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

Abstract

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.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Flow diagram of patient distribution.

US =  ultra sound. PCA =  patient-controlled analgesia.

Figure 2. Effects of the adductor canal block on pain during 45 degrees flexion of the knee.

Pain was assessed with a visual analogue scale (0–100 mm; with 0 equal no pain and 100 being the worst imaginable pain). Pain scores were lower in the ropivacaine group at 4 hours (primary endpoint (P = 0.04), but not when calculated as area under the curve (1–8 h, P = 0.11). Data are expressed as mean ±SD. ACB =  adductor canal block.

Figure 3. Effects of the adductor canal block on pain at rest.

Pain was assessed with a visual analogue scale (0–100 mm; with 0 equal no pain and 100 being the worst imaginable pain). Comparisons between the groups were made as area under the curve (AUC) for the interval 1–8 h postoperatively, showing no statistically significant difference between the groups (P = 0.43). Data are expressed as mean ±SD. ACB =  adductor canal block.