Original article Regional Anesthesia & Pain Medicine: first published as 10.1136/rapm-2018-000002 on 3 January 2019. Downloaded from Spread of dye injectate in the distal femoral triangle versus the distal adductor canal: a cadaveric study David F Johnston,1 Nicholas D Black,2 Rebecca Cowden,3 Lloyd Turbitt,1 Samantha Taylor4

1Department of Anaesthesia ABSTRACT the sartorius muscle superficially, the vastus medi- and Perioperative Medicine, The Background and objectives The nerve to vastus alis muscle (VMM) anterolaterally and the adductor Royal Victoria Hospital, Belfast Trust, Belfast, UK medialis (NVM) supplies sensation to important longus muscle (ALM) and adductor magnus muscle 2Department of Anesthesia and structures relevant to total knee arthroplasty via a medial posteromedially. The AC extends proximally from Perioperative Medicine, Toronto parapatellar approach. There are opposing findings in the apex of the femoral triangle (FT), at which Western Hospital, Toronto, ON, the literature about the presence of the NVM within the point it communicates with that compartment, Canada 3 adductor canal (AC). The objective of this cadaveric study and distally to the adductor hiatus, through which Undergraduate, Queen’s University Belfast, Belfast, UK is to compare the effect of injection site (distal femoral it communicates openly with the popliteal fossa. 4Centre for Biomedical Sciences triangle (FT) vs distal AC) on injectate spread to the Compared with femoral nerve block, an AC block Education, Queen’s University saphenous nerve (SN) and the NVM. has the desirable effect of preserving quadriceps Belfast, Belfast, UK Methods Four unembalmed fresh-frozen cadavers function while maintaining a similar analgesic acted as their own control with one thigh receiving profile.4,5 Correspondence to 20 mL of dye injected via an ultrasound-guided Dr David F Johnston, A consistent contributor of knee innervation is Department of Anaesthesia and injection in the distal FT while the other thigh received provided by the nerve to vastus medialis (NVM). Perioperative Medicine, The an ultrasound-guided injection in the distal AC. A The NVM has large intramuscular and extramus- Royal Victoria Hospital, Belfast standardized dissection took place 1 hour later to cular branches that travel obliquely through and Trust, Belfast BT12 6BA, UK; observe the extent of staining to the NVM and SN in all 6 davidf. johnston@belfasttrust. round the medial (deep) aspect of the VMM belly. hscni.net cadaver thigh specimens. These branches are in close proximity to the junc- Results In all specimens where the injectate was tion of the medial epicondyle and femoral shaft and

Received 20 October 2017 introduced into the distal FT, both the SN and NVM were terminate distally on the anteromedial knee capsule copyright. Revised 17 April 2018 stained. In contrast, when the dye was administered in 7 Accepted 22 April 2018 via the medial retinacular nerve. It is this supply the distal AC only the SN was stained. to the medial retinacular complex that makes the Conclusions Our findings suggest that an injection in NVM such a vital nerve to target when managing the distal AC may be suboptimal for knee analgesia as pain for patients undergoing surgery involving the it may spare the NVM, while an injection in the distal medial region of the knee at the distal portion of FT could provide greater analgesia to the knee but may the femur and the anterior capsule (ie, TKA via a result in undesirable motor blockade from spread to the medial parapatellar approach).8 nerve to vastus intermedius. There is inconsistency in the literature as to the presence of the NVM within the AC. Burckett-St Laurant et al found 100% of the intramuscular INTRODUCTION NVM branches and 35% of extramuscular branches within the AC.6 In contrast, Horner and Dellon

