Capped Elbow in Horses: Treatment, Shoe Boils and When To Call a Vet

A capped elbow is usually a cosmetic swelling, but it becomes more serious if it grows, becomes painful, gets infected, or keeps returning.

By Dr Duncan Houston

A soft swelling at the point of a horse’s elbow can look dramatic, especially when it appears suddenly or keeps getting bigger after the horse lies down. In many cases, this is a capped elbow, also called a shoe boil or olecranon bursitis.

The good news is that most capped elbows are not dangerous and many horses are not lame.

The frustrating part is that they can be hard to make disappear completely. Once a fluid-filled bursa forms and the area keeps being bumped by the hoof, shoe, or hard bedding, it can refill again and again. Draining the swelling may make it smaller for a while, but unless the trauma stops, the bursa often comes back with the enthusiasm of a bad sequel.

The key is knowing when to leave it alone, when to prevent further trauma, and when swelling at the elbow needs veterinary treatment.

Quick Answer

A capped elbow, or shoe boil, is a fluid-filled swelling over the point of the elbow caused by repeated trauma, most commonly the horse’s hoof or shoe hitting the elbow when lying down. It is often nonpainful and cosmetic, but it can become serious if it becomes infected, painful, draining, very large, or associated with lameness. Treatment focuses on removing the cause, using a shoe boil roll or padded pastern collar, improving bedding, and avoiding unnecessary drainage unless your vet recommends it. MSD Veterinary Manual notes that capped elbows are usually cosmetic unless infected, and that the bursa often refills after aspiration. (MSD Veterinary Manual)

What Is a Capped Elbow?

A capped elbow is swelling over the olecranon, which is the point of the elbow.

The medical term is olecranon bursitis. A bursa is a small fluid-filled sac that forms or enlarges where tissue is repeatedly rubbed, compressed, or traumatised. In horses, capped elbows often develop as an acquired bursa, meaning a fluid-filled swelling forms where repeated trauma has irritated the tissue.

Merck Veterinary Manual describes capped elbow and capped hock as inflammatory swellings of subcutaneous bursae in horses, also called hygromas. The affected bursa may start soft and fluid-filled, then become firmer and more fibrous over time, especially if the trauma keeps happening. (Merck Veterinary Manual)

In everyday terms: a capped elbow is usually a protective fluid pocket that formed because the area kept being hit or pressured.

Useful, in theory.

Very annoying, in practice.

Why Is It Called a Shoe Boil?

The name “shoe boil” comes from the classic cause: the horse’s shoe or heel striking the elbow when the horse lies down or gets up.

This can happen when:

• The horse lies with the front limb folded tightly

• The heel or shoe contacts the elbow

• The shoe projects behind the heel

• The horse lies on hard ground or thin bedding

• The horse repeatedly rests in a position that puts pressure on the elbow

MSD Veterinary Manual states that olecranon bursitis is thought to be caused by the shoe hitting the point of the elbow when the horse lies down. Merck also lists trauma from hard floors, kicks, shoes projecting beyond the heels, prolonged recumbency, and horses hitting their own elbows while trotting as causes of capped elbows. (MSD Veterinary Manual)

Despite the name, barefoot horses can still develop capped elbows if the hoof, heel, or repeated pressure hits the same area.

So yes, “shoe boil” can happen without a shoe. Horses enjoy making terminology irritating.

What Does a Capped Elbow Look Like?

A capped elbow usually appears as a swelling at the back or point of the elbow.

It may be:

• Soft and fluid-filled

• Round or oval

• Moveable under the skin

• Nonpainful

• Cool or only mildly warm

• Larger after lying down

• Smaller at some times than others

• Firm or fibrous if chronic

• On one elbow, occasionally both

Most uncomplicated capped elbows do not cause obvious lameness. MSD notes that olecranon bursitis usually develops as a nonpainful swelling that does not typically interfere with movement unless it becomes greatly enlarged. (MSD Veterinary Manual)

More concerning signs include:

• Pain on palpation

• Heat

• Redness

• Rapid enlargement

• Lameness

• Drainage

• A wound over the swelling

• Thick pus or foul smell

• Fever or depression

• Swelling spreading down the limb

Those signs change the conversation from “cosmetic shoe boil” to “possible infection, abscess, trauma, or deeper elbow problem.”

Why Capped Elbows Are So Hard To Treat

Capped elbows are frustrating because the problem is mechanical.

If the horse keeps hitting the elbow, the body keeps reacting.

