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The Effect of Local Anesthetic Volume Within the Adductor Canal on Quadriceps Femoris Function Evaluated by Electromyography: A Randomized, Observer- and Subject-Blinded, Placebo-Controlled Study in Volunteers

Grevstad, Ulrik MD, PhD; Jæger, Pia MD, PhD; Sørensen, Johan Kløvgaard MS; Gottschau, Bo MD; Ilfeld, Brian MD, MS; Ballegaard, Martin MD, PhD; Hagelskjaer, Mike MSc; Dahl, Jørgen Berg MD, DMSc, MBA

doi: 10.1213/ANE.0000000000001310
Regional Anesthesia and Acute Pain Medicine: Original Clinical Research Report

BACKGROUND: Single-injection adductor canal block (ACB) provides analgesia after knee surgery. Which nerves that are blocked by an ACB and what influence—if any—local anesthetic volume has on the effects remain undetermined. We hypothesized that effects on the nerve to the vastus medialis muscle (which besides being a motor nerve innervates portions of the knee) are volume-dependent.

METHODS: In this assessor- and subject-blinded randomized trial, 20 volunteers were included. On 3 separate days, subjects received an ACB with different volumes (10, 20, and 30 mL) of lidocaine 1%. In addition, they received a femoral nerve block and a placebo ACB. The effect on the vastus medialis (primary endpoint) and the vastus lateralis was evaluated using noninvasive electromyography (EMG). Quadriceps femoris muscle strength was evaluated using a dynamometer.

RESULTS: There was a statistically significant difference in EMG response from the vastus medialis, dependent on volume. Thirty-five percent (95% confidence interval [CI], 18–57) of the subjects had an affected vastus medialis after an ACB with 10 mL compared with 84% (95% CI, 62–94) following 20 mL (P = 0.03) and 100% (95% CI, 84–100) when 30 mL was used (P = 0.0001). No statistically significant differences were found between volume and effect on the vastus lateralis (P = 0.81) or in muscle strength (P = 0.15).

CONCLUSIONS: For ACB, there is a positive correlation between local anesthetic volume and effect on the vastus medialis muscle. Despite the rather large differences in EMG recordings, there were no statistically significant differences in quadriceps femoris muscle strength. Subsequent clinical studies comparing different volumes in a surgical setting, powered to show differences not only in analgesic efficacy, but also in adverse events, are required.

Published ahead of print May 5, 2016

From the *Department of Anaesthesia and Intensive Care Medicine, Copenhagen University Hospital, Gentofte Hospital, Hellerup, Denmark; Department of Anaesthesia, Centre of Head and Orthopaedics, Copenhagen University Hospital, Rigshospitalet, Denmark; Department of Anesthesiology, University California San Diego, San Diego, California; and §Department of Clinical Neurophysiology, Rigshospitalet, Copenhagen, Denmark.

Accepted for publication February 24, 2016.

Published ahead of print May 5, 2016

Funding: Departmental.

The authors declare no conflicts of interest.

Ulrik Grevstad and Pia Jæger share the first authorship.

Reprints will not be available from the author.

Address correspondence to Ulrik Grevstad, MD, PhD, Department of Anaesthesia and Intensive Care Medicine, Gentofte Hospital, Kildegårdsvej 28, 2900 Hellerup, Denmark. Address e-mail to ulrik.grevstad@hotmail.com.

The adductor canal is an aponeurotic tunnel within the thigh containing both vascular structures and various peripheral sensory and motor nerves. A single-injection adductor canal block (ACB) provides analgesia after surgical procedures of the knee.1–7 Which specific nerves are affected by an ACB has not been explored. Studies in healthy volunteers indicate that the mixed sensorimotor nerve to the vastus medialis muscle is affected, because a small decline in quadriceps muscle strength was found after ACBs,8,9 and clinical studies demonstrate that a spread all the way to the femoral nerve is possible.4,10,11

In theory, increasing the local anesthetic volume for an ACB will increase the spread through the canal and block not only the saphenous nerve, but also other nerves with sensory branches to the knee, including the medial femoral cutaneous nerve, terminal branches of the obturator nerve, and the nerve to the vastus medialis.12 However, whether the volume of local anesthetic administered in the adductor canal influences the number of nerves affected remains undetermined.

