Hock Swelling in Horses and How to Manage It Effectively

Hock swelling in horses is one of the most common things owners find on a hind leg, and it covers everything from an old blemish that will never bother the horse to a joint infection that needs a vet the same day. The hocks do a great deal of the work every time your horse strikes off into canter, so it pays to know what a swelling there is likely to be. This guide works through where the swelling sits, what it usually means, how to check it yourself, how your vet will investigate it and what treatment involves, using UK vets and the published research rather than guesswork.

If you only read one section, read the next one. Everything after it is for the swelling that turns out not to be an emergency.

Hock Swelling in Horses: Is It an Emergency?

Writing in Horse & Hound in May 2020, Matt Smith MRCVS suggested owners ask four questions about any lump on a hock. Is it new? Has lameness appeared alongside it? Is it warm, or painful to touch? Is it large or tense? If the answer to any of them is yes, he says it would be prudent to consult your vet (Horse & Hound, 15 May 2020).

Some hock swellings cannot wait for a routine visit. Phone your vet straight away if you see any of these:

• Any wound on or near the hock, however small. Horse & Hound's vet advice is that the wounds with the most serious consequences tend to be the smallest, and that a wound is often far too dirty for you to see joint fluid leaking from it (Horse & Hound, Don't panic over wounds).
• Oily, clear-to-yellow fluid coming from a wound. The same article explains that this is joint fluid, and that if you see it you know a joint is involved.
• A horse that is more lame than the wound seems to justify. Horse & Hound's advice is to suspect serious damage and contact your vet immediately.
• Heat, pain and swelling around the joint with lameness, lethargy or a raised temperature. These are the signs of infectious arthritis listed by the British Horse Society. The BHS gives a healthy temperature as 37.5 to 38.5°C (BHS, Disease prevention); our guide to taking your horse's temperature, pulse and respiration shows you how.
• Sudden, severe lameness, or a horse that will barely put weight on the leg after a kick, a fall or being cast. Horse & Hound's advice on kick injuries is that any kick wound resulting in severe lameness deserves urgent veterinary attention (Horse & Hound, Dealing with kick injuries).

Why the fuss over a small hole? The hock contains joints, a tendon sheath and bursae, all lined with synovial membrane, and Horse & Hound's vet advice points out that tendon sheaths and joints are poorly designed to cope with infection, which becomes trapped inside them. A puncture at the point of the hock may not make the horse very lame at first: the MSD Veterinary Manual notes that horses with an infected calcaneal bursa might not show substantial lameness initially, then progress to not bearing weight once infection develops in the deeper bursa (MSD Veterinary Manual, Calcaneal bursitis in horses).

The research on wounds at the point of the hock shows what is at stake. In a University of Liverpool study of 24 horses with infected wounds into the calcaneal bursae, wounds reaching only the bursa under the skin had an excellent prognosis, 75% of horses survived when the deeper intertendinous bursa was involved, and only 44% survived when the bone of the point of the hock was involved (Post and colleagues, Equine Veterinary Journal 2003, PMID 14649357). A later study of 128 horses treated by endoscopic flushing of the calcaneal bursae at seven equine hospitals found 84.4% survived to leave hospital, and of the 57 with follow-up on their work, 91.2% returned to the same or a higher level. Damage to 30% or more of a tendon's cross-section made death more likely, while horses whose own vet had already given systemic antibiotics before referral were less likely to die (Isgren and colleagues, Equine Veterinary Journal 2020, PMID 31502700). The phone call costs you nothing. Waiting can cost the horse a great deal.

How the Hock Works and Why It Swells

The hock is the horse's tarsus, the joint halfway up the hind leg that corresponds to the human ankle. Matt Smith describes it as comprising at least six bones, four major joints, various supporting ligaments and a number of tendons. Horse & Hound's vet library divides it into two parts: the hock joint proper, the tarsocrural joint at the top, which provides nearly all the movement, and the lower 'spavin area' of small bones bound tightly together, which are compressed on impact and absorb the stress (Horse & Hound, All about hocks).

