Septic Arthritis

Question 1

Define septic arthritis and what is the most common joint affected

Answer 1

Infection of 1 or more joints caused by pathogenic inoculation of microbes

most common site of infection is the hip (75%)

Question 2

What are the causes of septic arthritis

Answer 2

Infection can occur either by direct inoculation (punctured wound, infected skin lesion) or via haematogenous spread
Staphylococci or Streptococci (91%)
Sexually active: gonococcal
Older/immunocompromised: gram-negative
Penetrating trauma: anaerobic organisms
Immunocompromised/endemic areas: TB

Question 3

What are the risk factors for septic arthritis

Answer 3

Underlying joint disease e.g. osteoarthritis, rheumatoid arthritis
Osteomyelitis (15% co-existent)
Prosthetic joint
Immunosuppression e.g. HIV, immunosuppressants
IVDU
Contiguous spread e.g. from cutaneous ulcers or skin infection
Exposure to ticks - travel to or residence in areas where Lyme disease is prevalent
Previous intra-articular corticosteroid injection, recent joint surgery, low SES

Question 4

What is the epidemiology for septic arthritis

Answer 4

Most common <4 years old
Estimated prevalence in developed countries is 6 cases per 100,000 population per year, which increases 10-fold in those with underlying joint disease or with prosthetic joints
Often diagnosed late due to normal X-ray at presentation

Question 5

What are the symptoms of septic arthritis

Answer 5

Joint pain and swelling + redness
- Hot, swollen, painful, restricted joint (monoarticular)
- Excruciating pain
- <2 weeks
- Most with septic arthritis of a weight-bearing joint will not be able to walk, and the joint is often held in a position that maximises joint space
Large joints: knee, hip, shoulder, ankle, elbow, wrist
Fever, chills, rigors

Question 6

What are the differentials for septic arthritis

Answer 6

Transient synovitis
Rheumatoid arthritis
Haemarthrosis in haemophilia
Trauma
Osteomyelitis
Bursitis
Cellulitis
TB
Lyme disease

Question 7

What are the signs of septic arthritis on examination

Answer 7

Ob: Pyrexia
Joint
- Painful, hot, swollen and immobile joint with overlying erythema
- Severe pain that prevents passive movement
- Reduced range of movement
- Pseudoparesis/pseudoparalysis - infants holding their joint still
- Joint held flexed, hip abducted, externally rotated
- Joint effusion
- Signs of aetiology e.g. small pustules near the joint for N. gonorrhoea

Question 8

What are the investigations for septic arthritis

Answer 8

Regard a hot, swollen, acutely painful joint with restriction of movement as septic arthritis until proven otherwise.

Bloods: FBC, Blood culture, CRP/ESR, viral serology, LFTs
Other:
- Joint aspiration for cytology, culture, sensitivities: grossly purulent, polarising microscopy negative
- Plain joint radiograph: initially normal, may show widening oof joint space
USS: for guidance of aspiration

Question 9

What is the management for septic arthritis

Answer 9

Hot, swollen, painful joint + fever → refer to emergency care
1. Admit
2. Aspirate for MC&S
3. Empirical antibiotics: consult microbiologist
4. Joint aspiration
5. Analgesia: paracetamol or NSAIDs
6. Monitor FBC, ESR, CRP, procalcitonin

Question 10

What are the complications of septic arthritis

Answer 10

Osteomyelitis (infection spreads to surrounding bone)
Joint destruction

Question 11

What is the prognosis for septic arthritis

Answer 11

Delayed or inadequate treatment may lead to irreversible joint destruction and subsequent disability
There is a single-joint estimated case fatality rate of 11%