Investigation of dye spread following ultrasound guided injection at the femoral nerve, proximal and distal adductor canal – A cadaver study

Abstract

Background

Total knee arthroplasty (TKA) is associated with significant postoperative pain. Regional analgesic techniques targeting femoral nerve (FN) and adductor canal (AC) are commonly employed; however, uncertainty persists regarding optimal injection site within the AC. Cadaveric investigations provide anatomical insights into injectate spread patterns, but their interpretation requires caution when extrapolating to clinical practice.

Methods

Twelve thighs from six embalmed human cadavers underwent ultrasound-guided injections of different-colored dyes, with equal volumes administered at three predefined locations: FN, proximal AC, and distal AC. Subsequent anatomical dissections were performed to assess nerve staining patterns. Injection sites and volumes were standardized to allow for comparative anatomical evaluation.

Results

Femoral-level injections stained the femoral nerve and its major branches. Proximal AC injections consistently stained both the saphenous nerve and nerve to vastus medialis, whereas distal canal injections predominantly stained the saphenous nerve with only variable distal obturator involvement. The vaso-adductor membrane stained consistently after proximal canal injection. No sciatic nerve staining was observed.

Conclusion

Equal-volume dye injections at the FN, proximal AC, and distal AC demonstrate distinct patterns of neural staining. Proximal AC injections resulted in consistent staining of both SN and NVM, whereas distal injections predominantly involved SN. These findings provide anatomical relevance regarding adductor canal block techniques but do not imply clinical superiority of any technique. Clinical correlation is required before extrapolating these observations to clinical practice.