MI: Wound, bone and joint infections Flashcards
Name three major pathogens that cause surgical site infections.
- Staphylococcus aureus
- Escherichia coli
- Pseudomonas aeruginosa
List some factors affecting the severity of the disease.
- Pathogenicity of the microorganism
- Inoculum of the microorganism
- Host immune response
What threshold of contamination of a surgical site is associated with increased risk of surgical site infections?
More than 105 organisms per gram of tissue
How does the dose of contaminating material required to establish infection change with prosthetic material?
Reduced
What are the three levels of surgical site infections?
- 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
How is a surgical site infection caused by MRSA treated?
IV linezolid
List some risk factors for surgical site infections.
- 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)
What should patients be advised to do on the day of the operation?
Shower with soap
Why should shaving be avoided where possible in surgery?
It can cause microabrasians which promote bacterial multiplication (electric clipper should be used instead)
Who should be offered nasal decontamination?
Patients who are found to be carrying S. aureus
When should antibiotic prophylaxis be given for patients undergoing surgery?
At the induction of anaesthesia
List some intra-operative measures that reduce the risk of surgical site infection.
- 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
List some risk factors for septic arthritis.
- Rheumatoid arthritis
- Osteoarthritis
- Crystal arthritis
- Joint prosthesis
- IVDU
- Diabetes, chronic renal diesase, chronic liver disease
- Immunosuppression
- Trauma (e.g. intra-articular injection)
Outline the pathophysiology of septic arthritis.
- 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
List some bacterial factors that enable bacteria to cause septic arthritis.
- 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
List some host factors that increase the risk of septic arthritis.
- Leukocyte-derived proteases and cytokines
- Raised intra-articular pressure
- Deletion of macrophage-derived cytokines
- Absence of IL-10
List some organisms that can cause septic arthritis.
- 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
Describe the clinical features of septic arthritis.
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
List some investigations for septic arthritis.
- 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)
How should septic arthritis be managed?
- Antibiotics (OPAT)
- Drainage of the joint
What are the two possible ways in which vertebral osteomyelitis can occur?
- Acute haematogenous spread (bacteraemia)
- Exogenous (implant during disc surgery)
List some organisms that can cause vertebral osteomyelitis.
- Staphylococcus aureus
- Coagulase-negative staphylococcus
- Gram-negative rods
- Streptococcus
In which region of the vertebral column is vertebral osteomyelitis most common?
Lumbar
What are the symptoms of vertebral osteomyelitis?
- Back pain
- Fever
- Neurological impairment
List some investigations for vertebral osteomyelitis.
- MRI
- Blood cultures
- CT-guided/open biopsy
How is vertebral osteomyelitis treated?
Antibiotics (at least 6 weeks)
Outline the presentation of chronic osteomyelitis.
- Pain
- Brodie’s abscess
- Sinus tract
How is chronic osteomyelitis diagnosed?
- MRI
- Bone biopsy for culture and histology
How is chronic osteomyelitis treated?
- Radical debridement down to living bone
- Remove sequestra (dead bone tissue) and infected bone disease
Name two techniques for treating chronic osteomyelitis.
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
What are the clinical features of prosthetic joint infection?
- Pain
- Early failure
- Sinus tract
Which organism most commonly causes prosthetic joint infection?
- Coagulase-negative staphylococcus
- Others: streptococci, enterococci, enterobacteriaciae, Pseudomonas aeruginosa, anaerobes
How is prosthetic joint infection diagnosed?
- 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)
How should specimens be taken intraoperatively?
- 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
What is the difference between single stage revision and two stage revision?
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