Total knee arthroplasty (TKA) is a common surgical http://rapm.bmj.com/ describe the NVM to be within the VMM belly in procedure for arthritis and is increasingly prevalent 9 with an ageing population. It is frequently associ- 90% of subjects throughout the AC. In addition, ated with severe postoperative pain, particularly the NVM has been shown to travel in a separate on movement.1 To enable successful rehabilita- fascial sheath distinct from the AC below the level 10 tion following TKA, multimodal analgesia incor- of the FT. porating a regional anesthetic technique should A further explanation for this variation in dissec- be used. Ideally, the regional anesthetic technique tion findings is the disparity in the definition of 11 should alleviate pain without causing significant leg where exactly the AC is located in the thigh. on 27 March 2019 by guest. Protected weakness. Manickam et al described the injection of local anes- Combining proximal nerve blocks (eg, femoral, thetic in the distal AC, just proximal to the adductor sciatic, and obturator) provides optimal analgesia hiatus to obtain an isolated saphenous nerve (SN) 12 for TKA,2 but the muscle weakness induced can block to provide medial ankle analgesia. Lund et impair postoperative mobility and contribute to an al described a more proximal approach directed © American Society of Regional 3 by surface anatomy to place local anesthetic at the Anesthesia & Pain Medicine increased risk of falls. Blocking nerves at a more 2019. No commercial re-use. distal site to maximize inhibition of nociceptive midpoint between the anterior superior iliac spine See rights and permissions. afferents while minimizing motor involvement is (ASIS) and the base of the patella to provide anal- Published by BMJ. desirable. gesia to the anterior knee.13 Using surface anatomy To cite: Johnston DF, One peripheral block that has gained much popu- to identify the midpoint of the thigh will result in Black ND, Cowden R, et al. larity for TKA is the adductor canal (AC) block. local anesthetic being injected into the FT, not the Reg Anesth Pain Med This involves depositing local anesthetic within the AC.14 This problem was highlighted in a recent 2019;44:39–45. triangular shaped neurovascular tunnel formed by meta-analysis comparing AC block with femoral

Johnston DF, et al. Reg Anesth Pain Med 2019;44:39–45. doi:10.1136/rapm-2018-000002 39 Original article Regional Anesthesia & Pain Medicine: first published as 10.1136/rapm-2018-000002 on 3 January 2019. Downloaded from nerve block where the authors concluded that a high variation in Injections were all performed by the same investigator (NB). A location of AC block performed in the literature made it difficult saline flushed 90 mm SonoPlex 20 G needle (Pajunk, Geisingen, to draw strong conclusions.15 Germany) attached to a 20 mL syringe containing saline was The inconsistency of anatomical study findings attempting to advanced in plane from an anterolateral to posteromedial locate the NVM in the AC and the variation in anatomical land- direction. Identical depth and gain settings were used for each mark description of the AC in study designs may explain why a injection. Distal FT or AC injections were carried out according degree of uncertainty exists regarding which nerves are affected to the coin toss at the exact point previously marked on the when one carries out what they perceive to be an AC block. specimen thigh. Once the needle tip had traversed through the The primary objective of this cadaver study is to determine deep fascia of the sartorius muscle at the 9–11 o’clock position the effect of injectate location site by comparing an injection relative to the superficial femoral artery, 2 mL of saline was in the distal FT with an injection in the distal AC on achieving injected to confirm position (red asterisk marked in figures 1 successful spread to the NVM. and 2). Once confirmed, a 20 mL syringe containing 19.5 mL Secondary objectives include: of methyl cellulose mixed with 0.5 mL green ink was attached ► Demonstration of a separate fascial sheath present around to the needle connecter. Continuous pressure was used to inject the NVM in the AC and if this could inhibit spread of injec- the entire contents over 30 s without moving the needle from its tate to this important nerve. confirmed position. ► Using discrete ultrasonographical landmarks to identify A separate study investigator (RC) performed all dissections reproducible locations in the distal FT and distal AC and which were commenced exactly 1 hour after injectate comple- comparing these with mid-thigh measurements based on tion. A longitudinal incision was made from the medial tibial surface anatomy landmarks of ASIS and the inferior border plateau as far superiorly as possible toward the midpoint of the of the patella. inguinal crease. A second incision was made from the ASIS to meet the proximal aspect of the first. A transverse incision was METHODS then made from the medial tibial plateau laterally toward the This cadaveric study was conducted in June 2017 within the head of the fibula. This pattern of dissection allowed reflection Anatomy Licensed Area in the Centre for Biomedical Sciences of the skin and subcutaneous tissue overlying the thigh laterally Education at Queen’s University Belfast. Four unembalmed fresh- in one piece. frozen human cadavers with no evident scars from previous hip, After skin and subcutaneous fat was reflected, the sartorius thigh, or knee surgery or trauma were used for this anatomical muscle was incised proximally, close to its origin at ASIS and study. Consent for anatomical examination had been obtained distally at the pes anserinus. The sartorius muscle was reflected medially in one piece to expose the underlying subsartorial canal. from each of the donors whose remains were used for this study. copyright. Identifiable information of the deceased (such as height, weight, The femoral nerve was identified in the FT, immediately inferior medical history, or ethnic background) was not available to study to the inguinal ligament. The branches of the nerve were then investigators. followed distally until the NVM and SN were located. Once the Prior to ultrasound-guided determination of injection loca- NVM had been located, the nerve with its muscular branches tions, surface anatomy landmarks frequently used in the liter- was dissected carefully taking care not to contaminate findings ature to identify the midpoint of the thigh were marked on the with spill of injected contents. After NVM dissection, the SN cadavers. These landmarks included the ASIS, the distal sartorius was then dissected out of the AC. All dissection findings were segment at the medial epicondyle of the femur and the midpoint photographed and archived by an independent observer blinded at the base of the patella. to injectate group.

