Total knee arthroplasty (TKA) is associated with severe postoperative pain that delays mobilization, prolongs hospital stay, and reduces patient satisfaction. Regional analgesia techniques have gained prominence due to their opioid-sparing effects and favorable complication profiles compared to general anesthesia. While adductor canal block (ACB) effectively manages anterior knee pain with preserved motor function, posterior knee pain remains a challenge. IPACK (Infiltration between the Popliteal Artery and Capsule of the Knee) and the Biceps Femoris Short Head (BiFeS) block are techniques targeting posterior capsule innervation without causing motor block.This prospective study aims to compare the postoperative analgesic efficacy of ultrasound-guided ACB+IPACK versus ACB+BiFeS block combinations in patients undergoing TKA under spinal anesthesia. Patients (ASA I-III, age 18-80, BMI ≤35) will be randomized into two groups (n=39 each). Primary outcomes include NRS pain scores at rest and on movement, and opioid consumption at 0, 1, 3, 6, 12, 18, and 24 hours postoperatively. Secondary outcomes include time to first mobilization, motor block incidence, quadriceps muscle strength assessment, PONV, and quality of recovery (QoR-15).

Total knee arthroplasty (TKA) is a widely performed surgical intervention for end-stage knee osteoarthritis and other debilitating knee conditions. Severe postoperative pain following TKA delays early mobilization and rehabilitation, prolongs hospital stay, reduces patient satisfaction, and increases complication risk. Regional analgesia techniques have emerged as the preferred approach due to their ability to reduce opioid consumption, minimize opioid-related side effects (nausea, vomiting, respiratory depression, constipation), and preserve motor function. Ultrasound guidance further improves block success rates and reduces the local anesthetic volume required.

Optimal postoperative analgesia in TKA requires consideration of the complex innervation of the knee joint. The anterior compartment is primarily innervated by branches of the femoral nerve, while the posterior capsule is supplied by branches of the sciatic nerve. Adductor Canal Block (ACB) reduces anterior knee pain by blocking the saphenous nerve and branches of the obturator nerve while preserving quadriceps strength compared to femoral nerve block; however, it may be insufficient alone for controlling posterior capsule pain. The IPACK block (Infiltration between the Popliteal Artery and Capsule of the Knee) addresses posterior knee pain by depositing local anesthetic between the popliteal artery and knee capsule, blocking sensory innervation of the posterior capsule without causing motor block. The Biceps Femoris Short Head (BiFeS) block is a novel ultrasound-guided technique targeting nerve branches innervating the posterolateral knee capsule, aiming to reduce posterior knee pain while preserving motor function.

Study Design:

This is a prospective, randomized, observational study conducted at Hitit University Erol Olçok Training and Research Hospital. Patients will be randomized into two groups by an investigator not directly involved in the study:

Group P (ACB+IPACK): Adductor canal block combined with IPACK block (n=39) Group B (ACB+BiFeS): Adductor canal block combined with Biceps Femoris Short Head block (n=39)

Inclusion Criteria:

Patients scheduled for TKA surgery, ASA physical status I-III, hemodynamically stable, aged 18 years or older, BMI ≤35 kg/m², and who have signed the informed consent form.

Exclusion Criteria:

Revision TKA surgery, simultaneous bilateral TKA, BMI >40 kg/m², ASA 4-5, inability to perform NRS pain scoring, allergy to local anesthetics, pregnancy or breastfeeding, age <18 or >80 years, uncontrolled anxiety, alcohol or drug dependency, neuromuscular or peripheral nerve disease, high-dose opioid use within 3 days prior to surgery, widespread chronic pain, diabetes mellitus, hepatic or renal insufficiency, coagulation disorders, anticoagulant use, or infection at the block needle insertion site.

Anesthetic and Block Technique:

All patients will receive standard anesthesia monitoring (non-invasive arterial blood pressure, heart rate, ECG, pulse oximetry) and IV access via a 20G catheter. Quadriceps muscle strength will be recorded before block application using the Medical Research Council (MRC) scale. Premedication will consist of midazolam 0.07-0.15 mg/kg and fentanyl 0.5 mcg/kg IV, with supplemental oxygen via face mask. All block procedures will be performed under standard sterile conditions.

