Seventy-four older patients (50-80 years) undergoing a first-time unilateral total knee arthroplasty were randomized to receive an adductor canal blockade with ropivacaine plus butorphanol as an adjuvant (n=37) or ropivacaine only (n=37). The primary outcome of interest was the duration of sensory block and Visual Analog Scale (VAS) pain scores at rest and with activity. Secondary outcomes of interest included patient-controlled analgesia demand, quadriceps strength, knee range of motion, time to first mobilization, Knee Society Score (KSS) function score at discharge, length of stay, and post-operative complications. The results found significantly longer sensory blockade, better knee range of motion and lower VAS pain scores in the early postoperative period, and lower demand for patient-controlled analgesia with adjuvant butorphanol vs. control. No differences in quadriceps muscle strength, time to mobilization, KSS function scores, length of stay or complications were observed between groups.