The Minimum Effective Dose (ED90) of Liposomal Bupivacaine for Preserving Motor Function

Inclusion Criteria: Age 41-65 years ASA physical condition 1-3 BMI 18-30 kg/m2 undergoing arthroscopic shoulder surgery Exclusion Criteria: Inability to consent to the study pregnancy allergy to local anesthetics preexisting neuropathy cervical pathologies (i.e., herniated disc, myelopathy) chronic pain syndromes (defined as reflex sympathetic dystrophy or complex regional pain syndrome) severe respiratory conditions psychiatric or cognitive disorders that prohibit patients from adhering to the study protocol history of drug or alcohol abuse chronic opioid use (longer than 3 months or daily morphine equivalents more than 5mg/day for 1 month) contraindication for general anesthesia and/or interscalene nerve block and planned open shoulder arthrotomies Muscle related diseases