Iselin disease is a rare cause of ache on the outer side of the feet in children and adolescents. This condition is an osteochondrosis or traction apophysitis in the base of the fifth metatarsal bone bone. The peroneal brevis tendon attaches on the area and puts the metatarsal with a lot of tension. https://podiatrynewyorkcity.com/iselins-disease-of-the-fifth-metatarsal/