156


PART III THE UPPER EXTREMITY Scapula Scapular plane


Frontal plane 30-45°


135°


Acromion of scapula


Manubrium of sternum


Figure 8.4 Superior view of the scapula in its resting position 30° to 45° from the frontal plane. (From Houglum B, Beroto D. Brunnstrom’s Clinical Kinesiology, 6th ed. Philadelphia, PA: F. A. Davis Company, 2012, p.163, with permission.)


tubercle, and the long head of the triceps attaches to the infraglenoid tubercle. The glenoid fossa is oriented approximately 35° anterior to the frontal plane. This orientation is referred to as the scapular plane and is illustrated in Figure 8.4. Most of the functional move- ments occurring between the scapula and the humerus take place in the scapular plane.


Humerus


The convex head of the humerus articulates with the slightly concave glenoid fossa to form the glenohumeral (GH) joint. The anatomical neck separates the head of the humerus from the shaft. The head is oriented medially and superiorly, forming a 130° to 150° angle of inclination with the humeral shaft (Fig. 8.5A). This angle is formed by the intersection of a line through the humeral head and neck and a line through the longitu- dinal axis of the humeral shaft. The head is inclined in relationship to the long shaft of the humerus. The head of the humerus is rotated posteriorly about 30° from the horizontal plane. This posterior rotation is referred to as retroversion, from the Latin retro, meaning “backward,” and verto, meaning “to turn” (Fig. 8.5B). The greater and lesser tubercles on the humerus are divided by the intertubercular (bicipital) groove. The tubercles and the deltoid tuberosity are points of attachment for shoulder complex muscle groups. On the posterior surface of the humerus is the radial groove that divides the lateral and medial heads of the triceps (Fig. 8.6).


JOINTS


There are four distinct joints within the shoulder complex: the sternoclavicular (SC), the acromioclavicular (AC), the scapulothoracic, and the GH joints. Movement in these joints is coupled so that each joint functions as a link in a chain contributing to the overall fi nal movement of


A Clavicle


Angle of


Inclination


Retroversion 30°


Horizontal plane


Lateral B


Medial


Figure 8.5 (A) The 135° angle between the shaft and head of the humerus in the frontal plane is referred to as the angle of inclination. (B) The humeral head is rotated posteriorly in relation to the distal humerus in 30° of retroversion. (From Houglum B, Beroto D. Brunnstrom’s Clinical Kinesiology, 6th ed. Philadelphia, PA: F. A. Davis Company, 2012, p.166, with permission.)


the upper extremity. Motion at the SC and the AC joints produces motion at the scapulothoracic joint. Dysfunc- tion in one of these joints can interfere with optimal movement and function of the upper extremity. Because of the scapula’s articulation with the clavicle, SC and AC joint motion is always linked to scapulothoracic move- ment. When there is movement at the scapulothoracic joint, movement will occur at the SC joint, the AC joint, or both joints. The position and movement of the scapula also infl uence movement between the humerus and the scapula.


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