http://pixvid.me/mdbonedocsShoulderNu... An interscalene brachial plexus block uses injected medication to numb the shoulder and upper arm prior to surgical procedures or repositioning (reduction) of a dislocated shoulder. An interscalene brachial plexus block delivers numbing medication to nerves in the shoulder and arm. It may be used for hand and wrist surgery as well, but additional medication is usually required. The nerve block is temporary, lasting up to several hours. Following the operation, the medication wears off and the sense of feeling returns.