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Pathology - Y5 > Wound, Bone and Joint Infections > Flashcards

Wound, Bone and Joint Infections Flashcards

1
Q

What are the major pathogens in surgical site infection?

A

Staph.aureus (MSSA and MRSA)

E.coli

Pseudomonas aeruginosa

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2
Q

What is the pathogenesis of a surgical site infection?

A
  • Contamination of wound at operation
  • Pathogenicity and innoculum of microorganisms
  • Host immune response

If surgical site is contaminated with > 10^5 microorganisms per gram of tissue, risk of SSI is increased. The dose of contaminating bacteria required to cause infection is much lower if there is foreign material present e.g silk suture.

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3
Q

What are the three levels of surgical site infection?

A

Superficial incisional: Affect skin and subcutaneous tissue.

Deep incisional: Affect fascial and muscle layers.

Organ/space infection: Any part of anatomy other than incision.

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4
Q

A patient is admitted in February, with a subarachnoid and subdural haemorrhage after a fall. Decompressive craniectomy. In April, they had a cranioplasty with titanium plate.

Patient was readmitted in October with large subdural collection with midline shift and had a subsequent abscess evacuation. Titanium plates removed. Underneath there was severe infection with 1-1.5cm thick pus.

What is the likely organism?

A

MRSA

Patient was given linezolid

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5
Q

What are three different phases where surgical site infections can be prevented?

A

Pre-operative phase

Intra-operative phase

Post-operative phase

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6
Q

What is the relationship between age and developing a surgical site infection?

A

An independent risk factor.

A direct linear trend of increasing risk until 65 years of age.

A prospective study examining patient undergoing total hip replacement. Age over 75 was found to be a significant risk factor.

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7
Q

Which underlying illnesses are risk factors for a surgical site infection?

A

ASA score of 3 or more

Diabetes: Two to three fold increased risk. Association with post-op hyperglycaemia. Control blood glucose. HbA1C < 7.

Malnutrition

Low serum albumin

Radiotherapy and steroid use: Taper steroids.

Rheumatoid arthiritis: Stop disease modifying agents for 4 weeks before and 8 weeks post-op.

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8
Q

Why is obesity a risk factor for surgical site infections?

A

Adipose tissue is poorly vascularised. Poor oxygenation of tissues and functioning of the immune response increases the risk of SSIs.

Risk increased by 2 to 7 in patients with a BMI of 35 or more.

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9
Q

How is smoking a risk factor for surgical site infections?

A

Smoking duration and number of cigarettes smoked.

Nicotine delays primary wound healing.

Peripheral vascular disease.

Vasocontrictive effect of reduced oxygen-carrying capacity of blood.

Encourage tobacco cessation.

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10
Q

How can pre-operative showering affect the risk of surgical site infections?

A

Microorganisms colonising the skin may contaminate exposed tissues and cause an SSI. There is no difference in SSI incidence when chlorhexidine or detergent/bar soap is used.

Patients should be advised to shower or bath using soap or on the day of surgery or the day before.

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11
Q

How can hair removal affect the risk of surgical site infections?

A

Micro-abrasions caused by shaving with a razor may lead to multiplication of bacteria. Use electric clippers on the day of surgery with single-use head.

Hair should not be removed unless it will interfere with the operation.

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12
Q

How can nasal decontamination affect the risk of surgical site infections?

A

S.aureus is carried in the nares of 20-30%.

A multivariate analysis demonstrated that S.aureus carriage was the most powerful independent risk factor for SSI following cardiothoracic surgery.

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13
Q

How can antibiotic prophylaxis affect the risk of surgical site infections?

A

Antibiotic prophylaxis should be given at induction of anaesthesia.

Bactericidal concentration of the drug should be established in serum and tissues at time of incision.

Additional doses may be necessary if there has been significant blood loss or if the operation has been prolonged.

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14
Q

How can ventilation affect the risk of surgical site infections?

