Musculoskeletal Ultrasound

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).

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.

  Muscle	O (Abbv.)	I (Abbv.)	Fxn (Main)	US View (Common)
  Supra	SS fossa	Gr. Tub.	Abduct	Crass
  Infra	IS fossa	Gr. Tub.	Ext. Rot.	Post. Trans/Long
  T. Minor	Lat. Bord.	Gr. Tub.	Ext. Rot.	Post. Trans/Long
  Subscap	SubS fos.	Les. Tub.	Int. Rot.	Ant. Trans/Long

• Pathologies: Tendinopathy, tears (partial/full), calcific tendinitis, bursitis, impingement (dynamic assessment).

⭐ 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).
• 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.

    ⭐ 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.
  • MCL/LCL: Sprains/tears.
  • Meniscal Cysts: From meniscal tears.
• Ankle/Foot:
  • Achilles: Tendinopathy (>6mm), tears.
  • 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.

• 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.