Distal FT injection point RESULTS A 13.6 MHz 6 cm high-frequency linear transducer Sonoite Results from the surface landmarks and cadaver age are recorded Edge (FUJIFILM SonoSite, Bothell, Washington) was used to in table 1. In all eight specimens, the SN and NVM were identi- http://rapm.bmj.com/ confirm FT position by scanning distally from the ASIS along fied. Results for staining of these nerves are displayed in figure 4. the sartorius muscle path (DFJ). The distal FT injection point In all specimens where the injectate was introduced into the was marked 1 cm proximal to the triangle apex (ie, its distal distal FT, the SN and NVM were both stained, while in all spec- margin). This was identified at the point where medial borders imens where the distal AC injection was performed, only the SN of sartorius muscle and ALM aligned (figure 1).11 was stained. A consistent finding was the presence of the tough fascial layer

of the vastoadductor membrane. This surrounded the AC and on 27 March 2019 by guest. Protected Distal AC injection point seemed to prevent the spread of the four AC injectates toward The AC was then scanned distally until the femoral artery could a more superficial and proximal direction. This fascial layer was be seen descending deep toward the adductor hiatus (DJ). The separate from the deep connective tissue layer of the investing point where the femoral vessels plunge between ALM and grac- sartorius muscle fascia. ilis muscles was taken as the distal margin of the AC.16 This is demonstrated in figure 2. The injection location was marked at 1 cm proximal to the divergence of the femoral artery at the AC DISCUSSION distal margin. This is the first cadaveric study to directly compare the impact Surface markings for injection points and surface anatomy of injection location on the reliability of staining the NVM using landmarks are shown in figure 3. reproducible sonographic landmarks. Numerous anatomical Each cadaver acted as their own control to compare injectate studies have confirmed the importance of the NVM contribution spread (ie, where an FT injection was placed in one thigh, an AC to knee innervation.6 17–20,, This is relevant for TKA via medial injection would be placed in the other). Laterality was decided parapatellar arthrotomy because the NVM enters the knee by the toss of a coin prior to starting injections. capsule deep to medial retinaculum, supplies the medial collateral

40 Johnston DF, et al. Reg Anesth Pain Med 2019;44:39–45. doi:10.1136/rapm-2018-000002 Original article Regional Anesthesia & Pain Medicine: first published as 10.1136/rapm-2018-000002 on 3 January 2019. Downloaded from copyright.

