Percutaneous tibial nerve stimulation (PTNS) is a clinical therapy for treating overactive bladder (OAB), where an un-insulated stainless steel needle electrode is used to target electrically the tibial nerve (TN) in the lower leg. Recent studies in anesthetized animals not only confirm that bladder-inhibitory reflexes can be evoked by stimulating the TN, but this reflex can also be evoked by stimulating the adjacent saphenous nerve (SAFN). Although cadaver studies indicate that the TN and major SAFN branch(es) overlap at the location of stimulation, the extent to which SAFN branches are co-activated is unknown. In this study, we constructed a finite element model of the human lower leg and applied a numeric axon model (MRG model) to simulate the electrical recruitment of TN and SAFN fibers during PTNS. The model showed that up to 80% of SAFN fibers (located at the level of the needle electrode) can be co-activated when electrical pulses are applied at the TN activation threshold, the standard therapeutic amplitude. Both the location of the inserted electrode and stimulation amplitude were important variables that affected the recruitment of SAFN branches. This study suggests further work is needed to investigate the potential therapeutic effects of SAFN stimulation in OAB patients.
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Medical engineering & physics. 2018 Feb 01 [Epub]
Christopher W Elder, Paul B Yoo
Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada., Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada; Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada. Electronic address: .