We therefore designed this study to investigate a possible association between volume and effect on the vastus medialis and the vastus lateralis of the quadriceps femoris muscle using noninvasive electromyography (EMG). We hypothesized that there is a positive correlation between volume of local anesthetic used for the ACB and effects on the vastus medialis. We compared 3 different volumes (10, 20, and 30 mL) of local anesthetic (lidocaine 1%) for an ACB. The primary endpoint was the rectified EMG amplitude from the vastus medialis muscle, expressed as a percentage of the preblock value. Secondary endpoints included proportions of subjects having an affected vastus medialis muscle, compound motor action potential from the vastus medialis and the vastus lateralis muscle, and quadriceps muscle strength.

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METHODS

Patients and Design

This randomized, observer- and subject-blinded, placebo-controlled study in healthy volunteers was approved by the local Regional Ethics Committee (H-8-2014-005), the Danish Medicines Agency (EudraCT: 2014-004601-32), and the Danish Data Protection Agency. Before enrollment, the trial was registered at clinicaltrials.gov (NCT02344589, January 16, 2015). The study was conducted at Copenhagen University Hospital, Rigshospitalet, in accordance with the Helsinki Declaration and was monitored by the Copenhagen University Hospital Good Clinical Practice Unit. Data are presented according to the Consolidated Standards of Reporting Trials (CONSORT) guidelines.

Twenty male volunteers were included after providing written informed consent. Inclusion criteria were age >18 years, ASA physical status I, body mass index of 18 to 30 kg/m2, and physical exercise 1 to 3 hours/wk (to ensure a “normal” activity level). Exclusion criteria were allergy to lidocaine, alcohol and/or drug abuse, pathology or previous surgery/trauma to either leg, intense exercise within 24 hours, and intake of any analgesic within 24 hours.

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Treatment Plan, Randomization, and Interventions

Each subject was investigated on 3 separate study days with a 1- to 2-day interval between study days. All subjects received a total of 5 single-injection nerve blocks (Table 1): three ACBs with different volumes (10, 20, and 30 mL) of lidocaine 1%; a placebo ACB with 20 mL of saline to ensure that the EMG recordings were not influenced by a simple expansion of the canal; and a femoral nerve block (FNB) with 20 mL lidocaine 1% to determine how the EMG signals were altered by anesthetizing the nerve and to establish a cutoff value for dichotomizing the data into affected/unaffected.

Table 1

Table 1

The order of the volume administered for the active ACBs followed a Williams design/randomization13 to ensure that each volume preceded every other volume the same number of times; hence, the design was balanced with respect to first-order carryover effects. Volumes were blinded to the subjects (view to injection site blocked by drapes) and the assessors but not the anesthesiologist performing the block. One investigator, not otherwise involved in the study, performed all blocks. Random allocation concealment was retained for the remainder of the investigators. The placebo ACB and the FNBs were not blinded.

The ACBs were performed approximately at the midthigh level after a dynamic ultrasound scan of the slightly externally rotated extremity. The probe was placed in an anterolateral to posteromedial direction medially over the sartorius muscle. The superficial femoral artery was identified deep to the sartorius muscle with the saphenous nerve lying in between the vastus medialis, the sartorius, and the superficial femoral artery. The needle was advanced using an in-plane technique (anterolateral to posteromedial direction) piercing the sartorius muscle, avoiding the vastus medialis fascia.

The FNBs were performed in-plane, short-axis view, proximal to the division of the femoral artery using a technique described previously.14

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Assessments

All assessments were performed at t0 = baseline (immediately preblock) in the following order: ability to discriminate cold in the saphenous area, knee extension force during quadriceps femoris maximal voluntary isometric contraction (MVIC), maximal voluntary EMG activity from vastus medialis (EMGmax,VM) and vastus lateralis (EMGmax,VL), and maximal compound motor action potential from vastus medialis (cMAPmax,VM) and vastus lateralis (cMAPmax,VL). The tests were repeated at t60 = 60 minutes postblock.

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Sensory Test

The ability to discriminate cold in the saphenous area (medial side of lower leg, 10 cm proximal to the medial malleolus) was evaluated using an alcohol swab. An area on the lateral side of the lower leg was used as a reference. An FNB was defined as failed if the decrease in cold sensation at t60 was not complete. ACB blocks were excluded from this definition because a lack of sensory response could be the result of an inadequate local anesthetic volume.

