Tissue and bone infection: Septic Arthritis

Question 1

How does infection spread to joints?

Answer 1

Haematogenous spread - via blood vessels most common

Eruption of bone abscess - either into the sub-periosteum or into the joint cavity

Direct invasion - penetrating wound, intra-articular injury, arthroscopy (endoscope into the joint - v uncommon)

Question 2

Common organisms causing Acute septic arthritis?

Answer 2

Staph A - most common

Strep pyogenes

E.Coli - common in neonates and elderly

Question 3

Pathology of Acute septic arthritis

Answer 3

When the organism enters the joint there is acute synovitis with purulent joint effusion

The articular cartilage is attacked by the bacterial toxins and cellular enzymes (produced by the neutrophils) which causes gradual damage

Complete destruction of the articular cartilage occurs if the infection is left untreated - picture C

Question 4

What are the possible outcomes of Acute septic arthritis?

Answer 4

• Complete recovery
• Partial loss of the articular cartilage causing gradual symptoms and subsequent OA later in life - picture B
• Fibrous or bony ankylosis - stiffening due to fusion of bones due to destruction of articular cartilage - loss of movement of the joint - picture D

Question 5

How do neonates present with Acute septic arthritis?

Answer 5

Neonates present with picture of septicaemia:

• Irritability
• Resistant to movement of the joint
• Ill

Question 6

What will doctors do if septic arthritis is detected in a neonate?

Answer 6

A full septic screen including a lumbar puncture, CXR and urine sampling

Question 7

How do adults present with Acute septic arthritis?

Answer 7

• Acute extreme pain in single large joint
• They will be reluctant to move the joint
• Swelling in superficial joint but not deeper joints like the shoulder or hip
• Increased temperature and pulse due to infection
• Increased tenderness of the joint

Question 8

How do children/adults present with Acute septic arthritis?

Answer 8

Often involves superficial joint (knee, ankle, wrist) Rare in healthy adults - often occurs in those with other co-morbidities May be a delayed diagnosis

Question 9

Investigations done for Acute septic arthitis?

Answer 9

FBC, WBC, ESR, CRP and blood cultures for signs of infection Imaging - X-ray, USS and MRI Aspiration of the joint and culture of the aspirate

Question 10

What is now the most common cause of septic arthritis in adults?

Answer 10

Infected joint replacement

Question 11

Differential diagnoses for Acute septic arthritis (7)

Answer 11

Acute osteomyelitis Trauma Irritable joint Haemophilia Rheumatic fever Gout Gaucher’s disease

Question 12

Treatment of Acute septic arthritis

Answer 12

• General supportive measures - patients are septic and unwell - IV fluids and antibiotics (3-4 weeks)
• Surgical drainage and lavage (wash out) - this is an emergency, the joint needs to be washed out (pus, organisms and neutrophils)