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MSK: Infection Flashcards

1
Q

How long will radiographs appear normal after the start of osteomyelitis?

A

7-10 days

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2
Q

What is the most likely location for osteomyelitis?

A

Pediatric: Long bone metaphyses (more likely to be hematogenous spread)
Adult: Foot (more likely to be direct spread)

Note: Hematogenous spread is classic in IV drug users (discitis/osteomyelitis).

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3
Q

Is it more common to have osteomyelitis or a septic joint?

A

Pediatrics: Osteomyelitis more common

Adults: Septic joints more common

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4
Q

What are the classic radiographic imaging features of osteomyelitis?

A
  • Bone destruction
  • Periosteal new bone formation

Note: Osteomyelitis can look like anything and occur at any age.

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5
Q

When should you consider a foot radiograph suspicious for osteomyelitis if there is clinical suspicion (e.g. foot ulcer in a diabetic)?

A

If there are bone erosions and/or periosteal reaction

Note: If negative, then recommend MRI.

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6
Q

Spinal osteomyelitis is classically associated with what pt demographic?

A

IV drug users

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7
Q

Osteomyelitis in the spine with kyphosis

A

Think tuberculosis

Note: This is a “Gibbus deformity.”

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8
Q

Unilateral sacroiliac joint osteomyelitis…

A

Think IV drug user

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9
Q

Psoas muscle abscess…

A

Think tuberculosis

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10
Q

Osteomyelitis sequestrum

A

A piece of necrotic bone surrounded by granulation tissue

Note: This acts as a nidus for chronic infection.

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11
Q

Osteomyelitis involucrum

A

A thick sheath of periosteal bone around a sequestrum

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12
Q

Osteomyelitis cloaca

A

A defect in the periosteum caused by infection

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13
Q

Osteomyelitis sinus tract

A

A channel from the infected bone to the skin (lined with granulation tissue)

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14
Q
A

Chronic osteomyelitis with sequestrum formation (arrow) surrounded by periosteal involucrum (arrowhead)

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15
Q
A

Brodies abscess (subacute osteomyelitis with expansile new bone formation)

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16
Q

Draining sinus tracts from osteomyelitis are at increased risk for…

A

Squamous cell carcinoma

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17
Q
A

Active chronic osteomyelitis

Note: Sequestrum formation with surrounding abscess.

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18
Q

Definition of chronic osteomyelitis

A

Osteomyelitis lasting at least 6 weeks

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19
Q

Arrowhead

A

Cloaca

Note: The central bone focus within the abscess is the sequestrum.

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20
Q

Arrows

A

Involucrum (thick sheath of periosteal bone surrounding an osteomyelitis abscess cavity)

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21
Q

What is the most specific sign of active chronic osteomyelitis?

A

The presence of a sequestrum

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22
Q

What MRI imaging finding lets you know that osteomyelitis has healed?

A

Return of normal fatty marrow signal

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23
Q

What is the most common location for hematogenous seeding of osteomyelitis in long bones?

A

Metaphyses (most blood flow)

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24
Q

When can metaphyseal osteomyelitis spread hematonegously to the epiphysis?

A

Before 18 months of age

Note: After ~2 years the trans-physeal vessels are closed and the growth plate stops hematogenous spread to the epiphysis (though direct spread can still occur). After the growth plates fuse, this barrier is gone and infection can again spread to the epiphysis.