The bursa can continue producing fluid, and the bursal wall can thicken over time. Merck notes that chronic bursitis develops with repeated trauma, fibrosis, and chronic change, with excess fluid accumulating and the bursal wall becoming thickened by fibrous tissue. (Merck Veterinary Manual)

This is why simply draining the fluid often fails.

The swelling may shrink temporarily, but the bursa can refill if the underlying trauma remains. MSD specifically notes that fluid can be removed aseptically, but the bursa usually refills over time. (MSD Veterinary Manual)

That is the whole capped elbow problem in one sentence:

If you do not stop the elbow being hit, the swelling usually keeps coming back.

How Worried Should You Be?

Low Concern

This is more likely when:

• The swelling is soft and nonpainful

• The horse is not lame

• The skin is intact

• There is no heat, discharge, or wound

• The swelling is stable or slowly improving

• The horse is bright and comfortable

Action: focus on prevention. Use deeper bedding, check shoe fit, and use a shoe boil roll or padded pastern collar if the hoof or shoe is striking the elbow.

Moderate Concern

This is more likely when:

• The swelling is getting larger

• The swelling keeps returning

• The area is mildly warm

• The horse reacts slightly when touched

• The swelling is becoming firm or fibrous

• The horse has recently changed shoeing, bedding, stabling, or turnout surface

Action: arrange a vet check. The aim is to confirm it is a capped elbow, rule out infection or deeper injury, and stop the repeated trauma early.

High Concern

This is more likely when:

• The horse is lame

• The swelling is painful

• The swelling is hot

• There is a wound over the elbow

• The bursa is draining

• The swelling is rapidly enlarging

• The skin looks stretched or damaged

• The horse has had the swelling drained before and it returned worse

Action: call your vet promptly. Infection, abscessation, deeper trauma, or elbow joint involvement needs to be ruled out.

Critical

Treat this as urgent if:

• The horse is significantly lame

• There is fever or depression

• There is pus or foul discharge

• The swelling bursts open

• The limb becomes swollen below the elbow

• The horse has severe pain around the elbow

• The horse cannot bear weight normally

• There has been a kick, fall, or collision

• An elbow fracture is possible

Action: call your vet urgently. Do not attempt to drain or lance the swelling yourself.

When Is a Capped Elbow an Emergency?

A simple, soft, nonpainful capped elbow is not usually an emergency.

Call your vet urgently if your horse has:

• Sudden severe lameness

• A hot, painful elbow swelling

• Drainage or pus

• A wound over the swelling

• Fever

• Depression or reduced appetite

• Rapid increase in size

• Swelling spreading down the limb

• Severe pain when the elbow is touched

• A dropped elbow or abnormal limb posture

• Recent trauma to the elbow

MSD notes that infection of the bursa is painful, causes lameness, and can break open and drain. Merck also states that septic bursitis is more serious and is associated with pain and lameness. (MSD Veterinary Manual)

A hot, painful, draining swelling is not a normal cosmetic shoe boil anymore. That horse needs a vet.

What Else Can Look Like a Capped Elbow?

Not every elbow swelling is a shoe boil.

Important rule-outs include:

Olecranon Fracture

A fracture of the point of the elbow is much more serious. MSD notes that olecranon fracture is the most common elbow injury in horses and can cause a characteristic dropped-elbow, flexed-carpus, non-weight-bearing lameness. (MSD Veterinary Manual)

Septic Bursitis

This is infection within the bursa. It may occur after drainage, a wound, puncture, or rupture. It is painful and can cause lameness and discharge.

Abscess

An abscess near the elbow may look like swelling but is usually more painful, warmer, and may develop drainage.

Cellulitis

Cellulitis can cause diffuse limb swelling, heat, pain, and lameness. It is usually not a neat, localised fluid pocket.

Haematoma or Seroma

A kick or blunt trauma may cause blood or serum accumulation under the skin.

Elbow Joint Disease

Uncommon, but elbow osteoarthritis, joint trauma, collateral ligament injury, or other deeper elbow problems can cause lameness and swelling.

Tumour or Mass

Rare, but persistent firm masses that do not behave like bursitis should be assessed.

Pressure Sore or Wound

Horses lying on hard ground can develop skin trauma, pressure sores, or infected wounds around bony points.

The main point: a classic shoe boil is usually soft, localised, and not painful. Pain, heat, lameness, drainage, or rapid change means you need to think wider.

How Do Vets Diagnose a Capped Elbow?

Diagnosis is often based on the appearance and location of the swelling, but your vet may need to rule out more serious causes.

