Introduction : Spine surgery is responsible for intense postoperative pain that can be treated by an analgesia multimodal approach (IV analgesic infusion and local anesthesia). Continuous wound infiltration is an efficient and simple technique with few adverse effects yet very few studies have investigated its potential use in spine surgery. Our randomised, controlled, double-blinded trial aims to evaluate efficacy of continuous wound infiltration after major spine surgery.

Methods : After written consent is obtained, the surgeon inserts, at the end of surgery, a multiholes catheter under muscular layers. Patients are randomised in two groups : The "treated group" receives ropivacaine 0.2% infusion (bolus of 10 milliliters (mL) followed by 8 mL/h continuous infusion during 48 hours) and the "control group" receives saline solution (0.9%). In addition, all patients receive patient-controlled intra-venous morphine analgesia. The investigators hypothesize that the "treated group" will consume morphine less than the "control group".

Inclusion Criteria:

• adults
• > 18 years
• Physical status score I, II or III (American Society of Anesthesiologists)
• lumbar or thoracic spine surgery with arthrodesis through posterior only approach
• signed informed consent
• beneficiary of social security

Exclusion Criteria:

• vulnerable persons according to law
• scoliosis surgery
• local anesthetic allergia
• contraindication to ketamine, acetaminophene, nefopam, non steroidal anti inflammatory, ropivacaine, morphine, droperidol
• long term anti platelet aggregants
• inability to comply to protocol requirements
• psychiatric disorders or cognitive disabilities
• chronic pain or long term opioids consumption
• diabetes
• obesity (BMI > 30)
• pregnancy or lactation