Axillary Wounds in Horses: Why Armpit Injuries Can Be Dangerous

By Dr Duncan Houston

A small wound between a horse’s front leg and chest can look harmless at first. That is exactly why axillary wounds are so easy to underestimate.

The axilla is the horse’s armpit region, where the forelimb meets the chest wall. Wounds here can be deep, hidden, difficult to bandage, and affected by constant limb movement. A small puncture or laceration can create a one-way valve that draws air under the skin every time the horse moves.

That trapped air is called subcutaneous emphysema. It can look dramatic and may feel like bubble wrap under the skin. In more serious cases, air can track deeper into the chest region, causing pneumomediastinum or pneumothorax, which can become life-threatening. Axillary wounds are recognised in equine surgery as common traumatic injuries that can appear minor at first but lead to severe complications. (IVIS)

Quick Answer

Axillary wounds in horses should be treated as urgent because they can draw air under the skin and, in some cases, lead to pneumomediastinum or pneumothorax. If your horse has a wound between the front leg and chest, spreading puffy swelling, crackling under the skin, rapid breathing, distress, fever, or dullness, call your vet promptly. The safest immediate steps are to restrict movement, keep the horse calm, cover obvious wounds cleanly if safe, and avoid probing, packing, or trying to drain the swelling yourself.

What Is the Axillary Area?

The axillary area is the space between the horse’s forelimb and chest wall.

It is easy to miss because the wound may be hidden when the leg is in a normal standing position. Owners may only notice a small scrape, a little blood, mild swelling, or later, a strange crackling puffiness spreading over the chest, shoulder, neck, or body.

This region is risky because:

• The skin and tissue planes can separate easily

• The forelimb moves constantly against the chest

• Wounds can extend deeper than they look

• Bandaging is awkward

• Drainage and contamination can be difficult to control

• Air can be pulled into the tissues as the horse walks

In practice, the wound you see at the surface may not represent the full depth or direction of the injury.

Why Axillary Wounds Are Dangerous

The classic complication of an axillary wound is subcutaneous emphysema.

This happens when air enters the tissue under the skin. The wound can act like a one-way valve: air is drawn in as the horse moves, but cannot escape easily. Over time, air accumulates under the skin and may spread across the chest, shoulder, neck, trunk, or even much of the body. (IVIS)

This is why an axillary wound may look minor on day one, then suddenly look much more dramatic two or three days later.

What Does Subcutaneous Emphysema Look Like?

Subcutaneous emphysema can look alarming.

You may notice:

• Puffy swelling under the skin

• Skin that looks inflated

• Swelling spreading away from the wound

• Crackling when the area is pressed

• A dry, airy feel rather than normal fluid swelling

• Worsening swelling after movement

• A small wound near the axilla, chest, shoulder, or neck

The crackling sensation is called crepitus. Owners often describe it as bubble wrap, Rice Krispies, or air pockets under the coat.

Subcutaneous emphysema may gradually resolve once the source of air entry is controlled, but the important point is that the cause must be addressed first. The swelling itself is not the only concern. The real concern is whether air is still entering, whether infection is developing, and whether air has tracked toward the chest. (IVIS)

How Fast Can This Develop?

It may not happen immediately.

A review of seven horses with axillary wounds found that all seven developed subcutaneous emphysema, five developed pneumomediastinum, and four developed pneumothorax. In the cases where timing was known, subcutaneous emphysema developed around two to four days after the original wound, with an average of just over three days. (Publishing Services)

That delay matters. A horse can seem stable at first, then worsen after continued movement and air accumulation.

What Is Pneumomediastinum?

Pneumomediastinum means air has entered the mediastinum, the central space in the chest between the lungs.

In horses, pneumomediastinum can be clinically quiet, meaning the horse may not show obvious signs at first. It is usually diagnosed using imaging such as radiographs. IVIS notes that pneumomediastinum is often clinically silent in horses, but cases still need monitoring because complications can include pneumothorax. (IVIS)

This is one reason vets take axillary wounds seriously even when the horse is not yet struggling to breathe.