A vet may assess:

• Size and shape of the swelling

• Whether it is soft, firm, or fluctuant

• Pain on palpation

• Heat

• Skin damage

• Drainage

• Lameness

• Shoe fit and hoof contact

• Bedding and stable surface

• Whether the horse’s heel or shoe can reach the elbow

• Whether deeper elbow structures may be involved

Imaging may be needed when the swelling is painful, chronic, infected, large, traumatic, or not typical.

MSD notes that radiography and ultrasonography are used to evaluate the bony and soft tissues associated with olecranon bursitis. (MSD Veterinary Manual)

Ultrasound

Ultrasound can help assess:

• Fluid content

• Bursa wall thickness

• Fibrous tissue

• Septations or internal bands

• Abscess formation

• Soft tissue damage

• Whether the swelling looks simple or complicated

Radiographs

X-rays may be recommended if:

• There was trauma

• The horse is lame

• A fracture is possible

• The swelling is very painful

• Bone involvement is suspected

• The elbow joint needs assessment

Radiographs are especially important if the horse has a dropped elbow, severe lameness, or a history of a kick or fall.

How Are Capped Elbows Treated?

Treatment depends on whether the swelling is new, chronic, infected, painful, cosmetic, or interfering with movement.

The treatment priorities are:

1. Remove the cause of trauma.

2. Prevent the hoof or shoe from hitting the elbow.

3. Improve bedding and surfaces.

4. Avoid unnecessary invasive treatment.

5. Treat infection promptly if present.

6. Consider surgery only for selected chronic or complicated cases.

Step One: Remove the Cause

This is the most important treatment.

If the horse’s hoof or shoe is hitting the elbow, use a shoe boil roll or padded pastern collar. This sits around the pastern and prevents the heel or shoe from contacting the elbow when the horse lies down.

MSD states that treatment generally involves applying a padded collar, also called a donut, to the pastern to prevent direct contact between the shoe and the skin over the elbow. Merck also states that a shoe-boil roll should be used to prevent recurrence when the hoof or shoe is causing the capped elbow. (MSD Veterinary Manual)

Also consider:

• Checking whether the shoe extends too far behind the heel

• Discussing shoeing changes with the farrier

• Removing sharp or projecting shoe edges

• Using deeper bedding

• Avoiding hard lying surfaces

• Using stall mats with adequate bedding over them

• Monitoring the horse when travelling or stabled away from home

If the cause stays, the swelling usually stays.

Early Mild Cases

Early, mild capped elbows may respond to conservative care.

Options may include:

• Removing the source of trauma

• Shoe boil roll or padded pastern collar

• Deep bedding

• Cold hosing or cold packs in early acute swelling

• NSAIDs if painful and prescribed by your vet

• Monitoring size and skin condition

• Avoiding unnecessary drainage

Merck notes that acute early cases may respond to cold water application and NSAIDs, with the underlying cause removed. (Merck Veterinary Manual)

In practice, the best outcome usually comes when the owner acts early, before the bursal wall becomes thick, fibrous, and permanent-looking.

Should a Capped Elbow Be Drained?

Sometimes, but not routinely.

Aspiration may temporarily reduce the size of the swelling, but it carries two problems:

• The bursa often refills.

• Introducing a needle can introduce infection.

MSD notes that bursal fluid can be removed aseptically but usually refills over time. Merck notes that aspiration and intrabursal treatment may be used when cosmetic results are important, but the procedure carries a risk of introducing infection. (MSD Veterinary Manual)

That means drainage should be a veterinary decision, not a DIY procedure.

Do not puncture, lance, squeeze, or inject a capped elbow at home.

A sterile swelling is annoying.

An infected bursa is a much bigger problem.

What About Corticosteroid Injection?

In selected noninfected cases, a vet may aspirate the bursa and inject medication such as a corticosteroid. This is sometimes considered when cosmetic reduction is important or when the swelling is persistent but not infected.

However, this must be done aseptically and only after infection has been ruled out.

It is not appropriate if:

• The bursa is infected

• The skin is damaged

• There is drainage

• The horse is systemically unwell

• There is significant wound contamination

• A deeper elbow problem has not been ruled out

Steroids in an infected bursa are a great way to make a problem more dramatic, and not in the fun show-jumping way.

When Are Antibiotics Needed?

Antibiotics are not needed for a simple, sterile capped elbow.

They may be needed if there is:

• Septic bursitis

• A draining wound

• Pus

• Cellulitis

• Fever

• Spreading swelling

• Confirmed bacterial infection

• Surgical treatment of an infected bursa

Merck states that local and systemic antimicrobials are indicated in infected bursitis, and that infected fluid drainage and debridement of infected bursal tissue are required. (Merck Veterinary Manual)

Antibiotics should be chosen by your vet. A capped elbow is not a “throw leftover antibiotics at it” situation.

