swollen joint

Back to Basics: Swollen Joint

A 64M with history of opioid use disorder, HCV, HTN presented to the ED with left knee pain and swelling 10 days after mechanical fall onto that knee.  He was unable to bear weight.  His knee was extremely swollen with an effusion, warm, and he had severe pain with any ROM of the joint.  His X-ray negative for fracture.  What else could be causing this patient's swollen painful knee?

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