Figure 1 Ultrasound image demonstrating the femoral triangle apex. This point was confirmed to lie distal to the femoral triangle injection point. Red asterisk: endpoint target for needle tip; yellow asterisk: alignment of medial borders of sartorius and adductor longus muscles. ALM, adductor longus muscle; AMM, adductor magnus muscle; FA, femoral artery; SM, sartorius muscle.

ligament and terminates as the medial retinacular nerve. This causing quadriceps weakness due to femoral nerve involvement. http://rapm.bmj.com/ terminal branch then pierces the medial knee capsule deep to the Consequently, a distal point of the AC was chosen to give suffi- medial retinaculum and supplies the ligamentous intra-articular cient distance from the FT injection point to allow a measurable knee structures and the undersurface of the patella.9 21 22 comparison between the distal margins of the two anatomical While addressing the issue of locating NVM it is important to locations. Choosing the proximal or midpoints of the AC may clarify the terms AC and FT. The FT is a region located between not have given the same contrasting results. One potential draw- the inguinal ligament proximally, the sartorius muscle laterally back of the distal AC location is the observation of injectate and the ALM medially. The apex of the FT is defined as the spread into the popliteal fossa via the adductor hiatus which has intersection between the medial borders of the sartorius muscle been previously described.24 Despite attempts to maintain motor on 27 March 2019 by guest. Protected and the lateral border of the ALM.23 The subsartorial canal exists sparing effects by placing distal AC injections, motor nerve immediately distal to the apex of the FT (ie, where the femoral involvement may still occur due to spread toward the popliteal vessels travel deep to the sartorius muscle). The AC continues fossa. distally until the superficial femoral artery descends through the We confirmed that the distal FT injection point defined sono- adductor hiatus. The take-off of the descending genicular artery graphically was consistently superior to the midpoint of the thigh is commonly seen just proximal to this point. Accessibility to (halfway point between ASIS and inferior border of patella) this region is aided by the patient’s ability to flex and externally consistent with the findings of Wong et al.14 The nomenclature rotate the hip. adapted for sonoanatomical descriptions of injection techniques The distal location of the FT injection point was chosen to of the thigh can be misleading. The injection performed in this minimize proximal injectate spread toward the inguinal liga- study for the FT was actually performed deep to the sartorius ment. This was to reflect clinical practice where regional anes- muscle 1 cm proximal to the apposition of the medial borders of thetists will often seek to achieve analgesia of distal femoral sartorius and ALM (ie, superior to the proximal margin of the nerve branches (eg, SN and NVM) while minimizing the risk of AC). This was not technically a direct FT injection but rather a

Johnston DF, et al. Reg Anesth Pain Med 2019;44:39–45. doi:10.1136/rapm-2018-000002 41 Original article Regional Anesthesia & Pain Medicine: first published as 10.1136/rapm-2018-000002 on 3 January 2019. Downloaded from copyright.

Figure 2 Ultrasound image demonstrating the distal adductor canal. The point at which the femoral artery descended toward the adductor hiatus was taken as the distal adductor canal margin. Red asterisk: corresponding endpoint target for needle tip (this was inserted just proximal to this image). AMM, adductor magnus muscle; DGA, descending geniculate artery; FA, femoral artery; SM, sartorius muscle; VMM, vastus medialis muscle.

subsartorial injection at the level of the FT. Injection here will of the NVM was demonstrated consistently for mid-thigh injec- http://rapm.bmj.com/ undoubtedly spread into the FT itself as it is a continuous plane tions nonetheless. with no fascial borders separating the two locations. In order In all AC injectates the echogenic vastoadductor membrane to define ultrasound-guided injections, where the needle will be could be readily visualized on ultrasound as well as sensed passed through the sartorius to juxtaposition the tip lateral to with a definite loss of tactile resistance change as the needle tip the superficial femoral artery, we as regional anesthetists have advanced into the AC. In contrast, the needle pass for the FT erroneously been calling this an FT block. Perhaps a ‘mid-thigh injections lacked the vastoadductor membrane ‘ceiling’ and the

