6: Nerve Blocks With Targeted Muscle Reinnervation Reduce Acute Postoperative Opioid Use in Major Lower Extremity Amputation

Abstract

Purpose: Major amputations of the lower extremity, specifically through and below the knee, are morbid procedures requiring general anesthesia typically followed by high doses of postoperative opioids. Many are performed on highly comorbid, chronic wound patients with a potential for increased opioid use following surgery. Given the current opioid epidemic, perioperative narcotic-reduction strategies are paramount. Our center instituted a protocol for major amputations that includes continuous regional anesthesia, for intraoperative and postoperative pain control, and targeted muscle reinnervation (TMR) nerve transfers to mitigate long-term pain. The aim of this study was to analyze the impact of continuous regional anesthesia and TMR on early postoperative opioid requirements after major lower extremity amputation at our limb salvage center. Methods: We retrospectively reviewed our center’s below-knee and through-knee-amputations from 2017-2019 for utilization of regional pain catheters and TMR nerve transfers. Opioid usage as morphine milligram equivalents (MMEs) was tracked for the first seven postoperative days. Baseline opioid dose was defined by the documented opioid use one day before amputation. Patients were categorized into one of four groups, based on whether regional pain catheter and/or TMR were used. Kruskal-Wallis testing was used to assess baseline opioid use between groups. Bivariate linear regression was used to assess postoperative opioid use of each group compared to the control group. Logistic regression analysis was conducted to examine association between TMR and changes in opioid use postoperatively versus baseline. Results: 198 patients were reviewed. 95 patients received perioperative regional anesthesia, of which 81 underwent TMR. 103 patients did not receive regional anesthesia, of which 30 underwent TMR. Average baseline opioid use was 40.6 MME in patients treated with TMR and regional anesthesia, 60.2 MME with TMR and without regional anesthesia, 28.7 MME without TMR and with regional anesthesia, and 132.6 MME without TMR and regional anesthesia (p=0.0004). Multivariate analysis showed that undergoing TMR, without regional anesthesia, significantly decreased postoperative opioid use by 111.7 MME, compared to the control group (p=0.006). Use of regional anesthesia, with TMR, provided an additive effect, significantly decreasing postoperative opioid use by 124.3 MME, compared to control (p<0.0001). Interestingly, regional anesthesia without TMR decreased postoperative opioid use by 93.4 MME, but without significance (p=0.08). Odds of decreased opioid use postoperatively compared to baseline was 1.91 times higher with TMR than without TMR (p=0.04). Conclusion: TMR nerve transfers were found to be independently effective at reducing postoperative opioid requirements after major lower extremity amputation. Concurrent use of regional anesthesia compounded this effect. Minimizing baseline opioid use prior to amputation may decrease opioid use postoperatively. TMR nerve transfer with continuous regional anesthesia protocol can decrease reliance on postoperative pain control with opioids in lower extremity major amputation patients.