Micro - Wound, Bone, and Joint infections

Question 1

Which organisms cause surgical site infections

Answer 1

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

Question 2

What are the levels of surgical site infections

Answer 2

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

Question 3

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

Answer 3

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

Question 4

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

Answer 4

Staph. aureus carriage in the nostrils

Question 5

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

Answer 5

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

Question 6

Why must normothermia be maintained in patients during surgery

Answer 6

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

Question 7

What are the risk factors for septic arthritis

Answer 7

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

Question 8

What is the pathophysiology of septic arthritis

Answer 8

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

Question 9

What are the most common causative organisms for septic arthritis

Answer 9

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

Question 10

What are the factors that contribute to septic arthritis

Answer 10

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

Question 11

What investigations should be done for septic arthritis

Answer 11

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

Question 12

What is the management for septic arthritis

Answer 12

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

Question 13

What are the causes of spinal epidural abscesses and vertebral osteomyelitis

Answer 13

Acute haematogenous spread or exogenous (disc surgery, implants)

Staph. aureus
Coagulase negative staph
Gram -ve rods
Streptococcus

Question 14

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

Answer 14

Lumbar (45%)
Cervical
Cervico-thoracic

Question 15

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

Answer 15

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

Question 16

What is the treatment for Spinal epidural abscesses and Vertebral Osteomyelitis

Answer 16

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

Question 17

What investigations should be done for chronic osteomyelitis

Answer 17

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

Question 18

What is the management for chronic osteomyelitis

Answer 18

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

Question 19

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

Answer 19

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

Question 20

What is seen on investigations for prosthetic joint infections

Answer 20

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

Question 21

What is the treatment for prosthetic joint infections

Answer 21

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