That top joint folds every time your horse sits behind for a downward transition, takes off at a fence, whips round the barrels in a barrel race or slides into a reining stop. The lower joints barely move at all, which turns out to matter a great deal when they become arthritic. The anatomy of the hock also includes the point of the hock, the calcaneus, where the big tendons at the back of the leg attach, and the tarsal sheath, which carries the deep digital flexor tendon over the back of the joint.

Most hock swellings are fluid, not bone. Joints, tendon sheaths and bursae are lined with a synovial membrane that produces lubricating fluid. When that lining is inflamed, which vets call synovitis, more cells, protein and fluid get in and the capsule visibly fills. As Matt Smith puts it, that inflammation is a sign of an underlying problem rather than the problem itself (Horse & Hound, 2020). Your job, and your vet's, is to work out what is behind it.

Where Is the Swelling? Reading a Swollen Hock by Location

Where a swelling sits narrows the list quickly. Treat this as a starting point, not a diagnosis: several of these can occur together, and a swelling that fits none of the rows is itself a reason to call your vet.

The locations come from the MSD Veterinary Manual's owner chapter on the hock by Jane Boswell MRCVS (MSD Veterinary Manual, Disorders of the tarsus in horses), Horse & Hound's vet library, which is also the source for blood spavin being a normal vein, and the description of bog spavin's front and back pouches. Each condition is covered in more detail below.

Common Causes of Hock Swelling in Horses

Hock swelling is a sign, not a diagnosis. These are the conditions behind most of it.

Bog Spavin

Bog spavin is swelling of the tarsocrural joint, the hock joint proper, with extra joint fluid. The MSD Veterinary Manual's professional chapter lists the possible causes as osteochondrosis, degenerative joint disease, trauma, poor joint conformation and infection, or no identifiable cause at all, with lameness present or absent depending on which (MSD Veterinary Manual, Synovitis/capsulitis of the tarsocrural joint). Horse & Hound's vet library notes that although it can follow an injury and come with lameness, it is usually seen with no lameness.

Because it can be a sign of something going on inside the joint, bog spavin deserves a vet's look even when the horse is sound. Jane Boswell's owner chapter says it should be evaluated by a vet, including X-rays to make sure there are no structural changes to the joint, and notes that in weanlings and yearlings the swelling may appear and disappear on its own.

In a young horse, think about osteochondrosis. A 2024 study of 79 Standardbred yearlings operated on for osteochondrosis of this joint described the condition as characterised by variable joint swelling in the absence of lameness, and found the amount of fluid depended on where the fragments sat and whether they were loose (Bertuglia and colleagues, Frontiers in Veterinary Science 2024, PMID 39113724). In other words, a puffy hock on a sound youngster is exactly how OCD in horses often shows itself. Our reference entry on osteochondritis dissecans covers the condition across all joints.

The MSD professional chapter adds that 'idiopathic' bog spavin, the kind with no cause found, can only be diagnosed once everything else has been ruled out, and that while it rarely interferes with the horse's use, swelling commonly returns after treatment.

Thoroughpin

Thoroughpin is swelling of the tarsal sheath, the covering of the deep digital flexor tendon just above the hock. Boswell describes fluid-filled swellings on both sides of the leg above the hock joint, which is what distinguishes it from bog spavin. It usually affects only one leg, varies in size and is usually not associated with lameness; it may resolve on its own and matters chiefly in show horses. It can also follow direct trauma such as a kick, with inflammation and bleeding into the sheath (MSD owner chapter). It is to the hock roughly what a tendon-sheath windgall is to the fetlock.

