Anatomy of the saphenous nerve, its branches within the adductor canal, and its relationship with clinical implications during ACL reconstruction

Abstract

Purpose: The saphenous nerve lies in close proximity to the hamstrings and is at risk of injury during autologous grafting. This study aims to describe the potential risk of surgical injury to the saphenous branches during a classic HT harvesting with a stripper and to evaluate the efficacity of the diffusion of methylene blue infiltration into the adductor canal from a single retrograde injection from the hamstring tendon (HT) harvesting site. Methods: Eighteen frozen cadaveric lower limbs from nine cadavers were selected for surgical dissection. The study was divided into two separate procedures: 1) Surgical dissection and detailed anatomic description of the saphenous nerve and its branches was performed. 2) Methylene blue infiltration was performed from the harvesting site of the hamstring tendons followed by dissection to evaluate the diffusion of methylene blue to the saphenous nerve and its branches. Results: The direct visualization of the sartorial branch of the saphenous nerve (SBSN) was reproducible during HT harvesting, minimizing the risk of its iatrogenic damage. Additionally, nine limbs were infiltrated with 20cc of methylene blue prior to dissection. The dissemination limits of the nine cadavers included the saphenous nerve and its two main branches, whether the division was in the adductor canal or downstream at the adductor hiatus, in all cases (100%). The upper limit of diffusion was located at an average of 17 cm from the medial tibial condyle, at the level of the fascia between the vastus medialis and the adductor longus muscle. The femoral vascular bundle, the saphenous nerve and the medial aspect of the vastus medialis were stained with methylene blue in all cases. Conclusion: Direct visualization of the SBSN branch of the saphenous nerve, close to the HT expansions, must be recognized and appreciated to limit iatrogenic injury. Also, infiltration of the adductor canal via the hamstring donor site during autologous HT harvesting leads to diffusion to the saphenous nerve and its main branches which can be utilized intraoperatively with local anesthetic for reliable post operative pain control. Level of Evidence: Level IV. Keywords: ACL reconstruction, analgesia, FNB, postoperative pain, saphenous nerve, cadaver