To the Editor:
It is with interest that we read the study by Kim et al.1 and the accompanying editorial by Mariano and Perlas.2
The patients involved in this study received effective multimodal analgesia, which included effective continuous epidural infusion, yet the title and abstract only mention the single-injection femoral nerve block (FNB) or adductor canal nerve block (ACB). The patient-controlled epidural analgesia contained 10 μg/ml hydromorphone combined with 0.06% bupivacaine set at 4 ml/h continuous infusion with 4 ml of patient-controlled boluses on demand every 10 min on the day of surgery (postoperative day 0 [POD 0]). This was reduced to 2 ml/h the next morning (POD 1), and continuous infusion was stopped at 5:00 pm that day (POD 1); however, the patient-administered boluses were not decreased, therefore the patients could still receive a total patient-controlled epidural analgesia infusion of up to 20 ml/h after the continuous infusion was stopped late on POD 1. Added to oxycodone/acetaminophen (5/325 mg) every 4 h and daily 7.5 to 15 mg meloxicam, this in and of itself represents an effective multimodal regimen. Any additional nerve block, when compared with FNB, would most probably have yielded similar results with this study design. With this level of multimodal analgesia, we agree with Mariano and Perlas2 that “…[the block] does not have to [provide enough analgesia for total knee arthroplasty].”
Furthermore, pain and muscle strength were assessed at 6 to 8 h postanesthesia, as well as at 24 and 48 h. As neither single-injection FNB nor ACB could be expected to last to 24 h, the later measurements are a true testament to the efficacy of the epidural and the other multimodal analgesics.
Although the local anesthetic total doses used for the single-injection nerve blocks were the same, the ACBs were performed with 15 ml of 0.5% bupivacaine, whereas the FNBs were performed with 30 ml of 0.25% bupivacaine. The question of whether volume, concentration, or total dose has a more significant effect on analgesia, motor function, and spread of local anesthetic has not been conclusively answered, but this is a confounding factor.
Finally, the finding that the FNB was responsible for the “buckling” in three patients while ambulating on POD 1 is most probably a coincidental finding after the single-injection nerve blocks have long worn off, while the patients still had continuous epidurals in place. An article by Memtsoudis et al.,3 of which Dr. Mariano, the principal author of the above-mentioned editorial,2 is a coauthor, in the same issue of Anesthesiology clearly demonstrated that peripheral nerve blockade is not a risk factor for falling after total knee arthroplasty.
The ACB may well have its effect simply by proximal spread of local anesthetic agent to the anterior and posterior divisions of the femoral nerve, as convincingly shown elsewhere.4–6 If it did not, the ACB would block only one of the seven nerves that innervate the knee joint7 and would most probably be ineffective. Due to this proximal spread, the lack of quadriceps muscle paralysis is not a constant characteristic of ACB.5,6 Quadriceps muscle dysfunction due to FNB, however, is only a minor issue when compared with the dysfunction caused by the original disease and the surgery itself,8–10 while effective postoperative analgesia is probably a major enabler of early ambulation.
Dr. Boezaart receives royalty payments from Teleflex (Wayne, Pennsylvania). Dr. Deloach declares no competing interests.