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YEAR 5: Microbiology and Infection > MI: Wound, bone and joint infections > Flashcards

MI: Wound, bone and joint infections Flashcards

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1
Q

Name three major pathogens that cause surgical site infections.

A
  • Staphylococcus aureus
  • Escherichia coli
  • Pseudomonas aeruginosa
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2
Q

List some factors affecting the severity of the disease.

A
  • Pathogenicity of the microorganism
  • Inoculum of the microorganism
  • Host immune response
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3
Q

What threshold of contamination of a surgical site is associated with increased risk of surgical site infections?

A

More than 105 organisms per gram of tissue

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4
Q

How does the dose of contaminating material required to establish infection change with prosthetic material?

A

Reduced

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5
Q

What are the three levels of surgical site infections?

A
  • Superficial incisional - skin and subcutaneous tissues
  • Deep incisional - fascial and muscle layers
  • Organ/space infection - any part of the anatomy that is not the incision
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6
Q

How is a surgical site infection caused by MRSA treated?

A

IV linezolid

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7
Q

List some risk factors for surgical site infections.

A
  • Age
  • ASA score > or equal to 3
  • Diabetes
  • Malnutrition
  • Hypoalbuminaemia
  • Radiotherapy and steroids
  • Rheumatoid arthritis (stop DMARDs 4 weeks before and until 8 weeks after operation)
  • Obesity (adipose tissue is poorly vascularised)
  • Smoking (nicotine delays wound healing)
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8
Q

What should patients be advised to do on the day of the operation?

A

Shower with soap

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9
Q

Why should shaving be avoided where possible in surgery?

A

It can cause microabrasians which promote bacterial multiplication (electric clipper should be used instead)

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10
Q

Who should be offered nasal decontamination?

A

Patients who are found to be carrying S. aureus

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11
Q

When should antibiotic prophylaxis be given for patients undergoing surgery?

A

At the induction of anaesthesia

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12
Q

List some intra-operative measures that reduce the risk of surgical site infection.

A
  • Limit the number of people in the operating theatre
  • Ventilation of the theatre (positive pressure)
  • Sterilisation of surgical instruments
  • Skin preparation (using povidone-iodine or chlorhexidine)
  • Asepsis and surgical technique
  • Normothermia (hypothermia causes vasoconstriction and decreases oxygen delivery to the wound space thereby increasing the risk of infection)
  • Oxygenation
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13
Q

List some risk factors for septic arthritis.

A
  • Rheumatoid arthritis
  • Osteoarthritis
  • Crystal arthritis
  • Joint prosthesis
  • IVDU
  • Diabetes, chronic renal diesase, chronic liver disease
  • Immunosuppression
  • Trauma (e.g. intra-articular injection)
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14
Q

Outline the pathophysiology of septic arthritis.

A
  • Proliferation of bacteria in the synovial fluid leads to generation of a host inflammatory response
  • Joint damage leads to exposure of host-derived protein (e.g. fibronectin) to which bacteria can adhere
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15
Q

List some bacterial factors that enable bacteria to cause septic arthritis.

A
  • Staphylococcus aureus has receptors such as fibronectin-binding protein
  • Kingella kingae have bacterial pili which adhere to the synovium
  • Some strains of S. aureus produce Panton-Valentine Leukocidin which is associated with fulminant infections
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16
Q

List some host factors that increase the risk of septic arthritis.

A
  • Leukocyte-derived proteases and cytokines
  • Raised intra-articular pressure
  • Deletion of macrophage-derived cytokines
  • Absence of IL-10
17
Q

List some organisms that can cause septic arthritis.

A
  • Staphylococcus aureus
  • Streptococci (pyogenes, pneumoniae, agalactiae)
  • Gram-negative organisms (E. coli, H. influenzae, N. gonorrhoeae and Salmonella)
  • Coagulase-negative staphylococci
  • RARE: Lyme disease, Brucellosis, Mycobacteria, Fungi
18
Q

Describe the clinical features of septic arthritis.

A

1-2 week history of red, painful, swollen joint with restricted movement

NOTE: 90% monoarticular, 50% knee involvement

NOTE: patients with rheumatoid arthritis may have more subtle signs

19
Q

List some investigations for septic arthritis.

A
  • Blood culture before antibiotics
  • Synovial fluid aspiration (send for MC&S, WCC > 50,000/mL is considered septic arthritis)
  • ESR and CRP
  • Ultrasound
  • CT (for bone erosion)
  • MRI (for joint effusion, articular cartilage destruction, abscess)
20
Q

How should septic arthritis be managed?

A
  • Antibiotics (OPAT)
  • Drainage of the joint
21
Q

What are the two possible ways in which vertebral osteomyelitis can occur?

A
  • Acute haematogenous spread (bacteraemia)
  • Exogenous (implant during disc surgery)
22
Q

List some organisms that can cause vertebral osteomyelitis.

A
  • Staphylococcus aureus
  • Coagulase-negative staphylococcus
  • Gram-negative rods
  • Streptococcus
23
Q

In which region of the vertebral column is vertebral osteomyelitis most common?

A

Lumbar

24
Q

What are the symptoms of vertebral osteomyelitis?

A
  • Back pain
  • Fever
  • Neurological impairment
25
Q

List some investigations for vertebral osteomyelitis.

A
  • MRI
  • Blood cultures
  • CT-guided/open biopsy
26
Q

How is vertebral osteomyelitis treated?

A

Antibiotics (at least 6 weeks)

27
Q

Outline the presentation of chronic osteomyelitis.

A
  • Pain
  • Brodie’s abscess
  • Sinus tract
28
Q

How is chronic osteomyelitis diagnosed?

A
  • MRI
  • Bone biopsy for culture and histology
29
Q

How is chronic osteomyelitis treated?

A
  • Radical debridement down to living bone
  • Remove sequestra (dead bone tissue) and infected bone disease
30
Q

Name two techniques for treating chronic osteomyelitis.

A

Laubenbach technique - debridement all the way to healthy bleeding bone and removal of all prosthetic material. Double lumen irrigation used to instil antibiotics into the central lumen.

Papineau technique - complete excision of infected tissue and necrotic bone followed by open cancellous bone grafting and split skin grafting to close the wound

31
Q

What are the clinical features of prosthetic joint infection?

A
  • Pain
  • Early failure
  • Sinus tract
32
Q

Which organism most commonly causes prosthetic joint infection?

A
  • Coagulase-negative staphylococcus
  • Others: streptococci, enterococci, enterobacteriaciae, Pseudomonas aeruginosa, anaerobes
33
Q

How is prosthetic joint infection diagnosed?

A
  • Radiology - shows loosening of the prosthesis
  • CRP > 13.5 for prosthetic knees
  • CRP > 5 for prosthetic hips
  • Joint aspiration WCC (>1700/mL if knee; >4200/mL if hip)
34
Q

How should specimens be taken intraoperatively?

A
  • Specimens should be taken from at least 5 sites around the implant and sent for histology
  • NOTE: if 3 or more specimens yield identical organisms, this is suggestive of prosthetic joint infection
35
Q

What is the difference between single stage revision and two stage revision?

A

Single stage revision

  • Remove all foreign material and dead bone
  • Re-implant new prosthesis with antibody-impregnated cement and give IV antibiotics

Two stage revision

  • Remove prosthesis and put in a spacer
  • Take samples for microbiology and histology
  • Period of IV antibiotics for 6 weeks then stop for 2 weeks
  • Re-debride and sample at second stage
  • Re-implantation with antibody impregnated cement
  • If antibiotics are needed, OPAT is used

YEAR 5: Microbiology and Infection (24 decks)

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