Evaluation of the proximal adductor canal block injectate spread: a cadaveric study

BACKGROUND AND OBJECTIVES: Quadriceps sparing adductor canal block has emerged as a viable intervention to manage pain after total knee arthroplasty. Recent studies have defined ultrasound (US) landmarks to localize the proximal and distal adductor canal. US-guided proximal adductor canal injection has not been investigated using these sonographic landmarks. The objectives of this cadaveric study were to evaluate dye injectate spread and quantify the capture rates of nerves supplying articular branches to the knee joint capsule using a proximal adductor canal injection technique. METHODS: A US-guided proximal adductor canal injection with 10 mL of dye was performed in seven lightly embalmed specimens. Following injection, specimens were dissected to document dye spread and frequency of nerve staining. RESULTS: Following proximal adductor canal injection, dye spread consistently stained the deep surface of sartorius, vastoadductor membrane, aponeurosis of the vastus medialis obliquus, and adductor canal. The saphenous nerve, posteromedial branch of nerve to vastus medialis, superior medial genicular nerve and genicular branch of obturator nerve were captured in all specimens at the proximal adductor canal. There was minimal to no dye spread to the distal femoral triangle, anterior division of the obturator nerve and anterior branches of nerve to vastus medialis. CONCLUSIONS: This anatomical study provides some insights into the mechanism of analgesia to the knee following a proximal adductor canal injection and its motor sparing properties. Further clinical investigation is required to confirm cadaveric findings.