What Is Pneumothorax?

Pneumothorax means air has entered the pleural space around the lungs. This can prevent the lungs from expanding normally.

Signs may include:

• Rapid breathing

• Shallow breathing

• Laboured breathing

• Flared nostrils

• Anxiety or distress

• Weakness or collapse

• Reduced or absent lung sounds on veterinary examination

A penetrating chest wound can lead to pneumothorax and respiratory distress. MSD Veterinary Manual notes that because the mediastinum in horses is incomplete, a one-sided chest wound can potentially lead to bilateral pneumothorax. (MSD Veterinary Manual)

Pneumothorax is the complication that changes the situation from concerning to potentially life-threatening.

Severity Guide

The main decision point is simple: any axillary wound that is more than a surface rub deserves veterinary attention.

What Else Can Cause Crackling Swelling?

Subcutaneous emphysema is strongly associated with air entering through a wound, but it is not the only concern.

Important rule-outs include:

Penetrating chest wound
A wound over the thorax can allow air into the chest cavity and cause pneumothorax.

Neck or tracheal injury
Air can escape from the airway and track under the skin.

Gas-producing infection
Some bacterial infections can produce gas in tissues. This is more concerning if the horse is painful, febrile, dull, or the swelling is hot and rapidly worsening.

Cellulitis or abscess
These usually feel warmer, firmer, more painful, or more fluid-like rather than airy and crackly.

Seroma or hematoma
Fluid or blood pockets may form after trauma, but they do not usually produce the classic bubble-wrap crackle unless air is also present.

The real veterinary question is not just, “Is there air?” It is, “Where did the air come from, and has it reached the chest?”

When Is This an Emergency?

Call your vet urgently if your horse has:

• Any wound between the forelimb and chest

• A wound near the chest, shoulder, neck, or upper limb

• Crackling swelling under the skin

• Swelling that spreads over hours or days

• Rapid breathing

• Shallow breathing

• Laboured breathing

• Flared nostrils

• Distress, weakness, or collapse

• Pale, grey, or blue gums

• Fever

• Depression or reduced appetite

• Severe pain

• A deep puncture wound

• A wound caused by a fence post, branch, metal, tack, fall, or collision

• A wound that looked minor but worsens two to four days later

MSD Veterinary Manual states that any horse with chest trauma and difficulty breathing should have open wounds sealed with airtight bandages and be evaluated for pneumothorax or pneumomediastinum. (MSD Veterinary Manual)

If breathing changes are present, do not wait.

What Should You Do Right Now?

1. Stop exercise immediately

Do not ride, lunge, walk unnecessarily, or turn the horse out.

Movement of the forelimb can keep drawing air into the tissues if the wound is acting as a one-way valve. Strict movement restriction is a major part of managing these wounds. IVIS recommends strict stall rest until the wound has healed to help prevent progressive air accumulation. (IVIS)

2. Move the horse carefully to a safe stable

If the horse is bright, breathing normally, and safe to move, place them in a clean, quiet stable.

If the horse is distressed, weak, severely lame, or struggling to breathe, do not force unnecessary movement. Call your vet immediately.

3. Inspect the axillary area carefully

Check between the front leg and chest wall.

Look for:

• Small punctures

• Blood

• Skin flaps

• Swelling

• Discharge

• Heat

• Pain

• Crackling under the skin

• Signs that the wound extends deeper than expected

Small wounds matter in this location. A tiny hole can create a large air problem.

4. Do not probe the wound

Do not put your fingers, cotton buds, forceps, syringe tips, or anything else into the wound to check the depth.

This can push contamination deeper and worsen tissue damage. The wound should be explored by a vet under controlled conditions.

5. Cover obvious wounds cleanly if safe

If there is a visible wound and you can safely cover it, use a clean dressing to reduce contamination while waiting for your vet.

Do not pack the wound yourself unless your vet has specifically instructed you. Packing can be important, but incorrect packing can trap contamination or fail to stop the valve effect.

6. Do not pop or drain the swelling

Do not lance, puncture, squeeze, or try to release the trapped air.

