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Microbiology > Wound Bone And Joint Infections > Flashcards

Wound Bone And Joint Infections Flashcards

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1
Q

What is the pathogenesis?

A

Contamination of the wound
Pathogenicity and innoculum of microorganisms
Host immune response
Group a strep more virulent than coagualse staph

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2
Q

What increases the risk of SSI?

A

Surgical site is contaminated with more than more than 10 to the 5 microorganisms per gram of tissue, risk of SSI increases
Dose requires of bacteria to cause infection is lower if foreign material is present eg silk suture

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3
Q

What are the 3 levels of SSI?

A

Superficial incisional- affect skin and subcutaneous tissue
Deep incisional- affect fascial and muscle layers
Organ/space infection- any part of any anatomy other than incision

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4
Q

What can mrsa be treated with?

A

Linezolid

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5
Q

What phases can SSI be prevented?

A

Pre operative phase
Intra operative
Post op

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6
Q

What is involved in the pre op phase?

A

Optimising patient
Age is independent, Over 75 major risk factor
Treat infections at other sites, postpone operation
ASA score of 3 or more
Diabetes, 2/3 fold increased risk. Control glucose, hba1c, less than 7
Malnutrition
Low serum albumin
Taper steroid use, radiotherapy
Stop DMARDS for RA 4 weeks before and 8 weeks after
Obesity- poor oxygenation of adipose tissue and functioning of immune system. Increase from 2 to 7 with Bmi of 35 or more

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7
Q

How can smoking increase risk of SSI?

A

Nicotine delays primary wound healing

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8
Q

Why is pre op showering recommended before surgery?

A

Microorganisms colonising the skin, contaminate exposed tissue and cause an SSI
no difference in using chlorhexidine and detergent bar soap
Shower on the day or day before

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9
Q

How should hair be removed before surgery?

A

Micro abrasions can lead to multiplication of bacteria
Use electric clippers with single use head
Try to avoid removing hair

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10
Q

How can nasal contamination affect SSI risk?

A

S aureus in the nose of 20-30% of people
Multi variate analysis demonstrated that s aureus was most powerful independent risk factor for SSI following cardio thoracic surgery

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11
Q

How should abx prophylaxis occur?

A

Given at induction of anaesthesia
Bactericidal concentration of the drug should be established in serum and tissues at time of incision
Additional dose may be necessary if there has been significant blood loss or if the operation has been prolonged

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12
Q

What should surgical personnel do to decrease risk of SSI?

A

If they have symptoms of transmissible infection report to occupational health

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13
Q

How can theatre traffic affect risk of SSI?

A

1 person sheds 1 billion skin cells per day, 10% carry bacteria
Microbial load is related to number of ppl present in theatre
Theatre personnel should be kept to a minimum

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14
Q

Why is ventilation important?

A 
Maintain positive pressure ventilation 
Maintain 20 air changes per hour of which at least 3 must be fresh air
Filter all air 
Keep operating room doors closed 
Consider laminar flow for ortho surgery 
Reduces bacterial load
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15
Q

What must be done to surgical instrument?

A

Sterilise them

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16
Q

How can skin be prepared?

A

At surgical site, use antiseptic preparation, povidine iodine, chlorhexidine in 70% alcohol use

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17
Q

How can surgical technique help reduce SSI?

A

Maintain effective haemostasis while preserving adequate blood supply
Gently handling tissue
Avoid inadvertent entries into hollow viscus
Remove devitilzed tissue and eradicating dead space
Adhere to asepsis when placing intravascular devices or epidural catheters

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18
Q

How can temperature affect risk of SSI?

A

Mild hypothermia can increase risk, vasoconstriction, decreased delivery of oxygen to wound space, and subsequent impairment of neutrophil function
Measure patients temp before inducing anaesthesia. Start forced warming if temp is below 36
Warm IV fluid, warm irrigation fluid

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19
Q

How can oxygen levels affect SSI risk?

A

Maintain optimal oxygenation during surgery to maintain a Hb sat of more than 95
Higher inspired oxygen concentration in peri operative period reduces SSI

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20
Q

How does RA effect septic arthritis risk?.

A

Increases incidence from 2-10 per 100000 to 28-38

Mortality is 7-15%, morbidity is 50%

21
Q

What are the risk factors for septic arthritis?

A

RA, osetoarthritis, crystal induced arthritis
Joint prosthesis, IVDU, diabetes, chronic renal disease, chronic liver disease
Immunosuppresion
A trauma- intra articular injury and penetrating injury

22
Q

What is the pathophysiology of septic arthritis?

A

Organisms Adhere to synovial membrane, bacterial proliferation, generation of host inflammatory response
Joint damage leads to exposure of host derived proteins such as fibronectin to which bacteria adhere

23
Q

What bacterial factors are involved in pathogenesis of septic arthritis

A

S aureus has receptors such as fibronectin binding protein
Kingella kingae synovial adherence is via bacterial pilli
Some strains of staph aureus produces cytokine pvl- Panton Valentine leucocidin, associated with fulminant infections

24
Q

What are the host factors involved in pathogenesis of septic arthritis?