sub-sartorial block’ would be technically more accurate. Altering change of needle resistance was much more subtle as the deep on 27 March 2019 by guest. Protected the name from a mid-thigh AC block to a mid-thigh FT block fascia of sartorius was breached. On dissection findings, the (or even to a mid-thigh subsartorial block) should not alter the vastoadductor membrane was easily located and could be seen results or interpretations of the published clinical findings that as a continuous partition throughout its length. The proximal describe subsartorial injections in the mid-thigh area. One such margin of the vastoadductor membrane was consistently found example of this was the volunteer study conducted by Grevstad et between our two chosen injection points. This may contribute to al.25 Healthy volunteers underwent ‘mid-thigh AC block’ proce- why proximal spread of AC injectate to stain other branches of dures with varying volumes of local anesthetic. The VMM had the femoral nerve was inhibited. volume dependent effects demonstrated by electromyography It is interesting that while vessels and nerves can pass from FT brought about by the mid-thigh injections. Details of specific to AC, proximal spread of injectate placed just 9–10 cm distally sonoanatomical landmarks for the injections of this study were is prevented. Our findings of reduced proximal spread of AC not included other than the injection point being described as injectate into the distal FT are consistent with previous cadaveric ‘mid-thigh ACB’. One could contend the injections were actu- studies. Dissections by Cowlishaw and Kotze26 and Ishiguro et ally being performed at the level of the FT, but the involvement al27 also demonstrated limited cephalad spread from the AC into

42 Johnston DF, et al. Reg Anesth Pain Med 2019;44:39–45. doi:10.1136/rapm-2018-000002 Original article Regional Anesthesia & Pain Medicine: first published as 10.1136/rapm-2018-000002 on 3 January 2019. Downloaded from

the FT with consequent sparing of femoral nerve branches to sartorius, rectus femoris and vastus lateralis. In live patients, elements including dynamic tissue planes, patient positioning and inflation of a thigh tourniquet may result in different spread than what was demonstrated in cadaver spec- imens. The use of methylcellulose as an injectate stabilizing agent to facilitate dissections may have limited proximal spread that may not have been reflective of less viscous injectates (such as local anesthetic agents or MRI contrast used by Jæger et al where injections of 20 mL into the AC spread proximally to the FT in 50% of cases).28 Consequently, a distal AC block in vivo could indeed still result in more proximal spread toward the NVM. The small number of cadaver specimens is a further limitation to this study. Cadaver 4 had an estimated weight of around 50 kg and in the FT injectate side, some of the dye spread proximally toward the inguinal crease and stained other branches of the femoral nerve (nerve to vastus intermedius). This only happened on one out of four FT injections but none of the AC injections. In clinical prac- tice, this may represent a potential drawback of performing an FT block at a more proximal location in an attempt to anesthe- tize the NVM; other branches of the femoral nerve may become blocked. This study does pose an important clinical question: If the NVM contributes significant analgesia for TKA undergoing medial parapatellar approach, should the regional anesthetist opt for a true distal FT block instead of distal AC block? The findings from this small cadaveric study suggest that a distal AC block may miss the NVM and likely result in suboptimal

analgesia compared with more proximal injections. This is copyright. in keeping with the findings by Burckett-St Laurant et al who recommended an injection in the mid-AC as a means to block both the SN and NVM.6 The converse argument would contend that injectate placed within the distal AC could avoid blocking the NVM as an advantage to prevent VMM weak- ness while still blocking the SN with its infrapatellar branch and the subsartorial plexus. This could contribute to analgesia without causing quadriceps weakness. A clinical study of TKA patients comparing distal AC with distal FT blocks is needed to compare outcomes of pain, analgesia consumption and quad- riceps strength. http://rapm.bmj.com/ CONCLUSIONS In summary, this small cadaveric study suggests that an injec- tion in the distal AC may consistently reach the SN only while it Figure 3 Surface landmarks of thigh (right). AC, adductor canal; FT, spares the NVM, while an injection in the distal FT consistently femoral triangle injection point; M EPI, medial femoral epicondyle; MID, reaches both nerves. In addition, our findings also suggest that midpoint of thigh. involvement of additional motor nerves (such as the nerve to on 27 March 2019 by guest. Protected

