Traumatic Posterior Dislocation Is Associated with Posterior Acromial Morphology

Area of Science:

• Orthopedic surgery
• Radiology
• Biomechanics

Background:

• Traumatic posterior shoulder dislocation is a rare injury.
• The association between posterior acromial morphology and acute traumatic posterior dislocation is not well understood.
• This study investigates the role of posterior acromial morphology in first-time traumatic posterior shoulder dislocations.

Purpose of the Study:

• To compare posterior acromial morphology in patients with first-time traumatic posterior shoulder dislocation versus first-time traumatic anterior shoulder dislocation.
• To identify specific radiographic parameters of the acromion associated with posterior shoulder dislocations.

Main Methods:

• Retrospective comparative cohort study of 34 patients with posterior dislocation and 34 with anterior dislocation.
• Standardized radiographs were used to measure posterior acromial tilt (PAT), posterior acromial coverage (PAC), posterior acromial height (PAH), and critical shoulder angle (CSA).
• Logistic regression analysis was performed to determine associations between acromial morphology and posterior dislocation, with interobserver and intraobserver reliability assessed.

Main Results:

• Patients with posterior dislocation showed significantly higher PAT, lower PAC, greater PAH, and smaller CSA compared to the anterior dislocation group.
• Higher PAH and PAT were most strongly associated with posterior dislocation.
• All measured parameters demonstrated good to excellent reliability.

Conclusions:

• Acute traumatic posterior shoulder dislocation is associated with distinct posterior acromial morphology.
• The identified acromial morphologies in acute posterior dislocations are similar to those seen in recurrent posterior instability.
• Posterior acromial morphology may play a role in the mechanism of acute traumatic posterior shoulder dislocation.