Analgesic Efficacy of the Infraspinatus-Teres Minor (ITM) Interfascial Plane Block After Shoulder Arthroscopy: A Simon's Two-Stage Design

The main study objective is to observe the ability of the ITM block to provide clinically acceptable pain control after elective shoulder arthroscopy as measured by pain scores and morphine consumption. The secondary objectives are determining its trajectory of efficacy up to 24 hours by measure of pain scores, morphine consumption and side effects.

Inclusion Criteria: * The study population inclusion criteria will be: * Patients of any sex * Class ASAI-III * Patients 18 years of age or older * Scheduled for elective shoulder arthroscopy * Able to give written informed consent autonomously * Sex and gender dimensions are irrelevant for this study as enrolled patients are benefitting from shoulder surgery without reference to gender and our standard care as well as our research disposition is indiscriminately applied to all genders. Exclusion Criteria: * The subject exclusion criteria will be: * Allergy to any of: ropivacaine, paracetamol, celecoxib, morphine, ondansetron or dexamethasone * Refusal or inability to give consent * Bleeding diathesis (according to HEMSTOP score) * Neurological deficit of the operative side * Existing preoperative chronic opioid use (greater than or equal to 3 months of use) * Renal insufficiency (GFR\