What is the appropriate workup and treatment for septic (infectious) arthritis?

From the Guidelines

Septic arthritis requires prompt diagnosis and treatment to prevent joint destruction, and the most appropriate approach is to start with empiric broad-spectrum antibiotics and surgical drainage, as recommended by the Surviving Sepsis Campaign guidelines 1. The workup begins with joint aspiration for synovial fluid analysis, including cell count, Gram stain, culture, and crystal examination. A white blood cell count >50,000 cells/mm³ with >90% neutrophils strongly suggests infection. Blood cultures should be obtained before antibiotics, as they are positive in 50-70% of cases. Imaging studies like plain radiographs can show joint effusion, while MRI may detect early osteomyelitis. Some key points to consider in the management of septic arthritis include:

• The choice of empiric antimicrobial therapy depends on complex issues related to the patient’s history, clinical status, and local epidemiologic factors, as outlined in the guidelines 1.
• The initial selection of antimicrobial therapy must be broad enough to cover all likely pathogens, and should be narrowed once pathogen identification and sensitivities are established and/or adequate clinical improvement is noted 1.
• Surgical intervention via arthroscopy or open arthrotomy is essential for adequate drainage, especially for hip, shoulder, and other deep joints, as recommended by the Infectious Diseases Society of America guidelines 1.
• Joint immobilization during the acute phase followed by early passive range of motion exercises helps preserve joint function.
• The urgency of treatment stems from the rapid destruction of cartilage by bacterial toxins and host inflammatory response, which can cause permanent joint damage within days if left untreated. In terms of specific antibiotic regimens, vancomycin 15-20 mg/kg IV every 12 hours plus ceftriaxone 2g IV daily is recommended for empiric coverage of Staphylococcus aureus (including MRSA) and gram-negative organisms in adults. For children, cefazolin 100-150 mg/kg/day divided every 8 hours is appropriate, with vancomycin added if MRSA is suspected. Antibiotics should be adjusted based on culture results, typically continuing for 2-4 weeks intravenously, followed by 2-4 weeks of oral therapy.

From the Research

Diagnosis of Septic Arthritis

• The diagnosis of septic arthritis requires prompt consideration in patients presenting with acute atraumatic joint pain, swelling, and fever 2.
• Risk factors for septic arthritis include age older than 80 years, diabetes mellitus, rheumatoid arthritis, recent joint surgery, hip or knee prosthesis, skin infection, and immunosuppressive medication use 2.
• Physical examination findings and serum markers, including erythrocyte sedimentation rate and C-reactive protein, are helpful in the diagnosis but are nonspecific 2.
• Synovial fluid studies are required to confirm the diagnosis, with a white blood cell count usually greater than 50,000 per mm3 in patients with septic arthritis 3.

Treatment of Septic Arthritis

• Empiric antibiotic therapy should be initiated if there is clinical concern for septic arthritis, with oral antibiotics given in most cases as they are not inferior to intravenous therapy 2.
• The choice of initial antibiotic should be guided by Gram stain results, with vancomycin used for gram-positive cocci, ceftriaxone for gram-negative cocci, and ceftazidime for gram-negative rods 3.
• Total duration of therapy ranges from two to six weeks, with consideration for microorganisms such as Neisseria gonorrhoeae, Borrelia burgdorferi, and fungal infections based on history findings and laboratory results 2.
• Evacuation of purulent material with arthrocentesis or surgical methods is necessary, with special consideration given to patients with prosthetic joint infection 3.

Causative Organisms

• Staphylococcus aureus is the most common pathogen isolated in septic arthritis, with other bacteria, viruses, fungi, and mycobacterium also capable of causing the disease 2.
• The most common bacteria isolated in native joint septic arthritis include Methicillin Sensitive Staphylococcus aureus (MSSA), Methicillin Resistant Staphylococcus aureus (MRSA), Coagulase Negative Staphylococci (CoNS), and Group B Streptococcus (GBS) 4.
• The knee is the most common joint affected, followed by the shoulder and hip, with shoulder septic arthritis most commonly caused by MRSA 4.