BACKGROUND AND OBJECTIVES: Adductor canal block (ACB) is predominantly a sensory nerve block, but excess volume may spread to the femoral triangle and reduce quadriceps strength. We hypothesized that reducing the local anesthetic volume from 30 to 10 mL may lead to fewer subjects with quadriceps weakness.
METHODS: We performed a paired, blinded, randomized trial including healthy men. All subjects received bilateral ACBs with ropivacaine 0.1%; 10 mL in 1 leg and 30 mL in the other leg. The primary outcome was the difference in number of subjects with quadriceps strength reduced by more than 25% from baseline in 2 consecutive assessments. Secondary outcomes were quadriceps strength as a percentage of baseline at predefined time points, functional outcome assessed by the 30-Second Chair Stand Test (1 leg at a time), and sensory block. Clinicaltrials.gov Identifier: NCT01981746.
RESULTS: We included and analyzed 26 subjects. For either volume, 2 subjects had a reduction in quadriceps strength by more than 25% from baseline (difference, 0%; 95% confidence interval, -13 to 13; P > 0.999). Similarly, we found no significant differences between volumes in quadriceps strength at any of the predefined time points or in sensory block. The only statistically significant difference between volumes was found in the 30-Second Chair Stand Test at 2 hours (P = 0.02), but this difference had disappeared at 4 hours (P = 0.06).
CONCLUSIONS: Varying the volume of ropivacaine 0.1% used for ACB between 10 and 30 mL did not have a statistically significant or clinically relevant impact on quadriceps strength.