Poster 183: Acromial Morphology Predicts Glenoid Bone Loss in Patients with Posterior Glenohumeral Instability

OBJECTIVES: The relationship between acromial morphology and glenohumeral instability is not well understood. It is unknown whether a flatter acromion predisposes a nonarthritic shoulder to increased posterior glenoid bone loss (GBL). The purpose of this study was to determine whether acromial morphology influences the extent or pattern of posterior glenoid bone loss in a cohort of patients with posterior glenohumeral instability. METHODS: A comprehensive review of case logs between two academic institutions was performed to identify patients treated for primary posterior glenohumeral instability. MRI and/or CT scans were examined by two independent reviewers and the following measurements were obtained: total area glenoid bone loss (GBL) using the perfect circle technique, glenoid version, obliquity of GBL relative to the long axis of the glenoid, arc of GBL, acromial tilt, posterior acromial height (PAH), and anterior/posterior acromial coverage. The primary outcome was the association between acromial morphology parameters and glenoid bone loss. RESULTS: A total of 89 shoulders with primary posterior glenohumeral instability were included. The mean age was 28.3 years (range 18-49), and male:female ratio was 11:1. Fifty-nine patients had measurable posterior glenoid bone loss and 30 patients had posterior labral tears without bone loss. Linear regression analysis revealed a significant negative correlation between acromial tilt and posterior GBL (R(2)= 0.09, p=0.005), a positive correlation between PAH and posterior GBL (R(2)= 0.04, p=0.046), and a negative correlation between posterior acromial coverage and posterior GBL (R(2)= 0.03, p=0.005). Increasing PAH and decreasing posterior acromial coverage were associated with a more superior extent of GBL (R(2)= 0.1, p=0.044 and 0.024, respectively). Subgroup analysis stratified by total area of GBL demonstrated that the area of posterior glenoid bone loss increases as the acromial tilt decreases. CONCLUSIONS: A flatter, higher acromion with less posterior coverage relative to the center of the glenoid is associated with increased posterior glenoid bone loss in patients with posterior glenohumeral instability.