We read with great interest the article by Campbell et al. comparing epidural anaesthesia (EDA) with lumbar plexus infusion following total knee arthroplasty, one of the most painful orthopaedic interventions. Early and efficient rehabilitation (mobilization) is of outstanding importance to achieve a good functional result. Because of the importance of postoperative analgesia in these patients, we would like to comment on this article to clarify some essential points.
First, EDA and continuous psoas compartment block (CPCB) are, compared with peripheral nerve blocks such as femoral block (‘three in one block’) and sciatic nerve block, more invasive, prone to higher block failure and associated with more severe complications [2–5]. In the CPCB group, significant hypotension (systolic pressure <5 mmHg) was seen by Campbell et al. in 26.9% of the cases. CPCB can certainly not be recommended for training novices, and, as a deep block, it is strongly dependent on patient size and BMI  and should be avoided, similar to EDA, in patients with abnormal clotting or platelet dysfunction. Thus, these contraindications further restrict the indications for CPCB, reducing the possibility of anaesthetists improving their technique.
Second, CPCB offers a good block of the lumbar plexus, but the sacral plexus is not reliably blocked by this approach. Innervation of the knee joint is not only derived from the lumbar plexus (femoral and obturator nerve) but also from the sciatic nerve through the genicular branches of both the tibial and common peroneal components (posterior aspect of the joint capsule and many of the intraarticular structures). In our experience a successful sciatic nerve block improves postoperative pain treatment and clearly contributes to rapid physiotherapy and full range of movement. Moreover, the combination of continuous femoral and sciatic nerve blocks has been shown to provide superior analgesia with less postoperative nausea and vomiting (PONV) when compared with other analgesic techniques . Considering the low success rate of CPCB (73%) and the high PONV rate in this group (35%), the additional block of the sciatic nerve should at least be evaluated.
Third, the description of the CPCB technique used by Campbell et al. is rather vague. The ‘standard’ approach with a fixed distance (4 cm in this study) from the not always easily palpable transverse process of L4 ignores anatomical variations. As recently shown by Ben-David et al., modification of Winnie's landmarks, after preliminary computed tomography studies for identification of a body structure-independent insertion point, leads to improved CPCB success rate. This was demonstrated by the low ropivacaine concentration used for the initial bolus: with 0.4 ml kg−1 ropivacaine, a 0.2% complete sensory block was obtained in 90% of the patients. Moreover, the placement of a catheter through the stimulation needle was not reported by Campbell et al. (before or after applying the initial bolus, how deep the lumbar plexus was, how deep the catheter was placed, etc.).
Fourth, although the sciatic nerve was not blocked in the CPCB group, target-controlled infusion-controlled propofol sedation (0.5–2 μg ml−1) was enough to avoid pain during and after release of the tourniquet. This effect site concentration of propofol is very high as 2 μg ml−1 is an anaesthetic dose for about 80% of patients. In our department, we use an effect site concentration of 0.3–1.0 μg ml−1 for sedation, and we surmise that the need to use such a high concentration was because of the pain sensation resulting from the unblocked sciatic nerve. Indeed, the study by Ben-David et al. clearly shows that sciatic nerve blockade provides a significant improvement in analgesia after total knee arthroplasty.
To avoid these problems, our technique for total knee arthroplasty includes sciatic nerve block with ropivacaine (0.5%) and clonidine (or catheter placement), a femoral catheter with ropivacaine (0.5%) and spinal anaesthesia. The sciatic nerve remains unblocked in case of extreme valgus position corrections until the surgeon has been able to check the state of the common peroneal nerve in the early postoperative period . This regimen is easy to teach and learn, targets analgesia to the involved limb, avoids centrally placed catheters and their drawbacks (dislocation, infection, bladder catheter), is associated with a high success rate and can be adapted to the surgeon's wishes. Making it easier and safer is a reasonable alternative.
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