Chronic Ankle Instability
Reviewed by Andrew Schox, BSc(Hons) PGradDipPod MPod, October 2026
Chronic ankle instability is when a sprain on the outer side of the ankle is followed by ongoing giving way, a wobbly or untrustworthy feeling, and more sprains. Most people recover well from a sprain, but some go on to have these problems: estimates start at 20 to 30 per cent and go higher. Exercise-based rehabilitation, such as balance and strength training, has the strongest support and can improve how the ankle works. A brace or tape can help too, especially for sport. Surgery is considered if a proper rehabilitation programme hasn't worked.
What is it?
Chronic ankle instability (often shortened to CAI) is ongoing trouble after a sprain to the outer side of the ankle. The ankle keeps giving way, feels unstable, or keeps getting sprained again. Most people recover fully from a sprain, but for some the problems don't go away.
CAI can show up in different ways. The ligaments (the strong bands that hold the ankle bones together) on the outer side may be loose. Or the ankle may simply feel unstable, or get sprained again and again. Some people have a mix of these. It can follow one sprain or a run of injuries.
It is defined in a few ways. One common description is giving way at least twice in the past 6 months. Another is ongoing pain, swelling or giving way, along with repeated sprains, for at least 12 months after the first sprain. There is no agreed measurement that defines a loose ankle joint.
Who does it affect?
Ankle sprains are very common in people who are physically active, and CAI mostly affects people who have had a sprain. Estimates of how many people go on to develop it vary widely, from 20 to 30 per cent up to 40 per cent, and up to 70 per cent of patients, depending on how it is defined. No reliable figure is available for the general population.
It is hard to predict who will be affected. After a first sprain, these things are linked with a worse outlook:
- not being able to jump and land within 2 weeks
- poor balance and control when moving
- looseness in the ankle ligaments 8 weeks later
- playing sport at a high level
- being a young male
- a higher body mass index (BMI) or being taller
Most of what is known comes from active adults, including people who play sport. How CAI behaves in children isn't clear yet.
Signs and symptoms
The main symptoms are the ankle giving way, a feeling that it is unstable, and more sprains. People often describe:
- the ankle turning over again and again, especially on uneven ground or in sport
- a wobbly or unstable feeling
- ongoing discomfort and swelling
- pain or tenderness
Over time, worry about the ankle giving way can lead people to do less. Ongoing instability has been linked with being less active and a lower quality of life.
What causes it?
CAI usually follows a sprain that hasn't healed fully or wasn't fully rehabilitated. Each new sprain is said to weaken or stretch the ligaments a little more, which makes the ankle less stable and more likely to be sprained again.
The full picture of why some people develop it isn't settled. Poor balance is the one factor that is well established. Weakness in the muscles that turn your foot outwards (the outer ankle muscles) may also be important, and it can be improved with exercise. Other things linked with CAI include loose ligaments, less bend at the ankle, weaker muscles, and changes in how you walk and control your movement. Changes in how the brain controls the ankle may also play a part, but this is not proven.
How is it diagnosed?
Your podiatrist will start by asking about your injury and symptoms. They will ask how the first sprain happened, how long the problems have lasted, how bad they are, how often the ankle gives way, what swells and when, and how much it limits what you do. They may also ask about any changes in the shape of your foot.
They will then examine your ankle. They may gently move it to test the ligaments (the anterior drawer test and the talar tilt test), and check how well it moves, where it is tender, your sensation and your muscle power. Balance tests can also show how steady you are on the ankle. Your podiatrist may also use a short questionnaire about how unstable your ankle feels.
This step matters because other problems can cause outer ankle pain. These include irritated tendons on the outer ankle (peroneal tendinopathy), damage to the joint surface or cartilage (osteochondral lesions), pinched nerves, sinus tarsi syndrome, an extra bone connection in the foot (tarsal coalition), and cuboid syndrome. Without a careful history and examination, CAI is hard to tell apart from these. Your podiatrist will also check for more serious problems, such as a fracture, a torn tendon, infection or an inflammatory joint condition, before putting your symptoms down to instability.
Treatment
Most people start with exercise-based care. Surgery is for people whose symptoms continue despite a proper rehabilitation programme.
Looking after it at home
The most useful thing you can do at home is keep up the exercises your practitioner gives you, little and often, over an extended period. Don't stop when the pain eases. Keep a note of how often your ankle gives way and what sets it off. This helps your practitioner plan your care.
