Research Review #6: Taller Youth Baseball Pitchers may be Predisposed to Throwing-Related Arm Pain

Greenberg EM, Lawrence JTR, Fernandez-Fernandez A, et al. Physical and functional differences in youth baseball players with and without throwing-related pain. Orthop J Sport Med. 2017;5(11):1-7. doi:10.1177/2325967117737731.

Background

Up to half of youth baseball players experience shoulder or elbow pain during the season1.  Risk factors include pitching with fatigue or pain, loss of shoulder range of motion (ROM), playing baseball more than 8 months per year, high pitch volume (per game and per season), and throwing breaking pitches at an early age.  Research is unclear on which physical factors (strength, velocity, body size, etc) are most associated with youth baseball injuries.  Humeral retrotorsion (HRT) and the associated ROM asymmetries are physical factors which have been implicated as potential risk factors for injury.

Purpose

The purpose of this study was to examine the relationship between physical characteristics, HRT, shoulder ROM, strength, pitching velocity, playing history, and pain in youth baseball players.

Study Population

Inclusion

  • Male baseball players (n=84) aged 8 to 14 years (mean age=11.9)
  • Currently participating in Little League or private baseball academies

Exclusion

  • Females
  • Participated in other overhead sports (i.e., tennis, swimming)
  • Current arm pain which limited sports participation
  • History of humeral fracture
  • Systemic disorders associated with joint hypermobility

Research Methods

This cross-sectional study utilized a questionnaire collecting player age, height, weight, arm dominance, months per year playing baseball, position, age at onset of baseball, other sports participation, previous injury, and any shoulder or elbow pain association with throwing within the last 30 days.  Shoulder internal (IR) and external (ER) rotation passive ROM was assessed at 90 degrees of abduction.  Shoulder IR and ER strength were assessed with a hand-held dynamometer in the same position.  Diagnostic ultrasound was utilized to assess HRT in both upper extremities.  Throwing velocity was assessed with a radar gun from the stretch position at a distance of 46 feet.  Players were divided into those with and without shoulder or elbow pain.

Key Results

  • Players with and without pain were similar in age, dominant arm total ROM, dominant arm HRT, and strength.
  • Players with pain exhibited greater height, weight, glenohumeral IR deficit (GIRD), side-to-side asymmetry in HRT (attributable to decreased nondominant arm HRT), pitch velocity, and baseball exposure.
  • After adjusting for performance and exposure variables, height was the primary factor which predicted injury with an odds ratio (OR) of 1.77 (95% CI: 1.17 to 2.66).
  • Every additional inch of height increased the rate of shoulder or elbow pain by 77%.

Study Limitations

  • Some parents assisted with questionnaires but recall and reliability of this method with youth research participants are unclear.
  • The cross-sectional nature of this study does not allow for cause and effect conclusions.
  • The study may have been underpowered by a small sample with reported pain (n=16).
  • Research participants were not dichotomized by pitcher vs. position player.

Practical Implications & Additional Thoughts

The results of this study suggest player height is an important risk factor for developing throwing-related arm pain in youth baseball players.  When youth baseball players throw with arm pain the risk of developing shoulder or elbow injury rises significantly.  It is important for parents and coaches to recognize these risk factors and monitor these youth athletes closely.  Tall pitchers are likely to throw with greater velocity and arm torque due to longer lever arms.  This could potentially contribute to increased microtrauma to upper extremity musculoskeletal structures (osseous and soft tissue).  Longer limbs may also increase torsional stress to active physes during overhead throwing.   Therefore, these players should be more closely monitored for other potential risk factors for injury.  This includes the modifiable risk factors of pitching volume, rest, and playing in multiple leagues.

Shanley et al.2 showed adolescent pitchers with arm pain and a mean age of 14.9 years exhibited a 13-degree loss of IR ROM compared to the non-dominant side.  The results of this study, in a younger sample (mean age 11.9 years), showed a 9.1-degree side to side difference in IR ROM for those with arm pain.  It is possible that younger players may have a lower tolerance to GIRD and the development of throwing-related arm pain.  Based on the quality and quantity of this evidence it would be premature to conclude that large-scale interventions should be employed to address GIRD in these players.  Studies with larger sample sizes across different age groups may help clarify any association between GIRD and throwing-related arm pain in youth baseball players.   However, screening youth players prior to the season may help identify risk with consideration for GIRD and all other modifiable risk factors.

HRT results in a more posteriorly oriented humeral head.  After birth, the humeral head undergoes derotation through adolescence.  However, the repetitive forces of throwing slow humeral derotation leading to a position of relative retrotorsion in the dominant arm compared to the non-dominant arm.  In this study, players with and without shoulder pain exhibited similar HRT in the dominant arms.  However, players with pain showed greater side-to-side asymmetry in HRT due to less HRT in the nondominant arm.  The nondominant arm HRT likely reflects an unaltered genetic position of the humeral head.  Players with less genetic HRT may undergo greater adaptive changes from the stresses of throwing in order to obtain the layback position.  The greater stresses needed to adapt may predispose the youth athlete to shoulder (i.e., Little League Shoulder) and elbow injuries (i.e., UCL tears).  Screening and monitoring youth baseball players HRT and side-to-side ROM asymmetries may help identify those at risk for pain and injury.

Further research is needed to elucidate which risk factors are most closely associated with youth throwing-related arm pain.  At this time, taller players should be most closely monitored by parents, coaches, and healthcare professionals.  Pre-season screening for shoulder ROM asymmetries and HRT may also help identify which players require closer monitoring or physical interventions such as an individualized exercise program.

References

  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. http://www.ncbi.nlm.nih.gov/pubmed/12130397.
  2. Shanley E, Kissenberth MJ, Thigpen CA, et al. Preseason shoulder range of motion screening as a predictor of injury among youth and adolescent baseball pitchers. J Shoulder Elb Surg. 2015;24:1005-1013. doi:10.1016/j.jse.2015.03.012.

 

 

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