Wound, bone, joint Infections

Question 1

Major pathogens causing Surgical site infections (SSI)

Answer 1

o Staphylococcus aureus (MSSA and MRSA)
o Escherichia coli
o Pseudomonas aeruginosa

Question 2

Three levels of SSIs

Answer 2

o Superficial Incisional skin and subcutaneous tissues
o Deep Incisional fascial and muscle layers
o Organ/Space Infection any part of the anatomy other than the incision

Question 3

Preventing SSIs pre-operatively

Answer 3

 Treat all remote infection (e.g. pneumonia, UTI) before operation
 Hair removal
• Shaving increases risk of SSI (micro-abrasions from shaving can multiply bacteria)
• Electric clipper should be used instead on the day of surgery with a single-use head
 Nasal Decontamination
• Staphylococcus aureus is carried in the nostrils of 20-30%
 Antibiotic Prophylaxis

Question 4

Intra-operative prevention of SSIs

Answer 4

 Limit number of people in theatre
 Ventilation of theatre (positive pressure)
 Sterilisation of Surgical Instruments
 Skin Preparation:
• Povidine-iodine
• Chlorhexidine (in 70% alcohol)
 Normothermia (if <36C, consider warming):
• Hypothermia  increase risk of SSIs by causing vasoconstriction and decreasing oxygen delivery to wound space with impairment of neutrophil function
• Measure the patient’s temperature before inducing anaesthesia
 Asepsis and Surgical Technique
• Remove all dead tissue

Question 5

Pathophysiology of septic arthritis

Answer 5

o Organisms adhere to synovium
o Bacterial proliferation in synovial fluid  host inflammatory response  joint damage
o Joint damage  exposure of host derived protein (e.g. fibronectin) to which bacteria can adhere

Question 6

Bacterial factors allowing septic arthritis

Answer 6

 S. aureus has receptors such as fibronectin-binding protein that recognise selected host proteins
 S. aureus (some strains) produce cytotoxin PVL (Panton-Valentine Leucocidin)  fulminant infection
 Kingella kingae synovial adherence is via bacterial pili

Question 7

Host factors allowing septic arthritis

Answer 7

 Genetic deletion of macrophage-derived cytokines  reduce host-response in S. aureus sepsis
 Absence of IL-10 increases the severity of staphylococcus joint disease

Question 8

Organisms causing septic arthritis

Answer 8

o	Staphylococcus aureus 						46%
o	Streptococci: 								22%
	Streptococcus pyogenes
	Streptococcus pneumoniae
	Streptococcus agalactiae

Question 9

Investigations of septic arthritis

Answer 9

o Blood cultures (before ABx)

o Synovial fluid aspiration MC&S synovial count >50,000 WBC/mL is used to suggest septic arthritis

Question 10

Management of SA

Answer 10

o ABx, 4-6 weeks (outpatient setting)

o Drainage of the joint

Question 11

Causes of vertebral osteomyelitis

Answer 11

o	Acute haematogenous spread (bacteraemia)
o	Exogenous (after disc surgery, implant associated)

Question 12

Causative organisms of VO

Answer 12

o Staphylococcus aureus (48.3%)
o Coagulase-negative staphylococcus
o Gram-negative rods
o Streptococcus

Question 13

Main location of VO

Answer 13

o	Lumbar 			(43.1%)
o	Cervical 				(10.6%)
o	Cervico-thoracic 			(0.4%)

Question 14

Ix for VO

Answer 14

• Investigations:
o MRI (90% sensitive)
o Blood cultures
o CT-guided/open biopsy

Question 15

Tx of VO

Answer 15

o ABx, 6 weeks

Question 16

Diagnosis of chronic osteomyelitis

Answer 16

o	XR (often first line to screen; early changes take ~10 days)
o	MRI (much more sensitive for changes)
o	Bone biopsy (culture and histology)

Question 17

Treatment of chronic OM

Answer 17

Radical debridement to living bone

Oral ABx 6 weeks

Question 18

Papineau Technique

Answer 18

 Complete excision of infected tissue and necrotic bone
 Followed by open cancellous bone grafting of the osseous defect
 Split skin grafting is used to close the wound
 Success rate of 89-93%

Question 19

Causative organisms of Prosthetic joint infections

Answer 19

 Coagulase-negative staphylococci > S. aureus

Question 20

Features of PJI

Answer 20

o Pain
o Patient complain joint was ‘never right’ after the operation  early failure
o Sinus tract

Question 21

Diagnosis of PJI

Answer 21

o Radiology – loosening (bone loss along the cement-bone interface)
o Raised CRP:
 CRP >13.5 for prosthetic knee joint infection
 CRP >5 for prosthetic hip joint infection
o Joint Aspiration:
 If >1,700 WCC/mL  knee PJI
 If >4,200 WCC/mL  hip PJI

Question 22

Tx of PJI

Answer 22

o Single Stage Revision (i.e. Endo-Klinik):
 Remove all foreign material and dead bone
 Change gloves and drapes etc.
 Re-implant new prosthesis with antibiotic impregnated cement and give IV antibiotics

o Two Stage Revision:
 Remove prosthesis and put in a spacer (to take up the space of the prosthesis)
 Take samples for microbiology and histology
 Period of IV antibiotics (for 6 weeks) then stop antibiotics for 2 weeks
 Re-debride and sample at second stage
 Re-implantation with antibiotic impregnated cement