The Development of Humeral Retrotorsion and Its Relationship to Throwing Sports.

CONTEXT: Several investigations have noted that throwing athletes exhibit a more posteriorly oriented humeral head (humeral retrotorsion) in the dominant arm. This asymmetry is believed to represent an adaptive response to the stress of throwing that occurs during childhood. The significance of this alteration and factors that affect its development are currently not clear. EVIDENCE ACQUISITION: Basic science, research studies, and review articles were searched through PubMed with search terms including humeral torsion, humeral retrotorsion, and with 1 of the following: pediatric, adult, baseball, pitching, shoulder, and range of motion. The references from each article were reviewed for further inclusion. This review included articles through March 2015. STUDY DESIGN: Clinical review. LEVEL OF EVIDENCE: Level 4. RESULTS: The throwing motion creates stressors that result in bony adaptations that occur while skeletally immature. These osseous changes likely contribute to the observed shift in the arc of rotational range of motion noted in throwing athletes and may play a protective role against injury. However, too much or too little retrotorsion may predispose the shoulder to injury. The degree of optimal humeral retrotorsion and factors that influence its development are not fully understood. CONCLUSION: Evidence supports the assertion that the throwing motion creates stressors that alter bony anatomy while young. It is important to determine what specific factors affect this adaptation and its relationship to injury