“…In 11 reports (39%), the principal aim of the study was to test whether equal analgesic efficacy but fewer adverse effects could be achieved with the combination of a small dose of an opioid with a reduced dose of an LA [4,5,7,12,24,34,38,39,42,43,46]. In the other 17 reports, there was a large variety of working hypotheses: different analgesic efficacy and different risks of adverse effects with experimental interventions [1,3,8,11,14,26,32,44]; improved analgesia and fewer adverse effects [13,25]; improved analgesia and equal risk of adverse effects [30]; equal analgesia and equal risk of adverse effects [22]; fewer adverse effects with no statement about analgesic efficacy [6,29,45]; and improved analgesia and potentially increased risk of adverse effects [27,35].…”