Jonathan D. Gelber, MD, MS; Lonnie Soloff, DPT, PT, ATC; Mark S. Schickendantz, MD


J Am Acad Orthop Surg. 2018;26(6):204-213. 

In This Article

Injuries in the Thrower'S Shoulder

To help guide treatment, injuries related to the thrower's shoulder can be generally classified into three groups. Group 1 injuries are caused by internal impingement. Group 2 injuries are caused by internal impingement with acquired secondary anterior instability. Group 3 injuries are the result of primary anterior or multidirectional instability. Within each group, athletes exhibit specific clinical histories, physical examination findings, and MRI changes.

Group 1

During the late-cocking phase, the arm is positioned in abduction and extreme external rotation. In this position, there is mechanical pinching of the posterolateral rotator cuff and the labrum between the posterolateral portion of the greater tuberosity and the posterosuperior glenoid (Figure 3). Although such pinching can be seen as part of a normal biomechanical process in high-level throwers, repeated mechanical impingement can lead to shoulder pathology. The thrower will experience posterior pain during late cocking. This pain is mechanical and positional in nature; it hurts each time the athlete moves the shoulder into the externally rotated/abducted position achieved during the late-cocking phase of the throwing motion. In addition, the athlete may have posterolateral cuff pain. On physical examination, a positive internal impingement sign of deep posterior shoulder pain is exhibited when the arm is brought into a position similar to the late-cocking phase of throwing, that is, abduction of 90° to 110°, extension of 10° to 15°, and maximal external rotation.[31] MRI findings that coincide with this posterolateral impingement include rotator cuff injury at the junction of the supraspinatus and infraspinatus, posterosuperior labral injury, and cystic changes in the posterolateral tuberosity (Figure 4).

Figure 3.

Arthroscopic image of a shoulder demonstrating internal impingement of the posterolateral rotator cuff and the labrum in the lateral decubitus position. B = biceps tendon, G = glenoid, H = humeral head, SS = supraspinatus. (Courtesy of Mark Schickendantz, MD, Cleveland, OH.)

Figure 4.

Axial T2-weighted MRI of the glenohumeral joint showing changes commonly found in throwers, including posterior capsule thickening and posterior cuff changes (A) and posterolateral glenoid cystic changes (B). (Courtesy of Mark Schickendantz, MD, Cleveland, OH.)

A so-called peel-back lesion of the biceps anchor and labrum occurs during abduction-external rotation (ABER) as the biceps tendon moves posterior to the joint behind the tuberosity and pulls on the labrum.[32] The fibers of the biceps tendon are oriented to resist traction. However, the strain pattern of the ABER position does not coincide with direct traction; instead, it causes a torsional strain that can lead to failure at the biceps anchor, resulting in a SLAP lesion. In the thrower, the SLAP lesion reveals a demonstrable peel-back sign extending posteriorly. The typical thrower's SLAP lesion does not extend anteriorly[33] (Figure 5).

Figure 5.

Arthroscopic images of a thrower's shoulder demonstrating type I (A) and type III (B) superior labrum anterior to posterior lesions. B = biceps tendon, G = glenoid, H = humeral head, L = labrum. (Courtesy of Mark Schickendantz, MD, Cleveland, OH.)

During the follow-through phase of throwing, repetitive loads to the posteroinferior capsule can lead to contracture of the posterior band of the inferior glenohumeral ligament (PIGHL).[7] After ball release, the arm moves ahead of the body and exerts a large distraction force of approximately 750 N (80% of body weight),[34] which acts on the posteroinferior capsule. A tight posterior capsular contracture has been shown to shift the glenohumeral rotation point in a posterior and superior direction.[35] As an adaptive response, it allows more clearance of the greater tuberosity over the glenoid rim during ABER; therefore, the athlete can hyperexternally rotate the shoulder.

A tight PIGHL can also lead to anterior pseudolaxity. The humeral head acts as a cam to tighten the anterior structures, but as the tight PIGHL shifts the center of rotation posteriorly and superiorly, the cam effect of the head is lost anteriorly. It is important to recognize that this apparent anterior pseudolaxity without subluxation is not the source of pathology, especially in the presence of a posterior SLAP tear.

