Shoulder Anatomy

Shoulder anatomy reference covering 32 structures across 7 layers — superficial and deep muscles, rotator cuff, tendons, bursae, ligaments, nerves, vessels, and bones — with clinical notes by Aurelia RMT.

Key Structures by Layer

• Superficial Muscles — Deltoid (anterior, middle, lateral heads), pectoralis major, latissimus dorsi, upper and lower trapezius
• Rotator Cuff (SITS) — Supraspinatus (initiates abduction), infraspinatus (external rotation), teres minor (external rotation), subscapularis (internal rotation)
• Tendons — Biceps long head tendon (runs through the bicipital groove), supraspinatus insertion on greater tuberosity
• Bursae — Subacromial bursa (between rotator cuff and acromion), subdeltoid bursa
• Ligaments & Capsule — Glenohumeral capsule, coracoacromial ligament, acromioclavicular ligament, coracoclavicular ligaments
• Nerves — Axillary nerve (C5–C6; wraps posterior humeral surgical neck), suprascapular nerve (supraspinatus and infraspinatus)
• Vessels — Anterior and posterior circumflex humeral arteries, subscapular artery, axillary vein
• Bones — Humerus (head, greater and lesser tuberosities, surgical neck), scapula (glenoid, acromion, coracoid process, spine), clavicle

Frequently Asked Questions

What is the rotator cuff?

The rotator cuff is a group of four muscles — supraspinatus, infraspinatus, teres minor, and subscapularis (SITS) — and their tendons that stabilize the glenohumeral joint and control shoulder rotation and abduction.

What causes shoulder impingement syndrome?

Shoulder impingement occurs when the supraspinatus tendon or subacromial bursa is compressed between the humeral head and the acromion during overhead movements. Contributing factors include rotator cuff weakness, poor scapular mechanics, and repetitive overhead activities.

What is frozen shoulder (adhesive capsulitis)?

Frozen shoulder involves thickening and inflammation of the glenohumeral capsule, leading to progressive stiffness and pain. It typically progresses through freezing, frozen, and thawing stages over 12–18 months.