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Acromial Part of Deltoid Muscle
Muscular System

Acromial Part of Deltoid Muscle

Pars acromialis musculi deltoidei

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Quick Facts

Origin: Acromion of scapula.

Insertion: Deltoid tuberosity of humerus.

Action: Abducts arm at glenohumeral (shoulder) joint.

Innervation: Axillary nerve (C5-C6).

Arterial Supply: Acromial and deltoid branches of thoracoacromial artery, anterior and posterior circumflex humeral and subscapular arteries, deltoid branch of deep brachial artery.

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The acromial part of the deltoid muscle originates from the lateral aspect of the acromion of the scapula.


The muscle bellies of the acromial, clavicular, and scapular spinal parts 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:

- a 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

Regarding the acromial part of deltoid specifically, it abducts the arm at the glenohumeral (shoulder) joint. Simultaneous contraction of the supraspinatus muscle is necessary to initiate abduction from the anatomical position.

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


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

Learn more about this topic from other Elsevier products

Deltoid Muscle

ScienceDirect image

61 The deltoid muscle reaches maximum EMG activity at approximately 110° of abduction and maintains a plateau level of activity.

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