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PART III THE UPPER EXTREMITY Pectoralis major Clinical Connection 8.1


Impingement syndrome is a condition in which structures within the subacromial space are com- promised and impinged. Chronic impingement can lead to infl ammation and tissue damage. During the early stages, people with impingement syndrome can experience shoulder pain when raising the arm. In more advanced injury, they may have discomfort even at rest.


Both intrinsic and extrinsic factors can lead to impingement, resulting in pain and upper extremity dysfunction. Intrinsic factors are related to muscle weakness. Rotator cuff muscle weakness can result in excessive humeral head elevation in the glenoid fossa during overhead lifting of the arm. The humeral head compresses the structures in the subacromial space, including the rotator cuff, coracoacromial ligament, bursa, and bicipital tendon. Repetitive overuse of the arm with this subacromial compres- sion can produce microtrauma, tendonitis, and GH instability. The subacromial space can also be compromised by excessive scapular protraction and tilt resulting from scapulothoracic muscle weak- ness. Extrinsic factors that can cause impingement include a malformation of the acromion that results in compression on the rotator cuff or degenera- tive joint changes in the AC joint. These bony factors, although extrinsic to the actual joint space, can produce external stresses to the subacromial structures.


Adduction Extension


Sternocostal head


Clavicular head


Figure 8.32 Anterior view of pectoralis major showing its clavicular and sternocostal heads.


which can lead to secondary impingement of structures in the subacromial space. Imbalances in the strength of these upward rotators of the scapula can also lead to shoulder injury, pain, and dysfunction. For example, if the upper trapezius muscle is strong in relation to a weaker lower trapezius or serratus anterior muscle, the scapula will be pulled superiorly before rotating in an upward direction during arm elevation. This superior motion causes the humeral head to migrate upward in the glenoid fossa, resulting in impingement of subacromial soft tissue structures.


FUNCTIONAL DEFICITS IN THE SHOULDER COMPLEX


Scapular motion is essential to achieve functional move- ment of the upper extremity. A defi ciency in one scapular muscle as a result of paralysis or injury can compromise the scapula’s position and correct pattern of movement. During arm elevation, the upper and lower trapezius and serratus anterior muscles work in synergy to rotate the scapula upward while maintaining it in contact with the thorax. If the serratus anterior is weak, the medial border of the scapula is “winged” and not held in contact with the thorax (Fig. 8.33). Normal scapulohumeral rhythm is disrupted, making effi cient arm elevation diffi cult. As dysfunction of the serratus anterior results in reduced upward scapular rotation, posterior tilting, and lateral scapular rotation, the subacromial space is reduced,


Chapter 5 explains how the malalignments of rounded shoulders and forward head posture affect the cervical spine. In this slumped posture, the scapulae are in a protracted position. The rhomboids and lower trapezius muscles are overlengthened and weakened, whereas the pectoralis minor muscles are often tight and shortened. The tight pectoralis muscles limit the scapula’s ability to rotate upward and tilt posteriorly during shoulder eleva- tion. This excessively protracted scapular position and the inability of the scapula to effectively rotate upward compresses the subacromial structures as the arm reaches overhead. The posterior GH joint capsule can also become excessively tight, which hinders the inferior glide of the humeral head during arm elevation. This capsular tightness can contribute to impingement of subacromial structures.


If the rotator cuff muscles are weak or malfunctioning and not countering this superior translation, the upward movement of the humeral head can be more substantial.


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