Sports Medicine Research: In the Lab & In the Field: Does the Glenohumeral Joint Structurally Adapt Over a High School Baseball Season? (Sports Med Res)
Monday, March 25, 2013

Does the Glenohumeral Joint Structurally Adapt Over a High School Baseball Season?

Changes in humeral torsion and shoulder rotation range of motion in high school baseball players over a 1-year period

Oyama S, Hibberd EE, Myers JB. Clin Biomech (Bristol, Avon). 2013 Feb 19. pii: S0268-0033(13)00015-6. doi: 10.1016/j.clinbiomech.2013.01.014. [Epub ahead of print]

Take Home Message: Over one year, high school baseball players had no bony changes (humeral retroversion) in their dominant arm’s humerus but had decreased shoulder internal rotation.

Unilateral overhead sports cause several bony and soft tissue adaptations on the dominant arm due to the large amounts of mechanical stress.  However, it is unknown when bony adaptations (e.g., humeral retroversion) occur during skeletal development.  Therefore, the authors examined the longitudinal change of humeral retroversion and glenohumeral range of motion in 138 high school baseball players between the start of 2 consecutive seasons.   Participants also completed a history questionnaire indicating the number of years they participated in baseball.  Players were excluded if they had a current injury or an injury within the past year.  The authors used an ultrasound technique to measures humeral retroversion and standard procedures (inclinometer) to measure glenohumeral range of motion.  The authors found that humeral retroversion did not change over a 1 year period regardless of the amount of years participating in baseball.  Dominant arm internal rotation decreased over the 1 year period but was not affected by the amount of years participating in baseball.  External rotation and total range of motion decreased bilaterally over the 1 year period among participants that only played baseball for 1 year prior. 

This study found that bony adaptation of humeral retroversion may be complete prior to high school.  This suggests that we need to examine younger adolescents to identify when this bony adaptation is occurring and how quickly it is occurs   In addition, this study used a simple ultrasound method to measure humeral retroversion, which can be implemented clinically if a diagnostic ultrasound is present.  The authors also found that dominant arm internal rotation decreased over the one year period.  This is in agreement with a previous study that examined female high school overhead athletes.  This may suggest that the deceleration stress caused during the throwing motion contributes to posterior shoulder soft tissue tightness.  Previous research has linked decreases in internal rotation to shoulder injuries and internal impingement.  Lastly, the authors found that external rotation and total range of motion to decreased bilaterally but only in players that only played the year prior.  This is an interesting finding and may suggest that there is a soft tissue reaction to the new stress placed on the shoulder joint among players that just started to play.  It would be interesting if this is only seen during the first year of participation and it resolves itself in time.  Clinically, these results demonstrate the importance of examining players longitudinally.  It suggests that if changes in range of motion are detected longitudinally in high school baseball players then the changes are indicative of soft tissue tightness and stretching should probably be implemented to reduce the risk of future shoulder injuries.  Do you examine glenohumeral range of motion over the season in your overhead athletes?  What information do you use to identify the players that need to be stretched?

Written by:  Stephen Thomas
Reviewed by: Jeffrey Driban

Related Posts:

Oyama S, Hibberd EE, & Myers JB (2013). Changes in humeral torsion and shoulder rotation range of motion in high school baseball players over a 1-year period. Clinical Biomechanics (Bristol, Avon) PMID: 23434341

4 comments:

Kaitlyn Kelly said...

Were there high school freshmen on the teams as well? Could the bony adaptations in the arm be something that has to occur before puberty? You have also stated that the internal rotation of the dominant arm decreases over the year, were these athletes stretching and being stretched out everyday? If not do you believe that them being passively stretched and actively stretching their Glenohumeral joint would help to keep or increase their internal rotation?
Thank you

Stephen Thomas, PhD, ATC said...

Kaitlyn thanks for the comment. The study included all levels of high school baseball players. What is your concern about freshman? Yes this study indicated that humeral retroversion clearly is occurring prior to high school. We need to start looking at even younger groups. It did not indicate if players were engaging in their own stretching programs. One might assume that stretching would prevent that decrease however the research is lacking long term stretching protocols on range of motion.

Will Bradley said...

Based on this study, do you think this decrease in IR and ER will lead to scapular dyskinesis?

Stephen Thomas, PhD, ATC said...

Will good question. We current don't know if glenohumeral internal rotation deficits (GIRD) cause scapular dyskinesis. It truly is the chicken or egg situation. I published a paper that found there was an association between the two (http://www.ncbi.nlm.nih.gov/pubmed/19841995). Specifically we found players with larger amounts of GIRD also had scapular dyskinesis. However, this doesn't demonstrate cause and effect.

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