JBJS - 2026-07-20 - Journal Article
Traumatic Posterior Dislocation Is Associated with Posterior Acromial Morphology.
Werthel JD, Vervaecke A, Petit M, Jamei-Martel O, Gerber C
Topics
Key Takeaway
Traumatic posterior shoulder dislocation is associated with greater posterior acromial height (27.0 vs. 22.0 mm) and steeper posterior acromial tilt (65.8° vs. 58.9°) compared to anterior dislocation, with PAH and PAT as the strongest independent predictors on logistic regression.
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Summary
This retrospective comparative cohort study asked whether posterior acromial morphology differs between first-time traumatic posterior and anterior shoulder dislocations, measuring PAT, PAC, PAH, and CSA on standardized radiographs in 34 matched pairs. Posterior dislocation patients had significantly higher PAT (65.8° vs. 58.9°, p<0.001), greater PAH (27.0 vs. 22.0 mm, p<0.001), lower PAC (55.6° vs. 59.5°, p=0.038), and smaller CSA (32.9° vs. 35.5°, p=0.009). Logistic regression identified PAH and PAT as the strongest independent morphologic predictors of posterior dislocation direction.
Key Limitation
The study uses an anterior dislocation control group rather than a non-dislocating normative population, so it cannot establish absolute morphologic thresholds that distinguish pathologic from normal posterior acromial anatomy.
Original Abstract
BACKGROUND
Traumatic posterior shoulder dislocation is rare, and the role of posterior acromial morphology in acute traumatic posterior dislocation is unknown. We compared posterior acromial morphology in first-time traumatic posterior versus first-time traumatic anterior dislocations.
METHODS
In this retrospective comparative cohort study, 34 consecutive patients with a first-time acute traumatic posterior shoulder dislocation were compared with 34 consecutive patients with a first-time acute traumatic anterior shoulder dislocation. The posterior dislocation cohort included 26 males and 8 females, with a mean age of 43.4 ± 16.5 years, and the anterior dislocation cohort included 29 males and 5 females, with a mean age of 41.3 ± 15.4 years. Posterior acromial tilt (PAT), posterior acromial coverage (PAC), posterior acromial height (PAH), and the critical shoulder angle (CSA) were measured on standardized radiographs. Comparisons between the groups were performed, and logistic regression analyses were used to assess associations between acromial morphology parameters and posterior dislocation. Interobserver and intraobserver reliability were assessed using intraclass correlation coefficients.
RESULTS
Compared with the anterior dislocation group, patients with posterior dislocation demonstrated a significantly higher PAT (65.8° ± 6.7° versus 58.9° ± 8.4°, p < 0.001), lower PAC (55.6° ± 6.6° versus 59.5° ± 8.4°, p = 0.038), greater PAH (27.0 ± 4.2 versus 22.0 ± 6.7 mm, p < 0.001), and smaller CSA (32.9° ± 4.0° versus 35.5° ± 4.1°, p = 0.009). Logistic regression showed that higher PAH and PAT were most strongly associated with posterior dislocation. Measurement reliability was good to excellent for all parameters.
CONCLUSIONS
Acute traumatic posterior shoulder dislocation is associated with distinct posterior acromial morphology similar to that described in recurrent posterior instability.
LEVEL OF EVIDENCE
Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.