Ultrasonographic Predictors of Adductor Canal Block Effectiveness in Total Knee Arthroplasty

Total knee arthroplasty (TKA) is associated with substantial postoperative pain and opioid requirements, making effective multimodal analgesia essential for early mobilization, functional recovery, and reduction of opioid-related adverse events \[1,2\]. Adductor canal block (ACB) has become a key component of enhanced recovery after surgery (ERAS) protocols because it provides effective anterior knee analgesia while largely preserving quadriceps muscle strength \[2-4\]. However, analgesic efficacy after ACB remains variable, and some patients require rescue opioid analgesia despite technically successful block placement \[5\]. Although ultrasound guidance improves block accuracy, factors such as tissue depth, anatomical variations, saphenous nerve visibility, and injectate spread pattern may influence clinical outcomes \[6,7\]. Prospective evidence regarding the predictive value of these ultrasound-derived parameters for ACB analgesic failure remains limited. Therefore, this study aims to evaluate whether preoperative ultrasound-derived tissue and target parameters-including skin-to-target depth, subcutaneous fat thickness, muscle thickness, saphenous nerve visibility, and injectate spread pattern-can predict ACB analgesic failure and early postoperative analgesic outcomes following TKA.

Inclusion Criteria: * Age ≥18 years * Scheduled for elective primary unilateral total knee arthroplasty under spinal anesthesia * American Society of Anesthesiologists (ASA) physical status I-III Exclusion Criteria: * Daily opioid use or chronic pain syndrome * Diabetic or other clinically diagnosed peripheral neuropathy * Coagulopathy * Infection at the injection site * Known allergy or hypersensitivity to local anesthetics * Revision total knee arthroplasty * Conversion from spinal anesthesia to general anesthesia during surgery * General anesthesia as the planned anesthetic technique