Micro - Wound, Bone, and Joint infections Flashcards

1
Q

Which organisms cause surgical site infections

A

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

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2
Q

What are the levels of surgical site infections

A

Superficial Incisional: skin and subcutaneous tissues
Deep Incisional: fascial and muscle layers
Organ/Space Infection: any part of the anatomy other than the incision

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3
Q

What are the pre-operative methods for preventing surgical site infections

A

Determine their risk (age, ASA score, co-morbs, medications, obesity, smoking)
Day of /day before surgery showering
Hair removal using an electric clipper on the day of the surgery
Nasal decontamination if carrying S. aureus
Abx prophylaxis

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4
Q

What is the most powerful risk factors for surgical site infections following cardiothoracic surgery

A

Staph. aureus carriage in the nostrils

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5
Q

What are the intra-operative management options to prevent surgical site infections

A

Limiting no. of people in theatre
Positive pressure
Sterilisation of surgical instruments
Skin prep: chlorhexidine in 70% alcohol
Maintain normothermia
Oxygenation >95%

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6
Q

Why must normothermia be maintained in patients during surgery

A

Hypothermia → increase risk of SSIs by causing vasoconstriction and decreasing oxygen delivery to wound space with impairment of neutrophil function

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7
Q

What are the risk factors for septic arthritis

A

Rheumatoid arthritis
Osteoarthritis
Crystal arthritis
Joint prosthesis
IVDU
Diabetes, chronic renal disease, chronic liver disease
Immunosuppression (e.g. steroids)
Trauma – intra-articular injection, penetrating injury

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8
Q

What is the pathophysiology of septic arthritis

A

Organisms adhere to synovial membrane
Bacterial proliferation in synovial fluid → host inflammatory response → joint damage
Joint damage → exposure of host derived protein (e.g. fibronectin) to which bacteria can adhere

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9
Q

What are the most common causative organisms for septic arthritis

A

Staph aureus (46%)
Streptococci pyogenes/pneumoniae/agalactiae
Gram -ves: E. Coli, H. influenzae, N. gonorrhoea, salmonella
Coagulase-negative staph
Lyme disease, Brucellosis, Mycobacteria, fungi

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10
Q

What are the factors that contribute to septic arthritis

A

Bacterial: Staph. aureus has fibronectin-binding protein and may produce cytotoxin PVL
Kingella kingae: synovial adherence via bacterial pili

Leucocyte → proteases and cytokines → cartilage and bone damage
Raise intra-articular pressure → impedes capillary blood flow → cartilage and bone ischaemia/necrosis
Genetic deletion of macrophage-derived cytokines
Absence of IL-10 → increases severity of staph.aureus joint disease

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11
Q

What investigations should be done for septic arthritis

A

Blood cultures
US with Synovial fluid aspiration for MC&S → synovial count >50,000 WBCs = septic arthritis
ESR/CRP
CT - check for erosive bone change, soft tissue extension
MRI - joint effusion, articular cartilage destruction, abscess, contiguous osteomyelitis

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12
Q

What is the management for septic arthritis

A

ABx, 4-6 weeks (outpatient setting)
- IV cephalosporin or flucloxacillin
- MRSA risk: vancomycin
Drainage of the joint - arthroscopic washout

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13
Q

What are the causes of spinal epidural abscesses and vertebral osteomyelitis

A

Acute haematogenous spread or exogenous (disc surgery, implants)

Staph. aureus
Coagulase negative staph
Gram -ve rods
Streptococcus

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14
Q

What is the most common site of Spinal epidural abscesses and Vertebral Osteomyelitis

A

Lumbar (45%)
Cervical
Cervico-thoracic

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15
Q

What investigations should be done for Spinal epidural abscesses and Vertebral Osteomyelitis

A

MRI (90% sensitivie)
blood cultures
CT-guided/open biopsy

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16
Q

What is the treatment for Spinal epidural abscesses and Vertebral Osteomyelitis

A

Abx for 6 weeks, longer if there is an undrained abscess
May required surgery for any spinal cord compression

17
Q

What investigations should be done for chronic osteomyelitis

A

XR (often first line to screen; early changes take ~10 days)
MRI (much more sensitive for changes)
Bone biopsy (culture and histology)

Presents with pain, brodies abscess and sinus tract

18
Q

What is the management for chronic osteomyelitis

A

Radical debridement to living bone (masquelet technique):
- Radical sequestrectomy
- Removal of foreign bodies: filling the defect with antibiotic loaded cement spacer and external fixation
- In 6-8 months, remove the cement spacer, and fill the defect with autologous bone graft

19
Q

What are the causative organisms of prosthetic joint infections (PJI)

A

Coagulase negative staph
S. aureus
Streptococci
Enterococci
Aerobic: Enterobacteriaceae, pseudomonas aeruginosa
Anaerobes
Polymicrobials

20
Q

What is seen on investigations for prosthetic joint infections

A

Radiology: loosening (bone loss along the cement-bone interface)
Raised CRP
Joint aspiration: >3000 WCC/ml
- Positive alpha-defensin on immunoassay
- intra-operative microbiological sampling

21
Q

What is the treatment for prosthetic joint infections

A

single stage revision (endo-klinik): remove all foreign material and dead bone, change gloves and drapes, re-implant the new prosthesis with Abx impregnated cement

Two-stage: replacing the prosthesis with a space, period of IV abx, debirdement and sample, and implantation with Abx impregnated cement

Debridement, antibiotics and implant retention (DAIR): Within 3 weeks of operation, radical debridement, exchange molecular components