When Is Surgery Needed?

Surgery is reserved for selected cases.

It may be considered when:

• The capped elbow is chronic and fibrous

• The swelling is very large

• It interferes with movement

• It repeatedly becomes infected

• It ruptures or drains

• Conservative treatment fails

• The horse is lame because of it

• There is significant bursal wall thickening or internal septation

MSD notes that surgical placement of drains with bandaging and rest for 8 weeks can be successful, but chronic or infected olecranon bursitis is difficult to treat. Merck states that surgical treatment, usually curettage and drainage, is recommended for advanced chronic cases causing lameness or cases that become infected. (MSD Veterinary Manual)

Surgery is challenging because the elbow is hard to protect. Every time the horse lies down, pressure and movement can stress the surgical site.

Postoperative care may involve:

• Bandaging where possible

• Drain management

• Strict rest

• Deep bedding

• Preventing the hoof from striking the elbow

• Shoe boil roll once safe

• Antibiotics if infected

• NSAIDs as prescribed

• Regular rechecks

• Careful wound monitoring

Some chronic cases are surgically manageable. Some are cosmetically imperfect forever. That is not failure. That is bursitis being bursitis.

What About Cauterisation or Strong Iodine?

Older treatment approaches have included chemical irritation or cauterisation techniques intended to scar down or shrink the bursa lining.

This is not a routine first-line treatment and should not be done by owners.

These methods can irritate tissue, worsen inflammation, damage skin, and complicate infection risk if used incorrectly. If a vet considers a chemical treatment in a specific case, it should be part of a controlled plan after proper diagnosis.

For most horses, the safer and more practical priority is still prevention of trauma, padding, bedding, and conservative management unless infection or severe chronic change forces a more aggressive approach.

What Should You Do Right Now?

If you find a swelling at your horse’s elbow:

1. Check Whether the Horse Is Lame

Walk the horse on safe, level ground.

If the horse is severely lame or unable to bear weight normally, call your vet urgently.

2. Look at the Swelling

Check whether it is:

• Soft or firm

• Painful or nonpainful

• Hot or cool

• Increasing in size

• Draining or dry

• Associated with a wound

• On one elbow or both

3. Check the Shoe and Heel

Look at whether the hoof or shoe could contact the elbow when the horse lies down.

Ask your farrier to check:

• Shoe length

• Heel extension

• Sharp edges

• Balance

• Whether shoeing changes could reduce trauma

4. Improve Bedding

Provide deep, soft bedding. Stall mats can help, but mats alone are not bedding. A hard rubber mat with one decorative shaving flake is still a hard surface wearing a small hat.

5. Use a Shoe Boil Roll if Contact Is Likely

A shoe boil roll or padded pastern collar can prevent the heel or shoe from striking the elbow.

6. Do Not Drain It Yourself

Do not puncture the swelling. Do not squeeze it. Do not inject it. Do not try to “let the fluid out.”

7. Call Your Vet if There Are Red Flags

Call your vet if there is pain, heat, lameness, drainage, a wound, rapid growth, fever, or repeated recurrence.

What Not To Do

Avoid these common mistakes:

• Do not lance it at home.

• Do not drain it with a needle yourself.

• Do not ignore a wound over the swelling.

• Do not keep the horse on hard bedding.

• Do not assume antibiotics are needed if there is no infection.

• Do not assume drainage will permanently fix it.

• Do not use harsh topical irritants without veterinary direction.

• Do not forget to check the shoe or hoof contact.

• Do not keep treating the swelling while leaving the cause unchanged.

The biggest mistake is focusing on the fluid and forgetting the trauma.

The fluid is the result. The repeated elbow hit is often the cause.

Can a Capped Elbow Go Away on Its Own?

A small, early capped elbow may reduce if the cause is removed quickly.

This is more likely when:

• The swelling is new

• The bursa wall has not become thick

• There is no infection

• The horse is not repeatedly hitting the elbow

• Bedding is improved

• A shoe boil roll is used early

Chronic capped elbows are less likely to disappear completely. Over time, the bursal wall can thicken and become fibrous, leaving a persistent firm swelling even if the horse is comfortable.

The owner expectation should be realistic:

Comfort usually matters more than perfect cosmetic disappearance.

Can You Ride a Horse With a Capped Elbow?

