This randomized, double-blind clinical trial aims to compare the effectiveness of the Deep Iliacus Plane Block (DIPB) and the Suprainguinal Fascia Iliaca Block (SIFIB) for postoperative pain control in patients undergoing primary total hip arthroplasty. Effective analgesia after hip surgery is essential for early mobilization, reduction of complications, and improved recovery outcomes.

Seventy patients scheduled for elective hip arthroplasty under spinal anesthesia will be randomly assigned to receive either DIPB or SIFIB at the end of surgery. Postoperative pain scores, opioid consumption, motor block, and block-related complications will be evaluated over a 48-hour period.

The study aims to determine whether DIPB provides superior or comparable analgesia with reduced motor blockade compared to SIFIB, thereby contributing to safer and more comprehensive postoperative pain management in hip surgery patients.

Hip arthroplasty is frequently associated with moderate to severe postoperative pain, which may negatively affect early mobilization, rehabilitation, and overall recovery. Adequate postoperative analgesia is therefore essential to reduce complications such as pulmonary morbidity, thromboembolism, delirium, and prolonged hospital stay.

The hip joint is innervated by both deep articular branches (femoral, obturator, and accessory obturator nerves) and superficial cutaneous branches (femoral nerve and lateral femoral cutaneous nerve). An optimal regional analgesic technique should provide effective blockade of both components. However, currently used techniques often fail to adequately block deep capsular innervation while preserving motor function.

The suprainguinal fascia iliaca block (SIFIB) is widely used in hip surgery and effectively blocks the femoral nerve and lateral femoral cutaneous nerve, providing reliable cutaneous analgesia. Nevertheless, insufficient spread to obturator and accessory obturator nerves may result in inadequate deep joint analgesia. Attempts to overcome this limitation using high-volume injections may increase the risk of quadriceps weakness and motor blockade.

The Deep Iliacus Plane Block (DIPB) is a recently described fascial plane block targeting the deep surface of the iliacus muscle at the level of the anterior inferior iliac spine. Anatomical and preliminary clinical findings suggest that DIPB allows spread of local anesthetic to femoral, lateral femoral cutaneous, and pericapsular articular branches of the hip joint, potentially providing both capsular and cutaneous analgesia with reduced motor impairment. DIPB has therefore been proposed as a hybrid technique combining advantages of existing regional blocks.

This prospective, randomized, controlled, double-blind clinical trial will be conducted at Sivas Numune Hospital. Seventy patients (ASA I-III) scheduled for elective primary total hip arthroplasty under spinal anesthesia will be enrolled and randomly assigned into two groups: the SIFIB group (n=35) and the DIPB group (n=35). Randomization will be performed using a computer-generated sequence.

All patients will receive standardized spinal anesthesia and multimodal systemic analgesia. At the end of surgery, ultrasound-guided SIFIB or DIPB will be performed by an experienced anesthesiologist using 0.25% bupivacaine (30-40 mL, weight-adjusted). Postoperative pain will be assessed using the Numeric Rating Scale (NRS) at rest and during movement at predetermined intervals up to 48 hours. Rescue analgesia with intravenous tramadol will be administered when NRS ≥4, and total opioid consumption will be recorded. Motor blockade will be evaluated using the modified Bromage scale. Block-related complications and adverse events will also be documented.

The primary aim of the study is to compare postoperative pain scores and opioid consumption between DIPB and SIFIB. Secondary outcomes include motor blockade, block-related complications, and overall analgesic effectiveness. The findings of this study are expected to clarify whether DIPB provides superior or comparable analgesia with less motor impairment, thereby contributing to safer and more comprehensive postoperative pain management in hip arthroplasty patients.

Inclusion Criteria:

• Patients aged ≥18 years
• ASA physical status I-III
• Scheduled for elective primary total hip arthroplasty under spinal anesthesia
• Ability to understand the study procedures and provide informed consent

Exclusion Criteria:

• Coagulation disorders or anticoagulant therapy contraindicating regional anesthesia
• Infection at the block application site
• Hemodynamic instability
• Known allergy to local anesthetics
• Pre-existing significant neurological or motor deficits in the lower extremities
• Cognitive impairment preventing pain assessment
• Refusal to participate or inability to provide informed consent