Shoulder

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Anterior Shoulder

This is a superficial view of the shoulder. Take note of the anatomical relationship of the major muscles surrounding the anterior shoulder. Observe the fibers of the large pectoralis major as its distal fibers twist before attaching to the humerus. Other notable muscles in this view are the deltoid and biceps brachii. Although the serratus anterior does not directly attach to or cross the shoulder, it is extremely important in scapular stabilization and changing the orientation of the glenoid fossa where the humeral head articulates.

Click here for a different view of the anterior shoulder structures.

The pectoralis major is removed in this image demonstrating the pectoralis minor and other important deeper structures.

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Posterior Shoulder

The superficial muscles of the posterior shoulder are important stabilizers of the glenohumeral joint. In this view, the deltoid is still attached, after it is reflected in later images the underlying muscles will be seen. Note the close location of the triceps brachii, teres major and infraspinatus muscles. Another important muscle that doesn't directly affect the shoulder joint is the trapezius muscle, namely its upper fibers. Observe the direction of the fibers of this muscle and how they attach to the scapular spine. Consider how activation of these fibers would orient the glenoid fossa.

Click here to see how these muscles interact when the humerus is abducted.

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Rotator Cuff

This posterior view of the scapula gives a good overall view of three of the four rotator cuff muscles. An acronym to help remember these muscles is S.I.T.S. (Supraspinatus, Infraspinatus, Teres Minor, and Subscapularis-not pictured). Please realize the deltoid muscle has been totally removed to provide for clear viewing in this demonstration.

Before attaching to the greater tubercle of the humerus (or lesser tubercle for the subscapularis), the tendons of the these muscles blend with the joint capsule that surrounds the glenohumeral joint. Here is a picture that illustrates this.

There are important anatomical spaces that are evident when the humerus is abducted. Click here to observe the quadrangular space, triangular space, and triangular interval. Review the borders of these spaces as well as the neurovascular structures that run through them. This view also demonstrates how the long head of the triceps brachii "weaves" between the teres major and teres minor muscles.

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Supraspinatus

The trapezius muscle has been removed from the scapular spine to achieve this superior view of the shoulder which demonstrates the supraspinatus muscle. Note how the muscle runs under the coracoacromial arch before inserting on the humerus. This is significant clinically for patients complaining of shoulder pain with abduction due to the fact that this tendon can become impinged if shoulder mechanics are improper.

Click here to see a closer view of the supraspinatus tendon as it blends with the superior glenohumeral joint capsule.

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Infraspinatus & Teres Minor

The infraspinatus and teres minor muscles are important muscles of the shoulder girdle because of the stabilization they give to the joint capsule. Their attachment to the greater tubercle of the humerus allows them to be the main external rotators of the humerus.

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Long Head of Biceps Brachii

Take note of the path of this long, fibrous tendon as it runs from the belly of the biceps brachii muscle to its attachment on the supraglenoid tubercle. The tendon passes through the intertubercular groove and under the tranverse humeral ligament. It then sharply turns medially to reach it's proximal attachment point.

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Coracoacromial Ligament

The coracoacromial ligament is a tough ligament that connects the coracoid and acromion processes of the scapula. As described above, it forms part of the coracoacromial arch. This arch provides excellent protection of superior (upward) displacement of the humerus. It can cause problems in individuals with faulty scapulohumeral rhythm causing structures that run under this arch to become impinged and inflamed.

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Coracoclavicular Ligament

The coracoclavicular ligament provides a bridge between the clavicle and the coracoid process of the scapula. It is composed of two parts, the conoid and trapezoid ligaments. The two parts are not always easily separated or recognized. This ligament provides stability between the scapula and the clavicle,which is the only bony attachment of the upper extremity to the axial skeleton. It is also important in preventing extreme medial movement of the scapula.

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Joint Capsule

Any joint capsule can be thought of as a "plastic bag" that surrounds the structures that compose a joint. This is illustrated by the fibrous joint capsule of the glenohumeral joint as it engulfs the head of the humerus and the outer rim of the glenoid fossa.

This joint is strengthened by the tendons of the rotator cuff (S.I.T.S.) muscles that blend with the capsule. Click here to see a picture of this. Also review the supraspinatus, infaspinatus, and teres minor muscles discussed above.

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Glenohumeral Joint

The articulation between the humeral head and glenoid cavity of the scapula comprises the glenohumeral (or shoulder) joint.

The glenohumeral joint is the most mobile joint in the body. The sacrifice for this increased mobility is that the joint is consequently the least stable joint of the body. The glenoid labrum which attaches to and surrounds the glenoid cavity provides some additional support against humeral dislocation. This image shows the very rounded, convex head of the humerus in contrast to the concave glenoid fossa.