Iselin's Disease: Outer Foot Pain in Young Athletes

Here's a situation I see often in clinic: an athletic child complaining of pain along the outer edge of the foot, parents thinking it's an ankle sprain that "never heals," and maybe they've already been to the emergency room where they were told there's no fracture. Yet the pain persists. In these cases, the answer is often Iselin's disease.

It's an apophysitis of the 5th metatarsal base — that bony point you can feel on the outer edge of the foot — where the peroneus brevis tendon inserts. In children aged 9 to 14, the growth plate at this site is still open and vulnerable to overload.

The main challenge with Iselin's disease is diagnostic: it's systematically confused with an ankle sprain (same painful area) or a 5th metatarsal base fracture. The difference is both clinical — gradual, sport-related onset is typical of apophysitis — and radiographic: Iselin's apophysis has smooth, regular borders, while a fracture has irregular margins.

It always resolves with skeletal maturity and treatment is conservative: load reduction, insoles, stable shoes, and peroneal stretching. A cast is rarely needed, only when pain is significant even during daily activities.