Mid-part of adductor canal: Is it the optimal injection site for performing adductor canal block? A cadaver-based injection study

Background and Aims: Adductor canal block (ACB) has emerged as a selective sensory technique to provide pain relief to the anterior aspect of the knee joint. Despite a large amount of available literature, the ideal site for performing ACB remains debatable. With the use of ultrasound, it is now possible to define the exact location of the adductor canal (AC). The objectives of our cadaveric study were to examine the nerves captured by methylene blue dye (MBD) and the stain pattern of the nerves within the AC following mid-AC injection. Methods: We scanned the thigh area of six lightly embalmed cadavers (12 specimens) and marked the midpoint of the AC using ultrasound and injected 10 mL of (MBD) at this level. Thirty minutes later, all the specimens were dissected to document the frequency and stain pattern of various nerves traversing through the AC. Results: The vastoadductor membrane and saphenous nerve got stained heavily (+3) in all twelve specimens, while the nerve to vastus medialis stained heavily (+3) in four and moderately (+2) in eight specimens. Both the medial cutaneous nerve of the thigh and the intermediate cutaneous nerve of the thigh were stained moderately (+2) in four and two specimens, respectively. There was no spread of the dye into the distal femoral triangle area. Conclusions: Injection of MBD in the sonographically located mid part of the AC consistently involved the saphenous nerve and nerve to vastus medialis, and hence may be the optimal site for performing ACB.