Septhic Arthritis

• It occurs most commonly during the first 2 years of life and adolescence.
• Half of all cases occur by 2 years and three-fourths occur by 5 years.
• Joints of the lower extremity constitute three-fourths of all cases.

• Hematogenous dissemination of bacteria.
• Contiguous spread from surrounding tissues.
• Spread of osteomyelitis through the epiphysis into the joint space in young children.
• Presenting in the first 3 days more often represents the hematogenous spread of bacteria.

Post Infectious Joint Effusion

• It is sterile.
• Caused by antigen-antibody complexes.
• Developed after 7 days of bacterial illness (e.g., bacteremia, meningitis, diarrhea, urethritis).

• S. aureus is the most common agent.
• H. influenzae type b is the most common factor in 3 months to 4 years.
• Streptococci, pneumococci, and meningococci may occur in the absence of sepsis or meningitis.
• Gonococcal arthritis is the most common cause of polyarthritis and monoarticular arthritis in adolescents.

• Erythema, warmth, swelling, and tenderness with a palpable effusion and decreased range of movement. Toddlers may demonstrate a limp.
• Acute septic arthritis most often involves a single joint.
• Multiple joints are affected in 10% of cases.
  • The onset may be sudden with fever and chills.
  • Alternatively, the onset may be insidious, with symptoms noted only when the joint is moved.
• Septic arthritis of the hip is often difficult to assess and may cause referred pain in the knee.
• To minimize pain from pressure, the hip may be positioned in external rotation and flexion.
• The knee and elbow joints are usually in flexion.

• Leukocytosis, elevated ESR, or CRP are common.
• Arthrocentesis is the test of choice for rapid diagnosis.
• Blood or joint cultures are positive in 70% to 85% of cases.
• Ultrasonography is helpful in detecting joint effusion and may guide localization for aspiration.
• Plain radiographs typically add little information to the physical findings.
  • Radiographs may show swelling of the joint capsule, a widened joint space, and displacement of adjacent normal fat lines.
• Radionuclide scans are of limited use, although technetium-99m bone scans may be helpful to exclude concurrent bone infection, either adjacent or distant from the infected joint.
• MRI is useful in distinguishing joint infections from cellulitis or deep abscesses.

Synovial Fluid Analysis

• Synovial fluid analysis for cell count, differential, protein, and glucose has limited usefulness.
• Non-infection inflammatory diseases can also increase cells and protein and decrease glucose (e.g., rheumatic fever, rheumatoid arthritis).
• In up to 30% of patients who have never received antibiotics, it may not reveal bacterial pathogens.
• In chronic arthritis, synovial biopsy may distinguish between a septic and a non-infection process.
• Radiography or bone scans of adjacent bone may be useful.

• Reactive arthritis is immune-mediated synovial inflammation that follows a bacterial or viral infection.
• Non-infectious conditions include:
  • Rheumatoid arthritis
  • SLE (Systemic Lupus Erythematosus)
  • Serum sickness
  • IBD (Inflammatory Bowel Disease)
• Henoch-Schönlein purpura, leukemia, metabolic diseases, foreign bodies, and traumatic arthritis should be considered.
• Viral infections may also cause arthritis.
• Suppurative arthritis must be distinguished from:
  • Lyme disease
  • Osteomyelitis
  • Suppurative bursitis
  • Fasciitis
  • Myositis
  • Cellulitis
  • Soft tissue abscesses
• Psoas muscle abscess often presents with fever and pain on hip flexion and rotation.

Toxic Tenosynovitis of the Hip

• Common condition in children aged 3-6 years.
• May be viral in etiology.
• Self-limited disorder and more common than septic arthritis.

Bacterial Infections

• TB, syphilis, and Lyme disease

• Treatment is based on:
  • Likely organism
  • Gram stain of joint fluid
  • Host immunologic status
• Parenteral antimicrobial agents are typically used.
• Surgical intervention is reserved for specific situations.
• Pyogenic arthritis of the hip or shoulder caused by S. aureus usually necessitates prompt surgical drainage.
• Staphylococcal infection of the knee may be treated with repeated arthrocenteses and continuation of appropriate IV antibiotics.

Empirical Therapy

• Neonates: Antibiotic against staphylococci, GBS, and aerobic gram-negative (cefotaxime or ticarcillin/clavulanate).
• Infants (3 months - 4 years): Antibiotic against S. aureus and H. influenzae type b until culture results are known (cefotaxime or ampicillin/sulbactam).
• IV Methicillin is the choice for S. aureus.
• Vancomycin is used for methicillin-resistant strains.

Duration of Therapy

• The length of therapy depends on:
  • Clinical resolution
  • Reduction of ESR
• S. aureus: 14-21 days or more.
• Gonococcal or meningococcal: 7 days of penicillin.

Oral Agents Against S. aureus

• Augmentin
• Cloxacillin
• Dicloxacillin
• Cephalexin
• Clindamycin
• Ciprofloxacin