Summary

We assessed glenoid anterior torsion angle in baseball players who underwent surgery for throwing related injuries by 3D-CT and found that glenoid anterior torsion angle was significantly greater in the dominant side than that in the nondominant side, suggesting that repetiting throwing motion increases the anterior torsion of the glenoid.

Abstract

Introduction

Previous studies have reported that repetitive throwing motion in baseball players causes retroversion and dysplasia of the glenoid. To date, there have been no studies investigating changes in the torsion of the glenoid. We aimed to investigate the effect of repetitive throwing motion on the torsion of the glenoid in baseball players by comparing the glenoid anterior torsion angles between the dominant and the nondominant shoulders using 3D-CT.

Methods

We stuidied 29 baseball players who underwent surgery for throwing related injuries. A three-dimensional bone model of the scapula was created using the three-dimensional resolution analysis system Volume Analyzer with CT scan data of both shoulders performed preoperatively. The glenoid anterior torsion angle was defined as the clockwise rotation of the glenoid articular surface with respect to the scapular body for the right shoulder and the semi-clockwise rotation for the left shoulder, then the angle between the approximate plane of the infraspinous fossa and the long axis of the glenoid was measured. We compared the glenoid anterior torsion angle between the dominant side and the nondominant side, pitchers and fielders, and the shoulder and elbow disorders. For the statistical analyses, paired t-test was used to compare the glenoid anterior torsion angle between the dominant side and the nondominant side, and the Wilcoxon signed rank test was used between pitchers and fielders, and between shoulder and elbow disorders.

Results

All players were male (pitchers:13 players, fielders :16 players, the shoulder disorder:14 players, the elbow disorder:15 players), and mean age at surgery was 19.3 years (14-36 years). The glenoid anterior torsion angle was significantly greater in the dominant side (22.8 degrees) than that in the nondominant sidd (19.5 degrees) (p<0.001). We found no significant difference between pitchers and fielders in the glenoid anterior torsion angle on the dominant side or the nondominat side, nor the side-to-side difference in glenoid torsion angle showed (dominat side: pitchers, 20.3 degrees vs fielders, 24.9 degrees, p=0.08; nondomint side: pitcher, 18.2 degrees vs fielder, 20.6 degrees, p=0.39; the side-to-side difference: pitcher, 2.1 degrees vs fielder, 2.9 degrees, p=0.08). In addition, we found no significant difference between the shoulder and elbow disorders in the glenoid anterior torsion angle on either the dominant side or the nondominat side, nor the side-to-side difference in glenoid torsion angle (the dominat side: shoulder disorders, 23.2 degrees vs elbow disorders, 22.5 degrees, p=0.84; nondomint side: shoulder disorders, 18.6 degrees vs elbow disorders, 20.4 degrees, p=0.29; the side-to-side difference: shoulder disorders, 2.8 degrees vs elbow disorders, 2.1 degrees, p=0.07).

Conclusions

Glenoid anterior torsion angle measured by 3D-CT was significantly greater in the dominant side than nondominant side, suggesting that repetiting throwing motion increase the anterior torsion of the glenoid.