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The Risk of Falls After Total Knee Arthroplasty with the Use of a Femoral Nerve Block Versus an Adductor Canal Block: A Double-Blinded Randomized Controlled Study

Elkassabany, Nabil M. MD, MSCE; Antosh, Sean MD; Ahmed, Moustafa MD; Nelson, Charles MD; Israelite, Craig MD; Badiola, Ignacio MD; Cai, Lu F. MD; Williams, Rebekah BS; Hughes, Christopher MPT; Mariano, Edward R. MD, MAS; Liu, Jiabin MD, PhD

doi: 10.1213/ANE.0000000000001237
Regional Anesthesia: Research Report

BACKGROUND: Adductor canal block (ACB) has emerged as an appealing alternative to femoral nerve block (FNB) that produces a predominantly sensory nerve block by anesthetizing the saphenous nerve. Studies have shown greater quadriceps strength preservation with ACB compared with FNB, but no advantage has yet been shown in terms of fall risk. The Tinetti scale is used by physical therapists to assess gait and balance, and total score can estimate a patient’s fall risk. We designed this study to test the primary hypothesis that FNB results in a greater proportion of “high fall risk” patients postoperatively using the Tinetti score compared with ACB.

METHODS: After institutional review board approval, informed written consent to participate in the study was obtained. Patients undergoing primary unilateral total knee arthroplasty were eligible for enrollment in this double-blind, randomized trial. Patients received either an ACB or FNB (20 mL of 0.5% ropivacaine) with catheter placement (8 mL/h of 0.2% ropivacaine) in the setting of multimodal analgesia. Continuous infusion was stopped in the morning of postoperative day (POD)1 before starting physical therapy (PT). On POD1, PT assessed the primary outcome using the Tinetti score for gait and balance. Patients were considered to be at high risk of falling if they scored <19. Secondary outcomes included manual muscle testing of the quadriceps muscle strength, Timed Up and Go (TUG) test, and ambulation distance on POD1 and POD2. The quality of postoperative analgesia and the quality of recovery were assessed with American Pain Society Patient Outcome Questionnaire Revised and Quality of Recovery-9 questionnaire, respectively.

RESULTS: Sixty-two patients were enrolled in the study (31 ACB and 31 FNB). No difference was found in the proportion of “high fall risk” patients on POD1 (21/31 in the ACB group versus 24/31 in the FNB group [P = 0.7]; relative risk, 1.14 [95% confidence interval, 0.84–1.56]) or POD2 (7/31 in the ACB versus 14/31 in the FNB group [P = 0.06]; relative risk, 2.0 [95% confidence interval, 0.94–4.27]). The average distance of ambulation during PT and time to up and go were similar on POD1 and POD2. Manual muscle testing grades were significantly higher on POD1 in the ACB group when compared with that in the FNB (P = 0.001) (Wilcoxon-Mann-Whitney odds, 2.25 [95% confidence interval, 1.35–4.26]). There were no other differences in postoperative outcomes.

CONCLUSIONS: ACB results in greater preservation of quadriceps muscle strength. Although we did not detect a significant reduction in fall risk when compared with FNB, based on the upper limit of the relative risk, it may very well be present. Further study is needed with a larger sample size.

From the Departments of *Anesthesiology and Critical Care, Orthopedic Surgery, and Physical Therapy and Rehabilitation, University of Pennsylvania, Philadelphia, Pennsylvania; §Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University School of Medicine, Stanford, California; and Anesthesiology and Perioperative Care Service, VA Palo Alto Health Care System, Palo Alto, California.

Accepted for publication January 10, 2016.

Funding: Education and Development funds, Department of Anesthesiology and Critical Care, University of Pennsylvania.

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

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website.

Reprints will not be available from the authors.

Address correspondence to Nabil M. Elkassabany, MD, MSCE, Department of Anesthesiology and Critical Care, University of Pennsylvania, 3400 Spruce St., Dulles 6, Philadelphia, PA 19104. Address e-mail to Nabil.Elkassabany@uphs.upenn.edu.

