Anatomical study of the adductor

canal: three-dimensional micro-

computed tomography, histological,
and immunofluorescence findings
relevant to neural blockade
Experimental
Shin Hyo Lee1,2,*†, Hee Jung Kim2,3,*, Shin Hyung Kim2,3,
Research Article
Tae-Hyeon Cho1,2,‡, Hyun-Jin Kwon1,2, Jehoon O4, Ju Eun Hong5,
Seung Hyun Nam3, Young-Il Hwang6, Hun-Mu Yang1,2,7
Korean J Anesthesiol 2023;76(3):252-260
1
https://doi.org/10.4097/kja.22499 Department of Anatomy, Yonsei University College of Medicine, 2Translational Research Unit
pISSN 2005–6419 • eISSN 2005–7563 for Anatomy and Analgesia, 3Department of Anesthesiology and Pain Medicine, Yonsei
University College of Medicine, 4Center of Biohealth Convergence and Open Sharing System,
Hongik University, Seoul, 5Department of Biomedical Laboratory Science, College of Software
and Digital Healthcare Convergence, Yonsei University MIRAE Campus, Wonju, 6Department
of Anatomy and Cell Biology, Seoul National University College of Medicine, 7Surgical Anatomy
Received: August 9, 2022
Education Center, Yonsei University College of Medicine, Seoul, Korea
Revised: September 25, 2022
Accepted: October 6, 2022
Corresponding author: Background: A precise anatomical understanding of the adductor canal (AC) and its
Hun-Mu Yang, Ph.D. neural components is essential for discerning the action mechanism of the AC block. We
Department of Anatomy, Yonsei University therefore aimed to clarify the detailed anatomy of the AC using micro-computed tomog-
College of Medicine, 50 Yonsei-ro, raphy (micro-CT), histological evaluation, and immunofluorescence (IF) assays.
Seodaemun-gu, Seoul 03722, Korea
Methods: Gross dissections of 39 thighs provided morphometric data relevant to injec-
Tel: +82-2-2228-1649
Fax: +82-2-365-0700
tion landmarks. Serial sectional images of the AC were defined using micro-CT and ul-
Email: yanghm@yuhs.ac trasonography. The fascial and neural structures of the AC proper were histologically
ORCID: https://orcid.org/0000-0003-1954-0114 evaluated using Masson’s trichrome and Verhoeff-Van Gieson staining, and double IF
staining using choline acetyltransferase (ChAT) and neurofilament 200 antibodies.
*Shin Hyo Lee and Hee Jung Kim are contributed
equally to this work as first authors. Results: The posteromedial branch insertion of the nerve to vastus medialis (NVM) into
†
the lateral border of the AC proper was lower (14.5 ± 2.4 cm [mean ± SD] above the base
Shin Hyo Lee is now with the Department of
of the patella) than the origin of the proximal AC. The AC consists of a thin subsartorial
Anatomy and Jesaeng-Euise Clinical Anatomy
fascia in the proximal region and a thick aponeurosis-like vastoadductor membrane in
Center, Wonkwang University School of
Medicine, Iksan, Korea the distal region. In the proximal AC, the posteromedial branch of the NVM (pmNVM)
‡
consistently contained both sensory and motor fibers, and more ChAT-positive fibers
Tae-Hyeon Cho is now with the Department
were observed than in the saphenous nerve (27.5 ± 11.2 / 104 vs. 4.2 ± 2.6 / 104 [counts/
of Anatomy, College of Korean Medicine,
µm2], P < 0.001).
Semyung University, Jecheon, Korea
Conclusions: Anatomical differences in fascial structures between the proximal and dis-
tal AC and a mixed neural component of the neighboring pmNVM have been visualized
using micro-CT images, histological evaluation, and IF assays.

Keywords: Anatomy; Anesthesia; Cadaver; Fascia; Histology; Immunohistochemistry.

