Posterior spinal fusion for scoliosis surgery may lead to severe postoperative pain which requires significant opioid use for adequate perioperative analgesia. This postoperative pain extends the time of recovery, and thus, safe, and efficient methods for perioperative analgesia are crucial and advantageous for early recovery and ambulation.

Traditional opioid-based analgesia techniques are characterized by well-known complications such as vomiting, nausea, sedation, and pruritus. Although regional anesthesia is an essential part of multimodal analgesia, available options are limited. Recently, an ultrasound (US)-guided erector spinae plane block (ESPB) method that anesthetizes ventral and dorsal rami of spinal nerves was introduced for the treatment of both postoperative and neuropathic pain.

Due to the arousing interest of several physicians, ESPB application is reported to be effective in the breast, weight loss, and lumbosacral spine surgeries as it reduces the need for analgesic drugs. The main advantages of the ESPB are technical simplicity, minimal risk for the spinal cord, and fewer complications.

The ESP block is a fascial plane block that aims to inject a local anesthetic mixture within a plane beneath the erector spinae muscle at the transverse process of the vertebra. ESP block can provide effective postoperative analgesia for upper abdominal surgery when performed at the thoracic vertebra 7-8 level. ESP block acts probably by diffusion of local anaesthetic into the paravertebral space. The advantages of ESP block are its ease of performance and safety. Owing to its superficial location, away from vessels and nerves, the complications associated with paravertebral block can be avoided.

The effect of magnesium was first recognized for the treatment of arrhythmia and preeclampsia, and its effect on anaesthesia and analgesia has recently been recognized. Magnesium sulphate has also been used as an adjunct to anaesthesia in recent years. It is also an effective analgesic agent for perioperative pain. Research has also reported that the intraoperative use of magnesium is characterized by a reduced use of anesthetics and muscle relaxants. Furthermore, opioid use, postoperative nausea and vomiting, hypertension, and shivering have met a decreased trend with the use of magnesium sulphate.

Magnesium sulfate (MgSO4) may be helpful as an analgesic adjuvant in regional anesthesia because it improves and prolongs the analgesic effect of local anesthetics; moreover, MgSO4 alone modulates the transmission of nociceptive stimuli and pain perception by blocking the N-methyl-D-aspartate (NMDA) receptor.

Dexmedetomidine (DE) is a potent α2 adrenoreceptor agonist and it is highly selective for α2 adrenoreceptor seven times more than clonidine. Many studies documented a prolonged duration and rapid onset of sensory block with the perineural injection of DE. Dexmedetomidine has been introduced as an adjuvant to local anaesthetics in both neuroaxial and peripheral nerve blocks. perineural dexmedetomidine has shown to prolong the duration of postoperative analgesia in addition to reducing the opioid consumption.

Inclusion Criteria:

• patients who will be scheduled for indicated open corrective scoliosis surgery in the prone position.
• physical status American Society of Anesthesiologists (ASA) I or II.

Exclusion Criteria:

• patients refuse to participate.

  . -ASA physical status >II.

• patients who have contraindications to regional analgesic procedures as infection at injection site

• patients who have major illnesses (e.g., cardiac, respiratory, renal, hepatic or neurological).

• allergy to the study drugs

• a known history of recent opioid use

• obesity (body mass index (BMI) > 35 kg/m2)

• those who underwent revision surgery

• coagulopathy

• drug or alcohol abuse

• epilepsy, or a psychiatric illness that would interfere with the perception and assessment of pain.