The hock is a complex and hard-working joint, operating in conjunction with the stifle to allow the powerful muscles of the upper limb to produce rear-end propulsion. Not surprisingly, the hock region is one of the most common sites of lameness in horses from all disciplines.

The joint comprises the high-motion tarsocrural (or tibiotarsal) joint, along with three low-motion joints — the proximal intertarsal, distal intertarsal (or centrodistal) and tarsometatarsal joints.

The tarsocrural joint is where the vast majority of flexion and extension movements occur in the hock. Due to the shape of the joint surfaces, this is limited to a single plane of movement (unlike a human ankle — the equivalent joint — which not only can flex and extend but also move inwards or outwards). The range of motion of the lower hock joints is very small, in contrast, although not insignificant.

When these small, low-motion joints develop arthritis, the normal, free-gliding functions of the joint start to fail during movement. As the problem progresses, the hock is sometimes described as “fusing”. This natural fusion is the end result of bone spavin of one or more of the low-motion hock joints. Once moderately advanced, a firm, bony swelling develops on the inside front of the hock, over the affected joint.

Bone spavin is a degenerative condition much like arthritis in humans. It can be considered a wear-and-tear condition and may be accelerated by more or harder work. Conformation and genetics are also involved in development of the problem — horses need not have a long or hard work history to suffer with the condition.

Most often, bone spavin is first identified in middle-aged horses between around nine to 11 years of age. It is not uncommon, however, to find early signs of arthritis in horses much younger than this, and some horses will develop lameness from bone spavin at only a few years of age. A wide range of breeds and disciplines are affected.

Treatment options

When considering treatments, it is important to understand that the majority of these are used to manage the condition and the associated lameness rather than trying to cure the problem. This is because the joint has become degenerative, which is irreversible.

A wide range of treatments are used for bone spavin. The most common initial approach is to inject the affected joint with an anti-inflammatory drug (a corticosteroid), similar to cortisone. Horses not being used for competition are then typically managed with long-term administration of low doses of non-steroidal anti-inflammatory drugs, such as phenylbutazone (“bute”), suxibuzone or meloxicam.

Bisphosphonate treatments such as tiludronate and clodronate are also commonly used and administered by intravenous injection to alleviate bone pain.

The practice of fusion through intervention aims to eliminate movement in the low-motion joints entirely — making the hock permanently pain free. This approach is usually reserved for when medical treatments are no longer working.

To achieve fusion, any remaining cartilage needs to be removed from the joint so that the bone surfaces can come into contact and eventually grow together. There are various methods used to remove cartilage and to try to promote hock fusion, including laser surgery, injection of alcohol or a chemical called monoiodoacetate (MIA) into the joint, or by surgical drilling of the joint.

Pros and cons

There are pros and cons of each approach to fusing the lower hock joints. Regardless of technique, fusion takes between six and 12 months to occur.

● Surgical drilling: drilling causes fusion of the joint, at least as “spot welds” at the sites of drilling. Due to the low risk of complications and good outcomes in many cases, this is the preferred technique of joint fusion for many surgeons. Despite this, it usually takes six to nine months for the joint to fuse and for lameness to improve sufficiently for the horse to return to work.

● Injection techniques: quick improvements may be seen following alcohol injection, but this is more likely due to desensitisation than fusion

of the joint — at least initially.

A sustained improvement is not seen in all cases and outcome is inconsistent, with around 60% of cases reportedly improving to some extent long term.

Both alcohol and MIA can be injected into the standing, sedated horse, but general anaesthesia is often recommended when using MIA to minimise the risk of leakage out of the joint and damage to the skin and soft tissues. In some horses, MIA injection causes significant pain during the first day or two following treatment.

MIA reliably causes destruction of cartilage and eventual joint fusion. Occasionally, however, the two low-motion joints communicate with the upper joints. Any injected alcohol or MIA that ends up in the upper joints can cause permanent and often severe lameness.

● Laser surgery: this is performed under general anaesthesia. Similar to treatment with alcohol injection, the benefits may not be limited to fusion — some horses reportedly come sound before fusion occurs on X-rays and are able to return to work quicker than with other techniques.