Usually, yes, if:

• The horse is sound

• The swelling is nonpainful

• There is no infection

• The swelling does not interfere with movement

• Your vet has no concern

Do not ride if:

• The horse is lame

• The swelling is painful

• There is heat or drainage

• There is a wound

• The swelling is rapidly enlarging

• Infection is suspected

• The elbow movement is restricted

Most capped elbows are cosmetic. Painful capped elbows are not.

How Long Does Recovery Take?

Recovery depends on whether the capped elbow is early, chronic, infected, or surgically treated.

A rough guide:

Situation	Expected course
New mild swelling	May reduce over days to weeks if trauma stops
Chronic fibrous swelling	May persist long-term, even if harmless
Drained swelling	Often refills unless the cause is removed
Infected bursa	Needs veterinary treatment, drainage, antimicrobials, and longer recovery
Surgical case	May need weeks of rest and careful aftercare

MSD notes that surgical placement of drains with bandaging and rest for 8 weeks can be successful in some cases. (MSD Veterinary Manual)

The practical timeline depends heavily on whether the horse keeps lying on or hitting the area. You cannot out-medicate repeated trauma.

Prevention: How To Stop Shoe Boils Returning

Prevention is the main treatment.

Practical steps include:

• Use a shoe boil roll or padded pastern collar

• Provide deep soft bedding

• Avoid hard lying surfaces

• Check shoe fit and heel extension

• Ask your farrier to smooth or shorten projecting shoe edges where appropriate

• Monitor horses after shoeing changes

• Check horses during travel or show stabling

• Use more bedding when away from home

• Avoid prolonged lying on hard ground where possible

• Treat small swellings early before they become fibrous

• Check both elbows regularly in horses with a history of shoe boils

MSD recommends a padded pastern collar and extra or nonabrasive bedding once the problem is noticed. (MSD Veterinary Manual)

This is one of those conditions where prevention beats treatment by a mile. Or by a large, squishy elbow lump.

Myth vs Reality

Myth	Reality
“A capped elbow is always dangerous.”	Most are cosmetic and nonpainful unless infected, large, or associated with lameness.
“Draining it will fix it.”	It often refills unless the cause of trauma is removed.
“Only shod horses get shoe boils.”	Barefoot horses can develop capped elbows from hoof or pressure trauma too.
“Antibiotics are always needed.”	Antibiotics are only needed if infection is present or strongly suspected.
“Surgery is the best first option.”	Surgery is usually reserved for chronic, infected, painful, or function-limiting cases.
“If it is soft, I should pop it.”	Never lance or drain it at home. Infection can make the problem much worse.

FAQs About Capped Elbows in Horses

Is a capped elbow painful?

Most simple capped elbows are not painful. They become more concerning if the swelling is hot, painful, draining, infected, very large, or causing lameness.

Will a shoe boil go away by itself?

A small early shoe boil may reduce if the cause of trauma is removed quickly. Chronic capped elbows often persist because the bursal wall becomes thick and fibrous.

Should a capped elbow be drained?

Not always. Draining can temporarily reduce swelling, but the bursa often refills and the procedure can introduce infection. It should only be done by a vet using sterile technique when there is a clear reason. (MSD Veterinary Manual)

Does my horse need a shoe boil roll?

If the hoof or shoe is striking the elbow, yes, a shoe boil roll or padded pastern collar is one of the most important prevention tools. It helps stop the repeated contact that causes recurrence. (MSD Veterinary Manual)

When should I call a vet?

Call your vet if the swelling is painful, hot, draining, rapidly enlarging, associated with a wound, causing lameness, or if the horse has fever, depression, or swelling spreading down the limb.

The Bottom Line

A capped elbow is usually more frustrating than dangerous.

Most simple shoe boils are cosmetic, nonpainful swellings caused by repeated trauma from the hoof, shoe, hard bedding, or pressure when the horse lies down. The real treatment is not just draining the fluid. It is stopping the elbow from being hit again.

That means better bedding, shoe assessment, and usually a shoe boil roll or padded pastern collar.

The cases that need more caution are the painful, hot, draining, infected, rapidly enlarging, or lame ones. Those need a vet, not a needle from the tack room and a brave volunteer with poor life insurance.

If the horse is comfortable, focus on prevention. If the swelling hurts, drains, grows quickly, or causes lameness, treat it as a veterinary problem.

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If your horse has a capped elbow and you are unsure whether it is cosmetic, infected, or linked to repeated shoe trauma, ASK A VET™ can help you organise the signs, prepare useful photos, and decide when hands-on veterinary assessment is needed.