Humeral Torsion as a Risk Factor for Shoulder and Elbow Injury in Professional Baseball Pitchers

OBJECTIVES: Participation in baseball causes increased mechanical stress to the throwing arm and has been linked to alterations in shoulder range of motion (ROM) and bony morphology. Range of motion changes, specifically GIRD, has been associated with increased shoulder injury. However, the role of humeral torsion is unclear in shoulder injury. The purpose of this study was to prospectively compare humeral torsion (HT) in professional pitchers who remain healthy as compared with those who go on to suffer shoulder injuries. METHODS: We prospectively measured and observed 255 professional pitcher-player seasons prior to 2009-2013 spring training. Bilateral HT was assessed in pitchers who were currently asymptomatic and participating without restriction, in all training, and practices. Humeral torsion was assessed via validated, indirect ultrasonography. Two trials of HT were averaged for data analysis. The side-to-side difference in HT was calculated by subtracting the dominant arm (D) HT from the non-dominant (ND) HT. The pitchers were then followed for the development of shoulder injury over the course of each season. Separate mixed model ANOVAs(side X injury) were used to compare pitchers’ dominant and non-dominant HT between those who suffered shoulder injury to those who did not miss games due to arm injury (α=0.05). Tukey's Post-Hoc tests were used to determine minimum significant differences for significant interaction effects. RESULTS: We observed 30 shoulder injuries. Pitchers with previous elbow injuries(n=30) were excluded from the comparison.(Table 1) Pitchers who suffered a shoulder injury displayed 3.5° less D humeral retrotorsion compared to those pitchers without injury(n=195; P=0.04).(Figure 1). CONCLUSION: This study showed that pitchers with decreased humeral retrotorsion had a significantly increased risk of shoulder injury. Decreased humeral retrotorsion may hinder the ability of the shoulder to obtain needed ROM, thus increasing stress to the shoulder in late cocking and follow through. Our results should be viewed in context of the relatively small injury numbers but provide preliminary evidence that the influence of HT should be closely examined when considering shoulder injury risk in professional pitchers.