Not every swelling in that spot is a true thoroughpin. Surgeons at Newmarket Equine Hospital described 15 horses with a 'synoviocoele', a fluid-filled pocket formed where a defect in the sheath wall acts as a one-way valve, and suggested this explains some so-called 'false thoroughpins' (Minshall and Wright, Equine Veterinary Journal 2012, PMID 21668493). A sheath swelling that persists alongside lameness needs investigating, not living with.

Capped Hock

A capped hock is a swelling right on the point of the hock. The MSD Veterinary Manual defines it as distension of the bursa under the skin over the point of the hock, usually from repetitive trauma such as kicking or leaning on stable walls; it is not generally associated with lameness and is a cosmetic blemish (MSD Veterinary Manual). Horse & Hound's vet library adds banging against a fence and too little bedding to the causes, and warns that while early anti-inflammatory treatment can help, capped hocks can be difficult to treat and are a blemish for life. The same kind of pressure swelling on the front of the knee is a carpal hygroma, or capped knee.

Two things change the picture. The first is a wound over it: MSD notes that a penetrating injury can leave an abscess under the skin, and as above, infection can reach the deeper bursae and the bone. The second is a swelling at the point of the hock that arrives with sudden, severe lameness, heat and swelling after the hock has been forced to bend. Boswell describes the superficial flexor tendon being displaced from the point of the hock in exactly those circumstances. Neither is a case for waiting to see.

Curb

Boswell describes curb as a thickening or bowing of the plantar tarsal ligament that runs down the back of the hock, typically from a strain such as falling, slipping, jumping or pulling, and seen from the side as an enlargement about 10 cm (4 in) below the point of the hock. A recently formed curb typically produces noticeable inflammation and lameness, while a chronic one rarely causes lameness or pain. She notes it is most common in Standardbreds, where hock conformation makes them prone to it (MSD owner chapter). Our full guide to identifying and managing curb in horses goes into it in detail.

Bone Spavin

Bone spavin is osteoarthritis of the lower hock joints. The Dick Vet Equine Practice's fact sheet from the University of Edinburgh says it usually affects the two lowest joints, the tarsometatarsal and distal intertarsal, and is most commonly seen in teenage to elderly horses. It links the condition to cow hocks, sickle hocks and being 'in at the hocks', to poor trimming or shoeing in any horse, and to work involving a lot of hock flexion or concussion, naming dressage, show jumping, hunting and racing (Dick Vet Equine Practice, Bone spavin fact sheet).

Swelling is a late and unreliable sign. Early on, the fact sheet describes sporadic, vague hind limb lameness often put down to 'stiffness' that eases with exercise, discomfort on one canter lead, stiffness walking downhill and, in jumpers, refusals. Advanced cases may have a bony swelling on the inside of the hock, and lameness, though usually worse in one leg, is commonly in both. The horse tends to land toe first and wear that toe down, with a lower, shorter arc of flight. The MSD professional chapter adds that horses with pain in these joints can also be sore over the lumbar region (MSD Veterinary Manual, Osteoarthritis of the distal tarsal joints), and the fact sheet notes the signs may even be put down to back pain. If your horse has been labelled as having a sore back or as stiff behind, ask your vet to look at the hocks as well. The BHS lists a change in warm-up, a horse that takes longer to feel loose and ready to work, among the signs of osteoarthritis (BHS, Arthritis). Our guide to arthritis in horses covers joint disease more broadly.

Kicks, Wounds and Fractures

A kick on the hock can bruise, cut, puncture a synovial structure or crack a bone. Horse & Hound's advice on kick injuries says any puncture-type skin wound over a joint should receive veterinary care, because an infected joint rapidly becomes septic, and lists among the reasons to call the vet that the skin over a joint or tendon sheath has been penetrated, that the horse is lame, or that its tetanus vaccination is not up to date (Horse & Hound, Dealing with kick injuries). Boswell notes that chip fractures are among the more common fractures of the hock and can be small enough not to cause obvious lameness, so a hock that stays swollen after a knock may need X-rays even if the horse seems sound.