A

Leucocyte derived proteases and cytokines can lead to cartilage degradation and bone loss
Raised ICP can hamper capillary blood flow and lead to cartilage and bone ischaemia and necrosis
Genetic deletion of macrophage derived cytokines (lymphotoxin alpha, tnf alpha, interleukin 1 receptor) reduces host response in s aureus sepsis
Absence of il 10 in Ko mouse, increase severity of staph disease

25
Q

What are the causative organisms of septic arthritis?

A

S aureus 46%
Strep pyo, pneumo, agalactiae 22%
Gram negative- E. coli, h influenzae, n gonorrhoea, salmonella
Rare- Lyme, brucellosis, mycobacterium, fungi

26
Q

What are the clinical features of septic arthritis?

A

1-2 weeks hx of red, painful, swollen restricted joint
Monoarticular in 90%
Knee is involved in 50%
Patients with RA, may show more subtle signs of joint infection

27
Q

What are the ix for septic arthritis?

A

Blood culture before abx given
Synovial fluid aspiration for microscopy and culture, esr crp
Traditionally a synovial count more than 50000 WBC, used to suggest septic arthritis
Negative culture does not exclude septic arthritis

28
Q

How can imaging help in diagnosing and Tx?

A

U.S.- confirm effusion, guide needle aspiration
CT- erosive bone change, periarticular soft tissue extension
MRI- joint effusion, articular cartilage destruction, abcess, contiguous osteomyelitis

29
Q

What does mx involve?

A

Abx- up to 6 weeks, outpatient parental antibiotic team

Drainage

30
Q

What is vertebral osteomyelitis caused by?

A

Bacteraemia- acute haematogenous

Exogenous- after disc surgery, implant associated

31
Q

What are the causative organism for vertebral osteomyelitis?

A

S aureus
CNS
GNR
Strep

32
Q

What are the most common sites for vertebral osteomyelitis?

A

Cervical- 10.6%
Cervico-thoraco 0.4%
Lumbar- 43.1%

33
Q

What are the symptoms of vo?

A

Back pain
Fever
Neurological impairment

34
Q

How do you diagnose vo?

A

90% sensitive MRI
Blood cultures
Ct/open biopsy

35
Q

What Tx can be given for brucella?

A

Cipro and doxycycline and rifampin

36
Q

What Tx can be given for cipro resistant salmonella?

A

Tx with ceft, azithromycin

37
Q

How do chronic osteomyelitis present?

A

Pain
Brodies abcess which drains
Sinus tract which discharges fluid or pus

38
Q

How is chronic osteomyelitis diagnosed?

A

MRI

Bone biopsy for culture and histology

39
Q

How is chronic osteomyelitis treated?

A

Radical debridement down to living bone
Remove sequestra, infected bone and soft tissue
Abx

40
Q

What is the Lautenbach technique?

A

Debridement and collection of multiple samples for culture and histology
All internal fixation devices removed and double ended reaming was performed
Osteoscopy used to ensure that healthy bleeding could be seen and any sequestra found removed. Pulse lovage
Double lumen suction irrigation system was introduced through a subcut tunnel

41
Q

What is the papineau technique?

A

Complete excision of infected tissue and necrotic bone
Open cancellous bone grafting of the osseous defect
Split skin grafting for wound closure

42
Q

What are signs and symptoms of prosthetic joint infection?

A

Pain
Joint was never right
Early failure
Sinus tract

43
Q

How is pji diagnosed?

A

Radiology loosening
Crp more than 13.5 for knee, more than 5 for hip
Joint aspiration 1700 WBC for knee, 4200 WBC for hip

44
Q

What should happen during surgery for intra operative microbial sampling?

A

Tissue specimens from at least 5 sites around the implant
Histopathology- infection defined as more than 5 neutrophils per high power field
If 3 or more specimens yield identical organisms, this is highly predictive of infection

45
Q

What is possible Tx of pji?

A

Single stage revision- remove all foreign material and dead bone
Change gloves and drapes
Re implant new prosthesis with antibiotic impregnanted cement and give IV antibiotics

46
Q

What is the endo Klinik single stage revision?

A

Aspirate joint to identify pathogen
Excision of infected tissue and synovectomy
Add abx to bone cement according to culture
Implantation of cemented hip or knee prosthesis using abx cement give 7-10 days of IV abx
Culture drain tips

47
Q

What is the 2 stage prosthesis?

A

Remove prosthesis
Take samples for microbiology and histology
Period of IV abx stop for 2 weeks
Re debridement and sample at second stage
Re implantation with abx cement
No further abx if samples clear
Opat

48
Q

What is the most causative organism for pji?

A

Coagualse neg staph

49
Q

What are the major pathogens involved in surgical site infections?

A

S aureus
E. coli
Pseudomonas aeruginosa

Microbiology (15 decks)

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