Reply to Drs. Abdallah and Brull

To the Editor: W e gratefully thank Drs. Abdallah and Brull for their valuable comments and suggestions about an ideal study design for reliable assessment of postoperative pain treatment after total knee arthroplasty (TKA). Furthermore, the simultaneously published systematic review by Drs. Abdallah and Brull enlightens the topic of the best pain management in patients undergoing TKA. In proposing an ideal trial design, Abdallah and Brull emphasized the role of an obturator nerve blockade, in addition to femoral and/or sciatic nerve blockade, with an anatomically based approach. From an academic point of view, the question of which nerves innervate which part of the knee and the possible role for effective postoperative pain therapy in patients undergoing TKA is very interesting and far from being solved. In our study, we chose a more practical approach. We did not set out to test the quality and extent of each blockade several times a day because we thought that this would go beyond clinical reality outside any randomized study. As a result of long-term knee osteoarthritis, patients undergoing TKA often have chronic pain. Pain in osteoarthritis is a complex integration of sensory, affective, and cognitive processes. Central sensitization has an important role in this pain condition. Thus, anatomic innervation is subject to substantial peripheral and central neuroplasticity. Therefore, next to the anatomic variations in knee innervations, the respective patients have undergone considerable neural plasticity of pain perception. Orthopedic surgeons perform different surgical techniques for TKAwith varying degrees of release of the posterior knee capsule, which is supplied by branches of the peroneal and tibial nerve and, to a variable extent, by the obturator nerve. Even with the same technique, the outcome in postoperative pain can vary interindividually. Thus, individual surgical techniques, as well anatomic innervations and neuronal plasticity, may influence postoperative pain. Taking these uncontrollable variables into account, we aimed for readiness for discharge as a well-defined and clinically important outcome parameter, whereas overall pain was a secondary outcome parameter. Drs. Abdallah and Brull have concerns regarding a possible bias because our study design lacks a ‘‘sham’’ catheter for the sciatic nerve in the single-shot sciatic and femoral catheter group and in the femoral-catheter-only group. From a scientific point of view, we agree that this might be a shortcoming in our study. Actually, we considered such a design while planning the study, but as Drs. Ilfeld and Madison appropriately point out in their editorial, a sciatic blockade/catheter is not without risk. Thus, we rated the risk of an unnecessary sciatic catheter as being higher than the scientific advantage of a ‘‘sham’’ catheter. In a clinical setting outside randomized trials, patients usually also have the potential placebo effect associated with a sciatic catheter. Finally and most importantly, such a scientifically correct study design with a ‘‘sham’’ blockade/ catheter has been deemed ‘‘unethical,’’ and it has been suggested that such trials should be excluded from Cochrane reviews. To conclude, from a purely scientific point of view, we agree that the study design suggested by Drs. Abdallah and Brull may be superior; however, from an ethical and more clinical, practical point of view, we favor the design chosen for the recent study. We strongly believe that the results obtained can be used for decision making in postoperative pain treatment and rehabilitation in patients undergoing TKA.