Location and size of the glenoid defect in patients with traumatic posterior shoulder instability

The size and location of the glenoid defect have been extensively studied in patients with anterior shoulder instability. However, in patients with traumatic posterior instability, little is known regarding the location and size of the bony defect of the glenoid. The purpose of the present study was to clarify the location and extent of the glenoid defect in shoulders with traumatic posterior instability with use of CT images.

Forty-three shoulders of 42 patients with traumatic posterior instability treated at 7 hospitals were included. Three-dimensional images of the glenoid reconstructed from computed tomography were assessed using image analysis software. The location and size of the glenoid defect were investigated and described on a clock face of the glenoid.

Thirty-eight of 43 shoulders (88 %) had a glenoid bony defect. Eleven shoulders (26 %) had a bony fragment. The defect width of the glenoid was 2.5 ± 1.3 mm (mean ± standard deviation), which was equivalent to 9.1 ± 5.3 % of the glenoid width. The mean orientation of the defect was pointing toward 8:12, at a mean angle of 246° ± 13.2° from the 12-o'clock direction in the right shoulder. The glenoid defects were located between 5:37 and 10:38.

The prevalence of the glenoid bony defect in patients with traumatic posterior shoulder instability was as high as that in patients with anterior shoulder instability. However, its size was smaller than the anterior instability and it was located posteroinferiorly. IRB APPROVAL: #2022-1-1168.