Deltoid

From Ganfyd

This page refers to the deltoid muscle. For other uses please see deltoid (disambiguation).

The deltoid is a large muscle of the shoulder.

Deltoid
System:	Muscle
Function:	Abduction, flexion, medial rotation, extension and lateral rotation of the humerus at the shoulder
Origin:	Lateral clavicle, acromion, spine of scapula to deltoid tubercle
Branches:
Insertion:	Middle of lateral humerus - deltoid tuberosity
Arterial supply:
Venous drainage:
Lymphatic drainage:
Innervation:	Axillary nerve (C5, C6)
Vertebral levels:
Search for Deltoid in Gray's.

Surface Anatomy

The deltoid forms the bulk of the shoulder area and is easily palpable there.

Shape

The deltoid is a a large triangular-shaped muscle which covers the superior, posterior and anterior surfaces of the shoulder joint. Its fibres converge from their widespread origin, the middle fibres passing inferiorly, the anterior fibres obliquely posterolaterally and the posterior fibres obliquely anterolaterally. The fibres unite into a thick tendon, which gives off an expansion to the deep fascia of the arm.

The arrangement of the fibres of deltoid is slightly strange, in that the fibres of acromial origin pass obliquely, with multiple heads between tendenous insertions which themselves insert into tendinous intersections.

Actions

• Abduction of the humerus at the shoulder

Anterior fibres:

• Flexion of the humerus
• Medial rotation of the humerus

Posterior fibres:

• Extension of the humerus
• Lateral rotation of the humerus

Joints Affected

• Shoulder

Origin

• Lateral third of the clavicle
• Acromion
• Spine of the scapula up to deltoid tubercle

Insertion

• Deltoid tuberosity of the humerus

Nerve Supply

• Axillary nerve (C5, C6)

Relations

• Superficial to muscles of the rotator cuff

Clinical Relevance

• Atrophies in axillary nerve injury leading to loss of the curve of the shoulder
• Test:
  • Abduct arm
  • Hold in abducted position against resistance

Variations

• Some splitting into the various portions is common
• May fuse with trapezius or pectoralis major
• May have additional slips from the medial or lateral borders of the scapula or the infraspinous fascia
• Insertion may vary, occasionally prolonged to the origin of brachioradialis