This prospective randomized controlled study aims to evaluate the effect of ultrasound-guided Biceps Femoris Short Head (BiFeS) block combined with adductor canal block on postoperative opioid consumption and pain control in patients undergoing elective total knee arthroplasty under spinal anesthesia.

A total of 60 patients aged 18-80 years with ASA physical status I-III scheduled for unilateral elective total knee arthroplasty will be randomized into two groups. The intervention group will receive spinal anesthesia followed by BiFeS block and adductor canal block before surgery, in addition to standard multimodal analgesia and postoperative morphine patient-controlled analgesia (PCA). The control group will receive spinal anesthesia and standard multimodal analgesia with postoperative morphine PCA without peripheral nerve block.

The primary outcome is total morphine consumption during the first 24 postoperative hours. Secondary outcomes include postoperative pain scores assessed by Numeric Rating Scale (NRS), time to first analgesic requirement, time to first foot movement, and Quality of Recovery-15 (QoR-15) scores.

Total knee arthroplasty is associated with significant postoperative pain and high opioid consumption. Peripheral nerve blocks are increasingly used as part of multimodal analgesia strategies to reduce opioid requirements and improve postoperative recovery.

This prospective, randomized, single-center clinical study will be conducted at Kayseri City Hospital Department of Anesthesiology and Reanimation. Sixty adult patients undergoing elective unilateral total knee arthroplasty under spinal anesthesia will be enrolled after written informed consent.

Participants will be randomized into two groups using the closed envelope method.

Intervention Group (n=30):

Patients will receive spinal anesthesia with 3.5-4 mL 0.5% hyperbaric bupivacaine. Before surgical incision, ultrasound-guided BiFeS block will be performed using 25 mL of 0.25% bupivacaine, followed by ultrasound-guided adductor canal block using 15 mL of 0.25% bupivacaine.

Control Group (n=30):

Patients will receive spinal anesthesia only without peripheral nerve block.

All patients will receive standard multimodal analgesia including intravenous paracetamol 1 g every 8 hours and intravenous dexketoprofen 50 mg every 12 hours. Postoperative analgesia will be provided using morphine PCA prepared as 1 mg/mL concentration with 15-minute lockout interval and maximum 4 boluses per hour.

Rescue analgesia will be administered as intravenous fentanyl 25 mcg in patients with NRS score ≥4 despite PCA use.

Primary outcome measure is total morphine consumption during the first 24 postoperative hours.

Secondary outcome measures include Numeric Rating Scale pain scores at postoperative 1, 6, 12, and 24 hours, time to first analgesic requirement, time to first active foot movement, rescue analgesic requirement, and postoperative Quality of Recovery-15 scores.

The study hypothesis is that combined BiFeS and adductor canal block will reduce postoperative opioid consumption and improve recovery quality compared with standard multimodal analgesia alone.

Inclusion Criteria:

• Patients aged 18 and older
• ASA I-III
• Patients scheduled for elective unilateral knee replacement
• Eligibility for and consent to spinal anesthesia

Exclusion Criteria:

• History of allergy or anaphylaxis to local anesthetics, animal gelatin, or chlorhexidine
• Bleeding diathesis/inability to discontinue anticoagulants
• Infection (at the injection site/sepsis)
• Neurological disorders or cognitive impairment affecting pain perception
• Pregnancy, breastfeeding
• Patients under 18 years of age