Septic arthritis is a bacterial infection inside a joint, most often caused by Staphylococcus aureus, that can destroy cartilage within days. It is an emergency: any acutely hot, swollen joint is treated as septic until the joint fluid proves otherwise.
Key symptoms
- Acute pain and swelling of one joint, usually the knee
- Fever and chills, though not always
- Unable to move the joint or bear weight
- A child refusing to walk or use a limb
What you find on exam
- Hot, red, swollen joint with an effusion
- Severe pain with even small passive movement
- Look for a source: skin wound, IV drug use, prosthetic joint
- Vital signs for sepsis
Tests
- Joint aspiration before antibiotics: WBC often over 50,000, Gram stain, culture, crystals
- Blood cultures, CBC, ESR and CRP
- Gonorrhea NAAT in sexually active young adults
- X-ray or ultrasound of the joint
Treatment basics
- Empiric IV antibiotics right after cultures, such as vancomycin plus ceftriaxone
- Drain the joint by repeated aspiration, arthroscopy or open surgery
- Adjust antibiotics to culture results, often 2 to 6 weeks in total
- Urgent orthopedic consult; early movement after the acute phase
Red flags
- Fever, low blood pressure or confusion, signs of sepsis
- Hot, swollen prosthetic joint
- Child with hip pain, fever and refusal to bear weight
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Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.