Bone and Joint Infection

Question 1

when do you start antibiotics in general terms? what is the exception to this?

Answer 1

don’t start antibiotics until you know what youre treating - i.e the pathogen
exception = meningitis, start antibiotics immediately

Question 2

why must a sample/specimen be taken before starting antibiotics?

Answer 2

so you know what youre treating

an organism might not grow if you’ve already started antibiotics giving a false negative

Question 3

what are the 2 most useful blood tests?

Answer 3

CRP

plasma vascosity

Question 4

name 3 other blood tests which can be useful in infection?

Answer 4

blood cultures - but most bone/joint infections don’t lead to bacteraemia
WCC
ESR

Question 5

what methods of investigation can help diagnose infection?

Answer 5

bloods
sample - e.g aspirate a joint
imaging - X rays, bone scan, MRI

Question 6

what is the only thing which can diagnose infection properly?

Answer 6

find the organism

Question 7

how does a bone scan show infection in bone?

Answer 7

shows increased osteoblast activity in the area

Question 8

how can an MRI show bone infection?

Answer 8

can show fluid/abscess

Question 9

which is more useful X ray or MRI?

Answer 9

MRI
shows earlier and more severe changes
up to 2 weeks earlier than X rays

Question 10

what are the 2 common causes of acute osteomyelitis?

Answer 10

1 = traumatic/open (e.g open fracture)
= inoculation
2 = children or immunosuppressed
= haematogenous

Question 11

2 common infecting organisms in acute osteomyelitis?

Answer 11

staph aureus

haemophilus

Question 12

how does acute osteomyelitis occur from trauma?

Answer 12

damage to endothelial cells of vessels in bone

> thrombus forms > bacteria settles ….

Question 13

what must be done for acute osteomyelitis?

Answer 13

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

Question 14

what process causes chronic osteomyelitis?

Answer 14

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

Question 15

do you have to operate on chronic osteomyelitis?

Answer 15

no

people can live with it for years - bugs can lie dormant and just flare up from time to time

Question 16

how can chronic osteomyelitis be cured?

Answer 16

only surgery

- would follow up with antibiotics

Question 17

what is involucrum?

Answer 17

the new bone which forms around the periosteum and surrounds the sequestra

Question 18

3 possible routes of septic arthritis development?

Answer 18

inoculation
metaphyseal spread
direct haematogenous

Question 19

how quickly can septic arthritis act?

Answer 19

very fast

can loose articular cartilage within 48 hrs

Question 20

patchy, mottled appearance on X ray?

Answer 20

gas produced by organisms

indicates necrotising fascitis

Question 21

how is cellulitis diagnosed?

Answer 21

cant get a sample as it doesn’t produce pus

best guess clincially

Question 22

how can cellulitis be treated?

Answer 22

best guess antibiotics to cover staph and strep

• fluclox
• benzylpenicillin

Question 23

how s necrotising fasciitis treated?

Answer 23

must have urgent surgery to remove tissue

follow with antibiotics but they wouldn’t cure it alone

Question 24

what is discitis?

Answer 24

septic arthritis within the disc space

Question 25

when are best guess antibiotics acceptable?

Answer 25

when obtaining a sample is too difficult or theres a high clinical suspicion of a particular organism

Question 26

how common is infection in a joint replacement?

Answer 26

should be no more than 1%

Question 27

important history of infected joint replacement?

Answer 27

was there a wound problem

has it ever been pain free (always been there = bad sign)

Question 28

tests for infected joint replacement?

Answer 28

CRP
joint aspiration
Bone scan
X ray

Question 29

presentation of joint replacement infection?

Answer 29

low grade
a little bit hot
slight niggling pain
can leak etc

Question 30

how successful is surgery in joint replacement infection?

Answer 30

two stage revision = 80-90%

one stage revision (rarely done) = 70-80%

Question 31

describe prophylaxis of joint replacement infection

Answer 31

clean air theatres
local antibiotics
systemic antibiotics
duration of surgery
neat surgery
quality of hand washing
theatre discipline

Question 32

what antibiotics are commonly used in prolphylaxis?

Answer 32

co-amoxiclav
flucloxacillin + gentamicin
clindamycin
Co-trimoxazole

Question 33

how are prophylactic antibiotics delivered?

Answer 33

laminar flow
24 hrs, starting with induction
antibiotics in cement

Question 34

most common infecting organism in knee and hip replacements?

Answer 34

hip = Coagulase negative staph (CNS) (then staph aureus)
knee = staph aureus