Teres Major Muscle Under the Skin, Posterior View

Description

Posterior left shoulder and upper back musculature is rendered beneath the skin in an adult male, with the infraspinatus highlighted over the infraspinous fossa inferior to the scapular spine and medial to the glenohumeral joint. Inferior to it, the teres major occupies the inferolateral border of the scapula and courses laterally toward the proximal humerus, lying posterior to the axilla and forming part of the posterior axillary fold with latissimus dorsi. The deltoid caps the lateral shoulder and overlaps the posterior aspect of the rotator cuff, while trapezius spans superiorly and medially toward the cervical and thoracic midline. Bony landmarks such as the acromion and scapular spine orient the fiber directions and layer relationships. This posterior perspective matters because it separates two often-confused contributors to shoulder adduction: the rotator cuff infraspinatus, which primarily externally rotates and stabilizes the humeral head in the glenoid, and the teres major, which adducts and internally rotates via its insertion near the medial lip of the intertubercular sulcus. Small distinctions. Clinically, posterior shoulder pain from infraspinatus tendinopathy or a suprascapular nerve entrapment at the spinoglenoid notch localizes to the infraspinous region, whereas teres major strain occurs in overhead and throwing athletes during forceful internal rotation and adduction, and it can be mistaken for latissimus dorsi injury without clear surface anatomy. Use this asset for teaching rotator cuff anatomy in gross anatomy and kinesiology courses, for illustrating posterior shoulder examination findings in sports medicine texts, or for surgical education when discussing posterior approaches and safe zones around the scapular spine and glenoid. It also reads well in rehabilitation materials that differentiate external rotation strengthening (infraspinatus) from adduction and internal rotation work (teres major and latissimus dorsi). Anatomical accuracy verified by SciePro's Medical Advisory Board.