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MBChB3 > Bone And Joint Infections > Flashcards

Bone And Joint Infections Flashcards

1
Q

Describe the presentation of septic arthritis?

A
  • new onset joint pain (atraumatic)
  • hot, red, swollen joint
  • reduced ROM
  • sepsis
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2
Q

What are the differential diagnoses for a hot, red and swollen joint?

A
  • rheumatoid arthritis
  • psoriatic arthritis
  • crystal induced arthritis
  • trauma
  • haemarthrosis
  • extra-articular infection: cellulitis/bursitis
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3
Q

Describe the different types of septic arthritis

A

Haematogenous spread: arising from a distal site (IE/skin infection/RTI/UTI/dental infection) - 80%

Direct inoculation: following surgery/arthroscopy/intra-articular injection/trauma/bite

Contiguous spread: from surrounding structures (osteomyelitis/bursitis/cellulitis/soft-tissue abscess)

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4
Q

What are the diagnostic tests for septic arthritis?

A
  • sepsis/fever >38 degrees (take blood cultures + start antibiotics)
  • FBC, CRP, ESR, Us and Es, LFTs
  • joint aspirate
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5
Q

What do WCC + synovial fluid results tell you?

A

High synovial WCC = septic arthritis, crystal-induced arthritis/ inflammatory arthritis

Low synovial WCC = early infections / immunocompromsied / low virulence organisms

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6
Q

What are the possible pathogens that cause septic arthritis?

A
  • S. aureus + enterococci (most common)
  • enterobacteriae
  • mycobacterium tuberculosis
  • neisseria gonorrhoeae

Children:
- streptococcus pneumoniae
- kingella kingae
- haemophilus influenzae type B

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7
Q

What do we consider with a S. aureus positive arthritis?

A
  • source = skin (send swabs for culture), IE
  • get blood cultures
  • echo (if positive blood cultures)
  • IV flucloxacillin/IV vancomycin (MRSA)
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8
Q

What do we consider with a S. viridans arthritis?

A
  • source = mouth, IE
  • blood cultures
  • echo (if positive blood cultures)
  • IV benzylpenicillin/ ceftriaxone/ vancomycin if B-lactam allergy
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9
Q

What do we consider with enterobacteriaceae arthritis?

A
  • source = abdomen/urogenital tract/IE
  • urine culture
  • imaging of abdomen + pelvis
  • IV ceftriaxone/meropenem if ESBL producing/IV gentamicin or ciprofloxacin if B-lactam allergy
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10
Q

Describe the antibiotic management for septic arthritis?

A
  • start empirical antibiotics as per guidelines
  • IV
  • bactericidal
  • spectrum to cover likely pathogens
  • consider allergies/toxicities/resistance
  • rationalise antibiotics based on culture results and clinical progress
  • 4-6 weeks
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11
Q

What antibiotic treatment is given for pseudomonas aeruginosa infection?

A

IV piperacillin-tazobactam/meropenem/ceftazidime/ ciprofloxacin

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12
Q

What is the effect of periprosthetic joint infections?

A
  • pain
  • reduced mobility
  • draining sinus
  • revision surgery
  • prolonged hospital stay
  • long antibiotic course
  • financial cost
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13
Q

Describe how a biofilm can form in periprosthetic joint infections

A
  • microorganisms can adhere to the surface of the prosthesis and secrete extracellular substances to form a complex glycocalyx matrix
  • microorganisms in biofilm communicate through quorum sensing to divide/evade host defence systems/become resistant to microbial therapy
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14
Q

Describe the presentation of acute PJI

A
  • acute = immature biofilm
  • red, hot, painful joint
  • fever/sepsis
  • prolonged leaking wound post-operatively
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15
Q

Describe the presentation of chronic PJI

A
  • chronic = mature biofilm
  • pain
  • stiffness
  • loosening of prosthesis on X-ray
  • mildly raised inflammatory markers
  • difficult to distinguish from aseptic loosening
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16
Q

Describe the pathogenesis of PJI

A

Early: within 4 weeks of implantation
- virulent pathogens (eg. S. Aureus/ strep/ aerobic gram-negative rods - E. coli, enterobacter spp., klebsiella spp., pseudomonas aeruginosa)
- acute presentation

Delayed 3 months- 3 years after implantation
- low virulence organisms (eg. Coagulase negative staphylococci/cutibacterium acnes)

17
Q

How would you diagnose a PJI infection?

A

Joint aspirate:
- WCC/ % PMN
- microscopy
Blood cultures
Biomarkers (in chronic)

Send multiple samples from separate sites (pus, fluid, synovium, membrane, bone)

Intra-operative samples:
- microbio = at least 2 intraoperative samples with the same microorganisms (unless virulent, then 1 is enough)
- histopatho = at least 5 neutrophils per high power field

18
Q

Describe how you can disrupt a prosthetic joint biofilm

A

Beadmill processing: shaking with glass beads to disrupt the biofilm and dissociate bacteria from biofilm

Sonification of explanted prosthesis: low intensity ultrasound to disintegrate biofilm (then culturing the sonicated fluid)

19
Q

Describe how laboratory antibiotic sensitivity testing occurs

A
  • disc diffusion agar plate with antibiotic impregnated discs
  • zone of inhibition forms around the discs to indicate antibiotic activity
  • zone measured and colony growth compared to note which antibiotic is effective
20
Q

