LAUSR

By a randomized controlled trial including 105 patients who underwent unilateral total knee arthroplasty (TKA), Et et al. [1] compared efficacy of the infiltration between the popliteal artery and the capsule of the posterior knee (iPACK) + adductor canal block (ACB) to the periarticular infiltration (PAI) + ACB and ACB alone for postoperative analgesia. They showed that addition of an iPACK block to the ACB significantly improved postoperative analgesia and reduced opioid consumption. As addition of a nerve block to multimodal analgesia protocol can improve postoperative pain control and is being emphasized in current practice of Enhanced Recovery After Surgery protocols [2], this study has the potential implications. Other than the limitations described in the discussion, however, we noted several issues in this study that needed further clarification. First, primary outcome of this study was the area under the curve (AUC) for numeric rating scale (NRS) pain score at 48 h after surgery and the sample size evaluation was based on a result of the analysis made with a pilot data of 15 people. However, the readers were not provided with the details of their pilot data, such as mean, standard deviation and inter-group difference of the AUC for NRS pain scores, which are the important components of power analysis for a randomized controlled trial. Most important, this study included three groups. A 0.32 assumed effect size was provided, but it was unclear whether this effect size was appropriate for all comparisons among the three groups [3]. Second, the 48-h AUC for movement NRS pain score was significantly lower in the iPACK + ACB group than in the PAI + ACB and ACB groups. According to the results of Fig. 3 in the Et et al.’ article [1], we noted that beside postoperative 6-h time point, the differences of mean movement NRS pain scores between the iPACK + ACB and PAI + ACB groups at other time points were less than 1, with the large standard deviation. For patients undergoing TKA, the recommended minimal clinically important difference of postoperative movement pain score in available literature is 1.8 on a 0–10 pain scale [4]. In this case, it is difficult for readers to determine whether improved postoperative movement pain control in the iPACK + ACB group compared with the iPACK + ACB group should be considered as being clinically important. Third, intravenous tramadol 100 mg was administered for rescue analgesia when patient complained of NRS pain score > 4. However, mean movement NRS pain scores within 8–24 h after surgery in the three groups are more than 4. As adequate movement pain control is very important for postoperative functional recovery in patients undergoing AKT, we were very interested in knowing why designed goal of postoperative pain control was not achieved in some time points, especially for patients receiving ACB alone. Finally, total intravenous tramadol (mg) consumption within 0–48 h postoperatively, and tramadol consumptions in first 24 h and 24–48 h postoperatively were significantly lower in the iPACK + ACB group than in the ACB and PAI + ACB groups. When opioid consumption of postoperative analgesia was compared, however, it is generally required that the usages of analgesics should be converted to morphine milligram equivalents (MMEs). In available literature, moreover, the recommended minimal clinically important difference of opioid consumption for postoperative analgesia is an absolute reduction of 10-mg This comment refers to the article available online at https:// doi. org/ 10. 1007/ s0054002203047-6.