Postoperative pain following total knee arthroplasty (TKA) is a significant clinical problem that delays early mobilization, reduces patient satisfaction, and increases analgesic requirements. The adductor canal block (ACB), which aims to provide analgesia while preserving motor function, is widely used in postoperative pain management after TKA. However, clinical and anatomical studies have demonstrated that ACB is effective only in the anteromedial sensory innervation of the knee and does not adequately block pain originating from the posterior knee capsule. This limitation reduces analgesic effectiveness, particularly in patients with a prominent posterior pain component.

The sciatic nerve block has long been considered the gold standard for managing posterior knee pain. However, due to disadvantages such as motor weakness and delayed rehabilitation, current pain management protocols increasingly favor motor-sparing and complementary approaches such as the Biceps Femoris Short Head (BiFeS) block and the Interspace Between the Popliteal Artery and the Capsule of the posterior Knee (IPACK) block for posterior knee analgesia.

In light of this information, the aim of our study is to guide clinical practice by comparing the postoperative analgesic efficacy, motor function outcomes, and patient satisfaction associated with sciatic nerve, BiFeS, and IPACK block techniques-each administered as a supplement to the adductor canal block-in patients undergoing total knee arthroplasty, with the ultimate goal of determining the optimal block combination for postoperative pain control.

The study was designed as a prospective, single-center, double-blind, randomized controlled trial to be conducted in the operating rooms of Erzincan Binali Yıldırım University Mengücek Gazi Training and Research Hospital. The study will begin after obtaining approval from the Erzincan Binali Yıldırım University Ethics Committee and written informed consent from all participants. A minimum of 102 patients (based on G-Power analysis), aged 18-75 years, scheduled for elective unilateral primary total knee arthroplasty by the Orthopedics and Traumatology Department and classified as American Society of Anesthesiologists (ASA) physical status I-III, will be included.

Patients with ASA ≥ IV, those undergoing revision total knee arthroplasty, bilateral arthroplasty, neuromuscular disease, cognitive dysfunction, drug allergies, a history of local anesthetic systemic toxicity, neurological deficits, bleeding diathesis, pregnancy, or those who decline participation will be excluded. The study will be conducted over a 12-month period between November 1, 2025 and November 1, 2026.

All patients will be informed about the study protocol and procedures one day before surgery, and written consent will be obtained. Upon arrival to the operating room, standard monitoring will be applied. As per routine practice, spinal anesthesia will be performed. Nasal oxygen at 2 L/min will be administered. During surgery, standard hemodynamic parameters (SpO₂, blood pressure, heart rate) will be recorded.

Spinal anesthesia will be conducted according to standard regional anesthesia protocols for total knee arthroplasty using a 25-gauge pencil-point spinal needle at the L3-L4 interspace in the sitting position. A total of 15 mg (3 mL) of 0.5% hyperbaric bupivacaine and 20 mcg (0.4 mL) fentanyl will be administered. Surgery will commence once a T10 sensory block level is achieved. Motor block will be assessed using the Modified Bromage Scale, and sensory block using pinprick or cold tests to determine dermatomal level.

At the end of surgery, under sterile conditions and ultrasound (USG) guidance, patients assigned to Group I will receive a Mid-Adductor Canal block with 20 mL (10 mL 0.25% bupivacaine + 10 mL 0.9% NaCl) and a Sciatic nerve block with 20 mL of the same local anesthetic solution. Group II patients will receive a Mid-Adductor Canal block and a BiFeS (Biceps Femoris Short Head) block using identical volumes and concentrations. Group III patients will receive a Mid-Adductor Canal block and an IPACK (Interspace Between the Popliteal Artery and the Capsule of the Posterior Knee) block with the same solution. All blocks will be performed by a single anesthesiologist with at least 3 years of experience in peripheral nerve blocks. Anesthesia technicians, operating room nurses, and postoperative assessors will be blinded to group allocation.

Patients will be randomized in a 1:1:1 ratio into three groups (Group I: Mid-Adductor Canal + Sciatic; Group II: Mid-Adductor Canal + BiFeS; Group III: Mid-Adductor Canal + IPACK). The randomization sequence was generated by a blinded statistician using computer-generated permuted blocks (block size = 6). To minimize prognostic imbalance, stratification was performed according to body mass index (BMI <30 / ≥30) and age (<66 / ≥66). Separate permuted block lists were created for each stratum, yielding: S1 (BMI<30, <66): 26; S2 (BMI<30, ≥66): 25; S3 (BMI≥30, <66): 26; S4 (BMI≥30, ≥66): 25 envelopes. Full blocks achieved a 1:1:1 balance within each stratum; partial blocks were algorithmically assigned to maintain stratified balance. Equal distribution across groups (34/34/34) was targeted.

Allocation concealment was ensured using sequentially numbered, opaque, sealed envelopes (SNOSE) prepared separately for each stratum by an investigator blinded to group assignments. Envelopes were stored in a locked cabinet. For each eligible patient, the anesthesiologist performing the intervention opened the next envelope corresponding to that patient's stratum at the end of surgery. While the anesthesiologist performing the block was aware of the allocation, postoperative data collectors and outcome assessors remained blinded. Randomization lists remained inaccessible until completion of data collection and were unblinded only during analysis.

After the procedure, patients will be transferred to the postoperative care unit as per routine. When the Aldrete score reaches ≥9, patients will be transferred to the ward. All patients will receive standard multimodal analgesia including IV paracetamol 1 g every 8 hours, IV ibuprofen 400 mg every 12 hours, and intravenous tramadol hydrochloride is planned to be used as rescue analgesia (rescue opioid) when needed. Tramadol hydrochloride administration will be regulated at a dose of 100 mg IV (intravenous), limited to a maximum of 400 mg (4 doses) within 24 hours.

VAS scores will be recorded at postoperative hours 1, 4, 8, 12, and 24. Motor block will be evaluated using the Modified Bromage Scale and peroneal nerve motor function via ankle dorsiflexion and great toe extension tests. Rescue opioid usage and time to first opioid requirement will be documented during the first 24 hours. All patients will complete the Quality of Recovery-40 (QoR-40) questionnaire at postoperative hour 24. Postoperative evaluations will be performed by a physician blinded to the type of block. PACU and ward nurses will also remain blinded to group assignments.

Inclusion Criteria:

• Patients classified as American Society of Anesthesiologists (ASA) physical status I-III
• Patients undergoing primary total knee arthroplasty
• Patients undergoing unilateral total knee arthroplasty
• Patients between 18 and 75 years of age

Exclusion Criteria:

• Patients classified as American Society of Anesthesiologists (ASA) physical status IV or higher
• Patients undergoing revision total knee arthroplasty
• Patients undergoing bilateral total knee arthroplasty
• Patients with neuromuscular disease
• Patients who decline to participate in the study
• Patients with cognitive dysfunction
• Patients with known drug allergies
• Patients with a history of local anesthetic systemic toxicity
• Patients with neurological dysfunction
• Patients with bleeding diathesis
• Pregnant patients