The critical shoulder angle does not change over time: a radiographic study

Abstract

Background: The anatomy of the scapula may predispose individuals to develop shoulder pathologies. The purpose of this study was to determine if the scapular anatomy, in particular the critical shoulder angle (CSA), changes over a long-term follow-up, or if it is a stable parameter. We hypothesized that increasing age would not influence the scapular morphology.

Methods: We analyzed shoulder radiographs in our database from 2002 to 2019 to extract radiographs at an interval of at least 10 years. Radiographic analysis included measuring the CSA and assessing the acromion type according to Bigliani and Morrison, the posterior acromial height and the posterior acromial tilt.

Results: A total of 41 patients (47 shoulders) with a mean age of 53 years (range, 15-76; standard deviation [SD], ±14) fulfilled the inclusion criteria. The mean interval between the 2 sets of radiographs was 12 years (range, 10-16; SD ±2).The mean CSA did not change significantly with 34° (range, 20-41; SD ±4) at the first and 34° (range, 19-44; SD ±5) (P = .597) at the second assessment. On the initial lateral radiographs ("Neer view"), there were 11 type 1 (24%), 32 type 2 (70%), and 3 type 3 (6%) acromia according to Bigliani and Morrison. At the second assessment, there were 16 type 1 (34%), 28 type 2 (60%), and 3 type 3 (7%). Between both sets of radiographs, 11 were different (23%), without a trend in the type of change being discernible. The posterior acromial height was stable with 19 mm (range, 2-36; SD ±8) at the first and 18 mm (range, 5-38; SD ±8) at the second assessment (P = .186). The posterior acromion tilt changed from 59° (range, 34-81; SD ±10) to 62° (range, 30-81; SD ±10) (P < .001). Among 6 cases with rotator cuff tears (RCTs) already at the first assessment, the CSA did not change significantly at 10 years' follow-up (P = .414). Among the 10 cases with new RCTs at the second assessment, the CSA did not change significantly at 10 years' follow-up from 34° (range, 25-41; SD ±5) to 35° (range, 24-44; SD ±6) (P = .510). In the group of 31 shoulders without RCT, the mean CSA at the first assessment of 34° (range, 28-41; SD ±3) stayed also stable with 34° (range, 28-40; SD ±3) (P = .796).

Conclusion: The CSA is an anatomical parameter of the scapula that does not change in size after closure of the physes.

Keywords: Scapular morphology; acromion type according to Bigliani and Morrison; critical shoulder angle; posterior acromial height; posterior acromial tilt.