like an accident, rather than use. Curb, a pull of the plantar ligament down the back of the hock, is one such injury. This is a bridging-type ligament that keeps the hock from bending too far. Certain situations could put too much stress on the ligament, causing it to tear. Occasionally, a foal is born with signs of curb, resulting from faulty conformation of the hocks.
A sprain or tear of a ligament is usually a very significant injury. Still if it is not too severe, a horse can return to top form.
?Rest is important, and the prognosis is going to be guarded until it is healed,? Dr. Swanson says.
Before any kind of treatment can begin for a hock injury, the exact cause and origin of the injury must be pinpointed. By observing the horse move on a hard surface, abnormalities in stride length or limb flight can be detected. Veterinarians observe horses moving to and away from them, and also going in circles. The gait to catch most problems is the trot. The flexion test is also used by veterinarians. With this process, the joint is flexed for one to two minutes, and the horse is then trotted. Accentuated lameness if the horse appeared sound can indicate pain in the flexed region. The test is nonspecific at times because in order to flex the hock joint, the stifle and hip joints are also flexed. But, how the horse moves after the test will indicate where the lameness is.
A common way for veterinarians to determine the origin of lameness is to block a specific area.
?You can put a local anesthesia in the joint that you think is the problem and see how the horse responds after a few minutes,? Dr. Swanson says. ?If you get a specific diagnosis, then you know where you need to aim your therapy.?
Once the cause of the hock problem has been pinpointed, a treatment plan can begin.
?The overall management of hock problems is a better term maybe than cure or treatment,? Dr. Swanson says. ?We really don't cure these problems. We are just trying to manage them.?
Rest is, of course, one significant thing that can help any problem.
?Any kind of injury takes time to heal, and without stress,? Dr. Swanson says. But horses have no rationalization to what is going on, so as soon as something doesn't hurt them enough to avoid using it, they are going to use it,? he says. Controlling the horse's rest may be difficult but is very important to the healing process.
Surgery may be necessary for a bone spavin if other conventional methods are unsuccessful. The process, called a cunean tenectomy, involves the removal of a short section of the cunean tendon, which crosses the tarsal joint. A cunean tenectomy relieves a source of pain where the tendon crosses the spavin area. Dr. Swanson says the tendon exerts a rotation when the muscles around the hock are used.
?To take a piece of that tendon out does not make a horse any less sound but usually makes him better to some degree,? he says. ?If doesn't fix all of them, but it is one therapy that is successful.?
Another therapy would be to medicate the bottom two joints with sodium hyaluronate, more commonly known as hyaluraonic acid, or HA. The product is not an acid in the same sense of other acids. It is not caustic but instead is in the salt form.
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?It is one of the least insulting things that can be put into a joint that has inflammation, so it is frequently used,? Dr. Swanson says. Hyaluronic acid reduces the inflammation without hurting the joint. The interval for this treatment would depend upon the severity of the injury, but usually is not any more frequent than every three or four months.
?It is something that probably won?t last forever, but it helps a lot of horses for a certain length of time,? Dr. Swanson says.
Cortisone can also relieve inflammation but is used sparingly in the upper joints of the hock because it has a negative effect on the joint, he says. Cortisone changes the moisture content of cartilage, which decreases the cushioning quality. It is used more often in the lower two joints because they are low-motion joints, and the cortisone is not as detrimental.
In some cases, the body will try to fuse the bones forming the distal intertarsal joint in the hock, Dr. Swanson says. It is an inconsistent process, as not all problems will result in fusion. Also, the rate of the fusion cannot be predicted. If the fusion does occur, there is less pain for the animal, with no negative effect. The joint also can be fused chemically by a veterinarian.
?Once the fusion occurs, then it is done. It is not like other medications where it needs to be repeated in the future,? Dr. Swanson says. ?It is not like a new joint when it is fused, but it becomes a more functional joint.?