Informed consent was obtained from the patient's parents, and the study was approved by the ethics committee of the Saitama Children's Medical Center. A 28-month-old boy presented to a hospital with symptoms of fever and right knee pain. He had been vaccinated with BCG at five months of age. The patient had no previous history of trauma or illness and no known history of tuberculosis contact. At the time of the initial examination, radiography of the knee showed no apparent abnormalities (Figure 1(a)). Magnetic resonance imaging (MRI) demonstrated a high-signal intensity area at the epiphysis of the right proximal tibia in the short tau inversion recovery sequence (Figure 1(b)). The peripheral white blood cell count (WBC) was 11,100/muL and the serum C-reactive protein (CRP) level was 5.8 mg/dL, indicating a mild inflammatory condition. The blood culture test was negative. After treatment with intravenous antibiotic chemotherapy (cefazolin 100 mg/kg/day) for four weeks, suspecting osteomyelitis, the symptoms of fever and knee pain improved and the WBC normalized. However, the symptom of limping persisted and CRP was slightly high (CRP 0.34 mg/dL). The patient was referred to our hospital two months after initial presentation of symptoms. The epiphyseal radiolucent lesion had increased in size and extended to the metaphysis through the physis on a plain radiograph of the right proximal tibia (Figure 2(a)). MRI of the knee demonstrated an abnormality at the same site, extending across the high-signal intensity area of the physis in the three-dimensional fast field echo sequence at the right proximal tibia (Figure 2(b)). Surgical drainage and curettage of the lesion was carried out in order to confirm the diagnosis and remove the lesion at five months after initial symptoms.
Surgical drainage and curettage of the lesion were performed with an endoscope under C-arm fluoroscopy (Figure 3). A 2 cm skin incision was made under fluoroscopic guidance at the lateral aspect of the proximal tibial metaphysis. A bone tunnel was created and a 4.0 mm-diameter endoscope was inserted. A punch was inserted into the same tunnel to remove a tissue sample for intraoperative histopathological examination. The lesion contained granulation tissue composed of caseous necrosis and Langerhans giant cells (Figure 4). Ziehl-Neelsen staining failed to identify any acid-fast bacteria. Curettage was advanced in the direction of the physis. The bone defect within the growth plate was identified by palpation with a probe. The debridement was performed especially gently around the growth plate. The endoscope was inserted deeper through the bone defect of the physis, and the inside of the epiphysis was examined. The abnormal tissue inside the epiphysis was carefully debrided. After confirming adequate removal of the lesion, the surgery was finished (Figure 5).