The investigators will be comparing pain scores and opioid use in patients receiving interscalene peripheral blocks with plain bupivacaine versus those receiving liposomal bupivacaine. Liposomal bupivacaine is described as releasing local anesthetic up to 72 hours after its injection; therefore if liposomal bupivacaine can provide extended pain relief compared to plain bupivacaine, the investigators can consider using it as our primary local anesthetic. As secondary outcomes, the investigators will also be looking at difference in functional status and long-term differences between the two local anesthetics.

Background:

The current standard of care for patients at the investigators' institution is to perform an interscalene peripheral nerve block for patients receiving arthroscopic shoulder surgery surgery as it is an effective opioid-free alternative for post-operative pain control. The investigators in the past perform both single shot injections and place catheter based on patient and surgical preferences. Catheters have shown to have extended benefit throughout the perioperative period, including lower pain scores, reduced analgesics and improved sleep. However, the negatives of catheters include the placement of a foreign body, increased time to perform the procedure, interference in surgical field and increased cost of catheter equipment and local anesthetic pump and premature catheter dislodgement. Therefore, pros and cons of deciding between placing a single shot injecting versus catheter has to be considered individually for each case.

Liposomal bupivacaine due to its liposomal outer layers, releases bupivacaine over a longer period of time than plain bupivacaine. A pharmacokinetic study showed the terminal half-life of bupivacaine to be 131 ± 58 minutes versus 1294 ± 860 minutes for liposomal bupivacaine.

In a recent study comparing liposomal bupivacaine to placebo for interscalene peripheral nerve blocks, patients receiving liposomal bupivacaine had significantly lower pain scores over 48 hours and received less opioid over 72 hours[6]. Therefore, if a single shot injection with liposomal bupivacaine can provide longer pain relief than plain bupivacaine, it makes the decision to perform single shot interscalene peripheral nerve blocks easier.

Study Objectives The investigators would like to study whether an interscalene peripheral block injection with liposomal bupivacaine provides superior pain control compared to an interscalene single shot with plain bupivacaine. The investigators will be looking at average daily pain scores, highest daily visual analog scale (VAS) pain scores at rest and with movement, total daily opioid consumption from immediately post-operative to 7 days post-operative, and functionality with physical therapy. The investigators will also plan to follow these patients 6 month and 12 months post-operative to determine whether there is any difference in incidence of persistent post-operative pain.

Inclusion Criteria:

• medically optimized patients that will undergo an elective surgery for arthroscopic shoulder surgery

Exclusion Criteria:

• under 18 years pregnant or breast-feeding, non-English speaking, have renal or hepatic dysfunction, history of chronic opioid use, receiving worker's compensation, smoker, receiving capsular release, respiratory compromise or BMI < 18 or > 35 or allergy to local anesthetics or opioids

The participants and data collectors are unaware of which group the patient belongs to. The anesthesiologist performing the nerve block will not be blinded.