Describe the surgical strategies that can be implemented to treat PJI

A
  • debridement, antibiotics and implantation retention (DAIR) - radical debridement/ thorough joint washout/ exchange of polyethylene liners
  • complete removal of prosthesis: one/two stage exchange
  • amputation
21
Q

Describe antimicrobial management of PJI

A
  • delay until theatre samples are taken unless patient is septic/clinically unstable
  • empirical gram positive and gram negative cover (vancomycin/gentamicin)
  • rationalise to pathogen-directed IV/highly bioavailable antimicrobials (after causative organism found)
  • 6 weeks following removal / 3-6 months following DAIR
  • antibiotic suppressive therapy (long term)
22
Q

Describe the Cierny-Mader classification

A

Anatomical type:
* stage 1 = medullary
* stage 2 = superficial
* stage 3 = localised
* stage 4 = diffuse

Host-physiology: A (no systemic/local compromising factors), B (systemic and/or local compromising factors), C (severely compromised/not surgical candidate)

23
Q

What are the limitations of the Cierny-Mader classification of osteomyelitis?

A
  • does not take duration of symptoms into account
  • placing patients in category C is subjective
24
Q

Describe the Waldvogel classification of osteomyelitis

A

Duration of symptoms: acute (days/weeks), chronic (months/years/persistent infection/low grade infection/sequestrum/fistulous)

Pathogenesis: haematogenous, contiguous

Presence or absence of vascular insufficiency (diabetic foot infection, poor glycaemic control/ischaemic bone and soft tissue/peripheral neuropathy)

25
Q

Describe the virulence factors S. aureus can produce which complicates an osteomyelitis infection

A
  • bacterial adhesins: promote attachment to ECM proteins
  • protein A, toxins, capsular polysaccharides: promote evasion from host defences
  • exotoxins: attack host cells aiding invasion
  • degrading of ECM
  • can form biofilm (escape immune response + resistance to antibiotics)
26
Q

Describe the clinical presentation of osteomyelitis

A
  • wound over open fracture
  • draining sinus/fistula
  • probe-to-bone test
  • no wound but swelling and bone tenderness
  • fever/rigors/sepsis
27
Q

How is osteomyelitis diagnosed?

A
  • blood cultures
  • image guided bone biopsy
  • micrbiology (aerobic and anaerobic culture)
  • histopathology (at least 5 neutrophils per high power field, presence of gramulomas - consider mycobacterial)
  • CRP/ESR
  • X rays for bone changea
  • MRI
28
Q

Describe acute contiguous osteomyelitis sources of infection + causative pathogens

A

Without vascular insufficiency:
- puncture wounds through footwear = pseudomonas aeruginosa
- bites = anaerobes/ strep/ eikenella corrodens/ pasteurella multocida
- dental infections = anaerobes/ strep

With vascular insufficiency:
- diabetic foot infection
- acute infection usually monomicrobial = S. aureus/ B-haemolytic strep
- chronic infections usually polymicrobial = enterococci, enterobacteriaeceae, P. Aeruginosa

29
Q

What are the common sites of infection for acute haematogenous osteomyelitis

A

Adults = vertebral bodies
Children = growing ends of long bones (metaphyses)

30
Q

List the common causative microorganisms of acute haematogenous osteomyelitis and the groups affected

A
  • neonates: group B strep/ S. aureus/ E.coli
  • children <5: S.aureus/ kingella kingae/ group A strep/ H.influenzae/ S.pneumoniae
  • children >5: S.aureus/ Group A strep
  • adults: S. aureus
  • elderly: S. aureus/ gram negative rods
  • IV drug users: S. aureus/ P.aeruginosa/ candida
  • sickle cell: S. aureus/ salmonella
  • IV devices/lines: S. aureus/candida
31
Q

Describe the clinical presentation of native vertebral osteomyelitis

A
  • back pain/ fever/ raised inflammatory markers
  • bloodstream infection/ IE
  • fever + new neurological symptoms
  • usually caused by haematogenous seeding of adjacent disc space
32
Q

Describe the microorganisms responsible for native vertebral osteomyelitis

A
  • most often S. aureus
  • elderly can involve urinary tract (gram-negative rods)
  • consider MTB if patient from endemic area/risk factors
  • consider brucella/fungal infection if patient from endemic area
33
Q

Describe how diagnosis of native vertebral osteomyelitis can be made

A
  • MRI spine
  • blood cultures
  • biopsy if negative blood cultures
  • delay antibiotics until diagnosis made (unless sepsis)
34
Q

Describe the possible treatments for native vertebral osteomyelitis

A

Empirical antibiotics (cover S. aureus./strep/aerobic gram negative rods):
- flucloxacillin + gentamicin
- fluycloxacillin + ciprofloxacin
- ceftriaxone + vancomycin

Surgery if:
- progressive neurological deficit
- progressive deformity
- spinal instability

35
Q

How is antibiotic management selected for diabetic foot infections?

A
  • clinical severity of infection
  • local guidelines/epidemiology
  • previous positive microbiology
  • MRSA status
  • comorbidities eg. Renal failure, type 2 diabetes
  • allergy
  • drug interactions eg. Quinolones + doxycycline with iron
  • 6 weeks +
36
Q

What are the challenges with antibiotic management of diabetic foot infections?

A
  • sub-optimal sampling
  • prior antibiotics
  • biofilm
  • polymicrobial infection

MBChB3 (100 decks)

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