The Korean Society of Anesthesiologists, 2023

This is an open-access article distributed under
the terms of the Creative Commons Attribution Introduction
Non-Commercial License (http://creativecommons.
org/licenses/by-nc/4.0/) which permits unrestricted
non-commercial use, distribution, and reproduc- The adductor canal (AC) is an intermuscular tunnel that conveys the saphenous nerve
tion in any medium, provided the original work is (SN) bordered by the vastus medialis (VM), adductors, and sartorius muscles [1]. The
properly cited.
AC surface is covered by a musculotendinous band called the vastoadductor membrane

252 Online access in http://ekja.org

 Korean J Anesthesiol 2023;76(3):252-260

(VAM) on the distal progression of the AC roof, which is a strong daver. Within 48 h of death, three fresh non-embalmed refrigerat-
fascia that extends between the fasciae investing the border mus- ed cadavers were investigated using double IF assays on their
cles [2,3]. The physiological extension of the interfascial space nerves within the AC.
and the composition of the fascial roof of the AC are important
factors affecting the spread of the injectate to the SN that inner- Morphometry of the AC and relevant structures
vates the knee joint [4,5]. Not much is known about the entire
fascial AC structures, although previous clinical trials have at- Experienced anatomists dissected the entire thighs including
tempted to evaluate the differences in the analgesic efficacy of their inguinal region, femoral triangle (FT), AC, adductor hiatus
AC blocks according to their target locations [6–9]. Furthermore, (AH), and base of the patella (PB). All distances from the PB to
the axonal components of the posteromedial branches of the anatomical landmarks were measured using a ruler: (1) anterior
nerve to the vastus medialis (pmNVM) that travel along the SN superior iliac spine, (2) apex of the FT, (3) insertion of the pmN-
have been predicted by their innervation patterns from gross ob- VM into the VM fascia, (4) proximal VAM border, (5) exit point
servations, but not based on the histological evidence [10–12]. of the SN from the AC, and (6) proximal end of the AH. In this
We therefore aimed to comprehensively determine the region- study, the proximal AC was defined as the proximal part of the
al structural features of the AC and pmNVM using three-di- AC, which is covered by the thin subsartorial fascia roof and
mensional micro-computed tomography (3D micro-CT), mac- reaches from the apex of the FT to the proximal border of the
roscopic and histological inspections, and ultrasonography. We thick VAM.
also investigated the motor and sensory axonal components of
the SN and pmNVM at the AC level using immunofluorescence Micro-CT preparation for 3D visualization
(IF) assays.
Based on the thigh morphometry results, four anteromedial
Materials and Methods thigh specimens from four embalmed cadavers were transected in
the axial plane at 6-cm intervals. The musculofascial tissue blocks
Study oversight that preserve the neurovascular contents of each specimen were
dehydrated with a graded series of 30%, 50%, and 70% ethanol
We obtained appropriate consent to use cadavers that had been solutions for one night each, and then soaked with phosphotung-
legally donated to the Surgical Anatomy Education Center of the stic acid to enhance the soft-tissue contrast through active infiltra-
Yonsei University College of Medicine (Approval no. 22-001). Be- tion of treatment solutions without losing the relevant AC land-
fore they died, each donor signed documents agreeing to their marks described in Fig. 1. Micro-CT images were acquired using
participation in the body donation program of the medical school a micro-CT scanner (Skyscan 1173, Bruker, Belgium) with a 70-
and to the use of their body for clinical studies. The study design kV source voltage, 114-μA source current, and 35-μm2 images.
was approved by the Institutional Review Board of Yonsei Univer- For 3D visualization and analysis, the acquired sectional images
sity Health System, although the board exempted this study from were reconstructed using NRecon and CTVox (Bruker). The 3D
a formal review due to its use of cadavers. This study was con- images representative of the AC are provided in Supplementary
ducted in accordance with the Declaration of Helsinki (2013). Video 1.

