Frahm Ken Steffen, Hennings Kristian, Vera-Portocarrero Louis, Wacnik Paul W, Mørch Carsten Dahl
Department of Health Science & Technology, Integrative Neuroscience Group, Center for Sensory-Motor Interaction (SMI), Aalborg University, Aalborg, Denmark.
Nordic NeuroSTIM Aps, Aalborg, Denmark.
Neuromodulation. 2016 Aug;19(6):587-96. doi: 10.1111/ner.12466. Epub 2016 Jun 29.
Peripheral nerve field stimulation (PNFS) is a potential treatment for chronic low-back pain. Pain relief using PNFS is dependent on activation of non-nociceptive Aβ-fibers. However, PNFS may also activate muscles, causing twitches and discomfort. In this study, we developed a mathematical model, to investigate the activation of sensory and motor nerves, as well as direct muscle fiber activation.
The extracellular field was estimated using a finite element model based on the geometry of CT scanned lumbar vertebrae. The electrode was modeled as being implanted to a depth of 10-15 mm. Three implant directions were modeled; horizontally, vertically, and diagonally. Both single electrode and "between-lead" stimulation between contralateral electrodes were modeled. The extracellular field was combined with models of sensory Aβ-nerves, motor neurons and muscle fibers to estimate their activation thresholds.
The model showed that sensory Aβ fibers could be activated with thresholds down to 0.563 V, and the lowest threshold for motor nerve activation was 7.19 V using between-lead stimulation with the cathode located closest to the nerves. All thresholds for direct muscle activation were above 500 V.
The results suggest that direct muscle activation does not occur during PNFS, and concomitant motor and sensory nerve fiber activation are only likely to occur when using between-lead configuration. Thus, it may be relevant to investigate the location of the innervation zone of the low-back muscles prior to electrode implantation to avoid muscle activation.
周围神经场刺激（PNFS）是慢性下腰痛的一种潜在治疗方法。使用PNFS缓解疼痛依赖于非伤害性Aβ纤维的激活。然而，PNFS也可能激活肌肉，引起抽搐和不适。在本研究中，我们建立了一个数学模型，以研究感觉神经和运动神经的激活以及直接的肌纤维激活。
基于CT扫描腰椎的几何结构，使用有限元模型估计细胞外场。将电极建模为植入深度为10 - 15毫米。模拟了三个植入方向；水平、垂直和对角。对单电极和对侧电极之间的“导联间”刺激都进行了建模。将细胞外场与感觉Aβ神经、运动神经元和肌纤维模型相结合，以估计它们的激活阈值。
该模型表明，感觉Aβ纤维可以在低至0.563 V的阈值下被激活，使用阴极最靠近神经的导联间刺激时，运动神经激活的最低阈值为7.19 V。直接肌肉激活的所有阈值都高于500 V。
结果表明，在PNFS期间不会发生直接的肌肉激活，并且仅在使用导联间配置时才可能同时发生运动和感觉神经纤维激活。因此，在电极植入前研究下背部肌肉的神经支配区位置以避免肌肉激活可能是有意义的。
