To date, approximately 8-10 patients at the investigator's institution have undergone simultaneous bilateral total knee arthroplasty with the use of liposomal bupivacaine without a known adverse event. A recent study published by Bramlett (2012) used 2 vials (532mg) in one knee to evaluate efficacy. There were no changes in patient's vitals signs or cardiac events in those patients receiving liposomal bupivacaine at the highest dose. In addition, a study by Bergese looked at doses of up to 600mg of liposomal bupivacaine in a Phase 2 safety study and found no adverse cardiac events. The purpose of this study is to evaluate the serum levels (pharmacokinetics) of bupivacaine in a series of patients undergoing simultaneous bilateral total knee arthroplasty with the use of a standardize periarticular injection containing free bupivacaine and liposomal bupivacaine.