A

Maintain positive pressure ventilation.

Maintain around 20 air changes per hour (of which at least 3must be fresh air).

Filter all air.

Keep operating room doors closed.

Consider laminar flow for orthopaedic implant surgery.

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15
Q

How can sterilisation affect the risk of surgical site infections?

A

Sterilise all surgical instruments.

Inadequate sterilisation of surgical instruments has resulted in SSI outbreaks.

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16
Q

How should skin be prepared to reduce the risk of surgical site infections?

A

When skin is incised microorganisms may contaminate tissues and cause an SSI.

Prepare skin at surgical site using antiseptic preparation: povidine-iodine or chlorhexidine.

Chlorhexidine in 70% alcohol is used.

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17
Q

What is an aseptic surgical technique?

A

Maintaining effective haemostasis while preserving adequate blood supply, gently handling tissues, avoiding inadvertent entries into hollow viscus, removing devitilised tissues and eradicating dead space.

Adhere to asepsis when placing intravascular devices or epidural catheters.

18
Q

How does hypothermia affect the risk of surgical site infections?

A

Mild hypothermia appears to increase the risk of SSIs by causing vasoconstriction, decreased delivery of oxygen to wound space and subsequent impairment of neutrophil function.

In theatre suite: Measure patients temperature before inducing anaesthesia. Start forced air warming if temperature is below 36ºC.

Warm intravenous fluid. Warm irrigation fluid.

19
Q

How does adequate oxygenation affect the risk of surgical site infections?

A

Maintain optimal oxygenation during surgery, to maintain a haemoglobin saturation of more than 95%.

Higher inspired oxygen concentrations in peri-operative period reduces SSIs.

20
Q

What are three common bone and joint infections?

A

Septic arthritis

Chronic osteomyelitis

Prosthetic joint infection

21
Q

What is the epidemiology and prognosis of septic arthritis?

A

Incidence is 2-10 cases per 100,000.

In patients with RA incidence is 28-38 per 100,000 population.

Mortality is 7-15%.

Morbidity is 50%.

22
Q

What are risk factors for septic arthritis?

A

Rheumatoid arthritis, osteoarthritis, crystal induced arthritis

Joint prosthesis

Intravenous drug abuse

Diabetes, chronic renal disease, chronic liver disease

Immunosuppression: Steroids

Trauma: Intra-articular injection, penetrating injury

23
Q

What is the pathophysiology of septic arthritis?

A

Organisms adhere to the synovial membrane, bacterial proliferation in the synovial fluid with generation of host inflammatory response.

Joint damage leads to exposure of host derived proteins such as fibronectin to which bacteria adhere.

24
Q

What are bacterial factors for pathogenesis of septic arthritis?

A

S.aureus has receptors such as fibronectin binding protein that recognise selected host proteins.

Kingella kingae synovial adherence is via bacterial pili.

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

25
Q

What are host factors for the pathogenesis of septic arthritis?

A

Leucocyte derived proteases and cytokines can lead to cartilage degradation and bone loss.

Raised intra-articular pressure can hamper capillary blood flow and lead to cartilage and bone ischaemia and necrosis.

Genetic deletion of macrophage –derived cytokines (lymphotoxin α, TNFα, interleukin 1 receptor) reduces host protection in S.aureus sepsis in animal models.

Absence of interleukin10 in knockout mice increases the severity of staphylococcal joint disease.

Genetic variation in expression of these cytokines may lead to differential susceptibility to septic arthritis.

26
Q

What are the main causative organisms for 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
27
Q

What are clinical features of septic arthritis?

A

1-2 week history of red, painful, swollen restricted joint:

  • Monoarticular in 90%
  • Knee is involved in 50%

Patients with rheumatoid arthritis may show more subtle signs of joint infection.

28
Q

What are appropriate investigations for septic arthritis?

