Glenoid Tilt Angle: A Novel and Potential Risk Factor for Anterior Glenohumeral Instability.

Abstract

Background: The alterations in glenoid morphology have been studied in its axial and coronal planes viz , glenoid version and inclination, respectively, and their significance with respect to shoulder instability has been reported. The glenoid also exhibits an anterior tilt around the scapular axis in the coronal plane, which we refer to as the "glenoid tilt angle". The principal objective of this study was to assess glenoid tilt angle in a cohort of Indian population to establish a baseline value and find its clinical significance with respect to anterior shoulder instability. To our knowledge there are no studies in the literature explaining this angle and its implications in shoulder pathologies.

Methods: Retrospective analysis was done on consecutive patients who underwent CT for anterior shoulder instability (Group 1, n = 100) and for other non-glenoid shoulder pathologies (Group 2, n = 100). Glenoid tilt and spinoglenoid distance were measured on lateral en face view of 3D-CT, while glenoid version and spinoglenoid angle were measured on axial view of CT. For group comparisons, independent samples t-tests were employed to analyse differences in all four parameters between the instability and control groups, reporting means, standard deviations, t-values, and p-values. The Mann-Whitney U test was used for the glenoid version, suggesting a non-normal distribution of this variable, with additional median and interquartile range reporting. Pearson correlation analysis was used to examine the relationships between glenoid tilt angle and glenoid version, as well as between spinoglenoid distance and spinoglenoid angle, both overall and within each group separately. Inter-observer reliability for glenoid tilt angle was assessed using the intraclass correlation coefficient (ICC) based on a two-way random effects model with absolute agreement.

Reults: In Group 1, the mean glenoid tilt angle was 25.1° ± 6.9°, the mean glenoid version was 1.84° ± 5.43°, the mean spinoglenoid distance was 18.6 ± 4.3 and the mean spinoglenoid angle was 31.6 ± 6. In Group 2, the mean glenoid tilt angle was 20.3° ± 7.1°, mean glenoid version was 1.46° ± 5.51°, mean spinoglenoid distance was 17.9 ± 4.6, and mean spinoglenoid angle was 30.0 ± 5.4. Between both the groups, differences were statistically significant for glenoid tilt angle with a P value of < 0.001. Inter-observer reliability for glenoid tilt angle measurement was excellent (ICC = 0.98) indicating high measurement reproducibility. In a reduced multivariate logistic regression model adjusting for age and sex, glenoid tilt angle demonstrated an independent positive association with anterior shoulder instability (adjusted OR 1.04 per degree). Correlational analysis showed stronger negative correlation between the glenoid tilt angle and glenoid version (r = - 0.253, p = 0.011) in the instability group. For other parameters, these correlations were weaker and not statistically significant in instability as well as the control group.

Conclusion: The glenoid tilt angle will be increased in patients with anterior shoulder instability. It may act as a non-modifiable anatomical risk factor of anterior shoulder instability. The glenoid tilt angle provides a new perspective on glenoid morphology in unstable shoulders and its biomechanical evaluation will certainly yield a better understanding about glenohumeral instability.