Case 326: Intra-Articular Osteoid Osteoma

History A 15-year-old male patient presented with a 3-week history of inner left thigh pain provoked by activity and experienced occasionally at rest. The patient denied nighttime pain, fever, or chills. Laboratory investigation revealed the following normal values: hemoglobin level of 15.6 g/dL (normal range, 13–16 g/dL), platelet count of 240 × 103/µL (normal range, 140–440 × 103/µL), and total leukocyte count of 7100 cells/µL (normal range, 4500–11 000 cells/µL). The percentage of neutrophils was considered low at 44% (normal range, 54%–62%), and the percentage of eosinophils was slightly high at 3.7% (normal range, 0%–3%). An anteroposterior radiograph of the left hip is shown. Physical therapy was initiated, with no improvement after 2 weeks of therapy. The patient was referred to an orthopedist for further evaluation. At physical examination, the patient endorsed marked left hip pain with hip flexion to 90°, limited internal and external rotation (5° and 15°, respectively), and antalgic gait favoring the left leg. Hip MRI and further serologic analysis were requested for further evaluation. Although the serologic testing was performed at an outside laboratory, the physician reported positive immunoglobulin-G Lyme titers, normal C-reactive protein level, and normal erythrocyte sedimentation rate. Pelvic CT was requested. The patient was prescribed a course of doxycycline (100 mg twice daily for 28 days), with reported resolution of symptoms 2 weeks after initiation of treatment. Three weeks later, the patient presented to our department with recurrent left hip pain, which was similar in severity compared with the initial presentation. A second MRI examination of the left hip was performed 4 months after the initial presentation.