Osteomyelitis Flashcards
What are the classifications for osteomyelitis?
Hematogenous or post-traumatic. Post-traumatic can be further subdivided into acute, subacute or chronic.
Post-traumatic is more common, although hematogenous osteomyelitis can occur in young animals.
What does the successful treatment of osteomyelitis depend on?
The viability and stability of bone, the virulence of the pathogen, state or condition of the soft tissue envelope
What is the most common type of osteomyelitis?
Bacterial
What is the most common organism implicated with bacterial osteomyelitis?
Staph pseud (multi resistant in up to 50% of cases), followed by E.coli and strep.
Polymicrobial infections are present in 42% of cases.
How does the radiographic appearance of aggressive bacterial osteomyelitis differ from less aggressive forms?
Less aggressive: slowly separates the periosteum leading to smooth thickening.
Aggressive: new lamellar bone is deposited, this is often perpendicular to the periosteum
How does biofilm formation occur?
The body produces a conditioning layer of proteins and polysaccharide molecules that absorb to the implant surface. Bacteria bind to fibronectin within this layer and colonization progresses.
What are the benefits of biofilm formation to bacteria?
ECM concentrates and captures nutrients, provides protection from shear stress, from phagocytic activities, and from protease and oxygen free radicals, acts as a barrier to antimicrobial agents, and alters the extracellular environment limiting efficacy (pH, partial pressure of O2, CO2 etc). The altered growth pattern of bacteria (quiescent) also limits antimicrobial efficacy.
What is the most common location of hematogenous osteomyelitis?
Metaphyseal regions of the bone. Potential reasons include capillaries lacking a basement membrane, sluggish blood flow +/- minor trauma.
Is hematogenous osteomyelitis more common in adult or juvenile patient?
Juvenile
What restricts osteomyelitis in the metaphyseal region of juvenile patients from spreading beyond the physeal plate?
Absence of transphyseal vessels.
What is an involucrum?
An area of live encasing bone that surrounds dead bone
What are the differences in clinical signs between patients with acute and chronic posttraumatic osteomyelitis?
Acute: erythema, soft tissue swelling, localized pain, fever, leukocytosis.
Chronic: localized signs (lameness, draining tract) with the absence of systemic illness.
What are some radiographic changes associated with post-traumatic osteomyelitis?
Cortical resorption, periosteal proliferation, loss of trabecular markings +/- sequestrum and involucrum
What is the imaging diagnosis in the following two images?
Is a sequestum always infection?
No, it can be sterile. May be less reaction surrounding a sterile sequestrum.
How can post-traumatic osteomyelitis be diagnosed?
Ultrasound, CT/MRI may be useful to identify sequestra and foreign material. Can also aid in collection of samples for cytology and culture (+/- bacterial PCR).
Negative culture with positive cytology may be indicative of fastidious anaerobic bacterial infection.
What are some clinical signs associated with hematogenous osteomyelitis?
Systemic illness, swelling of the metaphyseal regions of long bones. Elevated leukocyte count, anemia, band neutrophilia, monocytosis.
What are some radiographic changes associated with hematogenous osteomyelitis?
Polyostic lesions in the metaphysis of long bones +/- those signs seen for posttraumatic osteomyelitis. Typically do not extend into the adjacent joint.
What is the treatment for post-traumatic osteomyelitis?
Drainage, debridement, direct bone/tissue culture, delayed closure.
Sequestra and foreign material should be removed and biofilm should be disrupted, with minimal additional damage to the surrounding vascular environment.
How long should antimicrobial therapy be continued for in patients with post-traumatic osteomyelitis?
4-6 weeks (ideally start with 3-5 days of IV). Radiographs should be taken 2-3 weeks after starting intervention.
With the use of antimicrobial beads how much higher are concentrations than with systemic administration?
500 times. Normally use heat stable hydrophilic agents with activity against staph (aminoglycosides, vancomycin)
What materials are often used as antimicrobial carriers for beads?
PMMA (requires removal), calcium sulfate, collagen fleece, synthetic polymers.
What are some empiric antimicrobials that could be considered for treatment of hematogenous osteomyelitis?
Note: Antimicrobial therapy normally continued for 21 days in cases of hematogenous osteomyelitis. Monitoring response to treatment with radiographs (as for post-traumatic).
What type of non-union is depicted?
In a study by Smith 2023 in JAVMA, what 2 factors were associated with an increased risk of failure of antimicrobial impregnated hydrogel in managing orthopedic SSI?
Previous surgeries (each surgery decreases success by 25%) and multi-resistant bacteria.
