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PATHOLOGY > bone and joint infections > Flashcards

bone and joint infections Flashcards

1
Q

consequences of surgical site infections

A

Increased length of stay ( THR- 11 days longer);
additional surgical procedures,
treatment in ITU,
higher mortality

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2
Q

what are the major pathogens involved in surgical site infections

A

Staph.aureus (MSSA and MRSA)
E.coli
Pseudomonas aeruginosa

bacteria depends on site of infection
intra-abdo - more likely gram -ve eg E coli
hip replacement - more likely S aureus

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3
Q

pathogenesis of surgical site infection

A

contamination of wound at op
> 10(5) microorganisms per gram of tissue, risk of SSI is increased.
dose of bacteria needed is lower if foreign material present

whether infection happens depends on:
pathogenicity and innoculum of microorganisms
host immune response
ie strep A more virulent than staph viridans
if immunosuppressed more likely infection

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4
Q

what are the 3 levels of surgical site infection

A

superficial incisional - affect skin and subcut tissue
deep incisional - fascial and muscle layers
organ/space infection - any part of anatomy other than incision

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5
Q

what are underlying conditions/states that lead to surgical site infections

A

ASA score of 3 or more
diabetes - 2-3x increase, association with post-op hyperglycaemia. control blood glucose, HbA1c <7
malnutrition
low serum albumin
radiotherapy
steroid use - taper steroids pre surgery
RA - stop disease modifying agents 4wk pre and 8wk post op

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6
Q

how does obesity increase risk of surgical site infections

A

adipose tissue poorly vascularised

poor oxygenation + poor functioning of immune response

risk increase 2-7x with BMI of 35 or more

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7
Q

how does smoking increase surgical site infection risk

A

duration and number smoked
nicotine delays primary wound healing
peripheral vascular disease
vasoconstrictive effect of reduced oxygen-carrying capacity of blood
encourage tobacco cessation pre-op

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8
Q

how does pre-op showering alter surgical site infections

A

microorganisms colonising the skin can contaminate exposed tissues -> SSI

no difference in SSI incidence when chlorhexidine or detergent/bar soap is used

advise to shower on day of surgery or day before

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9
Q

how does hair removal alter surgical site infections

A

Micro-abrasions caused by shaving with a razor may -> multiplication of bacteria

Use electric clippers on the day of surgery with single-use head on day of op
Hair should not be removed unless it will interfere with the operation

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10
Q

should nasal decontamination happen to prevent surgical site infections

A

S.aureus is carried in the nares of 20-30%
carriage is the most powerful independent RF for SSI
so should have decontamination

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11
Q

antibiotic prophylaxis for SSI

A

given at induction of anaesthesia
Bactericidal concentration of the drug should be established in serum and tissues at time of incision.
additional doses needed if sig blood loss or op prolonged

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12
Q

how many people should be in theatre - in terms of surgical site infection

A

all carry bacteria on skin
microbial load in theatre is related to number of people present
so keep people to a min

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13
Q

how should theatres be ventilated to prevent SSIs

A

maintain positive pressure ventilation
20 air changes per hour (of which at least 3must be fresh air)
filter all air
keep op room doors closed
Consider laminar flow for orthopaedic implant surgery

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14
Q

what skin prep should be done to prevent SSIs

A

antiseptic prep
chlorhexidine in 70% alcohol used

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15
Q

what temperature should people be kept at to prevent SSIs

A

normothermia
mild hypothermia increases risk of SSIs -> vasoconstriction -> reduced oxygen to wound space and impairment of neutrophil function

measure temp before anaesthesia
start forced air warmining of temp <36 (warm IV fluid and irrigation fluid)

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16
Q

what level of oxygenation should patients be kept at to prevent SSIs

A

keep Hb sats above 95%
higher ox = reduced SSIs

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17
Q

epidemiology of septic arthritis

A

Incidence is 2-10 cases per 100,000
Mortality is 7-15%
Morbidity is 50%
incidence higher if have rheumatoid arthritis

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18
Q

RF for septic arthritis

A

rheumatoid arthritis
osteoarthritis
crystal induced arthritis
joint prosthesis
IVDU
dm
chronic renal disease
chronic liver disease
immunosuppression - steroids
trauma - intra-articular injection, penetrating injury

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19
Q

pathophysiology of septic arthritis

A

organisms adhere to synovial membrane
bacterial proliferation in synovial fluid - generation of host inflammatory immune response
joint damage -> exposure of host derived proteins such as fibronectin that bacteria adhere to

20
Q

bacterial factors that contribute to pathogenesis of septic arthritis

A

S.aureus: receptors eg fibronectin binding protein that recognise selected host proteins.

Kingella kingae: synovial adherence is via bacterial pili (cause septic arth in children)

Some strains produce the cytotoxin PVL ( Panton-Valentine Leucocidin) which have been associated with fulminant infections.

