Sir: We read with interest the article of Tarkkila et al.[1] comparing the effects of either intrathecal morphine or continuous femoral 3-in-1 block on pain after knee surgery. In contrast to the authors, we are not surprised by the results of their study. Moreover, we have some comments on the Methods and Discussion. In the Methods section, the authors did not describe clearly the criteria that are judged necessary with regard to the correct placement of the needle. Stimulation of the medial cutaneous nerve or the intermediate cutaneous nerve of the thigh may lead to wrong placement of the catheter. Unfortunately, the authors did not describe clearly whether or not they had checked separately to determine whether the block reached the territories of the three main nerves together (femoral, lateral cutaneous and obturator). This is particularly important because the obturator nerve may frequently be missed by a 3-in-1 block. Lang et al.[2] achieved using a single short bolus, only 4% success of obturator block, while Singelyn et al.[3] achieved, using a continuous infusion through a catheter inserted in the femoral sheath, 40% and 55% success of obturator block, depending on whether the catheter was inserted 10-15 cm or more than 15 cm respectively. The placing of the femoral catheter at the end of the surgical procedure is debatable. The residual effects of the spinal anaesthesia may render the evaluation of the block more difficult. The use of the verbal rating scale, with only four possibilities for assessing postoperative pain, is also debatable. The difference between mild and moderate pain may vary by more than 40 points on a visual analogue scale (from 0 to 100) and, therefore, some bias in evaluating post-operative pain is easily introduced with such a practice. In Tarkkila et al.'s study [1], both groups consisted of 17 knee prostheses and three major ligament operations. Although analgesia given through a femoral catheter is sufficient for ligament repair [4], Hirst et al.[5] have shown this technique to be insufficient after total knee arthroplasty, explained in this study by insufficient analgesia to the back of the knee, a territory innervated by the sciatic nerve. Unfortunately, the authors did not describe the location of the knee pain in their study. We believe that blocking the sciatic nerve is essential to achieve good post-operative analgesia after major knee surgery, particularly after total knee replacement, which always involves the back of the knee, the innervation of which depends on the sciatic nerve. Finally, we disagree with the authors when they suggest that, by blocking the sciatic nerve, the simplicity of the method is lost. By placing the patient in the lateral decubitus position, it is possible to block the sciatic nerve using Labat's approach, and to block the femoral nerve with or without catheter by the posterior approach to the lumbar plexus. This latter technique has been shown to be superior to the 3-in-1 technique, particularly because of more successful blockade of the lateral cutaneous femoral and obturator nerves [6]. In conclusion, we are not surprised by the disappointing results obtained by the authors with the continuous femoral 3-in-1 block and believe that this technique is inadequate to provide pain control after major knee surgery and should therefore not be applied in this context. A. BORGEAT TH. SINGER Department of Orthopaedics, University Clinic of Zurich/Balgrist, Zurich, Switzerland
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Sep 1, 2003
A Casati 
Open Access