Chapter 5

At the conclusion of this chapter, the student should be able to:

• 1. Name, locate, and describe the structure and ligamentous reinforcements of the articulations of the shoulder region.
• 2. Name and demonstrate the movements possible in the joints of the shoulder region regardless of starting position.
• 3. Name and locate the muscles and muscle groups of the shoulder region, and name their primary actions as agonists, stabilizers, neutralizers, or antagonists.
• 4. Analyze the fundamental movements of the arm and trunk with respect to joint and muscle actions.
• 5. Describe the common injuries of the shoulder region.
• 6. Perform an anatomical analysis of the shoulder region in a motor skill.

Anatomical cooperation is beautifully illustrated in the movements of the arms on the trunk. The arm travels through a wide range of movements, and in each of these the scapula cooperates by placing the glenoid fossa in the most favorable position for the head of the humerus. This is known as scapulohumeral rhythm. When the arm is elevated sideward (abducted), for instance, the scapula rotates upward; when it is elevated forward (flexed), the scapula not only rotates upward but it tends to slide partially around the rib cage (abducted). Although occasionally movement of the scapula is deliberately repressed (as in some stylized dance movements, and in some posture exercises), in all natural movements, the scapula shares with the humerus in the movements of the arm on the trunk. In abduction of the arm, for instance, the movements of the scapula and humerus are continuous throughout the movement, with the humeral movement accounting for approximately two-thirds of the total movement and the scapular movement for one-third. It is important to remember, however, that this cooperative scapulohumeral rhythm is not a linear relationship. It varies with individuals and with the phase of the movement. Scapulohumeral rhythm may vary across age groups and with certain types of activity, including throwing. Load and speed of movement may also produce variations. In the normal adult, however, this cooperation is fairly predictable.

The upper extremity is suspended from the axial skeleton (head and trunk) by means of the shoulder girdle. The latter consists of the sternum and two clavicles in front, and two scapulae in back. The sternoclavicular joints connect the sternum and each clavicle, and the acromioclavicular joints connect the acromion process of each scapula with the corresponding clavicle. Because there is no union between the two scapulae in back, this is an incomplete girdle. The upper extremity’s connection with the shoulder girdle is made through the glenohumeral joint, the joint between the head of the humerus and the glenoid fossa of the scapula, better known as the shoulder joint.

The sternoclavicular joint is an exceedingly small one, about the size of the joint between the great toe and the first metatarsal bone, yet it is the sole skeletal connection between the upper extremity and the trunk. This anatomical arrangement ...

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