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Arthritis, Septic

Basics

  • Infection of joint space by bacteria.
  • Synonyms: suppurative arthritis, pyogenic arthritis, bacterial arthritis, pyarthrosis.
  • Systems affected: musculoskeletal.

Epidemiology

  • Bimodal age peaks: childhood and ≥55 years.
  • Incidence: 40-60/100,000 per year overall.
  • Immunocompromised and prosthetic joint patients: ~70/100,000 per year.
  • Gonococcal arthritis more common in females; nongonococcal more in males.
  • Prosthetic joint infections rising; infected hardware now most common septic arthritis type.

Etiology & Pathophysiology

  • Common pathogens:
  • Nongonococcal: Staphylococcus aureus (most common), MRSA (elderly, IVDU), Streptococcus spp.
  • Gram-negative rods in IVDU, trauma, immunosuppressed.
  • Neisseria gonorrhoeae in young sexually active adults.
  • Polymicrobial infections after penetrating trauma.
  • Others: fungal, mycobacterial, rickettsial (Lyme).
  • Pathogenesis:
  • Hematogenous spread most common.
  • Direct inoculation (trauma, surgery).
  • Adjacent spread (osteomyelitis).
  • Microorganisms invade synovium and synovial fluid; inflammatory response causes joint damage.

Risk Factors

  • Age >80 years, alcoholism, low socioeconomic status.
  • Skin infections, cellulitis, ulcers.
  • Joint capsule violation, orthopedic surgery, intraarticular injections.
  • History of joint disease: RA, osteoarthritis, crystal arthritides.
  • Systemic illnesses: diabetes, liver disease, HIV, malignancy, ESRD, immunosuppression, sickle cell.
  • IVDU, severe sepsis.

Prevention

  • Prompt treatment of skin/soft tissue infections.
  • Control risk factors.
  • Immunizations: S. pneumoniae, N. meningitidis.

Diagnosis

History

  • Joint pain, swelling, warmth, decreased ROM.
  • Usually monoarticular (>80%), mostly large joints (knee 50%, hip 20%, shoulder 8%, ankle 7%).
  • Fever common but may be absent in immunosuppressed.
  • Gonococcal arthritis: migratory polyarthritis, tenosynovitis, dermatitis.
  • Prosthetic joint infection may present with draining sinus.

Physical Exam

  • Fever, joint tenderness, effusion, erythema, warmth.
  • Pain on passive motion.
  • Infants may hold joint in position of comfort (flexion, external rotation).
  • Purpura in disseminated gonococcal infection.

Differential Diagnosis

  • Crystal arthritis: gout, pseudogout.
  • Infectious arthritis: fungal, viral, spirochetes.
  • Inflammatory arthritis: RA, spondyloarthropathy, SLE.
  • Osteoarthritis.
  • Trauma: meniscal tear, hemarthrosis.
  • Bursitis, cellulitis, tendinitis.

Diagnostic Tests

Lab/Imaging

  • Arthrocentesis (gold standard): Gram stain, culture, cell count, differential, crystal analysis.
  • Synovial WBC >50,000/HPF with >90% PMNs suggestive but not definitive.
  • Culture positive in ~80%.
  • Synovial leukocyte esterase with high negative predictive value.
  • Blood cultures positive in ~50%.
  • Serum markers: ESR (>15 mm/hr), CRP (>20 mg/L).
  • Imaging:
  • X-rays: nonspecific; rule out trauma, osteoarthritis.
  • Ultrasound: guide arthrocentesis, detect effusion.
  • MRI: differentiate transient synovitis vs septic arthritis in children.
  • Special:
  • Gonococcal: culture blood, mucosal sites, synovial fluid.
  • Lyme arthritis: PCR, Borrelia titers.

Treatment

General Measures

  • Admit for IV antibiotics and monitoring.
  • Drain purulent fluid—surgical drainage for hip in pediatrics, prosthetic joints may require revision.
  • Duration: 4-6 weeks (native joints ≥2 weeks IV + oral; prosthetic joints longer).
  • Consult infectious disease and orthopedics as needed.

Medications

  • Guided by Gram stain, culture, clinical context.

Nongonococcal

  • Gram-positive cocci: Vancomycin 15-20 mg/kg 2-3x daily or linezolid 600 mg BID.
  • Gram-negative rods: Cefepime 2 g BID, ceftriaxone 2 g daily, ceftazidime, or cefotaxime.
  • Cephalosporin allergy: Ciprofloxacin.
  • Negative Gram stain: Vancomycin + 3rd generation cephalosporin empirically.

Gonococcal

  • Ceftriaxone 1 g IV/IM daily 7-14 days.
  • Treat for at least 24-48 hrs after symptom resolution.
  • Consider doxycycline or azithromycin for chlamydia coverage.

Lyme arthritis

  • Doxycycline 100 mg BID or amoxicillin 500 mg TID for 28 days; ceftriaxone if neurologic involvement.

Issues for Referral

  • Infectious disease for IVDU, immunosuppressed.
  • Orthopedics for prosthetic infections.

Surgery/Procedures

  • Drainage essential, especially shoulder, hip, prosthetic joints.
  • Repeat aspiration, arthroscopy, arthrotomy as needed.

Inpatient Care

  • Average hospitalization: ~12 days.

Ongoing Care & Follow-up

  • Monitor synovial fluid WBC and sterility.
  • Reevaluate if no improvement in 24 hours.
  • Follow-up 1 week and 1 month post-therapy for relapse.

Prognosis

  • Early treatment improves outcome.
  • Delayed therapy increases morbidity, mortality.
  • Poor outcomes with elderly, RA, S. aureus, hip/shoulder involvement.

Complications

  • Mortality 3-25%.
  • Joint ankylosis, limited ROM, osteomyelitis, synovitis.
  • Secondary osteoarthritis, flail or dislocated joint.
  • Sepsis, septic necrosis.
  • Sinus tract formation.
  • Limb length discrepancy (in children).

ICD10 Codes

  • M00.079 Staphylococcal arthritis, unspecified ankle and foot
  • M00.829 Arthritis due to other bacteria, unspecified elbow
  • M00.011 Staphylococcal arthritis, right shoulder

Clinical Pearls

  • Arthrocentesis and synovial fluid analysis mandatory in suspected septic arthritis.
  • Synovial WBC >50,000/HPF suggests infection but must be interpreted contextually.
  • Early IV antibiotics plus drainage critical for successful management.
  • Crystalline arthritis may coexist with septic arthritis.
  • Initial antibiotics guided by Gram stain, age, and risk factors.