Effect of periarticular morphine injection for total knee arthroplasty. A randomized, double-blind trial

Background The periarticular multimodal cocktail injection including morphine is currently commonly used to treat postoperative pain after total knee arthroplasty (TKA). Despite its analgesic effect, it is frequently reported to cause nausea and vomiting, which are adverse effects of opioids. This study aimed to assess the efficacy of morphine as a component of a multimodal cocktail injection for providing postoperative analgesia and alleviating swelling in patients who underwent TKA. Materials and Methods This was a prospective, single-center, randomized controlled trial involving 102 patients scheduled for unilateral TKA. A mixture of steroids, local anesthetics, NSAIDs, and epinephrine with or without morphine (10 mg), was injected to randomly assigned patients. Postoperative assessment was performed with all attending personnel and patients blinded to group assignment. Visual analog scale (VAS) of pain, range of motion (ROM), nausea numerical rating scale (NRS), the number of patients with vomiting, the total dose of antiemetic drugs used, thigh swelling, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, and adverse outcomes were compared between groups on postoperative days. Results VAS scores did not differ between the 2 groups at any postoperative time-point. The nausea NRS scores during the postoperative period from 30 minutes to 9 h, the number of vomiting episodes, and the total dose of antiemetic drugs administered was significantly higher in the morphine group. The thigh girth, WOMAC and the incidence of complications were not different between groups. Conclusions The results of this study suggested that addition of morphine to the multimodal cocktail injection is not effective for relieving postoperative pain, alleviating swelling, or improving ROM, and results in nausea and vomiting.