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
Mx of septic arthritis
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
causes of vertebral osteomyelitis
acute haematogenous - bacteraemia and bacteria seed to vertebrae exogenous - after disc surgery - implant associated -> infection
27
causative organisms of vertebral osteomyelitis
**Staph aureus strep** CNS GNR
28
main location of vertebral osteomyelitis
lumbar
29
sx of vertebral osteomyelitis
back pain fever neurological impairment
30
ix into vertebral osteomyelitis
MRI blood cultures if were bacteraemic CT/open biopsy
31
Rx of vertebral osteomyelitis
6wks - longer if undrained abscess/implant associated surgery if spinal cord compression
32
brucella granuloma
33
signs of chronic osteomyelitis
pain brodies abscess (intraoseous abscess) sinus tract discharging pus
34
chronic osteomyelitis femur is very deformed arrow - sequestra/dead bone half bone - involucrum - new bone formation
35
diagnosis of chronic osteomyelitis
MRI bone biopsy for culture and histology
36
treatment of chronic osteomyelitis
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
**prosthetic joint infection (PJIs)** Black gap – loosening between bone and prosthetic
38
signs and sx of prosthetic joint infection
Pain Patient complains that the joint was ‘never right’ Early failure Sinus tract
39
causative organisms of prosthetic joint infections
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
diagnosis of prosthetic joint infections
41
intraoperative microbiological sampling
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
single stage revision for prosthetic joint infection
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
Endo Klinik single stage revision for prosthetic joint replacement
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
two stage revision for prosthetic joint infection
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
DAIR for prosthetic joint infection
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