Acromial morphology: reliability of computer tomography-based assessment and association with age: a study of 420...

Acromial morphology is considered an important factor in the pathophysiology and development of subacromial impingement and rotator cuff disorders. The Bigliani classification remains widely used to describe acromial shape in both clinical practice and research, mainly because of its simplicity; however, its reliability on computed tomography (CT) imaging, including CT arthrography, has been poorly investigated. In addition, the relationship between acromial morphology and age remains unclear. The primary objective of this study was to assess the intrarater and inter-rater reliability of the Bigliani classification on CT imaging. The secondary objective was to analyze the association between acromial morphology and age.

This was a single-center retrospective observational study. Five shoulder surgeons with different levels of experience independently assessed the morphology of 420 acromions using standardized slices derived from three-dimensional CT reconstructions. Acromial morphology was classified according to the Bigliani classification. All evaluations were performed in a blinded fashion.

Among the 2,100 evaluations performed, 28.7% of acromions were classified as type I, 59.7% as type II, and 11.6% as type III. The Bigliani classification demonstrated good intrarater reliability (κ = 0.61) but poor inter-rater reliability (κ_f = 0.32). A significant association was observed between age and acromial morphology.

Even with optimized CT imaging, the Bigliani classification demonstrated good intrarater reliability but poor inter-rater reliability for the assessment of acromial morphology. A significant association between age and acromial morphology was identified. These results should be interpreted with caution, as this study was designed as a methodological evaluation of a widely used classification system rather than to establish clinical or causal relationships, with potential implications for clinical decision-making and research reproducibility.