Effects of Ultrasound-guided Adductor Canal Block Versus Femoral Nerve Block on Pain and Quadriceps Strength After Ambulatory Knee Arthroscopic Surgery
Phase: PHASE4
Conditions: Anterior Cruciate Ligament Tear, Knee Meniscus Tear
Sponsor: University of California, San Francisco

Cover Page 
 
Date: 3/20/2023 
 
NCT05190120 
 
Brief Title: Effect of Adductor Canal Block Versus Femoral 
Block on Pain and Quadriceps Strength 
 
Official Title: Effects of Ultrasound-guided Adductor 
Canal Block Versus Femoral Nerve Block on Pain and 
Quadriceps Strength After Ambulatory Knee Arthroscopic 
Surgery 
 
 
 
 
 
 
 
 
 
 
 
 
 

Study Protocol/Design 
 
Patients undergoing arthroscopic knee surgery (ACL and non-ACL surgery) typically receive an 
ultrasound-guided femoral nerve block or an adductor canal block in the pre-operative phase 
for post-operative pain control. While an effective method for post-operative analgesia, the 
femoral nerve block is associated with profound quadriceps weakness for the duration of the 
nerve block, which can impair ambulation, rehabilitation, and increase the risk of falls. The 
more distal adductor canal block, however, contains primarily sensory branches of the femoral 
nerve and has been been purported by small volunteer studies to provide equally effective 
analgesia with minimal motor block and quadriceps weakness (as compared to femoral nerve 
block). We will prospectively randomize patients undergoing knee arthroscopy at the UCSF 
Orthopaedic Institute to receive either a single-shot femoral nerve block (control) or adductor 
canal block preoperatively after taking baseline measurements of quadriceps strength 
(quantified by maximum voluntary isometric contraction). The quadriceps muscle strength will 
be checked 20 minutes after the nerve block to assess strength. All patients will subsequently 
undergo a general anesthetic. The primary outcome variable will be post-block quadriceps 
strength as a percentage of baseline from pre-block values. Secondary outcome variables that 
we will also investigate include: VAS pain score in the post anesthesia recovery unit and post-
operative day 1, time to onset of sensory block, duration of nerve blockade, block performance 
time, patient satisfaction score, perioperative opioid use, perioperative analgesic consumption, 
incidence of paresthesias, number of needle passes, incidence of post-operative nausea, 
vomiting, constipation, and any other complications. 
 
Statistical Analysis: 
This study is designed as a prospective two-treatment parallel-design study. The primary 
outcome is quadriceps strength (as measured by maximal voluntary isometric contraction, or 
MVIC, using a dynamometer). We will obtain baseline measurements of quadriceps strength in 
the pre-operative phase (pre-block), as well as post-block before surgery. Based on previous 
research, we assume a reduction in quadriceps strength from baseline of 48% in the adductor 
canal block group and 82% in the femoral block group. Setting α = 0.05 and power = 0.8 we 
calculated 30 patients per group to show a significant difference with a two-sided test. To 
adjust for drop out and lost to follow up we increased the sample size by 10% and plan to 
recruit 33 patients per study group per surgery type (ACL vs. non-ACL arthroscopic surgery). 66 
patients will be in the ACL surgery group and 66 patients will be in the non-ACL group. 
Secondary outcomes will be analyzed separately. Categorical data will be analyzed using 
Chisquare analysis or Fischer's exact test, depending on sample size. Comparison of means will 
be performed using the independent sample t-test or the Mann-Whitney U test, depending on 
distribution. A P-value of 0.05 or smaller will be considered statistically significant.