Deltoid Muscle, Posterior View

Description

Posteriorly, the paired deltoid muscles are highlighted over the lateral shoulder, draping from the clavicle and acromion and taking a broad origin along the spine of the scapula before converging on the deltoid tuberosity of the humerus. Superior to the deltoid, the trapezius spans from the nuchal region to the scapular spine, while inferiorly the latissimus dorsi sweeps superolaterally toward the humerus, forming the posterior axillary fold medial to the deltoid. Along the scapular spine, the deltoid’s posterior (spinal) fibers sit lateral to the infraspinous fossa and overlie the rotator cuff interval where infraspinatus and teres minor pass toward the greater tubercle. Fiber direction is easy to read. This posterior perspective matters because the scapular spine and acromion define the deltoid’s mechanical line of pull and separate the posterior deltoid from the rotator cuff tendons that often drive shoulder pain. Clinically, distinguishing deltoid strain from infraspinatus or teres minor pathology helps frame examination findings such as pain with resisted horizontal abduction versus weakness in external rotation, and it also reinforces why the axillary nerve and posterior circumflex humeral artery are at risk in surgical approaches near the quadrangular space or with proximal humeral fractures. The view also supports safe intramuscular injection teaching by orienting the acromial landmarks, even when the deltoid cap appears symmetric on the surface. Use this artwork in gross anatomy and kinesiology courses when teaching the three deltoid parts (clavicular, acromial, and spinal) and their actions, or in orthopedic and sports medicine materials discussing posterior shoulder impingement, rotator cuff referral patterns, and deltoid-splitting approaches for proximal humerus fixation. It also fits patient education handouts that need an accurate posterior map of the shoulder and back musculature with the deltoid clearly isolated by color. Anatomical accuracy verified by SciePro's Medical Advisory Board.