Arthritis, Septic

Description

• Bacteria can be introduced into a joint by:
  • Hematogenous spread (most common)
  • Invasive procedures
  • Contiguous infection (e.g., osteomyelitis, cellulitis)
  • Direct inoculation such as plant thorns or nails
• Acute inflammatory process results in migration of WBCs into joint
• Synovial hyperplasia, cartilage damage, and formation of a purulent effusion
• Irreversible loss of function in up to 50%
• Mortality rate reported as high as 11%

• Hip infections are most common:
  • Often in patients with otitis media, upper respiratory tract infections, or history of femoral venipuncture
  • Complications of septic arthritis (SA) of hip in children: Avascular necrosis, epiphyseal separation, pathologic dislocation, and arthritis
• 50% occur in children <3 yr old
• Infants present with irritability, fever, and loss of appetite
• Older children present with fever, and a limp or refusal to bear weight or use joint

Etiology

• Risk factors:
  • Old age, infancy
  • Rheumatoid arthritis and degenerative joint disease
  • Intravenous drug user (IVDU), endocarditis
  • Females (gonococcal [GC] infection)
  • Immunosuppression (AIDS, diabetes, chemotherapy, steroid therapy)
  • Repeated joint injections, pre-existing joint diseases, trauma, or prosthesis
  • Skin infection, cutaneous ulcers
• No bacterial pathogen is identified in 10–20%
• Most common organisms:
  • Staphylococcus aureus in adults, hip infections (80%), and patients with rheumatoid arthritis or diabetes
  • Multidrug-resistant S. aureus (MRSA) has been noted in some studies to be the most common organism in community-onset adult SA
  • Neisseria gonorrhoeae most common in young, healthy, sexually active patients (incidence has decreased over the past decades due to a decrease in the incidence of mucosal GC infections)
• Other pathogens: Group A β-hemolytic and group B, C, and G Streptococci:
  • Gram-negative rods (e.g., Pseudomonas aeruginosa, Escherichia coli) in 10% of cases
  • Neisseria meningitidis (12% of patients with meningococcal meningitis)
• Common in old age, infancy, immunosuppression, and IVDU (Pseudomonas)
• Anaerobes: Diabetes, prosthetic joints
• Mycobacterial and fungal causes: Atypical (e.g., in advanced HIV); more indolent course