The air is not one contained bubble. It is spread through tissue planes. IVIS notes that subcutaneous catheters may sometimes be used in extensive cases, but this carries risks such as local infection and skin damage, so it should only be done when a veterinarian decides it is necessary. (IVIS)

7. Monitor breathing and temperature

Watch for:

• Breathing rate

• Breathing effort

• Gum colour

• Heart rate if you can safely check it

• Rectal temperature

• Appetite

• Depression

• Worsening swelling

Extensive subcutaneous emphysema can have an insulation-like effect, and IVIS notes that body temperature should be monitored because hyperthermia can occur in warm climates or seasons. (IVIS)

How Vets Diagnose Axillary Wounds

Your vet will usually start with a full clinical assessment.

This may include:

• Temperature, heart rate, and respiratory rate

• Gum colour and capillary refill time

• Breathing pattern

• Lung auscultation

• Wound location and depth

• Whether swelling is spreading

• Whether crepitus is present

• Whether the horse is lame or painful

• Whether infection is present

IVIS guidance recommends evaluating the horse’s general condition, performing a thorough physical examination, sedating the horse for full wound evaluation when needed, and determining the wound’s depth and direction. It also highlights the need to assess possible involvement of the elbow joint, cranial mediastinum, and cranial thorax. (IVIS)

Depending on the case, your vet may recommend:

• Wound exploration

• Ultrasound

• Radiographs

• Thoracic imaging

• Bloodwork

• Culture if infection is suspected

• Monitoring for delayed pneumothorax

• Referral if chest involvement is suspected

How Axillary Wounds Are Treated

Treatment depends on the wound depth, contamination, swelling, breathing status, and whether the chest is involved.

A typical veterinary plan may include the following.

Cleaning, lavage, and debridement

The wound may need careful cleaning, flushing, and removal of damaged tissue.

High-pressure lavage should be avoided in deep dissecting axillary wounds because it may push contaminants deeper into fascial planes. IVIS specifically warns against overusing high-pressure lavage in these wounds. (IVIS)

Packing the wound

Packing is often a key step.

Sterile gauze or laparotomy sponges may be placed into the wound to stop air migrating into the subcutaneous tissue planes. In the seven-horse case series summarised by the University of Minnesota, subcutaneous emphysema did not resolve until treatment included packing the wound to stop it acting as a one-way valve. (Publishing Services)

Partial closure or stenting

The vet may partially close the wound or use a stent and bandage system to hold the packing in place.

Full tight closure is not always appropriate because contaminated deep wounds may need drainage and repeated dressing changes.

Antibiotics, pain relief, and tetanus protection

Horse wounds often require pain control, antimicrobials when indicated, and tetanus prophylaxis. MSD Veterinary Manual lists wound assessment, debridement, bandaging, antimicrobials, pain management, and tetanus prophylaxis as key wound-care steps in horses. (MSD Veterinary Manual)

Strict stall rest

Movement restriction is important to stop more air being pumped into the tissues.

If the horse rolls, spins, or is very active in the stable, your vet may recommend additional movement control.

Repeated bandage and packing changes

Axillary wounds usually need ongoing care, not one visit and done.

IVIS guidance describes bandage changes every 24 to 48 hours or as needed, depending on drainage and bandage condition, with cleaning and fresh sterile packing at each change. (IVIS)

Chest treatment if pneumothorax develops

If pneumothorax develops and the horse is in respiratory distress, emergency treatment may include removing air from the chest through thoracocentesis or thoracic drains. In the axillary wound case series, horses with pneumothorax and respiratory distress were treated with thoracocentesis or thoracic drains, while those without respiratory distress were managed conservatively. (Publishing Services)

Should the Wound Be Sutured Closed?

Sometimes, but not always.

Axillary wounds are often contaminated and deep. They may dissect under the skin, which makes complete cleaning difficult. Closing the skin too tightly can trap contamination and prevent drainage.

In some cases, partial closure is useful to reduce air entry and stabilise the wound while leaving an opening for packing changes and drainage. In other cases, the wound may need to heal by second intention with repeated packing and bandaging.

