Sever's injury: a stress fracture of the immature calcaneal metaphysis.

Magnetic resonance imaging (MRI) in children with a presumptive diagnosis of Sever's apophysitis and with continuing pain after conservative treatment demonstrated bone bruising within the trabecular bone of the metaphyseal region adjacent to the calcaneal apophysis. Limited portions of the apophyseal secondary ossification center showed similar increased signal changes. MRI studies following treatment with immobilization showed subsidence or disappearance of the metaphyseal but not any apophyseal signal changes commensurate with improvement in symptoms. Accordingly, the disorder commonly referred to as Sever's ''apophysitis'' may be a metaphyseal trabecular stress fracture, similar to the toddler's calcaneal stress fracture that has minimal or no involvement of the apophyseal ossification center, and thus should not be referred to as an apophysitis. Rather, it appears to be an overuse injury causing microinjury within the developing metaphyseal "equivalent" trabecular bone that has not completely adapted to the changing biologic (biomechanical) requirements of the growing, athletically active child.