Posttraumatic intra-articular heterotopic ossification of the shoulder joint in a 15-month-old boy.

Heterotopic ossification (HO) can result from a single severe injury, repeated microtrauma, central nervous system injury, extensive burns, or muscular bleeding due to hemophilia. Although relatively rare in childhood and extremely rare within a joint, HO should be included in the differential diagnosis of an intra-articular mass when indicated by clinical, radiographic, and histologic findings. Here, we report a posttraumatic intra-articular HO of the shoulder joint in a 15-month-old boy without underlying hematologic disease. Intra-articular HO in a healthy infant has not been reported previously in the published literature. Because of the unusual presentation and location in a patient of such young age, tumorigenic conditions were considered in the differential diagnosis.