Reply to Dr. Brull

To the Editor: T hank you to Dr. Brull for his comments regarding 2 recent trials published in Regional Anesthesia and Pain Medicine by Wagener et al and Cappelleri et al, which delve into the existing gap in regional anesthesia literature regarding the role of sciatic nerve block (SNB) in analgesia and outcome after total knee arthroplasty (TKA). Because of the frequency of TKA operations (500,000 cases annually in the United States alone), improving analgesia after major knee surgery represents an important challenge for regional anesthetists. Recently, several authors have studied the role of either single or continuous SNB after TKA; there seems to be a lack of evidence that SNB provides additional analgesia or any recovery benefit. Nevertheless, ‘‘the absence of evidence does not equate to evidence of absence. ’’ In fact, in clinical practice, many patients complain of pain after TKA, although a femoral catheter has been correctly positioned. I agree with Dr. Brull that the true analgesic role of SNB in TKA remains undefined and that the valid and definitive answer awaits the ideal study design. He suggests ‘‘a rigorous double-blinded, randomized trial that uses a combination of continuous femoral/lumbar plexus and placebo sciatic catheters with staged activation according to the source of pain. ’’ Unfortunately, in that ‘‘ideal’’ trial, the difference between treatment and placebo could be wide enough to unmask the study blinding. In our double-blinded trial, all patients received a single SNB, then 1 group received an infusion of local anesthetic (0.06% levobupivacaine 7Y10 mL/kg) through the sciatic catheter, whereas the other group received a placebo infusion. At our surgeon’s request, we injected the sciatic catheter in all patients after sciatic nerve damage had been ruled out immediately after surgery. Nevertheless, all patients complained of severe pain (visual analog scale score 9 7) before SNB, despite well-functioning lumbar plexus catheters. For this reason, we did not include a third group with lumbar plexus plus placebo-sciatic block plus placebo sciatic infusion. To perform the ‘‘ideal’’ study design, we should be able to distinguish all sources of pain after TKA. Ben-David et al have been able to block separately the anterior region of the knee (by continuous femoral nerve block) and the posterior region (by continuous SNB). In fact, they activated the sciatic infusion when the patient had pain despite a well-functioning femoral catheter. In patients with both sciatic and femoral infusions, they demonstrated lower visual analog scale scores, although no patient was totally free from pain. The explanation for this pain has been the absence of a reliable obturator nerve block. Two previous studies have demonstrated that adding the obturator nerve block to the femoral nerve block, alone or in combination with SNB, improves postoperative relief after TKA. In our ‘‘ideal’’ study design, if we add sciatic nerve infusion to a criterion standard femoral block with staged activation according to the source of pain, some patients may still require rescue because of absent obturator nerve block. Lumbar plexus block provides a reliable obturator nerve block. But unfortunately, the literature does not support the hypothesis that continuous lumbar plexus block offers any benefit compared with continuous femoral nerve block in postoperative analgesia after TKA, and further head-to-head comparisons are needed. Having patients totally free from pain after TKA might lead to the improvement of the outcome or shorten hospital length of stay. In the trial by Wagener et al, the group of patients with a continuous SNB had significantly lower pain in the first 24 hours, but they were not discharged earlier. After 4 days, all patients showed a range of motion of 80 degrees and were able to walk at least 25 meters with no difference between groups. In contrast, in our study, patients with continuous SNB plus LPB showed a significantly improved range of motion (100 vs 60 degrees in patients receiving single SNB) and a longer walking distance (average distance of 31 vs 20 meters only 2 days after surgery). Unfortunately, our double-blinded trial was not designed to detect readiness for discharge. In conclusion, the 2 studies have provided meaningful information, with small differences in study design. To definitively answer the question of whether SNB improves postoperative outcome after TKA, future studies should be larger and should distinguish among all sources of pain involving TKA, with a rigorous method to determine whether adding SNB can improve the outcome, such as shortening the hospital length of stay.