All surgeries were performed by the same orthopaedic surgeon. Two groups, one receiving Exparel® (bupivacaine liposome injectable suspension) plus bupivacaine with epinephrine (LB group) and the other receiving bupivacaine with epinephrine (Control group), will be compared using post-operative pain scores, hospital length of stay, time to ambulation, falls, narcotic use, and narcotic-related adverse effects. Aside from hospital length of stay, all outcomes were recorded for up to 72 hours following surgery. An a priori power analysis was performed to calculate the total number of patients that needed to be enrolled to achieve a minimum 90% power, with the threshold of statistical significance set to 0.05. Based on a previous study reporting a mean oral opioid consumption of 57.04mg ± 25.6 at 24 hours post THR, a mean difference of 17.14mg was considered to be clinically significant. Thus, at least 26 patients were necessary in each group for an adequately powered assessment. The diagnosis for osteoarthritis was determined by patient history, physical examination, and imaging findings. Each patient received a thorough explanation of the protocol, and willing patients signed an informed consent form. All patients underwent a personal preoperative education program regarding pre, intra-, and post-procedural information including physical therapy, expectations, discharge goals, home therapy, and pain management. After written consent was collected, the form was sent to the hospital pharmacy for randomization. Envelopes were randomized, sealed, numbered, and given to the pharmacy staff, ultimately dispensing the envelopes to the nurse in the operating room in numerical order. The pharmacy documented the required information, selected medication, and drug accountability forms according to the contents of the envelopes.

A nurse delivered study drugs to the operating room in a sealed, non-descriptive envelope. During the standard anterior approach procedure, an anesthesiologist administered fentanyl or hydromorphone as needed for analgesia. The local anesthetics were administered after reduction of the implants. Patients in the LB group received 20cc liposomal bupivacaine, 40cc 0.25% bupivacaine with epinephrine, and 20cc of normal saline. Each patient in the control group received 60cc of 0.25% bupivacaine with epinephrine. Using a 20-gauge spinal needle, the local anesthetics were injected using a deep tissue administration technique. Structures innervated by the femoral nerve, superior gluteal nerve, or lateral femoral cutaneous nerve were considered suitable for injection. Throughout administration, frequent aspirations were performed to check for blood and minimize the risk of intravascular injection. The patients, surgical team, and floor staff was blinded to the local anesthetic drugs given.

During hospitalization, patients were observed, evaluated and treated according to postoperative protocols. Patients received opioids for pain management as needed, which was routinely documented by hospital staff. Opioids included fentanyl, hydromorphone, oxycodone, codeine, tramadol, morphine, and hydrocodone. All opioid dosages were converted into morphine equivalent dosages for analysis. Each patient began physical therapy within the first 24 hours postoperatively. Patients were discharged when they were able to begin self-care, their pain was controlled utilizing an oral regimen, and they were able to tolerate oral medication intake.