Adductor canal block versus femoral nerve block and quadriceps strength: a randomized, double-blind, placebo-controlled, crossover study in healthy volunteers.

BACKGROUND: The authors hypothesized that the adductor canal block (ACB), a predominant sensory blockade, reduces quadriceps strength compared with placebo (primary endpoint, area under the curve, 0.5-6 h), but less than the femoral nerve block (FNB; secondary endpoint). Other secondary endpoints were adductor strength and ability to ambulate. METHODS: The authors enrolled healthy young men into this double blind, placebo-controlled, randomized, crossover study. On two separate study days, subjects received either ACB or FNB with ropivacaine, and placebo in the opposite limb. Strength was assessed as maximum voluntary isometric contraction for quadriceps and adductor muscles. In addition, subjects performed three standardized ambulation tests. Clinicaltrials.gov Identifier: NCT01449097. RESULTS: Twelve subjects were randomized, 11 analyzed. Quadriceps strength (area under the curve, 0.5-6 h) was significantly reduced when comparing ACB with placebo (5.0 ± 1.0 vs. 5.9 ± 0.6, P = 0.02, CI: -1.5 to -0.2), FNB with placebo (P = 0.0004), and when comparing FNB with ACB (P = 0.002). The mean reduction from baseline was 8% with ACB and 49% with FNB. The only statistically significant difference in adductor strength was between placebo and FNB (P = 0.007). Performance in all mobilization tests was reduced after an FNB compared with an ACB (P < 0.05). CONCLUSIONS: As compared with placebo ACB statistically significantly reduced quadriceps strength, but the reduction was only 8% from baseline. ACB preserved quadriceps strength and ability to ambulate better than FNB did. Future studies are needed to compare the analgesic effect of the ACB with the FNB in a clinical setting.

Adductor canal block for postoperative pain treatment after revision knee arthroplasty: a blinded, randomized, placebo-controlled study.

BACKGROUND: Revision knee arthroplasty is assumed to be even more painful than primary knee arthroplasty and predominantly performed in chronic pain patients, which challenges postoperative pain treatment. We hypothesized that the adductor canal block, effective for pain relief after primary total knee arthroplasty, may reduce pain during knee flexion (primary endpoint: at 4 h) compared with placebo after revision total knee arthroplasty. Secondary endpoints were pain at rest, morphine consumption and morphine-related side effects. METHODS: We included patients scheduled for revision knee arthroplasty in general anesthesia into this blinded, placebo-controlled, randomized trial. Patients were allocated to an adductor canal block via a catheter with either ropivacaine or placebo; bolus of 0.75% ropivacaine/saline, followed by infusion of 0.2% ropivacaine/saline. Clinicaltrials.gov ID: NCT01191593. RESULTS: We enrolled 36 patients, of which 30 were analyzed. Mean pain scores during knee flexion at 4 h (primary endpoint) were: 52 ± 22 versus 71 ± 25 mm (mean difference 19, 95% CI: 1 to 37, P = 0.04), ropivacaine and placebo group respectively. When calculated as area under the curve (1-8 h/7 h) pain scores were 55 ± 21 versus 69 ± 21 mm during knee flexion (P = 0.11) and 39 ± 18 versus 45 ± 23 mm at rest (P = 0.43), ropivacaine and placebo group respectively. Groups were similar regarding morphine consumption and morphine-related side effects (P > 0.05). CONCLUSIONS: The only statistically significant difference found between groups was in the primary endpoint: pain during knee flexion at 4 h. However, due to a larger than anticipated dropout rate and heterogeneous study population, the study was underpowered. TRIAL REGISTRATION: Clinicaltrials.gov NCT01191593.