Radiologic capsular abnormalities on shoulder MRI: associations with rotator cuff and biceps tendon tears and implications for the diagnosis of adhesive capsulitis

Capsular abnormality on shoulder MRI may suggest adhesive capsulitis, but similar findings can occur in patients with other shoulder pathologies such as rotator cuff tears. This study investigated the clinical and imaging factors associated with radiologic capsular abnormality (RCA). This retrospective study included 483 adults who underwent shoulder MRI between January and December 2020. Two musculoskeletal radiologists independently assessed abnormalities of the rotator interval (RI) and axillary pouch (AP), as well as tears of the supraspinatus tendon (SST), infraspinatus tendon (IST), subscapularis tendon (SSc), and long head of the biceps tendon (LHBT). RCA was defined as abnormalities of both the RI and AP. Univariable and multivariable logistic regression analyses were performed. Four-group subgroup analyses compared patients with no capsular abnormality, isolated AP abnormality, isolated RI abnormality, and RCA, with adjustment for age where appropriate. Of 483 patients, 234 (48.45%) had RCA. Clinically diagnosed adhesive capsulitis was present in 45 patients (9.32%), of whom 43 had RCA. In multivariable analysis, older age was associated with higher odds of RCA (odds ratio (OR), 1.05; 95% confidence interval (CI), 1.03–1.07; P < 0.001). SSc tears were positively associated with RCA (Lafosse type I: OR, 1.82; 95% CI, 1.17–2.83; P = 0.008; type II or higher: OR, 2.15; 95% CI, 1.04–4.44; P = 0.039), whereas SST and IST tears were negatively associated with RCA. In subgroup analyses, isolated RI abnormality was associated with higher prevalence of SSc and LHBT tears than no capsular abnormality after age adjustment. RCA is common on shoulder MRI but is not synonymous with adhesive capsulitis. The substantial difference between the prevalence of RCA and clinically diagnosed adhesive capsulitis suggests that reliance on capsular abnormalities on MRI alone may lead to overdiagnosis of adhesive capsulitis. Particular caution is warranted in older patients and those with SSc or LHBT pathology. Conversely, the lower frequency of RCA in patients with SST or IST tears is consistent with the traditional concept of adhesive capsulitis as a diagnosis of exclusion, in which other shoulder pathologies are excluded. The use of the term RCA for these capsular abnormalities on MRI may promote appropriate clinical correlation.