Femoral nerve block (FNB) is a commonly used modality for postoperative analgesia after total knee arthroplasty (TKA). It is considered by some as the gold standard for postoperative analgesia after TKA.1 However, FNB reduces quadriceps muscle strength essential for mobilization and can potentially limit a patient’s ability to actively participate in any physical rehabilitation program. Quadriceps weakness places patients at risk of falling,2 which may be detrimental to postoperative recovery and may increase the hospital length of stay. Adductor canal block (ACB) has emerged as an appealing alternative to FNB that produces a predominantly sensory nerve block by anesthetizing the saphenous nerve.3 Studies have shown greater quadriceps strength preservation with ACB compared with FNB in healthy volunteers4 and in patients undergoing TKA.5 No study has reported the association between ACB and falls after TKA. Assessment of patients’ falls as an outcome may be difficult because it is a rare event (2–2.5 falls per 1000 hospital days) and frequently underreported.6,7 In addition, the definition of falls can vary between different institutions,8 which may make it difficult to define what constitutes a fall as a measurable endpoint across different studies. The Tinetti scale for gait and balance is a validated instrument that offers assessment of the individual patient’s risk for falls.9 Scoring is done on a 3-point scale with a range on each item of 0 to 2, with 0 representing the most impairment. Individual scores are then combined to form 3 scales: a Gait Scale, a Balance Scale, and overall Gait and Balance score. The maximal score for gait is 12 points, whereas the maximum for balance is 16 points with a total maximum for the overall Tinetti instrument of 28 points. Patients scoring 19 or less are considered at high risk for falls.

Assessment of the adequacy of pain control and its impact on patients’ perioperative experience goes beyond the traditional assessment of pain scores and the total amount of opioids.10 Patient-centered outcomes are becoming increasingly important in the era of pay for performance and the Affordable Care Act. The American Pain Society Patient Outcome Questionnaire Revised (APS-POQ-R) was designed and validated for assessment of the quality of pain management in hospitalized adults.11 The questionnaire assesses the effect of postoperative pain on patient experience in 5 domains: (1) pain intensity and interference with activity, (2) interference with sleep, (3) affective subscale, (4) adverse effects of pain treatment, and (5) patient perception of care.

Quality of recovery (QOR) has also been recognized as an important patient-oriented outcome and has been correlated with other measures of health-related quality of life in the postoperative period.12 It has been used to measure and compare the impact of different perioperative interventions on patient health status.

The primary aim of this study was to test the hypothesis that FNB results in a greater proportion of “high fall risk” patients postoperatively using the Tinetti score compared with ACB. Secondary endpoints of the study included comparing multiple physical therapy (PT) performance endpoints, including strength of the quadriceps muscle using manual muscle testing (MMT), ambulation distance, and Timed Up and Go test (TUG). Pain scores, the quality of pain management, and the QOR were also compared between the 2 groups.

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METHODS

This prospective, randomized, double-blind study with a parallel design and an allocation ratio of 1 to 1 for the treatment groups was approved by the institutional review board of the University of Pennsylvania (Philadelphia, PA). The study was registered with ClinicalTrials.gov, Identifier NCT02314832.

Patients scheduled for primary TKA with American Society of Anesthesiologists physical status I to III, mentally competent, and able to give consent for enrollment in the study were included in the study. Exclusion criteria included allergy to local anesthetics or any of the drugs included in the multimodal perioperative pain protocol (MP3) was considered as an exclusion criterion. Revision surgeries, the second surgery of staged bilateral TKA, and patients with body mass index of 40 kg/m2 or higher were excluded. Patients with impaired kidney functions and/or coagulopathy were also excluded. Patients with chronic pain syndromes or chronic opioid use, defined as the use of regular daily doses of systemic opioids for the past 6 months before the surgery, were also excluded from the current study.

Patients were identified from the surgical schedule the day before surgery and scanned for eligibility for enrollment. They were assigned to participate in the study the morning of their surgery by 1 of the study investigators or the research coordinator. A computer-generated randomization table was used for patient allocation to 1 of the 2 study groups, the FNB group or the ACB group. Randomization was performed in blocks of 10 patients. Patients’ assignments were written in a sealed envelope that was opened only after patient consent for the study. The nurses on the floor, the research coordinator, and the physical therapist were all blinded to the nature of patient assignment. The dressing over the catheter was made wide enough to conceal the difference of the catheter location between FNB and ACB groups.