Table 1 Age, gender and thigh measurements of cadaver specimens Cadaver 1 2 3 4 Gender Male Female Male Male Age 66 90 82 86 Injection given ACB FTB FTB ACB ACB FTB ACB FTB ASIS to inferior patella border 54 54 49 50 51 51.5 50 49 ASIS to midpoint of thigh 27 27 24.5 25 25 25 25 24 ASIS to distal margin of AC 34 33 30 30 31 30.5 31 29 Distance between injection points 10 8.5 9 10 Age in years and measurements in centimeters. Blue shading corresponds to left thigh. Orange shading corresponds to right thigh. AC, adductor canal; ACB, adductor canal injection; ASIS, anterior superior iliac spine; FTB, femoral triangle injection.

Johnston DF, et al. Reg Anesth Pain Med 2019;44:39–45. doi:10.1136/rapm-2018-000002 43 Original article Regional Anesthesia & Pain Medicine: first published as 10.1136/rapm-2018-000002 on 3 January 2019. Downloaded from copyright. http://rapm.bmj.com/ Figure 4 Dissection findings of four cadaver thigh specimens one hour after femoral triangle injections (left column) and adductor canal injections (right column). DIST, distal; FA, femoral artery; NVM, nerve to vastus medialis; PROX, proximal; SM, sartorius muscle; SN, saphenous nerve; VMM, vastus medialis muscle. vastus intermedius) is more likely to occur with an injection in 3 Muraskin SI, Conrad B, Zheng N, et al. Falls associated with lower-extremity-nerve blocks: a pilot investigation of mechanisms. Reg Anesth Pain Med 2007;32:67. the FT compared with the distal AC. on 27 March 2019 by guest. Protected 4 Macrinici GI, Murphy C, Christman L, et al. Prospective, double-blind, randomized study to evaluate single-injection adductor canal nerve block versus femoral nerve Acknowledgements Thanks to Declan McLaughlin who photographed the block: postoperative functional outcomes after total knee arthroplasty. Reg Anesth anatomy specimens following dissection. Pain Med 2017;42:10–16. Funding The authors have not declared a specific grant for this research from any 5 Gao F, Ma J, Sun W, et al. Adductor canal block versus femoral nerve block for funding agency in the public, commercial or not-for-profit sectors. analgesia after total knee arthroplasty: A systematic review and meta-analysis. Clin J Provenance and peer review Not commissioned; externally peer reviewed Pain 2017;33:356–68. 6 Burckett-St Laurant D, Peng P, Girón Arango L, et al. The nerves of the adductor canal and the innervation of the knee: an anatomic study. Reg Anesth Pain Med REFERENCES 2016;41:321–7. 1 Fischer HB, Simanski CJ, Sharp C, et al. A procedure-specific systematic review 7 Franco CD, Buvanendran A, Petersohn JD, et al. Innervation of the anterior capsule and consensus recommendations for postoperative analgesia following total knee of the human knee. Implications for radiofrequency ablation. Reg Anesth Pain Med arthroplasty. Anaesthesia 2008;63:1105–23. 2015;40:363–8. 2 Terkawi AS, Mavridis D, Sessler DI, et al. Pain management modalities after total 8 Orduña Valls JM, Vallejo R, López Pais P, Valls JM, Pais PL, et al. Anatomic and knee arthroplasty: a network meta-analysis of 170 randomized controlled trials. ultrasonographic evaluation of the knee sensory innervation. Reg Anesth Pain Med Anesthesiology 2017;126:923–37. 2017;42:90–8.

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