Background: Peripheral nerve blocks (PNB) are widely used for anaesthesia and postoperative pain control in orthopaedic limb surgery. However, little is known about the pain profile in acute fracture surgery and rebound pain following PNB might outweigh the benefits of longer analgesia. “AnAnkle Trial” aimed to investigate the effect of PNB anaesthesia compared with spinal anaesthesia (SA) on postoperative pain in acute ankle fracture surgery.

Methods: Randomised, open label trial on adult patients undergoing ankle fracture surgery. The study underwent ethical approval and GCP audit. Participants were randomised to PNB anaesthesia or SA. PNBs were ultrasound guided, popliteal sciatic and mid-femoral saphenous blocks with ropivacaine. SAs were unilateral with hyperbaric bupivacaine. The postoperative regimen was paracetamol, ibuprofen and patient controlled i.v. morphine (PCA).
Patients registered pain scores on a numeric rating scale 0-10 (NRS) every three hours for 27 hours and PCA use was registered. The primary endpoint was the pain intensity and opioid consumption (PIOC) score calculated by ranking both the NRS area under the curve (AUC) and total morphine 0-27h across both groups. PIOC is the sum of deviation from the mean rank in both parameters, equalling between -200% and +200%. Effect size is calculated as the probability of having a better PIOC with PNB compared with SA (p’). NRS AUC and total morphine were analysed separately as secondary endpoints.

Results and Discussion: We included 150 patients. The groups were comparable regarding comorbidity, preoperative pain scores and baseline characteristics. Conversion to general anaesthesia was necessary in five patients with PNB and none with SA (not significant). PIOC was significantly lower in the PNB group (median -26.5% vs. +54.3%, p<.001) with a probability of a better PIOC with PNB of p’=74.8% (67.0-82.6, 95%CI). The secondary endpoints also yielded significant reductions in the PNB group. The PNBs provide excellent analgesia and longer duration than SA and both PIOC and secondary outcomes revealed a clear benefit with the PNBs. However, the post-block pain levels and opioid need in the PNB group also indicate a considerable rebound pain when the PNBs subside.

Conclusions: PNB anaesthesia is efficient for ankle fracture surgery and provides superior postoperative pain control compared with SA. However, the rebound pain following cessation of the blocks warrants attention in clinical practice.

07 / Peripheral nerve block anaesthesia is superior to spinal anaesthesia regarding postoperative pain control in primary ankle fracture surgery: results from the randomised “AnAnkle Trial”