Optimizing electrode placement for saphenous nerve conduction study based on cadaveric dissection and probabilistic mapping

초록

Background and aims: Saphenous nerve (SN) conduction studies are often unreliable even in healthy individuals, raising questions about whether absent responses reflect pathology or suboptimal electrode placement. Anatomical textbooks suggest that the SN passes anterior to the medial malleolus (MM), but cadaveric studies have yielded conflicting descriptions. Recent literature points toward a course between the tibialis anterior (TA) tendon and the anterior margin of the MM. The purpose of this study is to identify the most accurate stimulation and recording sites for SN conduction studies by combining detailed cadaveric dissection with probabilistic modeling. Methods: Eighteen lower limbs from nine cadavers were dissected. SN trajectories and branch thicknesses were recorded at five anatomical landmarks (ANT, TIP, ANT10, ANT12, and POS). Positions were normalized using MM width and tibial length. A custom analysis tool (“Nerve-Morphology-2.0”) applied Gaussian convolution across nerve pathways to generate probability heatmaps for optimal electrode placement. Results: Contrary to prior reports, only 7 of 39 branches passed between TA tendon and MM; the majority coursed directly over the MM. The most probable recording site was 4 mm posterior to ANT. The optimal stimulation site was ANT12 or 2.98 mm anterior to it. Probabilistic mapping outperformed simple median-based estimates. Clinical validation in healthy volunteers confirmed maximal SN response between ANT and ANT-1 cm. Conclusions: This study provides an evidence-based anatomical and probabilistic guideline for SN conduction studies, enhancing diagnostic reliability and clinical applicability. Further studies with more diverse specimens are warranted for broader generalization.