bone and wound infections

Question 1

what percentage of HAIs are surgical site infections

Answer 1

15%

Question 2

major pathogens causing SSIs?

Answer 2

staphaylococcus aureus, e coli, p. aeruginosa

Question 3

Intra operative

Answer 3

 Limit number of people in theatre (people shed skin cells)
 Ventilation of theatre (positive pressure)  laminar flow for orthopaedics
 Sterilisation of Surgical Instruments
 Skin Preparation:
• Povidine-iodine
• Chlorhexidine (in 70% alcohol)
 Asepsis and Surgical Technique
• Remove all dead tissue
• IV devices should follow aseptic procedures
 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
 Oxygenation
• SpO2 >95%
• Higher O2 saturations  reduced SSIs

Question 4

septic arthritis risk factors

Answer 4

o Risk Factors:
 Rheumatoid arthritis Osteoarthritis
 Crystal arthritis Joint prosthesis
 IVDU Diabetes, chronic renal disease, chronic liver disease
 Immunosuppression (e.g. steroids) Trauma – intra-articular injection, penetrating injury

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

o Bacterial Factors:
 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 6

what host factors cause damage in septic arthritis

Answer 6

o Host Factors:
 Leucocyte derived proteases and cytokines can cause cartilage and bone damage
 Raised intra-articular pressure impedes capillary blood flow  cartilage and bone ischaemia/necrosis
 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 7

causes of septic arthritis

Answer 7

o Staphylococcus aureus 46%
o Streptococci: 22%
 Streptococcus pyogenes
 Streptococcus pneumoniae
 Streptococcus agalactiae
o Gram-negative organisms:
 Escherichia coli Haemophilus influenzae
 Neisseria gonorrhoea Salmonella
o Coagulase-negative staphylococci 4%
o Lyme disease, Brucellosis, Mycobacteria, Fungi Rare

Question 8

vertebral osteomyelitis causes

Answer 8

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

•	Causative organisms:
o	Staphylococcus aureus (48.3%)
o	Coagulase-negative staphylococcus 
o	Gram-negative rods 
o	Streptococcus 

 

Question 9

treatment of chronic osteomyelitis

Answer 9

• Treatment = radical debridement to living bone:
o Modified Lautenbach technique:
 Debridement and collection of multiple samples for culture and histology
 All foreign prosthetic material is removed
 Debridement done all the way down to healthy bleeding bone (check using osteoscopy)
 Double lumen irrigation system is introduced through a subcutaneous tunnel
 Antibiotics (chosen based on culture results) instilled into affected bone through the central lumen

 Every week 1 L of Hartmann’s solution is infused through each drain and suction fluid is sent for culture
 Irrigation is continued for 3 weeks
o Oral ABx (up to 6 weeks after discharge)
o Papineau Technique:
 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 10

prosthetic joint infection causative organisms

Answer 10

•	Causative Organisms:
o	Gram-positive cocci:
	Coagulase-negative staphylococci > S. aureus
	Streptococci 
	Enterococci 
o	Aerobic Gram-negative bacilli:
	Enterobacteriaceae
	Pseudomonas aeruginosa
o	Anaerobes
o	Polymicrobials
o	Culture-negative 
o	Fungi

Question 11

Diagnosis prosthetic joint infection

Answer 11

• Diagnosis:
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
o Intraoperative Microbiological Sampling:
 Tissue specimens taken from at least 5 sites around the implant
 Histopathology (if >3 specimens yield identical organisms  suggestive of PJI)

Question 12

treatment of prosthetic joint

Answer 12

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
 NO further antibiotics needed if the samples are clear
• If antibiotics are required, OPAT is used