Peroneal Tendon Tear

Two tendons — the peroneals (peroneus brevis and peroneus longus) — run together in a groove right behind the bony bump on the outside of your ankle. Their job is to roll your foot outward and stop your ankle from rolling inward. The most common injury is a lengthwise split in the peroneus brevis, right where it sits in that groove behind the ankle bone. It often comes along with a chronically loose ankle that's been sprained over and over. The classic clue: lateral ankle pain that just won't quit after what was supposed to be a routine ankle sprain.

• Pain behind the outer ankle bone — a sharp or aching pain right behind the bony bump on the outside of your ankle, worse when you push off or change direction.
• Swelling along the peroneal tendons — puffiness running down the groove behind the ankle bone toward the outside of your foot.
• Ankle giving way — your ankle feels loose or buckles, especially on uneven ground.
• Snapping or popping sensation — you feel (or even hear) the tendon flipping in and out of its groove when you roll your foot.
• Lingering pain after a "healed" sprain — weeks or months after an ankle sprain, the outer ankle still hurts and isn't improving.

Tenderness behind and just below the bony bump on the outside of your ankle, pain when you push your foot outward against resistance, and pain when your provider squeezes the back of the calf muscles where the tendons originate. An MRI is the definitive test — a split tendon shows up flattened or as two separate slips on the cross-section views. A live ultrasound (where the technician moves your foot during the scan) can also catch a tendon snapping in and out of its groove.

Surgery is the answer when the tendon is split all the way through, when it keeps snapping out of its groove, or when months of bracing and rehab haven't quieted the pain.

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

• Britannica — Ankle (anatomy)
• AAOS OrthoInfo — patient education library
• OSI glossary — orthopedic terminology in plain language