Makindo Medical Notes

Related Subjects: |Monoarticular arthritis |Polyarticular arthritis |Rheumatoid arthritis |Gout |Pseudogout |Septic Arthritis |Osteomyelitis |Systemic Lupus Erythematosus (SLE) |Enteropathic Spondyloarthritis |Reactive Arthritis

Septic arthritis is a medical emergency that can cause rapid joint destruction and systemic sepsis if not treated promptly. It most commonly affects a single joint but can involve multiple joints, especially in immunocompromised individuals. Although bacterial infections are the primary cause, fungal and mycobacterial infections can also be implicated. Prosthetic joint infections require specialist management by orthopaedic surgeons due to their complexity.

About

• Urgency: Septic arthritis is an orthopaedic emergency that requires rapid diagnosis and treatment to prevent irreversible joint damage. Pus in a joint is destructive: the proteases produced by leukocytes destroy both the bacteria and the collagen matrix of the articular cartilage. AVN may occur secondary to pressure effects or ischaemic infarction. The treatment of a presumed septic arthritis therefore requires the prompt removal of pus from the joint and appropriate adequate antibiotic therapy.
• Diagnosis: Should be considered whenever a patient presents with a painful, swollen joint, especially if they have risk factors such as recent surgery or systemic infection.
• Complications: Delayed diagnosis can result in joint destruction, sepsis, and potential mortality.

Infectious Agents

The most frequently identified organism is Staphylococcus aureus. Streptococcal infection is also common and other organisms are more prevalent in certain age groups, e.g. the neonate, in certain conditions, e.g. sickle cell disease, or in certain countries. The Haemophilus influenzae type B (Hib) vaccine has essentially eliminated H. influenzae as a cause of infection, but in some countries Kingella kingae has taken its place.

• Common Bacteria:
  • Staphylococcus aureus, including MRSA, is the most common cause.
  • Streptococci, including Group A and B Streptococcus.
  • Neisseria gonorrhoeae in sexually active adults.
  • Haemophilus influenzae (rare with vaccination).
  • Gram-negative organisms (e.g., E. coli, Pseudomonas) in elderly or immunocompromised patients.
• Fungal and Atypical Infections: Candida spp., mycobacteria (e.g., Mycobacterium tuberculosis) in immunocompromised patients.

Aetiology

• Joint Susceptibility: Damaged or abnormal joints (e.g., rheumatoid arthritis, osteoarthritis, prosthetic joints) are more prone to infection.
• Pathways of Infection:
  • Haematogenous spread from remote infections (e.g., skin infections, endocarditis).
  • Direct inoculation from trauma, injections, or surgery.
  • Extension from adjacent osteomyelitis or soft tissue infection.
• Common in Infants and Children: Must be considered in any child with a painful, swollen joint, fever, and limp. Diagnosis is difficult in neonates and the immunocompromised. Typical presentation is pain, fever and a reluctance to move the joint or weight bear

Risk Factors in Adults

• Age >80 years, immunosuppression, diabetes mellitus, rheumatoid arthritis, IVDU (intravenous drug use).
• Recent joint surgery or prosthetic joint implantation.
• Underlying joint disease, skin infections, and chronic renal or liver disease.

Clinical Presentation

• Symptoms: Rapid onset (1-2 weeks) of joint pain, swelling, erythema, and decreased range of motion.
• Systemic Features: Fever, chills, and malaise are common but may be absent in elderly or immunosuppressed patients.
• Joint Involvement: Usually monoarticular; knee is involved in about 50% of cases, but hips, shoulders, ankles, and wrists can also be affected.
• Multiple Joints: Involved in about 15% of cases, especially with gonococcal infections.
• Joint Positioning: Patients often hold the joint in a position that maximises space (e.g., flexed for the knee) due to pain and swelling.

Investigations

• Laboratory Tests: Elevated CRP, ESR, and leukocytosis (FBC). Blood cultures should be taken before starting antibiotics.
• Arthrocentesis:
  • Essential for diagnosis. Perform Gram stain, culture, cell count, and crystal analysis.
  • Appearance of synovial fluid: cloudy or purulent with WBC >50,000/mm³ and predominantly neutrophils is highly suggestive of infection.
• Imaging:
  • X-rays may show joint space narrowing or erosions in chronic infections but are often normal early on.
  • MRI or ultrasound can detect effusion and soft tissue involvement.
  • Radionuclide scans may help in difficult cases or deep-seated infections.
• Consider Screening for Gonococcal Infection: Swab urethra, cervix, pharynx, and rectum if gonococcal arthritis is suspected.

Joint Aspiration Analysis

Differential Diagnosis in Children

• Transient synovitis, Still's disease, Rheumatic fever, Lyme disease, Perthes disease.

Differential Diagnosis in Adults

• Gout, Pseudogout, Rheumatoid arthritis, Reactive arthritis, Osteoarthritis flare.

Clinical Predictors

• History of fever >38.5°C
• Non-weight bearing
• Erythrocyte sedimentation rate >40 mm/hour
• White cell count >12 × 109/L

Management (Consult Microbiology for Advice)

The treatment of a presumed septic arthritis therefore requires the prompt removal of pus from the joint and appropriate adequate antibiotic therapy. Pain relief and rest are key as are the general health and nutrition of the patient. The joint is aspirated and, if pus is confirmed, a formal washout is mandatory; standard teaching states that the joint must be opened, irrigated and free drainage encouraged via the capsulotomy. Recent literature supports repeated aspiration/irrigation via a large-bore cannula or a small arthroscope for all joints except the hip joint. Antibiotic usage is guided by the local hospital policy, the source of the infection, the Gram stain, the culture and sensitivity of the organism identified

• Prosthetic Joint Infections: Should be managed in conjunction with orthopaedic surgeons and may require joint washout or revision surgery.
• Initial Antibiotic Therapy: Flucloxacillin 2 g IV every 6 hours +/- Fusidic acid 500 mg 8 hourly. Adjust according to culture results.
• If Gram-negative organisms are suspected, add Ciprofloxacin 500 mg BD.
• Treat for 6 weeks total: 2 weeks IV, followed by 4 weeks of oral therapy based on sensitivities.
• Joint Drainage: Needle aspiration, arthroscopic drainage, or open surgical drainage as indicated.
• Pain Management: NSAIDs, opioids as needed, and joint immobilisation in the acute phase.
• Early Mobilisation: Initiate physiotherapy once acute inflammation subsides to prevent stiffness and contractures.
• Special Considerations for Gonococcal Arthritis: Requires longer treatment duration and additional testing for other sexually transmitted infections.
• TB Arthritis: Requires 9-month TB regimen with initial immobilisation and joint rest.

References

• Septic Arthritis Review
• Septic Arthritis: Current Concepts