MMD I: Week 3 - General Principles for MSK Imaging

Exam 1 Content

What is the #1 terminal course learning objective regarding imaging?

Identify normal radiographic anatomy

T/F: Advanced Imaging Modalities include X-rays, MRI, US, CT, and bone scan.

FALSE. X-rays are not considered an advanced imaging modality.

What is the process of attenuation?

The patient’s tissues absorb part of the X-rays, then the “remnant radiation” hits the receptor to produce an image

X-Rays: Pros and Cons

• Indicated for bone and chest imaging

Pros: Inexpensive, readily available, no preparation required, non-invasive

Cons: Radiation exposure (significant), caution in pregnancy - cannot do on fetus

MRI: Pros and indications

• Indicated for ligament, cartilage, intraosseous abnormalities, and bone tumors

Pros: Multi-plane images, no known health hazards, good contrast in water-density tissue

• Good for LE ST injuries, peripheral, spinal, and nerve root compression and injury,

• Better than CT at soft tissue differentiation

MRI: Cons and contraindications

• Contraindicated with claustrophobia, metal clips/devices, and pacemakers

Cons: More expensive than intro studies, LONG time scans (+motion artifacts), limited availability, bone trauma poorly shown

CT: Pros and indications

• Indicated to visualize complex fracture patterns, better than MRI for cortical bone

Pros: Improved ability to identify subtle and complex pathology, less expensive

What are the “shades of gray” on a CT scan?

• Air = black

• Fat = Gray/black

• Water (ST)= Gray

• Bone = Gray/White

CT: Cons and contraindications

• Condraindication for radiation exposure

Cons: HIGH doses of radiation, hard to differentiate soft tissue

US: Pros and indications

• Indicated for superficial structures - thinner areas

Pros: Real-time observation, fast, cheap, functional, NO CONTRAINDICATIONS

US: Cons and contraindications

• NO CONTRAINDICATIONS - but do consider that risks are not well understood

Cons: Poor modality for metallic objects or bone, cannot go beyond the cortex

• Radiologist training/experience is KEY in diagnostic utility for US

Scintigraphy: Pros and indications

• Indicated to identify bone changes due to fracture, tumor, or infection (indicates ↑ metabolism)

Pros: VERY sensitive, can show stress fx 6-72 hrs from onset (better than radiograph), defines the EXTENT of multifocal lesions

• Normal ↑ in WB surfaces, bladder, bone marrow

Scintigraphy: Cons and contraindications

• Uses radioactive dye

Cons: Does not define the anatomy/mets of lesions, LOW SPECIFICITY

• It will also reveal healed fractures, DJD, or growth plates

• Abnormal ↑ in shafts and non-loading surfaces

Define radiodensity

Property of the tissue regarding ray absorption/attenuation

• Composition and thickness of tissue

Define the radiopaque components and how they show on a radiograph:

• Radiopaque structures are NOT easily penetrated by x-rays (eg. metals)

• They will show lighter/whiter in the radiograph

Define the radiolucent components and how they show on radiograph:

• Radiolucent structures are easily penetrated by x-rays (eg. air)

• They will show lighter/whiter in the radiograph

*think about the fact that there is nothing that would absorb the X-ray, so it shows up black/intact)

Label the following from most radiopaque to most radiolucent:

• Water/ST

• Fat

• Bone

• Metal

• Air

See image

T/F: Depending on the angle of projection in the curved plane, the portion parallel to the image receptor is the thickest

FALSE. The section parallell to the receptor is the thinnest, the perpendicular section is the thickest

T/F: For curved objects, there will be more attenuation observed in the edges

True

T/F: Fractures usually appear as black lines on x-rays

True

For x-rays one view is the same as no view, therefore we need a minimum of 2 views offset by ____

90°

What are the two main pitfalls of image interpretation?

1. Errors of observation

2. Errors of interpretation (failure to link clinical data, over reliance on imaging, 20-40% of reports have errors!)

According to Shelbourne JBJS 2010, what % of ortho specialists touched the involved knee AND had a comparison of the uninvolved site?

ONLY 37% of the 89% ortho specialists that touched the knee had ALSO touched the uninvolved side for comparison

According to Shelbourne JBJS 2010, out of the 89% of ortho specialists that performed a physical exam, how many performed an exam through clothes?

79%

According to Shelbourne JBJS 2010, out of the 11% ortho specialists that DID NOT do a physical exam, what % ordered an MRI anyway?

73%

T/F: The ACR Appropriateness Criteria was designed in the 90s to inform clinicians of which imaging modality is appropriate, and when imaging is indicated

FALSE. The ACR does NOT provide information on WHEN imaging is appropriate

What are the ABCS of radiographic evaluation?

• Alignment

• Bone density

• Cartilage spaces

• Soft tissues

Alignment: What are the components you are examining?

• General skeletal architecture

  • # of bones, size & shape, congenital

• Countours (smooth and continuous)

  • Look for fracture lines, spurs, irregularities, and cortex disruption.

• Relative position (good articulation)

  • Fractures, sublaxation, dislocation [need multiple views!]

T/F: If an edge is round and smooth, it indicates that bone has been there for a long time

True (eg. Os naviculare)

Bone Density: What are the components you are examining?

• General and focal BD (contrast between ST and bone + cortical shell and cancellous center)

  • Loss of contrast means we are losing density

• Localized contrast changes

  • Look for sclerosis (excessive/reactive) or spurs

  • This can happen due to fx, osteomyelitis, OA, or tumors \

• Texture (normal trabecular architecture)

  • Thin, delicate, coarse, lacy, fluffy

What does “sclerosis” mean in radiology terms?

Areas of increased density(↑radiopaque)

Cartilage Space: What are the components you are examining?

• Joint space (normal width/symmetry)

  • ↓ joint spaces, osteophytes + sclerosis, loss of smooth joint surface (contour)

• Subchondral bone (Smooth surface - no irregularity)

  • ↑ sclerosis and erosion

• Epiphyseal plates (normal thickness/position relative to secondary epiphysis)

  • Abnormal thickness, irregular margin

What is wrong with this patient?

Nothing, this is a pediatric radiograph. The lines show epiphyseal plates

Soft tissue: What are the components you are examining?

• Gross musculature contour

  • Wasting, swelling, and calcification

• Joint capsule (normally you CAN’T see it)

  • distended by effusion/hemorrhage, or calcified

• Fat pad sign (not visible OR very thin)

  • Enlarged, displaced, elevated, blurry → indicates trauma nearby

• Periosteal reaction (not visible)

  • Fuzzy, indistinct margin → physiological healing response (like stress injury)

Where can you observe a “sail sing” and what does it indicate?

Disruption in the ANTERIOR fat pad, correlates to:

• Kids: Epicondyle/humeral fracture

• Adults: Radial head fracture

Does an abnormal finding on imaging imply a significant pathological process?

NO, an abnormality on imaging DOES NOT mean it’s significant or symptomatic

What is the most important requirement for the appropriate utilization of imaging?

Quality patient examination

What are the three ways in which harm can be caused with the inappropriate use of imaging?

1. Misinterpretation by providers

2. Misinterpretation by patients

3. Radiation exposure