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Muscle Strength

MVIC of the quadriceps femoris muscle was measured using a handheld dynamometer with the subject in the sitting position, knee flexed 90°, and both feet off the ground.15 A nonelastic strap fixed the dynamometer to the subject’s ankle. Subjects were instructed (and had trained before baseline values) to reach maximal force and to sustain it for 3 seconds. We used the mean value of 3 consecutive measurements with a 30-second rest period in between attempts to calculate the postblock percentage of the preblock values.

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Maximal Voluntary Electromyographic Activity

After skin preparation (shaving and cleansing with alcohol), the active surface Ag/AgCl-electrodes (Ambu® BlueSensor, NF10-A; Ambu A/S, Ballerup, Denmark) were placed in a pseudo-monopolar montage using a standardized position over the vastus medialis and the vastus lateralis muscle.16 The positions of the electrodes were chosen to be approximately 20 mm distal to the estimated innervation zones of the muscles. This should give the optimal signal amplitude without the signal cancellation seen at the innervation zone. The reference electrodes were placed over the tibial protuberance (Figure 1). The electrode positioning was marked with a water-resistant marker to make sure that the positioning remained constant all 3 days. The same electrodes remained in place for pre- and postblock measurements. New electrodes were used on separate study days.

Figure 1

Figure 1

Figure 2

Figure 2

The EMG signal was filtered, amplified (1–20 kHz, ×1.000, DISA 15C01 Amplifier; DISA A/S, Tåstrup, Denmark), digitized (sample rate 25 kS/s, NI9239; National Instruments, Hørsholm, Denmark), and ultimately displayed on a LabVIEW-based interface (National Instrument, LabView2011) to allow for online visual inspection. During the MVIC measurements, a 5-second period of rectified EMG signal was recorded simultaneously from the vastus medialis and the vastus lateralis. The rectified EMG signals were visually inspected on the computer, and the maximal value of a 2-second average of the amplitude (mV) was selected during a period of stable EMG signal (Figure 2). This was done during each MVIC trial, and the mean value was used to calculate the postblock percentage of the preblock values from the vastus medialis (EMGmax,VM) and the vastus lateralis (EMGmax,VL).

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Maximal Compound Motor Action Potential

The femoral nerve was stimulated transcutaneously using a bipolar handheld electrical stimulator (cMAP filtered at 5–5000 Hz, Dantec™ Keypoint®, G4; Natus Medical Inc, Pleasanton, CA). Using ultrasound guidance, the stimulator was placed over the femoral nerve, just below the inguinal ligament, proximal to the division of the femoral artery. The femoral nerve was stimulated and the resultant compound motor nerve action potential, from the vastus medialis (using the same surface recording electrodes as for the EMGmax,VM), was visually inspected on the computer. The stimulator was slightly moved and the nerve stimulated again. This was repeated until the optimal position for nerve activation was found. Thereafter, the current was increased until no further increase in signal from the vastus medialis was observed. The highest obtainable amplitude of the negative peak from baseline was used to calculate the postblock percentage of the preblock value (cMAPmax,VM). To obtain the cMAPmax,VL, the procedure was repeated using the surface electrodes over the vastus lateralis.

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Endpoints

The primary endpoint was the rectified EMG amplitude from the vastus medialis muscle, expressed as a percentage of the preblock value. Secondary endpoints included proportions of subjects having an affected vastus medialis muscle, compound motor action potential from the vastus medialis and the vastus lateralis muscle, and quadriceps muscle strength.

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Sample Size, Statistical Analysis, and Data Handling

Sample size calculations were centered around our primary hypothesis that affection of the nerve to the vastus medialis is dependent on the volume of local anesthetic used for the ACB. The primary outcome measure was the postblock EMGmax,VM amplitude expressed as a percentage of the preblock value.

Because EMG is not a method routinely used to examine the effect of a nerve block, we had no estimates for the variance. Therefore, to estimate an adequate sample size, we made assumptions based on a study involving healthy volunteers9: a small decline (8%) in quadriceps muscle strength was found after an ACB with 30 mL of local anesthetic. We assumed this decline was caused by an affection of the nerve to the vastus medialis. We speculated that in 90% of subjects, the vastus medialis would be affected after an ACB with 30 mL and that the incidence would decrease with lower volumes: 50% after an ACB with 20 mL and 10% when 10 mL was used for the ACB. We found it unlikely that a subject would experience any effect on the vastus medialis at a low volume and no affect with a higher volume. Hence, all possible differences were likely to be discordant. With 80% power to detect the 40% difference between volumes and a 2-sided type I error protection of 0.05, 15 subjects were required. We included 20 volunteers to allow for greater than anticipated variability.

