Muscle
Deltoid
Shoulder cap with three directions of pull
High-yield
Deltoid and supraspinatus cooperate during abduction; their roles do not switch at one exact angle. Axillary nerve damage can reduce deltoid strength and shoulder contour.
Overview
The deltoid wraps around the shoulder and converges on the humeral shaft. Its middle portion lifts the arm sideways, while the front and rear portions help move and rotate it in opposite directions.
Reference facts
- Origin
- Lateral third of the clavicle, acromion and scapular spine
- Insertion
- Deltoid tuberosity on the humerus
- Action
- Middle part: abduction; front part: flexion and medial rotation; rear part: extension and lateral rotation
- Innervation
- Axillary nerve, mainly C5–C6
- Blood supply
- Posterior circumflex humeral artery and deltoid branches of the thoracoacromial artery
Clinical correlation
An axillary nerve injury can combine deltoid weakness or wasting with reduced sensation over the outer shoulder. The nerve is vulnerable around the humeral surgical neck, including in some fractures and dislocations.
Frequently asked questions
What does the deltoid do?
Middle part: abduction; front part: flexion and medial rotation; rear part: extension and lateral rotation.
What nerve innervates the deltoid?
The deltoid is innervated by the axillary nerve, mainly C5–C6.
Where does the deltoid attach?
Origin: Lateral third of the clavicle, acromion and scapular spine. Insertion: Deltoid tuberosity on the humerus.
What is the blood supply of the deltoid?
Posterior circumflex humeral artery and deltoid branches of the thoracoacromial artery.