Deltoid Muscle (Left)

Origin

The clavicular part of the deltoid muscle originates from the anterosuperior aspect of the lateral one third of the clavicle. The acromial part originates from the lateral aspect of the acromion of the scapula. The scapular spinal part originates from the inferior aspect of the spine of the scapula.

Insertion

The fibers of the deltoid muscle travel inferolaterally and converge to a single tendon. This tendon is short, thick and inserts onto the deltoid tuberosity of the humerus.

Key Features & Anatomical Relations

The deltoid muscle is the thick triangular muscle that gives the shoulder its rounded contour. It is composed of three heads:

- Aa clavicular part, which is the anterior unipennate portion;

- an acromial part, which is the middle multipennate portion;

- a scapular spinal part, which is the posterior unipennate portion.

The deltoid muscle is located:

- superficial to the glenohumeral (shoulder) joint, the proximal tendons of the biceps brachii and triceps brachii muscles, and the axillary nerve;

- deep to the deltoid fascia and the superior lateral brachial cutaneous nerve;

- lateral to the pectoralis major, trapezius and infraspinatus muscles.

Actions & Testing

The deltoid muscle is involved in multiple actions:

- abducts the arm at the glenohumeral (shoulder) joint when the acromial part contracts individually;

- flexes and medially rotates the arm at the glenohumeral joint when the clavicular part contracts individually;

- extends and laterally rotates the arm at the glenohumeral joint when the scapular spine part contracts individually.

The deltoid muscle can be tested by abducting the arm beyond the 30° position, against resistance, during which it can be seen and palpated (Standring, 2016).

List of Clinical Correlates

- Site for intramuscular injection

References

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.