Laser surgery causes smaller “spots” of fusion, however, than MIA injection or surgical drilling.

What’s the prognosis?

In the early stages of bone spavin, it is not uncommon for vets to advise an owner to put the horse on bute and keep working him in the hope that the joint will eventually fuse naturally. Although this is a good approach in many cases, the concept that “all hocks eventually fuse” is a falsehood. It is the exception rather than the rule which gets to this point naturally. Most horses will show lameness again as soon as the painkillers are stopped.

Successful fusion of the lower hock joints by intervention enables most horses to return to work and experience a good improvement in lameness. No technique is 100% successful at achieving fusion, however. Success rates for drilling are typically around 70%, with results following alcohol injections seemingly less consistent.

If bone spavin is detected at a vetting, as a purchaser you should proceed with caution.

It is of vital importance that the severity of spavin is assessed with X-rays and that veterinary advice is sought. Mild spavin changes that are not making the horse lame are a relatively low risk for development of lameness in the short or medium term (months to a couple of years), but, because the condition is degenerative and progressive, long-term lameness problems may occur.

In addition, once bone spavin has been detected on a vetting, insurance companies will exclude the hocks from cover. Any treatments that may be necessary in the future will be at the new owner’s expense.

Bog vs. bone spavins

Bog spavin and bone spavin are colloquial terms describing distinctly different conditions, but due to the similar names they are often confused.

Bog spavin describes a fluidy swelling of the high-motion tarsocrural joint — the “bog” is the fluid-filled swelling you can feel, most commonly at the inside front of the hock.

A small bog spavin is a common, incidental finding of no concern, but larger bog spavins are most usually a result of bone chips in the joint.

The bony growth of a bone spavin occurs lower down the hock, frequently affecting both legs.

Ref: Horse & Hound; 16 March 2017

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What treatment options are available if your horse is diagnosed with bone spavins? H&H finds out

• Injection of the joint with corticosteroids. This reduces inflammation, provides pain relief and can be repeated as required.

• Tiludronate (Tildren) alters bone metabolism in an attempt to slow the progression of osteoarthritis. A recent large study by Gough et al showed improvement in lameness after treatment with this drug.

• Pentosan polysulphate (Cartrophen) has cartilage protecting properties and is licensed for use in dogs but not horses. There is no large clinical study in horses available, but beneficial effects have been shown in laboratory models.

• Extracorporeal shockwave therapy. Long-term evidence of the efficacy of this treatment is lacking.

• Arthrodesis (fusion) of the joint performed surgically. But effective in only approximately 60% of horses used for general riding and seems to be less so in high-level competition animals.

• Non-steroidal anti-inflammatory treatment, such as bute. Less useful in competition horses owing to doping regulations.

This is an extract from a veterinary feature on dealing with hock problems, first published in Horse & Hound (19 August, ’10)

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Osteoarthritis of the lower hock joint, also known as bone spavin, is incurable, and the aim of treatment is to manage the pain.

It has been suggested that with time the lower hock joints will spontaneously fuse and subsequently become pain-free. In my experience this is very rare. Rest may result in temporary resolution, but generally lameness recurs when work starts.

In horses with minor X-ray changes or certain types of bone spurs around the joint, my preferred treatment is to inject medicines into the joints. Corticosteroids are often effective, but the degree of response and its duration vary hugely and is unpredictable.

Some horses become pain-free for up to six months, whereas in others improvement is only seen for two to three months. It is my impression that the best results come from combining corticosteroids with a joint lubricant (hyaluronan).

Although there is physical communication between the two lower joints in only about 35% of horses, a recent study showed that therapeutic concentrations of drugs can be achieved in both joints by injecting the lowermost joint only. This is good news because it is physically easier and safer to inject into this joint.

There is an alternative medication that can be injected into the lower joints called Adequan. This works differently to corticosteroids and may prevent further degenerative change within the joint. Despite spavin being quite common, there has been no good clinical trial to compare the efficacy of this with corticosteroids.

