Acromial morphology

The purpose of this paper was to determine whether acromial morphology influences anteroposterior shoulder stability. They hypothesized that a more horizontal; and higher position of the acromion in the sagittal plane associated with posterior instability. There was a significant correlation between specific acromial morphology; and the direction of glenohumeral instability, according to results.

“In shoulders with posterior instability, the acromial is situated higher and oriented more horizontally in the sagittal plane; than in normal shoulders and those with anterior instability; this acromial position may provide less osseous restraint against posterior humeral; head translation,” the authors wrote.

Control group of patients

However, in this retrospective study, patients with unidirectional posterior instability age; and sex-matched to a cohort of patients with unidirectional anterior instability. Both cohorts compared with a control group of patients with no instability; and no degenerative glenohumeral (rotator cuff and/or joint surface) or acromial changes. Measurements on radiographs included posterior acromial tilt; anterior and posterior acromial coverage (AAC and PAC), posterior acromial height (PAH), and the critical shoulder angle (CSA).

But researchers performed a retrospective study of 41 patients with unidirectional posterior instability; and 41 patients with unidirectional anterior instability. Patients with instability compared to 53 control patients with no instability; degenerative glenohumeral changes or acromial changes. Posterior acromial tilt, anterior acromial coverage; posterior acromial coverage, posterior acromial height and critical shoulder angle among the radiograph measurements assessed.

Specific acromial morphology

Results from the logistic regression model showed posterior acromial height had the most significant correlation with posterior instability. Patients with posterior instability compared with patients with anterior instability had a significantly greater posterior acromial height. The odds ratio for posterior instability was 39 when investigators used a posterior acromial height cutoff of 23 mm. Shoulders with posterior instability compared with normal shoulders significantly different with regard to posterior acromial height and posterior acromial coverage.

However, in shoulders with anterior instability, no difference was compared with normal shoulders apart from the anterior acromial coverage. Specific acromial morphology is significantly associated with the direction of glenohumeral instability. A steep “Swiss chalet roof-type” acromion virtually excluded recurrent posterior instability in an albeit relatively small cohort of patients. Additional investigation needed to determine the relevance of these findings for future treatment.