ACB and iPACK Blocks With Intravenous Dexamethasone and Perineural Dexmedetomidine in Total Knee Arthroplasty

Postoperative pain following total knee arthroplasty (TKA) remains a major clinical challenge and may negatively affect early mobilization, rehabilitation, patient satisfaction, and postoperative recovery. Inadequate pain control after TKA is associated with increased opioid consumption and opioid-related adverse events, including nausea, vomiting, sedation, urinary retention, respiratory depression, and postoperative delirium, particularly in elderly patients.

Ultrasound-guided Adductor Canal Block (ACB) combined with iPACK (Infiltration between the Popliteal Artery and Capsule of the Knee) block has become an increasingly popular regional anesthesia strategy for TKA because it may provide effective analgesia while preserving quadriceps muscle strength and facilitating early mobilization. The ACB primarily targets the sensory innervation of the anterior and medial aspects of the knee, whereas the iPACK block supplements analgesia of the posterior knee capsule.

Several adjuvant medications have been investigated to prolong the duration and improve the quality of peripheral nerve blocks. Intravenous dexamethasone is widely used as a perioperative analgesic adjunct and may prolong postoperative analgesia while also reducing postoperative nausea and vomiting. Perineural dexmedetomidine has been shown to prolong sensory blockade, improve analgesia quality, and reduce opioid requirements. However, the optimal combination of systemic and perineural adjuvants for ACB and iPACK blocks in TKA remains unclear.

The aim of this prospective randomized controlled trial is to compare three perioperative analgesic strategies in patients undergoing elective primary unilateral total knee arthroplasty under spinal anesthesia:

Standard ACB + iPACK without adjuvants, ACB + iPACK with intravenous dexamethasone 8 mg, ACB + iPACK with intravenous dexamethasone 8 mg combined with perineural dexmedetomidine.

All participants will receive standardized spinal anesthesia with 0.5% ropivacaine (3-4 mL). Ultrasound-guided ACB and iPACK blocks will be performed using 20 mL of 0.2% ropivacaine for each block. In the dexmedetomidine group, 12.5 µg of dexmedetomidine will be added to each regional block.

The primary endpoint of the study will be total postoperative opioid consumption during the first 48 postoperative hours expressed as intravenous morphine equivalents. Secondary endpoints will include postoperative pain scores at rest and during movement, time to first rescue analgesia, duration of analgesia, quadriceps muscle strength, early mobilization, opioid-related adverse events, dexmedetomidine-related adverse events such as bradycardia and hypotension, inflammatory markers, and length of hospital stay.

The study hypothesis is that intravenous dexamethasone will improve postoperative analgesia compared with standard ACB + iPACK alone, while the addition of low-dose perineural dexmedetomidine will further prolong analgesia duration and reduce opioid consumption without significantly increasing adverse events or impairing postoperative mobilization.