High Yield Overview
Musculoskeletal Ultrasound
Real-Time Dynamic Imaging
7-15MHzMSK Probe Frequency
0Ionizing Radiation
Real-timeDynamic Assessment
93%Sensitivity for Full-Thickness RC Tears
Tissue Echogenicity
Hyperechoic (Bright)
PatternBone cortex, calcification, fibrous tissue
TreatmentStrong reflection
Isoechoic
PatternSimilar to surrounding tissue
TreatmentReference
Hypoechoic (Dark)
PatternMuscle, some fluid, pathology
TreatmentPartial transmission
Anechoic (Black)
PatternSimple fluid, blood vessels
TreatmentComplete transmission
Acoustic Shadow
PatternBehind bone, calcification
TreatmentNo transmission
Critical Must-Knows
- Frequency determines resolution: Higher frequency = better resolution but less penetration.
- Anisotropy: Tendons appear artifactually hypoechoic when beam is not perpendicular.
- Normal tendon: Fibrillar hyperechoic pattern with parallel echogenic lines.
- Effusion: Anechoic or hypoechoic fluid distending joint capsule/bursa.
- Dynamic assessment: Can stress structures and assess in real-time (snap, subluxation).
Examiner's Pearls
- "Always compare with contralateral side for normal reference.
- "Anisotropy artifact mimics pathology - adjust probe angle to confirm.
- "Rotator cuff US has 90%+ accuracy for full-thickness tears in experienced hands.
- "US-guided injection improves accuracy compared to landmark technique.
- "Doppler shows increased vascularity in tendinopathy and inflammation.
Clinical Imaging
Imaging Gallery
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Operator Dependence
Ultrasound accuracy is highly operator-dependent. Systematic technique, knowledge of anatomy, and experience are essential. In expert hands, MSK ultrasound approaches MRI accuracy for many soft tissue conditions, but results vary significantly with operator skill.
Physics Fundamentals
Sound Wave Principles
- Frequency: Number of cycles per second (Hz). MSK uses 7-15 MHz (high frequency).
- Wavelength: Distance between wave peaks. Shorter wavelength = better resolution.
- Velocity: Speed of sound in tissue (approximately 1540 m/s in soft tissue).
Resolution vs Penetration Trade-off
Frequency Selection
| Frequency | Resolution | Penetration | Application |
|---|---|---|---|
| 5-7 MHz | Lower | Deeper (10-15cm) | Hip, deep structures |
| 7-12 MHz | Medium | Medium (5-7cm) | Shoulder, knee, ankle |
| 12-15 MHz | Higher | Superficial (3-4cm) | Hand, foot, superficial tendons |
| 15-18 MHz | Highest | Very superficial | Finger tendons, nerves |
Tissue Interactions
Reflection
Sound bounces back at tissue interfaces. Greater impedance difference = stronger reflection. Creates the image.
Transmission
Sound passes through tissue. Fluids transmit well (posterior enhancement). Bone blocks transmission (shadowing).
Refraction
Sound bends at angled interfaces. Can cause positional errors.
Attenuation
Sound energy decreases with depth. Higher frequency = more attenuation.
Equipment & Technique
Probe Selection
Ultrasound Probes for MSK
| Probe Type | Frequency | Best For |
|---|---|---|
| Linear High-Frequency | 10-15 MHz | Superficial tendons, nerves, small joints |
| Linear Standard | 7-12 MHz | Shoulder, knee, ankle, medium-depth structures |
| Curvilinear | 3-5 MHz | Hip, deep muscles, obese patients |
| Hockey Stick | 12-15 MHz | Fingers, toes, small superficial structures |
Scanning Technique
Mnemonic
CALMSystematic MSK Ultrasound
C
Compare
Always scan contralateral side for comparison
A
Anisotropy
Adjust probe angle to avoid false hypoechogenicity
L
Long and Short
Scan in both longitudinal and transverse planes
M
Move
Dynamic assessment - move the joint, stress the structure
Memory Hook:Stay CALM and scan systematically
Key Technical Points
- Gel: Adequate coupling gel eliminates air interface
- Probe pressure: Light pressure for superficial structures, firm for deep
- Gain: Adjust so fluid is black, normal tissue is grey
- Depth: Set to visualize structure of interest plus some background
- Focus: Position at level of structure of interest
Anisotropy
Understanding Anisotropy
Anisotropy is the most important artifact in MSK ultrasound. Tendons have highly organized parallel collagen fibers that reflect sound optimally when the beam is perpendicular.
