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

Humeral Retroversion and Adaptive Bony Changes

The proximal humerus is retroverted in utero (mean, 78°) and derotates over time.[22] It reaches a mean of 65° from 4 months to 4 years of age and is approximately 38° in children 10 to 12 years of age.[22] The most rapid changes occur before age 8 (± 2.12) years and continue until the appearance of the radial groove (approximately age 16 years).[22] In the average adult, mean retroversion differs between 33° in the dominant arm and 29° in the nondominant arm. No substantial differences between sexes were observed in a study of retroversion of the humeral head.[23]

In contrast, further increased humeral retroversion is found in the thrower's dominant shoulder. These bony adaptations contribute to the rotational changes found in these shoulders.[24] These adaptive and often asymptomatic physeal changes occur throughout adolescence and have been observed in the dominant throwing arms of skeletally immature baseball players.[25] It has been proposed that these adaptive bony changes are the result of derotation restriction rather than an active increase of retroversion from throwing[26] (Figure 2).

Figure 2.

Photographs showing decreased internal rotation (A) and increased external rotation (B) in a thrower's shoulder. (Courtesy of Mark Schickendantz, MD, Cleveland, OH.)

Collegiate throwers have an increased average retroversion of 36.6° (±9.8°) and a total arc of motion of 159.5° in the dominant arm versus a decreased average retroversion of 26° (±9.4°) and total arc of motion of 157.8° in the nondominant arm.[27] Collegiate pitchers had increased dominant arm external rotation when measured at zero and 90° of abduction, which was associated with greater humeral retroversion.[28] Similarly, professional baseball pitchers' dominant shoulders showed increased external rotation and humeral/glenoid retroversion.[29] These adaptive changes are thought to pre-position the throwing arm in external rotation, leading to less anterior shoulder strain and imparting greater kinetic energy via increased rotational torque while throwing.

In addition to enhancing performance, adaptive changes to the shoulder may decrease injury rates. In one recent study, a correlation was found among injured professional pitchers with more missed playing days and a lower degree of retroversion shoulder dominance.[30]

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