Structures Deep to (Under Cover of) Deltoid

The deltoid covers the shoulder joint and a large number of important structures. These can be organised by category.

Bones

• Upper end of the humerus
• Coracoid process of the scapula

Joint and Ligaments

• Shoulder (glenohumeral) joint
• Coracoacromial ligament

Bursae

All bursae around the shoulder joint, including:

• Subacromial (subdeltoid) bursa — the largest bursa in the body, situated below the coracoacromial arch and the deltoid, above the supraspinatus tendon and greater tubercle of the humerus
• Subscapular bursa
• Infraspinatus bursa

Functional Role of the Subacromial Bursa

• Protects the supraspinatus tendon from friction against the acromion.
• During overhead abduction, facilitates smooth passage of the greater tubercle of the humerus under the acromion.

Muscles

Insertions (muscles inserting on the humerus, covered by deltoid)

• Pectoralis minor — on the coracoid process
• Supraspinatus, infraspinatus, and teres minor — on the greater tubercle of the humerus
• Subscapularis — on the lesser tubercle of the humerus
• Pectoralis major, teres major, and latissimus dorsi — on the intertubercular sulcus (bicipital groove) of the humerus

Origins (muscles arising from structures under deltoid)

• Coracobrachialis and short head of biceps brachii — from the coracoid process
• Long head of biceps brachii — from the supraglenoid tubercle
• Long head of triceps brachii — from the infraglenoid tubercle
• Lateral head of triceps brachii — from the upper part of the posterior surface of the humerus

Vessels

• Anterior circumflex humeral artery
• Posterior circumflex humeral artery (and vein)

Nerve

• Axillary nerve, accompanied by the posterior circumflex humeral vessels, lies on the deep aspect of the deltoid as it winds around the surgical neck of the humerus.

Spaces

• Quadrangular space
• Triangular (subscapular) intermuscular space

Musculotendinous Cuff (Rotator Cuff) — Brief Note

The flattened tendons of subscapularis, supraspinatus, infraspinatus, and teres minor blend with the capsule of the shoulder joint, forming the rotator cuff, which strengthens the capsule on all sides except inferiorly. This cuff lies deep to the deltoid and crosses the shoulder joint before the respective insertions listed above.