Bog Spavin and Bone Spavin: Equine Hock Headaches

Despite having similar names, bog spavin and bone spavin refer to two separate conditions that can both affect a horse’s hocks.

BOG SPAVIN

You have a young horse that has been doing well in his training and you are gradually ramping up the speed and intensity of his workouts. When you groom him one afternoon, you notice a large soft swelling on one hock. You walk him around the yard and longe him. He doesn’t seem lame, but the swelling worries you.

What It Is: Bog spavin is a swelling of the upper joint – called the tarsocrural joint and also known as the tibiotarsal joint – of the hock, caused by some of the synovial fluid that normally fills the joint space leaking out into the surrounding tissue. “It is more commonly seen in younger horses, and there may be an exercise-related component,” explained Dr. David G. Wilson, DVM, Diplomate American College of Veterinary Surgeons and professor of Large Animal Surgery at the University of Saskatchewan.

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Some horses develop bog spavin because they have synovitis (inflammation of the lining of the joint capsule – a potentially very serious condition, which should be seen by a veterinarian) or have put excessive strain on the joint capsule during exercise. Most often, though, said Dr. Wilson, it is the sign of an underlying osteochondrosis lesion.

Osteochondrosis is a developmental orthopedic condition, said Dr. Wilson. In some young horses, for various reasons, some parts of the cartilage that should have hardened into bone do not, and become instead thickened areas of cartilage with an inadequate blood supply. This area of cartilage is weaker than normal, and it can be damaged during exercise that puts strain on the hocks so that fluid leaks into the joint, causing the swelling that defines a bog spavin.

While the horse is usually not lame at the time the swelling is first seen, if he continues to be worked and is not treated, lameness will eventually develop. It is recommended that the horse be seen by a veterinarian to identify the underlying causes of the bog spavin, even if lameness is not yet present.

Genetics play a small role in pre-disposing a horse to this condition, according to Dr. Wilson. Rapid growth, high energy diets and mineral imbalances can all be factors, however.

Diagnosis & Treatment: To determine the cause, a veterinarian would typically do radiographs of the affected hock to look for evidence of one or more lesion. If there are any present, the usual treatment would be arthroscopic surgery to remove the fragment of abnormal bone and cartilage.

Dr. Wilson added, however, that some veterinarians may drain the affected joints and medicate them with hyaluronic acid, corticosteroids or a combination of the two, injected into the joint. This is usually only temporarily helpful, though, and the area is likely to fill with fluid again after a period of time.

Prognosis: After surgery, the horse may need a period of rest and controlled exercise, but should eventually be able to return to normal work, according to Dr. Wilson, who said that the expected outcome for a horse with bog spavin is positive. “With surgery, there is a very good chance that the joint effusion will resolve and return to a normal appearance.”

Prevention: Developing a conditioning program that minimizes stress or injury to the hock joints can help prevent bog spavin. Ensuring the horse has a balanced diet, with no mineral deficiencies is also important. Little can be done, however, for cases caused by poor conformation.

BONE SPAVIN

Your nine-year-old gelding has been competing in show jumping for several years, but early in the show season you notice he is having some stiffness when cantering on the left lead. Later that week, when riding at home, you notice that he seems lame while walking downhill. At this point, you don’t see any swelling or tender area on the hock.

What It Is: Bone spavin is a degenerative joint disease in the lower joints of the hock that has progressed to osteoarthritis. There are three lower hock joints: the tarsometatarsal and the distal intertarsal are most often affected. The third joint, the proximal intertarsal, is less likely to develop bone spavin.

“To a large degree, it is an over-use scenario,” said Dr. Wilson. These joints are “high load,” he explained, often bearing most of the horse’s weight and energy during particular movements. As the cartilage between the joints is repeatedly compressed, it becomes eroded and can be damaged, and sometimes new bone growth appears in the area.

Horses that are required to work off their hind legs much of the time are more likely to develop bone spavin, he added. That would include, for example, reining horses, cutting horses, dressage horses and show jumpers. Conformation faults such as sickle hocks or cow hocks put additional strain and often causes uneven wear on these joints, increasing the risk.

Even if the horse has good conformation, poor trimming or shoeing can cause uneven pressure and lead to extra compression of the cartilage on one side of the joint, which puts stress on the whole joint. Sometimes bone spurs will appear at the site of the damage as well.

While bog spavin more often affects young horses, bone spavin is more common in middle-aged and older horses.

At first, the horse may only be lame in certain situations (such as walking downhill or when performing certain movements requiring the hind legs to be flexed) and the lameness may be mild. Over time, the lameness tends to become worse and to happen more often.

