Reduction of Postoperative Pain by Addition of Intravenous Acetaminophen after Total Hip Arthroplasty: A Retrospective Cohort Study

We evaluated the analgesic effects of multimodal pain control in which intravenous acetaminophen (IV APAP) was added to the standard protocol for Japanese patients who had undergone a total hip arthroplasty (THA). We performed a retrospective cohort study of 180 patients aged 66.4±10.5 years (30% male) who had undergone a THA (Oct. 2014 to Feb. 2015) at our hospital. The control patients were administered the standard analgesic protocol: flurbiprofen axetil as a continuous intravenous infusion and oral celecoxib (NAPAP; n=109). The patients in the new analgesic protocol group received IV APAP in addition to the standard analgesic protocol (APAP; n=71). The primary outcome was the maximum value of postoperative pain the patients reported on a numerical rating scale (NRS) during the first 24 h post-surgery. A univariate analysis and multivariate analyses adjusted for age, sex, the stage of hip osteoarthritis, preoperative pain, and surgical time showed that the maximum postoperative pain NRS scores during the first 24 h after surgery was significantly lower when the APAP protocol was used. The addition of IV APAP to the current standard multimodal analgesia protocol for Japanese patients who have undergone a THA may decrease the patients’ postoperative pain.