2025 Workshop Handout Bundle-W116RTC Localization Atypical Muscles

W116RTC Localization Atypical Muscles - Chuang

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This presentation by Dr. Kathy Chuang (2025) provides detailed guidance on localizing atypical muscles for needle electromyography (EMG), emphasizing anatomical landmarks and proper technique to ensure accuracy and avoid complications.

Key general advice includes using an anatomic localization reference, relying on bony landmarks and their orientation, and visualizing muscles when possible. For bipennate muscles, the motor point often lies about one-third along the muscle’s length from origin to insertion. When bony landmarks are hard to palpate—such as ribs for serratus anterior or rhomboid muscles—ultrasound or visualization is recommended rather than blind needle insertion.

Muscle-specific localization tips include:

- <strong>Serratus Anterior:</strong> Locate the mid-axillary or nipple line and insert near ribs 1-9; block the intercostal space to isolate.

- <strong>Rhomboid Major:</strong> Find the spinous processes (T2-T5) and insert at scapular spine level halfway between the scapula’s medial border and spine, passing through trapezius.

- <strong>Supraspinatus:</strong> Insert above mid scapular spine all the way to bone to avoid trapping trapezius; volume conduction often occurs from trapezius.

- <strong>Infraspinatus:</strong> Insert just below scapular spine to bone, then withdraw slightly to avoid trapezius.

- <strong>Teres Minor and Major:</strong> Key landmarks involve distances from the scapula's lateral border and inferior angle; ensure proper mediolateral positioning.

- <strong>Latissimus Dorsi:</strong> Insert about three fingerbreadths below posterior axillary fold; avoid going too medial into teres major.

- <strong>Iliopsoas:</strong> Find the femoral pulse, then insert 2 fingerbreadths lateral and 1 distal to inguinal ligament, avoiding neurovascular bundle medially.

- <strong>Adductor Longus/Brevis:</strong> Four fingerbreadths distal to pubic tubercle, with superficial muscle being longus and deep being brevis.

- <strong>Biceps Femoris (Long and Short Heads):</strong> Insert respectively at midpoint between ischial tuberosity and fibular head, and four fingerbreadths from fibular head medial to LH tendon.

- <strong>Flexor Hallucis Longus:</strong> Four fingerbreadths above ankle just anterior to Achilles tendon; avoid going too deep (tibialis posterior) or too anterior (flexor digitorum longus).

Throughout, emphasis is placed on precise anatomical knowledge, careful needle trajectory, and avoidance of nearby structures to improve EMG accuracy in atypical muscles.

Keywords

needle electromyography

atypical muscles

anatomical landmarks

muscle localization

bipennate muscles

ultrasound guidance

serratus anterior

rhomboid major

supraspinatus

infraspinatus