Shoeing

Corrective trimming and shoeing may help some horses, but should be used with care and with reference to each horse’s conformation and the way it both stands and moves.

A horse with a base-narrow conformation that overloads the outside of the limb, or one who twists the foot a lot during weight bearing may benefit from a small extension to the outside branch of the shoe (making the outside branch wider), or the use of a trailer (an outward projecting spur from the heel of the shoe). Keeping the toe short and rolling the toe may facilitate breakover and help to reduce pain.

Shockwaves

Recently, shockwave therapy has been introduced as an additional treatment, and there is some indication that it may help reduce pain. However, I think that it should be seen as an extra rather than primary means of treatment. Many horses with bone spurs can return to full function managed in this way.

Obviously, in a competition horse any medication has to be carefully timed so that it complies with rules. But horses with predominantly destructive X-ray changes respond poorly to these treatments and provide a much greater challenge.

Clinical trials are now taking place to assess the efficacy of a currently unlicensed drug, Tildren, in the management of spavin. This may modify bone metabolism and stop further bone destruction, perhaps allowing repair to take place.

Joint fusion

For horses with major bone destruction, this leaves joint fusion as currently the most appropriate treatment. Joint fusion can be achieved surgically, by drilling into the joint spaces under X-ray control. The aim is to remove some of the cartilage and stimulate accelerated fusion of the joint.

The speed of response and the efficacy of fusion seem to vary hugely; some tend to develop a lot of bone around the surgical sites, which is probably not good. Generally, fusion takes six to nine months to develop and, at most, 65% of treated horses are able to return to some work.

An alternative means of fusion is to inject a chemical called sodium moniodoacetate (MIA) into the joints. This destroys the cartilage and probably local nerve endings as well. It is only feasible if the joint spaces are not already narrowed to such an extent that injection is not physically possible.

The treatment is often associated with quite severe pain within the first 15hr of treatment, but with appropriate painkillers this can usually be managed satisfactorily. Chemical fusion can be very effective and in my experience, if successful, tends to be quicker than surgical fusion.

However, if the horse has some communication between the lower and uppermost moving hock joints, it is not a suitable candidate for chemical fusion.

Whichever method of joint fusion is used, the biomechanics of the hock alter. Some horses that were successfully treated initially have gone on to develop recurrent lameness associated with osteoarthritis in the upper hock joints, or a fracture of the fused lower bone unit.

This veterinary feature was first published in Horse & Hound (8 September ’05)

Spavin is a term horse owners dread; it is the standard name for osteoarthritis of the lower hock joints. Bone spavin in horses may affect one or both of the lower hock joints, and frequently affects both legs.

The hock is a complex of several joints, with most movement occurring in the uppermost joint. There is relatively little movement of the two lowest joints, but a lot of force is transmitted through them.

Like osteoarthritis in people, the cause of spavin is not very well understood. There is a very high incidence of it in Icelandic ponies, suggesting that in this breed there is a genetic predisposition. Other factors, including trauma and conformation, may play a role. Although we tend to think of osteoarthritis as occurring in older individuals, the disease can affect horses of all ages.

For a pleasure horse, use of bute to provide long-term pain relief can be a very reasonable option. However, this depends on the degree of lameness and the response to medication. Some horses respond well, whereas others do not. This is generally related to the degree of lameness. But it has to be said that in some horses spavin is a career-ending disease.

Diagnosis of bone spavin in horses

The presence of X-ray abnormalities that are consistent with osteoarthritis does not always mean that a horse will suffer from lameness. A sound horse may have X-ray abnormalities and in many lame horses diagnosed with spavin, X-ray changes are fairly advanced when the diagnosis is first made. This means that the disease predated the onset of clinical signs.

However, once pain has been triggered it tends to be persistent. It’s therefore important to prove that the lameness is because of hock pain and not something else. This is achieved using nerve blocks. The entire hock region can be desensitised using tibial and fibular nerve blocks, or local anaesthetic solution can be placed into the lower hock joints — so-called intra-articular anaesthesia.

