Bone and Joint Infection Flashcards
when do you start antibiotics in general terms? what is the exception to this?
don’t start antibiotics until you know what youre treating - i.e the pathogen
exception = meningitis, start antibiotics immediately
why must a sample/specimen be taken before starting antibiotics?
so you know what youre treating
an organism might not grow if you’ve already started antibiotics giving a false negative
what are the 2 most useful blood tests?
CRP
plasma vascosity
name 3 other blood tests which can be useful in infection?
blood cultures - but most bone/joint infections don’t lead to bacteraemia
WCC
ESR
what methods of investigation can help diagnose infection?
bloods
sample - e.g aspirate a joint
imaging - X rays, bone scan, MRI
what is the only thing which can diagnose infection properly?
find the organism
how does a bone scan show infection in bone?
shows increased osteoblast activity in the area
how can an MRI show bone infection?
can show fluid/abscess
which is more useful X ray or MRI?
MRI
shows earlier and more severe changes
up to 2 weeks earlier than X rays
what are the 2 common causes of acute osteomyelitis?
1 = traumatic/open (e.g open fracture)
= inoculation
2 = children or immunosuppressed
= haematogenous
2 common infecting organisms in acute osteomyelitis?
staph aureus
haemophilus
how does acute osteomyelitis occur from trauma?
damage to endothelial cells of vessels in bone
> thrombus forms > bacteria settles ….
what must be done for acute osteomyelitis?
drain the pus and remove the dead tissue
antibiotics are also given - can help but wouldn’t cure if there’s an abscess or pus etc
what process causes chronic osteomyelitis?
sclerotic reaction causes pus to travel either to joint capsule or under periosteum - causes death of bone - sequestrum forms as dead bone separates from the living bone
new bone forms under the periosteum
do you have to operate on chronic osteomyelitis?
no
people can live with it for years - bugs can lie dormant and just flare up from time to time
how can chronic osteomyelitis be cured?
only surgery
- would follow up with antibiotics
what is involucrum?
the new bone which forms around the periosteum and surrounds the sequestra
3 possible routes of septic arthritis development?
inoculation
metaphyseal spread
direct haematogenous
how quickly can septic arthritis act?
very fast
can loose articular cartilage within 48 hrs
patchy, mottled appearance on X ray?
gas produced by organisms
indicates necrotising fascitis
how is cellulitis diagnosed?
cant get a sample as it doesn’t produce pus
best guess clincially
how can cellulitis be treated?
best guess antibiotics to cover staph and strep
- fluclox
- benzylpenicillin
how s necrotising fasciitis treated?
must have urgent surgery to remove tissue
follow with antibiotics but they wouldn’t cure it alone
what is discitis?
septic arthritis within the disc space
when are best guess antibiotics acceptable?
when obtaining a sample is too difficult or theres a high clinical suspicion of a particular organism
how common is infection in a joint replacement?
should be no more than 1%
important history of infected joint replacement?
was there a wound problem
has it ever been pain free (always been there = bad sign)
tests for infected joint replacement?
CRP
joint aspiration
Bone scan
X ray
presentation of joint replacement infection?
low grade
a little bit hot
slight niggling pain
can leak etc
how successful is surgery in joint replacement infection?
two stage revision = 80-90%
one stage revision (rarely done) = 70-80%
describe prophylaxis of joint replacement infection
clean air theatres local antibiotics systemic antibiotics duration of surgery neat surgery quality of hand washing theatre discipline
what antibiotics are commonly used in prolphylaxis?
co-amoxiclav
flucloxacillin + gentamicin
clindamycin
Co-trimoxazole
how are prophylactic antibiotics delivered?
laminar flow
24 hrs, starting with induction
antibiotics in cement
most common infecting organism in knee and hip replacements?
hip = Coagulase negative staph (CNS) (then staph aureus) knee = staph aureus
