MSK - Septic Arthritis

Question 1

Definition

Answer 1

Septic arthritis refers to infection inside a joint.
This can occur at any age, but is most common in children under 4 years.
Infection in a joint = emergency, as the infection can quickly begin to destroy the joint and cause serious systemic illness.

Question 2

Signs and symptoms

Answer 2

Usually only affects a single joint = often a knee or hip. It presents with a rapid onset of:
- Hot, red, swollen and painful joint
- Refusing to weight bear
- Stiffness and reduced range of motion
- Systemic symptoms such as fever, lethargy and sepsis
Septic arthritis can be subtle in young children, so always consider it as a differential when a child is presenting with joint problems.

Question 3

Common bacteria

Answer 3

• Staphylococcus aureus (MC)
• Neisseria gonorrhoea (gonococcus) in sexually active teenagers
• Group A streptococcus (Streptococcus pyogenes)
• Haemophilus influenza
• Escherichia coli (E. coli)

Question 4

Differential Diagnosis

Answer 4

• Transient sinovitis
• Perthes disease
• Slipped upper femoral epiphysis
• Juvenile idiopathic arthritis

Question 5

Kocher Criteria for diagnosis of septic arthritis

Answer 5

fever >38.5 degrees C
non-weight bearing
raised ESR
raised WCC

Question 6

Investigations

Answer 6

Joint aspiration: for culture. Will show a raised WBC
raised inflammatory markers
blood cultures

Question 7

Management

Answer 7

Suspected arthritis = admission to hospital + orthopaedic team involvement
- Joint aspiration prior to Abx admission
= gram staining
= crystal microscopy
= culture
= antibiotic sensitivities
= the joint fluid
= the joint fluid may be purulent (full of pus)
- Empirical IV Abx = should be given until microbial sensitivities are known
- Abx usually continued for 3-6 weeks in total when septic arthritis confirmed.
- Px may require surgical drainage and washout of the joint to clear the infection in severe cases