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Liv Path > Micro - Skin, Bone and Joint Infections > Flashcards

Micro - Skin, Bone and Joint Infections Flashcards

1
Q

Major Pathogens in Surgical Site Infections

A

Staph.aureus (MSSA and MRSA)
E.coli
Pseudomonas aeruginosa

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2
Q

Surgical Site Infections - Pathogenesis

A
  • Contamination of wound at operation
  • Pathogenicity and innoculum of microorganisms
  • Host immune response
  • If surgical site is contaminated with > 10^5 microorganisms per gram of tissue, risk of SSI is increased.
  • The dose of contaminating bacteria required to cause infection is much lower if there is foreign material present e.g silk suture
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3
Q

3 Levels of Surgical Site Infections

A

Superficial incisional- affect skin and subcutaneous tissue

Deep incisional- affect fascial and muscle layers

Organ/space infection- any part of anatomy other than incision

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4
Q

Subdural collection culturing MRSA Rx

A

IV linezolid

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5
Q

RFs - Surgical Site Infections

A
  • Age
  • Underlying illness
  • Obesity (adipose poorly vascularised - poor oxygenation of tissues and immune functioning). Risk increased by 2-7 in pts with BMI >35
  • Smoking (nicotine delays primary wound healing, peripheral vascular disease)
  • Pre-operative showering (better than chlorhexadine)
  • Don’t remove hair unless it will interfere with operation (get micro abrasions)
  • Nasal decontamination (2030% have s. aureus)
  • Antibiotic prophylaxis
  • Ill surgical staff (transmissible infection –> occ health)
  • Number of people in theatre
  • Ventilation (maintain positive pressure ventilation, filter free air, keep theatre doors closed)
  • Surgical instrument sterilisation
  • Skin prep (iodine/chlorhexadine)
  • Surgical technique/asepsis
  • Hypothermia increases risk (vasoconstriction –> neutrophils can’t get there). Keep pt normothermic.
  • Oxygenation (optimal >95%)
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6
Q

Septic Arthritis - General

A
  • Increased incidence in those with RA

- High morbidity snd mortality

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7
Q

Septic Artritis - RFs

A

Rheumatoid arthritis , osteoarthritis, crystal induced arthritis

Joint prosthesis

Intravenous drug abuse

Diabetes, chronic renal disease, chronic liver disease

Immunosuppression- steroids

Trauma- intra-articular injection, penetrating injury

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8
Q

Septic Arthritis - Pathophysiology

A

Organisms adhere to the synovial membrane, bacterial proliferation in the synovial fluid with generation of host inflammatory response.

Joint damage leads to exposure of host derived proteins such as fibronectin to which bacteria adhere.

Bacterial factors:

  • S aureus - fibronectin binding protein recognises selected host proteins. Some strains produce the cytotoxin PVL (Panton-Valentine Leucocidin) which have been associated with fulminant infections.
  • Kingella kingae synovial adherence is via bacterial pilli

Host factors:

  • Leucocyte derived proteases and cytokines can lead to cartilage degradation and bone loss.
  • Raised intra-articular pressure can hamper capillary blood flow and lead to cartilage and bone ischaemia and necrosis.
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9
Q

Septic Arthritis - Causative Organisms

A

Staph. aureus (46%)
- Coagulase negative staphylococci 4%

Streptococci (22%)

  • Streptococcus pyogenes
  • Streptococcus pneumoniae
  • Streptococcus agalactiae

Gram negative organisms

  • E.coli
  • Haemophilus influezae
  • Neisseria gonorrhoeae
  • Salmonella

Rare- Lyme, brucellosis, mycobacteria, fungi

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10
Q

Septic Arthritis - Presentation, Ix, Rx

A

1-2 week history of red, painful, swollen restricted joint
Monoarticular in 90%
Knee is involved in 50%

(Patients with rheumatoid arthritis may show more subtle signs of joint infection)

Investigations
- Blood culture pre-ABX
- Synovial fluid aspiration for microscopy and culture
- ESR, CRP
Negative cultures do not exclude
- US- confirm effusion and guide needle aspiration
- CT- erosive bone change, periarticular soft tissue extension
- MRI- joint effusion, articular cartilage destruction, abscess, contiguous osteomyelitis

Rx: ABX and drainage

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11
Q

Vertebral Osteomyelitis - Types/Causes

A
  • Acute haematogenous

- Exogenous - after disc surgery, implant associated

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12
Q

Vertebral Osteomyelitis- Causative Organisms

A

S.aureus- 48.3%
Coagulase negative staph
Gonorrhoea
Strep

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13
Q

Vertebral osteomyelitis - localisation

A

cervical- 10.6%
cervico-thoraco- 0.4%
lumbar- 43.1%

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14
Q

Vertebral osteomyelitis - presentation, diagnosis and Rx

A

Symptoms:

  • Back pain- 86%
  • Fever- 60%
  • Neurological impairment 34%

Diagnosis:

  • MRI: 90% sensitive
  • Blood cultures
  • Serology
  • CT/ open biopsy

Rx:

  • Six weeks of treatment (abx)
  • empirical IV ceftriaxone, empirical TB treatment
  • Then target organism once identified
  • Longer treatment if undrained abscesses/implant associated
  • May need debridement and stabilisation of sprine
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15
Q

Chronic Osteomyelitis

A

Presentation:

  • Pain
  • Brodies abscess
  • Sinus tract

Diagnosis:

  • MRI
  • Bone biopsy for culture and histology

Rx:
Radical debridement down to living bone –> remove sequestra, and remove infected bone and soft tissue

Modified lautenbach technique
Papineau technique

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16
Q

Signs/Symptoms of Prosthetic Joint Infection

A

Pain
Patient complains that the joint was ‘never right’
Early failure
Sinus tract

17
Q

Prosthetic Joint Infection - Causative Organisms

A 
Gram positive cocci
-coagulase negative staphylococci
-staphylococus aureus
Streptococci sp
Enterococci sp

Aerobic gram negative bacilli

  • Enterobacteriaceae
  • Pseudomonas aeruginosa

Anaerobes
Polymicrobial
Culture negative
Fungi

18
Q

Prosthetic Joint Infection - Diagnosis

A

Radiology- loosening
If CRP>13.5 for prosthetic knee joint infection
CRP> 5 for prosthetic hip joint infection
Joint aspiration
- If >1700/ml of WCC correlates with knee PJI
- If > 4200/ml of WCC correlates with hip PJI

19
Q

Prosthetic Joint Infection - Intraoperative Microbiological sampling

A

Tissue specimens from at least 5 sites around the implant

Histopathology – infection defined as >5 neutrophils per high power field.

If 3 or more specimens yield identical organisms, this is highly predictive of infection (sensitivity 65%, specificity 99%)

20
Q

Prosthetic Joint Infection - Rx

A
  • Single stage revision
  • Endo Klinik single stage revision
  • Two stage revision (take it out and give them abx for 6 weeks before re-doing)

Liv Path (24 decks)

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