The purpose of this study is to compare the quality and duration of pain relief after shoulder surgery provided by a single injection of liposomal bupivacaine versus standard bupivacaine when administered as an interscalene brachial plexus block. It is hypothesized that the liposomal bupivacaine formulation will provide more effective pain relief than standard bupivacaine.

Inclusion Criteria:

• English speaking adults (age >17 years) of American Society of Anesthesiologists (ASA) I-III physical class scheduled for elective arthroscopic shoulder surgery will be eligible to participate regardless of race/ethnicity.

Exclusion Criteria:

• Subjects will not be eligible for this trial if they report a history of an allergy to a local anesthetic, baseline neurological deficit, a medical condition that would make it difficult to assess sensory distribution or communicate with the staff, a recent history (< 3 months) of drug or alcohol abuse, concomitant opioid therapy, or a preexisting coagulation disorder.