Variation in the EMGmax recordings was greater than that in the cMAPmax recordings. Therefore, we chose to use the cMAPmax and not the EMGmax recordings to construct the cutoff limits for affected/unaffected. Because postblock EMG values were expected to be lower than preblock values after the FNB, only high values are suspicious, and a right-sided 95% upper reference limit was created. Because of the small sample size, we used the robust method17 with a bootstrapped18 (10,000 iterations) confidence interval (CI). To be conservative, the upper part of the 90% CI for the limit was used (corresponding to 68% of the preblock value for the vastus medialis and 55% for the vastus lateralis). For example, if the cMAPmax,VM decreased to 60% of the preblock value, we considered the nerve to vastus medialis to be affected.

For the MVIC results, a right-sided 90% reference limit was created instead of a 95% reference limit because the upper part for the bootstrapped 95% reference limit exceeded the highest value measured in the FNB group with as much as 20% and included 10% of the subjects in the placebo group. The 90% reference limit included all FNBs and no placebo blocks.

Continuous outcomes (MVIC, EMGmax, and cMAPmax) were found to be skewed (visual examination of histograms, Q-Q plots, box plots, and Shapiro and Wilk test; P < 0.05) and hence analyzed as nonparametric data using the Friedman test. If significant, separate Wilcoxon signed rank tests were conducted. For the multiple Wilcoxon signed rank test comparisons, P values are presented as uncorrected, but a conservative Bonferroni correction is applied in interpretation of these results. Hence, only P values <0.05/10 = 0.005 are considered significant. Dichotomous data (number of subjects with an affected nerve to the vastus medialis, etc) were analyzed using the Cochran Q test. If significant, pairwise comparisons were made using the McNemar test.

All data were entered into a spreadsheet and checked for errors by 2 investigators. The person who created the randomization list assigned the different volumes into 3 groups: A, B, and C without revealing to which volumes these corresponded. After completion of data analysis and conclusions were drawn, unmasking occurred.

Data were analyzed using IBM SPSS Statistics version 20 (Armonk, NY). The reference limits were calculated using MedCalc version 15.4 (Ostend, Belgium).

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RESULTS

Twenty subjects were enrolled in January 2015. Of these, 3 subjects had an incomplete FNB (only partial loss of sensation in the saphenous area and they maintained EMG values >89% of preblock values). FNB data from these 3 subjects were excluded because the FNB data were used to establish the reference interval for affected versus unaffected. Data regarding the ACBs from these subjects were included. We discarded data from one subject after an ACB with 20 mL lidocaine 1% (before data analysis and unmasking) because MVIC of the subject increased to 180%, and a major discrepancy between EMGmax,VL and cMAPmax,VL recordings suggested that the preblock MVIC was submaximal.

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EMGmax,VM (Primary Endpoint)

Figure 3

Figure 3

There was a statistically significant difference among blocks in EMGmax amplitude from the vastus medialis x2(4) = 38.7 (P < 0.0001). Pairwise comparisons (Wilcoxon signed rank test) revealed significant differences (Z = −2.69 to −3.92; P = 0.001–0.0001) among most blocks, except between ACB 20 versus FNB (Z = −0.57; P = 0.57), ACB 30 versus FNB (Z = −0.47; P = 0.64), and ACB 20 versus ACB 30 (Z = 0.32; P = 0.75) (Figure 3). In other words, the decline in EMGmax,VM seen after the ACB 20 and the ACB 30 was similar to the decline seen after the FNB.

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Maximal Compound Motor Action Potential from Vastus Medialis

There was a statistically significant difference among blocks in cMAPmax amplitude from the vastus medialis x2(4) = 44.2 (P < 0.0001). Pairwise comparisons (Wilcoxon signed rank test) revealed significant differences (Z = −2.94 to −3.92; P = 0.003–0.0001) among most blocks, except between ACB 20 versus FNB and ACB 30 versus FNB (Table 2; Figure 3).

