Pericapsular Nerve Group Block Versus Intrathecal Morphine for Pain After Hip Surgery

Postoperative pain after total hip arthroplasty is frequently severe and limits early mobilization. Systemic opioids remain widely used but are associated with respiratory depression, sedation, urinary retention, constipation and postoperative nausea and vomiting. Intrathecal morphine added to spinal anesthesia provides prolonged analgesia but shares these opioid-related adverse effects. The pericapsular nerve group (PENG) block, first described by Giron-Arango and colleagues, targets the articular branches of the femoral, obturator and accessory obturator nerves that supply the anterior hip capsule by injecting local anesthetic into the fascial plane between the psoas tendon anteriorly and the pubic ramus posteriorly. Because the block spares motor fibers, it may provide effective analgesia without impairing early mobilization. Direct comparisons of the PENG block with intrathecal morphine in hip arthroplasty are limited.

This will be a prospective, randomized, controlled, open-label, single-center study conducted at Selcuk University Faculty of Medicine Hospital. Local ethics committee approval has been obtained, and written informed consent will be obtained from every participant before enrollment. Sixty-four patients aged 18 to 65 years with an American Society of Anesthesiologists physical status of I to III scheduled for unilateral hip surgery under spinal anesthesia will be allocated to one of two equal groups of 32 patients using a sealed-envelope randomization method, so that the allocation sequence is concealed from the investigator enrolling the patient. Owing to the nature of the interventions, participants, treating anesthesiologists and outcome assessors will not be blinded to group allocation. Before surgery, demographic data (age, height, weight, body mass index), comorbidities, physical status classification, type of surgery and fracture location will be recorded.

Peripheral venous access will be obtained with an 18 or 20 gauge cannula. Standard non-invasive monitoring of heart rate, systolic, diastolic and mean arterial pressures and peripheral oxygen saturation will be applied and recorded at predefined intervals from the intraoperative period until the 48th postoperative hour, with intraoperative measurements every 5 minutes. Spinal anesthesia will be performed in the sitting position under aseptic conditions at the L3-L4 or L4-L5 interspace using a 25 to 27 gauge, 90 mm Quincke spinal needle, after confirming free and clear cerebrospinal fluid flow.

Patients in Group 1 will receive 10 mg of hyperbaric bupivacaine 0.5% together with 100 micrograms of morphine hydrochloride into the intrathecal space. Patients in Group 2 will receive 10 mg of hyperbaric bupivacaine 0.5% intrathecally without morphine, followed by an ultrasound-guided PENG block on the operative side. For the block, patients will be placed supine and the area will be prepared with aseptic technique. A low-frequency (2 to 5 MHz) curvilinear ultrasound probe will be placed over the anterior inferior iliac spine and rotated approximately 45 degrees counterclockwise to align with the iliopubic eminence, visualizing the anterior inferior iliac spine, iliopubic eminence, iliopsoas tendon and femoral artery. A 21 gauge, 80 to 100 mm insulated, echogenic short-bevel needle will be advanced in-plane from lateral to medial until the tip lies in the plane between the iliopubic eminence and the iliopsoas tendon. After negative aspiration for blood and sonographic confirmation of needle position, 20 mL of 0.5% bupivacaine will be injected. Adequacy of the neuraxial block will be confirmed before surgery begins.

Postoperative analgesia will be provided with intravenous patient-controlled analgesia using morphine, programmed to deliver a 1 mg bolus dose with a 10-minute lockout interval and no background infusion. Intravenous paracetamol 1000 mg will be administered on demand as rescue analgesia, without exceeding a total daily dose of 4000 mg. Pain intensity at rest and on movement will be assessed with a Visual Analog Scale at the 1st, 3rd, 6th, 12th, 24th and 48th postoperative hours. Analgesic consumption, patient-controlled analgesia demand and delivery ratios, time to first rescue analgesic request, the incidence of nausea and vomiting, and block-related complications such as arterial puncture, hematoma, paresthesia during injection and signs of local anesthetic systemic toxicity will be recorded during the 0 to 1, 1 to 3, 3 to 6, 6 to 12, 12 to 24 and 24 to 48 hour intervals. Total analgesic consumption over 48 hours will also be recorded. Before every regional block, the expiry date and availability of 20% lipid emulsion will be checked, and the anesthesia machine, circuit leak test, defibrillator and emergency drug trolley will be verified.

The primary outcome will be cumulative morphine consumption during the first 24 postoperative hours. Secondary outcomes will include cumulative morphine consumption over 48 hours, pain scores at rest and on movement at each assessment point, time to first patient-controlled analgesia demand, total paracetamol consumption, incidence of postoperative nausea and vomiting and block-related complications.

Inclusion criteria

• Age 18 to 65 years
• American Society of Anesthesiologists physical status I, II or III
• Scheduled for unilateral hip surgery under spinal anesthesia, including hip fracture surgery and hip replacement surgery
• Able to understand and use the Visual Analog Scale and the patient-controlled analgesia device
• Written informed consent

Exclusion criteria

• Refusal to participate
• Known allergy or hypersensitivity to local anesthetics, morphine or paracetamol
• Any contraindication to spinal anesthesia, including coagulopathy, ongoing anticoagulant therapy, thrombocytopenia, infection at the puncture site, or raised intracranial pressure
• Local infection or previous surgery at the pericapsular nerve group block site
• Chronic opioid use or history of substance use disorder
• Chronic pain requiring regular analgesic treatment before surgery
• Cognitive impairment, psychiatric disorder or communication difficulty preventing use of the pain scales
• Pre-existing neurological deficit in the operative lower limb
• Body mass index above 40 kg/m²
• Pregnancy or breastfeeding