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Distribution of Injectate and Sensory-Motor Blockade After Adductor Canal Block

Gautier, Philippe E. MD*; Hadzic, Admir MD, PhD; Lecoq, Jean-Pierre MD; Brichant, Jean Francois MD; Kuroda, Maxine M. PhD, MPH§; Vandepitte, Catherine MD

doi: 10.1213/ANE.0000000000001025
Regional Anesthesia: Brief Report

BACKGROUND: The analgesic efficacy reported for the adductor canal block may be related to the spread of local anesthetic outside the adductor canal.

METHODS: Fifteen patients undergoing knee surgery received ultrasound-guided injections of local anesthetic at the level of the adductor hiatus. Sensory-motor block and spread of contrast solution were assessed.

RESULTS: Sensation was rated as “markedly diminished” or “absent” in the saphenous nerve distribution and “slightly diminished” in the sciatic nerve territory without motor deficits. Contrast solution was found in the popliteal fossa.

CONCLUSIONS: The spread of injectate to the popliteal fossa may contribute to the analgesic efficacy of adductor canal block.

From the *Department of Anesthesiology, Clinique Ste Anne-St Remi, Brussels, Belgium; Ziekenhuis, Oost-Limburg, Genk, Belgium; Department of Anesthesia and Intensive Care Medecine, Liege University Hospital, Liege, Belgium; and §North American Institute for Continuing Education (NAICE), New York, New York.

Admir Hadzic, MD, PhD, and Catherine Vandepitte, MD, are currently affiliated with The New York School of Regional Anesthesia, New York, New York.

Accepted for publication August 7, 2015.

Funding: Department of Anesthesiology, Clinique Ste Anne-St Remi, Brussels, Belgium.

Conflict of Interest: See Disclosures at the end of the article.

Address correspondence to Admir Hadzic, MD, PhD, 2753 Broadway, Suite 183, New York, NY 10025. Address e-mail to admir@nysora.com.

The adductor canal block (ACB) is gaining popularity as an analgesic technique after knee surgery. Local anesthetic injected at the level of the adductor hiatus is thought to block the saphenous nerve, the nerve to the vastus medialis, and the articular contribution of the obturator nerve.1 ACB appears to decrease the likelihood of quadriceps muscle weakness,2–6 although femoral and popliteal nerve blockade have been described.7 ACB anesthetizes some nerves that innervate the knee joint; yet, the analgesic efficacy of ACB is surprising because both sciatic and femoral nerves contribute sensory supply to the knee.8

We evaluated the spread of local anesthetic after ACB. We reasoned that, in addition to the branches of the femoral and obturator nerves in the adductor canal, the analgesic efficacy of ACB might be related to the spread of injectate into the popliteal fossa.

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METHODS

After approval by the Ethical Committee of the University of Liège: No. 2013/298, written consent to participate was obtained from patients scheduled to undergo knee surgery with ACB for analgesia. Patients who were <18 years of age, who were pregnant, who had ASA physical status >3, body mass index >30, or a history of allergic reaction to local anesthetics or to contrast media were excluded.

Figure 1

Figure 1

Patients received ACB with the use of a trans-sartorial approach with an Aplio XG equipped with a 6-Mhz curved probe (PVT-674BT; Toshiba, Tokyo, Japan) and a 100-mm 21G needle (SonoPlex Stim, Pajunk Gmbh, Germany). The needle was inserted under ultrasound guidance approximately 15 cm above the medial femoral condyle, next to the femoral artery, and underneath the sartorius muscle at the point just before the femoral artery coursed through the adductor hiatus to become the popliteal artery (Fig. 1). At this point in the adductor canal, 20 mL of mepivacaine 1% solution (AstraZeneca) was injected. Mepivacaine 1% was chosen for its greater motor-blocking property than more common choices, such as bupivacaine or ropivacaine, thus providing greater sensitivity to detect popliteal spread. Extent of sensory-motor block was assessed at baseline and at 30 and 60 minutes after block placement by a research assistant blinded to study purpose.

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Sensory Evaluation

Pinprick was used to test sensation in the territories of the infrapatellar and distal branches of the saphenous nerve and in the peroneal and tibial nerve territories at the dorsal and plantar aspects of the foot, respectively. Sensation was rated as 3 (similar to contralateral side), 2 (slightly diminished), 1 (markedly diminished), or 0 (absent).

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Motor Evaluation

Maximal voluntary isometric force was assessed with an electronic dynamometer (MicroFET2; Hoggan Industries, West Jordan, UT).9 With the patient supine, force was measured (3 times each) during extension of the knee and during extension and flexion of the foot. Patients attempted their maximal force, whereas the assessor exerted an equivalent isometric force. Maximal force over 3 seconds was recorded. Percentage change in force from baseline was calculated for measurements taken at 30 and 60 minutes.