Perpendicular Beam
- Sound reflects back to probe
- Tendon appears normally hyperechoic
- Fibrillar pattern visible
- TRUE appearance
Oblique Beam
- Sound reflects away from probe
- Tendon appears artifactually hypoechoic
- May mimic tear or tendinopathy
- FALSE appearance (artifact)
Avoiding Anisotropy Errors
- Heel-toe maneuver: Rock probe to find perpendicular angle
- Dynamic assessment: Real pathology stays abnormal, anisotropy corrects
- Contralateral comparison: If both sides look the same, likely technique
- Orthogonal views: Pathology visible in multiple planes
Normal Appearances
Tissue Echogenicity
Normal Tissue Appearances
| Tissue | Echogenicity | Pattern | Notes |
|---|---|---|---|
| Tendon | Hyperechoic | Fibrillar (parallel lines) | Affected by anisotropy |
| Muscle | Hypoechoic | Pennate (feather-like) | Hyperechoic fascia/perimysium |
| Nerve | Hypoechoic | Fascicular (honeycomb in short axis) | Less anisotropic than tendon |
| Ligament | Hyperechoic | Compact fibrillar | More compact than tendon |
| Cartilage | Hypoechoic | Homogeneous | Thin layer over bone |
| Bone | Hyperechoic | Bright line + shadow | Only cortex visible |
| Fluid | Anechoic | Black, compressible | Posterior enhancement |
Important Artifacts
Posterior Acoustic Enhancement
Brightness deep to fluid-filled structures (cysts, vessels). Confirms fluid content.
Acoustic Shadowing
Dark area deep to highly reflective structures (bone, calcification). Confirms dense material.
Reverberation
Multiple parallel lines deep to strong reflector or superficial to needle. Common with metal.
Edge Artifact
Shadow at curved surfaces (vessel edges, cyst margins). Normal finding.
Orthopaedic Applications
Tendon Pathology
Full-Thickness Tear:
- Complete discontinuity of tendon fibers
- Hypoechoic/anechoic gap
- Retraction of torn ends
- Non-visualization of tendon
Partial-Thickness Tear:
- Focal hypoechoic defect not extending full thickness
- Surface irregularity (articular or bursal)
- Thinning of tendon
Joint Assessment
Effusion
- Anechoic or hypoechoic fluid
- Distends joint capsule
- Compressible with probe pressure
- Compare to normal side
Common locations: Knee (suprapatellar), hip (anterior), shoulder (posterior), ankle
Synovitis
- Thickened synovium (hypoechoic)
- Non-compressible (unlike fluid)
- Increased Doppler signal
- May have frond-like projections
Seen in: RA, inflammatory arthritis, infection
Regional Applications
Regional Ultrasound Applications
| Region | Key Structures | Common Pathology |
|---|---|---|
| Shoulder | Rotator cuff, biceps, bursa | RC tears, biceps tendinopathy, bursitis |
| Elbow | Common extensor/flexor, ulnar nerve | Lateral epicondylitis, cubital tunnel |
| Wrist/Hand | Tendons, carpal tunnel, TFCC | DeQuervain, CTS, trigger finger |
| Hip | Labrum (limited), tendons, bursae | Trochanteric bursitis, effusion (children) |
| Knee | Quadriceps, patellar tendon, collaterals | Tendinopathy, Bakers cyst, MCL injury |
| Ankle/Foot | Achilles, peroneals, plantar fascia | Achilles pathology, plantar fasciitis |
US-Guided Procedures
Advantages of US guidance:
- Real-time needle visualization
- Improved accuracy vs landmark technique
- Avoid vessels and nerves
- Confirm medication delivery
Common procedures:
- Joint injection (shoulder, hip, knee)
- Bursa injection (subacromial, trochanteric)
- Tendon sheath injection (DeQuervain, trigger finger)
- Aspiration (cyst, effusion, abscess)
- Calcific barbotage
Doppler Imaging
Doppler Modes
Color Doppler
- Shows flow direction and velocity
- Red toward probe, blue away (usually)
- Useful for identifying vessels
- Assessing vascularity in masses/inflammation
Power Doppler
- More sensitive to slow flow
- No directional information
- Better for small vessel detection
- Useful for synovitis, tendinopathy vascularity
Clinical Applications
- Inflammation: Increased Doppler signal in synovitis, tendinopathy
- Tumor: Vascularity assessment (malignancy often hypervascular)
- Infection: Hyperemia in cellulitis, abscess rim
- Post-treatment: Response monitoring (Doppler should decrease)
US vs MRI
Ultrasound vs MRI for MSK
| Feature | Ultrasound | MRI |
|---|---|---|
| Cost | Lower | Higher |
| Availability | High, portable | Limited, fixed |
| Radiation | None | None |
| Dynamic assessment | Excellent | Limited |
| Bone marrow | Cannot assess | Excellent |
| Deep structures | Limited | Excellent |
| Operator dependence | High | Lower |
| Interventional guidance | Real-time | Possible but complex |
| Cartilage | Limited (surface only) | Excellent |
| Rotator cuff tears | 90%+ accuracy (expert) | 95%+ accuracy |
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
Ultrasound Physics Viva
EXAMINER
"Explain the concept of anisotropy and why it's important in musculoskeletal ultrasound."
EXCEPTIONAL ANSWER
Anisotropy is an artifact that occurs because tendons have highly organized parallel collagen fibers that reflect ultrasound optimally only when the beam is perpendicular to the fibers. When the probe is angled obliquely, sound reflects away from the transducer rather than back to it, causing the tendon to appear artifactually hypoechoic or even anechoic - mimicking pathology such as a tear or tendinopathy. This is the most common pitfall in MSK ultrasound. To avoid this error, I always use the heel-toe maneuver to find the optimal perpendicular angle, confirm findings in multiple planes, perform dynamic assessment, and compare with the contralateral side. True pathology will appear abnormal regardless of probe angle, while anisotropy artifact will correct when the probe is properly aligned.
