MICRO: Wound, Bone and Joint Infections Flashcards
What pathogens most commonly cause SSIs (surgical site infections)?
- Staphylococcus aureus (MSSA and MRSA)
- Escherichia coli
- Pseudomonas aeruginosa
What is the pathogenesis of SSIs?
- Surgical site is contaminated
- SSI risk increased if surgical site is contaminated with >105 microorganisms / gram of tissue
- Lower dose required if foreign material present (i.e. silk suture)
- Host immune response also plays a role in pathogenesis as well as the pathogenicity of the pathogen
What are the three levels of SSIs?
- Superficial Incisional- skin and subcutaneous tissues
- Deep Incisional - ascial and muscle layers
- Organ/Space Infection - any part of the anatomy other than the incision
- Case 1:
- Admitted with SAH and sub-dural haemorrhage after a fall–> decompressive craniectomy
- 2/12 later had a cranioplasty with titanium plate
- 6/12 later admitted with large subdural collection and midline shift à abscess evacuation and infection
- What is the organism?
- Ecoli, enterobacter, MRSA, neisseria meningitides?
MRSA
Gram positive (dark purple, neg would be pale pink) and beta haemolytic
How can preventing SSIs be divided?
- Pre
- Intra
- Post - operative
What are the pre-operative measures to prevent SSIs?
- Age (an independent risk factor) - increasing risk until 65 years
- Treat all remote infection (e.g. pneumonia, UTI) before operation
- Underlying illness risk factors (e.g. ASA score >3, diabetes, smoking)
-
Pre-operative Showering
- Either chlorhexidine or normal detergent/bar soap (both same incidence of SSI)
- Advised to showed with soap on the day of surgery or the day before
-
Hair removal
- Shaving increases risk of SSI (micro-abrasions from shaving can multiply bacteria)
- Electric clipper should be used instead on the day of surgery with a single-use head
-
Nasal Decontamination
-
Staphylococcus aureus is carried in the nostrils of 20-30%
- SA carriage = MOST POWERFUL risk factor for SSI following cardiothoracic surgery
- Nasal decontamination should be offered if they are found to be carrying S. aureus
-
Staphylococcus aureus is carried in the nostrils of 20-30%
- Antibiotic Prophylaxis – administer at time of induction of anaesthesia:
To ensure bactericidal concentration in serum & tissue at time of incision
Which underlying conditions increase risk of SSIs?
- ASA score >3
- Diabetes (2-3x increased risk à control blood glucose, HbA1c <7)
- Malnutrition
- Low serum albumin
- Radiotherapy and steroids
- Rheumatoid arthritis (stoop DMARDs before operation)
- Obesity (adipose poorly vascularised à poor access for immune system à risk of SSIs)
- Smoking (nicotine delays wound healing and leads to PVD – see above poor vascularisation)
How does smoking increase risk of SSI?
Is shaving necessary to prevent SSIs?
- Shaving with razor increases risk of SSI (micro-abrasions from shaving can multiply bacteria)
- Electric clipper should be used instead on the day of surgery with a single-use head
- Shaving should only be done if hair will interfere with the surgery
What kind of antibiotic prophylaxis can be given to prevent SSIs pre-op?
- Antibiotic Prophylaxis – administer at time of induction of anaesthesia:
- To ensure bactericidal concentration in serum & tissue at time of incision
- Must have some bactericidal activity
What intra-op measures can be taken to prevent SSIs ?
- 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):
- Oxygenation
- SpO2 >95%
- Higher O2 saturations à reduced SSIs
What temperatures should be used intra-op?
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
Start warming air if <36 degrees C
What oxygenation levels should be aimed for pre-op and why?
- SpO2 >95%
- Higher O2 saturations –> reduced SSIs
Why is it important to reduce theatre traffic intra-op?
One person sheds 1 billion skin cells per day - 10% of these carry bacteria
Microbial load in threatre is related to the number of people present
Theatre personnel should be kept to a minimum
How common is septic arthritis?
- Incidence: 2-10 per 100,000
- More common in patients with RhA; 28-38 per 100,000
- Mortality 7-15% and morbidity 50%
Risk factors for septic arthritis?
- 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
What is the pathophysiology of septic arthritis?
- Organisms adhere to synovium
- Bacterial proliferation in synovial fluid –> host inflammatory response –> joint damage
- Joint damage –> exposure of host derived protein (e.g. fibronectin) to which bacteria can adhere
Which bacterial factors are important in septic arthirtis?
- 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) à fulminant infection
- Kingella kingae synovial adherence is via bacterial pili
Which host factors are important in pathophysiology of septic arthritis?
- 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
What are the most common organisms causing septic arthritis? Which is the single most common?
