Background <p>Frozen shoulder is a challenging musculoskeletal disorder, affecting between 2 and 5% of people, with a higher incidence among those with diabetes and thyroid issues. This condition can persist for years and can be very demanding for both patients and healthcare providers due to the intense pain and restricted shoulder movement. Literature shows that intra-articular corticoid injection (IACI) and suprascapular nerve block (SSNB) can improve pain and range of motion in these patients. The objective of this study is to investigate if there is any significant difference in pain reduction and functional recovery when treated with a combination of gleno-humeral IACI and SSNB compared to a gleno-humeral IACI paired with a placebo SSNB.</p> Methods <p>A two-arm, single-centre, randomized, parallel-group controlled trial will be conducted. Eligible patients will be randomly assigned (1:1 allocation) to long-acting SSNB + IACI and placebo SSNB + IACI. The primary endpoint is the mean change from baseline to 3 months in the Shoulder Pain and Disability Index (SPADI) score. Secondary outcomes will evaluate quality of life, functionality, pain (measured by a Numeric Pain Rating Scale), kinesiophobia, work status, health care service, and a safety assessment.&#xa0;The main paper will be based on the repeated measures collected up to 12 months from baseline. </p> Discussion <p>The aim of this study is to determine the additional effect on pain relief and functional improvement in frozen shoulder patients when a long-acting SSNB is administered, compared to a placebo SSNB, in combination with an intra-articular corticosteroid injection. Additionally, we will aim to determine which patients benefit most from these treatments. This study could lead to a change in the standard of care for patients in the painful phase of frozen shoulder.</p> Trial registration <p>ClinicalTrials.gov NCT06229964. Registered on 9 January 2024.</p>