Difference in Occurrence of Rebound Pain in Patients Undergoing Surgery Under Popliteal Block or Ankle Block

This is a monocentric, comparative prospective randomized controlled trial. Patients will be randomised into 2 groups and will receive either a sciatic popliteal nerve block or an ankle block (single dose locoregional block injection before the surgery) for elective forefoot surgery in addition to general anaesthesia. The study will: * Compare the occurrence of rebound pain and its recovery between a peripheral nerve block of the popliteal sciatic nerve and an ankle block in patients undergoing lower limb (forefoot) bone surgery under general anaesthesia combined with a PNB achieved in preoperative single injection. * To identify the role of the type of nerve fibers anesthetized and the local inflammatory process in rebound pain development. * Assessing the amount of the local sympathetic block induced by the locoregional anesthesia could be used a non-invasive predictive indicator of the occurrence of rebound pain depending on the nerve fibers involved (purely sensitive versus sensitive and motor).

The use of peripheral nerve block (PNB) via administered local anesthetics may exacerbate the acute inflammatory process induced by surgical trauma. This exacerbation of local inflammation is a likely cause of the hyperalgesia phenomena reported upon PNB removal in the first 24 hours postoperatively. This local hyperalgesia is responsible for intense pain that is difficult to control with conventional analgesics. It is also called "rebound pain (RP)". Local anesthetics (e.g. bupivacaine) used in PNB can stimulate the expression of genes involved in inflammation and thus induce hyperalgesia following the local release of pro-inflammatory mediators (prostaglandins (prostaglandins E2 and interleukin 1β). One mechanism of action involved would be that PNB-induced increased tissue oxygen saturation ( and caused by sympathetic block associated with sensory and motor blocks). Sympathetic block and local vasodilation would promote immune cell migration at the incision site. The primary objective will be to identify a difference in the occurrence of RP between a popliteal sciatic nerve PNB (sensory-motor block) and an ankle PNB (pure sensory block). Sensory block is currently becoming more popular because it allows for faster mobilization/functional recovery. The secondary objective will be to identify the involvement of local sympathetic block (local vasoplegia) in the RP phenomenon. The intensity of local sympathetic block would be an indirect, non-invasive indicator of a possible modulation of local inflammation (repeated non-invasive measurement of temperature and tissue oxygen perfusion changes) Method: Randomized patients will receive either a popliteal sciatic nerve block or an ankle block. A local anesthetic solution of 30ml of ROPIVACAINE 0. 5%,(4mg/kg maximum) will be used for popliteal sciatic nerve block (popliteal sciatic, saphenous) and a maximum solution of 15ml of ROPIVACAINE 0. 5%( 4mg/kg maximum) for ankle block (saphenous, superficial peroneal, deep peroneal and tibial nerves). Each nerve will be treated separately, anesthetized by real-time ultrasound guidance. Both groups will also receive standardized general anesthesia (induction of anesthesia by intravenous injection of Propofol, Sufentanil with maintenance of inhalation anesthesia with Sevoflurane). All patients will benefit from a standardized postoperative analgesia. The reactivation to stress of the patients will be measured perioperatively by a non-invasive monitoring of the sympathetic-parasympathetic balance (ANI, antinociception index; Metrodoloris®) based on the variability of the heart rate. The evaluation of the modulation of the local inflammation will be objectivated in an indirect way by the repeated non-invasive measurement of the modifications of temperature and tissue perfusion in oxygen (sympathetic block) at the level of the tissues close to the surgical site. The neuropathic or catastrophic nature of the pain as well as the preoperative anxiety will be collected by means of specific questionnaires (APAIS /Catastrophisation /CSI..). Patients will be discharged from the hospital on day 1 or day 2 postoperatively with a standardized analgesic treatment. Under the close coordination of the investigating physician, the monitoring of the patients' postoperative pain will be done from the PACU with the participation of the recovery room nursing team, but also by the Pops pain team during their brief period of hospitalization on the floor. Patients will be discharged from the hospital on postoperative day 1 or 2 with standardized analgesic treatment. On their return home, the patients will be followed up by telephone calls (investigating physician), according to the study protocol established at D4 D30 and at 3 months postoperatively.