Normal skeletal development and imaging pitfalls of the calcaneal apophysis: MRI features

Heel pain in children and secondary MR imaging (MRI) of the hindfoot have been increasing in incidence. Our purpose is to illustrate the, previously unreported, MRI stages in development of the posterior calcaneal apophysis, with attention to imaging pitfalls. This should aid in distinguishing normal growth from true disease. Consecutive ankle MRIs in children <18 years, from 2008-2014, were subdivided into 0≤5, 5≤10, 10≤15 and 15≤18 age groups and retrospectively reviewed for development of the calcaneal apophysis. 204 ankle MRI studies in 188 children were identified. 40 studies were excluded with final cohort of 164 studies in 154 patients (82 boys, 72 girls). The calcaneal apophysis was cartilaginous until age 5. Foci of decreased as well as increased signal were embedded in cartilage, prior to ossification. Early, secondary ossification centers appeared in plantar third of the apophysis in 100 % of children by age 7. Increased T2 signal in the ossifications was seen in 30 % of children. Apohyseal fusion began at 12 and was complete in 78 % of 14≤15 year olds and in 88 % of 15≤18 year olds. Curvilinear low signal in the ossification centers, paralleling, but distinguished from growth plate, and not be confused with fracture line, was common. Development of the posterior calcaneus follows a unique sequence. Apophyseal fusion occurs earlier than reported in the literature. Familiarity with this maturation pattern, in particular the apophyseal increased T2 signal and the linear low signal paralleling the growth plate, will avoid misinterpreting it for pathology. (orig.)