Adductor Canal Block Ultrasound Anatomy in Volunteers

Overview

There has been dispute about the location at which the adductor canal block should be performed (3-6). Two Common approaches have been used for ultrasound guided adductor canal blocks with the 'point of entry' being: 1. Point A: midway point between the ASIS and base of patella 2. Point B: Point which is 2-3 cm proximal to the site where the femoral artery becomes the popliteal artery as it traverses away from the sartorius muscle towards the femur at the adductor hiatus (2) We want to determine ultrasound anatomy in healthy volunteers by: 1. Measuring the distance between Point A and Point B 2. Studying the ultrasound anatomy at Point A and B - Determine their location with respect to the adductor canal and femoral triangle. This will allow us to determine which is the best site for performing an adductor canal block

It is important to answer the primary question because of the variable length of the adductor canal and we would like to determine the optimal position to perform the adductor canal block. The adductor canal typically contains the saphenous nerve, nerve to vastus medialis muscle and on occasion, the obturator nerve (1). The roof of adductor canal is the vasto-adductor membrane and its length is reported to range from 5.5 cm to 15 cm with a mean of 7.6 cm2 and would suggest the length of the AC is variable. We would like to determine the length of the AC with the use of ultrasound. The AC would be determined to begin at the apex of the femoral triangle and end just proximal to the adductor hiatus. The length and location of the AC would be important to characterize as the volume of local anesthetic used and associated quadriceps weakness could be of significance in a shorter AC. There has been dispute about the location at which the adductor canal block should be performed (3-6). Point A has been disputed to be within the femoral triangle and would therefore be a femoral nerve block as suggested by a small body of evidence (4-5). Clinically, it is unclear if there is a difference between quadriceps muscle weakness between the two approaches although it could be hypothesized placing a block at point A would lead to more quadriceps muscle weakness. With information gathered from this study, we plan to perform a clinical study by performing the nerve blocks at these two points with different volumes of local anesthetic and compare the amount analgesia and motor weakness between the two different approaches. 60 Volunteers (30 male and 30 female) aged between 18 to 75 years with a body mass index of 18 to 35 kg/m2 will be included in this study. Volunteers with previous surgery or deformities of the lower extremity will be excluded from the study This is an observational study without a control group. Several reference points will be marked by anatomical landmarks and/or ultrasound: A. the anterior superior iliac spine (landmark); B. the base of the patella (landmark); C. apex of femoral triangle (ultrasound); and D. distal most portion of adductor canal (Point B described earlier; ultrasound). The primary outcome measure we are looking at is the distance between Point A and Point B. We also plan to measure the distance (in centimeters) from: 1. Base of patella to Point A 2. Base of patella to Point B 3. Apex of the femoral triangle