Letters to the Editor: Letter to the Editor
To the Editor
We read with great interest the recent clinical study conducted by Rousseau-Saine et al1 evaluating knee extensor muscle strength 6 weeks postoperatively from unilateral total knee arthroplasty. The authors use a continuous adductor canal block in one of their treatment arms. We would like to discuss the inconsistency of the authors’ description of the adductor canal and highlight the debate that has evolved over the past couple of years regarding the definition of the adductor canal and potential clinical significance.2
The authors define the adductor canal block location in their study as halfway between the anterior superior iliac spine and the patella. Previous literature, as the authors correctly cite, used similar terminology to define what was perceived to be the adductor canal. However, various researchers have challenged this definition, even before the commencement of this study, such that the halfway point between anterior superior iliac spine and the patella most likely represents the femoral triangle.3,4 In contrast, the adductor canal proper is consistently found to be distal to this point3,4 and begins when the medial border of the sartorius muscle intersects the medial border of the adductor longus muscle, which can be observed via ultrasound guidance.3 Furthermore, the vastoadductor membrane can be used as a confirmatory ultrasonographic finding to locate the adductor canal proper.3
The clinical implications remain speculative because there is a void of information comparing the analgesic efficacy of the femoral triangle block to the adductor canal proper in patients undergoing total knee arthroplasty. It is important to note that although communicative with the adductor canal, the femoral triangle contains the saphenous nerve, nerve to vastus medialis, and medial femoral cutaneous nerve.4 Blockade of these nerves within the femoral triangle will provide pain relief to the anteromedial aspect of the patella although the contributions of each individual nerve have yet to be determined. In the adductor canal proper, the saphenous nerve is the only nerve noted to reliably lie within the canal, while the nerve to the vastus medialis rests in its own fascial sheath superficial to the vastoadductor membrane.4,5
We believe that the authors incorrectly interpret the adductor canal for the femoral triangle in their study. As the clinical significance with respect to outcome measures between a femoral triangle and adductor canal block is unknown, we urge that future studies characterize their block technique accordingly so that we can ultimately learn if a clinically meaningful difference exists or whether this is simply an academic discussion.
Jason K. Panchamia, DOAdam D. Niesen, MDAdam W. Amundson, MDDepartment of Anesthesiology and Perioperative MedicineMayo ClinicRochester, MinnesotaPanchamia.Jason@mayo.edu
1. Rousseau-Saine N, Williams SR, Girard F, et al. The effect of adductor canal block on knee extensor muscle strength 6 weeks after total knee arthroplasty: a randomized, controlled trial. Anesth Analg. 2018;126:1019–1027.
2. Bendtsen TF, Moriggl B, Chan V, Pedersen EM, Børglum J. Redefining the adductor canal block. Reg Anesth Pain Med. 2014;39:442–443.
3. Wong WY, Bjørn S, Strid JM, Børglum J, Bendtsen TF. Defining the location of the adductor canal using ultrasound. Reg Anesth Pain Med. 2017;42:241–245.
4. Bendtsen TF, Moriggl B, Chan V, Børglum J. The optimal analgesic block for total knee arthroplasty. Reg Anesth Pain Med. 2016;41:711–719.
5. Runge C, Moriggl B, Børglum J, Bendtsen TF. The spread of ultrasound-guided injectate from the adductor canal to the genicular branch of the posterior obturator nerve and the popliteal plexus: a cadaveric study. Reg Anesth Pain Med. 2017;42:725–730.