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Statistical Analysis

Statistical analyses were performed using STATA 13 statistical software, Dallas, TX. Demographic data were analyzed using the Student’s t test or Fisher’s exact test as appropriate. Tinetti scores, other PT endpoints, the results of QOR-9 questionnaire, and the results of the APS-POQ-R were analyzed using the Mann-Whitney U test. Categorical data were analyzed using χ2 analysis or Fisher’s exact test. Normally distributed data are presented as mean ± SD; nonnormally distributed data are presented as median ± quartiles (interquartile range); and categorical data are presented as raw data and as frequency. The relative risk estimates were calculated via a log-binomial regression model with the data treated as binary variables. The confidence interval was calculated via generalized linear models under binomial distribution assumption and log transformation. In addition, we also calculated Wilcoxon-Mann-Whitney odds (WMWodds) and 95% confidence interval as previously described as the summary measure after Mann-Whitney U test.13,14 The WMWodds can highlight the discordance between medians and rank-order test results. The α level for all analyses was set as P < 0.05.

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Sample Size Calculation

Pilot data from 20 patients before the current study showed that 80% of patients receiving continuous femoral nerve block will score 19 or less on the Tinetti scale 24 hours after surgery, which indicated that these patients are at risk for fall.9 With estimated α = 0.05, power at 0.8, and a 2-sided test, 23 patients per group are needed to detect a 50% reduction in the risk of fall. To allow for dropouts, we inflated the sample size by 30%, which resulted in an estimated 30 patients per group.

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Study Procedures

Anesthetic management was left to the discretion of the anesthesiologist. All patients received their MP3 medication per protocol on admission to the hospital. After patients had consented, their group assignment was revealed to the anesthesiologist on the acute pain service who performed the block before surgery. Blocks were performed in the block room attached to the patient receiving area.

All blocks were performed under ultrasound guidance. A SonoSite S nerve machine was used with a high-frequency linear ultrasound probe with 6 to 13 MHz frequency.

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For Continuous Femoral Nerve Block

Images of the femoral nerve were obtained in the short axis. One percent lidocaine was used for local infiltration of the skin. A 2-inch 18-G Tuohy needle was advanced in-plane under ultrasound guidance. A bolus of 20 mL ropivacaine 0.5% was injected in increments of 5 mL. A nonstimulating catheter was advanced through the needle to a distance of 2 to 3 cm beyond the needle tip. The catheter was secured in place using SurgiSeal®, Steri-Strips, and Tegaderm™.

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For the Adductor Canal Block

In a short-axis view, the femoral artery was traced from the inguinal crease inferiorly on the medial side of the thigh until the femoral artery was centrally located under the sartorius muscle with the vein just inferior and the saphenous nerve just lateral to the artery. The Tuohy needle was introduced in-plane, and 2 to 3 mL of local anesthetic was used to verify correct placement of the needle in the vicinity of the saphenous nerve in the adductor canal. A bolus of total volume of 20 mL of ropivacaine 0.5% was injected through the needle. The catheter was introduced and advanced 2 to 3 cm beyond the tip of the needle under ultrasound guidance; 2 to 3 mL of local anesthetic was injected through the catheter to verify the spread of local anesthetic through the catheter. This technique was previously described in different studies.15,16

At the conclusion of surgery, a large opaque dressing was applied from the femoral crease to the midthigh region so that the catheter location was concealed. Ropivacaine 0.2% at 8 mL/h was started in the postanesthesia care unit (PACU). In the PACU, intermittent boluses of hydromorphone or fentanyl were used as needed for analgesia based on patients’ reported pain scores. All patients received the MP3 for postoperative analgesia. Medications used for the multimodal analgesia protocol include acetaminophen (1 g every 8 hours for 72 hours), celecoxib (200 mg every 12 hours for 72 hours), gabapentin (400 mg before surgery to be followed by 300 mg every 8 hours; patients remained on gabapentin for 1 week), and oxycodone (given as needed every 4–6 hours; the dose of oxycodone was given based on reported pain score by the patient).

