Deltoid Muscle, Posterior View

Description

Arising from the lateral third of the clavicle, acromion, and spine of the scapula, the deltoid forms a thick muscular cap over the glenohumeral region in posterior view. Posterior fibers sweep inferolaterally from the scapular spine toward the lateral humerus, where the muscle converges on the deltoid tuberosity. Superiorly, the acromial portion overlaps the subacromial region, while inferiorly the deltoid’s posterior border approaches the posterior axillary fold and the long head of triceps brachii as it descends along the posterior humerus. Clear surface anatomy. Posterior deltoid anatomy matters when you need to distinguish extension and horizontal abduction mechanics from the larger rotator cuff and scapular stabilizers. Hypertrophy, strain, or injection-related injury commonly localizes to the mid-belly, but the deeper clinical concern is proximity to the axillary nerve and posterior circumflex humeral artery as they traverse the quadrangular space deep to the deltoid. This perspective also supports teaching safe intramuscular deltoid injection placement in the upper lateral arm, avoiding the nerve as it courses inferior to the acromion. Use this illustration in gross anatomy and kinesiology modules on shoulder abduction versus extension, and in sports medicine content addressing posterior shoulder pain patterns in throwing and weightlifting. It also fits orthopedic patient education and surgical atlases when orienting readers to posterior shoulder landmarks before deltoid-splitting approaches. Anatomical accuracy verified by SciePro's Medical Advisory Board.