Peroneal Tendinitis

The peroneal tendons — the peroneus longus and peroneus brevis — run together behind the outer ankle bone (lateral malleolus) and down to their attachments on the outer foot. Their primary function is to evert the foot and stabilize the lateral ankle during walking, running, and uneven terrain. When these tendons become inflamed from overuse or mechanical stress — peroneal tendinitis — they produce a characteristic pattern of outer ankle pain that is one of the most common running injuries and one of the most commonly misdiagnosed as a lateral ankle sprain.

The distinction between peroneal tendinitis and a lateral ankle sprain is clinically important. Both produce outer ankle pain, both worsen with activity, and both can follow an inversion injury. However, the tenderness patterns differ — ligament sprains produce tenderness at specific ligament attachment points, while peroneal tendinitis produces tenderness along the tendon course behind the lateral malleolus and distally. A patient with recurrent outer ankle pain attributed to repeated sprains who is not responding to sprain management should be evaluated for peroneal tendon involvement.

Peroneal tendinitis is particularly common in runners who increase mileage too rapidly, in patients with a cavus foot (high arch) — where the foot's tendency toward supination places chronic eccentric load on the peroneals — and in patients with chronic lateral ankle instability, where the peroneals work continuously to compensate for ligament laxity. These associations mean that effective management addresses not only the acute tendon inflammation but the mechanical and structural factors predisposing the tendon to overload.

Less commonly, the peroneal tendons can develop tears — partial or complete — particularly at the peroneus brevis as it wraps around the lateral malleolus. A peroneal tendon tear that is managed as simple tendinitis will not respond adequately. Dr. Gunter evaluates the peroneal tendons clinically and with imaging when the presentation suggests tendon tear rather than simple tendinitis.