Microbiology 12 - Wound, bone and joint infections

Question 1

What is the major pathogen involved in wound, bone and joint infections?

Answer 1

MRSA/ MSSA

Can also be caused by Kingella kingae- have bacterial pili which adhere to the synovium

Question 2

What are the 3 levels of wound infection?

Answer 2

Superficial incisional
Deep incisional
Organ/ space infection

Question 3

Recall 2 important risk factors for wound/ bone/ joint infection

Answer 3

Diabetes

Obesity (adipose tissue is poorly-vascularised)

Question 4

What can be done during orthpaedic procedures to reduce risk of infection?

Answer 4

Laminar flow

Question 5

Which patient group is particularly at risk of septic arthritis?

Answer 5

Those who already have rheumatoid arthritis

Question 6

Where in the joint do organisms adhere to in septic arthritis?

Answer 6

Synovial membrane

Question 7

What are the symptoms of septic arthritis?

Answer 7

Red, painful and swollen joint with restricted movement

Question 8

What investigations for septic arthritis should be done before starting antibiotics?

Answer 8

1. Blood cultures

2. Synovial fluid aspiration

Question 9

When is MRI indicated for septic arthritis patients?

Answer 9

When osteomyelitis is suspected

Question 10

How is septic arthritis managed?

Answer 10

4-6 weeks IV antibiotics

Surgical washout

Question 11

What are the symptoms of vertebral osteomyelitis?

Answer 11

Back pain and fever

Question 12

How is osteomyelitis diagnosed?

Answer 12

MRI

Question 13

How is vertebral osteomyelitis treated?

Answer 13

At least 6w of antibiotics

Question 14

What is the most common pathogen implicated in prosthetic joint infections?

Answer 14

Coagulase negative staphylococcus

Staph saprophyticus (novobiocin resistant)
Staph epidermidis (novobiocin sensitive)

Question 15

What would an x ray show in prosthetic joint infections?

Answer 15

Loosening (space between prosthetic and tissue)

Question 16

How many tissue samples are required for the lab when a patient goes to theatre for a suspected joint infection?

Answer 16

5 (If >3 yield same organism = infection)

Question 17

What are the 2 options for management of prosthetic joint infection?

Answer 17

1. Single stage revision (removal of manky prosthesis and replacement with antibiotic-impregnated material prosthesis)
2. Two stage revision (firstly remove prosthesis and send off samples, put in a spacer, wait a few weeks, then put new prosthesis in)

Question 18

What does mild hypothermia do to risk of SSI (surgical site infection)?

Answer 18

Mild hypothermia appears to increase risk of SSIs by causing:

o Vasoconstriction

o Decreased delivery of oxygen to wound space

o Subsequent impairment of neutrophil function

• In theatre suite: measure patient’s temperature before inducing anaesthesia. Start forced air warming if temperature is < 36oC.
• Warm IV fluids and warm irrigation fluids should be given

Question 19

Factors increasing risk of SSI (Surgical Site Infection)

Answer 19

ASA score >3 (American Society of Anaesthesiologists (ASA) Score is a global score that assesses the physical status of patients before surgery)

Diabetes
o 2-3-fold increased risk
o Associated with post-operative hypoglycaemia
o Control blood glucose with an ideal HbA1c < 7

• Malnutrition
• Low serum albumin
• Radiotherapy and steroid use – taper steroids pre-operatively
• Rheumatoid arthritis
  o Stop disease modifying agents (DMARDS) for 4 weeks before and 8 weeks post-operatively.

If the surgical site is contaminated with > 10^5 microorganisms per gram of tissue, the risk of SSIs is INCREASED

Question 20

MOST POWERFUL independent risk factor for SSI following cardiothoracic surgery?

Answer 20

S. aureus carried in the nasal cavities- present in 20-30% of patients

Question 21

What synovial count suggests septic arthritis?

Answer 21

> 50,000 WBCs

Question 22

Rather niche but- spine infections, vague granulomas, rogue travel history, what is the possibility of pathogen

Answer 22

Brucella