Introduction
Anterior cruciate ligament (ACL) reconstruction can cause considerable postoperative discomfort. After ACL reconstruction, femoral nerve blockade was reported to provide analgesia effect[1-3]. However, many patients with femoral nerve blockade still complained of knee pain after ACL reconstruction. The articular branches of the tibial nerve provide sensory afferents to the posterior knee, while the articular branches of the common peroneal nerves contribute sensory afferents to the anterior knee. Therefore, even in the case of a femoral nerve block (FNB), blockade of the tibial and common peroneal nerves through a sciatic nerve block could reduce the severity of pain in both anterior and posterior knees[4, 5].
The analgesic benefits of adding sciatic nerve blockade to femoral nerve blockade to knee surgeries is controversial [6-9]. Retrospective data showed that compared with FNB alone, combined femoral-sciatic nerve blockade (CFSNB) performed before complex knee surgery may improve analgesia and decreases opioid consumption[10, 11]. Several recent randomized controlled studies of total knee arthroplasty have shown that CFSNB provides superior pain control[12, 13], and a recent randomized controlled trial by Abdallah et al.[4]demonstrated that CFSNB specifically reduces posterior knee pain after total knee arthroplasty. Currently, limited data, with only 1 randomized study, on the analgesic role of sciatic blockade in ACL reconstruction can be found[14].
Ropivacaine, a long-acting local anesthetic, has also been used for administering sciatic nerve blockade. Ropivacaine offers two advantages over bupivacaine: in low doses it provides similar sensory blockade to bupivacaine with less motor block, and its systemic toxicity will be less[15], which can provide better conditions for knee joint functional reconstruction after ACL surgery.
This study aims to evaluate the median effective analgesic concentration (MEAC, EC50= effective concentration in 50% of patients) of ropivacaine required for successful postoperatively analgesia with sciatic blockade.