Comparison of dynamics in 3D glenohumeral position between primary dislocated shoulders and contralateral healthy shoulders.

Backgrounds: After shoulder dislocation, kinematic changes in shoulder, including translation of the humeral head, ensue. There have been many attempts to measure these changes using motion measurement techniques, but in vivo three-dimensional (3D) glenohumeral changes have not been appreciated until now. The purpose of this study was to measure and analyze changes in glenohumeral translation in patients with shoulder dislocation and compare these changes with healthy shoulder.

Methods: We included 20 subjects who had suffered shoulder dislocation for first time, and 3D models of their humerus and scapula were obtained using computed tomography and fluoroscopic images during scapular plane abduction and external rotation of shoulder with elbow flexed at 90° and arm abducted at 90°. We measured the superior/inferior (SI) and anterior/posterior (AP) translations for both shoulders.

Results: No statistically significant difference between healthy and dislocated shoulders was detected in SI translation for scapular plane abduction with increasing elevation angles. In AP translation, the humeral head was located 2.29 mm more anteriorly in the dislocated shoulder than in the healthy shoulder. However, no statistically significant difference was seen. For internal to external rotation, the angle of the rotated arm had an effect on AP translation. However, no statistically significant difference was detected. In the apprehension test, there was no significant difference in the mean value of AP translation.

Conclusion: Compared with the contralateral healthy shoulder, changes in glenohumeral translation during in vivo movement after shoulder dislocation were found to be non-significant.