Comparison of Two Different Ultrasound Guided Techniques for Saphenous Nerve Block

Study Overview
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Brief Summary
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Saphenous nerve blocks can be technically challenging. Recently described ultrasound techniques have improved the success rate of saphenous nerve blocks, but randomized controlled trials comparing these techniques are lacking. The investigators compared two common ultrasound guided approach for saphenous nerve block: saphenous nerve block at the adductor canal (ACSNB) vs. block by the distal trans-sartorial (DTSNB) approach.

Detailed Description
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Patients received either ACSNB or DTSNB in this prospective randomized, blinded, non-inferiority clinical trial. The primary objective was to show the non-inferiority of ACSNB to DTSNB in terms of block success. Secondary outcome measures were time required to perform the block, time to onset of successful block, and the visibility of the nerve using ultrasound. Sample size calculation: To address the primary objective of the study--to show non-inferiority of the ACSNB to DTSNB in terms of success as defined above- the investigators used the test of non-inferiority of two proportions. DTSNB is the primary technique of doing saphenous nerve block at the investigators' institution. From chart review of the electronic records from 2011 to 2012, the investigators found there was a 3% incidence of rescue blocks among saphenous nerve blocks (19 out of 667 blocks) at their institution. This assumed a success rate of approximately 97%. A study by Saranteas et al reported a success rate of 95.6% in healthy volunteers undergoing saphenous nerve block just after it exited from the adductor canal. Based on these two observations, the investigators expected the success rate of DTSNB to be 95%. To establish the non-inferiority of ACSNB to DTSNB, the investigators pre-determined that the success rate of ACSNB should not be lower than 85% (the expected difference in proportions should be less than (95% - 85%) 10%). Under these assumptions, to achieve 80% power, with a one-sided type I error rate of 0.05, the study needed 59 subjects per group; 118 patients total. 120 patients were enrolled for this study., randomized to receive either ACSNB (n=58) or DTSNB (n=62).To show the non-inferiority of the ACSNB to DTSNB, the upper 95% confidence bound of the success rates (πDTSNB - πACSNB) should be less than 10%. The normality of continuous variables was tested by the Shapiro Wilk's test. Based on the normality assumption, two independent samples t-test or Mann-Whitney U test was performed for continuous variables. Chi-square test or Fisher's exact test was performed for categorical variables.

Official Title
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A Comparison of Two Different Ultrasound-Guided Approaches to the Saphenous Nerve Block - Adductor Canal vs. Distal Trans-sartorial: A Prospective, Randomized, Blinded, Non-Inferiority Trial

Conditions
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Efficacy of Ultrasound Guided Nerve Block

Intervention / Treatment
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* Procedure: Saphenous nerve block


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Patients undergoing elective foot and ankle surgery receiving saphenous nerve block for pain management American Society of Anesthesiologists Physical Status (ASA PS) scores 1, 2 and 3 Exclusion Criteria: Neuropathy Allergy to local anesthetics ASA PS scores 4 and 5

Ages Eligible for Study
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Minimum Age: 17 Years
Maximum Age: 70 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Supportive Care
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: DTSNB<br>Distal transsartorial saphenous nerve block | Procedure: Saphenous nerve block<br>* Ultrasound guided saphenous nerve blocks with 0.5% Ropivacaine for patients undergoing elective foot and ankle surgery for post-operative pain relief.<br>|
| Active Comparator: ACSNB<br>Adductor canal saphenous nerve block | Procedure: Saphenous nerve block<br>* Ultrasound guided saphenous nerve blocks with 0.5% Ropivacaine for patients undergoing elective foot and ankle surgery for post-operative pain relief.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Success rate of the saphenous nerve block | Loss of pin prick sensation to 2 of the 3 pre-defined areas of saphenous nerve distribution in the operative leg after performing the nerve block. | 30 minutes | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Speed of onset of saphenous nerve block | Time taken for loss of pinprick sensation in 2 of the 3 pre-defined areas of saphenous nerve distribution in the leg after performing the nerve block. | 30 minutes | 
| Nerve visibility under ultrasound | Nerve visibility under ultrasound guidance, graded as 1 (clearly visible) to 3 (not visible even after local anesthetic infiltration) | 30 minutes | 
| Time taken to perform block | Time taken from skin infiltration of local anesthetic to the nerve block needle removed from patient | 30 minutes |