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MSK > Osteomyelitis > Flashcards

Osteomyelitis Flashcards

1
Q

why has the incidence of chronic osteomyelitis increased?

A

increased prevalence of predisposing conditions eg DM and peripheral vascular disease

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2
Q

What is the age distribution of osteomyelitis?

A

bimodal - children and adolescents and then the elderly from DM/PVD/arthroplasties

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3
Q

Give examples of where direct inoculation of the bone can occur

A

trauma

surgery

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4
Q

What is direct inoculation?

A

Where the body part is open and the bacteria enter the bone from the environment or the skin

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5
Q

What is contiguous spread of infection to bone?

A

spread of infection from adjacent soft tissues and joints

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6
Q

What are the risk factors for contiguous spread?

A

DM
chronic ulcers
vascular disease
arthroplasty

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7
Q

What is haematogenous seeding?

A

transient bacteraemia

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8
Q

In children which bones are most affected by haematogenous seeding and why?

A

the long bones as the metaphysis has a good blood supply in childhood

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9
Q

In adults which bones are most affected by haematogenous spread?

A

vertebrae and clavicle

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10
Q

Is haematogenous spread polymicrobial or monomicrobial

A

monomicrobial

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11
Q

What are the host factors that affect osteomyelitis formation?

A

behavioural factors
vascular supply
pre-existing bone/joint problem
immune deficiency

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12
Q

give examples of host vascular supply factors that affect development of osteomyelitis

A

arterial disease
DM
sickle cell disease

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13
Q

Which bones are affected by osteomyelitis in IVDUs?

A

clavicle and pelvis

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14
Q

Give examples of people with risk factors for bacteraemia

A 
central lines 
dialysis 
sickle cell disease 
urethral catheterisation 
UTI
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15
Q

What factors in the metaphysis lead to more likely infections in the bone?

A
  • blood flow is slower
  • endothelial basement membranes are absent
  • The capillaries lack or have inactive phagocytic lining cells
  • High blood flow in developing bones in Children
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16
Q

Why are the vertebra more likely to be infected in elderly people?

A

With age the vertebrae become more vascular, making bacterial seeding of the vertebral endplate more likely

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17
Q

How do infections spread from the urethra and bladder and prostate to the vertebrae?

A

lumbar vertebral veins communicate with those of the pelvis by valveless anastamoses - retrograde flow through these vessels can spread the infection from the pelvis to the vertebrae

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18
Q

How does coagulase make a bacterium more virulent?

A

Coagulaseis aproteinenzyme produced by severalmicroorganisms that enables the conversion offibrinogen intofibrin.
The fibrin clot may protect the bacterium from phagocytosis and isolate it from other defenses of the host.

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19
Q

what factor of pathogens make them more likely to cause infection in the bone?

A

surface components for adhesion to matrix molecules

20
Q

Which bacteria cause osteomyelitis?

A 
S. aureus 
CNS 
G- bacilli 
streptococci, 
enterococci, 
anaerobes, 
fungi, 
mycobacteria eg TB
21
Q

Which bacterium causes osteomyelitis in sickle cell disease?

A

Salmonella

22
Q

What are the chronic histological changes seen with osteomyleitis?

A

necrotic bone seen as an island = sequestra
new bone formation = involucrum
multinucleated giant cells
neutrophils and exudates from neutrophils
lymphocytes
histiocytes

23
Q

How do the sequestra and the involucrum form?

A
  1. inflammatory exudate in the marrow leads to increased intramedullary pressure
  2. exudate extends into the bone cortex
  3. rupture through the periosteum
  4. interruption of periosteal blood supply causes necrosis
  5. there are separated pieces of dead bone called sequestra
  6. new bone forms in these areas called involucrum
24
Q

What are the symptoms of osteomylelitis?

A

onset over several days
dull pain at the site of OM
pain may be aggravated my movement

25
Q

What are the signs of osteomyelitis?

A

systemic - fever, rigors, sweats, malaise

local: 
acute OM: 
- tenderness
- warmth
- erythema
- swelling

chronic OM:

  • tenderness, warmth, erythema, swelling
  • draining sinus tract
  • deep ulcers that fail to heal despite treatment
  • non-healing fractures
26
Q

What additional signs may be seen with vertebral OM?

A

epidural and subdural abscesses
meningitis
paravertbral, retropharyngeal, mediastinal, subphrenic, retroperitinoeal and psoas abscesses

27
Q

Septic arthritis can be a manifestation of OM, T or F?

A

true

28
Q

How does OM spread to the joint?

A

infection breaks through the cortex of the bone and discharges pus into the joint

29
Q

How is OM diagnosed?

A

blood tests :

  • FBC - acute gives high WCC, but can be normal if chronic
  • ESR, CRP, but can be normal

XR
MRI

bone biopsy (ie deep biopsy) and send to microbiology 
positive blood cultures
30
Q

what are the XR changes seen with chronic osteomyelitis?

A 
cortical erosion 
periosteal reaction
mixed lucency 
Sclerosis
sequestra 
soft tissue swelling
31
Q

VIP question: How long does it take an XR to show changes in OM?

A

2 weeks

32
Q

How long does it take to show OM on MRI?

A

3-5 days

33
Q

What changes are seen on MRI with OM?

A

bone marrow oedema

and soft tissue inflammation

34
Q

clinically, which radiology scan would be first line for OM and why?

A

XR - as XR is much faster

35
Q

How many specimens at bone biopsy are needed?

A

2

36
Q

what is seen on biopsy in OM?

A

inflammation

osteonecrosis

37
Q

List some differential diagnoses of OM

A 
soft tissue infection eg cellulitis and erysipelas
Charcot joint
avascular necrosis of bone 
gout 
aseptic fracture
bursitis 
malignancy
38
Q

How is OM treated?

A

debridement
hardware placement or removal
initially empirical and then targeted antibiotics

in pts with sickle cell disease, IVDUs and vascular disease need to give a prolonged duration of antibiotics

39
Q

What is the most common causative organism of osteomyelitis?

A

S. aureus

40
Q

Which antibiotics are commonly used for OM?

A

Flucloxacillin and fusidic acid

for 4-6 weeks, starting IV

41
Q

What test is treatment guided by?

A

ESR and CRP

42
Q

What should be done if ESR and CRP fail to respond to antibiotics?

A

re-imaging

43
Q

What investigation is essential in OM due to TB?

A

biopsy

44
Q

What is seen on biopsy in OM caused by TB?

A

caseating granulomata

45
Q

What is the name given to spinal TB and how does it present?

A

Potts disase - presents with chronic low grade back pain

46
Q

What are the differences between normal OM and TB OM?

A 
TB OM has: 
slower onset
Systemic symptoms
Epidemiology different from pyogenic OM
Blood Culture less use
Biopsy essential 
longer treatment - 12 months instead of 4-6 weeks 
XR changes only seen when very advanced ie Potts disease, so MRI may be more useful

MSK (12 decks)

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