A 52-year-old African American homeless man visited a clinic at the local shelter, complaining of pain in his left knee for the past 2 days. He denied trauma or any history of knee injuries. He also denied any recent sexual activity. The patient was limping from significant pain. The patient’s clothes and hygiene were in poor condition. He worked in the fish market and had taken on the odor of his workplace. He admitted to a history of alcohol and substance abuse and was unwilling to discuss his psychiatric history. His chart indicated he had been diagnosed with schizophrenia.
The patient was afebrile and had a swollen warm left knee (Figure 1). A crusty skin lesion with a small amount of purulence was seen over his patella. There was evidence of a joint effusion and the skin appeared red around the whole knee region. The patient could not fully flex his knee. The physical exam demonstrated normal ligamentous stability.
What procedure would be appropriate to perform?
What diagnostic tests would be helpful?