This randomized, double-blind, controlled trial is designed to compare the analgesic efficacy and safety of perineural dexamethasone versus perineural dexmedetomidine as adjuvants to ropivacaine for ultrasound-guided interspace between the popliteal artery and the capsule of the posterior knee (iPACK) and adductor canal blocks in patients undergoing primary unilateral total knee arthroplasty (TKA). Elderly participants scheduled for elective TKA will be randomized into three parallel groups: ropivacaine alone (control), ropivacaine combined with perineural dexamethasone, or ropivacaine combined with perineural dexmedetomidine. The primary objective is to determine whether the addition of either adjuvant reduces postoperative opioid consumption compared with ropivacaine alone and to assess potential differences in analgesic efficacy between the two adjuvants. Secondary outcomes include pain intensity at rest and during mobilization, time to first rescue analgesia, quality of early functional recovery, and the incidence of adverse events, including postoperative nausea and vomiting, motor impairment, and hemodynamic instability.