Total knee arthroplasty (TKA) is frequently associated with moderate to severe postoperative pain, which may delay mobilization, increase opioid consumption, and impair functional recovery. Ultrasound-guided adductor canal block (ACB) is widely used as part of multimodal analgesia because it provides effective analgesia while preserving quadriceps muscle strength. However, ACB alone may provide insufficient analgesia for the posterior aspect of the knee. The biceps femoris short head (BiFeS) block is a novel ultrasound-guided regional anesthesia technique targeting the posterolateral sensory innervation of the knee and may enhance postoperative analgesia when combined with ACB. However, clinical evidence regarding its analgesic efficacy in patients undergoing total knee arthroplasty remains limited. This prospective, randomized, controlled trial aims to compare postoperative analgesia between ultrasound-guided adductor canal block alone and adductor canal block combined with a biceps femoris short head block in adult patients undergoing primary total knee arthroplasty under spinal anesthesia. Participants will be randomly assigned in a 1:1 ratio to receive either ACB alone or combined ACB plus BiFeS block. The primary outcome is cumulative opioid consumption during the first 48 postoperative hours. Secondary outcomes include postoperative pain intensity, time to first analgesic request, quadriceps muscle strength, functional recovery, postoperative recovery quality, postoperative nausea and vomiting, patient and surgeon satisfaction, length of hospital stay, and block-related complications.
Scheduled for elective primary unilateral total knee arthroplasty under spinal -anesthesia.
American Society of Anesthesiologists (ASA) physical status I-III.
Body mass index (BMI) <40 kg/m².
Ability to understand the study procedures and provide written informed consent.
Refusal to participate or inability to provide informed consent.
Body mass index 40 kg/m2 or higher.
ASA physical status IV or V.
Known allergy or hypersensitivity to local anesthetics, opioids, or other study -medications.
Parallel
Ultrasound-Guided Adductor Canal Block
Procedure/SurgeryAn ultrasound-guided adductor canal block will be performed before the induction of spinal anesthesia using a standardized technique. Following ultrasound identification of the adductor canal, 30 mL of 0.25% bupivacaine will be injected into the adductor canal adjacent to the femoral artery to provide perioperative analgesia for primary unilateral total knee arthroplasty.
Ultrasound-Guided Biceps Femoris Short Head Block
Procedure/SurgeryAn ultrasound-guided biceps femoris short head block will be performed before the induction of spinal anesthesia using a standardized technique. Following ultrasound identification of the fascial plane adjacent to the short head of the biceps femoris muscle, 20 mL of 0.25% bupivacaine will be administered to provide additional posterolateral knee analgesia as an adjunct to the adductor canal block.
Cumulative Opioid Consumption
Cumulative opioid consumption during the first 48 postoperative hours, recorded as intravenous morphine equivalent dose (mg).
Postoperative Pain Intensity
Postoperative pain intensity will be assessed using the 11-point Numeric Rating Scale (NRS). Scores range from 0 to 10, where 0 indicates no pain and 10 indicates the worst imaginable pain. Pain will be evaluated both at rest and during knee flexion. Lower scores indicate better postoperative analgesia.
Time to First Rescue Analgesic Administration
Time from completion of surgery to the first administration of rescue analgesic medication, recorded in hours. Longer time intervals indicate prolonged postoperative analgesic effectiveness.
Quadriceps Muscle Strength
Quadriceps muscle strength will be assessed using the Manual Muscle Testing (MMT) Scale, ranging from 0 to 5, where 0 represents no visible muscle contraction and 5 represents normal muscle strength against full resistance. Higher scores indicate greater quadriceps muscle strength.
Functional Mobility
Functional mobility will be evaluated using the Timed Up and Go (TUG) Test. The total time (seconds) required to stand from a seated position, walk 3 meters, turn, return, and sit down will be recorded. Shorter completion times indicate better functional mobility. Participants who were unable to perform the TUG test independently at 24 hours after surgery were withdrawn from the study according to the study protocol.
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