Septic Arthritis

Question 1

What is septic arthritis?

Answer 1

Septic arthritis is defined as the infection of 1 or more joints caused by pathogenic inoculation of microbes. It occurs either by direct inoculation or via haematogenous spread.

Question 2

What % mortality does septic arthritis have?

Answer 2

Septic arthritis has a mortality of around 10%.

Question 3

What is the most common causative organism causing septic arthritis?

Answer 3

Staphylococcus aureus is the most common causative organism.

Question 4

Other than Staphylococcus aureus, give examples of other bacteria causing septic arthritis

Answer 4

• Neisseria gonorrhoea (gonococcus) in sexually active individuals
• Group A Streptococcus (most commonly Streptococcus pyogenes)
• Haemophilus influenza
• Escherichia coli (E. coli)

Question 5

What are the risk factors for septic arthritis?

Answer 5

• Pre-existing joint disease (e.g., rheumatoid arthritis or osteoarthritis)
• Joint prostheses
• Intravenous drug misuse
• Immunosuppressive medication
• HIV infection
• Alcohol use disorder
• Diabetes
• Previous intra-articular corticosteroid injection
• Recent joint surgery

Question 6

What are the signs of septic arthritis?

Answer 6

• Passive and active movement of the joint will be limited and very painful in septic arthritis
• In practice, most patients with septic arthritis of a weight-bearing joint will not be able to walk

Question 7

What are the symptoms of septic arthritis?

Answer 7

• Hot, red, swollen and painful joint
• Stiffness and reduced range of motion
• Systemic symptoms such as fever, lethargy and sepsis

Question 8

What investigations should be ordered for septic arthritis?

Answer 8

• Synovial fluid microscopy and gram stain
• Synovial fluid culture and sensitivites
• Synovial fluid white cell count
• Blood culture and sensitivities
• White cell count
• ESR
• U&Es
• LFTs
• X-ray

Question 9

Why investigate synovial fluid microscopy and gram stain?

Answer 9

Aspirate synovial fluid for Gram stain and culture before starting antibiotic therapy unless more urgent treatment is indicated.

Microscopic analysis may reveal the causative organism.

Question 10

Why investigate synovial fluid culture and sensitivities?

Answer 10

Aspirate synovial fluid for culture and sensitivities before starting antibiotic therapy unless more urgent treatment is indicated.

Microscopic culture may reveal the causative organism and its sensitivity to antibiotics.

Question 11

Why investigate synovial fluid white cell count?

Answer 11

Aspirate synovial fluid for WBC count before starting antibiotic therapy unless more urgent treatment is indicated.

It is the most useful test in differentiating between septic arthritis and other diagnoses.

Question 12

Why investigate blood culture and sensitivities?

Answer 12

Draw blood for cultures before starting antibiotic therapy.

Because of haematogenous spread of infection, blood cultures are positive in 25% to 50% of patients with septic arthritis.

Question 13

Why investigate white cell count?

Answer 13

Take blood for WBC count as it can help inform a diagnosis, but clinical judgement and results of synovial fluid microscopy are more important.

Question 14

Why investigate ESR?

Answer 14

Take blood for ESR as it can help inform a diagnosis, but clinical judgement and results of synovial fluid microscopy is more important.

May be elevated, only moderately elevated, or normal.

Question 15

Why investigate CRP?

Answer 15

Take blood for CRP as it can help inform a diagnosis, but clinical judgement and results of synovial fluid microscopy is more important.

May be elevated, only moderately elevated, or normal.

Question 16

Why investigte U&Es?

Answer 16

Take blood for urea and electrolytes. These provide baseline parameters and help assess for sepsis and end-organ damage as these may influence antibiotic choice.

Question 17

Why investigate LFTs?

Answer 17

Take blood for LFTs to assess for sepsis and end-organ damage as these may influence antibiotic choice.

Question 18

Why investigate using x-ray?

Answer 18

Obtain an x-ray of the joint/s as a baseline investigation.

Not urgent, as is not diagnostic for septic arthritis.

May reveal degenerative changes or chondrocalcinosis.

Question 19

Briefly describe the treatment for septic arthritis

Answer 19

Admit the patient for intravenous antibiotic treatment and joint drainage.

Question 20

Briefly describe the empirical antibiotic therapy used to treat septic arthritis

Answer 20

Empirical IV antibiotics should be given until the sensitivities are known. Antibiotics are usually continued for 3-6 weeks in total. Choice of antibiotic depends on the local guidelines. Example regimes are:

• Flucloxacillin plus rifampicin is often first line
• Vancomycin plus rifampicin for penicillin allergy, MRSA or prosthetic joint

Question 21

How long is antibiotic treatment required for in treating septic arthritis?

Answer 21

3-6 weeks in total:

• ~2 weeks IV
• Following this, 2-4 week PO

Question 22

Briefly describe the role of therapeutic joint aspiration in septic arthritis

Answer 22

Repeat joint aspiration to dryness as often as necessary.

This helps remove infection and manage pain by relieving pressure within the joint.

Question 23

When is arthroscopic washouts used in septic arthritis?

Answer 23

Repeated arthroscopic washouts are indicated if temperature and inflammatory markers do not improve after the initial aspiration and treatment.

Question 24

What are the complications of septic arthritis?

Answer 24

• Antibiotic associated allergic reaction
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Question 25

What differentials should be considered in septic arthritis?

Answer 25

1. Gout
2. Pseudogout
3. Reactive arthritis
4. Haemarthrosis

Question 26

How does septic arthritis and gout differ?

Answer 26

Differentiating signs and symptoms:

• Known history of gout

Differentiating investigations:

• Synovial fluid polarising microscopy will reveal urate crystals

Question 27

How does septic arthritis and pseudogout differ?

Answer 27

Differentiating signs and symptoms:

• Known history of pseudogout

Differentiating investigations:

• Synovial fluid polarising microscopy will reveal pyrophosphate crystals

Question 28

How does septic arthritis and reactive arthritis differ?

Answer 28

Differentiating signs and symptoms:

• Clinical symptoms typically begin within 1 to 4 weeks after the onset of infection
• After exposure to certain gastrointestinal and genitourinary infections

Differentiating investigations:

• There is no specific test for diagnosing reactive arthritis
• Routine cultures and cultures to rule out gonorrhoea and other infectious processes should be performed on synovial fluid

Question 29

How does septic arthritis and haemarthrosis differ?

Answer 29

Differentiating signs and symptoms:

• Known history of a bleeding diathesis

Differentiating investigations:

• Joint aspiration will reveal blood