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a10. MSK (Medical Knowledge) > Bone & Soft TIssue Infections > Flashcards

Bone & Soft TIssue Infections Flashcards

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USMLE® Step 1 flashcards
1
Q

This deck covers:

A

Acute & Chronic Osteomyelitis
Septic Arthritis
TB

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2
Q

What are the risk factors for acute osteomyelitis?

A

Diabetes mellitus
Peripheral vascular disease
Malnutrition
Immunosuppression
Malignancy
Extremes of age
Local factors e.g chronic lymphedema, vasculitis, neuropathy etc.

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3
Q

Who suffers from acute osteomyelitis?

A

Mostly kids, and generally boys with a trauma history

Others:
Adults with another disease:
* DM
* RA
* Immune compromise
* Long-term steroid treatment
* Sickle cell

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4
Q

What are the different sources for infection in acute OM infection?

A
  • Haematogenous: from bacteremia (commonly affects kids & elderly)
  • Non-hematogenous: local spread from trauma (open farcture) & surgery, joint replacement
  • 2ndry to vascular insufficiency
  • Infants: infected umbilical cord
  • Children: boils, tonsilitis, skin abrasions
  • Adults: UTI, arterial lines
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5
Q

What is a common source of infection for OM in the elderly and kids?

A

Haematogenous (bacteremia)

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6
Q

What is the source of acute OM infection in children?

A
  • Boils
  • Tonsilitis
  • Skin abrasions
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7
Q

What is the source of acute OM infection in adults?

A
  • UTI
  • Arterial lines
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8
Q

What is a non-hematogenous source of acute OM infection?

A

Local spread from the contiguous site of infection:
* Trauma (open farcture)
* Bone surgery (ORIF)
* Joint replacements

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9
Q

What is the source of acute OM infection in infants?

A

Umbilical cord infection

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10
Q

What organism is the main cause of OM

A

1) Staph Aureus

It’s the biggest cause in any patient group. However certain groups (e.g. by age, co-morbidity or immunocompromise) are at risk of other specific organisms

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11
Q

What organisms cause acute OM in infants <1yr?

A

1) Staph Aureus
2) Group B Strep
3) E. Coli (most common if under <1month old)

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12
Q

What organisms cause acute OM in older children?

A
  • Staph aureus
    *Strep pyogenes
  • Haemophilus Influenza (immunization sig. reduced)
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13
Q

What organisms cause acute OM in adults?

A
  • Staph aureus
  • Mycobacterium tuberculosis
  • Pseudomonas aeroginosa (esp. secondary to penetrating foot injuries, IVDAs)
  • Coagulase negative staphylococci (prostheses)
  • Propionibacterium spp (prostheses)
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14
Q

What organisms commonly cause acute OM infections in adults, with penetrating foot injuries or IVDAs?

A

Pseudomonas aeroginosa

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15
Q

What organisms commonly cause acute OM infection in pts with prosthesis?

A
  • Coagulase negative staphylococci (prostheses)
  • Propionibacterium spp (prostheses)
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16
Q

What organisms cause OM in diabetics?

A

Staph Aureus
Mixed infection incl. Anaerobes

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17
Q

What organisms cause OM in Sickle Cell patients?

A

Staph Aureus
Salmonella

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18
Q

What organisms cause OM in HIV/AIDS patients?

A

Staph Aureus
Candida

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19
Q

Where in the bone is acute OM likely to arise?

A

The metaphysis of long bones:
* Distal femur
* Proximal tibia
*Proximal humerus

or

Joints with an intra-articular metaphysis e.g. hip/elbow (this can lead to septic arthritis or arise from SA)

20
Q

Describe the pathogenesis of acute OM?

A

The infection starts at the metaphysis of bone
-> Vascular stasis (venous congestion +artehrial thrombosis)
-> Acute inflammation causes an increase in pressure
-> Suppuration
-> Pressure released into joint (medulla, sub-periosteal or into joint)
-> Necrosis of bone (sequestrum)
-> New Bone growth (involucrum)
-> Resolves or Chronic

21
Q

What do we call necrosed bone?

A

Sequestrum

22
Q

What do we call new bone growth?

