The Impact of Leg Movement on the Skin to Adductor Canal Distance: a Potential Cause for Catheter Displacement?
Conditions: Knee Arthritis
Sponsor: University of British Columbia

Study Protocol and Statistical Analysis Plan 
 
The impact of leg movement on the skin to adductor canal distance: a potential cause for 
catheter displacement? 
 
NCT 03562559 
 
April 15th 2019 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Objectives: 
The primary goal of this study was to discover if there is significant change in the distance from 
the skin to the adductor canal with typical movements that happen after total knee arthroplasty. 
The secondary goals were to see absolute skin to adductor canal distance and if these changes 
in distance had any relation to the BMI and leg circumference. 
 
Background Information: 
Total knee arthroplasty (TKA) is increasingly common in North America due to growing obesity 
rates and an aging population​1​ . Effective pain control using a multimodal approach decreases 
narcotic use, enhances patient satisfaction and leads to quicker recovery​2​ . Regional anesthetic 
techniques such as the adductor canal block (ACB) have become a major component of the 
pain management strategy post TKA​3-5​. 
 
Single injection ACB and continuous infusion via a catheter are both currently utilized with the 
latter conferring the theoretical benefit of prolonged analgesia​6​. The efficacy of catheter 
analgesia is predicated primarily on its proper placement and maintenance. Despite growing 
expertise and the use of ultrasound, catheter tip displacement has been reported as high as 
26%​7-8​. In addition, recent trials did not show clear benefit of ACB catheters over single 
injections in terms of opioid consumption​9​ and pain scores​10​. This observational study seeks to 
investigate simple anatomic and mechanical factors that may contribute to catheter failure. 
Specifically, the trial examines the average SAC distance, and measures the relative distance 
changes as the leg is moved in various positions. It is hypothesized that the SAC distance 
changes with leg movement. If so, one may infer that repeated leg movements could gradually 
cause catheter tip migration while the catheter is secured to a fixed point on the skin.  
 
 
Study Design and Methods: 
After gaining ethics approval from the University of British Columbia (H17-02633) and 
registration with ClinicalTrials.gov (NCT 03562559) 40 patients undergoing total knee 
arthroplasty (TKA) were selected. Inclusion criteria were patients over the age of 18 undergoing 
TKA under spinal anesthetic that were capable of signing informed consent. 
 
Demographic data was collected including height, weight, BMI, and sex. 
 
Postoperatively, while still under the effects of the spinal anesthetic, measurements were made 
of the patient’s surgical leg from the skin to the adductor canal using a HLF50X 15-6 MHz 
transducer on a SonoSite SII ultrasound machine (Fujifilm, Toronto, ON). The adductor canal 
was identified with the transducer in the transverse plane on the patient’s thigh and the 
transducer footprint marked on the skin and the leg circumference was measured. This location 
is where one would normally perform the ACB at our institution with the superficial femoral 
artery (SFA) roughly abutting the trough of the sartorius muscle. The SFA in the adductor canal 
was used as a reference point for measurement. The distance from the skin to the most 
superficial and nearest point of the SFA was measured in the following positions: 1) neutral, 2) 

neutral position with manual lateral displacement of the skin, 3) 30 degree external rotation, 4) 
straight leg raised to 30 degrees and 5) knee and hip flexed to 90 degrees. For each position 
the ultrasound image was saved and a measurement from the upper lateral corner of the image 
to the SFA was taken and recorded. A single operator (MT) performed all scanning and 
measurement, while a single assistant facilitated the various passive leg movements. The 
ultrasound transducer was kept in the premarked footprint and oriented perpendicular to the 
thigh to provide consistency. 
 
Statistical Analysis Plan: 
All data were tabulated using Microsoft Excel and difference in distance between the leg 
positions were calculated. The means of these distances were used to discover the 90% 
confidence interval in each of the leg positions relative to the neutral position. For the secondary 
objective the data were graphically tabulated relative to the patient’s BMI and leg circumference. 
A line of best fit was then calculated using Excel.