A 15 year old boy presents with dull, aching pain just above the right knee for 3 months, which is worse at night. The pain commenced after he slipped and fell on the floor. His movements are unaffected. He is otherwise asymptomatic with an unremarkable medical history. A full blood count is found to be normal, while his ESR is 13 mm in the first hour.
A mixed sclerotic and lytic lesion is noted in the distal femoral metaphysis. No soft tissue masses or ossifications are seen.
The MRI shows an area of abnormal signal intensity in the distal femoral metaphysis along with a small soft tissue mass. The epiphysis and neurovascular bundle appear normal. No satellite lesions or skip lesions are identified.
A wedge biopsy is obtained. Histological analysis shows atypical spindle cells with abnormal mitosis forming an osteoid matrix. Muscle infiltration is present.
The CT scan of the chest is normal. Bone scintigraphy shows a single area of increased uptake in the distal femur, which is congruent with the lesion identified earlier.