KEY POINTS TO SCORE
Anisotropy = artifact from oblique beam angle
Tendons appear falsely hypoechoic when beam not perpendicular
Heel-toe maneuver to find optimal angle
Compare to other side and use dynamic assessment
COMMON TRAPS
✗Not mentioning how to distinguish from real pathology
✗Forgetting that this affects tendons more than other tissues
✗Not explaining the underlying physics
LIKELY FOLLOW-UPS
"What other artifacts are common in MSK ultrasound?"
"How does frequency affect resolution and penetration?"
"When would you use Doppler in MSK imaging?"
VIVA SCENARIOStandard
Rotator Cuff Assessment
EXAMINER
"How do you assess the rotator cuff with ultrasound and what findings indicate a full-thickness tear?"
EXCEPTIONAL ANSWER
I assess the rotator cuff systematically using a high-frequency linear probe (10-15 MHz). I examine the subscapularis in internal rotation, the biceps tendon in the bicipital groove, and the supraspinatus and infraspinatus in the modified Crass position (hand on ipsilateral back pocket). I compare to the other side. For supraspinatus, the normal tendon appears hyperechoic with a fibrillar pattern, convex superficially (beak sign). Full-thickness tear findings include: complete discontinuity of the tendon, a hypoechoic or anechoic gap, non-visualization of the tendon, retraction of the torn ends, and herniation of the deltoid muscle toward the humeral head. Indirect signs include cartilage interface sign (fluid at bare area) and loss of the subdeltoid bursa-supraspinatus interface. Sensitivity for full-thickness tears is 92-95% in experienced hands.
KEY POINTS TO SCORE
Systematic examination: subscapularis, biceps, supraspinatus, infraspinatus
Modified Crass position for supraspinatus
Full-thickness tear: discontinuity, anechoic gap, retraction
Compare to contralateral side
COMMON TRAPS
✗Forgetting to assess all four rotator cuff tendons
✗Not mentioning patient positioning
✗Confusing anisotropy artifact with tear
LIKELY FOLLOW-UPS
"How do you differentiate partial from full-thickness tears?"
"What is the accuracy of US compared to MRI for rotator cuff?"
"When would you prefer MRI over ultrasound?"
VIVA SCENARIOStandard
US-Guided Injection
EXAMINER
"What are the advantages of ultrasound-guided injection over landmark technique?"
EXCEPTIONAL ANSWER
Ultrasound-guided injection offers several advantages over landmark technique. First, improved accuracy - studies show significantly higher rates of correct needle placement, particularly for small joints and bursae. For example, landmark glenohumeral injection is accurate only 50-70% of the time, while US-guided approaches are greater than 90% accurate. Second, real-time visualization allows me to see the needle path, avoid neurovascular structures, and confirm delivery of medication to the target. Third, I can visualize pathology before injection and potentially aspirate fluid for analysis. Fourth, it allows access to difficult targets like hip joints, which are too deep for reliable landmark technique. Finally, patient safety is improved by avoiding vessels and nerves. The main disadvantage is the need for equipment and training. For large superficial joints like the knee, landmark technique may be adequate, but for deeper or more technically challenging targets, ultrasound guidance is preferred.
KEY POINTS TO SCORE
Improved accuracy vs landmark (90% vs 50-70%)
Real-time needle visualization
Avoid neurovascular structures
Confirm medication delivery to target
COMMON TRAPS
✗Not mentioning specific accuracy data
✗Forgetting that landmark is acceptable for some joints
✗Not discussing any limitations of US guidance
LIKELY FOLLOW-UPS
"How do you visualize the needle tip during injection?"
"What structures would you inject under US guidance?"
"What are the complications of joint injection?"
MSK Ultrasound Exam Day Cheat Sheet
High-Yield Exam Summary
Physics Basics
- •Higher frequency = better resolution, less penetration
- •MSK uses 7-15 MHz linear probes
- •Anisotropy = artifact from oblique beam angle
- •Always compare to contralateral side
Tissue Echogenicity
- •Tendon: Hyperechoic, fibrillar pattern
- •Muscle: Hypoechoic, pennate pattern
- •Nerve: Hypoechoic, fascicular/honeycomb
- •Fluid: Anechoic (black), compressible
Pathology Features
- •Full-thickness tear: Discontinuity, anechoic gap
- •Tendinopathy: Thickening, hypoechoic, loss of fibrillar pattern
- •Effusion: Anechoic fluid, distends capsule
- •Synovitis: Thickened, non-compressible, Doppler positive
US vs MRI
- •US: Dynamic, portable, real-time guidance, cheaper
- •US cannot assess: Bone marrow, deep structures, cartilage detail
- •RC tear accuracy: US 92-95%, MRI 95%+
- •US is operator-dependent