Adductor Canal Block (ACB): With the patient in supine position and the hip in slight external rotation, a linear ultrasound probe is placed vertically at the midpoint between the patella and inguinal crease on the medial thigh. The femoral artery is identified in short-axis view and tracked medially until it appears deep to the sartorius muscle. A 10 cm peripheral nerve block needle is advanced in-plane, and 15 mL of 0.25% bupivacaine is injected around the femoral artery deep to the sartorius muscle, with negative aspiration confirmed every 5 mL.

IPACK Block: With the patient in prone position, a linear probe is placed over the popliteal crease to visualize the space between the popliteal artery and femoral condyles. A 10 cm needle is inserted in-plane from medial to lateral. After negative aspiration and hydrodissection with 1-2 mL of local anesthetic to confirm correct placement, 25 mL of 0.25% bupivacaine is injected with negative aspiration confirmed every 5 mL, distributed evenly between the initial needle tip position (2 cm lateral to the popliteal artery) and the posteromedial border of the femur.

BiFeS Block: With the patient in supine position and the knee in slight flexion, a linear ultrasound probe is placed transversely on the lateral surface of the distal third of the thigh. The biceps femoris short head muscle is identified along the linea aspera of the femur. The needle insertion point is determined at the level of the lateral supracondylar line of the femur, approximately 6-8 cm proximal to the lateral femoral epicondyle. A 10 cm needle is advanced in-plane from lateral to medial, targeting the plane between the biceps femoris short head and the lateral femoral cortex. After hydrodissection with 1-2 mL to confirm correct plane, 25 mL of 0.25% bupivacaine is injected slowly with negative aspiration confirmed every 5 mL.

Following block application, spinal anesthesia will be performed with the patient in sitting position. The L4-L5 interspace will be identified, and 12.5 mg of 0.5% hyperbaric bupivacaine will be administered intrathecally via a 25G spinal needle over 1 minute. Surgery will commence when Bromage score reaches 3 and sensory block level reaches T10.

Postoperative Management and Outcome Measures:

Postoperative analgesia will be standardized for all patients: IV paracetamol 1g every 8 hours and patient-controlled analgesia (PCA) with tramadol (bolus dose 10 mg, lockout interval 20 minutes, no basal infusion, maximum 400 mg/day). Rescue analgesia with IV fentanyl 25 mcg will be administered for NRS ≥4, with total dose recorded.

Pain assessment using the Numeric Rating Scale (NRS, 0-10) will be performed at rest and during active movement (sitting up from bed) at postoperative hours 0, 1, 3, 6, 12, 18, and 24 by a blinded nurse or pain monitoring team.

Quadriceps muscle strength will be assessed at postoperative hours 2 and 24 using the MRC scale (0-5), with the contralateral unoperated leg serving as the control reference. A score of 4 or above will be considered indicative of preserved motor function.

Additional outcomes recorded will include tramadol consumption at 0-1, 1-12, 12-24, and total 24 hours; time to first opioid requirement; PONV severity (PONV scale 1-4) with ondansetron 4 mg IV administered for PONV score ≥2; vital signs at postoperative hours 0, 1, 3, 6, 12, 18, and 24; Quality of Recovery (QoR-15) scores preoperatively and at postoperative hour 24; time to first oral intake, flatus, and defecation; and time to first assisted mobilization.

Study Termination Criteria:

NRS >7 for 4 consecutive hours despite tramadol therapy, inability to perform NRS assessment, or incomplete surgery.

Inclusion Criteria:

• Scheduled for primary total knee arthroplasty surgery
• ASA physical status classification I-III
• Hemodynamically stable
• Age ≥ 18 years and ≤ 80 years
• BMI ≤ 35 kg/m²
• Signed written informed consent form

Exclusion Criteria:

• Revision total knee arthroplasty surgery
• Simultaneous bilateral total knee arthroplasty
• BMI > 40 kg/m²
• ASA physical status classification 4-5
• Inability to perform NRS pain scoring
• Known allergy to local anesthetics
• Pregnancy or breastfeeding
• Age < 18 or > 80 years
• Uncontrolled anxiety disorder
• Alcohol or drug dependency
• Neuromuscular disease or peripheral nerve disease
• High-dose opioid use within 3 days prior to surgery
• Widespread chronic pain syndrome
• Diabetes mellitus
• Hepatic or renal insufficiency
• Coagulation disorders
• Current use of anticoagulant medications
• Infection at the peripheral nerve block needle insertion site
• Refusal to participate in the study