Abnormality of the fifth metatarsal bone Fifth metatarsal apophysitis 2025-10-06T08:03:46Z Iselin's disease is a traction apophysitis of base of fifth metatarsal. The apophysis is within the peroneus brevis tendon insertion site and appears radiographically at about age 10 in female and age 12 in male and usually fuses by age 11 in female and by age 14 in male. Repetitive microtrauma from the peroneus brevis tendon, as occurs in sports activities is the cause of traction apophysitis. It can be ascertained by oblique foot radiographs showing apophyseal irregularity (enlarged apophysis, disordered ossification, widened chondro-osseous junction) at the base of the fifth metatarsal. Iselin disease