Deltoid Posterior Head Detail

pars spinalis m. deltoidei detail

The posterior deltoid head is the extension and external rotation component. It works with the infraspinatus and teres minor in posterior shoulder stabilisation and is a key muscle in athletes performing pulling and rowing movements.

Nerve: Axillary nerve (C5, C6) Blood Supply: Posterior circumflex humeral artery Region: Shoulder

Anatomical Data

Origin, Insertion & Supply

Origin	Spine of the scapula — lower border
Insertion	Deltoid tuberosity — posterior fibre insertion
Nerve Supply	Axillary nerve (C5, C6)
Blood Supply	Posterior circumflex humeral artery

Biomechanics

Function & Actions

Actions	Extends the shoulder from flexion; Horizontally abducts the arm; Laterally rotates the humerus

Clinical Relevance

Clinical Notes

Posterior deltoid atrophy from axillary nerve injury is tested by resisted shoulder extension and horizontal abduction. The posterior deltoid is the muscle split in the posterior approach to the shoulder for posterior labrum repair and reverse arthroplasty — splitting more than 5 cm risks the axillary nerve branches.

Palpation

Palpated as the posterior shoulder muscle bulk during resisted shoulder extension and horizontal abduction.

Pathology

Common Injuries & Conditions

Posterior Deltoid Denervation in Axillary Nerve Palsy

Selective posterior deltoid weakness from axillary nerve posterior branch injury producing loss of shoulder extension and horizontal abduction power.