MI: Wound, bone and joint infections Flashcards
Name three major pathogens that cause surgical site infections.
- Staphylococcus aureus - MSSA and MRSA
- Escherichia coli - more likely in bowel surgery
- 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 10^5 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 pre-operative risk factors for surgical site infections.
- Age
- ASA score > or equal to 3 - they have a systemic illness
- Diabetes
- Malnutrition
- Hypoalbuminaemia
- Radiotherapy and steroids - steroids should be tapered pre-op
- Rheumatoid arthritis (stop DMARDs 4 weeks before and until 8 weeks after operation)
- Obesity (adipose tissue is poorly vascularised)
- Smoking (nicotine delays wound healing)
Pre-operative factors
What drugs should be tapered/stopped due to mittagate SSI risk pre-op
steroids - tapered off
DMARDS - stopped 4 weeks before and only restarted 8 weeks after
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
especially in cardiac surgery
When should antibiotic prophylaxis be given for patients undergoing surgery?
At the induction of anaesthesia
so effictive conc in tissue at time of incision
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 –> catilage + bone damage
- Raised intra-articular pressure –> cartilage + bone ischaemia
- Deletion of macrophage-derived cytokines
- Absence of IL-10 - genetic susceptibility
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
in order of how common
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, osteomyelitis)
IMaging not always necessary
How should septic arthritis be managed?
- IV abx for first 2 weeks
- Switch to oral afterwards for 2 weeks if good initial response
- 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
- Streptococcus
- Gram-negative rods
in order of how common
In which region of the vertebral column is vertebral osteomyelitis most common?
Lumbar
