Target driven analgesia for total knee arthroplasty

The diversity of anaesthetic and analgesic interventions for total knee arthroplasty (TKA) can be confusing for the clinician, and we applaud the Prospect working group for reviewing the literature in order to address this important issue [1]. The Prospect systematic review focuses on postoperative analgesia, but it is worth emphasising the interaction between analgesia, rehabilitation and length of hospital stay. In recent years there has been an emphasis on early active mobilisation following TKA, and on reducing the length of hospital stay [2, 3]. This requires effective analgesia without the prolonged use of parenteral opioids, the ability to mobilise, and the absence of adverse effects from analgesics. Femoral nerve blockade has been shown to reduce opioid consumption and improve pain scores [1]. However there is limited evidence on how best to use femoral nerve blocks to strike the optimal balance between adequate analgesia and the timely achievement of mobility goals. Issues such as how much drug, at what concentration and rate, the optimum duration of perineural infusions, and attendant risks such as falls, were not the primary focus of the Prospect review, and still require further investigation [3–5]. The Prospect review included two studies on femoral block vs combined femoral and sciatic blocks, and each reached different conclusions on the benefit of adding sciatic block [6, 7], and duly called for further evaluation. Another study, which appears to meet the Prospect inclusion criteria, has found significantly lower opioid consumption with combined femoral and sciatic blocks compared to femoral block alone, or psoas compartment block alone after TKA [8]. This finding was most notable in the first 24 h after surgery. These results may tip the balance in favour of adding a sciatic block, particularly in terms of an opioid sparing effect. However there are important differences between the designs of these studies, especially in the use of single injections vs catheters. Again this provokes more questions about how best to apply the technique to achieve the desired outcome. We are also mindful that a lack of clear evidence to recommend a technique is not the same as evidence that a technique has no merit. The interaction between analgesia and mobility goals, and the balance between opioids and regional techniques, mean that analgesic choices are still open to debate. Further research is required to clarify how best to achieve analgesia, and avoid adverse effects, in the context of functional recovery targets.

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