Swollen ankle on one side: what it means and which causes surgery fixes

One puffy ankle is not the same problem as two. When only one side swells, the cause is often in the ankle itself, which is where a Foot and Ankle Surgeon comes in.

When is a swollen ankle on one side an emergency?

• A blood clot (DVT). A clot in a deep leg vein most often affects one side. It can make the leg red, warm, swollen and sore.^[7] New or worsening swelling in only one leg needs a call to your doctor right away.^[6] A piece of clot can travel to the lungs. Call 911 for chest pain, coughing up blood, trouble breathing or fainting.^[7]
• A joint infection (septic arthritis). Fever with swelling in one joint and intense pain that gets worse with movement.^[8] A red or warm swollen leg, or swelling with a fever, also needs a call to your doctor right away.^[6] Delay can permanently damage the joint.^[8] Go to the emergency room.
• A broken bone. If you can’t put any weight on the ankle after an injury, or it looks deformed, a bone may be broken.^[2] Go to the emergency room.

What is a swollen ankle a sign of?

Swelling is extra fluid in the tissues, called edema.^[6] Where it shows up is the first clue.

Both feet and ankles often swell from whole-body causes: long periods of standing, long trips, extra weight, weak leg veins, pregnancy, certain medicines, or heart, kidney or liver failure. Never stop a medicine without asking the doctor who prescribed it. If you’re pregnant and swelling rises suddenly, call your doctor, because it can be a sign of preeclampsia.^[6]

One ankle points to the ankle itself, or to the leg it sits on. Injury or surgery, a blood clot and infection are on the list,^[6] along with the problems below.

Cause	Clues	When surgery helps
Sprain or ligament tear	Bruising, tenderness, the ankle giving way[1]	When it keeps giving way after a full exercise program[11]
Broken bone	Severe pain at once, can’t put weight on it[2]	When the fracture is unstable[2]
Peroneal tendon tear	Pain on the outside, easy to mistake for a sprain[12]	Repairing or rebuilding the torn tendon[13]
Posterior tibial tendon	Swelling along the inside, a dropping arch[3]	When pain lasts several months despite care[3]
Arthritis	Swelling and warmth, worse in the morning or after rest[4]	Fusion or ankle replacement for worn-out joints[14]
Gout	A red, swollen joint that flares for a week or two[5]	Medicine treats the flare[5]
Infection	Fever, one red, swollen joint[8]	Severe cases need the joint drained and washed[8]

Sprain or ligament tear: a common cause

A sprain happens when the ligaments that support the ankle stretch past their limit and tear, often on the outside. Swelling and bruising are common signs, and how bad they are depends on how badly the ligaments are hurt.^[1]

An evidence-based guideline makes a brace or tape plus an exercise program the first-line care, and a short time immobilized can ease pain and swelling.^[11] But a high share of people go on to have lasting symptoms and an ankle that keeps rolling, called chronic ankle instability.^[15] When symptoms don’t improve, surgery can repair or rebuild the torn ligaments.^[1] In a review of 1,384 patients who had their outer ankle ligaments repaired or rebuilt, 95% returned to sport, 83% at their old level, at about 12 weeks on average.^[9]

See chronic ankle instability and our Center for Lower Extremity Surgery’s guide to ankle ligament reconstruction (external site).

Broken ankle: when one side swells after a fall

A broken ankle hurts right away and swells, and you may not be able to put any weight on it.^[2] A short checklist called the Ottawa ankle rules helps decide who needs an X-ray. It is very accurate at ruling out a fracture and could cut unneeded X-rays by 30% to 40%.^[16]

X-rays show whether the bone has shifted, and a special stress X-ray can show whether the fracture is stable or unstable and needs surgery. A shifted break of the inner ankle bone can be fixed with one or two screws. Outer ankle fractures that leave the joint unstable are repaired with a plate and screws or a rod.^[2] See sprain or fracture.

Torn tendon: the swelling that won’t go down

On the outside of the ankle, the peroneal tendons run behind the outer ankle bone. Problems with them are an under-appreciated cause of pain there and are hard to tell apart from a ligament injury. Ultrasound and MRI help sort it out.^[12] One review notes that peroneal tendons slipping out of place are misdiagnosed in up to 40% of cases.^[17] In a review of 336 surgically treated tears, average pain dropped from about 5 out of 10 to about 1.^[13] See peroneal tendon problems.

On the inside of the ankle, the posterior tibial tendon runs along the inside of the foot and ankle. When it is inflamed or torn, there may be swelling along it, and the arch can slowly collapse. Inserts and braces come first. When they don’t bring relief after several months, surgery can ease the pain and improve how the foot works. In mild cases, a surgeon can clean the inflamed tissue from around the tendon and repair small tears.^[3] For a flatfoot that has started to collapse, a tendon transfer with a heel bone realignment left 87% of patients pain free and doing well 15 years later, with pain falling from about 7 out of 10 to about 1.^[10]

Arthritis: swelling that’s worse in the morning

An arthritic ankle can be swollen, warm and red, with more pain and swelling in the morning or after sitting.^[4] For end-stage ankle arthritis, the two main operations are fusion and total ankle replacement. In a trial of 303 patients aged 50 to 85, both operations improved walking and standing scores at one year, with similar numbers of complications.^[14] See arthritis.

The limits. Surgery has risks. In the peroneal tendon review, 38.7% of patients had a complication, most often ankle pain.^[13] After ankle replacement there were more wound healing problems and nerve injuries, and after fusion more blood clots, with 7% of fusions failing to heal.^[14] Flatfoot reconstruction is often complex, and most patients still notice some limits on activity afterward.^[3] The chance of not returning to sport after ligament surgery rose with age and body weight.^[9] The ankle sprain guideline recommends a full exercise program before surgery.^[11] Advice for peroneal tendon problems rests mostly on case series and expert opinion.^[12]

How we decide

Dr. Efe Ozturk is a Foot and Ankle Surgeon and podiatrist. We check each ligament, tendon and joint, compare both ankles, and take X-rays and ultrasound at the practice, with an MRI arranged when needed. If the cause is structural and the first steps have failed, we talk through the operation that fixes it. See ankle pain. We see patients in Lyndhurst, Paramus and Millburn, NJ.

Common questions

Does gout in the foot cause swelling?

Yes. Gout flares cause pain, swelling and redness in one or more joints, often the big toe or another joint in the leg.^[5]

Why does an ankle sprain cause swelling?

Swelling is one of the most common signs of the ligament injury, and it tends to be worse when more of the ligament is torn.^[1] An ankle that stays swollen or painful for several weeks should be checked for a severe sprain or fracture.^[1]

Why are both my feet and ankles swollen?

Often fluid buildup from standing, travel, weight, pregnancy, a medicine or a heart, kidney or liver problem. Raising your legs, moving them and cutting salt can help. Call 911 if swelling comes with shortness of breath or chest pain.^[6]

When to see a Foot and Ankle Surgeon or podiatrist