Chronic Adaptations of the Long Head of the Biceps Tendon and Groove in Professional Baseball Pitchers.

BACKGROUND And Hypothesis: The long head of the biceps tendon (LHBT) plays a significant shoulder stabilizing role during pitching, with the large forces and repetitions involved in overhead throwing likely contributing to LHBT pathology. Determining whether the LHBT undergoes adaptive changes in baseball pitchers and how these changes relate to bicipital groove morphology can improve our understanding of the biceps function at the glenohumeral joint. Therefore, the purpose of this study was to determine the chronic adaptations of the bicipital groove morphology and the LHBT in professional baseball pitchers, with a secondary purpose of evaluating biceps integrity as it relates to torsional changes of the bicipital groove. We hypothesized that the throwing arm of professional baseball pitchers would exhibit chronic adaptations of the LHBT compared to their non-throwing arm, and that these adaptations would be related to the bicipital groove morphology. MATERIALS AND METHODS Fifty-three professional baseball pitchers were enrolled at the beginning of the 2015 Major League Baseball spring training. Ultrasound was used to bilaterally measure humeral retroversion and to capture images of the bicipital groove and the LHBT. MATlab software was used to calculate area of the bicipital groove, and ImageJ software was used to quantify area, echogenicity, and circularity of the LHBT. RESULTS Dominant arm LHBT cross-sectional area was significantly smaller than the non-dominant arm (9 mm2 vs. 10 mm2; p=0.011), while dominant arm LHBT echogenicity was significantly higher than the non-dominant arm (65 optical density vs. 59 optical density; p=0.002). Pitchers with more bicipital groove rotational adaptation (more retroversion) had significantly more LHBT echogenicity adaptation compared to pitchers with less bicipital groove rotational adaptation (12 vs. 2; p=0.023). CONCLUSION There are significant bilateral differences in the LHBT of professional baseball pitchers. An adaptation in bony rotation was associated with a larger bilateral difference in LHBT echogenicity but was not related to bilateral differences in LHBT area or circularity. Therefore, the bilateral difference in echogenicity is impacted by bony morphology, while the bilateral difference in cross-sectional area may be independent of bony morphology in this healthy population.