The Risk of Falls After Total Knee Arthroplasty with the Use of a Femoral Nerve Block Versus an Adductor Canal Block: A Double-Blinded Randomized Controlled Study

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Abstract

BACKGROUND:

Adductor canal block (ACB) has emerged as an appealing alternative to femoral nerve block (FNB) that produces a predominantly sensory nerve block by anesthetizing the saphenous nerve. Studies have shown greater quadriceps strength preservation with ACB compared with FNB, but no advantage has yet been shown in terms of fall risk. The Tinetti scale is used by physical therapists to assess gait and balance, and total score can estimate a patient’s fall risk. We designed this study to test the primary hypothesis that FNB results in a greater proportion of “high fall risk” patients postoperatively using the Tinetti score compared with ACB.

METHODS:

After institutional review board approval, informed written consent to participate in the study was obtained. Patients undergoing primary unilateral total knee arthroplasty were eligible for enrollment in this double-blind, randomized trial. Patients received either an ACB or FNB (20 mL of 0.5% ropivacaine) with catheter placement (8 mL/h of 0.2% ropivacaine) in the setting of multimodal analgesia. Continuous infusion was stopped in the morning of postoperative day (POD)1 before starting physical therapy (PT). On POD1, PT assessed the primary outcome using the Tinetti score for gait and balance. Patients were considered to be at high risk of falling if they scored <19. Secondary outcomes included manual muscle testing of the quadriceps muscle strength, Timed Up and Go (TUG) test, and ambulation distance on POD1 and POD2. The quality of postoperative analgesia and the quality of recovery were assessed with American Pain Society Patient Outcome Questionnaire Revised and Quality of Recovery-9 questionnaire, respectively.

RESULTS:

Sixty-two patients were enrolled in the study (31 ACB and 31 FNB). No difference was found in the proportion of “high fall risk” patients on POD1 (21/31 in the ACB group versus 24/31 in the FNB group [P = 0.7]; relative risk, 1.14 [95% confidence interval, 0.84–1.56]) or POD2 (7/31 in the ACB versus 14/31 in the FNB group [P = 0.06]; relative risk, 2.0 [95% confidence interval, 0.94–4.27]). The average distance of ambulation during PT and time to up and go were similar on POD1 and POD2. Manual muscle testing grades were significantly higher on POD1 in the ACB group when compared with that in the FNB (P = 0.001) (Wilcoxon-Mann-Whitney odds, 2.25 [95% confidence interval, 1.35–4.26]). There were no other differences in postoperative outcomes.

CONCLUSIONS:

ACB results in greater preservation of quadriceps muscle strength. Although we did not detect a significant reduction in fall risk when compared with FNB, based on the upper limit of the relative risk, it may very well be present. Further study is needed with a larger sample size.

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