PENG Block Versus Intrathecal Morphine for Early Postoperative Recovery After Total Hip Arthroplasty

Total hip arthroplasty is a major orthopedic procedure associated with substantial postoperative pain, which may interfere with early mobilization, functional recovery, and overall quality of recovery. Effective multimodal analgesia is therefore an important component of perioperative care. Intrathecal morphine provides prolonged postoperative analgesia but may be associated with opioid-related adverse effects, including nausea and vomiting, pruritus, urinary retention, and respiratory depression. The pericapsular nerve group (PENG) block is a regional analgesic technique targeting the sensory innervation of the anterior hip capsule and has been proposed as a potentially motor-sparing approach to analgesia after hip surgery.

This is a prospective, randomized, controlled, assessor-blinded, single-center clinical trial comparing PENG block with intrathecal morphine in patients undergoing elective primary unilateral total hip arthroplasty under spinal anesthesia. A total of 90 participants will be enrolled and randomly assigned in a 1:1 ratio using computer-generated randomization. Allocation will be concealed using sealed opaque envelopes. Because of the nature of the interventions, the anesthesiologist performing the procedures cannot be blinded. Investigators performing postoperative assessments and the investigator performing the statistical analysis will be blinded to group allocation.

Perioperative anesthesia and analgesia will be standardized for both groups. All participants will undergo routine standard monitoring and receive spinal anesthesia with 10-15 mg of 0.5% hyperbaric bupivacaine. All participants will also receive 8 mg of intravenous dexamethasone intraoperatively.

Participants assigned to the PENG group will receive an ultrasound-guided PENG block with a total injectate volume of 20 mL. The intended PENG block dose will be 100 mg of bupivacaine (20 mL of 0.5% bupivacaine). For safety, the bupivacaine dose will be reduced when necessary to ensure that the total bupivacaine dose, including the dose administered for spinal anesthesia, does not exceed 2 mg/kg. When dose reduction is required, an appropriate volume of 0.5% bupivacaine will be combined with 0.9% saline to maintain a total PENG block injectate volume of 20 mL.

Participants assigned to the intrathecal morphine group will receive 100 micrograms of preservative-free intrathecal morphine during spinal anesthesia. Apart from the randomized analgesic intervention, perioperative management will be standardized between the two groups.

Postoperative multimodal analgesia will be standardized for all participants. Paracetamol 1 g will be administered intravenously or orally every 8 hours, and dexketoprofen trometamol 50 mg will be administered intravenously every 12 hours. Rescue analgesia will consist of intravenous tramadol 1 mg/kg when the Numeric Rating Scale (NRS) pain score is 4 or higher. Postoperative opioid consumption will be recorded and converted to morphine-equivalent doses.

The study is designed to compare the effects of these two analgesic strategies on early patient-centered recovery after total hip arthroplasty while also evaluating their analgesic, functional, and adverse-effect profiles. Recovery status will be assessed before surgery to account for individual differences in baseline recovery-related health status, and postoperative assessments will be performed by investigators blinded to treatment allocation.

Inclusion criteria

• Age 18-85 years
• American Society of Anesthesiologists (ASA) physical status I-III
• Scheduled for elective primary unilateral total hip arthroplasty
• Planned spinal anesthesia
• Ability to understand and complete the Quality of Recovery-15 (QoR-15) questionnaire and Numeric Rating Scale (NRS) pain assessments
• Provision of written informed consent

Exclusion criteria

• Contraindication to spinal anesthesia or PENG block
• Known allergy or hypersensitivity to local anesthetics or morphine
• Coagulation disorder
• Therapeutic anticoagulant use
• Infection at the planned injection site
• Chronic opioid use
• History of substance abuse
• Severe cognitive impairment that prevents reliable completion of study assessments
• Advanced hepatic or renal failure
• ASA physical status IV or higher
• Revision total hip arthroplasty
• Surgery for pathological fracture or tumor
• Pregnancy
• Requirement for general anesthesia
• Refusal to participate in the study