Deltoid

Written by Oliver Jones

Last updated October 9, 2022 • 3 Revisions •

The deltoid is an intrinsic muscle of the shoulder region. It is shaped like an inverted triangle and can be divided into three parts (anterior, middle and posterior).

  • Attachments: Originates from the lateral third of the clavicle, the acromion and the spine of the scapula. It attaches to the deltoid tuberosity on the lateral aspect of the humerus.
  • Innervation: Axillary nerve.
  • Actions:
    • Anterior fibres – flexion and medial rotation at the shoulder
    • Posterior fibres – extension and lateral rotation at the shoulder
    • Middle fibres – abduction at the shoulder (takes over from the supraspinatus, which abducts the first 15 degrees).
  • Blood supply: Anterior and posterior circumflex humeral artery.

Fig 1
The deltoid and teres major

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