Table

Table

Figure 4

Figure 4

After dichotomizing the cMAPmax,VM measurements (Figure 4), we found that only 7/20 = 35% (95% CI, 18–57) of the subjects had an affected nerve to the vastus medialis after the ACB 10. This proportion was significantly lower than seen with the higher volumes: 16/19 = 84% (95% CI, 62–94; P = 0.03) after the ACB 20 and 20/20 = 100% (95% CI, 84–100; P < 0.0001) after the ACB 30.

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Maximal Compound Motor Action Potential from Vastus Lateralis

There was a statistically significant difference among blocks in cMAPmax amplitude from the vastus lateralis x2(4) = 32.5 (P < 0.0001). Pairwise comparisons (Wilcoxon signed rank test) revealed that the cMAPmax,VL was significantly lower in the FNB group compared with all other groups (Z = −3.62 to −3.51; P < 0.0001). No significant differences were detected among ACB 10, ACB 20, ACB 30, and the placebo ACB (Table 2; Figure 3).

Figure 5

Figure 5

Subjects id9, id7, and id18 had an affection of the nerve to vastus lateralis after the ACB 20, the ACB 30, and after the placebo ACB, respectively (P = 0.61; Figure 5).

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Maximal Voluntary Isometric Contraction

There was a statistically significant difference among blocks in MVIC x2(4) = 31.7 (P < 0.0001). Pairwise comparisons (Wilcoxon signed rank test) revealed that MVIC was significantly lower in the FNB group compared with all other groups (Z = −3.62; P < 0.001). No statistically significant differences were detected among ACB 10, ACB 20, ACB 30, and the placebo group (Table 2; Figure 3).

Figure 6

Figure 6

One subject (id9) had a substantial decrease in MVIC to 12% after the ACB 20 and another subject (id7) decreased in MVIC to 49% after the ACB 30. Both values were well below the cutoff limit for an FNB (P = 0.61; Figure 6).

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Success Rate—Loss of Sensation Within the Saphenous Nerve Cutaneous Distribution

No blocks (except placebo) resulted in a completely preserved sensation; so by our a priori definition, there were no “failed blocks.” However, some subjects had only a partial loss of sensation: 3/20 after the FNB (the excluded subjects), 4/20 after the ACB 10, 1/20 after the ACB 20, and 1/20 after the ACB 30 (P = 0.22). The remainder had complete loss of sensation.

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DISCUSSION

The aim of this study was to compare the effect of 3 different volumes of local anesthetic (10, 20, and 30 mL) injected into the adductor canal on the vastus medialis and the vastus lateralis of the quadriceps femoris muscle evaluated by EMG. Our results suggest a strong association between volume and vastus medialis effects. A volume of 30 mL resulted in an affection in all subjects, a volume of 20 mL resulted in an affection in 84% of the subjects, whereas a volume of 10 mL only resulted in an affection in 35% of the subjects.

Despite the rather large differences in EMG recordings, there were no statistically significant differences in quadriceps femoris muscle strength noted. Subjects preserved median MVIC values of 95% (10 mL), 99% (20 mL), and 92% (30 mL) of their preblock values compared with 18% after the FNB.

The nerve to the vastus medialis and the nerve to the vastus lateralis of the quadriceps femoris muscle as well as the saphenous nerve all derive from the posterior division of the femoral nerve. Because the nerve to the vastus lateralis leaves the femoral nerve just distal to the inguinal ligament to pierce the vastus lateralis, an affection of the vastus lateralis, after an ACB, must be equivalent to a proximal spread of local anesthetic to the femoral nerve.

This is in conjunction with our results, because the 2 subjects experiencing a decline in MVIC after an ACB (subject id7 after receiving a volume of 30 mL and id9 after a volume of 20 mL) both had a concomitant affection of the vastus lateralis. No decline in MVIC was seen in the subjects who only had affection of the vastus medialis and/or the saphenous nerve. Although one subject (id18) experienced an affection of the vastus lateralis after a placebo ACB, we suspect this to be a result of an erroneous preblock measurement, because we found no simultaneous decrease in MVIC.

