An 83 year old Portuguese woman presented to the hospital with worsening chronic right knee pain, dull in nature, worse after a recent fall and with weight bearing. She had a history of hypothyroidism and chronic atrial fibrillation. Her medications included levothyroxine, digoxin, and warfarin. The patient had been an immigrant to the United States 10 years previously and had not visited home since then.

The physical examination revealed a flexed and swollen right knee with a moderate effusion but no surrounding oedema. A small skin opening draining serosanguineous fluid was noticed in the popliteal fossa. The laboratory findings included a raised erythrocyte sedimentation rate of 86 mm/hour and C reactive protein of 10.3 μg/ml. Other laboratory tests were unremarkable. The patient's chest radiograph (fig 1) was unchanged from an old x ray done four years before, and it shows old right lower lung and hilar shadows.

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Figure 1

Chest radiograph showing old right lower lung and hilar infiltrates, unchanged from four years before.

Aspiration of the knee, besides revealing large amounts of red blood cells, was essentially unremarkable. The plain knee radiograph (fig 2) was abnormal. A popliteal sinogram was performed (fig 3) showing a sinus tract, opening into the popliteal fossa, but not quite communicating with the knee joint. Finally, the patient underwent arthroscopy with synovial biopsy that was diagnostic. Cultures of the biopsy tissue confirmed the diagnosis.

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Figure 2

Right knee radiograph.

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Figure 3

Sinogram (with contrast) of the right popliteal fossa sinus.