Lymphoma of the knee joint simulating patellar fracture

Fracture of the patella is not uncommon after direct anterior knee trauma. However, there are other medical situations that resemble it radiologically. We present a patient mistakenly diagnosed as having a patellar fracture who had primary, solitary, malignant B-cell lymphoma of the knee space eroding the lower pole of the patella. We have found no reports of such a lesion in the literature. Another common benign condition that might erode adjacent bone is chronic synovitis. Our patient was treated with chemo- and radiotherapy and the lesion fully regressed with no evidence of local or systemic recurrence 1.5 years after diagnosis.