Ch 47 - Osteomyelitis and Implant-associated Infections Flashcards

1
Q

Successful treatment of osteomyelitis is heavily influenced by what three factors?

A
  • The viability and stability of the bone
  • The virulence and antimicrobial susceptibility of the organism
  • The state or condition of the soft tissue envelope
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2
Q

What are the most common bacteria isolated in osteomyelitis?

A
  • Staph
  • E.Coli
  • Strep

In some studies, methicillin resistant strains represent close to 50%

Polymicorbial in up to 42% and anaerobic organisms may be present in up to 64%

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3
Q

Describe the pathogenesis of osteomyelitis

A
  • Cytokines and growth factors are found in altered local concentrations during infection
  • Contribute to necrosis and resorption of the bone
  • Leads to ischaemia due to collapse of vascular channels (Haversian, volksman and canaliculi)
  • Segments of bone lacking an adequate blood supply have a propensity to form sequestra and offer a protected environment for bacterial organisms
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4
Q

How is the degree of periosteitis correlated with the aggressiveness of the infection?

A

positively correlated
- Less aggressive infection, slowly seperates the periosteum from the bone, resulting in thickening of the cortex
- More aggressive infection causes lamellar changes where layers of bone are laid down next to each other

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5
Q

Dogs with pre-op nasal/rectal swabs which isolated methicillin resistant sS.Pseud were….

A

13-14 times more likely to develop a SSI cause by the rganism within 30 days

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6
Q

How does a biofilm form on a surgical implant?

A
  • Host lays down a layer of proteins and polysaccharides which are adsorbed to the implant and contain fibronectin
  • Bacteria adhesion can then occur via the fibronectin and bacterial adhesins
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7
Q

What is quorum sensing?

A

The ability of bacteria to coordinate gene expression based on population density and the role of secreted signal molecules

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8
Q

How do biofilm communities have improved survival and appose antimicrobial therapy?

A
  • Extracellular matrix can capture and concentrate nutrients
  • The matrix provided protection from shear stresses, host phagocytic activity and from protease and oxygen radical defenses
  • Undergo genotypic and phenotypic alteration (quorum sensing)
  • Altered or quiescent growth
  • Extracellular matrix alters antimicrobial activity
  • Changes to microenvironment (hydration, CO2, decreased O2, lower pH)
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9
Q

What predisposed metaphyseal bone to haematogenous osteomyelitis?

A
  • Incomplete basement membrane and endothelial gaps
  • Relatively inaccessible to the host inflammatory cells
  • Sluggish blood flow
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10
Q

In which form of posttraumatic osteomyelitis are dogs systemically unwell?

A

Acute

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11
Q

What is the sensitivty and specificity of radiographs in the diagnosis of osteomyelitis?

A
  • Sensitivity 62.5%
  • Specificity 57%

Cortical resorption, periosteal proliferation, loss of trabecular markings, lucency around implants, involucrum

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12
Q

What is an involucrum?

A

An area of live, encasing bone surrounding dead bone (sequestrum) within a compromised soft tissue envelope

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13
Q

What is a cloaca?

A

Draining tract from the radiolucent area of necrosis that surrounds the sequestrum and extends to the skin surface

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14
Q

What is a rapid molecular technique for the diagnosis of osteomyelitis?

A

multilocus PCR electrospray ionisation mass spectrometre (PCR/EXI-MS)

  • 91% correctly identified to genus level
  • 74% correctly identified to species level
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15
Q

How can you improve the culture and sensitivty results from surgical implants?

A
  • Sonication of the implants after retrieval and culturing the sonication fluid
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16
Q

What animals are predisposed to haematogenous osteomyelitis?
What are the radiographic signs?

A
  • Very young or immunocompromised
  • Polyostotic lesions in the metaphyseal regions of long bones, bone resorption, lysis or periosteal new bone, increased medullary opacity
17
Q

What are the primary objectives of posttraumatic osteomyelitis treatment?

A
  • Removal of necrotic bone, sequestra and foreign material
  • Meticulous debridement, minimise durther disruption to vascular supply
  • Biofilm removal/disruption
18
Q

What are the recommendations regarding systemic and local treatment with ABx?

A

Systemic
- IV for 3-5 days
- Followed by oral for at least 4-6 weeks

Local
- ABx impregnated beads
- Initial concentration is 500x greater than typical serum concentrations
- heat-stable, hydrophilic and active against methicillin-resistant Staph (aminoglycosides, vancomycin)

19
Q

What is the prognosis with osteomyelitis?

A

Variable - relapse or reinfection is possible weeks, months ot years later
Fungal infections are particular problematic and expensive to treat

20
Q

List some implant surface coatings which may help to reduce the incidence of SSI

A
  • bioabsorbable polymeric coatings containing antimicrobials
  • resorbale calcium-based matrices with antimicrobials added
  • Silver-coated implants