The aim of this clinical trial is to determine whether point-of-care ultrasound-guided corticosteroid injection is more effective than conventional injection guided by anatomical landmarks or standard oral medication for patients with upper-extremity conditions (subacromial impingement syndrome [SAS] or carpal tunnel syndrome [CTS]) in primary care.

The main questions this study seeks to answer are:

Does ultrasound-guided injection provide superior long-term pain relief compared to blind anatomical injection and oral medication?

Does ultrasound-guided injection lead to better functional recovery and improved health-related quality of life in patients?

Is ultrasound-guided injection a cost-effective strategy from both the healthcare system and societal perspectives (including reducing sick leave)?

This study represents the quantitative phase of the mixed-methods Q-EPICAP study. Researchers will compare three parallel groups across 23 primary care centers to determine the most effective and efficient treatment strategy.

Participants will:

Receive one of three assigned treatments: blind anatomical infiltration (Group I), ultrasound-guided infiltration (Group UI), or standard oral drug therapy (Group P).

Attend follow-up assessments at baseline and at 15, 30, 90, and 180 days after the initial intervention.

Complete questionnaires to assess pain intensity (Visual Analog Scale), upper limb function (ASES or Boston Disability Assessment Questionnaire), and quality of life (EQ-5D-5L).

Provide data on medical resource utilization and sick leave to assess socioeconomic costs.

Upper extremity pathologies, particularly subacromial impingement syndrome (SAS) and carpal tunnel syndrome (CTS), represent a significant clinical and socioeconomic burden for primary care systems, primarily due to functional disability and prolonged sick leave.

Although corticosteroid injections are frequently used, traditional blind injections guided by anatomical landmarks often lack anatomical precision. Point-of-care ultrasound-guided injections offer greater accuracy and better short-term clinical outcomes; however, their cost-effectiveness in routine clinical practice has not yet been adequately assessed.

This pragmatic, prospective, multicenter, cluster-randomized clinical trial includes 23 participating primary care centers (clusters) in Lleida, Spain, with a 6-month longitudinal follow-up. This study constitutes the quantitative phase of the mixed-methods Q-EPICAP project.

A total of 225 adult patients diagnosed with SAS or CTS and presenting with baseline pain (VAS ≥ 3) were divided into three parallel groups:

1. Group I: Anatomical landmark-guided infiltration.
2. Group UI: Ultrasound-guided infiltration performed by family physicians.
3. Group P: Standard oral pharmacological treatment.

Data collection was performed at baseline and at 15, 30, 90, and 180 days post-intervention. The primary outcome measure was pain intensity (VAS). Secondary outcomes included upper limb function (ASES and Boston questionnaires), health-related quality of life (EQ-5D-5L), and a comprehensive economic evaluation (cost-effectiveness and cost-utility indices) that integrates the perspectives of healthcare systems and society.

Inclusion Criteria:

• Patients aged 18 years or older presenting in primary care. Clinical diagnosis of subacromial impingement syndrome (shoulder pain from tendon compression) or carpal tunnel syndrome (wrist nerve compression). Moderate to severe pain intensity, defined as a score of greater than or equal to 3 on the Visual Analog Scale (VAS >= 3) at baseline. Patient must understand the study procedures and provide written informed consent.

Exclusion Criteria:

• Previous corticosteroid infiltration in the target joint/structure within the last 6 months. History of major trauma, active infection, or previous surgery in the affected shoulder or wrist. Underlying systemic inflammatory diseases (for example, rheumatoid arthritis, polymyalgia rheumatica). Known hypersensitivity or contraindications to corticosteroids (Betamethasone) or local anesthetics (Mepivacaine). Pregnancy or breastfeeding. Red flags suggesting tumor, fracture, or severe neurological deficit.

Anonymized individual participant data that support the results to be published in the future will be available to qualified researchers who reasonably request them for academic research purposes. Data sharing will be subject to a formal request to the corresponding author, approval from the Institutional Ethics Committee, and the signing of a data access agreement.

Data will be available beginning 12 months after publication of the main results in the scientific journal and will remain accessible for a period of 3 years.

• Who: Qualified academic researchers with a methodologically sound proposal and approved institutional affiliation.
• What: Anonymized individual participant data (IPDs) that support the primary results, along with the Study Protocol and Statistical Analysis Plan (SAP).
• How: Access requests must be formally submitted via email to the corresponding author. To obtain the data, the requester must obtain approval from their own Institutional Ethics Committee and sign a legally binding Data Access Agreement to ensure data confidentiality and guarantee that the data will only be used for the approved research purpose.

Due to the nature of the interventions (ultrasound-guided infiltration versus conventional infiltration guided by anatomical landmarks versus oral pharmacological treatment), it is impossible to blind the family physicians performing the procedures.

However, a single-blind design is maintained for the participants (patients), who are unaware of the alternative pharmacological or procedural strategies assigned to other groups. To minimize bias, outcome assessments and data analysis will be performed by researchers or statistical evaluators independent of the clinical intervention and unaware of the treatment groups.