Sample recruitment AC histomorphology and neural components analysis

This study used 29 cadavers (14 male and 15 female) with a Tissue block specimens used for micro-CT analysis then un-
mean age at death of 82.2 years. Specimens with visible signs of derwent routine histological processing and cut into 5-µm-thick
deformity and previous operative procedures in the thigh were sections, which were stained using Masson’s trichrome and Ver-
excluded. Gross dissections and conventional macroscopic exam- hoeff-Van Gieson to compare the fascial components of the prox-
inations were performed on 39 thighs from 21 embalmed cadav- imal and distal parts of the AC. Choline acetyltransferase (ChAT)
ers to analyze the morphometry of the structures relevant to the selectively labels peripheral motor axons in humans [13]. To
AC. A 3D topographic analysis of the micro-CT images and his- quantify motor and sensory makeup of the pmNVM and SN, sec-
tological revalidation were performed on four embalmed cadav- tions were incubated with the primary antibody against neurofila-
ers. Ultrasonographic images were obtained from one fresh ca- ment 200 (NF200; mouse, diluted 1:400; Abcam) and ChAT (goat,

https://doi.org/10.4097/kja.22499 253
Lee et al. · Detailed anatomy of the adductor canal

Table 1. Morphometric Data of Structures Relevant to the VAM

1
Measure Value
1. PB to ASIS 41.3 ± 1.5
2. PB to FT 19.0 ± 1.5
3. PB to X 14.5 ± 2.4
4. PB to Y 13.7 ± 1.8
5. PB to Z 10.6 ± 2.4
6. PB to AH 9.4 ± 1.8
a. Proximal AC 5.2 ± 2.0
b. Distal AC 4.3 ± 1.5
Values are mean ± SD values in centimeters. AC: adductor canal (entire
AC = a + b), AH: adductor hiatus, ASIS: anterior superior iliac spine,
FT: femoral triangle apex, PB: base of patella, pmNVM: posteromedial
branch of the nerve to vastus medialis, SN: saphenous nerve, VAM:
vastoadductor membrane, VM: vastus medilais, X: insertion of the
2 pmNVM to the lateral border of the AC proper, Y: proximal margin of
3 the VAM originating from the VM, Z: exit site of the SN from the AC.
a
4

b Statistical analysis
5
6
Morphometric data are presented as mean ± SD values. To
compare motor axon counts between the pmNVM and SN at the
proximal AC, the nonparametric Mann–Whitney U test was used
due to the non-normal data distribution. All statistical analyses
PB were performed using the Statistical Package for the Social Sci-
ences (version 25.0, IBM Corp., USA), and P < 0.05 was consid-
ered significant.

5 cm Results

AC topography
Fig. 1. Morphometry of the AC-related structures. Measured distances
are listed in Table 1. AC: adductor canal, AH: adductor hiatus, AL:
adductor longus, FT: femoral triangle, PB: base of patella, pmNVM:
The AC is a subsartorial fascial compartment anterolaterally
posteromedial branch of the nerve to vastus medialis, S: sartorius, bordered by the VM and posteromedially by the adductor longus
SN: saphenous nerve, VAM: vastoadductor membrane, VM: vastus (AL) or adductor magnus (AM) muscles. Measurements from 39
medialis, green area: FT, 1: anterior superior iliac spine, 2: FT apex, 3:
thighs were used to determine the distances between the PB and
entry point of the pmNVM, 4: proximal margin of the VAM, 5: exit
site of the SN from AC, 6: proximal end of the AH, a: proximal AC, b: relevant landmarks (Fig. 1, Table 1). The AC was subdivided into
distal AC. its proximal and distal parts according to the fascia thickness.
The apex of the FT (intersection of the medial borders of the sar-
torius and AL muscles) was considered as the beginning of the
diluted 1:100; Abcam). Antigens were observed in each section proximal AC. The beginning of the proximal AC (19.0 ± 1.5 cm
using the Abcam Alexa Fluor 488 donkey antimouse IgG and Ab- from the PB) was approximately 2 cm more distal than the mid-
cam Alexa Fluor 555 donkey antigoat IgG. The ratio of point of the thigh (21 cm from the PB). The proximal AC roof
ChAT-positive neurons to the cross-sectional area of each fascicle was covered with thin fascia. At 13.7 ± 1.8 cm from the PB, the
was computed in microns squared for each cross-sectional image fascia became distinctly thickened (the true VAM) in all speci-
(Image J version 1.53n, NIH, USA). mens. The length of the entire AC between the apex of the FT
and the AH was approximately 9.5 cm. The mean length of the
proximal AC invested by the thin subsartorial fascia was 5.2 cm,

