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 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 (oxazolidinone class)
List some risk factors for surgical site infections.
- Age
- ASA score of 3 or more
- Diabetes (±postop hyperglycaemia)
- 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 (delayed wound healing)
What should patients be advised to do on the day of the operation?
Shower with soap
on day / day before surgery
Why should shaving be avoided as a method of hair removal 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
(esp. cardiothoracic surgery)
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)
ortho = laminar flow - Sterilisation of surgical instruments
- Skin preparation (using povidone-iodine or chlorhexidine in 70% alcohol)
- Asepsis and surgical technique
- Normothermia (hypothermia causes vasoconstriction and decreases oxygen delivery to the wound space thereby increasing the risk of infection)
- Oxygenation >95%
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, penetrating injury)
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 (septic arthritis in children)
- Some strains of S. aureus produce Panton-Valentine Leukocidin which is associated with fulminant infections
List some host factors that damage the joint in septic arthritis
- Leukocyte-derived proteases and cytokines - joint damage
- Raised intra-articular pressure - impairs blood flow leading to ischaemia
- Genetic variation in cytokine expression - may lead to reduced immune response
List some organisms that can cause septic arthritis.
- Staphylococcus aureus (46%)
- Streptococci (22%) (pyogenes, pneumoniae, agalactiae)
- Gram-negative organisms (E. coli, H. influenzae, N. gonorrhoeae and Salmonella)
- Coagulase-negative staphylococci (4%)
- 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)
- ESR and CRP
What WBC in synovial fluid aspirate is suggestive of septic arthritis?
> 50,000 cells/ml
Which imaging techniques are used in septic arthritis
Ultrasound - shows effusion and guides needle aspiration
MRI - shows joint effusion, cartilage destruction, abscess, contigous osteomyelitis
How should septic arthritis be managed?
- Antibiotics
- Drainage of the joint (arthroscopic washout) - if infection does not respond to ABx
Describe the antibiotic regime in septic arthritis
Flucloxacillin
* 2 weeks IV (OPAT)
* 4 weeks oral
Vancomycin if MRSA
Gonococcal or gram-negative infection - cefotaxime/ceftriaxone
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 (48%)
- Streptococcus (43.1%)
- Gram-negative rods (23.1%)
- Coagulase-negative staphylococcus
In which region of the vertebral column is vertebral osteomyelitis most common?
Lumbar (43%)
Cervical (10.6%)
What are the symptoms of vertebral osteomyelitis?
- Back pain
- Fever
- Neurological impairment
List some investigations for vertebral osteomyelitis.
- MRI (90% sensitive)
- Blood cultures
- CT-guided/open biopsy
How is vertebral osteomyelitis treated?
Antibiotics (at least 6 weeks)
Surgery if there is spinal cord compression
Outline the presentation of chronic osteomyelitis.
- Pain
- Brodie’s abscess - intraosseous abcess
- 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
- Sequestrectomy - remove sequestra (dead bone tissue) and infected bone disease
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
- Staph aureus
- Gram-negative less likely
Others: streptococci, enterococci, enterobacteriaciae, Pseudomonas aeruginosa, anaerobes
How is prosthetic joint infection diagnosed?
- Radiology - shows loosening of the prosthesis
- 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
1 surgical procedure
* Remove all foreign material and dead bone
* Re-implant new prosthesis with antibody-impregnated cement and give IV antibiotics
Two stage revision
2 surgical procedures
* 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
