Although documented as an effective analgesic technique for major knee surgeries, the adductor canal block provides only minor analgesic benefit after ambulatory arthroscopic knee surgery, a study has concluded. In addition, a systematic review and meta-analysis found that the role of the block in anterior cruciate ligament (ACL) reconstruction also may be limited.
“Adductor canal block is widely used for knee surgeries,” said Herman Sehmbi, MD, assistant professor of anesthesia and perioperative medicine at Western University’s Schulich School of Medicine & Dentistry, in London, Ontario. “It is particularly attractive because of its motor-sparing properties. Although there’s quite a bit of evidence of its effectiveness in knee arthroplasty, this is not the case for arthroscopic knee surgery. So we decided to conduct a systematic review and meta-analysis in this area.”
Previous research supporting the use of the adductor canal block in ambulatory arthroscopic knee surgery is conflicting (Can J Anaesth 2013;60:874-880; Anaesthesia 2014;69:1337-1344).
Pain Tested 6 Hours Post-op
To explore this question further, Dr. Sehmbi and his colleagues searched a variety of electronic databases for randomized controlled trials comparing the analgesic effects of adductor canal block with either placebo or any other analgesic modality in the setting of multimodal analgesia. Both minor arthroscopic and ACL reconstruction surgeries were considered.
The primary outcome of the analysis was postoperative pain severity (visual analog scale [VAS] score) at rest six hours after arthroscopic knee surgery. “We chose six hours for two reasons,” Dr. Sehmbi said. “First of all, it roughly coincides with patients’ arrival at home, which would be meaningful for the patient. Secondly, if we chose a time point that was more immediately postoperative, the results may have been muddied by IV analgesics given in the PACU.”
As Dr. Sehmbi reported at the 2017 annual meeting of the Canadian Anesthesiologists’ Society (abstract 283054), the literature search yielded 10 randomized controlled trials comparing adductor canal block with either placebo or femoral nerve block. “We looked only at randomized controlled trials done on an ambulatory basis, including a multimodal analgesic regimen,” he added. “We did that because we thought it would provide the highest quality of evidence and would be generalizable to our own practice.”
The analysis revealed that when compared with placebo in minor knee arthroscopic surgery, the adductor canal block reduced postoperative resting pain scores by a weighted mean difference of 1.46 cm on a 10-point VAS 10-cm scale (95% CI, 2.03 to –0.90; P<0.00001) at zero hours, 0.51 cm (95% CI, –0.92 to –0.10; P=0.02) at six hours and 0.48 cm (95% CI, –0.93 to –0.04; P=0.03) at eight hours.
Similarly, dynamic pain scores were reduced by a weighted mean difference of 1.50 cm (95% CI, –2.10 to –0.90; P<0.00001) at zero hours, 0.50 cm (95% CI, –0.95 to –0.04; P=0.03) at six hours and 0.59 cm (95% CI, –1.12 to –0.05; P=0.03), compared with control. Finally, adductor canal block was found to reduce cumulative 24-hour oral morphine equivalent consumption by 7.41 mg (95% CI, –14.75 to –0.08; P=0.05), compared with control.
“But if you look closely at these numbers, these are very marginal,” Dr. Sehmbi discussed. “At best, it was modest in terms of its efficacy, which we found disappointing.” The block did not provide any analgesic benefit and was not different from placebo or femoral nerve block in ACL reconstruction surgery. No major complications occurred as a result of the block.
These results led the researchers to question th