The aim of this clinical trial is to evaluate the efficacy of adding magnesium sulfate to bupivacaine in ultrasound-guided transmuscular quadratus lumborum block for postoperative analgesia in adult patients underdoing hip arthroplasty. The main questions it aims to answer are:

• Does Magnesium sulphate lower Pain score (VAS) postoperatively.
• Does Magnesium sulphate lowerTotal opioid consumption postoperatively. and What side effects do participants have when taking Magnesium sulphate? Researchers will compare Magnesium sulphate to a placebo (a look-alike substance that contains no drug) to see if Magnesium sulphate works to lower pain score.

Participants will:

• Take with have ultrasound-guided transmuscular quadratus lumborum block after surgery using bupivacaine with Magnesium sulphate or with placebo
• Followed up 48 hours postoperatively to monitor pain score or any reported side effect.

The quadratus lumborum block (QLB) is an abdominal wall fascial block plane block described for providing perioperative analgesia for abdominal, hip and lower limb surgeries . Opioid-sparing analgesic treatments for hip arthroplasty such as lumbar plexus and femoral nerve blocks, are effective but they carry a high risk of undesirable lower limb motor or muscle weakness. Fascia iliaca block, on the other hand, does not consistently provide adequate pain relief. Quadratus lumborum (QL) block is a relatively new truncal regional block technique that provides effective pain control after upper and lower abdominal surgeries. ersalis fascia laterally. The anterior QL block was also classified as transmuscular approach (in between QL and PM muscles) in earlier studies . Local anesthetic injected between the QL muscle and anterior layer of the thoracolumbar fascia can potentially spread to the thoracic paravertebral (PVB) space.

Magnesium plays an important role in the physiological function of the human body. A large number of studies have reported the safetyand effectiveness of adding magnesium sulfate in various regional anesthesia techniques . Therefore, this prospective randomized controlled study to compare the analgesic efficacy of combining magnesium sulfate with bupivacaine in QLB.

Inclusion Criteria:

• Age ≥ 18 years.
• American Society of Anesthesiology (ASA) class I-III
• Undergoing hip arthroplasty .

Exclusion Criteria:

• Patient refusal.
• Body mass index (BMI) > 40 Kg/m2.
• Allergy to local anesthetics or magnesium sulphate.
• coexisting coagulopathy.
• Local infection at puncture site.
• Severe renal impairment ( eGFR < 30 ml/min)