A 9-WEEK-OLD girl was seen for a 12-day history of fever (38.5°C), vomiting, and refusal to move the left arm for 24 hours prior to admission. There was no history of trauma. She was born at 36 weeks' gestation by cesarean delivery because of fetal distress. On physical examination she was irritable, pale, and did not move her left arm in response to painful stimuli; she cried when it was manipulated at the shoulder. Movement of the right arm and both legs were normal. Laboratory findings included white blood cell count, 14.8 × 109/L, with differential showing myelocytes, 0.15 × 109/L; bands, 0.59 × 109/L; segmented neutrophils, 4.88 × 109/L; and lymphocytes, 8.14 × 109/L. Hematocrit was 0.23; reticulocyte count, 0.15; platelet count, 293 × 109/L; and erythrocyte sedimentation rate, 110 mm/h. Findings from serum chemistry, glucose-6-phosphate dehydrogenase activity, Coomb test, and blood cultures were normal. Radiographs of the shoulders and humeri were unremarkable. A 3-phase technetium 99m methylene diphosphonate bone scan was performed on the first and fifth hospital days with normal results. Axial computed tomography of the humeri (Figure 1) and additional long bone radiographs (Figure 2 and Figure 3) were obtained.