[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.