A patient with acute right knee pain and a history of intravenous drug abuse is most likely suffering from which condition?

In patients with a history of intravenous drug abuse, septic arthritis is a significant concern due to the potential for bacteremia and direct intro-articular infection from contaminants introduced through non-sterile needles. Septic arthritis often presents with acute onset of joint pain, swelling, and warmth, particularly in a single joint like the knee. The acute nature of the patient's right knee pain, combined with their history, makes it highly suggestive of this condition.

Gouty arthritis typically occurs in individuals with metabolic disturbances leading to uric acid crystal deposition rather than being associated with intravenous drug use. Similarly, rheumatoid arthritis and psoriatic arthritis are chronic inflammatory conditions characterized by joint pain and swelling but do not typically present acutely or are influenced by the patient's drug use history in this manner. Therefore, the characteristics and risk factors for the condition suggest that septic arthritis is the most likely diagnosis in this scenario.