Eighty-four patients undergoing unicompartmental knee arthroplasty were randomized to receive a periarticular injection performed prior to joint incision (early stage; n=42) or after implantation of the prosthesis (late stage; n=42). The primary outcome of interest was pain intensity, measured on a 100-point Visual Analog Scale (VAS). Secondary outcomes of interest included range of motion, rescue analgesia consumption, and in-hospital complications, measured up to 120 hours post-operation. The results of this study found early-stage injection to provide superior pain relief in the post-operative recovery room. However, no differences in pain intensity were observed between the two groups at 3-120 hours post-operation. No differences in secondary outcomes were observed between the two groups.