Micro 4 - Wound, bone and joint infections Flashcards
Define superficial incisional and deep incisional infection
- Superficial incisional – skin + SC tissue
* Deep incisional – fascial + muscle layers
Gram +ve, Cocci, yellow colony on blood agar which is β haemolytic - which is the causative organism and how do you treat it?
MRSA (IV linezolid)
When should DMARDs be stopped and when should they be continued after the operation?
4 weeks before and 8 weeks post-op.
What is the goal of antibiotic prophylaxis given before induction of anaethesia?
Bactericidal concentration of the drug should be established in serum and tissues at time of incision.
Ventilation in an operating theatre
o Maintain positive pressure ventilation
o Filter all air
o Maintain around 20 air changes per hour
o Keep operating room doors closed
o Consider laminar flow for orthopaedic implant surgery
How does hypothermia increase the risk of infection?
o Mild hypothermia increased risk of SSIs vasoconstriction, decreased delivery of oxygen to wound space + subsequent impairment of neutrophil function
Causative organisms in septic arthritis
o Staph aureus – most common
o Streptococcus – second most common
o Most common cause in young sexually active (18-30y/o)
– N. gonorrhoea
– Gram-ve diplococci
– IV cefotaxime 4-6/52
o Most common cause in older patients + overall
– Staph. aureus [gram +ve cocci]
– IV flucloxacillin 4-6/52
How do host factors contribute to the destruction of the bone in septic arthritis?
o Leucocyte derived proteases + cytokines cartilage degeneration + bone loss
o intra-articular pressure hamper capillary blood flow cartilage + bone ischaemia + necrosis
Pathophysiology of septic arthritis
o Organisms adhere to the synovial membrane bacterial proliferation in the synovial fluid generation of host inflammatory response
o Joint damage exposure of host derived proteins (e.g. fibronectin) to which bacteria adhere
o S. aureus
Has receptors e.g. fibronectin binding protein that recognise selected host proteins
How is vertebral osteomyelitis caused and which is the most common causative organism?
- Acute haematogenous (bacteraemia that settles in the vertebrae)
- Staph aureus
Vertebral osteomyelitis ix
o MRI – 90% sensitive – to confirm vertebral osteomyelitis
o Blood cultures – to identify the causative organism
o Biopsy (CT-guided/open) – 2nd line
Brucella forms _ on agar plate
silvery colonies
Chronic osteomyelitis presentation
Pain
Brodies abscess
sinus tract
Where is the Lautenbach technique used? Describe it
used in the treatment of chronic osteomyelitis
= debridement down to healthy bleeding bone + irrigation system used for 3 weeks
Make sure debridement has occurred all the way down to healthy bleeding bone – check using osteoscopy
Double lumen suction irrigation system introduced through a SC tunnel
Abx (chosen based on culture results) instilled through the central lumen
1L of Hartmanns solution every week – suction fluid sent for culture
Irrigation continued for 3 weeks after discharge
Oral abx continued for 6 weeks after discharge
Where is the Papineau technique used? Describe it
used in the treatment of chronic osteomyelitis
complete excision of the infected tissue and necrotic bone
open cancellous bone grafting of the osseous defect
Causative organisms in prosthetic joint infection
o Gram +ve cocci Coagulase -ve staphylococci – more common than staph. aureus Staph aureus Streptococci sp Enterococci sp
o Aerobic gram -ve bacilli
Enterobacteriaceae
Pseudomonas aeruginosa
o Anaerobes
o Polymicrobial
o Culture negative
o Fungi
Diagnosis of PJI
Imaging
WCC
CRP
Intraoperative microbiological sampling
Knee
Hip
Imaging XR/CT/MRI - loosening Knee WCC >1700/ml CRP >13.5
Hip
WCC >4200/ml
CRP >5
Intraoperative microbiological sampling
o Tissue specimens from at least 5 sites around the implant
o Histopathology
Infection = >5neutrophils per high power field
o If >3 specimens yield identical organisms – highly predictive of infection
patient complains that joint was never quite right
Treatment of PJI
Endo Klinik
• Endo Klinik single stage revision
o Excision of infected tissue, synovectomy
o Add antibiotics to bone cement according to culture results
o Implantation of new cemented hip/knee prosthesis using abx impregnated cement
o 7-10 days of IV Abx
Treatment of PJI
Two stage revision
o Remove prosthesis – spacer put in the joint to take the place of the prosthesis
o Period of abx – 6 weeks
o Stop abx for 2 weeks
o Re-debride sample at second stage
o Re-implantation with abx impregnated cement
o No further abx if samples clear
Soft tissue infections - causative agents
- Wound infection
- Open wound, gas gangrene
- Child red oedematous rash on face, spreads quick
- Most common cause of cellulitis
- Wound infection – Staph. aureus, Flucloxacillin
- Open wound, gas gangrene – Clostridium perfringens
- Child red oedematous rash on face, spreads quick – Erysipelas
- Most common cause of cellulitis – Strep. Pyogenes (Group A strep) (+staph aureus)
Aetiology of
osteomyelitis septic arthritis (+rf) prosthetic joint infection
spread
organism
ix
spread - local or heam for all
IV abx for all
osteomyelitis
s aureus
MRI, blood culture, bone biopsy for culture/histology
septic arthritis s aureus (step, e coli) RF - abnormal joint e.g. RA, prosthetic joint joint aspirate MCS blood culture
prosthetic joint infection coag neg staph (s aureus, e coli) XR CT MRI loosening joint aspirate
