Letter to the Editor: Single-injection or Continuous Femoral Nerve Block for Total Knee Arthroplasty?

To the editor, I read the study by Albrecht et al. [1] with great interest. The authors should be commended for attempting to answer the complex question of whether there is any benefit of continuous femoral nerve block over a single shot nerve block. Clearly this was one of the major unanswered questions in the meta-analysis from Paul et al. [3]. However, there seem to be several problems with this study. First, their choice of ropivacaine concentrations was odd, given previous work by Brodner et al. [2] who showed 0.1% ropivacaine to be ineffective when used as a continuous infusion for femoral nerve blockade. Was this overlooked, or were Albrecht et al [1] certain that with ultrasound guidance for placement of catheters their accuracy was such that they could use 0.1% ropivacaine successfully? Second, it seems unusual that their patient cohort had such high pain scores despite what seems like an exceptional analgesic regimen. Certainly, the pain scores reported were different (roughly two points higher, a clinically significant difference) than a group of patients with a very similar analgesic regimen in a study by Spangehl et al. [6]. This, combined with the lack of ability to show any difference in quadriceps strength between the three groups, calls into question the success of the continuous femoral nerve block. Certainly, a difference in quadriceps strength has been an important finding of those studies looking at differences between adductor canal and femoral nerve blocks [4, 5]. While the tide may be turning against continuous femoral nerve blockade following TKA, we must be careful with the evidence we base this on.