Infective Arthritis: Septic arthritis

Question 1

Definition

Answer 1

MEDICAL EMERGANCY: Refers to infection of a joint. It requires a high index of suspicion and can affect both native + prosthetic joints
- MC bacterial infection, with the microbes either invading the joint directly or via the bloodstream

Question 2

Epidemiology

Answer 2

Increasing incidence with age = +65

Question 3

Risk factors

Answer 3

• Underlying joint disease: 10-fold increased risk; conditions such as rheumatoid arthritis, osteoarthritis and gout
• Intravenous drug use
• Immunocompromised: elderly, diabetes, HIV
• Prosthetic joint

Question 4

Aetiology

Answer 4

• Staphylococcus aureus = The most common cause in all age groups
• Staphylococcus epidermidis = Prosthetic joints
• Streptococcus pyogenes = Children under 5 years old
• Neisseria gonorrhoeae = Young, sexually-active adults
• Pseudomonas aeruginosa + E.coli = Immunosuppressed, elderly, and IV drug abuse

Question 5

Pathophysiology

Answer 5

Bacteria will seed to the joint from the bacteraemia (e.g. recent cellulitis, UTI, chest infection) or spreading from adjacent osteomyelitis. Septic arthritis can cause irreversible articular cartilage destruction as bacteria release chondrocytes proteases to damage joint leading to severe osteoarthritis

Question 6

Signs

Answer 6

Hot, tender erythematous, swollen joint
Very limited range of movement
Effusions may also be evident
Often joint is rigid and patient will be unable to weight bare

Question 7

Symptoms

Answer 7

Difficulty weight bearing
Fever

Question 8

Diagnosis

Answer 8

FIRST LINE = Blood culture
- FBC
- CRP
- ESR
- Urate levels
GOLD STANDARD = Joint aspiration with MC+S
- ID causative organism
- yellow and cloudy colour > 50,000 WBC/uL
X-ray = not diagnostic but recommended to assess underlying joint disease - joint effusions

Question 9

Treatment

Answer 9

FIRST LINE = Joint aspiration (drainage) then Abx
- Flucloxacillin (gram -ve: E. coli, Aeruginosa)
* Clindamycin = penicillin allergy *
- Vancomycin (MRSA - S. aureus)
- IM Ceftriaxone + azithromycin (gonorrhoea)
Stop methotrexate
If on steroids = DOUBLE PREDNISOLONE = Increase stress response
Surgery = arthroscopic washout, or surgical debridement
NSAIDs = for analgesia