W18 - Wound, bone, and joint infection Flashcards
What are the 3 main pathogens in surgical site infections?
- Staph. aureus (MSSA and MRSA)
- E Coli
- Psuedomonas aeruginosa
Describe the 3 layers of surgical site infections (SSIs)
- Superficial incisional - affect skin + subcut tissue
- Deep incisional - affect fascial + muscle layers
- Organ/space infection - any part of anatomy other than incision
Name 9 pre-operative factors that affect chance of SSI
- Age (higher age - higher risk)
- Remote infections (to the surgical sites)
- Underlying illness (diabetes, malnutrition, low serum albumin, radiotherapy, steroid use, rheumatoid arthritis)
- Obesity
- Smoking
- Pre-op showering
- Hair removal (only remove if interfering with operation)
- Nasal decontamination
- Antibiotic prophylaxis
How does obesity cause increased risk of SSI?
Adipose tissue is poorly vascularised. Poor oxygenation of tissues and functioning of the immune response increases the risk (2-7x higher in those with BMI of >=35) of SSIs
How does smoking cause increase risk of SSI?
Nicotine delays primary wound healing => Peripheral vascular disease => Vasocontrictive effect of reduced oxygen-carrying capacity of blood
Intra-operative factors that affect risk of SSIs - name 7
- Theatre traffic
- Ventilation
- Instrument sterilisation
- Skin preparation (iodine or chlorhexidine)
- Surgical technique
- Normothermia
- Oxygenation
How does intra-operation patient temperature affect risk of SSI?
Mild hypothermia increases risk of SSI by casing vasoconstriction => reduced O2 delivery to wound space => impaired neutrophil function
Which of the following is associated with a reduced risk of SSI?
A) Obesity
B) Bactericidal concentration of abx in serum at time of incision
C) smoking
D) Diabetes
B) Bactericidal concentration of abx in serum at time of incision
Risk factors (5) for septic arthritis
- Joint disease: RA, osteoarthritis, cyrstal-induced arthritis, joint prosthesis
- IVDU
- Chornic disease: Diabetes, chronic renal disease, chronic liver disease
- Immunosuppression: steroids
- Trauam: intra-articular injection, penetrating injury
Septic arthritis - top causative organisms
Staph aureus 46%
Coagulase negative staphylococci 4%
steptococci (pyogenes, pneumoniae, etc) 22%
G- (E coli, haemophilus influenzae, neisseria gonorrhoeae, salmonella)
Septic arthritis - clinical features
1-2 week history of:
- red, painful, swollen joint
- restricted movement
90% monoarticular, 50% knee involved
If septic arthritis is suspected, what 4 investigations would you order?
- Blood cultures (before abx given)
- FBC incl. ESR and CRP
- Synovial fluid aspiration for MC&S
- negative culture does not exclude septic arthritis - Imaging - X-ray, US, CT, or MRI
2 step management of septic arthritis
- Abx - likely IV cephalosporin or fluxloxacillin
- may add vancomycin if high risk of MRSA
- up to 6w of abx may be given
- refer to OPAT (outpatient parenteral abx team) - drainage (arthoscopic washout)
Vertebral osteomyelitis - aetiology (2)
- Acute haematogenous
- Exogenous - i.e. after disc surgery, implant associated
Vertebral osteomyelitis - casusative organisms (3)
S aureus - 48%
Strep - 43%
Gram - rods - 23%
Vertebral osteomyelitis - which region does it affect (most to least)
cervico-thoracix
cervical
lumbar
lumbar > cervical > cervico-thoracic
Vertebral osteomyelitis - clinical features (3)
- Back pain (90% of cases)
- Fever (60% of cases)
- Neurological impairment (35% of cases)
4 investigations for vertebral osteomyelitis
- Imaging - MRI (90% sensitive)
- Blood cultures
- FBC + ESR, CRP
- CT/open biopsy
- 76 year old man
- Admitted with a 4 month history of back pain with radiation down left leg
- Weight loss of 25kg over the last 6 months
- PMH: fracture right femur 25yrs ago in Kuwait. Metal plate inserted.
Arthritis right knee, Hypertension. Lived in Iraq, Jordan and Singapore. Arrived in UK in 1993.
MRI: discitis of L2/3
Spinal biopsy in September 2010
Tissue sent for culture. Coagulase negative staphylococci grown from enrichment.
Histology : vague granuloma
Empirical anti- tuberculous treatment commenced ( rifater and ethambutol)
Empirical iv ceftriaxone commenced
- L2/3 debridement and stabilisation
- Tissue- no growth
- Tissue sent for 16S PCR
What do you think the causative organism is:
- Staph aureus
- Salmonella
- Tuberculosis
- Brucella
- Brucella
- acquired by drinking unpasteurised milk, cheese, or uncooked meat
- may form brucella granulomas
Prosthethic joint infections - what is it?
Lysis of bone between the prosthesis and the cement of the bone
Prosthethic joint infection - clinical features (4)
- Pain
- Early failure
- Sinus tract formation
- Pt complains joint was “never right”
Prosthethic joint infection - common causative organisms (3 groups)
- Gram + cocci
=> coagulase negative staphylococci
=> staphylococcus aureus
=> streptococci sp
=> enterococci sp
- Aerobic G - bacilli
=> Enterobacteriacae
=> Pseudomonas aeruginosa
- Anaerobes
=> polymicrobial
=> fungi
Prosthesis joint infection - investigations (3)
- FBC including CRP + ESR
- Blood culture
- Joint aspiration
- Imaging - usually shows loosening of prosthesis
- Age- 70yrs old
- 1994 Right THR; 1998 Revision of acetabular component
- X-ray: lysis around distal part of femoral component
- Diabetic
- What is the most likely organism causing prosthetic joint infection?
1) Coagulase negative staphylococci
2) E coli
3) Haemophilus influnzae
4) Pseudomonas
1) Coagulase negative staphylococci
