Introduction: Although the lack of internal rotation (IR) and total range of motion (TRM) has been identified as a significant contributing factor of shoulder injuries, our goal was to determine whether a relationship exists between glenohumeral internal rotational deficits (GIRD), TRM, and shoulder strength in professional baseball pitchers. Our hypothesis was that GIRD with TRM differences within 5° will not lead to decreased shoulder strength; however, a shoulder with >5° of TRM difference with GIRD will lead to decreased shoulder strength.
Methods: The study was conducted over a 4-year period and included 193 major and minor league pitchers. All measurements were taken prior to the pitcher’s engaging in any baseball-related activities on the day of measurements. The entire measurement arc of passive range of motion (PROM), including external rotation (ER) and IR, was defined as the TRM. GIRD was defined as a loss of 25° or more of IR of the throwing shoulder compared with the nonthrowing shoulder. Shoulder strength measurements were obtained using a validated digital dynamometer with the arm in 90° of abduction and with the arm in 110° of flexion and 30° of abduction measured in pounds.
Results: The IR deficit was 5.89° (SD = 9.24°) in non-GIRD pitchers and 25.52° (SD = 4.35°) in GIRD pitchers (P > 0.001). The ER change was 124.08° (SD = 11.21°) in non-GIRD pitchers and 127.79° (SD = 9.15°) in GIRD pitchers. The total arc of motion was 179.54° (SD = 14.53°) in non-GIRD pitchers and 171.93° (SD = 12.34°) in GIRD pitchers (P > 0.001). The strength in the shoulder, measured with the arm in 90° of abduction, was 29.61 lb (SD = 4.76 lb) in non-GIRD pitchers versus 28.65 lb (SD = 4.81 lb) in GIRD pitchers. The strength with the arm in 110° of flexion and 30° of abduction was 29.43 lb (SD = 5.01 lb) in non-GIRD pitchers versus 28.13 lb (SD = 4.76 lb) in pitchers with GIRD (P = 0.043). Deficiencies in total arc of motion (P < 0.001) and shoulder strength (P < 0.043) were significantly associated with GIRD.
Discussion: In our evaluation of 193 pitchers examined during their preseason physical examinations, we identified a statistically significant association between decreased total arc of motion, decreased shoulder strength, and GIRD.