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Critical Findings on MR-Arthrogram in Posterior Shoulder Instability Compared to an Age-Matched Controlled Cohort

      Introduction

      The purpose is to determine the prevalence and severity of radiographic risk factors on shoulder MR-arthrogram in patients with arthroscopically confirmed posterior labral tear and symptomatic posterior shoulder instability compared to an age-matched cohort without posterior instability who received shoulder arthroscopy for a distal clavicle excision.

      Methods

      Patients presenting at an academic institution over a 5-year period with symptomatic posterior shoulder instability that had arthroscopically confirmed repair of a posterior labral tear (66 patients) were compared with an age-matched control group of patients without posterior instability (56 patients) who had a shoulder arthroscopy for a distal clavicle excision. All patients received a shoulder MRA preoperatively and we excluded patients who had prior surgery and collagen disorders. Glenoid version, posterior humeral head subluxation, glenoid dysplasia, and linear and capsular area measurements were evaluated between the two groups. Interobserver reliability for continuous and categorical variables was performed for all measurements.

      Results

      Multivariable logistic regression revealed that the presence of glenoid dysplasia, posterior humeral head subluxation, and increased axial posterior capsular cross-sectional area were significant risk factors for posterior labral tears and symptomatic shoulder instability in comparison to the control group. Glenoid version was found to be a statistically significant risk factor with univariate analysis for posterior shoulder instability but not with multivariate logistic regression. Interobserver reliability was good to excellent for all measurements but poor for total capsular area.

      Conclusion

      The presence of glenoid dysplasia, posterior humeral head subluxation and increased posterior capsular area are independent radiographic risk factors in patients with posterior labral tears who develop symptomatic posterior shoulder instability. Identification of the critical radiographic variables on MRA assists in the accurate diagnosis and management of clinically significant posterior shoulder instability.