Adaptive range-of-motion changes in overhand-throwing athletes have been observed for some time. Common adaptations occur in horizontal adduction and in external and internal rotation of the glenohumeral joint at 90 of abduction. Asymptomatic pitchers have been reported to manifest an increase of up to 30 of glenohumeral external rotation in both the frontal and scapular plane when compared with their nondominant shoulders. Glenohumeral internal rotation deficits of 15 to 20 have also been associated with asymptomatic pitchers, whereas symptomatic pitchers have reported deficits as high as 45. These changes have been attributed to numerous factors including a posteriorinferior capsular restriction, muscular inflexibility of the external rotators, eccentric loading of the external rotators, and osseous adaptations of humeral head or glenoid. Since the late 1990s, numerous studies have determined the passive range of motion of the overhand-throwing athlete. Some of these studies have addressed the issueof humeral retroversion.  The study of humeral retroversion may be relatively new in the sports medicine world; however, it was described as far back as 1881 in the anthropology literature. The relationship of the distal humerus with the proximal humerus changes through the skeletal maturation process. Adults have humeral retroversion in the range of 25 and 35. Fetal skeletons (N ¼ 50) have been measured with a mean retroversion angle of 78. By the age of 8 years, most of the derotation occurs, and in the following 8 years, the process is complete. During overhand throwing, humeral torque is developed as the distal portion of the humerus is externally rotated at a rate greater than the proximal end, in an attempt to achieve maximum glenohumeral rotation. Humeral peak torque peaks immediately before maximum external rotation. It appears that the stress endured by the maturing proximal humerus during the overhand throw slows the derotation in the dominant arm. In a cross-sectional study of 294 Little League and adolescent baseball players between 8 and 16 years old, peak changes in elevation, external rotation, and internal rotation occurred between the ages of 11 and 13 years. Significant changes in internal rotation of the dominant shoulder occurred between the 12- and 13-year-old groups. Changes in internal rotation of the nondominant shoulder was seen between the 14- and 15-year-old groups. When the youngest group of baseball players was compared with the oldest group, the differences in internal rotation, external rotation, and total range of motion were significant. Internal rotation in the dominant shoulder decreased by an average of 17, and it decreased by 9.1 in the nondominant shoulder. External rotation in the dominant shoulder decreased by an average of 20.5, and this value decreased by 23.5 in the nondominant shoulder. Thus, the total range of motion decreased by 38.2 in the dominant shoulder as compared with 32.5 in the nondominant shoulder. Pappas et al  reported a significant limitation of glenohumeral internal rotation range of motion and posterior shoulder tightness as measured by horizontal abduction with scapula stabilization in patients diagnosed as having subacromial impingement. Brown et al  recorded the range of motion for multiple upper extremity movements in two separate groups consisting of professional pitchers and position players. The pitchers had significant increases of 9

of external rotation in 90 abduction. The pitchers had significant decreases of 5 shoulder flexions and 15 internal rotations in 90 abduction relative to their non-dominant side. Position players had a significant increase of 8 external rotations in 90 abduction. Verna et al measured 137 professional baseball players bilaterally for internal rotation by fixing the scapula and medially rotating the humerus while abducted 90 ° in the supine position. Correlation of dominant shoulder internal rotation deficits with injury history revealed that pitchers reporting a shoulder or elbow problem had an average internal rotation deficit of 41%. Position players who reported a shoulder or elbow problem had an average deficit of 43%. The uninjured athletes, whether they were pitchers or position players, recorded an internal rotation deficit of just 24% on average. Warner et al demonstrated significant limitation of internal rotational range of motion and posterior shoulder tension, measured in horizontal abduction, in a group of impingement patients compared to patients with shoulder instability and control patients. Kugler et al attempted to identify features that could be related to shoulder injuries in highly skilled volleyball forwards, an aerial activity. To measure posterior shoulder tension, the researchers measured the distance from the lateral epicondyle to the acromion of the opposite shoulder during maximum horizontal adduction. The researchers did not report whether the scapula was stabilized. They found that the dominant posterior shoulder was significantly narrower in attackers with shoulder pain than in attackers with no shoulder pain or compared to a control group. The offenders without shoulder pain had significantly tighter shoulders than the control group. Both groups of volleyball players had increased stress on the dominant shoulder versus the non-dominant shoulder. Bigliani et al examined upper limb range of motion and glenohumeral joint laxity in a study of 148 healthy professional baseball players, 72 pitchers, and 76 positional players. Internal glenohumeral rotation was recorded as the highest spinal level reached by the thumb along the spine. This record has been converted to a numerical value in accordance with US Shoulder and Elbow Standards to allow for statistical comparisons. External rotation of the shoulder with the humerus in 90 ° abduction in the frontal plane and internal rotation, measured as previously described, demonstrated statistically significant differences between dominant and non-dominant shoulders.

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