The Journal of Bone and Joint Surgery

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Bilateral Acute Knee Pain in a Woman with Systemic Lupus Erythematosus¹
A thirty-year-old woman with a sixteen-year history of systemic lupus erythematosus and recently diagnosed fibromyalgia was brought by ambulance to a local emergency department because of bilateral knee pain and an inability to bear weight on either leg. She was taking prednisone (20 mg/day) on an ongoing basis. She described a sharp pain in the right knee while standing still, which caused her to shift her weight to the left knee, followed by a twisting sensation in the left knee with subsequent pain and an inability to bear weight on either leg. Physical examination showed a left knee effusion and an inability to actively extend either knee. Radiographs of the left knee were taken (Fig. 1). The patient was diagnosed as having a knee sprain; she was treated with a knee immobilizer bilaterally and was given crutches for walking.
Fig. 1	Fig. 1. Lateral radiograph of the knee, made at the time of initial presentation. For larger view, click on image

Twenty-five days after the initial injury, the patient presented to a rheumatologist because of continuing inability to walk or to extend the knees. Examination showed bilateral knee effusion, tenderness, and absence of active knee extension.

What is the diagnosis?