When the Whole Leg Is Swollen: Filled Legs, Cellulitis and Lymphangitis

Sometimes the hock looks swollen because the whole leg is. Horse & Hound describes filled legs as common in autumn and winter when horses stand in more, with the hind legs typically more swollen than the front and each pair filling about equally. Legs filled with this kind of fluid are cold, soft, dent under your finger and are not painful, and the swelling goes down with gentle exercise or turnout. As long as there is no heat and it does disappear with exercise or turnout, it is not usually a cause for concern (Horse & Hound, Filled legs in horses).

One hot, painful, swollen hind leg is a different matter. The same article explains that a localised infection, often from a tiny puncture or a patch of mud fever, can make the whole leg swell, and that cellulitis from a wound can cause swelling up to above the hock. When the lymphatic vessels are involved it is lymphangitis, which is more common in the hind legs; the horse is lame, in pain and often has a raised temperature. Both need your vet.

How to Check a Swollen Hock at Home

A calm, methodical look gives your vet far more to work with than 'it looks a bit puffy'. Work through it in this order:

1. Stay safe. A sore horse is less predictable and hind legs kick. Have someone hold the horse and work from the side, not directly behind.
2. Look from behind and from each side. Compare the two hocks for shape and fullness. Note exactly where any swelling sits, using the table above, and whether it is one leg or both.
3. Feel for heat and texture. Use the back of your hand on the same spot on each hock, then press gently. Joint or sheath fluid feels soft and may shift from one pocket to another, bone feels hard, and filled legs dent under a finger. Watch for flinching.
4. Check the skin. Part the hair and look carefully for any wound, scab, puncture or ooze, especially around the point of the hock and the front of the joint.
5. Take the temperature. The BHS gives a healthy range of 37.5 to 38.5°C. A swollen hock with a raised temperature is a vet call that day.
6. Watch the horse move. Walk it in a straight line on a firm, level surface, and only trot it up in hand if it is comfortable at walk. Look for a shorter stride, toe dragging or a hip that rises and falls unevenly. Our guide to lameness in horses explains how to spot a hind limb lameness.
7. Write it down and photograph it. Note when you first saw the swelling and anything that might explain it: a kick in the field, a fall, a journey, being cast, a change of bedding or work. Photograph the hock from the same angle each day so you can show your vet how it has changed.

While you wait for advice, do not work a lame horse to see if it wears off, do not lance or drain a swelling, and do not give bute or any medicine left over from a previous problem without speaking to your vet first. Bandaging needs care too: Matt Smith points out that the hock is a difficult area to bandage properly and that skin sores are a risk.

How Vets Diagnose Hock Problems

Expect your vet to watch the horse walk and trot in a straight line and on the lunge, on hard and soft ground, as the BHS describes, and then use some or all of the following:

• Flexion tests. The vet holds the hind leg flexed for 30 to 60 seconds and the horse is trotted away immediately, as described by both the BHS and the Dick Vet fact sheet. A worse trot afterwards supports hock pain but, as the fact sheet stresses, it is supportive rather than diagnostic.
• Nerve and joint blocks. Local anaesthetic placed in a joint or around nerves should abolish or reduce lameness coming from that area. The Dick Vet fact sheet notes it is not absolutely specific: anaesthetic in the lowest hock joint can occasionally numb the top of the suspensory ligament, which sits right next to it, so proximal suspensory desmitis can look like hock pain.
• X-rays. The fact sheet says four views from different angles are usually needed, looking for bony spurs, new bone, bone destruction, narrowing of the joint spaces or fusion.
• Ultrasound to look at tendons, ligaments, the tarsal sheath and the bursae, and the fluid inside them.
• Fluid sampling (synoviocentesis) when infection is possible. The Liverpool study of septic calcaneal bursitis called radiography, ultrasonography and synoviocentesis essential in those cases.
• Bone scans (scintigraphy) and other imaging in complicated cases. The Dick Vet fact sheet describes scintigraphy helping to tell bone spavin from suspensory problems, and MSD notes it can show distal hock pain when there is little change on X-ray.

