An observation of the relation between the cyst on magnetic resonance imaging at bare-area of humeral head and the adhesive capsulitis of the shoulder.

BACKGROUND: To investigate whether bare-area cysts of the humeral head, detected on magnetic resonance imaging (MRI), are associated with adhesive capsulitis and to evaluate their diagnostic value compared with other imaging features.

METHODS: This retrospective study included 138 patients with adhesive capsulitis and 114 control subjects identified from hospital records (February 2021-May 2024). Only patients with primary idiopathic adhesive capsulitis were included in this study. Patients with secondary adhesive capsulitis related to trauma, surgery, rotator cuff tear, or other identifiable shoulder pathologies were excluded. The diagnosis of adhesive capsulitis was established based on clinical evaluation by experienced orthopedic specialists, including progressive shoulder pain and significant restriction of both active and passive range of motion. In particular, loss of external rotation at the side was considered a key diagnostic feature. Range of motion limitation was evaluated by comparison with the contralateral shoulder, and internal rotation was assessed using vertebral level measurements. MRI examinations were assessed for the presence, size, and signal characteristics of bare-area cysts. Two musculoskeletal radiologists independently reviewed the images. Interobserver agreement was analyzed using intraclass correlation coefficients for continuous variables and Cohen κ for categorical variables. Binary logistic regression identified predictors of adhesive capsulitis, reported as odds ratios (ORs) with 95% confidence intervals (CIs). Receiver operating characteristic analysis was used to evaluate diagnostic performance, including area under the curve, optimal cutoffs, sensitivity, and specificity. Continuous variables were expressed as mean ± standard deviation.

RESULTS: Bare area cysts were significantly more common and larger in the adhesive capsulitis group (mean size, 13.3 ± 15.1 mm) than in controls (1.8 ± 4.7 mm, P < .001). Bare area hyperintensity was also more frequent (109 vs. 29, P < .001). Multivariable logistic regression analysis including age and sex as covariates demonstrated that bare area cyst size remained independently associated with adhesive capsulitis (OR: 1.27; 95% CI: 1.17-1.37; P < .001). Female sex was also independently associated with adhesive capsulitis (OR: 3.10; 95% CI: 1.57-6.13; P = .001), whereas age showed a significant association (OR: 1.05; 95% CI: 1.03-1.08; P < .001). Receiver operating characteristic analysis demonstrated good diagnostic performance, with an area under the curve of 0.837 for cyst size and 0.773 for bare-area hyperintensity.

CONCLUSION: Bare area cysts of the humeral head, particularly when enlarged or hyperintense, represent a useful MRI marker for adhesive capsulitis. Recognition of this feature may enhance diagnostic accuracy and facilitate differentiation from other shoulder disorders.