254 https://doi.org/10.4097/kja.22499
 Korean J Anesthesiol 2023;76(3):252-260

and the mean length of the distal AC invested by the thick VAM the subsartorial fascia traversing between the AL and VM was
was 4.3 cm. The entry point of the pmNVM into the lateral VM close to the femoral artery. More distally, the thick VAM appeared
border was within the proximal AC (14.5 ± 2.4 cm from the PB) between the AM and VM in all specimens. With the change of the
in 38 of 39 specimens. In one specimen the entry point was prox- distal AC roof thickness, the transition of the AL/AM proportion
imal to the apex of the FT. (cross sectional area) in the medial boundary of the AC also coin-
cided with the ultrasonography finding that the AM occupied
AC structures by micro-CT images and ultrasound more areas than the proximal AC (Fig. 2).
imaging Both the comparative location of the nerves and the compart-
mentation of the fascial layers could be identified clearly on the
The micro-CT images allowed observation of the intact struc- micro-CT images. The subsartorial proximal AC fascia was con-
tures of the AC contents without deformation due to performing nected to the fascial septum elongation from the fascia lata. Con-
direct dissection. In the proximal AC, a thin superficial layer of secutively, a thick VAM originating from the VM fascia traversed

S S
S
A A
AL AL
VM A
VM
AM AM AL
S AM
VM
L Aʹ 1 cm Aʹʹ Aʹʹʹ

S
V
A V A
V A
AL
AM
VM
Bʹ Bʹʹ Bʹʹʹ
A
B
C
S
D

A
V A A V
V
AM VM

Cʹ Cʹʹ Cʹʹʹ

A
A A AM VM
V V
V
Dʹ Dʹʹ AM Dʹʹʹ

Fig. 2. Comparison of micro-CT, gross-section, and ultrasonography images according to the relative locations. The AC roof is positioned in a
superficial position corresponding to the ultrasonographic positions. A′–D′: Cross-sectional image of anteromedial thighs on micro-CT. The
medial AC border consists of the AL (area shaded in pink) or AM (area shaded in green). Arrowheads indicate the VAM investing the distal AC. A′′‒
D′′: Gross sections of the same specimen. Arrowheads indicate the VAM. A′′′: Ultrasonography corresponding to the micro-CT and gross section
images. The intersection of the sartorius and AL (arrow) indicates the apex of the FT, which is the initiation of the proximal AC. B′′′: The area of
the AL decreased in the distal part of the proximal AC. C′′′: The thick VAM (asterisks) above the femoral vessels and the double contour of fascial
layers of the VM and VAM (arrowheads) in the distal AC. D′′′: Descending femoral vessels divided the AM into the tendinous part (superficial)
and femur insertion (deep) in the AH. A: femoral artery, AC: adductor canal, AL: adductor longus, AM: adductor magnus, FT: femoral triangle,
micro-CT: micro-computed tomography, V: femoral vein, VAM: vastoadductor membrane, VM: vastus medialis.

https://doi.org/10.4097/kja.22499 255
Lee et al. · Detailed anatomy of the adductor canal

toward the distal part of the AM, as the cross-sectional areas of cia between the AL and VM, was connected to the femoral artery
the AL decreased toward the distal femur. Furthermore, the thin by loose connective tissues. At this level, the SN (the terminal
superficial fascia continued to the subsartorial proximal AC fascia femoral nerve branch) descended lateral to the femoral artery and
invested between the subsartorial space and the distal AC VAM. medial to the VM. The pmNVM coursed adjacent to the SN and
This subsartorial fascia still existed continuously between the VM was encased by a thin fascia between the VM and subsartorial fas-
and semimembranosus muscles at the level below the AH (Fig. 3, cia at the proximal AC level (Fig. 4A). Contrary to the proximal
Supplementary Video 1). AC, the pmNVM exited the subsartorial space and was separated
from the SN in the AC proper at the distal AC level. The distal AC
Configuration of the AC contents by histological roof was identified as a double-layered structure with the appear-
observation ance of an additional thick fascia in the deeper layer. The thin
subsartorial fascia, which elongated from the FT invested the
The fascia forming the AC roof, composed of the proximal thin VAM as a superficial layer in the distal AC. Consequently, the dis-
and distal thick fascia, also differed with the anatomical site on tal AC roof was composed of multiple fascial layers. Microscopi-
microscopic analysis. In the proximal AC, a thin layer elongating cally, the VAM consisted of relatively parallel collagen bundles,
from the fascia investing the FT, consisting of the subsartorial fas- compared to the subsartorial fascia that had thin collagen fibers

