This prospective, randomized, double-blind clinical trial aims to compare the effects of two different posterior knee analgesia techniques-iPACK block (Interspace Between the Popliteal Artery and the Capsule of the posterior Knee) and the Biceps Femoris Short Head (BiFeS) block-when combined with an adductor canal block (ACB) in patients undergoing elective unilateral total knee arthroplasty (TKA). Effective postoperative analgesia is essential for early mobilization, enhanced recovery, and patient satisfaction after TKA. Although ACB provides good anterior knee analgesia while preserving quadriceps strength, additional posterior knee analgesia is often required. The iPACK block is a commonly used technique that targets the posterior knee capsule, whereas the newer BiFeS block aims to provide more selective posterolateral sensory blockade with potentially reduced risk of motor involvement. However, comparative clinical data between these two techniques are limited. The primary objective of this study is to evaluate the difference between the iPACK and BiFeS blocks in terms of Quality of Recovery-15 (QoR-15) scores at 24 hours postoperatively. Secondary objectives include comparisons of postoperative pain scores, opioid consumption, time to first analgesic request, quadriceps and anterior tibialis muscle strength, functional test performance, time to mobilization, active range of motion, and the incidence of adverse events. A total of 74 adult patients scheduled for elective unilateral TKA under spinal anesthesia will be randomized in a 1:1 ratio into two groups: ACB + iPACK block or ACB + BiFeS block. All blocks will be performed under ultrasound guidance by an experienced anesthesiologist. Outcome assessments will be conducted by blinded investigators. The study aims to provide high-quality clinical evidence regarding the effectiveness of the BiFeS block compared to the widely used iPACK technique.