A
  • Blood culture before antibiotics are given
  • Synovial fluid aspiration for microscopy and culture
  • ESR, CRP
  • Traditionally a synovial count >50,000 cells/mm3 used to suggest septic arthritis. Negative culture result does not exclude septic arthritis.
29
Q

Which imaging modalities are useful for septic arthritis?

A

X-rays: Soft tissue oedema.

US: Confirm effusion and guide needle aspiration.

CT: Erosive bone change, periarticular soft tissue extension.

MRI: Joint effusion, articular cartilage destruction, abscess, contiguous osteomyelitis.

30
Q

What is the management for septic arthritis?

A

Antibiotics: IV Cephalosporin or Flucloxacillin. May need to add vancomycin if at high risk of MRSA.

No data on optimum duration of treatment. Up to 6 weeks of antibiotics may be given.

OPAT (outpatient parenteral antibiotic team).

Drainage: Arthoscopic washout

31
Q

What are two different classifications of vertebral osteomyelitis?

A

Acute haematogenous

Exogenous: After disc surgery. Implant associated.

32
Q

What are common causative organisms of vertebral osteomyelitis?

A

Causative Organisms:

  • S.aureus: 48.3%
  • CNS: 6.7%
  • GNR: 23.1%
  • Strep: 43.1%
33
Q

What is the general localisation of vetebral osteomyelitis?

A

Cervical: 10.6%

Cervico-thoraco: 0.4%

Lumbar: 43.1%

34
Q

What are symptoms of vetebral osteomyelitis?

A

Back pain: 86%

Fever: 60%

Neurological impairment: 34%

35
Q

What are appropriate investigations for vertebral osteomyelitis?

A

MRI: 90% sensitive

Blood cultures

CT/open biopsy

36
Q

What is the management of vertebral osteomyelitis?

A

Six weeks of treatment

Longer treatment if undrained abscesses/implant associated

37
Q

What are signs and symptoms of a prosthetic joint infection?

A

Pain

Patient complains that the joint was ‘never right’

Early failure

Sinus tract

38
Q

What are causative organisms for a prosthetic joint infection?

A

Gram positive cocci:

  • Coagulase negative staphylococci
  • Staphylococus aureus
  • Streptococci sp
  • Enterococci sp

Aerobic gram negative bacilli:

  • Enterobacteriaceae
  • Pseudomonas aeruginosa

Anaerobes

Polymicrobial

Culture negative

Fungi

39
Q

What are investigations for a prosthetic joint infection?

A

Radiology: Loosening

If CRP>13.5 for prosthetic knee joint infection; CRP> 5 for prosthetic hip joint infection.

Joint aspiration:

  • If >1700/ml of WCC correlates with knee PJI
  • If > 4200/ml of WCC correlates with hip PJI

May only get planktonic bacteria in joint fluid, may need to sample bacteria where infection is most likely.

40
Q

How is intraoperative microbiological sampling conducted?

A

Tissue specimens from at least 5 sites around the implant.

Histopathology: Infection defined as >5 neutrophils per high power field.

If 3 or more specimens yield identical organisms, this is highly predictive of infection (sensitivity 65%, specificity 99%).

41
Q

What is single stage revision for a prosthetic joint infection?

A

Aspirate joint to identify pathogen.

Excision of infected tissue, synovectomy.

Add antibiotics to bone cement according to culture results.

Implantation of a cemented hip or knee prosthesis using antibiotic loaded cement.

Give 7-10 days of IV antibiotics.

Culture drain tips.

Success rate is 89% in 2002.

42
Q

What is two stage revision for a prosthetic joint infection?

A

Remove prosthesis.

Take samples for microbiology and histology.

Period of IV antibiotics (6weeks). Stop antibiotics for 2 weeks.

Re-debride and sample at second stage.

Re-implantation with antibiotic impregnated cement.

No further antibiotics if samples clear.

Pathology - Y5 (59 decks)

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