Paresthesia Coverage Research Articles

Spinal Geometry and Paresthesia Coverage in Spinal Cord Stimulation

Objective. To test the following hypotheses, based on computer modeling studies of spinal cord stimulation, by the analysis of data from chronic pain patients: I. the probability-of-paresthesia in a dermatome is highest when the cathode is placed at the corresponding segmental level; II. variation of the rostrocaudal position of the cathode in the lower cervical/high thoracic region results in less variation of the probability-of-paresthesia in a dermatome than stimulation in more caudal regions; III. when stimulating in the midthoracic region, the probability-of-paresthesia in a dermatome is low in comparison to other regions when the cathode is not at the corresponding segmental level. Method. The probability-of-paresthesia in 16 body segments as a function of the rostrocaudal position of the cathode was analyzed from the paresthesia coverage with 3,897 bipolar and unipolar combinations from 106 chronic pain patients. Results. The distributions of the probability-of-paresthesia in the upper and lower limb are in accordance with the hypotheses, but different distributions were found in all trunk areas. Conclusion. The success to be expected from spinal cord stimulation in chronic pain management is inversely related to the thickness of the dorsal cerebrospinal fluid layer at the cathode level. Therefore, preoperative measurement from transverse images can be helpful as a predictor for success.

Analysis of Spinal Cord Stimulation and Design of Epidural Electrodes by Computer Modeling

This paper is an overview of the results of computer modeling of spinal cord stimulation, started ten years ago at the University of Twente, The Netherlands. Results are given of the analysis of various geometrical factors, including spinal anatomy, which influence the effect of spinal cord stimulation on nerve fiber recruitment and paresthesia coverage. In a second phase, the computer model was used for the design of new electrode configurations expected to give a better paresthesia coverage in the management of chronic pain. Two new electrode types are presented: the narrow bi-/tripole and the transverse tripole. The latter also enables adjusting the body area affected with paresthesia by means of a dual channel pulse generator giving simultaneous pulses, thereby limiting surgical interventions for electrode repositioning.

Effect of anode-cathode configuration on paresthesia coverage in spinal cord stimulation.

To provide a theoretical basis for the selection of the anode-cathode configuration in spinal cord stimulation for the management pain when one percutaneous epidural electrode or two electrodes in parallel are used. A computer model of spinal cord stimulation at T8-T9 was used to calculate the dorsal column areas recruited in stimulation by various configurations used in clinical practice. Tripolar (or bipolar) stimulation by a single electrode, symmetrically placed over the dorsal columns, recruits the largest area and will give the widest paresthesia coverage. Stimulation by two symmetrically placed electrodes connected in parallel to a single channel pulse generator may give similar results, because of their generally smaller distance from the spinal cord, but a "summation effect" does not exist. A smaller dorsal column area is activated when two offset electrodes are used. An electrode placed laterally or transverse bipolar stimulation results in unilateral, usually segmentary, paresthesia. The relative positions of cathodes and anodes and their distance from the spinal cord are the major determinants of dorsal column/dorsal root activation and paresthesia distribution. The large interpatient variability of the intraspinal geometry is the main cause of differences in paresthesia coverage among patients having optimally placed electrode(s). Changes of paresthesia coverage over time are more probable when multiple electrodes are used.

Effect of Anode-Cathode Configuration on Paresthesia Coverage in Spinal Cord Stimulation

Effect of Anode-Cathode Configuration on Paresthesia Coverage in Spinal Cord Stimulation

Effectiveness of Spinal Cord Stimulation in the Management of Chronic Pain: Analysis of Technical Drawbacks and Solutions

