Septic arthritis

Question 1

Define septic arthritis.

Answer 1

Joint inflammation resulting from intra-articular infection. AKA infective arthritis.

Question 2

What is the aetiology of septic arthritis?

Answer 2

May be idiopathic, although mostly there is systemic infection allowing for haematogenous spread, recen orthopaedic procedures, osteomyelitis, diabetes, immunosuppression, alcoholism.

Question 3

Which organisms commonly cause septic arthritis?

Answer 3

Bacteria -

All ages - staphylococcus aureus, myobacterium tuberculosis

<4years - steptococcus pneumoniae, streptococcus pyogenes, neisseria meningitidis, gram -ve rods.

16-40yrs - mainly neisseria gonorrhoea

Viruses - rubella, mumps, HBV, parvovirus B19

Fungi - candida

Question 4

Which age groups is septic arthritis most common in?

Answer 4

Children and elderly

Question 5

What is the typical presentation of septic arthritis?

Answer 5

• Fever
• Excruciating joint pain
• Redness
• Swelling
• Loss of joint function
• Usually affects single large joint - polyarthritis in immunosuppressed
• Tuberculous arthritis is much more insidious and chronic

Question 6

What are the signs of septic arthritis on examination?

Answer 6

• Painful
• Hot
• Swollen
• Immobilie joint with overlying erythema
• Severe pain presents passive movement
• Pyrexia
• Look for signs of aetiology e.g. small pulses near joint in N. gonorrhoea

Question 7

What investigations would you do for septic arthritis?

Answer 7

Bloods:

• FBC - high WCC, high neutrophils,
• CRP/ESR - raised
• Cultures - MC&S
• Viral serology

Imaging:

• Plain radiographs - affected joint may initially be normal, useful when assessing joint damage in later films
• MRI scan - detects associated osteomyelitis

Invasive:

• Joint aspiration - KEY INVESTIGATION - grossly purulent, send for cytology, polarising microscopy (for gout/pseudogout crystals), MC&S,
• PCR of aspirate - if suspected viral aetiology

Question 8

Why must you exclude septic arthritis in any acutely inflammed joint?

Answer 8

Consider septic arthritis in any acutely inflamed joint, as it can destroy a joint in under 24h and has a mortaility rate up to 11%.

Inflammation may be less overt if immunocompromised (eg from medication) or if there is underlying joint disease.

Question 9

What joint is most commonly affected in septic arthritis?

Answer 9

The knee is affected in >50% cases.

Question 10

What are the risk factors for septic arthritis?

Answer 10

• Pre-existing joint disease - esp rheumatoid arthritis
• Diabetes mellitus
• Immunosuppression
• Chronic renal failure
• Recent joint surgery
• Prosthetic joints (where infection is particularly difficulty to treat)
• IV drug abule
• Age >80 years