Bone and Joint Infections Flashcards
haematogenous causes of osteomyelitis?
septicaemia
asymptomatic bacteraemia
non hematagenous causes (direct innoculation) of osteomyelitis?
trauma (including compound fractures, puncture wounds)
surgery (including pins)
non hematogenous causes (local invasion) of osteomyelitis?
pressure ulcer
periodontal disease
sinus infection
why do bone infections in children tend to spread into the joints more often than in adults?
in adults, the growth plate acts as a barrier to infection spreading towards the joint. Instead it spreads transversely along Volkmann’s canals and elevates the periosteum.
in children, the growth plate is not well developed and terminal branches of epiphyseal arteries form loops at the growth plate and enter irregular venous sinusoids. Slow blood flow here makes it a catch basin for bacteria and abscess may form.
two most common gram positive pathogens found in bone infections?
- Staphylococcus aureus
- streptococcus pyogenes (group A beta hemolytic strep)
NB: not just most common gram positive, these are the most common pathogens causing bone infections. FULL STOP.
two most common gram negative pathogens found in bone infections?
Kingella Kingae
Salmonella
both e coli and staph aureus cause bacteraemia, why is only staph commonly implicated in bone infections?
staph has the right virulence factors, enzymes and toxins to invade the immune system.
what is a common source of bacteraemia (within the body)?
staph from the nose (1/3 of people have staph in their nose). often staph found in bacteraemia clonal matched nose staph (83% of the time).
most common pathogen involved in bone infections post surgery/trauma?
coagulase negative staphylococci (gram positive)
most common pathogens involved in bone infections of newborns and infants?
(gram positive)
Group B streptococci
(gram neg) Haemophilius influenzae type B Enterobacter Pseudomonas E coli
Case:
Kid steps on a nail while playing in a construction site because he’s a punk. The nail perforates his shoe and goes deep into his foot. He’s wearing old sneakers. He develops bacteraemia, what is the likely pathogen?
Pseudomonas.
loves living in dark, moist conditions, produces characteristics smell in sneakers
most common pathogens involved in bone infections in developing countries?
Gram Neg:
Haemophilius influenza type B
Other:
Tuberculosis
which groups are at most risk of bone infections:
- young boys and girls
- boys risk 2x as girls
- sickle cells disease (commonly salmonella from the gut)
- aboriginal and maori children
- neonates and immunocompromised
characteristics of bones most succetible to infection?
- fastest growing bones (ex femur)
- tubular more than flat bones
which bones tend have the most delayed presentation? insidious progression
how would they present?
vertebral bones >8yrs dull back pain for years followed by acute infection x ray shows changes MRI better than bone scan for diagnosis
