Effects of morphine on peri-articular infiltration analgesia in total knee arthroplasty: a prospective, double-blind, randomized controlled trial

Peri-articular infiltration analgesia (PIA) is a widely used method to control post-operative pain in total knee arthroplasty (TKA) patients. However, there are limited data that support the use of morphine in PIA. This study aims to evaluate the efficacy of peri-articular morphine infiltration for pain management in TKA patients. Based on a double-blind, randomized approach, patients were allocated to the morphine or control group. Patients in the morphine group received a peri-articular infiltration of an analgesic cocktail consisting of ropivacaine, epinephrine, and morphine. Morphine was omitted from the cocktail in the control group. Primary outcomes were post-operative consumption of morphine hydrochloride used for rescue analgesia and post-operative pain as assessed by visual analog scale (VAS) score. Secondary outcomes were functional recovery as assessed by a range of knee motion, quadriceps strength, and daily ambulation distance. The duration of hospital stay was also recorded. Tertiary outcomes included the occurrence of post-operative adverse effects and the consumption of antiemetics. Patients in the morphine group had significantly lower post-operative morphine consumption in the first 24 h and total morphine consumption. There was no significant difference between the two groups in post-operative VAS pain scores at rest or during motion. There was no significant difference between the two groups in the post-operative knee range of motion, quadriceps strength, daily ambulation distance, or duration of post-operative hospital stay. The two groups were similar in the incidence of adverse effects and the consumption of antiemetics. Adding morphine into the analgesic cocktail of PIA could reduce postoperative morphine consumption in TKA patients, but does not improve early pain relief or accelerate functional recovery or provide clinical benefits for TKA patients. In addition, the complications and safety of peri-articular morphine infiltration need to be further investigated in larger sample studies.