Continuous block at the proximal end of the adductor canal provides better analgesia compared to that at the middle of the canal after total knee arthroplasty: a randomized, double-blind, controlled trial

Abstract

Background: The 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).

Methods: Sixty-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.

Results: Sixty 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.

Conclusions: Continuous 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 registration: This study was registered at ClinicalTrials.gov ( NCT03942133 ; registration date: May 06, 2019; enrollment date: May 11, 2019).

Keywords: Adductor canal block; Analgesia; Opioid-sparing; Sufentanil; Total knee anthroplasty.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Ultrasound-guided proximal end adductor canal block (ACB) (A/a) and middle ACB (B/b) techniques. (A) Ultrasound probe position of short-axis scanning at the proximal end of the AC and needle orientation for proximal end ACB. (a) Short-axis ultrasound scan image at the proximal end of the AC. (B) Ultrasound probe position of long-axis scanning with the cranial end of the probe aligned with the proximal end of the AC and needle orientation for middle ACB. (b) Long-axis ultrasound scan image with the cranial end of the probe aligned with the proximal end of the AC (at the cranial side in the image). The purple arrow indicates the skin mark of the puncture point for proximal end ACB; the purple dotted line indicates the skin mark of the proximal end of the AC; the red asterisk indicates the endpoint target for the needle tip; the yellow asterisk indicates the alignment of the medial borders of the SM and ALM. ALM, adductor longus muscle; AMM, adductor magnus muscle; FA, femoral artery; FV, femoral venous; SM, sartorius muscle

Fig. 2

CONSORT patient flowchart