Muscle
Deltoid
Prime arm abductor
High-yield
Abducts arm 15-90°; axillary nerve injury (surgical neck fracture) causes deltoid paralysis and loss of the rounded shoulder.
Overview
The triangular muscle that caps the shoulder, giving it rounded contour. Its middle fibers are the main abductor beyond the first 15 degrees.
Reference facts
- Origin
- Lateral third of clavicle, acromion, and spine of the scapula
- Insertion
- Deltoid tuberosity of the humerus
- Action
- Middle fibers abduct the arm; anterior fibers flex and medially rotate; posterior fibers extend and laterally rotate
- Innervation
- Axillary nerve (C5, C6)
- Blood supply
- Posterior circumflex humeral artery
Clinical correlation
Axillary nerve damage → deltoid wasting, weak abduction, and a patch of numbness over the lateral shoulder ('regimental badge').
Frequently asked questions
What does the deltoid do?
The deltoid middle fibers abduct the arm; anterior fibers flex and medially rotate; posterior fibers extend and laterally rotate.
What nerve innervates the deltoid?
The deltoid is innervated by the axillary nerve (C5, C6).
Where does the deltoid attach?
The deltoid originates from the lateral third of clavicle, acromion, and spine of the scapula and inserts on the deltoid tuberosity of the humerus.
What is the blood supply of the deltoid?
The deltoid is supplied by the posterior circumflex humeral artery.