Frozen shoulder remains a challenging disease to treat as pain and loss of range of motion can persist for many months or even years. This loss of function can have a severe impact on the patient's activities, participation and overall quality of life. The use of ultrasound-guided (USG) suprascapular nerve blocks (SSNB) and/or intra-articular corticoid injections (IACI) has been supported by many studies. However, double blinded randomized clinical trials using a combination of SSNB and IACI are rare. The primary objective of this study is to compare the effectiveness of a glenohumeral IACI combined with a SSNB, compared to a glenohumeral IACI combined with a sham SSNB. Outcome measures of interest are shoulder-related disability reported by the patients, shoulder pain and shoulder stiffness. These outcome parameters will be compared between both treatment arms with an intention-to-treat analysis. As key secondary objectives, the investigators aim to identify which physical examination tests, or combinations of those, are correlated with MRI diagnostic criteria and favor a more positive evolution. Finally, through predictive analysis the investigators will try to establish which patients benefit the most from the combined SSNB + IACI.