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

Disclosures

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

In This Article

Anatomy, Pathoanatomy, and Adaptive Changes

The shoulder joint is stabilized by both static and dynamic structures. The static stabilizers include the glenohumeral joint geometry, the glenohumeral ligaments, and the capsulolabral complex, which act via joint conformity as well as adhesion-cohesion. These stabilizers are subject to mechanical failure.

The most important dynamic stabilizers are the rotator cuff and the long head of the biceps. The long head of the biceps tendon acts as a dynamic stabilizer in the abducted and externally rotated position.[15,18] These structures also actively stabilize the glenohumeral joint via concentric and eccentric muscle contraction forces and are subject to fatigue as well as overt mechanical failure.

Injury to the thrower's shoulder is often acute on chronic, with overuse and fatigue as important factors. When the kinetic chain is evaluated, scapular dysfunction and rotator cuff imbalance may be present. As noted previously, the thrower's shoulder may develop an excessively tight posterior capsule, resulting in a glenohumeral internal rotation deficit (GIRD) that leads to internal impingement with or without secondary instability. Primary or multidirectional instability may also be present.

When evaluating the thrower's shoulder for pathoanatomy, the clinician must understand the coexistence of adaptive anatomic and nonpathologic changes that are the result of repetitive stresses associated with throwing (Table 1). As a result of these changes, a high percentage of throwing athletes demonstrate asymptomatic but abnormal findings on MRI.

Lesniak et al[19] evaluated the MRI results of 21 asymptomatic professional pitchers and found that 52% had rotator cuff tears (RCTs), 48% had superior labrum anterior to posterior (SLAP) tears, and 62% had anterior or posterior labral tears. These findings correlated with the number of career innings pitched. In another MRI study of asymptomatic professional baseball pitchers, Miniaci et al[20] found that 79% of shoulders had labral pathology, with no statistically significant difference between the dominant and nondominant shoulders. In a prospective cohort study, Connor et al[21] evaluated MRI shoulder scans of asymptomatic elite overhead athletes and found that although their nondominant rotator cuffs were normal, 40% of the dominant shoulders exhibited findings consistent with partial- or full-thickness RCTs. Despite these findings, none of the athletes reported any shoulder problems during the 5 years after the MRIs were obtained.

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