Comparison of Two Different Ultrasound Guided Techniques for Saphenous Nerve Block
Condition: Efficacy of Ultrasound Guided Nerve Block
Study type: Interventional

Summary: 
      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: 
      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.
    

Intervention name(s): Saphenous nerve block
Intervention type(s): Procedure
Intervention description(s): Ultrasound guided saphenous nerve blocks with 0.5% Ropivacaine for patients undergoing elective foot and ankle surgery for post-operative pain relief.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Outcomes Assessor)
Primary purpose: Supportive Care