First, I'd like to thank my co-authors, and I'd also like to thank AOSSM for inviting us to present here today. Here are our disclosures. It's well known that significant differences in glenohumeral range of motion and humeral torsion exist between elite pitchers and the non-throwing population. Specifically, retro torsion, external rotation, and glenohumeral internal rotation deficit are all increased in the throwing population. However, no studies have found significant differences associated with throwing arm dominance in this population. So our clinical question is we wanted to know if differences existed in glenohumeral range of motion and humeral torsion between right and left-handed pitchers, because understanding such differences would help assess progress through rehab, guide training programs, and inform injury risks. Our study population consisted of 217 professional pitchers from one MLB organization. 160 of these were right-handed, and 57 were left-handed. Measurements were taken over a seven-year period, and players with multiple measurements over this time were averaged into a single data point. Torsion is the angle between the axis through the humeral head proximally and through the humeral condyles distally. Retro torsion, or a more posteromedial position of the humeral head, results in more external rotation of the distal humerus. So to measure torsion, we used an ultrasonographic measurement that was first described by Myers et al. We used an ultrasound probe to put the humeral head in neutral position, and then used a digital inclinometer placed on the ulna to give us our measurement of humeral torsion. We also measured external rotation, internal rotation, total arc of motion, and forward flexion. The measurements were taken in both the throwing and non-throwing arms, and were compared within cohorts to give us a side-to-side difference in between cohorts. Right-handed pitchers had 10 degrees more retro torsion in their throwing arms compared to left-handed pitchers. With regards to side-to-side difference, right-handed pitchers had 23.1 degrees more retro torsion in their throwing arm compared to their non-throwing arm, while left-handed pitchers had a non-significant difference of 2.2 between their throwing and non-throwing arms. With respect to external rotation, right-handed pitchers also had significantly more external rotation in their throwing arm than left-handed pitchers. And there were also significant side-to-side differences in both groups, with right-handed pitchers having 13.9 degrees of external rotation, and left-handed pitchers having 2.2 degrees external rotation difference between the arms. This graph here shows that we noticed that as retro torsion increased, so did the amount of external rotation in our cohort, and as we can see, right-handed pitchers were near the part of the spectrum with the highest measurements. Right-handed pitchers and left-handed pitchers also had significant differences in internal rotation deficit, and we saw this is consistent with associations of GERD and retro torsion that have been previously shown in the literature. And here we again see that players with more internal rotation deficit also showed more retro torsion, and again, the right-handed pitchers typically had higher measurements. So torsion contributes to the range of motion measurements, which are important for training and rehab programs engaging a player's progress through these. External rotation and internal rotation deficit that have contributing factors that are obvious adaptations such as retro torsion are non-modifiable and would show little progress over the course of a program. Furthermore, training rooms have limited access to ultrasound, and so often the medical staff would not know the amount of torsion in a given player. Retro torsion has also been correlated with some increased injury risk, specifically UCL damage at the elbow. So the big question that remains is why. Given our population of professional pitchers, we think that competitive selection plays a large role. Professional teams desire left-handed pitchers because of their different arm slot, and so with the relative rarity of left-handed pitchers in the population, it creates an easier path to the highest level. Furthermore, the higher competition for right-handed pitchers would then select for those that max out their throwing metrics as well as their associated range of motion measurements. To look at the biological reason for this, we would have to go back to adolescence, because differences in retro torsion would arise during peak growth velocity. Future research should take a look at the differences in throwing volume in young athletes. There are a couple limitations. First, we use only a single MLB organization, and our cohort was not sufficient to examine the injury risks that might be associated with handedness, torsion, or external rotation in GERD. The evidence in the literature for these associations isn't strong, and so more research would be needed to quantify the risks. In conclusion, in the throwing arm, right-handed pitchers demonstrate significantly greater measures of external rotation, glenohumeral internal rotation deficit, and humeral retro torsion compared to left-handed pitchers. Right-handed pitchers also demonstrated significant side-to-side torsion differences, while left-handed pitchers did not. These are our references, and thank you.

glenohumeral range of motion

humeral torsion

right-handed pitchers

left-handed pitchers

MLB organization