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25
What are the classic MRI findings of osteomyelitis?
- High STIR signal in bone adjacent to an ulcer/cellulitis (more sensitive) - Corresponding low T1 signal (more specific)
26
Osteomyelitis Note: This is the "ghost sign" where the infected bone disappears on T1 (due to ill-defined margins), but then reappears on T2 or post-contrast sequences.
27
What is usually the first location to be seeded is discitis/osteomyelitis?
A vertebral endplate
28
Discitis/osteomyelitis (later findings) Note: T1 dark/T2 bright vertebral marrow and post contrast enhancement.
29
Early imaging findings in discitis/osteomyelitis
- Paraspinal and epidural inflammation - T2 bright disc signal and disc enhancement Note: These are only seen on MRI early on.
30
Late imaging findings in discitis/osteomyelitis
- Irregular endplate desctruction and disc space narrowing (radiographs) - T1 dark and T2 bright vertebral body marrow signal (MRI)
31
Is a WBC scan or gallium scan better for discitis/osteomyelitis?
Gallium
32
What is the most common pathogen in discitis/osteomyelitis?
Staph aureus (think IV drug user)
33
What lab abnormalities are almost always present (80%) in the setting of discitis/osteomyelitis?
Elevated ESR/CRP
34
Which pts are more prone to paraspinal/epidural abscesses in the setting of discitis/osteomyelitis?
- HIV pts - Poorly controlled diabetics
35
discitis/osteomyelitis with paraspinal abscess formation
36
what are the imaging features of a paraspinal/epidural abscess?
- T1 dark and T2 bright - Peripheral enhancement - Restricted diffusion
37
Elevated ESR/CRP
Epidural abscess
38
Epidural abscess in the setting of discitis/osteomyelitis
39
Young kid (< 4 y/o) with lower back pain following an upper respiratory infection
Think discitis Note: Unlike adults, young kids can get isolated discitis.
40
3 y/o with history of recent upper respiratory infection
Isolated discitis Note: Young kids have a direct blood supply to the intervertebral disc, allowing them to get isolated discitis (which virtually never happens in adults).
41
Vertebral body osteomyelitis with relative sparing of the disc space...
Think Potts disease (tuberculous osteomyelitis of the spine) or Brucellosis (if it is an Amish person chugging unpasteurized milk)
42
Think Potts disease (tuberculous osteomyelitis of the spine) or Brucellosis (especially if it is an Amish person who drinks unpasteurized milk) Note: Relative sparing of the disc space.
43
Think Potts disease (tuberculous osteomyelitis of the spine) Note: Involvement of multiple vertebrae with skipped vertebrae and paraspinal abscesses.
44
Partially calcified psoas abscess, think tuberculosis
45
7 y/o F
Think tuberculous dactylitis (AKA spina ventosa) Note: Diaphyseal expansile lytic lesion in the tubular bones of the hands/feet with soft tissue swelling in a pediatric pt.
46
Differential for Potts disease (tuberculous osteomyelitis of the spine)
- Neurogenic (Charcot) spine - Lymphoma - Metastases
47
How does a neurogenic spine usually differ from Potts disease?
Neurogenic (Charcot) spine usually involves both the anterior and posterior vertebral body cortex and usually has increased density
48
How does spinal lymphoma usually differ from Potts disease?
Lymphoma usually has homogenous enhancement
49
How do spinal metastases usually differ from Potts disease?
Metastases usually involve the posterior elements (e.g. pedicles)
50
Knee joint rice bodies Note: Rice bodies are seen in end stage rheumatoid arthritis and tuberculous infections.
51
Which joints are most commonly involved in a septic joint?
- Shoulder - Hip - Knee Note: Septic joints are usually larger joints with abundant blood supply to the metaphyses.
52
Which septic joints are more common in IV drug users?
- Sacroiliac joint - Sternoclavicular joint
53
Risk factors for septic joint
- Old age - AIDS - Rheumatoid arthritis - Prosthetic joints
54
Pneumoarthrogram sign
If you can demonstrate air within a joint, you can exclude a joint effusion (which excludes septic joint)
55
Risk factors for necrotizing fasciitis
- HIV - Transplant pts - Diabetics - Alcoholics
56
What is the most common pathogen in necrotizing fasciitis?
Polymicrobial Note: Second most common is Group A strep.
57
Think necrotizing fasciitis Note: Extensive, streaky gas in the soft tissues.
58
Think necrotizing fasciitis
59
Think necrotizing fasciitis Note: Gas tracking along fascial planes (arrows) and fascial edema (arrowheads).
60
Fournier gangrene
61
T2 fat-sat and T1 postcontrast
Think necrotizing fasciitis Note: Fascial edema and enhancement (arrowheads).

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