Septic Arthritis

Question 1

Septic arthritis is when there is inflammation of a joint that is caused by a microorganism. It can be very dangerous and destroy a joint in <24h. For this reason it is classed as an orthopaedic emergancy. What is the most common microorgaism that leads to septic arthritis?

1 - Klebseilla
2 - Escherichia coli
3 - Staphylococcus aureus
4 - Clostridium difficile

Answer 1

3 - Staphylococcus aureus
- this is because this bacteris resides on the skin and is forced into the joint or tissues
- can also be caused by viruses or fungi

Question 2

Which joint is most commonly affected in septic arthritis?

1 - vertebral
2 - knee
3 - shoulder
4 - hip

Answer 2

2 - knee

• 50% of cases affect the knee
• in children knee and hip are affected

Question 3

Does septic arthritis only affect synovial joints?

Answer 3

• no
• it can affect any joint including fibrous, cartilaginous, and synovial joints

Question 4

What is the incidence (number of new cases over a specificed time) of septic arthritis?

1 - 1-2/100,00 per year
2 - 10-20/100,000 per year
3 - 100-200/100,000 per year
4 - >1000/100,000 per year

Answer 4

1 - 1-2/100,00 per year

Question 5

Does septic arthritis affect older or younger patients?

Answer 5

• both
• biomodal meaning it can affect <2 up to >60 y/o

Question 6

All of the following are risk factors for septic arthritis, EXCEPTY which one?

1 - age <20 years
2 - pre existing joint disease (RA especially)
3 - diabetes
4 - immunocomprimised
5 - CKD
6 - recent joint surgery
7 - prosteic joint
8 - IV drug use
9 - recent infection (endocarditis or bacteraemia)

Answer 6

1 - age <20 years

• age is a risk factor, but generally affects those >80 y/o

Question 7

All of the following are several ways in which joints can become infected causing septic arthritis, what is the most common way the causative agent is spread?

1 - haematogenous
2 - penetrating wound
3 - post surgery
4 - diabetci foot infeciton

Answer 7

1 - haematogenous

• can be causes by a penetrating wound

Question 8

What is primarily destroyed within joints by the causative agent during an attack of septic arthritis?

1 - synovial fluid
2 - blood vessels
3 - inner synovial membrane
4 - articular cartilage

Answer 8

4 - articular cartilage
- can be destroyed within 8 hours

Question 9

If not treated aggressivley, what is most likely to occur to the infected joint in septic arthritis?

1 - osteoperosis
2 - ankylosis
3 - osteomyelitis
4 - haemorrhage

Answer 9

2 - ankylosis

• stiffness of the joint due to abnormal adhesions

Question 10

What are the 2 key symptoms (what a patient describes or experiences) in septic arthritis?

1 - pain in the joint
2 - swollen joint
3 - unable to weight bear or use the joint
4 - hair loss

Answer 10

1 - pain in the joint
3 - unable to weight bear or use the joint

Question 11

All of the following are key signs (what a clinician sees as a manifestion of a disease/condition) in septic arthritis, EXCEPT which one?

1 - unwell patient/fever (unless diabetic)
2 - hot, red, tender and swollen joint
3 - joint in maximum volume
4 - hair loss

Answer 11

4 - hair loss

• microorganisms have PAMPs that elicit an immune response
• immune response leads to blood and fluid entering the joint

Question 12

Septic arthritis can present in a similiar way to other conditions. All of the following are potential differentials, which is the LEAST likely?

1 - Crystal arthropathy (Gout or
Pseudogout)
2 - Cellulitis
3 - Bursitis
4 - Acute flare-up of RA
5 - Osteoarthritis
6 - Lyme disease

Answer 12

5 - Osteoarthritis

Question 13

Although there are multiple investigations that need to be perfromed in a patient with suspected septic arthrits. But which one is the most urgeny?

1 - CRP
2 - joint aspiration
3 - WBC
4 - plain radiography

Answer 13

2 - joint aspiration

• all the other could be normal

Question 14

Aspirating a joint is the most urgent investigation in a patient with suspected septic arthritis. Which of the following is NOT something that is commonly performed on a joint aspiration?

1 - gram staining
2 - cell counts
3 - collagen count
4 - cell culture
5 - crystal analysis

Answer 14

3 - collagen count

Question 15

Which of the following is NOT a typically raised blood marker in a patient with suspected septic arthritis?

1 - WBC
2 - CRP
3 - LFTs
4 - Erythrocyte Sedimentation Rate (ESR)

Answer 15

3 - LFTs

• ESR is raised as RBCs can clump together and be heavier and they are likley to have more proteins, again making them heavier

Question 16

Are imaging methods such as X-ray, MRI or CT useful?

Answer 16

• in acute setting maybe not
• but they can show boney changes

Question 17

If a patient has suspected septic arthritis, should they wait for the bacterial culture results to come back or should they be treated with empirical antibiotics?

Answer 17

• start empirical antibiotics
• this can be changed once bacterial cell culture and antibiotic sensitivtiy resuls have been returned

Question 18

In septic arthritis, should antibiotics be given orally or IV?

Answer 18

• IV
• quicker acting and this is most likely the location where the microorgansim has been able tonspread to the joint

Question 19

Depending on the severity of the septic arthritis, which of the following is NOT an option for treatment?

1 - amputation
2 - surgical irrigation
3 - debridement of joint and any prothesis
4 - irrigation

Answer 19

1 - amputation

• in all of these we need to ensure we get tissue samples for diagnosis purposes