Septic arthritis

Question 1

Septic arthritis is a medical emergency. It is a d_____ b_____ infection of a joint

Answer 1

direct bacterial

Question 2

Which joint is typically affected?

Answer 2

Knee

Question 3

What 2 things are key presentation signs

Answer 3

Acutely inflamed joint with a fever

Question 4

What organism most commonly causes septic arthritis?

Answer 4

Staphylococcus aureus

Question 5

Is staph aureus gram positive or negative?

Answer 5

Positive

Question 6

Is staph. aureus catalase positive or negative?

Answer 6

Positive

Question 7

When is a catalase test particularly useful?

Answer 7

When determining whether a gram-positive cocci is a staphylococci or streptococci

Question 8

Why do some bacteria make catalase?

Answer 8

The enzyme protects bacteria from toxic H2O2 by converting it into water and oxygen

Question 9

What is seen in a positive catalase test?

Answer 9

There are bubbles in a catalase positive sample due to bubbles of oxygen forming

Question 10

Is staph. aureus coagulase positive or negative?

Answer 10

Positive

Question 11

When is the coagulase test used?

Answer 11

To differentiate staphylococcus aureus from s. epidermis and s. saprophyticus which don’t produce coagulase

Question 12

The enzyme ______ activates fibrinogen in the blood and results in coagulation. This allows staph aureus to “wall” it’s infection off from the host’s protective mechanisms

Answer 12

coagulase

Question 13

How is the coagulase test carried out?

Answer 13

Add bacteria sample to rabbit plasma. Heat and wait 30 mins.
Any coagulation (cloudy tube) means positive test so is staph aureus.

Question 14

What other microorganisms commonly cause septic arthritis?

Answer 14

H. influenza (now rare due to immunisation)
Neisseria gonorrhoea
E Coli
Pseudomonas aeruginosa

Question 15

What are risk factors for septic arthritis?

Answer 15

IVDU
Immunosuppression
Recent surgery
Trauma
Prosthetic joints
Inflammatory joint disease
Diabetes
Osteomyelitis
HIV

Question 16

What type of bacteria commonly infect prosthetic joints?

Answer 16

Coagulase negative staph. epidermis

Question 17

How do you diagnose septic arthritis?

Answer 17

Urgent joint aspiration with MC+S and polarised light microscopy

Question 18

What is the diagnosis if the tests came back sterile and with no crystals?

Answer 18

Reactive arthritis

Question 19

What is the diagnosis if the tests came back sterile and with positive birefringent rhomboid crystals?

Answer 19

Psuedogout

Question 20

What is the diagnosis if the tests came back sterile and with positive birefringent needle crystals?

Answer 20

Gout

Question 21

What would the ESR and CRP levels do in septic arthritis

Answer 21

Rise

Question 22

If the joint aspirate showed causative organism as n. gonorrhoea, other than immediate management, what else is considered?

Answer 22

Sexual health review

Question 23

How do you treat septic arthritis?

Answer 23

Joint aspirate to drain
Then empirical antibiotic

Question 24

What antibiotic is used for gram -ve bacteria like E. coli or p. aeruginosa?

Answer 24

Flucloxacillin

Question 25

What antibiotic is used for MRSA (staph aureus)?

Answer 25

Vancomycin

Question 26

What antibiotic is used for gonorrhoea?

Answer 26

IM ceftriaxone and azithromycin

Question 27

If the patient with septic arthritis is on methotrexate or anti-tnf, what should happen?

Answer 27

They should stop taking these as they are immunosuppressives

Question 28

If the patient with septic arthritis is on steroids what should happen?

Answer 28

Double the prednisolone dose as there is an increased stress response

Question 29

What is used for analgesia in septic arthritis?

Answer 29

NSAIDs