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11. CP - Diseases of the musculoskeletal system > (56) Bone and joint infections > Flashcards

(56) Bone and joint infections Flashcards

1
Q

What is infection of bone known as?

A

Osteomyelitis

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2
Q

Give 3 features of osteomyelitis?

A
  • heterogeneous disease (diff pathogens, diff sites, diff clinical contexts)
  • difficult to diagnose in some cases
  • difficult to treat
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3
Q

State 3 methods of pathogenesis of osteomyelitis

A
  • haematogenous
  • contiguous-focus
  • direct inoculation
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4
Q

Describe how haematogenous spread may cause osteomyelitis

A

Bacteria shed into the blood stream from other infection eg. endocarditis, and then seeds bone - infants and children

vertebral body osteomyelitis usually haematogenous

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5
Q

What does contiguous-focus cause of osteomyelitis mean?

A

Spread from adjacent area of infection (focus of infection next to bone, can spread into bone)

eg. diabetic foot - deep infection around ulcers spreads to bone

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6
Q

How can osteomyelitis be caused by direct inoculation?

A

Through trauma or surgery

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7
Q

State the 4 stages of classification of osteomyelitis

A
  • stage I medullary
  • stage II superficial
  • stage III localised
  • stage IV diffuse
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8
Q

What does stage I medullary osteomyelitis mean?

A

Necrosis of medullary contents/endosteal surface - confined to medulla of bone - haematogenous

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9
Q

What does stage II superficial osteomyelitis mean?

A

Necrosis limited to exposure surface, periosteum disrupted - contiguous - eg. diabetic foot, sacral pressure sore infection in elderly

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10
Q

What does stage III localised osteomyelitis mean?

A

Full thickness cortical sequestration, stable before and after debridement (trauma/stage I or II evolving)

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11
Q

What does stage IV diffuse osteomyelitis mean?

A

Extensive, unstable bone

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12
Q

What is debridement?

A

The process of removing dead (necrotic) tissue or foreign material from and around a wound to expose healthy tissue

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13
Q

If infected bone is necrotic and lacks blood supply, how does this cause trouble with treatment?

A

Can’t deliver antibiotics are they are delivered via the blood stream, need surgery to get rid of the infected bone

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14
Q

How does osteomyelitis present clinically?

A
  • pain that is localised, constant and progressing (and nocturnal)
  • soft tissue swelling
  • erythema
  • warmth
  • localised tenderness
  • reduced movement of affected limb
  • systemic flu-like symptoms (fever, chills, night sweats, rigor)
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15
Q

Clinical presentation of osteomyelitis varies with which factors?

A
  • age
  • type of infecting organism
  • location of infection
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16
Q

What is the most common causative organism of osteomyelitis?

A

Staphylococcus aureus (at least 60%)

  • especially haematogenous
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17
Q

Give some other causative organisms of osteomyelitis (other than staph. aureus)

A
  • streptococci (group A and B)
  • enterococci
  • gram negative bacilli
  • anaerobes
  • mycobacterium tuberculosis, brucella spp.
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18
Q

Give some examples of gram negative bacilli that may cause osteomyelitis

A
  • slamonella spp.
  • klebsiella spp.
  • pseudomonas aeruginosa

(in premature babies, IVDU, sickle cell disease)

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19
Q

Myco. TB can cause indolent osteomyelitis, particularly where?

A

In the vertebral bodies

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20
Q

What is the gold standard test for osteomyelitis?

A

Cultures and histology of bone biopsy/needle aspirate (needle into bone or area of adjacent pus)

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21
Q

Other than culture and histology, what are other tests used in osteomyelitis diagnosis?

A
  • superficial swabs
  • leukocytosis (not diagnostic)
  • C-reacitve protein (usually raised, monitor response to therapy)
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22
Q

Why are superficial swabs not very useful in diagnosing osteomyelitis?

A

Limited value in contiguous-focus infections as will grow lots of different bacteria, including normal bacteria on skin etc.

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23
Q

What is the therapy for osteomyelitis?

A

Antimicrobials +/- surgery depending on site/stage

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24
Q

What type of antimicrobial treatment should you avoid in osteomyelitis?

A

Avoid empirical antimicrobial therapy if possible - give directed antimicrobial therapy guided by causative organism

25
Q

Antimicrobials should be administered by which route initially in osteomyelitis?

A

Intravenous - this ensures compliance and optimal bone levels - penetration into bone is low orally

26
Q

Which antibiotics achieve acceptable levels in bone and so can be used in osteomyelitis?

A
  • clindamycin
  • ciprofloxacin
  • vancomycin
  • B-lactams
  • gentamicin
27
Q

What is the antimicrobial of choice for S. aureus OM in patients who are not penicillin-allergic?

A

Flucloxacillin IV

28
Q

Vancomycin is often used for OM when?

A

When the patient has a penicillin allergy

29
Q

Vancomycin is effective against which type of bacteria?

