Why is the humeral retroversion of throwing athletes greater in dominant shoulders than in nondominant shoulders?

Humeral torsion and throwing proficiency in early human evolution

“…Torsion increases from birth to maturity (Krahl, 1947;Edelson, 2000;Cowgill, 2007;see Fig. 3), and it is thought that variation in the degree of torsion between individuals may simply be a product of when this developmental trajectory ends (Yamamoto et al, 2006). Humeral torsion varies across different human groups, is often lower in males than in females, and is often lower in the dominant arm than the nondominant arm (Martin, 1933;Krahl and Evans, 1945;Churchill, 1994;Edelson, 1999;see Fig.…”

Reliability and validity in measurement of true humeral retroversion by a three-dimensional cylinder fitting method

“…12,13,18,25,40 In baseball players and other throwing athletes, humeral retroversion is greater in the dominant arm than in the nondominant arm. 7,19,20,22,26,35,[38][39][40] This increased humeral retroversion has been linked to upper extremity disorders including throwing-related shoulder and elbow injuries. 20 Humeral retroversion as well as posterior capsule thickness has a considerable influence on shoulder range of motion, including decreased glenohumeral internal rotation.…”

“…19,26,31 Baseball players exhibiting a decrease in passive internal rotation !25 in the dominant shoulder were approximately 4 to 5 times at greater risk of an upper extremity disorder than were players with <25 decrease in passive internal rotation. 29 Various methods using radiography, 22,26 computed tomography (CT), 2,7,18 or ultrasonography [18][19][20]23,32,[34][35][36][38][39][40] have been proposed to measure the humeral retroversion angle; however, no widely accepted standard method exists. 2,18,25 Establishing a valid and reliable method is challenging work for several reasons, including the definition of humeral retroversion, range of imaging methods in use, and validity of anatomic landmarks or reference axes used to determine humeral retroversion.…”

“…2,18,25 Establishing a valid and reliable method is challenging work for several reasons, including the definition of humeral retroversion, range of imaging methods in use, and validity of anatomic landmarks or reference axes used to determine humeral retroversion. The cartilage/ metaphyseal interface 2,18 and bicipital groove, [18][19][20]23,32,[34][35][36][38][39][40] identified from 2-dimensional CT or ultrasound images, are commonly used to define the proximal axis of the humerus. However, the retroversion angle measured with these anatomic landmarks varies, depending on the level at which it is measured in the axial plane.…”

“…12,13 The results indicate that the more proximal cartilage/metaphyseal interface or groove we select as reference in the axial plane, the greater the value obtained for the humeral retroversion angle. The humeral epicondyles 2,18 and ulna [18][19][20]23,32,[34][35][36]38,39 are used as reference points for the distal humeral axis (transepicondylar axis by the CT method, and forearm axis by indirect ultrasound assessment, respectively). However, morphologic variability in the medial epicondylar epiphyses and some degree of elbow valgus laxity have been observed in the dominant elbows of baseball players, 1,6,11 which may reduce the reliability of conventional methods using CT slices or indirect ultrasound technique.…”