Chronic Ankle Instability

Quick answer

Chronic ankle instability (CAI) is the long-term result of one or more ankle sprains that didn’t fully heal. The ankle becomes prone to giving way — especially on uneven ground — and re-spraining. The good news: it’s largely preventable with proper rehab after the first sprain, and treatable with focused exercise and (rarely) surgery.

How to recognize it

• Repeated ankle sprains, often from minor mechanisms (curbs, uneven ground)
• A feeling that the ankle isn’t trustworthy
• Frequent rolling of the ankle
• Persistent swelling even when not actively sprained
• Lingering pain that doesn’t fully resolve between sprains
• Difficulty with sports that require cutting, pivoting, or running on uneven surfaces
• Reduced confidence — avoiding hiking, sports, dancing because the ankle feels unreliable

Why some sprains lead to instability

Two overlapping mechanisms:

Mechanical instability

The ligaments themselves are physically loose:

• Stretched or torn ligaments healed in a lengthened position
• Most often the anterior talofibular ligament (ATFL) on the outside of the ankle
• Sometimes the calcaneofibular ligament (CFL) as well

This is the “structural” component — the ankle physically allows more motion than it should.

Functional instability

The nervous system’s “sense” of the ankle is impaired:

• Proprioception — your sense of where your ankle is in space — is disrupted
• Reflexive muscle responses that normally catch a roll are slower
• Balance is impaired

Most chronic instability cases involve both mechanical and functional components.

Why the first sprain matters so much

The strongest predictor of future ankle sprains is a previous ankle sprain. People who don’t fully rehab after their first sprain are far more likely to sprain again. Each subsequent sprain:

• Stretches the ligaments further
• Disrupts proprioception more
• Damages cartilage (osteochondral lesions)
• Can lead to early ankle arthritis

This is why aggressive rehab after the first sprain is so important.

Diagnosis

A clinician evaluation typically includes:

• History — number and severity of prior sprains, residual symptoms
• Anterior drawer test — checking ATFL integrity
• Talar tilt test — checking CFL integrity
• X-rays to rule out missed fractures or osteochondral lesions
• Stress X-rays in some cases
• MRI if cartilage damage or other soft tissue injury is suspected

Treatment

Conservative care (first-line for most)

The cornerstone is balance and proprioception training — much more effective than people expect:

• Single-leg balance — start with eyes open, progress to eyes closed
• Wobble board / balance disc training
• Single-leg hops for advanced rehab
• Sport-specific cutting and pivoting drills
• Strengthening of the peroneal muscles (which evert the foot)
• Calf and Achilles flexibility

A typical rehab program runs 6–12 weeks, with significant improvement in stability and reduction in re-sprain rates.

Bracing

• Lace-up brace for everyday wear
• Stirrup brace for higher-risk activities
• Useful both during rehab and long-term for high-risk activities like basketball, hiking on uneven terrain
• Doesn’t weaken the ankle when used appropriately (a common myth)

Surgery

For chronic instability that fails 3–6 months of dedicated rehab:

• Broström-Gould procedure — most common; tightens the ATFL and CFL using local tissue
• Anatomic reconstruction — uses a tendon graft for severe cases
• Recovery typically 8–12 weeks in a boot, then progressive rehab
• Outcomes generally good in well-selected patients

Living with chronic ankle instability

Practical adaptations:

• High-top shoes for activities with rolling risk
• Brace for sports
• Careful on uneven terrain — hiking poles can help
• Continue maintenance rehab — single-leg balance daily even after symptoms improve
• Address the cause — high arches, prior poor rehab, returning to sport too early

Bottom line

Chronic ankle instability is one of the most common consequences of sprained ankles — and one of the most preventable. If you’ve sprained an ankle, dedicated balance training is the most important thing you can do to avoid this. If you already have it, the same training (more intensive) often resolves it without surgery.