This is why owners should not try to close these wounds at the yard.

Common Mistakes Owners Make

Assuming the wound is minor because the skin opening is small
Axillary wounds can extend deeply under the skin.

Turning the horse out
Movement can keep pumping air into the tissue planes.

Trying to drain the air swelling
This does not fix the source and may introduce infection.

Probing the wound
This can drive contamination deeper and worsen the injury.

Using high-pressure hosing
Forceful lavage can spread contamination through tissue planes.

Closing the wound too tightly
Deep contaminated wounds often need drainage and packing, not simply suturing shut.

Ignoring delayed swelling
Subcutaneous emphysema may develop days after the original wound.

Forgetting tetanus status
Any horse wound should trigger a tetanus protection check.

How To Prevent Axillary Wounds

You cannot prevent every paddock injury, but you can reduce risk.

Useful prevention steps include:

• Check fencing for broken rails, sharp posts, nails, wire, and protruding metal

• Inspect stable walls, gates, feeders, and partitions

• Remove branches, sharp debris, and broken timber from turnout areas

• Check trailers and floats for exposed edges or hardware

• Use safe turnout pairings to reduce kick and collision injuries

• Check the axilla after falls, collisions, fence injuries, or unusual swelling

• Remove damaged tack or equipment that can snag

• Keep tetanus vaccination current

• Train staff to report all wounds near the chest or forelimb immediately

The most important prevention habit is not fancy. It is looking carefully after an accident. Axillary wounds like to hide.

Will My Horse Recover?

Many horses recover well when the wound is recognised early, air entry is controlled, infection is prevented, and breathing complications are monitored.

In the seven-horse case series summarised by the University of Minnesota, all horses survived to discharge, including horses that developed pneumomediastinum and pneumothorax, but treatment included appropriate wound management and respiratory intervention when needed. (Publishing Services)

The prognosis is better when:

• The wound is found early

• The horse is breathing normally

• The valve effect is stopped

• Movement is restricted

• Infection is controlled

• Pneumothorax is ruled out or treated quickly

• Bandage and packing changes are consistent

The cases that worry vets most are those with delayed recognition, progressive swelling, fever, infection, laboured breathing, or chest involvement.

FAQs

Is an axillary wound in a horse always an emergency?

It should always be treated seriously. A superficial rub may be less urgent, but any puncture or laceration between the front leg and chest should be assessed by a vet because it can draw air under the skin and lead to deeper complications.

Why does my horse’s skin crackle after a wound?

Crackling under the skin usually means air is trapped in the subcutaneous tissues. In axillary wounds, this often happens because the wound acts as a one-way valve and pulls air inward as the horse moves.

Can subcutaneous emphysema go away on its own?

Residual trapped air may gradually reabsorb after the source of air entry is controlled. The priority is stopping more air from entering and checking that the chest is not involved.

Should I try to pop the air pocket?

No. Do not puncture, lance, squeeze, or drain it yourself. The air is spread through tissue planes, not contained in one bubble, and puncturing the skin can introduce infection.

What signs suggest pneumothorax?

Rapid or shallow breathing, laboured breathing, distress, weakness, collapse, pale or blue gums, and abnormal chest movement are serious warning signs. Pneumothorax needs urgent veterinary care.

Final Thoughts

Axillary wounds in horses are deceptive.

The surface wound may look small, but the deeper tissue tract can be significant. Because the forelimb moves against the chest with every step, these wounds can act like a pump, pulling air under the skin and sometimes allowing complications to progress toward the chest.

The safest response is to stop exercise, restrict movement, inspect carefully, avoid probing or draining, cover obvious wounds cleanly if safe, and call your vet early. If breathing changes develop, treat it as an emergency.

With axillary wounds, the real danger is not always the cut you can see. It is the air, contamination, and chest involvement you cannot.

If you are unsure whether your horse’s axillary wound, crackling swelling, or breathing change is urgent, ASK A VET™ can help you work through the signs and decide what to do next.