This prospective randomized interventional study aims to compare the effects of two peripheral nerve blocks, the periencapsular nerve block (PENG) and iliopsoas block (IPB), on analgesia and motor function after hip surgery.

The main questions it aims to answer are the effectivity of postoperative pain management the preservation of motor movement.

Participants will receive standardized general anesthesia and postoperative PENG or IPB in either Group.

Researchers will compare the total amount of rescue analgesia and numeric rating scale with accompanying evaluating motor function at the same time intervals within 24 hour.

Providing postoperative analgesia after hip joint surgery is essential in ensuring patient recovery and rehabilitation. The blocks that can be used as alternatives in these surgeries have diversified in recent years, and their superiority over each other is being investigated. The aim is to reach a method that provides more effective analgesia, is more practical and does not cause muscle weakness. For this reason, PENG, which has no previous comparative randomized studies, and iliopsoas blocks, which have more recent clinical studies, need to be examined.

All patients received standard general anaesthesia under standard monitoring along with the bispectral index (Medtronic) and nociception level index (NOL, MedaSense). Intubation was performed by administering intravenous (IV) 0,03 mg/kg midazolam 2 mg/kg, propofol (Lipuro, Braun), 2 mcg/kg fentanyl (Talinat, VEM), 0,6 mg /kg rocuronium (Esmeron, Alessandroorsini) followed by 1 MAC sevoflurane (Sevorane, Abbott) in an air-oxygen mixture for maintenance of anaesthesia. All participants received 20 mg tenoxicam and 1 gr paracetamol along with 8 mg dexamethasone before surgical incision as part of multimodal analgesia. All blocks were performed before surgical incision following the induction of general anaesthesia by a single experienced regional anaesthesiologist (B.C.) under ultrasound guidance (Esaote MyLab ™ Seven). Both groups received lateral femoral cutaneous nerve (LFCN) block by using a high-frequency probe to visualize LFCN between sartorius and tensor of fascia lata in line with the inguinal ligament, and 5 ml 0,375 bupivacaine was injected. After applying PENG or IP block in accordance with randomization, the surgery was set to begin after at least 15 minutes of block procedures. The intraoperative analgesic need was supplied by remifentanil infusion (2 mcg/mL) and determined by NOL index level, and a value over 25 for more than one minute was accepted as pain to be treated by increased remifentanil infusion doses. All patients received 8 mg of ondansetron and suggamadex (2 mg/kg) for decurarization before arousal under BIS guidance. From the beginning of acclaimed arousal till the 24th hour, rescue analgesia as tramadol 100 mg (maximum daily dose 400 mg) is applied if NOL is over 25 at the recovery room or NRS over 4 or with the patient's request. The routine analgesia regimen was 1 gram iv paracetamol 6th hourly postoperatively at the orthopaedic ward.

PENG block procedure Immediately after the insurance of general anaesthesia and LFCN block application, PENG block was performed by the primary investigator (B.C) following proper skin disinfection with the patient in the supine position. Under the guidance of a low-frequency curvilinear ultrasound probe, the iliopubic eminence and the psoas tendon were identified, and local anaesthetic (20 ml 0,375% bupivacaine) was injected between the periosteum and psoas tendon following negative aspiration.

IPB procedure After ensuring aseptic conditions, the low-frequency curvilinear ultrasound probe was transversely placed caudad to the anterior superior iliac spine, then rotated anticlockwise and slid along the inguinal ligament to detect the head of the femur, as described by Nielsen et al. The primary investigator (B.C.) directed the needle tip into the iliopsoas plane between the iliopsoas muscle and iliofemoral ligament through an in-plane approach, and 10 ml of 0,375% bupivacaine was injected.

Inclusion Criteria:

• Patients eligible for inclusion in this study were those aged 18 to 90 years who had undergone total hip arthroplasty surgery and had an American Society of Anesthesiologists (ASA) Physical Status classification of I to III and body mass index (BMI) between 18 and 30 kg/m2.

Exclusion Criteria:

• Patients were excluded if they had one of the following criteria: refusal to participate, a history of neurological deficits or neuropathy affecting the lower extremity, infection at the site of block application, coagulopathy; allergy to local anaesthetics, epilepsy or treatment with antipsychotics; abuse of alcohol or drugs; previous surgery distorting the anatomy of the inguinal or supra inguinal areas; severe organ dysfunction ( kidney, liver and other); uncooperative patients who fail to respond reliably to verbal pain assessment.

The participants under general anaesthesia and the orthopaedic surgeon responsible for the study will be blinded to the study groups and the specific block procedures. This surgeon will serve as the sole evaluator of postoperative outcomes. Intraoperative results will be recorded by the anaesthesia technician, who is present in the operating room and unaware of the block procedures. Moreover, the data analysis will be conducted before the data are unblinded.