Early Sports Specialization and Playing Year-Round Associated with Shoulder Abnormalities in Little Leaguer’s

Pennock AT, Dwek J, Levy E, et al. Shoulder MRI abnormalities in asymptomatic Little League baseball players. Am J Sports Med. 2018;6(2):1-6. doi:10.1177/2325967118756825.


Up to 50% of youth baseball players, ages 9 to 14 years, may experience arm pain during a single season1,2.  Multiple risk factors may be responsible, including year-round play, pitching for more than one team, pitch velocity, player height, and loss of shoulder range of motion.  Common shoulder injuries in Little League baseball players include labral tears, rotator cuff injury, internal impingement, and growth plate injuries (i.e., “Little League Shoulder”).   It is unclear which risk factors may be most closely associated with specific shoulder injuries in youth baseball players.


The purpose of this study was to examine magnetic resonance imaging (MRI) abnormalities in the shoulders of asymptomatic Little League baseball players and to correlate findings with throwing history and physical examination findings.

Study Population

  • Volunteers (n=23) from a single Little League District in Southern California
  • Currently asymptomatic , ages 10 to 12 years
  • No history of seeking treatment for any shoulder injury
  • Exclusion: Any complication which would prohibit MRI


A detailed throwing history using a questionnaire was collected for all research participants.  A physical examination of both shoulders was then conducted by an orthopedic surgeon.  Each participant underwent an MRI of both shoulders.  Bilateral shoulder ultrasonography was performed to assess humeral torsion.

Participants who reported a history of shoulder pain from baseball were compared with those who had a negative history in terms of clinical examination, questionnaire data, and MRI findings. The clinical examination and questionnaire data for players whose MRI results indicated an abnormality of their dominant arm were compared with the data for players whose MRI results did not indicate an abnormality.

Key Findings

  •  83% reported experiencing arm pain at some point during their playing career
  • 61% reported experiencing shoulder pain at some point during their career
  • History of shoulder pain was associated with throwing curveballs or cutters, sliders, or sinkers (p < .05)
  • 52% of participants showed abnormalities of their throwing shoulder on MRI
  • The most common abnormalities were edema or widening of the proximal humeral physis (5 players), followed by labral tear (4 players), and partial rotator thickness tear (4 players).
  • Abnormal MRI findings did not correlate with player position, years of play, compliance with Little League throwing guidelines, or a prior history of arm or shoulder pain.
  • MRI abnormalities were associated with 2 factors: year-round play and single-sport participation (P < .05). Players with 1 risk factor had a 71% chance of having an abnormal MRI, and players with both risk factors had a 100% chance of having an abnormal MRI.
  • Players with an abnormal MRI played an average of 9.1 months of baseball per year, whereas players with normal MRIs averaged 6.3 months of play per year (P < .01).

Study Limitations

  • Participants were recruited and volunteers from a single Little League district where year-round play is common.
  • Radiographs may have revealed more subtle bony changes of physis
  • Recall bias with use of a retrospective questionnaire for player throwing history
  • Cost of imaging limited the number of recruited research participants

Practical Implications & Additional Thoughts

The findings from the present study suggest Little League baseball players who specialize and compete year-round are at risk for developing shoulder abnormalities.   Players with normal shoulders upon MRI, participated in baseball for an average of 6 months, while those with abnormalities participated for an average of 9 months per year.   All of these shoulder abnormalities were asymptomatic at the time of MRI examination.  However, the early evidence of these abnormalities may be associated with excessive throwing at an early age.  The cumulative stress placed on the shoulder may become symptomatic later in the youth athlete’s playing career.

Shoulder pain has been shown to be more closely associated with the cumulative number of throws over the course of a season than with the actual number of pitches in a single game3. The present study also suggests that MRI abnormalities are driven more by months of play than by position.  Thirty-eight percent of non-pitchers in this study had an MRI abnormality of the shoulder.  Therefore, tracking the number of throws over the course of a single season and full year is recommended to reduce risk for shoulder injury in youth baseball players.  The ideal limit of pitches thrown over these time periods has not yet been established.

Earlier research by Pennock et al.4 found year-round play to be the most significant risk factor for MRI abnormalities of the elbow in asymptomatic Little League players.  The present study showed that 100% of “specialized” baseball players had an abnormal shoulder MRI.  This underscores the importance of youth athletes engaging in multiple sports over the course of year in order to reduce injury risk.

Current Little League guidelines can potentially decrease arm injuries.  However, these guidelines do not address year-round play, early sports specialization, and pitch type.  This study supports avoiding year-round play (4 months off per year), engaging in multiple sports other than baseball, and postponing off-speed pitches (sliders and curveballs) until later in development.  Controlling the current epidemic of arm injuries across all levels of baseball, should begin with youth athletes.


  1. Lyman S, Fleisig GS, Andrews JR, Osinski ED. Effect of pitch type, pitch count, and pitching mechanics on risk of elbow and shoulder pain in youth baseball pitchers. Am J Sports Med. 2002;30(4):463-468.
  2. Lyman S, Fleisig GS, Waterbor JW, et al. Longitudinal study of elbow and shoulder pain in youth baseball pitchers. Med Sci Sport Exerc. 2001;33(11):1803-1810.
  3. Fleisig GS, Andrews JR, Cutter GR, et al. Risk of serious injury for young baseball pitchers: A 10-year prospective study. Am J Sports Med. 2011;39(2):253-257.
  4. Pennock AT, Pytiak A, Stearns P, et al. Preseason assessment of radiographic abnormalities in elbows of little league baseball players. J Bone Jt Surg. 2016;98-A(9):761-767.

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