Chronic Ankle Instability

Chronic ankle instability, sometimes shortened to CAI, develops in about about 20% of people after a serious ankle sprain. It's the persistent feeling that the ankle is going to give way, recurring sprains from minor twists, and a general sense that you can't trust the joint. Two things go wrong together: the ligaments on the outside of the ankle didn't fully heal (mechanical looseness), and the small muscles that should reflexively catch the ankle when it starts to roll have lost their timing (functional weakness). Left alone, CAI can grind down the joint surfaces and lead to ankle arthritis years later.

The defining symptom is the feeling that your ankle is about to "give way", a sense of looseness or unreliability, especially on uneven ground, stairs, or during cutting and pivoting sports. You may actually roll the ankle repeatedly from minor twists that wouldn't bother a normal joint, sometimes with each episode causing a new sprain. Between episodes there's often a dull, lingering ache on the outer side of the ankle and mild swelling that never fully clears.

Over time you may notice that you unconsciously avoid certain movements, cutting on that foot, landing from a jump, walking on rocky trails, because you've learned not to trust the ankle. Some people describe a clicking or catching sensation inside the joint, which can signal cartilage damage that's developed from the repeated rolling. If your ankle swells significantly or locks after a giving-way episode, that's a reason to be seen sooner rather than later, it can mean a piece of cartilage has loosened.

Your story tells most of it, repeated sprains and the distinctive feeling of the ankle giving way. A focused physical exam of the ankle checks for excess looseness compared with the other side. MRI shows whether the ligaments are intact, whether there are bone-cartilage injuries hidden inside the joint, and any other associated damage. Stress X-rays taken under live X-ray (fluoroscopy) measure the looseness objectively.

Most chronic ankle instability responds to non-operative care. The plan rebuilds the two things that went wrong, the mechanical looseness and the lost reflex timing, and the steps below are introduced in the order we usually start them. Each one builds on the one before, not instead of it.

Surgery is considered when a real, sustained, structured rehabilitation program hasn't resolved the instability, typically a procedure to tighten or reconstruct the loose lateral ankle ligaments.

External patient-education references and related OSI pages for additional background:

• AAOS OrthoInfo, patient education library
• OSI glossary, orthopedic terminology in plain language