Overview
Definition
A highly destructive bacterial infection within a joint cavity.
Epidemiology
An orthopedic emergency. Risk factors include pre-existing joint disease (RA, osteoarthritis), prosthetic joints, IV drug use, and immunosuppression.
Etiology & Risk Factors
- Staphylococcus aureus (Most common overall)
- Neisseria gonorrhoeae (Most common in young, sexually active adults)
- Streptococcus species, Gram-negative bacilli (in IV drug users/elderly)
- Usually hematogenous spread, but can be from direct inoculation (trauma/surgery).
Clinical Symptoms
- Acute onset of severe pain, swelling, warmth, and erythema in a single joint (Monoarticular)
- The Knee is the most commonly affected joint
- Patient strictly limits ANY movement of the joint (active and passive range of motion are intensely painful)
- Fever and chills
Clinical Approach
Diagnosis
- Arthrocentesis (Joint Aspiration) is MANDATORY and the Gold Standard:
- Synovial fluid analysis: WBC > 50,000 cells/µL with > 90% neutrophils
- Gram stain and Culture of synovial fluid
- Blood cultures (often positive)
Management
- EMERGENT joint drainage (via repeated needle aspirations, arthroscopy, or open arthrotomy) to remove the purulent fluid and prevent cartilage destruction
- Empiric IV Antibiotics (e.g., Vancomycin + Ceftriaxone) IMMEDIATELY after joint aspiration, then tailored based on culture results
Complications
- Rapid, irreversible articular cartilage destruction (can occur within days)
- Osteomyelitis
- Sepsis
- Permanent joint disability