Patients experience significant postoperative pain following shoulder surgery, Single shot interscalene block is used in ambulatory shoulder surgery for its advantages that include significant reduction in acute pain and analgesic requirements, prolonged time to first analgesic request, decreased incidence of nausea, as well as earlier hospital discharge.The process of nerve block requires several needle passes, with each of them being at risk of causing nerve injury either by direct trauma or intraneural injection even with the use of the ultrasound. These facts raised concerns and several authors stated that maybe the anesthesiologists should be more careful, keep a safe distance from the nerve, and inject the local anesthetics into fascial planes containing the nerve and not attempt to place the needle in close proximity to the nerve. This study is designed to determine the maximal effective distance away from the nerve for the injection to be effective.