A “flexion test” is sometimes used to help diagnose the condition, and is something a horse owner who is concerned could try at home. For this test, one person holds the horse while a second person holds the hind leg suspected of having bone spavin in a flexed position for 45-60 seconds. When the leg is released, the person holding the horse should immediately lead him forward in a trot. If the lameness seems much worse at that point, it is likely to be a case of bone spavin.

Diagnosis & Treatment: To make a firm diagnosis, the veterinarian will consider the horse’s history of lameness and the outcome of the flexion test, and may use injections of local anaesthetics to help locate the area where the horse is experiencing pain.

“Local anaesthetic may be needed to localize the lameness to the lower joints of the hocks,” explained Dr. Wilson. When the anaesthetic medication is injected into the joint where the bone spavin is suspected, the horse should become pain-free in that area and no longer lame. (If the horse is still lame, that suggests a different cause stemming from another area of the leg or hoof.) Dr. Wilson pointed out, though, that only about half of the horses with bone spavin who are tested this way will respond to the anaesthetic. As well, the anaesthetic can spread to nearby areas, such as the suspensory ligaments. If the horse’s lameness was caused by problems in these ligaments, and not in the joints, relying on the anaesthetic injection to distinguish between bone spavin and other causes of lameness may result in misdiagnosis.

Radiographs of the hocks may also be used to help with diagnosis. The veterinarian may be able to see bone spurs, new bone growth where the cartilage is damaged, and narrowing of the joint where cartilage should be.

In many cases, the bone spavin is present in both hind legs, but it can cause lameness in just one.

Once the presence of bone spavin has been confirmed, the veterinarian’s first goal for treatment is to reduce the inflammation of the joint. While some vets might use NSAIDS (non-steroidal anti-inflammatory drugs) first, these can cause kidney damage and ulcers at high doses and can’t be used with horses competing in shows. For these reasons, corticosteroid injections into the joint are more commonly used. “Many horses respond well to this treatment,” said Dr. Wilson, “although the injections may need to be repeated.”

Other horses, he added, will not respond at all to the corticosteroids, or will respond initially, but then stop responding to ongoing injections. For these horses, injections of alcohol into the joint may be helpful.

A study led by Dr. James Carmalt of the University of Saskatchewan included 11 horses with painful bone spavins that were causing lameness. They placed 3ml. of 70 per cent ethyl alcohol in each joint, taking care to inject only those joints that did not share fluid with other nearby joints. The horses were returned to work and followed up for the next year. At the end of that year, 10 of the 11 horses were determined to be completely sound, and the remaining horse had a very low level of lameness. None needed corticosteroids or other medications, none needed a re-injection of the alcohol and no white hairs or scars were seen at the injection site. A follow-up study of 10 more horses had similar results. The horses will be re-checked five years after the initial treatment.

“In this treatment, the alcohol is thought to desensitize the joint and damage the cartilage,” Dr. Wilson said. While cartilage damage sounds like a bad thing, it is actually good, as it can speed up the process of the bones of the joint fusing and becoming stable once again. While the initial treatments were intended to relieve the horse’s pain, the ultimate goal is this bony fusion of the joint which can eventually return the horse to soundness.

Another treatment that Dr. Wilson mentioned as sometimes beneficial is systemic use of the osteoporosis drug Tildren®.

To encourage the joint to fuse, regular daily exercise is desirable. Some veterinarians recommend that work in a round pen or longeing should be avoided because the movement in a circle will put uneven stress on the joint and increase the pain. Being turned out in pasture is fine but additional exercise might still be needed – many horses don’t move around much while out in the field.

Good trimming/shoeing can also help the horse to be more comfortable by helping to make sure the wear and tear on the joint is even. Each case is somewhat different, depending on the horse’s conformation and the severity of the case so there is not one specific shoeing technique for all horses with bone spavin.

When the medications are effective, the horse can generally be ridden or worked within a month from the start of treatment, and continue to be comfortable during the time the bony fusion of the joint is taking place. It may take a year or more for the horse’s joint to completely fuse and the lameness disappear.

In horses that are still lame despite treatment with corticosteroids or alcohol, or who are taking much longer than usual for bony fusion to be completed, Dr. Wilson said surgery may be recommended. The surgery destroys part of the articular cartilage by drilling across the joint; this encourages the bone to grow and stabilize the joint.

Prognosis: Dr. Wilson said the long-term prognosis for horses with bone spavin is generally favourable. Many can return to work shortly after beginning treatment with corticosteroids or when treated with alcohol. Some horses are not able to continue at the level of competition they were being used for before the bone spavin developed, but they can often be ridden in activities that put less stress on their hocks and they will benefit from ongoing exercise.

Prevention: To prevent bone spavin, horse owners should consider whether their horses’ conformational is suitable for the sports they want to pursue.

Paying attention to trimming and shoeing is also important, to avoid joint strain and compression.