21
Q

host factors that contribute to pathogenesis of septic arthritis

A

Leucocyte derived proteases and cytokines -> cartilage degradation and bone loss.

Raised intra-articular pressure reduces capillary blood flow -> cartilage and bone ischaemia and necrosis.

Genetic variation in expression of cytokines may -> differential susceptibility to septic arthritis.

22
Q

causative organisms of septic arthritis

A

Staph. aureus 46%
- Coagulase negative staphylococci 4%

Streptococci 22%
* Streptococcus pyogenes
* Streptococcus pneumoniae
* Streptococcus agalactiae

Gram negative organisms
* E.coli
* Haemophilus influezae
* Neisseria gonorrhoeae
* Salmonella

Rare- Lyme, brucellosis, mycobacteria, fungi

23
Q

clinical features of septic arthritis

A

1-2 week history of red, painful, swollen restricted joint
mainly monoarticular
knee half the time

if rheumatoid arthritis - signs more subtle

24
Q

investigations for septic arthritis

A

blood culture before abx if pyrexial
synovial fluid aspiration fro MC&S
ESR
CRP
a synovial count> 50,000 cells/mm3 used to suggest septic arthritis
negative culture doesnt exclude septic arthritis

US - confirm effusion and guide needle aspiration
MRI - joint effusion, articular cartilage destruction, abscess, contiguous osteomyelitis

25
Q

Mx of septic arthritis

A

ABx - IV cephalosporin or flucloxacillin (may need vancomycin if at high risk of MRSA). IV abx for up to 2wks, then 4 oral wks

arthoscopic wash out

26
Q

causes of vertebral osteomyelitis

A

acute haematogenous - bacteraemia and bacteria seed to vertebrae

exogenous - after disc surgery - implant associated -> infection

27
Q

causative organisms of vertebral osteomyelitis

A

Staph aureus
strep
CNS
GNR

28
Q

main location of vertebral osteomyelitis

A

lumbar

29
Q

sx of vertebral osteomyelitis

A

back pain
fever
neurological impairment

30
Q

ix into vertebral osteomyelitis

A

MRI
blood cultures if were bacteraemic
CT/open biopsy

31
Q

Rx of vertebral osteomyelitis

A

6wks - longer if undrained abscess/implant associated
surgery if spinal cord compression

32
Q
A

brucella granuloma

33
Q

signs of chronic osteomyelitis

A

pain
brodies abscess (intraoseous abscess)
sinus tract discharging pus

34
Q
A

chronic osteomyelitis
femur is very deformed
arrow - sequestra/dead bone
half bone - involucrum - new bone formation

35
Q

diagnosis of chronic osteomyelitis

A

MRI
bone biopsy for culture and histology

36
Q

treatment of chronic osteomyelitis

A

abx and surgery
masquelet technique:
* radical sequestrectomy
* removal of forgein bodies
* fill defect with abx loaded cement spacer and external fixation
* in 6-8wks - remove cement spacer, fill with autologous bone graft
* if bone culture grew bacteria - rx with 6wks abx

37
Q
A

prosthetic joint infection (PJIs)
Black gap – loosening between bone and prosthetic

38
Q

signs and sx of prosthetic joint infection

A

Pain
Patient complains that the joint was ‘never right’
Early failure
Sinus tract

39
Q

causative organisms of prosthetic joint infections

A

Gram positive cocci
-**coagulase negative staphylococci – commonest **
-staphylococus aureus
Streptococci sp
Enterococci sp

Aerobic gram negative bacilli
Enterobacteriaceae
Pseudomonas aeruginosa

Anaerobes
Polymicrobial
Culture negative
Fungi

40
Q

diagnosis of prosthetic joint infections

A
41
Q

intraoperative microbiological sampling

A

tissue specimen taken from at least 5 sites around implant
Histopathology – infection defined as >5 neutrophils per high power field.
if 3 or more specimens show identical organisms - very likely infection

42
Q

single stage revision for prosthetic joint infection

A

remove all foreign material, prosthesis and dead bone
change gloves, drapes etc
re-implant new prosthesis with abx impregmented cement and give new abx

43
Q

Endo Klinik single stage revision for prosthetic joint replacement

A

aspirate joint to determine pathogen
excision of infected bone tissue, synovectomy
add abx to bone cement according to culture results
implantation of cemented prosthesis with abx loaded cement
IV abx
culture drain tips

44
Q

two stage revision for prosthetic joint infection

A

remove prosthesis
take samples for micro and histo
6wk IV abx
stop abx for 2wks
re-debride and sample at 2nd stage
re-implant with abx impregnated cement
no further abx if samples clear
OPAT

45
Q

DAIR for prosthetic joint infection

A

debridement, antibiotics and implant retention
if dx is within 3wks of operation
tissue sampling
radical debridement
exchange of molecular components
abx for at least 6wks

PATHOLOGY (94 decks)

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