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Deltoid Muscle - want to learn more about it?

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Deltoid Muscle

The deltoid muscle is a large and powerful muscle of the shoulder joint. Being such a prominent muscle, the deltoid is one of a bodybuilder's favourite to train and an anatomy professor's favourite topic to ask about on your upcoming exam.

Originating from three points, this muscle inserts into the humerus and is innervated by the axillary nerve and has a crucial role in moving your shoulder joint.

This article will describe in detail the origins, attachments, innervation, and exact functions of the deltoid muscle, together with some brief clinical aspects to place it in perspective.

Key facts about the deltoid muscle
Origins Lateral third of the clavicle, acromion, and spine of scapula
Insertions Deltoid tuberosity of the humerus
Innervation Axillary nerve
Function Abduction and stabilization of the shoulder joint

Anatomy and Innervation

It distinctively shapes the surface anatomy of the shoulder and this muscle is supplied by the axillary nerve, a branch of the brachial plexus.

The deltoid has three parts, each with their own origin:

Together they all insert laterally at the humeral shaft into the deltoid tuberosity. In its course, the muscle lies in close relation to the cephalic vein which runs in the deltopectoral groove between the deltoid and pectoralis major muscle becoming the axillary vein.

Function

The deltoid moves and stabilizes the shoulder joint. The movements of the different deltoid parts can interact both synergistically and antagonistically depending on the specific part and the position of the humerus. The deltoid is the most important abductor of the shoulder joint.

Recommended video: Deltoid muscle
The deltoid muscle is a large and powerful muscle of the shoulder joint. On this video, we will explore the attachment points, innervation and functions of the deltoid.

The abduction is mainly initiated and held by the acromial part. Both the clavicular and spinal parts function as adductors up to 60° and abductors over 60°. Furthermore the clavicular part causes an inward rotation and anteversion, the spinal part an outward rotation and retroversion.

Clinical Aspects

An axillary nerve injury may lead to paralysis of the deltoid muscle. The affected patients typically show a clinical picture of an atrophic shoulder in comparison to the healthy side.

Another classic sign is the acromion standing out prominently (“scaphoid sign”). Even though the limitations of movement are partly compensated by the other shoulder muscles especially the abduction and outward rotation become tremendously difficult. Isolated lesions of the axillary nerve occur rarely. More common are injuries due to a dislocated shoulder or proximal humerus fracture.

Deltoid Muscle - want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

Sign up for your free Kenhub account today and join over 931,206 successful anatomy students.

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

Show references

References:

  • D. Drenckhahn/J. Waschke: Taschenbuch Anatomie, 1.Auflage, Urban & Fischer Verlag/Elsevier (2008), S.33
  • M. Schünke/E. Schulte/U. Schumacher: Prometheus – LernAtlas der Anatomie – Allgemeine Anatomie und Bewegungssystem, 2.Auflage, Thieme Verlag (2007), S.298-299, 372
  • G. D. Giacomo et. al.: Atlas of Functional Shoulder Anatomy, 1.Auflage, Springer-Verlag Italia (2008), S.62-68
  • E. G. McFarland: Examination of the Shoulder, 1.Auflage, Thieme Verlag (2006), S.107-110
  • D. H. Johnson/R. A. Pedowitz: Practical Orthopaedic Sports Medicine and Arthroscopy, 1.Auflage, Lippincott Williams & Wilkins (2006), S.121-124

Author & Layout:

  • Achudhan Karunaharamoorthy
  • Christopher A. Becker
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

Related diagrams and images

Muscles of the arm and the shoulder

Main muscles of the upper extremity

Deltoid muscle level

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