Location of the Glenoid Defect in Shoulders With Recurrent Posterior Glenohumeral Instability

Abstract

Background: Posterior glenoid bone deficiency is an increasingly recognized entity in the setting of recurrent posterior shoulder instability; however, little is known about the subject. Due to the paucity of literature on posterior bone loss, historical comparisons with anterior bone loss may not be fully accurate. Purpose: To systematically describe the morphology of posterior bone defects in the setting of recurrent posterior shoulder instability based on several quantitative parameters, including the mean location, orientation, and extent of bone loss on a clockface model, as well as the angle of the defect relative to the long axis of the glenoid. Study Design: Cross-sectional study; Level of evidence, 4. Methods: Three-dimensional reconstructed computed tomography scans of serially collected patients with a history of recurrent posterior shoulder instability were evaluated by 3 separate reviewers. The posterior glenoid bone defect was characterized using the following measures: (1) the mean lesion location and orientation based on a clockface model with 6 o’clock denoted as inferior and 9 o’clock as directly posterior for all patients; (2) the total extent of the posterior bone defect based on the clockface; and (3) the average angle of the bone loss relative to the long axis of the glenoid. Results: A total of 70 male patients and 1 female patient with a mean age of 29.3 years (range, 24.4-35.1 years) were included in the analysis. The mean clockface location of the posterior glenoid defect originated at 6:44 (range, 4:16-8:12) and extended to a mean of 9:28 (range, 7:02-10:38). The mean extent of the posterior glenoid defect was 2:43 (range, 1:08-4:50), which corresponds to a mean total bone loss arc of 81.5° (range, 34.2°-144.9°), nearly 1 quadrant of the glenoid. Posterior bone loss occurred in a posteroinferior direction at a mean angle of 30.7° (range, 8.0°-80.0°) relative to the long axis of the glenoid. Conclusion: Posterior bone defects in the setting of posterior shoulder instability most commonly occur in the posteroinferior quadrant of the glenoid and extend on average from 6:44 to 9:28 (81.5° total degrees of arc) on a clockface model. Posterior bone loss occurs at a mean of 30° off the long axis of the glenoid in a posteroinferior direction, which is historically different from anterior bone loss, which occurs parallel to the long axis of the glenoid. This study serves to highlight the location and orientation of bone loss that one can expect in a patient with recurrent posterior shoulder instability, although additional work is needed to assess why this develops.