What should you know about peroneus tertius tendonitis?

The peroneus tertius runs along the front and outer side of the lower leg toward the foot. Repeated loading, a change in training, uneven ground, or footwear that changes foot mechanics can irritate the tendon. Tenderness may sit near the outer ankle or the top outer edge of the foot. Swelling or pain when turning the foot outward can occur. A clinician may compare both feet, check strength and range of motion, and consider imaging when the diagnosis is uncertain or another injury needs to be excluded.

Reduce the activity that provokes the pain while keeping gentle, comfortable movement. Supportive footwear, a short period of relative rest, and cold treatment wrapped in cloth may help settle symptoms. Do not push through sharp pain or return suddenly to sprinting, hills, or uneven surfaces. Physiotherapy can guide mobility, calf and ankle loading, balance work, and a gradual return to activity. Strength Training Rehabilitation may be useful when weakness or altered movement is contributing. Shockwave Therapy or PRP Injection may be discussed in selected persistent cases after assessment.

Arrange an assessment if pain persists, returns whenever activity resumes, or limits normal walking. Seek prompt care after a sudden injury with marked swelling, inability to bear weight, deformity, numbness, or a foot that feels unusually cold. Fever, spreading redness, or rapidly increasing warmth also needs urgent medical review because the cause may not be tendon irritation.

Ask which tendon or joint is tender, whether a stress injury or ankle sprain should be ruled out, and which activities are safe during recovery. Ask how to progress exercises and what change should prompt a follow-up.