Article Text

Download PDFPDF

Anatomical evidence supporting the revision of classical landmarks for genicular nerve ablation
  1. Loïc Fonkoue1,2,
  2. Catherine Wydemans Behets1,
  3. Arnaud Steyaert3,4,
  4. Jean-Eric Kouame Kouassi2,
  5. Christine Detrembleur2 and
  6. Olivier Cornu2,5
  1. 1 Pole of Morphology, Experimental and Clinical Research Institute, Université Catholique de Louvain, Brussels, Belgium
  2. 2 Neuro-Musculo-Skeletal Pole, Experimental and Clinical Research Institute, Université Catholique de Louvain, Brussels, Belgium
  3. 3 Department of Anesthesiology and Pain Medicine, Cliniques universitaires Saint-Luc, Bruxelles, Belgium
  4. 4 Institute of Neuroscience, Université catholique de Louvain, Brussels, Belgium
  5. 5 Department of Orthopedics and Trauma, Cliniques universitaires Saint-Luc, Bruxelles, Belgium
  1. Correspondence to Dr Loïc Fonkoue, Pole of Morphology, Experimental and Clinical Research Institute, Universite catholique de Louvain, Brussels, Belgium; loic.fonkoue{at}uclouvain.be

Statistics from Altmetric.com

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.

We would like to thank Tran et al 1 for their interest in our paper.2 They expressed their concerns about two of the five anatomical landmarks we proposed to target with increased accuracy for genicular nerve ablation: the superior medial genicular nerve (SMGN) and the superior lateral genicular nerve (SLGN). We would like to respond to the issues raised and to clarify some anatomical and methodological disagreements.

Concerning our landmark for SMGN, located just anterior to the adductor tubercle (AT), Tran et al 1 stated that it would capture ‘only the distal branches of SMGN which supply the knee joint capsule in the region of medial epicondyle (figure 1B, blue lesion)’. When looking carefully at their figure 1B,1 there seems to be a confusion between the AT and the medial epicondyle (ME): the blue lesion (their representation of our landmark) is incorrectly placed above the ME rather than just anterior to the AT. If that blue lesion is raised a little bit to fit the real point we described (figure 9),2 it would capture the trunk of the SMGN, like what we observed in our validation study.2 It is important to note that in their figure 1B,1 the classical lesion (orange) has been moved posteriorly, whereas it should be normally centered at the midpoint of the femoral shaft, represented by the longitudinal dashed line. Moreover, the distal distribution they draw in their figure map do not correspond to our findings.2 3 In a very recent review of the knee joint innervation published at the same time as our current study, Roberts et al 4 stated that ‘the adductor tubercle is a more precise anatomic target for the SMGN than the current target’. In our study,2 the injection performed just anterior to the AT captured the trunk of the nerve, before its distribution, leading to ablation of all its terminal branches. The classical landmark, at the midpoint of the femoral shaft, would not capture the SMGN (figure 1).

Figure 1

Comparison of classical (SLGN/c, SMGN/c, and IMGN/c) and our proposed landmarks for fluoroscopic-guided GNB and RFA. The trajectory of the SLGN (blue) from sciatic or common fibular nerve, SMGN (yellow) from nerve to vastus medialis and IMGN (green) have been drawn on fluoroscopic images. ((A) (A-P view) and (B) (lateral view)) Differences between classical and our proposed treatment targets areas for the SMGN (white arrow), and SLGN (black arrow) on the A-P and lateral views. (C) Trunk of the SMGN (yellow) captured before its distribution, by the active tip of an RF cannula with our new positioning (white). Note that the classical electrode position (upper black electrode) could not intercept the trunk of SMGN. (D) SLGN trajectory (blue) captured by the active tip of an RF cannula with our new positioning (white). If the classical electrode (upper black electrode) is lowered a bit, it would target only the transversal terminal branch of the SLGN. GNB genicular nerve blockade; IMGN, inferior medial genicular nerve; RFA, radiofrequency ablation; SLGN, superior lateral genicular nerve; SMGN, superior medial genicular nerve.

The Tran et al’s5 description of the distribution of the SLGN is somewhat short. They just stated that the SLGN ‘joins the superior lateral genicular vessels just before entering the knee capsule’. Similar to Sutaria et al,6 who performed the only published study specifically dedicated to the terminal branches of the SLGN, we found that the SLGN runs under the deep surface of the biceps femoris muscle toward the area connecting the lateral femoral condyle and the posterior edge of the lateral side of femoral shaft, and then divides into two terminal branches: a transversal branch (lateral retinacular nerve) and a longitudinal (descending) branch.2 These can be observed on Tran et al’s figure 2B.5 Based on that figure, an injection performed at the point of bifurcation of the SLGN would capture both terminal branches. Surprisingly, on their figure 1A1 (dissection), Tran et al represented the classical landmark for the SLGN (orange lesion) almost behind the midline. If the orange lesion was centered on the midpoint of the femoral shaft (longitudinal dashed line), corresponding then to the true classical target, the SLGN would not be captured. Moreover, if our proposed landmark was properly placed on the superior edge of the femoral condyle (horizontal dashed line), it would capture the nerve before its bifurcation, ablating all its terminal branches. Although with a slightly different terminology, the Roberts et al’s4 proposed target for this nerve is similar to ours. The classical landmark would only targets its transversal terminal branch.

In conclusion, the need for revisiting anatomical landmarks for GNB/RFA is emphasized by a number of recently published studies based on anatomical updates (including Tran et al’s5 study), proposing modified targets.4 7 8 Also, recent reviews9 10 of the effectiveness of RFA to relieve chronic knee pain concluded that the anatomical basis is unclear and more research is needed to identify better targets. This shows that there is a real need of precise, validated anatomical landmarks for GNB/RFA to optimize clinical outcomes.11 In their conclusion, Tran et al 1 stated that ‘the accuracy of their proposed landmarks should not be concluded as the need to revise classical landmarks’. This is paradoxical since the need to revise the classical landmarks is also corroborated by the appropriate analysis of the results of their cadaveric dissections.

References

Footnotes

  • Contributors LF contributed to the manuscript writing. CWB, AS, J-EKK, CD, and OC contributed to the manuscript revision.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; internally peer reviewed.

Linked Articles