Deltoid

Musculus deltoideus

A thick, triangular muscle covering the shoulder joint. It originates from the lateral third of the clavicle, acromion, and spine of the scapula, and inserts on the deltoid tuberosity of the humerus. Innervated by the axillary nerve (C5, C6).

Tür Muscle
Vücut Sistemi Muscular
Vücut Bölgesi Shoulder
Latince Adı Musculus deltoideus
FMA ID 32521

İşlev

The primary abductor of the shoulder joint. The anterior fibers flex and medially rotate the arm. The posterior fibers extend and laterally rotate the arm. Gives the shoulder its rounded contour.

Klinik Önemi

Deltoid paralysis from axillary nerve injury prevents arm abduction. The deltoid is a common site for intramuscular injections. Rotator cuff tears may cause compensatory deltoid overuse.

Sıkça Sorulan Sorular

What is the primary action of the deltoid muscle?
The deltoid muscle is the primary abductor of the shoulder joint, lifting the arm away from the body in the coronal plane. Abduction beyond 15 degrees at the glenohumeral joint is almost entirely dependent on an intact deltoid. The muscle's three portions—anterior, middle, and posterior—also contribute to shoulder flexion, extension, and rotation.
What are the distinct functional contributions of each deltoid portion?
The anterior deltoid fibers flex and medially rotate the arm, making them active in forward-reaching movements. The middle (lateral) fibers are the primary abductors. The posterior fibers extend and laterally rotate the arm, contributing to backward arm movement and rowing-type motions. All three portions converge on the deltoid tuberosity of the humerus.
Which nerve supplies the deltoid, and what happens if it is injured?
The deltoid is innervated by the axillary nerve (C5, C6), which wraps around the surgical neck of the humerus. Injury to the axillary nerve—from a shoulder dislocation, proximal humerus fracture, or improper injection—results in inability to abduct the arm beyond about 15 degrees and loss of sensation over the lateral shoulder (regimental badge area).
Why is the deltoid a common site for intramuscular injections?
The deltoid is preferred for intramuscular injections because it is readily accessible, has adequate muscle mass in most adults, and has few major underlying structures compared to other injection sites. The injection is typically given into the middle third of the muscle, two to three finger-breadths below the acromion, to avoid the axillary nerve and vessels located inferiorly.
What gives the shoulder its rounded contour?
The deltoid muscle is responsible for the rounded, cap-like contour of the shoulder. When the deltoid is paralyzed or significantly atrophied, the shoulder takes on a squared or flattened appearance because the underlying bony prominences of the humeral head and acromion become more visible.

İlgili Yapılar

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Educational Disclaimer

This content is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for medical decisions.

Data sources: Terminologia Anatomica, Foundational Model of Anatomy, Wikidata.