Lameness and X-rays do not always agree. The MSD professional chapter notes that the severity of lameness and the extent of change on X-ray are poorly correlated, so a horse with dramatic films can be sound and one with subtle changes can be quite lame. Treat the horse, not the picture.

Treatment for Hock Swelling in Horses

Treatment follows the cause, which is why the diagnosis comes first. These are the main routes your vet may discuss.

A New Soft Swelling After Work or a Knock

For a fresh fluid swelling with no wound and no sign of infection, Matt Smith's advice is to rest the horse in the acute phase, with cold hosing and anti-inflammatory treatment such as phenylbutazone (bute) or meloxicam in consultation with your vet. He puts the acute phase at typically 10 to 14 days, after which a gradual return to work may be possible, but any persistence of significant swelling and lameness should be investigated further (Horse & Hound, 2020). For an old, cool swelling that has been there as long as you can remember and is not causing a problem, he suggests it may be enough to monitor it and otherwise leave it alone unless it changes.

Bog Spavin and Thoroughpin

Boswell's owner chapter says the fluid in a bog spavin may be drawn off by your vet to check for infection or bleeding into the joint, that corticosteroid injections into the joint give variable and short-term relief, and that keyhole surgery may be needed where bone and cartilage are involved. Bog spavin tends to recur, especially where conformation is poor. Draining it without dealing with the cause rarely lasts, which is why the X-rays come first. Where X-rays confirm OCD, Horse & Hound's vet library notes that surgery to remove the fragments is commonly performed.

For thoroughpin, the same chapter describes drawing off the fluid and injecting hyaluronic acid or a long-acting corticosteroid, sometimes repeated until the swelling stays down, and rest, anti-inflammatory drugs and cold therapy when it follows trauma. In the Newmarket synoviocoele series, endoscopic surgery to enlarge the defect in the sheath wall gave good results in 10 of the 15 horses.

Capped Hock

Early anti-inflammatory treatment can help a fresh capped hock, but the most useful thing you can do is remove the cause: deeper bedding, padding or rubber matting where the horse kicks or leans, and dealing with the kicking itself. If it is a stable habit, our guide to retraining a horse that kicks covers the behavioural side. An established capped hock on a sound horse with intact skin is usually best monitored and left alone. An infected one is a different problem: MSD says an abscess needs surgical removal and antibiotics.

Bone Spavin

The Dick Vet fact sheet is blunt that the bony changes are irreversible; the aim is to slow progression, ease pain and keep the horse working. The options it and the MSD manual describe include:

• Anti-inflammatory painkillers (NSAIDs) such as bute. MSD notes that when NSAIDs are the only treatment, lameness typically returns once they stop. The BHS warns that continuous use of bute over a long period has been associated with gastric ulcers and liver and kidney damage, and that your vet should advise on the dose.
• Joint injections. Corticosteroids are the most commonly used, alongside hyaluronan, polysulfated glycosaminoglycans and 'orthobiologic' treatments made from the horse's own blood (MSD).
• Tiludronate (Tildren). In the UK this bisphosphonate is licensed 'as an aid in the treatment of clinical signs of lameness associated with bone spavin in combination with a controlled exercise regime', for horses over 3 years old, and not for pregnant or lactating mares or horses with impaired kidney function (VMD, Tildren summary of product characteristics). A double-blind, placebo-controlled trial in 108 horses with bone spavin, 87 of which completed it and whose lead author was employed by the drug company CEVA Animal Health, found treated horses significantly less lame than those given the placebo (Gough, Thibaud and Smith, Equine Veterinary Journal 2010, PMID 20636772). Licences differ between countries, so in South Africa ask your vet what is registered locally.
• Farriery. The fact sheet calls proper shoeing critical, with shoes that ease breakover, such as a square or rolled toe, and heel support such as an egg bar helping some horses. Plan it with your vet and farrier together.
• Daily work. The fact sheet says horses with bone spavin are best exercised daily, preferably ridden or driven because lungeing puts uneven stress on the joint, and that frequent light exercise is much better than none. The BHS likewise advises avoiding long periods stabled and making the most of turnout with quiet companions on flat, even ground.
• Fusion. Because the lower hock joints barely move, they can fuse, naturally or with veterinary help, and Boswell notes the horse may then be more comfortable and able to perform. Vets can encourage fusion surgically by drilling across the joints, after which MSD says a return to full athletic performance usually takes 10 to 12 months, or chemically. In a Royal Veterinary College-led series of 24 horses given injected ethanol after joint steroids had stopped working, 11 of the 21 horses followed up long term (52%) improved, while 4 (19%) got worse, 2 of them with significant complications (Lamas and colleagues, Equine Veterinary Journal 2012, PMID 22128830).

