Pericapsular Nerve Block Versus Intrathecal Morphine for Analgesia After Primary Hip Arthroplasty

Spinal anesthesia will be performed as follows: patient will be placed in the lateral decubitus position on the non-operative side. Using sterile gloves red chlorhexidine 2% alcohol solution will be used for skin disinfection. The site will be secured with a sterile drape, and the L4-L5 lumbar space identified. After subcutaneous local infiltration with 1% lidocaine, a 25G Whitacre pencil point spinal needle will be used to access the intrathecal space with free flow of cerebrospinal fluid as confirmation. A mixture of 12.5 mg of isobaric bupivacaine and 100 mcg of morphine will be administered intrathecally. After the spinal anesthesia, the intrathecal morphine (ITM) group will receive a sham PENG block with the block needle inserted subcutaneously, the anesthesiologist using the same verbal block confirmation commands "aspirate, inject" but the needle withdrawn without injection. This will create the appearance of an identical cutaneous injection site to ensure patient blinding.

Spinal anesthesia with intrathecal injection of 12.5 mg of isobaric bupivacaine will be performed, followed by a PENG block. After skin disinfection, a low frequency curvilinear ultrasound probe (2-5 MHz 8870, BK ultrasound, Peabody Massachussets, US) with a sterile covering will be used to identify the anterior inferior iliac spine, the pubic eminence and the psoas tendon with its fascial plane. A 22 gauge 10cm block needle (Sonoplex® Pajunk, Geisingen, DE), will be used to enter the fascial plane and 20ml of 0.75% Ropivacain (Fresenius Kabi, Krienz CH) will be injected.