A

Gram-positive (staphylococci, streptococci, enterococci - has to be given IV)

30
Q

Gentamicin is effective against which type of bacteria?

A

Gram-negative

31
Q

What is septic (infective) arthritis?

A

Inflammatory reaction in joint space (arthritis) caused by infection - result from direct invasion of the joint

32
Q

How is septic arthritis classified?

A
  • native (natural) joint infection

- prosthetic (artificial) joint infection (early/late)

33
Q

Describe the pathogenesis in native joint infection

A
  • organisms enter a joint via the blood (haematogenous) or trauma (surgery or injection)
  • cartilage erosion causes joint space narrowing/impaired function
34
Q

What about native joint infection causes impaired function?

A

Narrowing of the joint space caused by cartilage erosion by the infection

35
Q

What are the predisposing factors of native joint infection?

A
  • rheumatoid arthritis
  • trauma
  • intravenous drug use
  • immunosuppressive disease
36
Q

Is native joint infection associated with mortality?

A

Low mortality condition but with significant dysfunction - unless it causes severe sepsis and then it is associated with mortality

37
Q

Describe the pathogenesis of prosthetic joint infection

A
  • organisms enter a joint via the blood (haematogenous), during surgery or following wound infection
  • joint prosthesis and cement provide a surface for bacterial attachment
  • polymorph infiltration results in tissue damage instability of the prosthesis
38
Q

How do polymorphs cause damage to joint and instability in prosthetic joint infection?

A

Polymorphs try to phagocytose the bacteria but cannot - so they give out lytic enzymes which cause damage to the joint

39
Q

What are the predisposing factors to prosthetic joint infection?

A
  • prior surgery at site of prosthesis
  • rheumatoid arthritis
  • corticosteroid therapy
  • diabetes mellitus
  • poor nutritional status
  • obesity
  • extremely advanced age
40
Q

What are the clinical features of septic arthritis?

A
  • joint pain, swelling, tenderness, redness, and limitation of movement
  • systemic upsets like fever, chills, night sweats
41
Q

Symptoms of septic arthritis depend on what?

A

Duration of symptoms is variable and influences by site of infection, type of joint (native vs. prosthetic) and causative organisms

42
Q

What are the causative bacteria of native joint infections?

A
  • staph. aureus
  • strep. A/B/C/G
  • haemophilus influenzae
  • gram neg bacilli
  • neisseria gonorrhoea
  • neisseria meningitidis
  • anaerobes
  • mycobacteria
43
Q

What are the causative bacteria in prosthetic joint infections?

A
  • staph. aureus
  • coagulase negative strep (CoNS)
  • step A/B/C/G
  • enterococci
  • gram neg bacilli
  • corynebacteria
  • propionibacteria
    etc
44
Q

Other than bacteria, what else can cause septic arthritis?

A
  • fungi eg. Candida spp.

- viruses eg. parovirus B19, rubella virus, mumps virus (usually self-limiting)

45
Q

How is a joint aspirate examined in diagnostics?

A
  • total white cell count
  • differential WCC
  • gram stain
  • crystal examination
  • culture
  • PCR
46
Q

WCC is normally what in infection?

A

Over 40,000/mm3 during infection - but raised in lots of things, not just septic arthritis

47
Q

What would a differential WCC show in infection?

A

Over 75% polymorphs during infection

48
Q

Why is gram stain not a very good test for septic arthritis?

A

Not very reliable (35-65% positive)

49
Q

What does doing a culture in septic arthritis allow?

A

Allows change from empirical therapy to direct therapy

50
Q

Describe the therapy for native joint infection

A
  • removal of purulent material (joint drainage/washout)
  • empirical IV antimicrobial therapy if required
  • direct IV antimicrobial therapy depending on causative organism and susceptibility
51
Q

How long is a native joint infection treated for?

A

2-4 weeks

52
Q

Which antimicrobial is used for native septic arthritis caused by S. aureus?

A

Flucloxacillin

53
Q

What should be done before empirical therapy is started for septic arthritis?

A

Take microbiology samples

54
Q

Describe the therapy for prosthetic joint infections

A
  • removal of implant or replacement of some elements, washout
  • empirical IV antimicrobial therapy if required
  • directed IV antimicrobial therapy depending on causative organism and susceptibility
55
Q

How long is a prosthetic joint infection treated for?

A

6 weeks (more complicated - so longer treatment)

NB. oral switch (OVIVA)

56
Q

Which antimicrobials would you use for staph. aureus prosthetic joint infection?

A

Flucloxacillin plus rifampicin (never give rifampicin on its own to treat S. aureus as often develops resistance)

57
Q

Which antimicrobials would you use to treat CoNS prosthetic joint infection?

A

Vancomycin IV plus rifampicin

58
Q

What is the most common bacterial pathogen causing septic arthritis?

A

Staphylococcus aureus

11. CP - Diseases of the musculoskeletal system (4 decks)

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