Residual Medial Ankle Pain After the Delayed Union of a Lateral Malleolus Fracture: A Case Report

A 17-year-old girl sprained her left ankle and was diagnosed with a lateral malleolar fracture. She was treated conservatively for six months but had medial ankle pain with activity. Imaging revealed an oblique lateral malleolar fracture, with posterolateral displacement and partial fusion of the bone fragments, and bone marrow edema on the medial articular surface of the talus and medial malleolus. We diagnosed ankle instability due to delayed union with a displacement of the lateral malleolus, which caused an osteochondral lesion. We performed arthroscopic and open surgery eight months after the injury, reducted the lateral malleolus anatomically, and fixed it with a plate. Postoperatively, the pain improved rapidly, and the bone marrow edema had almost disappeared on an MRI. In this case, we think rotational instability of the ankle mortise caused abnormal pressure and continuous stress on the medial malleolus after injury, which may have contributed to persistent medial ankle pain.