G
G
S S

A A
V VM
VM
ASIS AM AL
AM A
L
S
AL S
L A Aʹ
A
Aʹ

B
C PB S S
G G

AM A VM VM
SM
V
A

BF
B C

Fig. 3. Detailed micro-CT images of the AC. A: The appearance of the continuum of the fascia lata (asterisk) and subsartorial fascia (shaded in
red). The SN (shaded in yellow) and the pmNVM (red arrow) are separated in the more distal section of the image (A′). B: The thick VAM (shaded
in blue) inserted to the AM fascia. C: The subsartorial fascia (arrowheads) between the fascia lata and the semimembranosus muscle fascia and the
posterior fascia (arrows) between the biceps femoris and the VM. AC: adductor canal, AM: adductor magnus, ASIS: anterior superior iliac spine,
G: gracilis, micro-CT: micro-computed tomography, pmNVM: posteromedial branch of the nerve to vastus medialis, S: sartorius, SN: saphenous
nerve, VAM: vastoadductor membrane, VM: vastus medialis.

256 https://doi.org/10.4097/kja.22499
 Korean J Anesthesiol 2023;76(3):252-260

AL

VM
A
A
V
L 5 mm A Aʹ
200 µm

A
B

AM
A VM

V
B Bʹ
5 mm 200 µm

Fig. 4. Histology of the fascia investing the AC. A: A single layer of subsartorial fascia (arrows) at the apex of the FT level, the beginning of the
proximal AC. Structures encircled by red and green dotted lines indicate the SN and pmNVM, respectively. A′ : Magnification of the box in A.
B: Distinct aponeurosis-like fascia (arrowheads) elongating from the VM fascia forming the barrier to the subsartorial space, as a distal AC roof.
B′: Multiple VAM layers covered with superficial thin fascia (arrows) in a magnification of the box in B. AC: adductor canal, FT: femoral triangle,
pmNVM: posteromedial branch of the nerve to vastus medialis, SN: saphenous nerve, VAM: vastoadductor membrane, VM: vastus medialis.

running in multiple directions with profound elastic fibers (Fig. in the proximal AC has a greater proportion of motor axons than
4B, Supplementary Fig. 1). the SN, and also a coexistence of motor- and sensory-dominant
fascicles.
Axonal components analysis
Discussion
The axonal components of the nerves related to the selective
sensory block were identified by applying IF labeling to the This study used micro-CT and histological evaluation to con-
transverse sections of the pmNVM and SN. Motor axon marker firm that the entire AC, from the apex of the FT to the AH, is
expression (ChAT) was dominantly identified in the pmNVM. roofed by multiple fascial layers, consisting of the proximal thin
In contrast, the SN mostly comprised ChAT-negative axons, with and distal thick parts of the AC. Our ultrasonography anatomical
smaller diameters than the ChAT-positive motor axons in the findings indicated that the starting point of the AC was the inter-
pmNVM (Fig. 5). The double-positive axons counts (ChAT and section of the medial borders of the sartorius and the AL, and
NF200) per fascicle area confirmed that the proportion of motor identified the aponeurotic thick VAM as the AL became smaller.
axon population in the pmNVM was significantly greater than The pmNVM, separated from the AC proper by a thin fascia,
that in the SN at the proximal AC level (27.5 ± 11.2 / 104 vs. 4.2 contained a mixed axonal component with both motor and sen-
± 2.6 / 104 [counts/µm2], P < 0.001). At low magnification, sory fibers at the proximal AC level.
nerve fascicles that mostly comprised ChAT-negative axons were Recent anatomical studies have constantly observed a strong
also identified in the pmNVM. This indicates that the pmNVM aponeurotic membrane in the distal part of the AC [1–3].

