Posterior spinal instrumentation can cause significant postoperative pain due to extensive muscle dissection, manipulation of bone tissue, and implant placement. Providing optimal analgesia in the postoperative period is important for patients' functional recovery and early mobilization. Inadequate control of postoperative pain may delay recovery, increase the risk of opioid dependence, and lead to respiratory complications.

Although opioid analgesics are effective in reducing pain during the postoperative period, they are associated with side effects such as nausea, vomiting, respiratory depression, and the risk of dependence. Therefore, the use of non-opioid analgesic approaches is important for patient safety and comfort. For these reasons, regional analgesia techniques such as the modified thoracolumbar interfascial plane (TLIP) block and the erector spinae plane (ESP) block have recently become increasingly popular for postoperative pain control. The quadro-iliac plane block is a novel technique that targets the attachment area of the posterior surface of the quadratus lumborum muscle on the inner surface of the iliac crest. In this block, the spread of local anesthetic along the fascial planes surrounding the quadratus lumborum muscle may provide an anatomical mechanism contributing to analgesia of the lumbosacral, paraspinal, lower abdominal, and gluteal regions. However, as the quadro-iliac plane block is a new technique, there are not yet sufficient studies on this topic in the literature.

The primary objective of our study is to evaluate the effect of ultrasound-guided quadro-iliac plane block (QIPB) on postoperative opioid consumption after posterior spinal instrumentation. The secondary objectives are to compare opioid-related side effects, such as nausea, vomiting, and respiratory depression, as well as postoperative NRS (Numeric Rating Scale) pain scores between the groups.

Inclusion Criteria: Posterior spinal instrumentation patients -

Exclusion Criteria: Contraindications for regional analgesia, allergies for local anesthetics

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Individual participant data (IPD) will not be shared because there is no plan for public data sharing for this study.