Spinal surgery is associated with severe pain in the immediate postoperative period. In a recent study evaluating pain intensity on the first day after surgery in a large range of surgical procedures, among the six most painful surgeries, three were major spinal procedures. Spinal surgery causes an accumulation of several types of pain. Incisional pain results from activation of peripheral nociceptors. Musculoskeletal pain arises from damage to structures, such as bone, ligaments, muscles, intervertebral disks, and zygapophyseal joints. In addition, neuropathic pain arises from compression and damage to nerve roots exiting the spinal canal and sometimes damage to the spinal cord itself.

Postoperative pain management requires multimodal analgesia, combining drugs and injection of a local anesthetic (LA) in order to reduce opioid consumption after surgery. Among regional anesthesia (RA) techniques, the thoraco-lumbar interfascial plane block (TLIP) was considered. It offers an effective and safe analgesia during the first 24h after herniated lumbar disc surgery. Ultrasound-guided TLIP block involves injection of LAs between longissimus and multifidus muscles (spinal lombar muscles). This injection allows to block the dorsal rami of spinal nerves innervating the paravertebral muscles and the vertebrae.

The objective of this study is to evaluate the interest of TLIP block to improve the postoperative analgesia in patients undergoing lumbar spinal fusion surgery.

This is a multicenter, randomized, double-blind (participant and care provider assessing outcomes), parallel-group controlled, trial assessing the interest of the association of TLIP block to general anesthesia for postoperative analgesia management in patients undergoing posterior lumbar spinal fusion.

This study compares two groups:

"Control" group: standard general anesthesia. "TLIP" group: standard general anesthesia + TLIP block with an injection of 40 ml of ropivacaine 0.25% (2 injections of 20 ml on each side) between multifidus and longissimus muscles.

• General anesthesia

General anesthesia will be standardized in the two groups:

• Induction with propofol 2-3 mg/kg, sufentanyl 0.2-0.3 µg/kg and ketamine 0.3 mg/kg

• Intubation facilitated according centre's protocol and ventilation performed with 50% oxygen and 50% air in order to maintain normocapnia and normoxia.

• Anesthesia maintained according to the centre's usual care.

• Prevention of postoperative nausea and vomiting (NVPO) according centre's protocol.

  • TLIP block technique ("TLIP" group only) The regional anesthesia procedure will be performed under general anesthesia and will be guided by ultrasound with high-frequency linear probe, patient in prone position or genupectoral (knee-chest) position. The probe will be positioned in order to have an axial view of lumbar vertebrae. The 3rd lumbar vertebra (L3), the 4th lumbar vertebra (L4) and the 5th lumbar vertebra (L5) will be identified after initial identification of the sacrum. A needle will be inserted in plane (IP) and advanced to reach the interspace between the multifidus and the longissimus muscles on the tip of the articular process. For each patient, the block will be performed bilaterally by injecting of 20 ml of Ropivacaine 0.25% on each side. Before each procedure, a skin disinfection will be carried out using an alcoholic iodine solution.

Patients will not receive any LA by intravenous injection or infiltration.

Inclusion Criteria:

• ≥ 18 years old,
• Undergoing posterior lumbar spinal one-level or two-level fusion surgery (L3-L4, L4-L5 and/or L5-S1),
• Having signed a written informed consent form,
• Affiliation to the social security system.

Exclusion Criteria:

• Contraindication for regional anesthesia (allergy to local anesthetics, neuropathic disease, infection at the puncture site, coagulation disorder, refusal of the technique,…)
• Contraindication to nonsteroidal anti-inflammatory drugs,
• Patient who have already had a spinal surgery,
• Patient with chronic pain syndrome (use > 3 months of morphine, opioid analgesics of class 3, pregabalin or gabapentin) or fibromyalgia,
• A mental or linguistic inability to understand the study,
• Patient under protection of the adults (guardianship, curators or safeguard of justice),
• Pregnant or or breastfeeding women.

To minimize assessment bias, patients and evaluators (nurse and physiotherapist) will be unaware of the intervention group. Only the investigator, who will include the patient and will realize the procedure, will know the arm of randomization.