https://doi.org/10.4097/kja.22499 257
Lee et al. · Detailed anatomy of the adductor canal

200 µm 200 µm
A B

(x104)
50

chAT+ axon counts/µm2

40

30

20

10

100 µm 100 µm pmNVM SN

Aʹ Bʹ C

Fig. 5. Double IF staining using ChAT and NF200 antibodies to identify the axon components of the nerve fascicle. Low magnification images of
the pmNVM (A) and SN (B) fascicles. A′: Representative images of ChAT-positive axons in a pmNVM fascicle (magnification of the box in A).
Red areas indicate motor nerve fibers overlapped by ChAT and NF200 signals. B′: Magnification of the box in B. ChAT-negative axons (green)
mostly consist of the SN in the proximal AC. C: Axon counts of double-positive ChAT and NF200 stains according to the area of each pmNVM
and SN fascicle (104 µm2). *: P < 0.001. AC: adductor canal, ChAT: choline acetyltransferase, IF: immunofluorescence, NF200: neurofilament 200,
pmNVM: posteromedial branch of the nerve to vastus medialis, SN: saphenous nerve.

Bendtsen et al. [9] defined the fascial roof as the VAM and stated section of the AL is almost absent.
that the VAM divided the intramuscular space between the AC This study found that a thin subsartorial fascia investing the
into the AC proper and the subsartorial space. Accordingly, our proximal AC extended to the distal AC, as observed on the anteri-
macroscopic findings confirmed that a distinct aponeurotic mem- or side at the level below the AH using micro-CT images and his-
brane, the VAM, presented only in the distal half of the AC. More- tological assays. The subsartorial fascia of the FT traversing the
over, ultrasonography findings from Wong et al. [14] indicated proximal AC continuously invested the VAM in the distal AC.
the VAM characteristic of a double contour at the distal AC. In This result was consistent with Tran et al. finding that the distal
our micro-CT image wherein the distal thick fascia overlapped AC was roofed by two superficial thin membrane layers and a
the VM fascia, the AL occupied a very narrow area of the medial deep aponeurosis of the VM obliquus (the lowest horizontal VM
AC border. This suggests that ultrasonography can be used to fibers) [11]. The subsartorial fascia, which elongates from the AC
identify the distal thick fascia, which begins at the level where the proper and continues to the superior region of the knee might re-

