Sport Comparison of Shoulder Adaptations in 8-10 Year Old Overhead Athletes

Abstract

Shoulder pain in adult, overhead athletes has been attributed to a loss of glenohumeral internal rotation. However, underlying soft tissue and bony changes that alter range of motion likely contribute to pain progression. Shoulder pain can begin as early as 8 years of age in overhead athletes, but little data exists on the adaptations that potentially occur at a young age. PURPOSE: To compare range of motion and tissue adaptations in the shoulders of swimmers, baseball players, and non-overhead athletic controls ages 8-10. METHODS: 55 youth athletes; 20 swimmers (years played=3.0±1.4), 15 baseball players (years played=4.9±1.7), and 20 non-overhead athletes participated. Glenohumeral internal (IR) and external rotation (ER) were measured with a digital inclinometer. Posterior capsule thickness (PCT) and humeral twisting (retrotorsion, HR) were examined using musculoskeletal ultrasound. All measures were taken bilaterally. The dominant arm was defined as the arm preferred to throw a ball for maximum distance. Age and years played were identified as potential co-variates, but neither significantly affected statistical models. Therefore, 3x2 ANOVAs and Tukey post-hoc testing were used to analyze group and arm dominance differences. RESULTS: Interaction effects were observed for IR (p=0.03), ER (p<0.01), PCT (p=0.02), and HR (p=0.01). Youth baseball players exhibited a 9.2±9.9° IR loss and 18±10.0° ER gain on the dominant arm compared to the non-dominant arm. These IR and ER differences did not exist in swimmers or controls. The dominant arms of baseball players manifested with greater PCT (1.29±0.24mm) than the dominant arms of all other populations. A significant main effect (p<0.01) was also observed for PCT, with swimmers (1.11±0.14mm) and baseball players (1.21±0.19mm) presenting with greater PCT than control subjects (1.04±0.12mm). The non-dominant arms of baseball players demonstrated the least HR (-21.6±10.5) of all participants (swim=-11.3±6.9, non-overhead=-11.3±7.7). CONCLUSIONS: Tissue adaptation occurs in youth athletes after only 3 years of overhead sport participation and at an age earlier than previously documented. Sport selection affects the scope of these changes, with the dominant arm of baseball players undergoing the greatest adaptation. Supported by NATA REF grant 13DGP016