Background: The purposes of this study were to investigate glenohumeral translation in normal and instable shoulders using open MRI and to investigate the correlation between the results and sulcus sign under anesthesia.
Methods: Eleven shoulders of 11 patients with traumatic anterior instability (8 men, 3 women, average age; 23.3 years old) were included in this study. In supine position, axial and oblique-coronal images of the glenohumeral joint were obtained by 0.4T open MRI. The examined shoulder positions were Series 1; abduction (Abd) 30°, 60°, 90°, 120°, and 150° at scapular plane, and Series 2; internal rotation (IR) 60°, 30°, external rotation (ER) 0°, 30°, 60°, and 90° at abduction 90° at frontal plane. Translation of the center of the humeral head from the center of the glenoid was measured. Eight normal shoulders (6 men, 2 women, average age; 28.4 years old) were also examined as a control group.
Results: Series 1; In the control group, centered movement was observed in both anterior-posterior and superior-inferior directions. The instability group showed significant posterior translation at Abd 30°. Series 2; The control group showed gradual anterior translation from IR to ER position. The instability group showed significant posterior translation at IR 30°. In superior-inferior translation, both groups showed gradual inferior translation from IR to ER position, however, the translation was significantly larger at IR 30°, 60°, ER 60° in the instability group. Remarkable inferior translation was observed in 2 shoulders out of 6 that showed positive sulcus sign.
Discussion: Open MRI analysis demonstrated anterior-inferior translation at ER position and posterior-inferior translation at IR position in instable shoulders.