- Staphylococcus aureus - 46%
-
Streptococci - 22%
- Streptococcus pyogenes
- Streptococcus pneumoniae
- Streptococcus agalactiae
- Gram-negative organisms:
- Escherichia coli
- Haemophilus influenzae
- Neisseria gonorrhoea
- Salmonella
- Coagulase-negative staphylococci - 4%
- Lyme disease, Brucellosis, Mycobacteria, Fungi - Rare
Which investigations should be done for septic arthritis? What is the WCC in the synovium in this condition? Which imaging is useful?
- Blood cultures (before ABx)
-
Synovial fluid aspiration MC&S- synovial count >50,000 WBC/mL is used to suggest septic arthritis
- USS confirms and guides aspiration of fluid
- ESR and CRP
- CT – check for erosive bone change, periarticular soft tissue extension
- MRI – joint effusion, articular cartilage destruction, abscess, contiguous osteomyelitis
What is the management of septic arthritis?
- ABx, 4-6 weeks (outpatient setting) - mostly IV
- Drainage of the joint
What are the most common causes of vertebral osteomyelitis?
-
Causes:
- Acute haematogenous spread (bacteraemia)
- Exogenous (after disc surgery, implant associated)
-
Causative organisms:
- Staphylococcus aureus (48.3%)
- Coagulase-negative staphylococcus
- Gram-negative rods
- Streptococcus
Where is vertebral osteomeylitis most commonly located?
- Lumbar (43.1%)
- Cervical (10.6%)
- Cervico-thoracic (0.4%)
What are the symptoms of VO? What investigations should be done?
- Symptoms:
- Back pain
- Fever
- Neurological impairment
- Investigations:
- MRI (90% sensitive)
- Blood cultures
- CT-guided/open biopsy
What is the management of vertebral osteomyelitis?
- Treatment:
- ABx, 6 weeks
- Case 1:
- 76yo man, 4/12 hx of back pain with left leg radiation
- WL 25kg over last 6/12
- PMHx of fracture with metal plate insertion, arthritis R-knee, HTN, lived overseas until 1993
- MRI: discitis of L2/L3–> spinal biopsy –> Coag -ve staph (staph epidermidis) grown –> histology shows vague granuloma
- Anti-TB treatment started, empirical IV ceftriaxone started
- Surgery debridement and stabilisation
- No growth on agar of standard organisms and further PCR and IgG showed brucella
What is the causative organism? Staph aureus, salmonella, TB, brucella?
Brucella - commonly from unpasterised milk, cheese and eating meat.
- Brucella IgG >1:2560
- Brucella DNA using PCR was positive
- Started on rifampicin, ciprofloxacin and doxycycline
How does chronic osteomyelitis present?
- Presentation:
- Pain
- Brodies abscess
- Sinus tract
MRI of child shown
How is chronic osteomyelitis diagnosed? How is it treated birefly?
- Diagnosis
- XR (often first line to screen; early changes take ~10 days)
- MRI (much more sensitive for changes)
- Bone biopsy (culture and histology)
- Treatment = radical debridement to living bone and oral ABx (up to 6 weeks after discharge)
What is the Papineau technique for chronic osteomyelitis?
- 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%
What is the presentation of prosthetic joint infections?
- Pain
- Patient complain joint was ‘never right’ after the operation à early failure
- Sinus tract releasing pus may be present
What are the causative organisms of PJI?
- Gram-positive cocci:
- Coagulase-negative staphylococci > S. aureus
- Streptococci
- Enterococci
- Aerobic Gram-negative bacilli:
- Enterobacteriaceae
- Pseudomonas aeruginosa
- Anaerobes
- Polymicrobials
- Culture-negative
- Fungi
How are PJI diagnosed?
- Radiology – loosening (bone loss along the cement-bone interface)
- Raised CRP:
- CRP >13.5 for prosthetic knee joint infection
- CRP >5 for prosthetic hip joint infection
- Joint Aspiration:
- If >1,700 WCC/mL = knee PJI
- If >4,200 WCC/mL = hip PJI
- Intraoperative Microbiological Sampling:
- Tissue specimens taken from at least 5 sites around the implant
- Histopathology (if >3 specimens yield identical organisms –> suggestive of PJI)
What is the management of PJI?
-
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
- ~89% success rate
OR…
-
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
- Remove prosthesis and put in a spacer (to take up the space of the prosthesis)
- 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
- Re-debride and sample at second stage
How many tissue samples should be sent from PJI? What is infection defined as on hitology in PJI? What about cultures?
Case 3:
- 70yo diabetic, 1994 right THR –> 1998 revision of acetabulum
- X-ray = lysis around distal femoral component
Likely pathogen? CNS, H. influenzae, E coli or pseudomonas?
Coagulase negative staphylococci
IMPORTANT to send multiple specimens as this is commonly a skin contaminant
Silvery white cultures = Brucella
