Ch 47 - Osteomyelitis and Implant-associated Infections Flashcards
Successful treatment of osteomyelitis is heavily influenced by what three factors?
- The viability and stability of the bone
- The virulence and antimicrobial susceptibility of the organism
- The state or condition of the soft tissue envelope
What are the most common bacteria isolated in osteomyelitis?
- 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%
Describe the pathogenesis of osteomyelitis
- 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
How is the degree of periosteitis correlated with the aggressiveness of the infection?
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
Dogs with pre-op nasal/rectal swabs which isolated methicillin resistant sS.Pseud were….
13-14 times more likely to develop a SSI cause by the rganism within 30 days
How does a biofilm form on a surgical implant?
- 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
What is quorum sensing?
The ability of bacteria to coordinate gene expression based on population density and the role of secreted signal molecules
How do biofilm communities have improved survival and appose antimicrobial therapy?
- 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)
What predisposed metaphyseal bone to haematogenous osteomyelitis?
- Incomplete basement membrane and endothelial gaps
- Relatively inaccessible to the host inflammatory cells
- Sluggish blood flow
In which form of posttraumatic osteomyelitis are dogs systemically unwell?
Acute
What is the sensitivty and specificity of radiographs in the diagnosis of osteomyelitis?
- Sensitivity 62.5%
- Specificity 57%
Cortical resorption, periosteal proliferation, loss of trabecular markings, lucency around implants, involucrum
What is an involucrum?
An area of live, encasing bone surrounding dead bone (sequestrum) within a compromised soft tissue envelope
What is a cloaca?
Draining tract from the radiolucent area of necrosis that surrounds the sequestrum and extends to the skin surface
What is a rapid molecular technique for the diagnosis of osteomyelitis?
multilocus PCR electrospray ionisation mass spectrometre (PCR/EXI-MS)
- 91% correctly identified to genus level
- 74% correctly identified to species level
How can you improve the culture and sensitivty results from surgical implants?
- Sonication of the implants after retrieval and culturing the sonication fluid