258 https://doi.org/10.4097/kja.22499
 Korean J Anesthesiol 2023;76(3):252-260

strict direct injectate spreading from the AC proper to the anteri- Acknowledgements
or knee. Instead, it would increase the risk of posterior leakage to
the popliteal fossa after a distal AC block [14]. We are grateful to the people who very nobly donated their
The distal pmNVM innervates most of the medial joint capsule bodies to the Surgical Anatomy Education Centre at the Yonsei
[12,15], whereas the SN primarily provides cutaneous innerva- University College of Medicine. Additionally, the authors wish to
tion. Based on studies of the gross anatomical branching patterns thank Jun Ho Kim, Jong Ho Bang, and Tae-Jun Ha for their tech-
and the intramuscular passage of the nerve, the NVM has lateral nical support (all are staff members of the Surgical Anatomy Edu-
proximal muscular branches running toward the superior part of cation Centre at the Yonsei University College of Medicine).
the VM after coursing a short distance from the inguinal liga-
ment, before terminating at the pmNVM descending along the Funding
SN [16]. An enhanced understanding of the entry point of the
NVM branches may help refine the AC block approach and mini- This work was supported by the National Research Foundation
mize quadriceps femoris weakness [17]. The most-inferior inser- of Korea (NRF) grant funded by the Korea government (No.
tion of the pmNVM to the AC proper was mostly within the mid- 2020R1F1A1058123 to H-MY) and Basic Science Research Pro-
point of the entire AC in the present study. The pmNVM laterally gram through the NRF funded by the Ministry of Education (No.
descends within its own fascia, separated from the AC proper in 2021R1F1A1045873 to SHK). No other external funding or com-
the proximal AC, whereas the pmNVM gradually exits the subsa- peting interests declared.
rtorial space of the distal AC proper (Fig. 4). This result supports
the study of Tran et al. [11] finding that a dye injected into the Conflicts of Interest
proximal AC proper penetrates through the proximal thin roof
and stains the pmNVM in cadavers. Moreover, we verified that No potential conflict of interest relevant to this article was re-
the pmNVM is a mixed nerve and consists of both motor ported.
(ChAT-positive/NF200-positive) and sensory (ChAT-negative/
NF200-positive) fibers. This is consistent with recent evidence Data Availability
that the pmNVM might also provide sensory innervation to the
knee giving off the superior medial genicular nerve [12]. This re- All data generated or analyzed during this study are inclyded in
sult also implies that pmNVM blockade may lead to a certain this published article and its supplementary infromation files.
amount of motor block. Further studies combined with the histo-
logical and morphometric methods could help clinicians refine Author Contributions
the AC block technique.
This study had some limitations. The absolute axon counts of Shin Hyo Lee (Conceptualization; Formal analysis; Visualization;
the motor and sensory proportions and the proximal courses of Writing – original draft)
the NVM and SN with variant bifurcation patterns were not Hee Jung Kim (Formal analysis; Methodology; Writing – original
performed. The NVM and SN arose from the common femoral draft)
nerve branch in the proximal FT and then had the muscular Shin Hyung Kim (Funding acquisition; Project administration;
branches lateral to the superior part of the VM [17]. This study Supervision; Writing – review & editing)
intensively investigated the proximal AC region, and further Tae-Hyeon Cho (Data curation; Formal analysis; Software; Visu-
studies are needed to clarify the anatomy and neural compo- alization)
nents of the distal AC and popliteal fossa region with larger Hyun-Jin Kwon (Data curation; Formal analysis; Investigation)
sample sizes. Jehoon O (Data curation; Methodology; Visualization)
In conclusion, 3D micro-CT and histological investigations Ju Eun Hong (Investigation; Methodology)
have revealed that the pmNVM, which is separated from the AC Seung Hyun Nam (Data curation; Methodology; Software)
proper by a very thin fascia contains both sensory fibers and Young-Il Hwang (Supervision; Writing – review & editing)
some motor fibers at the proximal AC level. Multidirectional ob- Hun-Mu Yang (Funding acquisition; Project administration; Re-
servations using micro-CT, histology, and ultrasonography could sources; Supervision; Writing – review & editing)
assist clinicians in further investigating and refining neural
blockade efficacy.

https://doi.org/10.4097/kja.22499 259
Lee et al. · Detailed anatomy of the adductor canal

Supplementary Materials Reg Anesth Pain Med 2021; 46: 581-99.

