Iselin’s Disease (Outer Foot)
Description
Iselin’s disease is an irritation of the growth center at the base of the fifth metatarsal — the bony bump on the outer edge of the foot, where a tendon attaches. It is the foot’s version of Sever’s and Osgood-Schlatter: a growth-center overuse condition in active, growing children.
How it happens (the mechanism)
Bones grow at special zones called growth plates. The main one, the physis, is what makes a bone longer. There is a second kind, called an apophysis — a growth center at a bony bump where a tendon anchors muscle to bone. The base of the fifth metatarsal, on the outer edge of the foot — where the peroneus brevis muscle attaches through its tendon — carries one of these apophyses.
While a child is still growing, that apophysis is made of cartilage, not yet hardened into bone. Cartilage — the same rubbery material as in the ear or the tip of the nose — is softer than bone and weaker under tension. So when its muscle pulls hard or often, the apophysis is the part that complains.
During a growth spurt, the bones lengthen faster than the muscles can keep up, so the muscles become relatively tight and tug harder on the apophysis. Here, a tight peroneal muscle pulls on the outer-foot bump during running, jumping, and cutting sports. Day after day, that extra, sustained tension irritates and inflames the growth center — essentially the growing child’s version of the insertional tendinitis adults get where a tendon meets bone. The pain is inflammatory and can be surprisingly sharp. (In an older teen, a single explosive effort can occasionally pull the apophysis off as an avulsion fracture; the everyday version is this inflammation.)
Symptoms
Pain, tenderness, and sometimes mild swelling over the bump on the outer edge of the midfoot, worse with activity and better with rest. Children may walk on the inner side of the foot to offload the sore spot.
Doctor examination and imaging
It is diagnosed from the exam — tenderness over the growth center at the base of the fifth metatarsal. X-rays may be used to tell it apart from a fracture at the same spot.
Treatment
Like its cousins, it settles with rest from aggravating activity, ice, and — the lasting fix — daily stretching of the calf and peroneal muscles to take tension off the growth center, along with supportive shoes. Activity is safe as tolerated.
Recovery and long-term outlook
It is self-limiting and resolves as the growth center matures, with no lasting harm. Recognizing it for what it is mainly matters so it is not mistaken for a fracture.
When to call the doctor
Call if pain is severe or worsening, your child will not bear weight or use the leg at all, the area becomes very swollen, red, or warm, your child develops a fever, or things are not improving with rest as expected.
Learn more
Lurie Children’s — Iselin’s Disease: www.luriechildrens.org/en/specialties-conditions/iselin-disease/
This information is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. For specific concerns about your child, consult a board-certified, fellowship-trained pediatric orthopaedic surgeon.