Bone Spavin

Among all the sports medicine problems faced by the horse, bone spavin is probably the most common. It affects jumping and dressage horses, endurance horses and hacks. Fortunately, with treatment it can be managed effectively for years with horses competing and with little or no limitations. With recent advances in treatment, even horses that once would have had to retired from serious work can now be treated successfully and go back to rigorous activity.

Bone spavin describes osteoarthritis in the lower three hock joints. It usually affects the two lowest joints of the hock (the tarsometatarsal and the distal intertarsal joints), with the third joint, the proximal intertarsal, being the least likely to develop bone spavin. The condition is most commonly seen in teenage and elderly horses, although it can also occur in horses from as young as 6 years.

The condition is most commonly observed in the most distal joints or low-motion joints, where the area of maximal weight bearing is almost stationary during locomotion producing a greater compressive stress compared to the high-motion joints making them susceptible to non-physiologic over loading and uneven loading and even metabolic disturbance.

Causes and Contributing factors

Whilst the exact causes are unknown, there appear to be predisposing factors:

Conformation

There are several conformational defects contributing to bone spavin.

Conformations causing uneven loading of the hocks, such as “sickle hocks” and “cow hocks”, are common.  Poor trimming or shoeing can also contribute to bone spavin in any horse, irrespective of conformation.

Activity

Types of activities, such as dressage, show jumping, hunting and racing, requiring significant hock flexion or where there may be excessive concussive or uneven forces acting on the joints, may contribute to bone spavin.

Other Factors

“Juvenile spavin” is the occurrence of spavin in horses less than 3 years old. It

usually occurs before the animal has done much work. While osteochondrosis lesions may be the likely cause in some cases, this condition can also occur secondary to distortion of the small cuboidal bones within the hock which can occur in premature or dysmature foals, or even those where turnout has been withheld at a young age.

It is also noted to have higher incidences in some breeds suggesting a genetic component such as in Icelandic Ponies

Signs of Bone Spavin

Initially, signs of bone spavin may include sporadic and vague hind limb lameness.

This is often assumed to be a “stiffness” which reduces following exercise.  In some instances it may be assumed to be due to back pain. Some horses become uncomfortable on one lead, demonstrate stiffness walking downhill or where being used for jumping, refuse or knock poles.

In many cases lameness worsens, becoming more obvious and consistent. Advanced cases may have a bony swelling on the hock, typically on the inside of the joint. Lameness, although usually worse in one leg, commonly affects both.  The affected limb usually lands toe-first, wearing down the foot faster and the affected limb usually has a shorter and lower arc of flight, as the horse tries to reduce painful flexion of the joint, giving the leg the appearance of being dragged.

Flexion tests often produce a temporary worsening of the lameness.  Although, such a response is supportive, it is not diagnostic.

Diagnosis 

A provisional diagnosis of bone spavin should be supported by further investigation to confirm the diagnosis. Like any lameness evaluation, this has to be done in a logical, progressive fashion to ensure an accurate diagnosis.

1. Intra-articular anaesthesia

Anaesthesia of an affected joint is the mainstay of confirming pain arising from that joint. Injecting local anaesthetic into the joint should abolish, or significantly reduce the lameness. The technique however, is not specific, as the lower pouches of the tarsometatarsal joint are adjacent to the suspensory ligament. This means that anaesthetic in the tarsometatarsal joint can occasionally desensitize pain arising from suspensory ligament, giving the false impression that joint pain has been abolished.

2. X-ray 

It is usually necessary to radiograph the hock.  Typical changes include bony spurs, new bone, bone destruction and/or narrowing of the joint space or even fusion of the joints.

3. Scintigraphy

Scintigraphy (bone scanning) can help in complicated cases to differentiate between suspensory desmitis and bone spavin and other differential diagnoses such as sacroiliac disease and facet joint osteoarthritis of the spine.