6. Lee B, Park SJ, Park KK, Kim HJ, Lee YS, Choi YS. Optimal loca-
Supplementary Video 1. The 3D sectional micro-CT image corre- tion for continuous catheter analgesia among the femoral trian-
spondent to Fig. 3. A: femoral artery, AL: adductor longus, AM: gle, proximal, or distal adductor canal after total knee arthro-
adductor magnus, G: gracilis, pmNVM: posteromedial branch of plasty: a randomized double-blind controlled trial. Reg Anesth
the nerve to vastus medialis, S: sartorius, SM: semimembranosus, Pain Med 2022; 47: 353-8.
SN: saphenous nerve, V: femoral vein, VM: vastus medialis. 7. Vora MU, Nicholas TA, Kassel CA, Grant SA. Adductor canal
Supplementary Fig. 1. Verhoeff-Van Gieson staining of the AC. block for knee surgical procedures: review article. J Clin Anesth
(A) Elastic fibers (black fragmented fibers) in the thin subsartorial 2016; 35: 295-303.
fascia of the proximal AC. (B) Thick collagen bundles of the 8. Jæger P, Jenstrup MT, Lund J, Siersma V, Brøndum V, Hilsted
VAM. The magnification of the blue boxes . Blue dotted lines: SN, KL, et al. Optimal volume of local anaesthetic for adductor canal
green dotted lines: pmNVM. A: femoral artery, AC: adductor ca- block: using the continual reassessment method to estimate
nal, AM: adductor magnus, pmNVM: posteromedial branch of ED95. Br J Anaesth 2015; 115: 920-6.
the nerve to vastus medialis, SN: saphenous nerve, V: femoral 9. Bendtsen TF, Moriggl B, Chan V, Børglum J. The optimal anal-
vein, VAM: vastoadductor membrane, VM: vastus medialis. gesic block for total knee arthroplasty. Reg Anesth Pain Med
2016; 41: 711-9.
ORCID 10. Runge C, Moriggl B, Børglum J, Bendtsen TF. The spread of ul-
trasound-guided injectate from the adductor canal to the genic-
Shin Hyo Lee, https://orcid.org/0000-0001-7031-7722 ular branch of the posterior obturator nerve and the popliteal
Hee Jung Kim, https://orcid.org/0000-0002-2143-3943 plexus: a cadaveric study. Reg Anesth Pain Med 2017; 42: 725-
Shin Hyung Kim, https://orcid.org/0000-0003-4058-7697 30.
Tae-Hyeon Cho, https://orcid.org/0000-0001-7230-620X 11. Tran J, Chan VW, Peng PW, Agur AM. Evaluation of the proxi-
Hyun-Jin Kwon, https://orcid.org/0000-0001-7752-6172 mal adductor canal block injectate spread: a cadaveric study. Reg
Jehoon O, https://orcid.org/0000-0003-4351-3183 Anesth Pain Med 2019. Advance Access published on Dec 25,
Ju Eun Hong, https://orcid.org/0000-0002-5357-4476 2019. doi: 10.1136/rapm-2019-101091.
Seung Hyun Nam, https://orcid.org/0000-0002-5736-2606 12. Tran J, Peng PW, Lam K, Baig E, Agur AM, Gofeld M. Anatomi-
Young-Il Hwang, https://orcid.org/0000-0002-5777-7983 cal study of the innervation of anterior knee joint capsule: impli-
Hun-Mu Yang, https://orcid.org/0000-0003-1954-0114 cation for image-guided intervention. Reg Anesth Pain Med
2018; 43: 407-14.
References 13. Gesslbauer B, Hruby LA, Roche AD, Farina D, Blumer R,
Aszmann OC. Axonal components of nerves innervating the
1. Uhl JF, Gillot C. Anatomy of the Hunter’s canal and its role in the human arm. Ann Neurol 2017; 82: 396-408.
venous outlet syndrome of the lower limb. Phlebology 2015; 30: 14. Wong WY, Bjørn S, Strid JM, Børglum J, Bendtsen TF. Defining
604-11. the location of the adductor canal using ultrasound. Reg Anesth
2. Tubbs RS, Loukas M, Shoja MM, Apaydin N, Oakes WJ, Salter Pain Med 2017; 42: 241-5.
EG. Anatomy and potential clinical significance of the vastoad- 15. Laurant D, Peng P, Girón Arango L, Niazi AU, Chan VW, Agur A,
ductor membrane. Surg Radiol Anat 2007; 29: 569-73. et al. The nerves of the adductor canal and the innervation of the
3. Elazab EE. Morphological study and relations of the fascia vas- knee: an anatomic study. Reg Anesth Pain Med 2016; 41: 321-7.
to-adductoria. Surg Radiol Anat 2017; 39: 1085-95. 16. Thiranagama R. Nerve supply of the human vastus medialis
4. Bendtsen TF, Moriggl B, Chan V, Børglum J. Basic topography of muscle. J Anat 1990; 170: 193-8.
the saphenous nerve in the femoral triangle and the adductor 17. Nada E, Elmansoury A, Elkassabany N, Whitney ER. Location of
canal. Reg Anesth Pain Med 2015; 40: 391-2. the entry point of the muscular branch of the nerve to vastus
5. Chin KJ, Versyck B, Elsharkawy H, Rojas Gomez MF, Sa- medialis. Br J Anaesth 2021; 127: e58-60.
la-Blanch X, Reina MA. Anatomical basis of fascial plane blocks.

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