Rotator cuff injury is common among overhead athletes, including baseball players [18] and tennis players [19]. Repetitive throwing motion leads to fatigue of the rotator cuff muscles and rotator cuff tears over time, usually involving the undersurface of the posterior half of the supraspinatus and superior half of the infraspinatus. Whereas articular-sided partial-thickness rotator cuff tears (PASTA lesion) are common in overhead athletes (Fig. 2.2) [20–22], full-thickness tears are diagnosed much less frequently.

Anterior shoulder instability due to dysfunction of the anterior capsular ligaments [14, 29, 30] may disable the throwing shoulder. Although traumatic subluxation causes anterior labral or capsular tears in some throwing athletes [31, 32], most cases of excessive anterior shoulder laxity (hypermobility of the humeral head) result from repeated stretching of the anterior capsular ligaments during the throwing motion [32–35]. Excessive anterior capsular laxity (elongation of the anterior capsular ligaments) is thought to cause shoulder subluxation during acceleration of the throwing motion, thus disabling the throwing shoulder. Anterior capsular-ligament tear or elongation can be diagnosed by using MR arthrography (Fig. 2.3).

Repetitive throwing motion in adolescent throwing athletes can lead to epiphyseal plate injuries, because the epiphyseal plate is weaker than the surrounding tendons and ligaments. This injury is called proximal humeral epiphysiolysis, or Little League shoulder. Proximal humeral epiphysiolysis causes shoulder pain localized to the proximal humerus during throwing and is diagnosed from radiographic or ultrasonographic evidence of widening of the proximal humeral epiphysis (Fig. 2.4) [37, 38]. Most patients feel tenderness of the epiphyseal plate in the proximal humerus.

In overhead athletes, less common causes of shoulder pain include quadrilateral space syndrome [39, 40] and suprascapular nerve entrapment [41–43], in addition to vascular problems such as effort thrombosis of the axillary artery or vein [44–47] and thoracic outlet syndrome [42, 43, 48, 49]. These neurovascular causes are difficult to diagnose and often require specialised tests such as electromyography and arteriography (Fig. 2.5).

Physical therapy is the most important treatment for preventing surgery in overhead athletes—especially in the early stage of the pathologic kinetic chain—and for improving shoulder function after surgery. When a pathologic kinematic chain, including scapular dyskinesis, muscle imbalance, posterior tightness, and increased anterior laxity, is ameliorated with physical therapy, shoulder pain during throwing decreases or disappears in most cases. An understanding of the interactions in the upper-extremity kinetic chain and determination of the precise pathological condition in each athlete are necessary for physical therapy to succeed (Fig. 2.6).

The Hara test is useful for assessing the upper-extremity kinetic chain for abnormalities leading to shoulder pain. The Hara test comprises 11 physical examinations relevant to the scapular and humeral kinetic chain: (1) scapula–spine distance (Fig. 2.7); (2) elbow extension test (Fig. 2.8); (3) elbow push test (Fig. 2.12); (4) manual muscle strength of abduction; (5) manual muscle strength of external rotation; (6) manual muscle strength of internal rotation; (7) combined abduction test (Fig. 2.9); (8) horizontal flexion test (Fig. 2.10); (9) capsular laxity tests; (10) subacromial impingement tests; and (11) hyper-external rotation test (Fig. 2.11). The total score (i.e., the number of “intact” results—see Fig. 2.12) for the Hara test and the abnormalities in each examination are evaluated.

In the scapula–spine distance test, the distance from the medial edge of the scapular spine to the spinous process of the thoracic spine is measured with the arms at the sides (Fig. 2.10). The reference point on the thoracic spine is defined as the nearest spinous process. A difference of more than 1.0 cm between the left- and right-side measurements is considered abnormal. To assess the scapular stabilizers, the elbow extension test and elbow push test are performed with the shoulders in 90° of forward flexion (Figs. 2.11 and 2.12). For the elbow extension test, the subject extends the elbow joint from 90° of flexion by using maximum force while the examiner holds the subject’s forearm to resist the extension force (Fig. 2.11). For the elbow push test, while grabbing the contralateral elbow with each hand, the subject pushes each elbow in turn anteriorly with maximum force as the examiner resists the subject’s pushing by holding the elbow (Fig. 2.12). Muscle strength is evaluated by manual muscle testing on a scale of 0–5. We assess the muscle strength of shoulder abduction with the subject’s thumb up; this is known as the “full can position” [26, 27, 70]. We measure external rotation strength with the subject’s arm at his/her side [71]. To assess internal rotation strength, we record the subject’s strength in lifting his/her hand off his/her back [72]. We consider the results of the elbow extension test, elbow push test, and manual muscle tests of abduction, external rotation, and internal rotation to be abnormal when the muscle strength on the dominant side is less than that on the non-dominant side. To assess the posterior tightness of the shoulder joint, subjects perform the combined abduction test and horizontal flexion test while the examiner fixes the scapula and prevents it from moving by holding it. The humerus is passively abducted in the coronal plane for the combined abduction test (Fig. 2.13) and horizontally flexed for the horizontal flexion test (Fig. 2.15). If the subject’s upper arm fails to touch his/her head during glenohumeral abduction with a fixed scapula, the combined abduction test is graded as abnormal. The horizontal flexion test is considered abnormal when the subject is unable to reach around the other shoulder to touch the bed during horizontal flexion with a fixed scapula. Capsular laxity is evaluated by load-and-shift testing in the anterior, posterior, and inferior directions; anterior apprehension and relocation tests are also done. When the dominant side shows increased laxity, or when the subject feels that the shoulder is unstable during any test, capsular laxity is considered abnormal. To evaluate subacromial impingement, we perform the Neer [24], Hawkins [25], and Yocum [26, 27] tests. If the subject feels shoulder pain during any of these tests, subacromial impingement testing is graded as abnormal. The hyper-external rotation test (Fig. 2.15), which evaluates peel-back of the superior labrum [12, 14, 16] and pathologic internal impingement [50, 53, 65], is performed in 90° of shoulder abduction with the elbow flexed at 90° in the supine position. The test is considered to be abnormal when a subject feels pain as the examiner applies external rotation torque beyond the maximum external rotation position. The number of “intact” results among the 11 physical examinations is recorded as the total Hara test score for each subject. The maximum total score (11 points) represents all “intact” results (i.e., no abnormality found) for all tests; subjects with lower scores are considered likely to have a problem in the upper-extremity kinetic chain.

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