Musculoskeletal Ultrasound

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MSK US Basics - Probing the Pixels

  • Transducer: High-frequency linear array (7-15 MHz) for superficial resolution.
  • Echogenicity: Tissue appearance relative to surrounding structures.
    • Hyperechoic: Brighter (e.g., bone cortex, tendons, ligaments).
    • Hypoechoic: Darker (e.g., muscle, hyaline cartilage, complex fluid).
    • Anechoic: Black (e.g., simple fluid, cysts, vessels).
  • Anisotropy: Crucial property; tendon/ligament echogenicity changes with insonation angle. Perpendicular beam = hyperechoic; oblique beam = hypoechoic (can mimic a tear).

    ⭐ Anisotropy is a critical artifact in MSK ultrasound; a normal fibrillar tendon can appear hypoechoic and mimic a tear if the ultrasound beam is not perpendicular to the tendon fibers.

  • Key Artifacts:
    • Acoustic Shadowing: Signal loss deep to highly attenuating structures (e.g., bone, calcification).
    • Posterior Acoustic Enhancement: Increased echo intensity deep to fluid-filled structures.
    • Reverberation: Multiple parallel echoes (e.g., metallic foreign bodies).
    • Edge Artifact (Refractive Shadowing): Shadowing at curved structure edges.
    • Comet Tail: Short reverberation artifact (e.g., small calcifications, gas).

MSK US: Anisotropy, shadowing, and enhancement

Upper Limb Scan - Shoulder & Elbow Focus

Shoulder: Scan rotator cuff (📌 SITS), long head of biceps (LHB) tendon, subacromial-subdeltoid (SASD) bursa, AC joint.

  • Rotator Cuff (📌 SITS): Supraspinatus (normal thickness 4-6mm), Infraspinatus, Teres Minor, Subscapularis.

    MuscleO (Abbv.)I (Abbv.)Fxn (Main)US View (Common)
    SupraSS fossaGr. Tub.AbductCrass
    InfraIS fossaGr. Tub.Ext. Rot.Post. Trans/Long
    T. MinorLat. Bord.Gr. Tub.Ext. Rot.Post. Trans/Long
    SubscapSubS fos.Les. Tub.Int. Rot.Ant. Trans/Long
  • Pathologies: Tendinopathy, tears (partial/full), calcific tendinitis, bursitis, impingement (dynamic assessment). Shoulder US: Axial assessment at the bicipital groove

⭐ Dynamic assessment during abduction and rotation is key for diagnosing subacromial impingement and rotator cuff abnormalities.

Elbow:

  • Common Extensor Origin (CEO): Tennis elbow (lateral epicondylitis). Ultrasound of lateral elbow anatomy and tennis elbow
  • Common Flexor Origin (CFO): Golfer's elbow (medial epicondylitis).
  • Ulnar nerve: Cubital tunnel assessment.

Lower Limb & Hand/Wrist - Joint Journeys

  • Wrist/Hand:
    • Carpal Tunnel: Median nerve CSA >10-12 mm². Ultrasound of median nerve in carpal tunnel

      ⭐ A median nerve cross-sectional area (CSA) greater than 10-12 mm² at the carpal tunnel inlet is a widely accepted sonographic criterion for carpal tunnel syndrome.

    • De Quervain's: 1st ext. compartment tenosynovitis.
    • Ganglion Cysts: Anechoic, compressible, stalk.
    • Trigger Finger: A1 pulley/flexor tendon thickening.
  • Hip:
    • Effusion/Synovitis: Anterior recess fluid/synovial thickening.
    • Trochanteric Bursitis: Fluid/thickening.
    • Gluteal Tendinopathy: Thickening/tears (medius/minimus).
  • Knee:
    • Patellar/Quad Tendinopathy: Thickening, hypoechoic.
    • Baker's Cyst: Medial gastroc-semimembranosus bursa. Ultrasound of Baker's Cyst with Anatomy Labels
    • MCL/LCL: Sprains/tears.
    • Meniscal Cysts: From meniscal tears.
  • Ankle/Foot:
    • Achilles: Tendinopathy (>6mm), tears. Achilles Tendinopathy Ultrasound Views
    • Plantar Fasciitis: Fascia >4mm thick, hypoechoic.
    • ATFL Sprain: Common.
    • Morton's Neuroma: Hypoechoic, 3rd intermetatarsal.
    • 📌 Medial Ankle: Tom, Dick And Very Nervous Harry (TP, FDL, A, V, N, FHL).

MSK Lesions & Procedures - Spot & Soothe

  • Common Pathologies:
    • Tendinopathy: Hypoechoic, thick, neovascularization (Power Doppler).
    • Tears: An-/hypoechoic defect, fiber discontinuity (partial/full, interstitial).
    • Bursitis: Distended fluid-filled sac.
    • Enthesopathy: Changes at tendon/ligament bony attachment.
    • Nerve Entrapment: Swollen, hypoechoic nerve; hypervascularity; sonographic Tinel's.
  • Soft Tissue Masses: Assess cystic vs. solid, vascularity.
MassKey US Features
CystAnechoic, posterior enhancement, no flow
LipomaHyperechoic (often), compressible, minimal flow
HematomaVariable echogenicity (age), non-compressible
AbscessComplex fluid, debris, peripheral hyperemia
  • US-Guided Procedures:
    • Aspiration: Cysts, effusions.
    • Injections: Steroids, anesthetics, PRP.
    • Biopsy.

⭐ Power Doppler is highly sensitive for neovascularity, a key sign of active inflammation in tendinopathies and synovitis.

High‑Yield Points - ⚡ Biggest Takeaways

  • Dynamic assessment is a key advantage, allowing real-time evaluation of joints and tendons.
  • Excellent for superficial soft tissues: tendons, ligaments, nerves, and fluid collections.
  • Anisotropy artifact: tendons appear falsely hypoechoic if not perpendicular to the ultrasound beam.
  • Guides interventional procedures like aspirations and injections with precision.
  • Power Doppler is crucial for assessing inflammation and abnormal vascularity.
  • Key for diagnosing rotator cuff tears, tendinopathies, carpal tunnel syndrome, and infant hip dysplasia.
  • No ionizing radiation, highly portable, and relatively inexpensive compared to MRI/CT.

Practice Questions: Musculoskeletal Ultrasound

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Ultrasound is the investigation of choice for

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Flashcards: Musculoskeletal Ultrasound

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Radiograph shows increased medial joint space on mortise view indicates injury to the _____ ligament

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Radiograph shows increased medial joint space on mortise view indicates injury to the _____ ligament

deltoid

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