Unstable ankle, pain / burning lateral ankle: Os peroneum

Pain, burning, and instability on the outside of the foot and ankle can have an unusual culprit: the os peroneum. This is a small sesamoid bone that sits within the peroneus longus tendon near the cuboid, on the outer edge of the foot. Not everyone has one, but in those who do, it can become a source of stubborn lateral foot pain. In the video below, Dr. Kevin Lam explains the condition.

What Is Painful Os Peroneum Syndrome?

When the os peroneum is injured — fractured, fragmented, or inflamed — or when the peroneus longus tendon around it is strained or torn, the result is painful os peroneum syndrome (POPS). The peroneal tendons stabilize the outer ankle and help turn the foot, so a problem here often produces both pain and a sense of instability.

Symptoms

• Pain and burning on the outside of the foot, just behind the little-toe area
• A feeling that the ankle is unstable or weak
• Pain that worsens with activity, pushing off, or walking on uneven ground
• Tenderness directly over the cuboid/peroneal tendon region

Diagnosis and Treatment

Because os peroneum pain mimics ankle sprains and other peroneal problems, an accurate diagnosis is key. We use a hands-on exam, X-rays (which can show a fractured or fragmented os peroneum), and diagnostic ultrasound or MRI to assess the tendon. Treatment usually begins conservatively — immobilization, bracing, orthotics, anti-inflammatory care, and physical therapy. When the bone is fractured or the tendon is torn and pain persists, surgery to remove the fragment and repair the tendon reliably relieves the pain.

Lingering outer-foot pain is worth a proper evaluation rather than repeatedly “walking it off.”

For more information or to schedule an evaluation with a board-certified foot and ankle specialist, call (239) 430-3668 (FOOT) or book online at NaplesPodiatrist.com.

Serving Southwest Florida since 2005, Family Foot & Leg Center has 9 convenient locations throughout Collier, Lee, Charlotte, and Sarasota Counties — Naples, Estero, Fort Myers, Cape Coral, Port Charlotte, and Sarasota. We provide pediatric to geriatric foot and ankle care: ingrown toenails, heel pain, bunions, foot & ankle arthritis, plantar fasciitis, foot & ankle surgery, custom orthotics, and diabetic wound care — with in-office X-rays, diagnostic ultrasound, and minor surgical suites. Home of the Lam Minimally Invasive No-Scar Bunion Surgery. Same-day appointments and easy online scheduling.