The peroneal muscles lay along the outside of the lower leg. Their tendons travel behind the lateral malleolus, or ankle bone, to insert onto the foot and help with the actions of plantar flexion, or toe pointing, and foot eversion, or turning the sole of the foot outward. Peroneal tenosynovitis, which refers to inflammation of a tendon and its sheath, often occurs when the peroneal tendons are irritated or stressed during repetitive ankle motion, such as sports-related jumping and running, or during acute ankle sprains. A high arch may contribute to peroneal tendon injury.
Pain and Stiffness
According to RadioGraphics Journal, lateral ankle pain commonly accompanies peroneal tendon injuries, especially at the point where the tendons travel behind the ankle bone. Also, pain in the back of the foot may signify peroneal tenosynovitis. Those areas are often tender, both with palpation and during activity, but generally the pain eases with rest. The ankle may feel stiff upon first rising after a long period of inactivity.
Since peroneal tenosynovitis is an inflammatory condition, swelling along the tendon is expected. This swelling is most common under and behind the lateral portion of the ankle bone. Generalized swelling may be visible or may be felt along the tendon itself. When compared to the healthy tendon on the other foot, the injured tendon often feels thicker.
Unusual Ankle Sensations
People suffering from peroneal tenosynovitis may also feel a "popping" or "snapping" in the ankle region on the affected side, according to RadioGraphics. Peroneal tenosynovitis may weaken the tendon, leading to a sensation of ankle weakness or instability.