Shoulder ranges of motion and humeral torsions of injured baseball players have different characteristics depending on their pitching sides

BACKGROUND: Right- and left-side throwers in baseball may have different shoulder conditions and throwing biomechanics. This study aimed to compare the passive range of motion, humeral torsion, and clinical findings between right- and left-handed throwers who sustained throwing shoulder injuries and confirm the differences in the characteristics between throwing sides. METHODS: A total of 52 pitchers diagnosed with throwing shoulder injuries were included in this study: 27 patients were right-side throwers (R group), and 25 were left-side throwers (L group). We measured the bilateral passive external and internal rotation angles in abduction position (ABIR) and total arc at their first visit. To assess posterior shoulder tightness, the internal rotation angles in forward flexion (FIR), and the abduction angle (AA) and horizontal flexion angle (HFA) without scapula motion were measured. The bilateral humeral torsion angles were also measured using ultrasonography. These values were compared between the participants' throwing and non-throwing sides and between the R and L groups' throwing sides. Furthermore, several physical findings in the shoulders were assessed, and the positive ratio was compared between the R and L groups. RESULTS: On comparing the throwing and non-throwing sides, the R group had significantly greater external rotation angles in the abduction position and humeral torsion angle, and smaller ABIR, total arc, FIR, AA, and HFA in the throwing side, while the L group showed no significant differences, except for a smaller ABIR and larger HFA in the throwing side. On comparing the throwing side between the R and L groups, the R group had a smaller FIR, AA, and FHA than the L group. Regarding the physical findings, the posterior jerk test, Kim test, anterior and posterior drawer sign, sulcus sign, and scapular winging in the L group were significantly more positive than in the R group. CONCLUSION: The range of motion and humeral torsions differed between the left- and right-side throwers, as did the pathology between their throwing sides. Clinicians should consider the possibility that the pathological condition differs between left- and right-side throwers.