Impact of Injection Level on Analgesic Efficacy of Adductor Canal Block Following Total Knee Arthroplasty: A Prospective Observational Study

Background/Objectives: Following total knee arthroplasty (TKA), adductor canal block (ACB) is usually used for postoperative analgesia; however, the optimal injection level is yet unclear. This study tried to determine how the injection level of the ACB had an impact on postoperative analgesic efficacy and functional results after total knee arthroplasty. Methods: A total of 108 patients undergoing unilateral total knee arthroplasty under spinal anesthesia were included in this prospective observational study and were categorized according to the level of ultrasound-guided adductor canal block performed (proximal [Group I], mid [Group II], or distal [Group III]). The visual analog scale (VAS) was used to measure postoperative pain at 1, 4, 8, 12, and 24 h. Additionally, functional pain throughout 24-h standardized static and dynamic tests was assessed. We noted 24-h opioid consumption, motor strength levels, and sensory and motor block features. Results: During each time point, the distal group’s VAS scores were considerably higher than those of the proximal and mid groups (e.g., 8th hour: 40.69 ± 10.50 vs. 26.94 ± 8.72 and 23.47 ± 7.64, p < 0.001), whereas there was no difference between the proximal and mid groups (p > 0.05). At 24 h, the distal group had significantly higher functional pain scores on all dynamic and static measures (p < 0.001). The proximal and mid groups had longer sensory block durations (5.38 ± 1.33 and 5.03 ± 1.29 h) than the distal group (2.95 ± 0.95 h, p < 0.001). While mid-level ACB maintained motor function, 13.9% of patients receiving proximal ACB experienced transient motor block. Conclusions: After TKA, injection level has a major impact on postoperative analgesia. Mid-level ACB supports the employment of multimodal analgesia techniques by offering the best possible compromise between efficient pain management and motor function maintenance.