A 24-year-old man is brought to the emergency department with a 2-day history of severe right knee pain, swelling, and redness. He is unable to bear weight on the right leg. He denies any recent trauma or new activities. He reports that he was treated for a urethral discharge two weeks ago. On physical examination, his temperature is 38.7°C (101.7°F). The right knee is warm, erythematous, and has a large effusion. Any passive or active range of motion is extremely painful. Arthrocentesis of the right knee is performed, revealing a leukocyte count of 85,000/mm3 with 92% neutrophils. Gram stain is negative.
Which of the following is the most appropriate next step in the management of this patient?
The correct answer is:
A) Intravenous ceftriaxone and vancomycin
This patient has septic arthritis, a joint-threatening emergency. The diagnosis is strongly supported by the pain with any movement, high fever, and synovial fluid analysis showing a WBC count >50,000/mm3. In a young, sexually active adult, Neisseria gonorrhoeae is a common cause, though Staphylococcus aureus remains the most frequent cause across all age groups. Because the Gram stain is often negative in gonococcal cases and coverage for methicillin-resistant Staphylococcus aureus (MRSA) is required until cultures return, the most appropriate next step is admission for joint drainage (aspiration or arthroscopy) and empiric intravenous antibiotics (typically ceftriaxone plus vancomycin).
Answer choice B: Oral ibuprofen and outpatient follow-up, is incorrect. This would be appropriate for a mild flare of osteoarthritis or a simple viral synovitis. Septic arthritis can destroy joint cartilage within hours to days, so outpatient management would likely result in permanent joint destruction or sepsis.
Answer choice C: Polyarticular joint survey and erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), is incorrect. While disseminated gonococcal infection can cause a migratory polyarthritis or tenosynovitis, this patient’s presentation is a clear monoarthritis. While ESR and CRP will be elevated, they are non-specific and do not dictate the immediate management of an infected joint.
Answer choice D: Probenecid and low-dose aspirin, is incorrect. Probenecid is a uricosuric agent used for chronic gout prevention. Low-dose aspirin can actually decrease uric acid excretion and worsen a gout flare. Neither is appropriate for an acute infection.
Answer choice E: Topical diclofenac, is incorrect. Topical NSAIDs like diclofenac can be used for localized osteoarthritis or minor sprains. They have no role in treating a systemic or deep-space infection like septic arthritis.
Key Learning Point
Septic arthritis presents as an acute, painful monoarthritis with fever and pain with movement of the joint. A synovial WBC count >50,000/mm3 is diagnostic. Immediate management includes joint aspiration/drainage and empiric IV antibiotics to prevent irreversible cartilage damage.
