This study seeks to determine whether a new sustained-release local anesthetic solution (Exparel - Liposomal Bupivacaine) injected into the soft tissues around the joint after surgery will decrease opioid consumption and adverse events in opioid-tolerant patients presenting for total knee arthroplasty. The research hypothesis is that the Exparel (study) group will use less opioid in the first 48 hours post-operatively than the control group.