Duration of analgesia after forefoot surgery compared between an ankle and a sciatic nerve block at the popliteal crease

Abstract

BACKGROUND Forefoot surgery is associated with severe postoperative pain. Ankle and sciatic nerve blocks provide satisfactory postoperative analgesia after forefoot surgery, but little is known on their respective duration of analgesia. OBJECTIVE This randomised controlled, single-blinded trial tested the hypothesis that after forefoot surgery in the setting of multimodal analgesia, an ankle block provides analgesia superior to that of a sciatic nerve block at the popliteal crease. DESIGN A randomised controlled study. SETTING A single centre study in a university hospital in Switzerland, from September 2018 to November 2022. PATIENTS From 91 patients scheduled for forefoot surgery, 60 met the inclusion criteria of which 56 completed the protocol and their data were available for analysis. Exclusion criteria were existing sciatic nerve deficit, pre-existing peripheral neuropathy, chronic pain diagnosis, pregnancy, or identified contraindications to peripheral nerve block. INTERVENTION Patients undergoing forefoot surgery were randomly allocated to either a multi-injection ankle block (partly under ultrasound guidance) or a sciatic nerve block at the popliteal crease (under ultrasound guidance) combined with a saphenous nerve block at the ankle. Patients in each group received a total of 30 ml of ropivacaine 0.5% and a multimodal analgesic regimen inclusive of dexamethasone, paracetamol, ketorolac then ibuprofen. MAIN OUTCOME MEASURE The primary outcome was duration of analgesia, defined as time to first morphine request. RESULTS Mean ± SD duration of analgesia was 15.4 ± 8.0 h in the ankle block group and 20.0 ± 10.3 h in the sciatic nerve block group (P = 0.32). Of note, 15 of 26 (58%) and 24 of 30 (80%) patients of the ankle and sciatic nerve block groups did not request any morphine (P = 0.09). Other secondary outcomes were similar between groups. CONCLUSION Compared with the ankle block, the sciatic nerve block at the popliteal crease does not provide a longer duration of analgesia in patients undergoing forefoot surgery in the setting of multimodal analgesia. TRIAL REGISTRATION Clinicaltrials.com identifier: NCT03683342.