• Yuda Fei, Xulei Cui, Shaohui Chen, Huiming Peng, Bin Feng, Wenwei Qian, Jin Lin, Xisheng Weng, and Yuguang Huang.
• Anesthesiology Department, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, and Peking Union Medical College, Shuaifuyuan 1#, Dongcheng District, Beijing, 100730, China.
• BMC Anesthesiol. 2020 Oct 9; 20 (1): 260.

BackgroundThe optimal position for continuous adductor canal block (ACB) for analgesia after total knee anthroplasty (TKA) remians controversial, mainly due to high variability in the localization of the the adductor canal (AC). Latest neuroanatomy studies show that the nerve to vastus medialis plays an important role in innervating the anteromedial aspect of the knee and dives outside of the exact AC at the proximal end of the AC. Therefore, we hypothesized that continuous ACB at the proximal end of the exact AC could provide a better analgesic effect after TKA compared with that at the middle of the AC (which appeared to only block the saphenous nerve).MethodsSixty-two adult patients who were scheduled for a unilateral TKA were randomized to receive continuous ACB at the proximal end or middle of the AC. All patients received patient-controlled intravenous analgesia with sufentanil postoperatively. The primary outcome measure was cumulative sufentanil consumption within 24 h after the surgery, which was analyzed using Mann-Whitney U tests. P-values < 0.05 (two-sided) were considered statistically significant. The secondary outcomes included postoperative sufentanil consumption at other time points, pain at rest and during passive knee flexion, quadriceps motor strength, and other recovery related paramaters.ResultsSixty patients eventually completed the study (30/group). The 24-h sufentanil consumption was 0.22 μg/kg (interquartile range [IQR]: 0.15-0.40 μg/kg) and 0.39 μg/kg (IQR: 0.23-0.52 μg/kg) in the proximal end and middle groups (P = 0.026), respectively. There were no significant inter-group differences in sufentanil consumption at other time points, pain at rest and during passive knee flexion, quadriceps motor strength, and other recovery related paramaters.ConclusionsContinuous ACB at the proximal end of the AC has a better opioid-sparing effect without a significant influence on quadriceps motor strength compared to that at the middle of the AC after TKA. These findings indicates that a true ACB may not produce the effective analgesia, instead, the proximal end AC might be a more suitable block to alleviate pain after TKA.Trial RegistrationThis study was registered at ClinicalTrials.gov ( NCT03942133 ; registration date: May 06, 2019; enrollment date: May 11, 2019).

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