Treatment from your podiatrist
Exercise-based rehabilitation is the best-supported treatment. Programmes usually combine strengthening (including the outer ankle muscles), balance training (proprioception, which is your body's sense of where your ankle is), and plyometrics (jumping and hopping exercises). Balance training in particular improves control of movement and can improve how stable the ankle feels. Proprioception training has been shown to cut the risk of another sprain by 36 per cent in people who have had a sprain. The best amount and intensity of exercise isn't clear yet.
A brace or tape can lower the chance of another sprain, especially if you play sport. No type of brace or tape has been shown to be better than another. They are often used alongside exercise, and one care pathway suggests trying a brace for 2 months.
Foot orthoses (shoe inserts) are sometimes used alongside physiotherapy, usually started in the first 2 months after injury. Neuromuscular training (exercises that retrain how your muscles react) and plantar sensory treatment (treatment to improve the feeling under your foot) may also help.
Other options
Hands-on treatment (manual therapy) and acupuncture have moderate support for improving ankle function. They are usually added to exercise rather than used alone.
Surgery
Surgery is mainly for people whose ankle is still unstable after a thorough exercise-based physiotherapy programme. It is usually considered after 3 to 6 months of treatment that hasn't worked, or after more than 6 months, with ankle tests and a scan confirming the problem. Surgery may suit professional athletes who want to return to sport sooner. The decision is made with you, one person at a time.
Keyhole (arthroscopic) repair and reconstruction are described as reliable. Surgeons may repair the ligament, or add extra support to it (called augmentation). The ankle bone moves forward a little less after augmentation. Whether it gives better everyday function than a standard repair isn't clear yet, and the risk of complications looks similar.
After keyhole surgery, the advice is to wait at least 6 weeks before returning to work and at least 8 weeks before recreational sport. If there is cartilage damage as well, wait at least a further 6 weeks. Follow your surgeon's advice.
Recovery
Most sprains recover, and exercise-based care can improve how the ankle works in people who develop CAI. How long it takes varies from person to person.
The outlook is better if you keep up your rehabilitation and avoid new sprains. Repeated sprains can make the ankle less stable each time. Lower body weight is linked with a lower risk of developing CAI.
If your ankle still gives way after a thorough programme of exercise and support, ask your GP or physiotherapist about referral to an orthopaedic foot and ankle service. Bring a record of what you have tried.
Preventing it
Treat a sprain as a real injury. Have it assessed by a trained health professional and finish the rehabilitation they advise, covering strength and balance, before you go back to full sport.
If you play sport and have had sprains before, talk to your podiatrist about whether a brace or tape would suit you.
When to see a podiatrist
When to book
Book an appointment with your podiatrist, GP or physiotherapist if your ankle keeps giving way or you keep going over on it and no longer trust it, or if it still isn't back to normal 6 weeks after a sprain. Book too if the pain is getting worse after 2 weeks, if numbness or pins and needles haven't improved after 2 weeks, or if there is bruising on the sole of your foot.
When to get help sooner
Call your local emergency number if, after an ankle injury, your toes look blue or white or feel numb. After an ankle injury, any of these needs urgent medical assessment: your ankle is at an odd angle, a bone is sticking out, you have a bad cut or wound, or the pain is severe. Also get urgent assessment if you think you may have broken your ankle, because a broken bone may need treatment to heal properly. See your GP today, or go to an urgent care clinic or the nearest emergency department. Don't wait to see if it settles.
Frequently asked questions
What is the Cumberland Ankle Instability Tool?
It is a short questionnaire (often called the CAIT) that scores how unstable your ankle feels and how it affects what you do. Other questionnaires, such as the Ankle Instability Instrument and the IdFAI, do a similar job. Ask your practitioner what your score means for you.
Can it lead to arthritis?
Chronic ankle instability has been linked with early-onset osteoarthritis (wear in the ankle joint). This is a link, not proof that one causes the other. Having your ankle assessed and keeping up your rehabilitation are the best steps you can take.
Will I need an X-ray or MRI?
Not always. After a severe sprain, your practitioner uses a set of simple checks, called the Ottawa ankle rules, to decide whether an X-ray is needed to rule out a broken bone. An MRI may be used if symptoms last, to look for damage inside the joint. Difficulty putting weight on the ankle, or an ankle that looks deformed, may mean you need imaging.
How is it different from a new sprain?
A new sprain is a fresh injury. Chronic ankle instability is the ongoing giving way, unstable feeling or repeated sprains that follow it. The two can look alike, so a careful history and examination help your practitioner tell them apart.