All patients received prophylaxis treatment for postoperative nausea and vomiting during surgery. The protocol for prophylaxis against postoperative nausea and vomiting included administration of 4 mg dexamethasone after induction of anesthesia and 4 mg ondansetron 20 minutes before recovery from anesthesia. Dexamethasone was withheld if the patient had poorly controlled diabetes mellitus, defined as random blood glucose level >250 mg/dL.

The perineural catheter remained in place until the morning of postoperative day (POD)1. The infusion was stopped at 7 AM, approximately 2 hours before starting PT. The catheter was removed if the patients were deemed comfortable on assessment during the acute pain service rounds.

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Measurements

All PT measurements were performed by the same physical therapist who was blinded to the nature of group assignment. The following PT measures were recorded at 24 and 48 hours (between 9 and 10 AM on POD1 and POD2): Tinetti score for gait and balance, MMT, TUG, ambulation distance, and pain scores before and after PT sessions. The MMT was done with patients in the sitting position. The patients were asked to extend their knee against gravity from a flexed position. Grading was from 0 to 5 of 5. If the patient was able to extend the knee to full extension against gravity, it was scored 3 of 5. If he or she was able to hold the knee in extension against resistance, the test was scored as 5 of 5. If the patient was unable to generate any contraction, the score was 0 of 5. The grading 0 to 2 of 5 was based on how much patients were able to move a limb (gravity eliminated) throughout the range of motion. TUG was defined as the time, in seconds, it took a patient to stand up from a chair, walk to a line 3 feet away, turn around, and get back to a sitting position in the chair. The use of an assisting device was allowed.

Measurement of the QOR was also recorded at 24 hours, 48 hours, and 1 week after surgery using the QOR-9 questionnaire (Supplemental Digital Content 1, http://links.lww.com/AA/B385). The quality of pain management was assessed using the revised APS-POQ-R at 24 hours (Supplemental Digital Content 2, http://links.lww.com/AA/B386). The questionnaires were administered by the same research assistant who was blinded to the group assignments. Opioid requirements were recorded in the PACU and at the end of each nursing shift. Opioids were converted to the equivalent dose of oxycodone using an online calculator.17 Opioid consumption was calculated and reported on the morning of POD1 and for the next 24 hours on the morning of POD2.

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RESULTS

A total of 165 patients were screened for eligibility for the study; 73 patients met inclusion criteria and were approached to participate in the study, and 11 patients declined to participate (Fig. 1). The enrollment period extended from June to September 2014. Sixty-two patients were enrolled in the study (31 ACB and 31 FNB). Patient characteristics were similar between the 2 groups (Table 1). No complications related to the performance of the blocks were encountered.

Table 1

Table 1

Figure 1

Figure 1

Patients were considered to be at high risk for fall if their total Tinetti score was <19. No difference was detected in the proportion of “high fall risk” patients on POD1 (21/31 in the ACB group versus 24/31 in the FNB group [P = 0.7]; relative risk, 1.14 [95% confidence interval, 0.84–1.56]) or POD2 (7/31 in the ACB versus 14/31 in the FNB group [P = 0.06]; relative risk, 2.0 [95% confidence interval, 0.94–4.27]). There was no difference in the ratio of patients at risk for falls between spinal (14/37) and general anesthesia (7/25) (P = 0.6). The average distance of ambulation during PT and TUG were similar on POD1 and POD2. MMT grades were significantly higher on POD1 in the ACB group when compared with the FNB (P = 0.001; WMWodds, 2.25 [95% confidence interval, 1.35–4.26]). However, its clinical indication might be limited with values ranging from 2 to 3 out of 5 MMT. No statistical difference was found by POD2 (P > 0.99) (Table 2).

Table 2

Table 2

There was no difference in pain scores measured by the physical therapist before and after sessions of PT at 24 and 28 hours. Opioid requirements in 24 hours were similar between the 2 groups, calculated on the mornings of POD1 and POD2, P = 0.9 and P = 0.4, respectively. Opioids other than oxycodone were converted to the milligram equivalent oral dose of oxycodone using an online calculator17 (Table 3).