Like all adaptive responses, too much compensation along the spectrum can lead to pathology. Although it was previously noted that pitchers gain increased external rotation and lose internal rotation, this should not come at the expense of total arc of motion. Thickening and contracture of the PIGHL can lead to GIRD. With a loss of ≥25° of total arc of motion, GIRD is symptomatic.[7] In the ABER position of late cocking, the posterior band of the IGHL is bowstrung beneath the humeral head. The biceps vector shifts posteriorly and twists at its base, maximizing peel-back forces. As a result of the tight posteroinferior capsule, a pitcher may show poor pitching mechanics and a breakdown in the kinetic chain. These breakdowns can include hyperexternal rotation, hyperhorizontal abduction (out of the scapular plane), a dropped elbow, and premature trunk rotation.[7] In fact, pitchers with GIRD are nearly twice as likely as pitchers without GIRD to be injured.[36]

As part of the internal impingement spectrum, the rotator cuff may be injured. During the late-cocking phase, the rotator cuff is twisted like a rope. During follow-through, the rotator cuff fibers are then placed under stretch or eccentric loading, resulting in further tensile stress. This repetitive twisting and pulling can result in tendon failure. In this case, overhead throwers may also experience anterolateral pain that is aggravated by overhead activities. They may experience more pain during the acceleration and follow-through phases. The pitcher may take longer to warm up. Once warmed up, the pitcher may feel okay; however, the pain may return later in the game.

The spectrum of rotator cuff injuries ranges from tendinitis and tendinosis to partial-thickness tears. Partial-thickness tears tend to be articular sided and most often occur at the junction of the supraspinatus and infraspinatus tendons (Figure 6). The acronyms PASTA (ie, partial articular supraspinatus tendon avulsion) and PAINT (ie, partial articular tear with intratendinous extension) are often used to describe these lesions.[37,38] Full-thickness tears are rare in the overhead athlete.[39]

Figure 6.

Arthroscopic images of a shoulder demonstrating partial-thickness (50%) rotator cuff tear before (A) and after (B) débridement. The star indicates an area of partial tear débridement. B = biceps tendon, H = humeral head, SS = supraspinatus. (Courtesy of Mark Schickendantz, MD, Cleveland, OH.)

Group 2

As mentioned previously, increased external rotation is an adaptive change that allows overhead athletes to improve their performance. However, some authors have speculated that this increase in external rotation can lead to repetitive microtrauma in the anterior structures, resulting in stretching of the anterior IGHL and anterior capsule. Excessive repetitive hyperexternal rotation and hyperhorizontal abduction and subsequent anterior stretching can lead to symptomatic anterior instability.[12,40] A cadaver study showed that increasing anterior capsular laxity could exacerbate internal impingement during the late-cocking phase of the throwing motion.[14]

In athletes with a group 2 injury, a deep anterior pain is experienced during the late-cocking and acceleration phases. Because of increased anterior translation and associated anterior instability, anterior labrum tears with or without an associated internal impingement type posterior-superior SLAP tear may develop in these athletes. Although most overhead athletes demonstrate 1+ passive anterior translation on physical examination (ie, increased anterior translation of the humeral head without subluxation) caused by adaptive changes, 2+ anterior translation (ie, translation with subluxation of the glenohumeral joint) should be considered pathologic.[39] Patients with group 2 injuries (ie, injuries caused by internal impingement with acquired secondary anterior instability) may experience tensile failure of the anterior supraspinatus (ie, PASTA lesions). In addition, anterior subluxation can lead to scuffing of the anteroinferior labrum or, in extreme cases, a Hill-Sachs impression lesion.

Group 3

As in any athlete with shoulder pain, primary or multiplane instability can be the source of pathology. Throwers with group 3 injuries experience extremity fatigue or describe a so-called dead arm. They may have nonspecific pain at the rotator cuff. Overhead athletes rely on the rotator cuff to keep the glenohumeral joint stable during the throwing motion; as the cuff fatigues, subluxation episodes may occur. When these athletes play, they start the game slowly but improve in the middle innings as the rotator cuff warms up. However, as the game progresses and the rotator cuff begins to fatigue, symptoms worsen. In these athletes, physical examination findings, such as the sulcus sign and positive apprehension and relocation tests, are consistent with primary anterior or multidirectional instability. Positive MRI findings are often minimal.