A tendon is a strong band of tissue that attaches muscle to bone. There are two peroneal tendons in each leg, also known as the peroneus longus, and peroneus brevis. They run side-by-side down the lower leg bone (fibula) and behind the bony lump on the outside (lateral) of the ankle called the lateral malleolus.
One peroneal tendon attaches to the outside of the foot at the base of the little toe, which is the fifth metatarsal. The second tendon goes right underneath the foot and attaches to the inside of the arch. The peroneal tendons help provide stability to the ankle when it is bearing weight and protect it from sprains. They also help turn the foot out and stabilize the arch when walking.
Peroneal tendonitis (ankle tendonitis) occurs when the peroneal tendons in the ankle become inflamed or injured. Over time, this can develop into a condition known as tendinosis. Tendinosis occurs when tendons degenerate, meaning that they begin to break down. Here, repeated friction, injury, or overuse cause a thickening or enlargement of the tendon that can lead to chronic pain issues.
Peroneal tendonitis is very common among athletes, especially those involved in sports that require running, sprinting with quick stops, starts, and pivoting movements. In some cases, it is easy to ignore the early warning signs of ankle tendonitis because the pain in the peroneal tendons may lessen as you warm up your body. However, this can cause further injury, pain, and instability in the ankle.