Deltoid

Joe Muscolino

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Deltoid_HR

The right deltoid. A, Lateral view (cut proximal end of brachialis is seen). B, Anterior view. C, Posterior view. Permission Joseph E. Muscolino

The deltoid is usually stated as having anterior, middle, and posterior parts.

ATTACHMENTS:

  • The deltoid attaches from the lateral clavicle, acromion process and spine of the scapula to the deltoid tuberosity (approximately 40% of the way down the humerus).

 

ACTIONS:

  • Abducts the arm at the glenohumeral joint (entire muscle)
  • Flexes the arm at the glenohumeral joint (anterior fibers)
  • Extends the arm at the glenohumeral joint (posterior fibers)
  • Medially rotates the arm at the glenohumeral joint (anterior fibers)
  • Laterally rotates the arm at the glenohumeral joint (posterior fibers)
  • Horizontally flexes the arm at the glenohumeral joint (anterior fibers)
  • Horizontally extends the arm at the glenohumeral joint (posterior fibers)
  • Adducts the arm at the glenohumeral joint (the very lowest fibers anterior and posteriorly)
  • Downwardly rotates the scapula at the scapulocostal joint (reverse closed-chain action)

 

TRIVIA NOTE:

  • The name “deltoid” comes from “delta” which is Greek for triangle and “oid” meaning resembling. In other words, the deltoid muscle is triangular in appearance.