Treatment of Bone Spavin

Bony changes of the lower hock joint are irreversible. It is possible, however, to manage the problem, slow progression, ease pain, and control the lameness. Surgery is an option for horses that do not respond to conventional treatments.

Medications

Non-steroidal anti-inflammatory drugs (NSAIDs), such as equipalazone (bute) often helps improve the lameness in the horse. However, it is important to note that high doses of NSAIDs given long term can be associated with side effects.  NSAIDs are also illegal in competition, so it may be necessary to stop therapy several days before competition.

Corticosteroid injections into the lower hock joints are the commonest approach to treatment and often resolve the lameness for weeks or months. Unlike other joints, the drugs can be repeatedly injected into the lower tarsal joints as necessary.  Again, it is important to check association rules to ensure compliance with competition rules.

Other joint medications, such as hyaluronic acid and polysulfated glycosaminoglycans

(PSGAGs), may alleviate the pain if the horse has mild bone spavin. However, they are less useful when treating moderate or severe cases.

Tiludronate, a drug given intravenously has also been used over several years with recent publications confirming the efficacy of the drug based on over 100 evaluated cases. This acts by regulating bone remodelling through a decrease of the resorptive process and therefore ameliorating the remodelling processes active in bone spavin and alleviating pain associated with abnormal bone lysis.  The primary issue with the drug is its high relative cost per treatment.

Shoeing

Proper shoeing is critical in management. Several shoeing techniques are described, of which lateral (outside) extensions or trailers, or heel elevations and rolled or squared off toes are most commonly used. These primarily assist in improving break-over and reducing loading on the joint.

Exercise and work

It is best for a horse with bone spavin to be exercised daily. Preferably, this should be ridden or driven work, as lunging exercise places uneven stress on the joint. Pasture turnout may not be beneficial if the horse does not move much.

It is best to decrease the intensity of the workload for a horse with bone spavin.  However, even with careful management, bone spavin will progressively get worse, and the animal may not be able to continue at the level of competition it was first used for once the lameness is consistent. However, many horses can still be successful in a less-strenuous career. Frequent, light exercise is much better than no exercise at all, and a change of career may prolong the horse’s useful life.

Physiotherapy

Back pain is often a secondary problem of bone spavin because the low grade but chronic lameness seen in early cases causes the horse to alter its gait and place asymmetric stresses on pelvic and back muscles. It is fairly common for a physiotherapist to get involved at this stage when the lameness is not that obvious. Secondary back pain due to lameness often responds well to initial physiotherapy treatment, but symptoms (i.e. high muscle tone and muscle spasm in the back) will re-occur fairly quickly. It is important to recognise this pattern and refer back to the veterinary surgeon as soon as possible. Physiotherapy treatment can be effective in reducing back pain secondary to bone spavin but only when the initial cause is treated first.

Surgery

If a horse becomes unresponsive to joint injections two alternatives remain. Both are attempts to cause complete fusion (arthrodesis) of the lower two joints in the hock. As stated above, these are the joints are causing the pain. However, these joints only contribute a very small part of to the range of motion in the hock. If the joints are fused, either naturally or through medical intervention, the pain caused by the bone spavin is eliminated.

Surgical options include destruction of the joint cartilage with a drill bit and possibly filling the holes with bone grafts, or chemical arthrodesis, where a caustic substance (MIA) is injected into the joint destroying the cartilage.   In a few cases both surgical procedures are undertaken (chemical arthrodesis followed by surgical arthrodesis).  After either procedure, the horse will be lame for weeks or months until the joint has fused.  Exercise can help accelerate the fusion, so exercise on anti-inflammatories is usually prescribed following surgery.

Prognosis 

Prognosis varies depending on several factors including the severity of changes, number of joints affected, how rapidly the lameness is progressing and what the horses’ role is.  Many affected animals return to their previous level of athleticism with ongoing treatment, such as oral anti-inflammatory medication or repeated injections into the joint. Horses competing at a high level may be required to scale down their competitive careers.

Illustration: Wikimedia

Author: Ben Sturgeon

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