A

Involucrum

23
Q

How might acute OM present in an infant?

A
  • Failure to thrive
  • +/-drowsy or irritable
  • Decreased range of movement or an odd position
  • Tenderness & swelling over metaphysis

Mostly in the knee

24
Q

What joint does acute OM affect in infants?

A

Knee joint (often multiple sites)

25
Q

How might acute OM present in a child?

A
  • Severe pain
  • Reluctant to move (neighboring joint flexed, no weight bearing, +/- tenderness)
  • fever (swinging pyrexia) and tachycardia
  • Systemic Symptoms e.g. fatigue, malaise & N&V
  • Toxaemia
26
Q

How might acute primary OM present in an Adult?

A

Mostly in the thoracolumbar spine
* backache
* Hx UTI or urological procedure
Esp. in the elderly, diabetic or immunocompromised

27
Q

Which joint/s does acute primary OM commonly affect in adults?

A

Thoracolumbar spine

28
Q

Which of primary or secondary acute OM affects adults more commonly?

A

Secondary acute OM

29
Q

How might acute secondary OM present in an adult?

A

More common
* Post an open fracture or surgery
Mix of organisms

30
Q

What tests could we do to diagnose OM?

A

FBC
Differential WCC
U&Es
3x Blood cultures
MRI
X-ray
Bone biopsy
ESR & CRP

Also Aspiration, US, ISotope bone scan and labelled WC scan
And swabs from site during implantation surgery

31
Q

What would appear on an acute OM Diff. WCC?

A

Neutrophilic Leucocytosis

32
Q

What would appear on an Acute OM X-ray?

A

nothing in first 2 wks
10-20 days you get Early periosteal changes

Then you get late bone necrosis (Sequestrum) and LAte periosteal growth (Involucrum)

33
Q

DDX for Acute OM?

A

Acute Septic Arthrits (more common)
Acute Inflammatory Arthritis
Trauma
Transient Synovitis
Soft Tissue Infection (e.g. erysipelas or Cellulitis)
Rarely sickle cell, rheumatic fever, necrotising fasciitis or Gaucher’s Disease

34
Q

Treatment for Acute OM?

A

Supportive Care
Rest & Splintage
Abx
Surgery

35
Q

Whats included in supportive care for acute OM?

A

Fluids
Analgesia

36
Q

What Abx are used for Acute OM?

A

Empircally Flucloxacillin & Benzylpenicillin

4-6 wks on an IV/oral switch at 7-10 days

37
Q

When would we perform surgery for Acute OM?

A

Refractory to Abx after 48 hours
Debride dead/infected tissue
Drain abscess
Aspirate abscess for culture

38
Q

What surgical treatments do we have for Acute OM?

A

Drainage
Lavage
Infected joint replacement

39
Q

Complications of Acute OM?

A

Think spread of infection:
- Septicaemia
- Metastatic infection
- Septic Arthritis

Think damage to bone:
- Pathological fracture
- Growth abnormality

Also Chronic OM

40
Q

How can Chronic OM originate?

A

Acute OM
De-novo (IVDA or ops in the elderly, immunosuppressed or diabetic)
repeated breakdown of ‘healed’ wounds

41
Q

What organisms cause Chronic OM?

A

1) Staph Aureus
2) E. Coli
3) Strep Pyogenes
4) Proteus
5) TB

42
Q

Complications of Chronic OM?

A

Metastatic Infection
Pathological fracture
Abnormal growth and deformity
Chronically discharging sinuses
SCC

43
Q

Treatment for Chronic OM?

A

Long Term Abx
Surgery
~Amputation

44
Q

What is the main causative organisms of Acute OM in adults?

A

Staph Aureus

Kids can get H influenzae and strep pyogenes

45
Q

Causative organisms of Acute OM in adults?

A

Adults can get:
- Coagulase -ve staph from prosthetics
- TB
- Pseudomonas from IVDA & Penetrating foot injury

Staph Aureus is still the main cause

46
Q

What is the source of acute OM infection in adults?

A
  • UTI
  • Arterial lines

a10. MSK (Medical Knowledge) (37 decks)

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