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Computed Tomography Imaging

The first 6 consecutive patients received 20 mL of a solution containing 18 mL of mepivacaine 1% (AstraZeneca) and 2 mL of radio-opaque contrast material (Isohexilisohexil 600). Computed tomography scans were obtained. A radiologist blinded to study purpose assessed the spread of contrast solution.

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Statistical Methods

Continuous variables are presented as mean ± SD; ordinal and nominal (categorical) variables as n (%). This preliminary study did not intend to test specific hypotheses nor was it powered for such tests; findings are presented descriptively.

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RESULTS

Table 1

Table 1

Table 2

Table 2

Table 3

Table 3

Figure 2

Figure 2

All 15 patients successfully completed the study (Table 1). Sensation in the distal and infrapatellar branches of the saphenous nerve was “markedly diminished” or “absent,” ranging from 13 of 15 patients (87%; 95% confidence interval, 60%–98%) at 30 minutes to 15 of 15 patients at 60 minutes (Table 2). Sensation in the peroneal and tibial nerve territories of the foot was “similar to contralateral side” or “slightly diminished,” ranging from 15 of 15 patients at 30 minutes to 13 of 15 patients (87%; 95% confidence interval, 60%–98%) at 60 minutes (Table 2). Motor weakness was not apparent for knee extension or for flexion or extension of the foot (Table 3). In all 6 patients who had computed tomography examinations, contrast solution was detected in the adductor canal and extended into the popliteal fossa in the vicinity of the popliteal vessels and the sciatic nerve (Fig. 2). A large amount of contrast medium was found between the popliteal artery and the femur in all 6 patients.

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DISCUSSION

The adductor canal is limited medially by the adductor longus, laterally by the vastus medialis, and superficially by the sartorius and the subsartorial fascia. It contains the femoral vessels, the saphenous nerve, and the nerve to the vastus medialis. Although the terminal branch of the obturator nerve enters the adductor canal distally; neither the sciatic nerve nor its branches pass through the canal.8 Thus, analgesia after ACB may be due to spread of local anesthetic into the popliteal space. We found that injection of 20 mL of local anesthetic at the level of the adductor hiatus resulted in spread of local anesthetic into the popliteal fossa. Spread appears to occur through the adductor hiatus, the accessory hiatus, and/or in the intermuscular plane of the adductor magnus, resulting in some sensory block of the sciatic nerve and/or its branches. Andersen et al.10 described the spread of dye into the popliteal fossa (1–2 cm) in cadavers but to a lesser extent than in our study. This could be explained by study differences in injection location, volumes, and subjects (patients versus cadavers). Our study used a single ACB technique and volume of local anesthetic; thus, findings could differ with other injection techniques and volumes. For instance, studies that used larger volumes (e.g., 30 mL) found greater spread of local anesthetic into the popliteal fossa and/or toward the femoral nerve, which may have contributed to the analgesic efficacy of ACB.2,6,8

In conclusion, injection of 20 mL of local anesthetic solution in ACB results in spread in the adductor canal and into the popliteal fossa. The resulting diminution of sensory sensation may contribute to the analgesic efficacy of ACB after major knee surgery.

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DISCLOSURES

Name: Philippe E. Gautier, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: This author has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Conflicts of Interest: Philippe E. Gautier reported no conflicts of interest.

Name: Admir Hadzic, MD, PhD.

Contribution: This author helped write the manuscript and interpret data.

Attestation: This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Admir Hadzic has consulted and advised for SkyePharma, GE, SonoSite, Codman & Shurtleff, Inc. (Johnson & Johnson), Cadence, Pacira, Baxter, and BBraun Medical. His recent industry-sponsored research includes Glaxo Smith-Kline Industries, Pacira, and Baxter. He receives royalty income from BBraun Medical.

Name: Jean-Pierre Lecoq, MD.

Contribution: This author helped write the manuscript.

Attestation: This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Jean-Pierre Lecoq reported no conflicts of interest.

Name: Jean Francois Brichant, MD.

Contribution: This author helped design the study and write the manuscript.

Attestation: This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Jean Francois Brichant reported no conflicts of interest.

Name: Maxine M. Kuroda, PhD, MPH.

Contribution: This author helped analyze the data and write the manuscript.

Attestation: This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Maxine M. Kuroda reported no conflicts of interest.

Name: Catherine Vandepitte, MD.

Contribution: This author helped write the manuscript and interpret data.

Attestation: This author has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Catherine Vandepitte reported no conflicts of interest.

This manuscript was handled by: Terese T. Horlocker, MD.

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REFERENCES

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