If you compete, check your governing body's rules before any medication. The Dick Vet fact sheet notes that NSAIDs are illegal in competition and that steroids may not be permitted, so treatment may need to stop before an event; your vet can advise on timing.

Infection and Wounds

An infected joint, tendon sheath or bursa is an emergency. Horse & Hound's vet advice describes the usual approach as a general anaesthetic and flushing large volumes of fluid through the area, sometimes several times and sometimes with an arthroscope, and says treatment must be started without delay to ensure a return to soundness. Antibiotics are part of it, and in the Isgren study horses whose own vet had started systemic antibiotics before referral were less likely to die. That is your vet's call, which is one more reason to ring early.

Preventing Hock Problems

You cannot prevent every hock problem. Matt Smith compares many sheath and bursa injuries to twisting an ankle, with little you can do to reduce the risk. These steps deal with the causes that are in your hands:

• Bed deeply and pad the hard spots. Too little bedding is a named cause of capped hock. Our guide to choosing shavings for bedding may help.
• Tackle stable kicking. Repeated kicking or leaning on walls is the usual cause of capped hock, so padding the walls and finding out why the horse kicks both pay off.
• Protect the hocks when travelling. Travel boots that cover the point of the hock guard against knocks against the ramp or partition. Our guide to travelling with horses covers loading and boots.
• Keep the feet balanced. Poor trimming or shoeing can contribute to bone spavin in any horse, whatever its conformation, according to the Dick Vet fact sheet. Keep to a regular farriery routine.
• Buy with your eyes open. Cow hocks and sickle hocks predispose a horse to bone spavin, and Horse & Hound's vet library links curb to poor hock conformation. Our guide to horse conformation explains what to look for, and the horse vetting checklist covers what a pre-purchase vet examination involves. A swollen hock on a horse you are buying is a good reason to ask the vetting vet about X-rays.
• Manage weight and fitness. The BHS points out that excess weight puts added stress and strain on the joints. Build work up gradually and warm up properly, and take note if your horse starts needing longer than usual to loosen up.
• Check the hocks every day. Run your hands down both hind legs when you pick out the feet. Knowing your horse's normal is what lets you spot a new swelling the morning it appears.

The Bottom Line on Hock Swelling

Most hock swelling in horses is fluid in a joint, a tendon sheath or a bursa, and many swellings, such as an old capped hock or a cold thoroughpin, never trouble the horse. The urgent ones announce themselves with a wound, heat, pain, a raised temperature or lameness, and those need your vet the same day. A quiet swelling is not automatically a harmless one, though: a youngster's bog spavin that comes and goes can still be OCD, which Matt Smith names as its most common cause in young horses, so it deserves your vet's look and X-rays even when the horse is sound. For everything else, Matt Smith's four questions are a good filter: is it new, is the horse lame, is it warm or painful, is it large or tense? Any yes is a phone call.

Frequently Asked Questions