Introduction <p>Adhesive capsulitis (AC), well-known as frozen shoulder, is characterized by restricted shoulder motility that affects daily activities. The prime of this study was to compare the long-term efficacy of fascia hydrorelease (FHR) versus anterior hydrodilatation via rotator interval (RI) in primary AC shoulders. The primary endpoint was the 12-month SPADI following both interventions.</p> Methods <p>120 patients diagnosed with unilateral resistant AC with moderate to profound pain and disability were recruited. Patients were randomized into two groups. Interrater reliability for the musculoskeletal ultrasound (MSUS) was investigated. Assessments were performed for up to 12 months. Both groups received guided rehabilitation after injection. Additionally, baseline, three, six, and 12-month Shoulder Pain, Disability Index (SPADI) and range of motion (ROM) had been recorded for all patients.</p> Results <p>There was no difference regarding clinical or sonographic characteristics between both groups at baseline. The interobserver reliability for MSUS demonstrated almost perfect agreement (kappa (κ) = 0.85, 95% confidence interval = 0.83–0.86). Both groups showed a decrease in SPADI and improvement in shoulder flexion and abduction immediately after injection. Repeated measures ANOVA showed a statistically significant difference in post-injection SPADI throughout follow-up across both groups (<i>p</i> &lt; 0.0001). The FHR group exhibited progress in internal rotation (IR), external rotation (ER), and extension better than the RI group. A significantly longer-term improvement was observed in the FHR group in the follow-ups in function and global ROM.</p> Conclusions <p>Ultrasound-guided FHR could be effective in addressing both pain and functional limitations with better longevity for AC. It is suggested that FHR could have enhanced hydration and gliding between the fascia and coracohumeral ligament (CHL) and may have freed extracapsular adhesions.</p>