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Question 33#

An 18-year-old high school student presents to the emergency room with 1-day history of right knee pain, swelling, and redness. He is a quarterback in the school’s football team. He remembers falling on the knee while practicing 2 days ago. The knee is tapped and 15 mL of cloudy fluid is sent for cell count, Gram stain, and culture. The Gram stain shows gram-positive cocci in clusters. Which of the following is the best course of action?

A) Start vancomycin and consult orthopedic surgery
B) Consult orthopedic surgery
C) Start linezolid awaiting culture results
D) Start ceftriaxone
E) Start telavancin and order magnetic resonant imaging of the knee

Correct Answer is A


The patient has right knee septic arthritis caused by bacteria that form gram-positive cocci in clusters. This is an orthopedic emergency requiring prompt management. Staphylococcus aureus is the most likely agent. Involvement in a contact sport puts the patient at risk for infections caused by community acquired methicillin-resistant S aureus (CA-MRSA). Consulting orthopedic surgery and starting an antibiotic with activity against MRSA while awaiting culture results is the most appropriate course of action. Antibiotics with activity against MRSA include vancomycin, linezolid, daptomycin, and telavancin. Appropriate antibiotics alone without getting orthopedic surgery involved is not enough. Antibiotics are much less effective in purulent secretions and pus. Joint drainage through daily closed-needle aspiration, arthroscopy, or arthrotomy helps in removing thick purulent material and lysis of adhesions. Ceftriaxone is not active against MRSA. Further testing, such as magnetic resonant imaging, will not add useful information at this point.