Iselin's disease is a traction apophysitis of the tuberosity of the fifth metatarsal. It occurs in physically active boys and girls between the ages of 9 and 14. It is caused by repetitive traction of peroneus brevis tendon at the site of its attachment. Clinically, there is a lateral midfoot pain aggravated by sports activities.

Differential diagnosis includes:

• Normal apophysis: painless longitudinally oriented apophysis without fragmentation or widening of chondro-osseous junction.
• Os vesalianum.
• The base of 5th metatarsal fractures: A fracture tends to be oriented transversally; whereas a growth plate has always a longitudinal orientation.

In this case, Iselin disease and an avulsion fracture are present simultaneously.