Can magnetic resonance imaging distinguish clinical stages of frozen shoulder? A state-of-the-art review

Background: Frozen shoulder (FS) is a common disorder causing shoulder pain and limited motion. Magnetic resonance imaging (MRI) is expected to help diagnose FS and realize the disease stage if stage-specific features are present. We aimed to survey stage-related MRI findings of FS in the literature. Methods: MEDLINE, SCOPUS, and Google Scholar databases were searched with search terms "frozen shoulder" or "adhesive capsulitis" combined with "magnetic resonance imaging." Studies that discussed MRI findings in relation to FS stages were retrieved. The course of FS was divided into stages 1 to 4 according to Hannafin and Chiaia. Results: Two of the noncontrast-enhanced MRI findings were stage-related. T2 signal hyperintensity of the joint capsule was more frequent in stages 1 and 2. The axillary capsule thickness was greater in stages 1 and 2. However, these findings were also seen in the later stages to a lesser degree. Effusion around the long head of biceps, subcoracoid fat obliteration, and coracohumeral ligament thickening were common in FS but their relation to the stages was not evident. Signal enhancement on contrast-enhanced MRI was not consistently linked to stages. Conclusion: T2 signal hyperintensity and axillary capsule thickening are characteristic of the early stages of FS, although MRI alone cannot completely define the disease stage.