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Pathology by week > W18 - Wound, bone, and joint infection > Flashcards

W18 - Wound, bone, and joint infection Flashcards

1
Q

What are the 3 main pathogens in surgical site infections?

A
  1. Staph. aureus (MSSA and MRSA)
  2. E Coli
  3. Psuedomonas aeruginosa
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2
Q

Describe the 3 layers of surgical site infections (SSIs)

A
  1. Superficial incisional - affect skin + subcut tissue
  2. Deep incisional - affect fascial + muscle layers
  3. Organ/space infection - any part of anatomy other than incision
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3
Q

Name 9 pre-operative factors that affect chance of SSI

A
  1. Age (higher age - higher risk)
  2. Remote infections (to the surgical sites)
  3. Underlying illness (diabetes, malnutrition, low serum albumin, radiotherapy, steroid use, rheumatoid arthritis)
  4. Obesity
  5. Smoking
  6. Pre-op showering
  7. Hair removal (only remove if interfering with operation)
  8. Nasal decontamination
  9. Antibiotic prophylaxis
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4
Q

How does obesity cause increased risk of SSI?

A

Adipose tissue is poorly vascularised. Poor oxygenation of tissues and functioning of the immune response increases the risk (2-7x higher in those with BMI of >=35) of SSIs

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5
Q

How does smoking cause increase risk of SSI?

A

Nicotine delays primary wound healing => Peripheral vascular disease => Vasocontrictive effect of reduced oxygen-carrying capacity of blood

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6
Q

Intra-operative factors that affect risk of SSIs - name 7

A
  1. Theatre traffic
  2. Ventilation
  3. Instrument sterilisation
  4. Skin preparation (iodine or chlorhexidine)
  5. Surgical technique
  6. Normothermia
  7. Oxygenation
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7
Q

How does intra-operation patient temperature affect risk of SSI?

A

Mild hypothermia increases risk of SSI by casing vasoconstriction => reduced O2 delivery to wound space => impaired neutrophil function

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8
Q

Which of the following is associated with a reduced risk of SSI?

A) Obesity

B) Bactericidal concentration of abx in serum at time of incision

C) smoking

D) Diabetes

A

B) Bactericidal concentration of abx in serum at time of incision

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9
Q

Risk factors (5) for septic arthritis

A
  1. Joint disease: RA, osteoarthritis, cyrstal-induced arthritis, joint prosthesis
  2. IVDU
  3. Chornic disease: Diabetes, chronic renal disease, chronic liver disease
  4. Immunosuppression: steroids
  5. Trauam: intra-articular injection, penetrating injury
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10
Q

Septic arthritis - top causative organisms

A

Staph aureus 46%

Coagulase negative staphylococci 4%

steptococci (pyogenes, pneumoniae, etc) 22%

G- (E coli, haemophilus influenzae, neisseria gonorrhoeae, salmonella)

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11
Q

Septic arthritis - clinical features

A

1-2 week history of:

  • red, painful, swollen joint
  • restricted movement

90% monoarticular, 50% knee involved

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12
Q

If septic arthritis is suspected, what 4 investigations would you order?

A
  1. Blood cultures (before abx given)
  2. FBC incl. ESR and CRP
  3. Synovial fluid aspiration for MC&S
    - negative culture does not exclude septic arthritis
  4. Imaging - X-ray, US, CT, or MRI
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13
Q

2 step management of septic arthritis

A
  1. Abx - likely IV cephalosporin or fluxloxacillin
    - may add vancomycin if high risk of MRSA
    - up to 6w of abx may be given
    - refer to OPAT (outpatient parenteral abx team)
  2. drainage (arthoscopic washout)
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14
Q

Vertebral osteomyelitis - aetiology (2)

A
  1. Acute haematogenous
  2. Exogenous - i.e. after disc surgery, implant associated
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15
Q

Vertebral osteomyelitis - casusative organisms (3)

A

S aureus - 48%

Strep - 43%

Gram - rods - 23%

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16
Q

Vertebral osteomyelitis - which region does it affect (most to least)

cervico-thoracix

cervical

lumbar

A

lumbar > cervical > cervico-thoracic

17
Q

Vertebral osteomyelitis - clinical features (3)

A
  • Back pain (90% of cases)
  • Fever (60% of cases)
  • Neurological impairment (35% of cases)
18
Q

4 investigations for vertebral osteomyelitis

A
  1. Imaging - MRI (90% sensitive)
  2. Blood cultures
  3. FBC + ESR, CRP
  4. CT/open biopsy
19
Q
  • 76 year old man
  • Admitted with a 4 month history of back pain with radiation down left leg
  • Weight loss of 25kg over the last 6 months
  • PMH: fracture right femur 25yrs ago in Kuwait. Metal plate inserted.

Arthritis right knee, Hypertension. Lived in Iraq, Jordan and Singapore. Arrived in UK in 1993.

MRI: discitis of L2/3

Spinal biopsy in September 2010

Tissue sent for culture. Coagulase negative staphylococci grown from enrichment.

Histology : vague granuloma

Empirical anti- tuberculous treatment commenced ( rifater and ethambutol)

Empirical iv ceftriaxone commenced

  • L2/3 debridement and stabilisation
  • Tissue- no growth
  • Tissue sent for 16S PCR

What do you think the causative organism is:

    1. Staph aureus
    1. Salmonella
    1. Tuberculosis
    1. Brucella
A
  1. Brucella
    - acquired by drinking unpasteurised milk, cheese, or uncooked meat
    - may form brucella granulomas
20
Q

Prosthethic joint infections - what is it?

A

Lysis of bone between the prosthesis and the cement of the bone

22
Q

Prosthethic joint infection - clinical features (4)

A
  1. Pain
  2. Early failure
  3. Sinus tract formation
  4. Pt complains joint was “never right”
23
Q

Prosthethic joint infection - common causative organisms (3 groups)

A

- Gram + cocci

=> coagulase negative staphylococci

=> staphylococcus aureus

=> streptococci sp

=> enterococci sp

- Aerobic G - bacilli

=> Enterobacteriacae

=> Pseudomonas aeruginosa

- Anaerobes

=> polymicrobial

=> fungi

24
Q

Prosthesis joint infection - investigations (3)

A
  1. FBC including CRP + ESR
  2. Blood culture
  3. Joint aspiration
  4. Imaging - usually shows loosening of prosthesis
25
Q
  • Age- 70yrs old
  • 1994 Right THR; 1998 Revision of acetabular component
  • X-ray: lysis around distal part of femoral component
  • Diabetic
  • What is the most likely organism causing prosthetic joint infection?
    1) Coagulase negative staphylococci
    2) E coli
    3) Haemophilus influnzae
    4) Pseudomonas
A

1) Coagulase negative staphylococci

Pathology by week (70 decks)

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