If the disease is advanced, intra-articular anaesthesia may give a false negative result — lameness may persist unchanged. This is because some of the pain comes from within the bones of the affected joints, which cannot be influenced by the local anaesthetic solution.

There are a variety of X-ray changes seen in horses with osteoarthritis, and recognition of these is important because it influences the likely response to treatment.

Some horses develop spurs of bone around the joints, called periarticular osteophytes. Others develop more destructive changes within the joints, with loss of cartilage resulting in joint space narrowing, with or without areas of adjacent bone loss. Such horses tend to be the lamest and most difficult to manage successfully.

Less commonly, lameness can be abolished by intra-articular anaesthesia, but the X-rays of the hock appear normal. Some of these respond very well to a single intra-articular treatment and probably had soft tissue inflammation.

However, there is a small group of horses without X-ray changes that responds very poorly to treatment. They don’t progress to develop X-ray changes and currently we don’t fully understand the mechanism of disease and pain in these. It is then important to rule out other problems, such as high suspensory injuries.

• This veterinary feature was first published in Horse & Hound (8 September ’05)

Q: Can you please explain exactly what bone spavins are, and can shoeing techniques help the condition?

Farrier Danny Eades DWCF replies: A bone spavin is a form of degenerative joint disease (DJD) found on the inside of the hock between the intertarsal and tarso-metatarsal joints.

New bone forms on these joints, distorting the outline of the inside of the hock. The horse finds flexion of the hock difficult and pain is caused when the joint is compressed. The horse will start to drag his toe as flexion of the hock becomes difficult.

With regard to shoeing, the best procedure is to roll the toe, thus easing the breakover, and elevate the heels preferably by shortening the toe and allowing the heels to grow. However, if this is not possible, sloping wedge heels should be applied. This will improve the horse’s action by relieving some of the pressure on the affected joints.

In some cases, elevating the heels can encourage the flexor tendons of the horse’s hind limbs to contract, causing problems, but unfortunately this is a risk that has to be taken.

Q: My horse has been diagnosed with spavin. The spavin is very active but he has had cortisone injected intothe tarsal bones and responded well. I want the spavin to fuse quickly and have been advised to work him hard on bute.

Can I do the usual schooling exercises, such as lungeing and circles, as long as he is sound or should I stick to riding straight lines? Also, is there a time span on the fusing or are all cases different?

Jo Holmes MRCVS replies Spavin describes arthritis in the small hock joints, usually in the Distal Intertarsal (DIT) and Tarso Metatarsal (TMT) joints.

These joints are ‘low motion’, making little contribution to flexion and extension, which is possibly why they are more susceptible to concussion.

Arthritis leads to joint fusion – cartilage is worn away and new bone grows across the joints to stabilise them.

This reduces the pain caused by instability. The process can take up to two years to complete; in the meantime, the horse shows varying degrees of lameness which often improves with exercise.

The affected leg maymove inwards, across the midline of the horse’s undercarriage.

Lack of hock flexion will cause the toe and the outside of the shoe to wear and the horse will respond positively to a flexion test.

Treating your horse medically is usually the easiest and cheapest way. Surgery can take two guises: joints are drilled across to promote rapid new bone growth or a chemical irritant is used to corrode cartilage to induce the same effect.

Surgery can achieve joint fusion in a matter of months, but having a general anaesthetic always carries a risk.

Intra-articular cortisone injections are most effective at reducing joint pain, but their effect tends to last only for six weeks and repeated injections are costly. Phenylbutazone (bute) can also relieve pain.

Work your horse normally, so long as he stays sound. If he is lame on a circle, keep to straight lines.

You may find a ‘spavin shoe’, made with a lateral extension to the outside heel, will help.

The lateral extension encourages the horse to place his weight further laterally, widening the hind limb stance back to normal and re-exerting force through the fusing joints.

Ask your farrier and check with your vet that such a shoe is appropriate.

Monitor your horse’s progress when he is off bute every so often – note how he feels when you ride him. Radiographic change to the joint can also assess the recovery speed.

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