To circumvent the affection of pain and surgery19 on MVIC, we chose to include healthy volunteers in this experimental study assessing the effect of volume on nerve involvement. However, that choice also led to the major limitation of our study being the clinical interpretation of the results. We can only speculate whether affection of the nerve to vastus medialis results in better postsurgical analgesia or just increases the risk of adverse events such as falling, decreased proprioception, or muscular instability of the knee. Hence, we have gained theoretical knowledge of the effects of volume of local anesthetic for an ACB, but our results do not bring us closer to understanding the optimal volume. Furthermore, the spread of local anesthetic within the adductor canal is most likely not dependent on volume and injection pressure alone; patient characteristics such as sex and age-related morphological changes20 may also be important.

Overall, the conclusions from EMGmax recordings concur with those of the cMAPmax, except that there is a statistically significant difference between ACB 20 and ACB 30 when analyzed using the EMGmax,VM recordings opposed to a nonsignificant difference when analyzed using cMAPmax,VM. As Figure 3 reveals, the variation in the EMGmax recordings was greater than that in the corresponding cMAPmax recordings. A possible explanation is that the EMGmax recordings are dependent on the subject’s ability and enthusiasm to maintain a stable maximal force during MVIC, whereas cMAPmax recordings only are reliant on the ability of the assessor to seek out the optimal positioning of the stimulus over the femoral nerve. (The subject has no way of “cheating” the assessor.) Therefore, we chose to use the cMAPmax recordings to construct our cutoff limits for affected versus unaffected.

The clinical relevancy of our use of lidocaine 1% may be questioned. We chose lidocaine because we were primarily interested in short-term effects. To the best of our knowledge, there are no data supporting the idea that increasing the concentration beyond 1% results in a more complete block. In addition, the success rate and MVIC results after the FNB indicate that we did obtain blocks comparable with what is found with the use of, for example, ropivacaine.8,9

The lack of blinding of the placebo control and of the active comparator (FNB) may be considered a limitation to the study. The marked reduction in MVIC after an FNB would have been difficult to mask, and although blinding the placebo ACB would have been easy, it would have been at the expense of not having all active ACBs administered in the same leg (risking potential between-leg differences).

In summary, we have demonstrated in healthy volunteers an association between volume and effects on the vastus medialis in EMG response but not quadriceps femoris muscle strength. In addition, the effect of volume on analgesic efficacy remains undetermined. Subsequent clinical studies comparing different volumes in a surgical setting, powered to show differences not only in analgesic efficacy, but also in adverse events, are required.

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DISCLOSURES

Name: Ulrik Grevstad, MD, PhD.

Contribution: This author helped in study design, conduct of the study, data collection, data analysis, and manuscript preparation.

Name: Pia Jæger, MD, PhD.

Contribution: This author helped in study design, conduct of the study, data collection, data analysis, and manuscript preparation.

Name: Johan Kløvgaard Sørensen, MS.

Contribution: This author helped in study design, conduct of the study, and manuscript preparation.

Name: Bo Gottschau, MD.

Contribution: This author helped in study design, conduct of the study, and manuscript preparation.

Name: Brian Ilfeld, MD, MS.

Contribution: This author helped in study design and manuscript preparation.

Name: Martin Ballegaard, MD, PhD.

Contribution: This author helped in study design and manuscript preparation.

Name: Mike Hagelskjaer, MSc.

Contribution: This author helped in technical design and manuscript preparation.

Name: Jørgen Berg Dahl, MD, DMSc, MBA.

Contribution: This author helped in study design and manuscript preparation.

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

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ACKNOWLEDGMENTS

The authors thank the staff at the Department of Clinical Neurophysiology, Rigshospitalet and at the Department of Anaesthesia, Centre of Head and Orthopaedics, Rigshospitalet, for letting them use their facilities. They also thank the Copenhagen University Hosptitals Good Clinical Practice Unit, Bispebjerg Hospital, for monitoring the study.

