Effect of adductor canal block combined with infiltration between the popliteal artery and posterior capsular of the knee on chronic pain after total knee arthroplasty: a prospective, randomized, double-blind, placebo-controlled trial

Total knee arthroplasty (TKA) is accompanied by severe postoperative pain, which is reported to be an important cause of chronic pain. Ultrasound-guided adductor canal block (ACB) combined with infiltration between the popliteal artery and posterior capsular of the knee (IPACK) has been proven to have a better effect on relieving acute pain after TKA. However, whether it has a significant effect on the incidence of chronic pain after TKA has not been reported. This trial was designed to investigate the effect of ultrasound-guided ACB combined with IPACK on the incidence and intensity of chronic pain after TKA. In this prospective, randomized, double-blind, placebo-controlled study, 100 subjects scheduled for TKA were randomly (1:1) divided into two groups: the ropivacaine group and the placebo group. Patients in each group received ultrasound-guided ACB + IPACK procedures with 0.25% ropivacaine or equal volume normal saline. All patients received multimodal analgesia. Pain intensity was assessed using the Numerical Rating Scale (NRS). The primary outcome was the incidence of chronic pain at 3 months after TKA by telephone follow-up. In addition, pain intensity in early resting and mobilized states, chronic pain intensity, the time to first rescue analgesia; opioid consumption; CRP and IL-6 after the operation; length of postoperative hospital stay; and cost of hospitalization and postoperative complications; as well as the function of the knee in the early stage after the operation, were recorded. Ninety-one participants were included in the final analysis. At 3 months, the incidence of chronic pain was 30.4% in the ropivacaine group, significantly lower than 51.1% in the placebo group. Compared with the placebo group, the ACB + IPACK with ropivacaine group had significantly lower pain scores at 4 hours, 8 hours, 16 hours, and 24 hours after the operation; increased the knee range of motion at 8 hours and 24 hours after the operation; and a significantly decreased incidence of chronic pain at 3 months after the operation. During the follow-up period, there were no nerve block-related complications in either group. In the context of multimodal analgesia protocols, ACB combined with IPACK before surgery decreases the incidence and intensity of chronic pain 3 months after TKA compared with placebo injection. In addition, it reduces the NRS scores, whether at rest or during mobilization, and improves knee function within 24 hours after TKA. This trial was registered in the China Clinical Trial Center (registration number ChiCTR2200065300) on November 1, 2022.