Table 3

Table 3

Table 4

Table 4

Table 5

Table 5

The quality of pain management in the first 24 hours was assessed using the APS-POQ-R. The research assistant administered the questionnaire on the morning of POD1. There was no difference in the 5 domains of the questionnaire between the 2 groups (Table 4). The QOR-9 score was not different between the ACB and the FNB groups at 24 hours, 48 hours, and 1 week (Table 5).

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DISCUSSION

Despite the significant preservation of the motor function of the quadriceps muscle with the ACB when compared with FNB, we failed to detect a significant reduction in the number of patients deemed to be at high risk for falls. However, based on the 4.27 relative risk upper limit, there could be as great as a 4.3-fold reduction in risk. Other PT endpoints, TUG, and average distance to ambulation were also similar between the 2 groups. Pain scores were comparable between the 2 groups before and after their PT sessions. From the patients’ perspective, the quality of pain management and the QOR were equivalent between the 2 block techniques.

There is a growing body of literature comparing the effect of ACB versus FNB for postoperative analgesia after TKA.5,18–23 Results of the current study were consistent with others in terms of preservation of the quadriceps muscle strength in healthy volunteers4,24 and after TKA.5,20 However, some authors still reported quadriceps muscle weakness after ACB and attributed the weakness to proximal spread of local anesthetic into the femoral triangle.25,26 Others explain the weakness of the quadriceps after TKA as a result of the pre-existing disease and surgery itself and argue that regional blocks promote analgesia, early movement, and rehabilitation.27,28 Grevstad et al.29 found that patients who had ACB after TKA did better in terms of their ambulation distance and TUG test when compared with those who received FNB. In the current study, ambulation distance and TUG were similar between the ACB and the FNB in the first 2 PODs. We may have been underpowered to detect these differences.

FNB, used for postoperative analgesia after TKA, has been associated with increased risk of falls because of quadriceps muscle weakness, impairment in proprioception, pivoting, and balance correction.30,31 These factors combined can result in decreased stability of the lower extremity and hence increase the fall risk. Other factors associated with increased risk of falls include female sex, age >65 years, and revision surgery.6 One study showed that 1.2% of all TKAs over 10 years period fell; 46% of the falls were related to using the bathroom, and 74% of patients fell while using a supporting device.7

Memtsoudis et al.32 examined risk factors associated with inpatient falls after orthopedic procedures in the Nationwide Inpatient Sample data files. They found that revision procedures, male sex, minority race, and higher comorbidity load were associated with more frequent inpatient falls. However, another recent analysis of the national premier database reported that the incidence of inpatient falls after TKA was 1.2%. Risk factors associated with higher odds of falls were advanced age and higher comorbidity index. There was no association between the use of peripheral nerve blocks in TKA and the patient falls.33 This study also showed that spinal anesthesia was associated with fewer patient falls than general anesthesia. In the current study, the risk of falls was similar between spinal and general anesthesia. However, we were not powered enough to detect the difference in the risk of falls based on the type of anesthesia.

Our results show that most patients (68% and 77% for ACB and FNB, respectively) were at high risk for falls in the 24 hours after surgery. Falls after TKA are not solely a function of quadriceps weakness. Other factors may contribute to increasing the risk of falls in these patients.

To our knowledge, this is the first study to assess the risk of falls using the Tinetti scale for gait and balance in the setting of comparing the 2 regional techniques after TKA. Kwofie et al.24 assessed quadriceps muscle strength and risk of falls using Berg’s balance scale in healthy volunteers after ACB versus FNB. They found that quadriceps muscle strength and balance were preserved in the ACB group compared with the FNB.