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REFERENCES

1. Jaeger P, Grevstad U, Henningsen MH, Gottschau B, Mathiesen O, Dahl JB. Effect of adductor-canal-blockade on established, severe post-operative pain after total knee arthroplasty: a randomised study. Acta Anaesthesiol Scand 2012;56:1013–9.
2. Grevstad U, Mathiesen O, Lind T, Dahl JB. Effect of adductor canal block on pain in patients with severe pain after total knee arthroplasty: a randomized study with individual patient analysis. Br J Anaesth 2014;112:912–9.
3. Memtsoudis SG, Yoo D, Stundner O, Danninger T, Ma Y, Poultsides L, Kim D, Chisholm M, Jules-Elysee K, Valle AG, Sculco TP. Subsartorial adductor canal vs femoral nerve block for analgesia after total knee replacement. Int Orthop 2015;39:673–80.
4. Grevstad U, Mathiesen O, Valentiner LS, Jaeger P, Hilsted KL, Dahl JB. Effect of adductor canal block versus femoral nerve block on quadriceps strength, mobilization, and pain after total knee arthroplasty: a randomized, blinded study. Reg Anesth Pain Med 2015;40:3–10.
5. Hanson NA, Derby RE, Auyong DB, Salinas FV, Delucca C, Nagy R, Yu Z, Slee AE. Ultrasound-guided adductor canal block for arthroscopic medial meniscectomy: a randomized, double-blind trial. Can J Anaesth 2013;60:874–80.
6. Espelund M, Grevstad U, Jaeger P, Hölmich P, Kjeldsen L, Mathiesen O, Dahl JB. Adductor canal blockade for moderate to severe pain after arthroscopic knee surgery: a randomized controlled trial. Acta Anaesthesiol Scand 2014;58:1220–7.
7. Andersen HL, Gyrn J, Møller L, Christensen B, Zaric D. Continuous saphenous nerve block as supplement to single-dose local infiltration analgesia for postoperative pain management after total knee arthroplasty. Reg Anesth Pain Med 2013;38:106–11.
8. Kwofie MK, Shastri UD, Gadsden JC, Sinha SK, Abrams JH, Xu D, Salviz EA. The effects of ultrasound-guided adductor canal block versus femoral nerve block on quadriceps strength and fall risk: a blinded, randomized trial of volunteers. Reg Anesth Pain Med 2013;38:321–5.
9. Jaeger P, Nielsen ZJ, Henningsen MH, Hilsted KL, Mathiesen O, Dahl JB. Adductor canal block versus femoral nerve block and quadriceps strength: a randomized, double-blind, placebo-controlled, crossover study in healthy volunteers. Anesthesiology 2013;118:409–15.
10. Chen J, Lesser JB, Hadzic A, Reiss W, Resta-Flarer F. Adductor canal block can result in motor block of the quadriceps muscle. Reg Anesth Pain Med 2014;39:170–1.
11. Veal C, Auyong DB, Hanson NA, Allen CJ, Strodtbeck W. Delayed quadriceps weakness after continuous adductor canal block for total knee arthroplasty: a case report. Acta Anaesthesiol Scand 2014;58:362–4.
12. Horner G, Dellon A. Innervation of the human knee joint and implications for surgery. Clin Orthop Relat Res 1994;221–6.
13. Senn S. Crossover Trials in Clinical Research: Concepts and Methodologies. 2002Chichester, UK: John Wiley & Sons, Ltd.
14. Murray JM, Derbyshire S, Shields MO. Lower limb blocks. Anaesthesia 2010;65(suppl 1):57–66.
15. Stark T, Walker B, Phillips JK, Fejer R, Beck R. Hand-held dynamometry correlation with the gold standard isokinetic dynamometry: a systematic review. PM R 2011;3:472–9.
16. Rainoldi A, Melchiorri G, Caruso I. A method for positioning electrodes during surface EMG recordings in lower limb muscles. J Neurosci Methods 2004;134:37–43.
17. Wayne P. Defining, establishing and verifying reference intervals in the clinical laboratory. Clin Lab Stand Inst 2008;CLSI C28-A.
18. Efron B, Tibshirani R. An Introduction to the Bootstrap. 1993New York, NY: Chapman and Hall.
19. Mizner RL, Petterson SC, Stevens JE, Vandenborne K, Snyder-Mackler L. Early quadriceps strength loss after total knee arthroplasty. The contributions of muscle atrophy and failure of voluntary muscle activation. J Bone Joint Surg Am 2005;87:1047–53.
20. de Oliveira F, de Vasconcellos Fontes RB, da Silva Baptista J, Mayer WP, de Campos Boldrini S, Liberti EA. The connective tissue of the adductor canal—a morphological study in fetal and adult specimens. J Anat 2009;214:388–95.
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