The Posterior Shoulder Pain of THE Fastball: Internal Impingement of the Shoulder

by Abigail Moffit, OMS II

The shoulder is known as a ball and socket joint; this type of joint is comparable to a golf ball on its tee. The size of the humeral (arm bone) head in comparison to the glenoid (the socket on the shoulder blade) allows for a greater range of motion, but also leads to an increased risk of injury. Majority of the stability of the shoulder comes from the surrounding musculature such as the biceps, the muscles surrounding the shoulder blade, and the rotator cuff muscles. The rotator cuff consists of four muscles, the supraspinatus, the infraspinatus, teres minor and subscapularis. The rotator cuff as a group of muscles is responsible for dynamic stability, with the ability to center the humeral head within the glenoid.

Internal impingement occurs when the shoulder is in maximum abduction and external rotation, a common occurrence in overhead athletes. This can occur during the late cocking and early acceleration phases of throwing. This motion causes the biceps to peel back the posterosuperior labrum (a cup of cartilage that helps to deepen and stabilize the shoulder joint).

Internal impingement is caused by repetitive impingement of the posterior supraspinatus tendon, infraspinatus tendon (rotator cuff muscles) between the humeral head (long bone of the arm) and the glenoid of the scapula (the cupped portion of the shoulder blade). Chronic repeated compression can cause fraying of the rotator cuff muscles as well as the superior labrum, leading to superior labrum anterior to posterior (SLAP) lesions. Scapular dysfunction, glenohumeral joint instability and restricted range of motion can contribute to or cause internal impingement.


Internal impingement can present as diffuse pain over the posterior aspect of the shoulder. This pain gets worse with throwing, especially during the late cocking phase. Upon evaluation by a physician, pain may be evident with palpation along the infraspinatus muscle, which sits at the bottom portion of the shoulder blade. Active and passive range of motion may show excessive external rotation and decreased internal rotation, however, there may be preservation of the total arc of motion. Glenohumeral internal rotation deficit (GIRD) is defined as the lack of internal rotation with excessive external rotation compared to the non-dominant shoulder.  Professional baseball players with GIRD are almost twice as likely to be injured than those without GIRD. It is not uncommon for loss of rotator cuff strength. Imaging studies such as MRI or CT scan can assess for complications of internal impingement and are helpful to making the diagnosis.


 a baseball pitcher throwing a pitch with copy spaceThe first line treatment is to decrease pain by conservative treatment. Cessation of activities, especially throwing, NSAIDs (or other oral anti-inflammatory medications), ice, physical therapy, posterior capsule stretching, and corticosteroid injections are all conservative options. If therapy has failed for an extended period of time, operative treatment may be considered. Other indications for surgical intervention include partial thickness rotator cuff tears, Bennett lesions, SLAP lesions and dislocations. The surgical treatment is typically done arthroscopically and may include subacromial decompression, debridement of the rotator cuff, and/or completion of the rotator cuff tear by arthroscopic repair. Talk to your physician for the best treatment option for you.

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