Chronic ankle instability

What is chronic ankle instability?

Chronic ankle instability (CAI) is when an ankle keeps giving way after an outer (lateral) ankle sprain. Most people recover from a sprain, but for some the instability carries on¹. The main symptoms are the ankle giving way, a sense that it can't be trusted, and further sprains². It can start after one sprain or after repeated injuries³.

How many people it affects isn't settled. Estimates run from 20–30% of ankle sprains⁴ up to 40% despite taping or bracing and rehabilitation⁵. The figures differ because CAI is defined in different ways.

What causes it, and who gets it?

Repeated sprains are a big part of it. Each sprain can further weaken or stretch the ligaments, making the ankle less stable and another sprain more likely⁶. CAI is often described as following a sprain that hasn't healed or been fully rehabilitated⁶.

The wider causes aren't fully settled. Impaired balance is the one factor that is well established⁷. Weakness in the muscles that turn the foot outwards may also matter, and rehabilitation can work on it⁷. After a first sprain, being unable to jump and land within 2 weeks, poor balance control while moving, loose ligaments and high-level sport are linked with a higher risk of CAI⁵. Most of this research is in active or sporting adults, so it may not apply to everyone.

Treat any sprain as a real injury worth having assessed by a trained health professional, not as something harmless⁸.

What does it feel like, and how is it diagnosed?

People with CAI often describe the ankle turning repeatedly, especially on uneven ground or in sport, a wobbly feeling, and ongoing discomfort, swelling or pain⁶.

A podiatrist, physiotherapist or doctor will ask how the ankle was injured and how often it gives way. They will check the ligaments with hands-on tests, plus movement, tenderness, feeling and strength⁹. You may fill in a short questionnaire about how stable the ankle feels, such as the Cumberland Ankle Instability Tool¹⁰. After a severe sprain an X-ray may check for a break, and an MRI may be used if symptoms persist, to look for damage inside the joint⁵.

Other problems can cause outer ankle pain, including peroneal tendon problems (the tendons along the outer ankle), a pinched nerve and cartilage damage in the joint⁹. They're hard to tell apart from CAI without a history and a hands-on examination¹⁰.

What helps first?

Exercise-based rehabilitation is the best-supported place to start¹¹. Balance training can improve control of balance while moving in adults with CAI¹², and rehabilitation often includes strengthening, especially for the outer ankle muscles³. Exercises are usually done over an extended period rather than a few days⁶, so give them time. A physiotherapist or podiatrist can set up a programme covering balance, strength and sport-specific work.

If you play sport, ask whether a brace or tape would suit you alongside exercise. In people with ankle sprains, a brace or tape reduced repeat sprains, especially in people who play sport, and no type did better than another⁵.

What helps if that isn't enough?

Surgery is the main next step, mainly for people who haven't responded to a comprehensive exercise-based physiotherapy programme⁵. Advice on timing differs: some say after 3–6 months without response to conservative care³, others after more than 6 months, with a positive ligament test and supporting imaging¹³. Keyhole (arthroscopic) repair and reconstruction are described as reliable treatments¹³.

If first-line care hasn't worked after several months, ask your GP or physiotherapist about referral to an orthopaedic foot and ankle service⁶, and bring a record of what you've tried. After keyhole surgery, expert guidance advises returning to work no earlier than 6 weeks and recreational sport no earlier than 8 weeks, with at least 6 weeks more if there is cartilage damage¹³. Your surgeon can set your own timeline.

How long does it take, and how can I stop it coming back?

Most sprains recover, but it's hard to predict who will go on to have CAI⁴. How long recovery takes with CAI isn't clear yet, so ask your practitioner what to expect for you.

To lower the chance of another sprain, finish the rehabilitation you're given rather than stopping when the pain eases, and build back to full sport gradually. Exercise therapy has moderate support for preventing repeat sprains, and balance training can improve the feeling of instability¹⁰. If you play sport and have had sprains, a brace or tape can reduce repeat sprains⁵. A lower body weight is linked with a lower risk of developing CAI¹¹.

It's worth tackling rather than putting up with: CAI is linked with lower quality of life and earlier-onset osteoarthritis (wear-and-tear arthritis)⁷.