Pain scores, postoperative opioid requirements, and the results of the APS-POQ-R were similar between the 2 groups in the 5 domains of quality of pain management. These findings may be attributable, in part, to the use of the MP3 and possible residual blockade, especially in POD1. Other studies were able to show similarity20,29 and/or noninferiority5 of the ACB to the FNB in terms of analgesia. Others have reported a more painful leg when the ACB was compared simultaneously with FNB in bilateral TKA.34 Critics of the analgesic efficacy of ACB after TKA make their case based on the anatomy of innervation of the knee.27,35 The magnitude of contribution of ACB to the efficacy of a multimodal analgesic protocol remains a subject of debate.36

Assessment of the overall quality of pain management and understanding the effect of pain management on patients’ QOR and satisfaction should be used to guide clinical practice. The QOR was similar between the 2 groups at 24 hours, 48 hours, and 1 week after surgery. The QOR is a patient-related health status measure that was developed for postoperative patient assessment.37 In the current study, we used the short version of the questionnaire (QOR-9) that has proven to be valid, reliable, and simple to use in routine clinical practice.38 Myles et al.39 have shown a correlation between the QOR and the patient satisfaction in a prospective study of 10,811 inpatients seen on POD1.

This study has several limitations. First, there was no formal assessment for the sensory and motor distribution of the block after its performance, which did not allow for verification of having a functioning block. Second, the local anesthetic infusion was stopped between 7 and 8 AM on POD1 and did not run for the entire period of observation (48 hours). We do not believe that stopping the infusion on POD1 was the reason for the similarity in the risk of falls, because the strength of the quadriceps muscle was still significantly more preserved in the case of the ACB on initial assessment. PT usually takes place only 2 hours after the infusion is stopped. Third, assessment of the quadriceps muscle strength using a handheld dynamometer may be more objective than using MMT.40 However, all measurements in our study were done by the same therapist, who was blinded to group assignment, to ensure consistency in evaluations. Fourth, patients with chronic pain syndromes were excluded from the study. These patients need more intense analgesia regimen, and it may be that a more effective regional block is needed to meet their increased postoperative analgesic needs. Exclusion criteria for this study may limit the generalizability of its results, especially in terms of the ACB analgesic efficacy. Last, we did not control for the type of anesthesia, which may or may not have contributed to the risk of fall after TKA.

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CONCLUSIONS

ACB results in greater preservation of quadriceps muscle strength. Although we did not detect a significant reduction in fall risk when compared with FNB, based on the upper limit of the relative risk, it may very well be present. The results of this study should be interpreted cautiously within the context of the aforementioned limitations. Factors in addition to quadriceps muscle strength likely contribute to patients’ falls and should be addressed through education and training in a well-defined fall prevention program. Within the context of a multimodal analgesia protocol, the quality of pain management and the QOR were similar between the 2 groups. Compared with FNB, the extent of contribution of the ACB into postoperative analgesia remains a subject for future studies, especially in patients with increased postoperative analgesic requirements.

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DISCLOSURES

Name: Nabil M. Elkassabany, MD, MSCE.

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

Attestation: Nabil M. Elkassabany 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: Nabil M. Elkassabany reported no conflicts of interest.

Name: Sean Antosh, MD.

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

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

Conflicts: Sean Antosh reported no conflicts of interest.

Name: Moustafa Ahmed, MD.

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

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

Conflicts: Moustafa Ahmed reported no conflicts of interest.

Name: Charles Nelson, MD.

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

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

Conflicts: Charles Nelson reported no conflicts of interest.

Name: Craig Israelite, MD.

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

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

Conflicts: Craig Israelite reported no conflicts of interest.

Name: Ignacio Badiola, MD.

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

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

Conflicts: Ignacio Badiola reported no conflicts of interest.

Name: Lu F. Cai, MD.

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

Attestation: Lu F. Cai has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts: Lu F. Cai reported no conflicts of interest.

Name: Rebekah Williams, BS.

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

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

Conflicts: Rebekah Williams reported no conflicts of interest.

Name: Christopher Hughes, MPT.

Contribution: This author helped conduct the study.

Attestation: Christopher Hughes has seen the original study data and approved the final manuscript.

Conflicts: Christopher Hughes reported no conflicts of interest.

Name: Edward R. Mariano, MD, MAS.

Contribution: This author helped prepare the manuscript.

Attestation: Edward R. Mariano has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Conflicts of Interest: Edward R. Mariano has received unrestricted educational funding paid to his institution for conducting workshops on regional anesthesia from I-Flow/Kimberly-Clark (Lake Forest, CA) and B. Braun (Bethlehem, PA).

Name: Jiabin Liu, MD, PhD.

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

Conflicts: Jiabin Liu reported no conflicts of interest.

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

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

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