Deltoid Anatomy

Anterior Deltoid

Origin: Anterior border of the lateral third of the clavicle
Insertion: The deltoid tuberosity on the lateral surface of the proximal humeral shaft
Actions: Flexion and internal rotation of the arm at the shoulder
Innervation: Axillary nerve (C5, C6)
Blood Supply: Posterior circumflex humeral artery

Primary Actions of the Anterior Deltoid

1. Flexion of the arm at the shoulder

  Agonists:

  • Biceps brachii
  • Coracobrachialis
  • Pectoralis major (clavicular head)

  Antagonists:

  • Deltoid (posterior part)
  • Triceps brachii (long head)
  • Latissimus dorsi
  • Pectoralis major (sternal head)
  • Teres major

2. Internal rotation of the arm at the shoulder

  Agonists:

  • Subscapularis
  • Pectoralis major
  • Latissimus dorsi
  • Teres major

  Antagonists: 

  • Infraspinatus
  • Teres minor
  • Deltoid (posterior)

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Middle Deltoid

Origin: Lateral border of the acromion process of the scapula
Insertion: The deltoid tuberosity on the lateral surface of the proximal humeral shaft
Actions: Abduction of the arm at the shoulder
Innervation: Axillary nerve (C5, C6)
Blood Supply: Posterior circumflex humeral artery

Primary Actions of the Middle Deltoid

1. Abduction of the arm at the shoulder

  Agonists:

  • Anterior Deltoid
  • Posterior Deltoid
  • Supraspinatus

  Antagonists:

  • Triceps brachii (long head)
  • Latissimus dorsi
  • Pectoralis major
  • Teres major

Posterior Deltoid

Origin: Inferior edge of the scapular spine
Insertion: The deltoid tuberosity on the lateral surface of the proximal humeral shaft
Actions: Extension of the arm at the shoulder
Innervation: Axillary nerve (C5, C6)
Blood Supply: Posterior circumflex humeral artery

Primary Actions of the Posterior Deltoid

1. Extension of the arm at the shoulder

  Agonists:

  • Triceps brachii (long head)
  • Latissimus dorsi
  • Pectoralis major (sternal head)
  • Teres major

  Antagonists: 

  • Deltoid (anterior part)
  • Biceps brachii
  • Coracobrachialis
  • Pectoralis major (clavicular head)

Secondary Actions of the Posterior Deltoid

1. Assists with external rotation of the arm at the shoulder

  Agonists:

  • Infraspinatus
  • Teres minor

  Antagonists: 

  • Deltoid (anterior part)
  • Teres major
  • Latissimus dorsi
  • Pectoralis major
  • Subscapularis