Question: Painful Knee Swelling.

19 year old female with right knee pain for 7 years and increased knee swelling for 6 months (Figs. 1, 2, 3, 4, and 5).

Fig. 1
figure 1

Clinical photograph of both knees showing marked swelling of the right knee

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Fig. 2
figure 2

a AP and b Lateral radiographs of the right knee

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Fig. 3
figure 3

Axial CT

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Fig. 4
figure 4

Hematoxylin and eosin staining of the curetted specimen from surgical biopsy

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Fig. 5
figure 5

AP radiograph of the right knee immediately post curetting and packing with bone graft substitute

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