Mapping the Saphenous Nerve from Surgical Landmarks: An Anatomic Guide for Adductor Canal Blocks
Authors: Talley Celine , Fadanelli Kara , Dash Suneeti 
Published: May 2022

Introduction & Objective

An adductor canal block (ACB) targets the saphenous nerve and provides significant pain control following total knee arthroplasties (TKA). Traditionally, the ACB is performed by an anesthesiologist as a pre‐operative procedure where the saphenous nerve is located via ultrasound. However, recent publications conclude orthopedic surgeons can feasibly and safely perform the block peri‐operatively. Researchers demonstrated that the saphenous nerve can be continually targeted from landmarks palpated during TKAs. While current literature supports consistent targeting of the saphenous nerve from palpated landmarks, the descriptive data mapping where the saphenous nerve travels in respect to those landmarks is limited. In this study we will attempt to determine if a consistent measurement exists between the surgically relevant adductor tubercle and the saphenous nerve as it exists within the adductor canal.

Materials & Methods

Eighteen (n=18) formalin‐embalmed cadavers from Kansas City University’s Gift Donor Program were examined. This inquiry yielded 34 (n=34) lower extremities for investigation. Dissections followed a standard medial parapatellar approach to identify the adductor tubercle. We identified and traced the saphenous nerve through an incision running from the anterior superior iliac spine to the tibial tuberosity. Pinning of the saphenous nerve occurred from the apex of the femoral triangle to its exit of the vasoadductor membrane. The pinned leg was photographed with a scale marker and the image uploaded for analysis in ImageJ. Distances from landmarks to the nerve were calculated in cm based on the center of each pin. The calculated measurements were transferred to GNU Octave to create a contour map. After dissection, the femur was disarticulated from the acetabular and knee joint and measured using an osteometric board. This measurement provided a better understanding of how the distances varied based on height.

Results

The average distance from the adductor tubercle to where the saphenous nerve exits the vasoadductor membrane was 9.58 cm (σ= 2.40 cm). The distance from the adductor tubercle to the apex of the femoral triangle is 24.32 cm (σ= 3.83 cm). Using these distances, we created a contour map to visualize the variation in measures.

Conclusion

This study demonstrates the spatial relationship between the adductor tubercle and the saphenous nerve and illustrates the most common distance the saphenous nerve is found from surgical landmarks. With this information, surgeons know where to target the saphenous nerve when performing a peri‐operative ACB.

Significance/Implications

Surgeon lead adductor canal blocks provide healthcare teams greater flexibility in treatment where anesthesiologists and technological resources may be limited. This study equips orthopedic surgeons with more descriptive knowledge about the spatial relationship between the saphenous nerve and the surgically relevant adductor tubercle in order to carry out ACB. Future work should repeat our methods to increase sample size to ensure the data better represents the population. Additional studies should include fresh frozen specimens to address the limitations that arise with stiff, formalin embalmed cadavers.