A major drawback of currently available spinal cord stimulation (SCS) systems for the management of chronic intractable pain, especially of widespread pain patterns as in reflex sympathetic dystrophy, is the generally limited paresthesia coverage. The aim of this study is to analyze the origin of this problem and to provide solutions. Results from theoretical studies, in which a computer model was used to mimic the effects of SCS on spinal nerve fibers, were used to analyze which factors may limit paresthesia coverage. Model predictions were verified by empirical data from clinical literature. When using common SCS electrodes, both perception threshold and motor/discomfort threshold are generally related to dorsal root stimulation. Because these thresholds have a small ratio (approximately 1:1.4), stimulation of dorsal column fibers and paresthesia coverage is limited by this small range of stimulation. When the distance between the epidural electrode and spinal cord is large (midthoracically), the threshold for dorsal column stimulation exceeds discomfort threshold, resulting only in segmental paresthesia. The range of dorsal column stimulation and paresthesia coverage can be improved when using either an optimally dimensioned rostrocaudal bi-/tripole or a transverse tripole ("guarded cathode"). When applying the latter in combination with a dual channel pulse generator providing simultaneous pulses, paresthesias can simply be changed to optimally cover the painful area. Paresthesia coverage and pain management by SCS can be improved when using electrodes as proposed.

Effectiveness of spinal cord stimulation in the management of chronic pain: analysis of technical drawbacks and solutions.

A major drawback of currently available spinal cord stimulation (SCS) systems for the management of chronic intractable pain, especially of widespread pain patterns as in reflex sympathetic dystrophy, is the generally limited paresthesia coverage. The aim of this study is to analyze the origin of this problem and to provide solutions. Results from theoretical studies, in which a computer model was used to mimic the effects of SCS on spinal nerve fibers, were used to analyze which factors may limit paresthesia coverage. Model predictions were verified by empirical data from clinical literature. When using common SCS electrodes, both perception threshold and motor/discomfort threshold are generally related to dorsal root stimulation. Because these thresholds have a small ratio (approximately 1:1.4), stimulation of dorsal column fibers and paresthesia coverage is limited by this small range of stimulation. When the distance between the epidural electrode and spinal cord is large (midthoracically), the threshold for dorsal column stimulation exceeds discomfort threshold, resulting only in segmental paresthesia. The range of dorsal column stimulation and paresthesia coverage can be improved when using either an optimally dimensioned rostrocaudal bi-/tripole or a transverse tripole ("guarded cathode"). When applying the latter in combination with a dual channel pulse generator providing simultaneous pulses, paresthesias can simply be changed to optimally cover the painful area. Paresthesia coverage and pain management by SCS can be improved when using electrodes as proposed.

Transverse tripolar spinal cord stimulation: theoretical performance of a dual channel system.

A new approach to spinal cord stimulation is presented, by which several serious problems of conventional methods can be solved. A transverse tripolar electrode with a dual-channel voltage stimulator is evaluated theoretically by means of a volume conductor model, combined with nerve fibre models. The simulations predict that a high degree of freedom in the control of activation of dorsal spinal pathways may be obtained with the described system. This implies an easier control of paraesthesia coverage of skin areas and the possibility to correct undesired paraesthesia patterns, caused by lead migration, tissue growth, or anatomical asymmetries, for example, without surgical intervention. It will also be possible to preferentially activate either dorsal column or dorsal root fibres, which has some important clinical advantages. Compared to conventional stimulation systems, the new system has a relatively high current drain.

Significance of the spinal cord position in spinal cord stimulation.

The effects of the antero-posterior and medio-lateral positions of the spinal cord in the dural sac on the perception threshold and paresthesia coverage in spinal cord stimulation were analyzed. The distributions of the dorsal cerebrospinal fluid (CSF) layer thickness, measured from transverse MR scans of normal subjects at various spinal levels, were used to calculate the distributions of threshold voltages for the stimulation of spinal nerve fibers by a computer model. These theoretical threshold distributions were shown to fit well to the corresponding distributions of perception threshold measured in patients. It is concluded that the thickness of the dorsal csf layer is the main factor determining the perception threshold and paresthesia coverage in spinal cord stimulation: an increasing thickness raises the threshold and reduces the coverage, and vice versa. The effects of an asymmetrical electrode position with respect to the spinal cord midline were also analyzed by computer modeling. It is concluded that a lateral asymmetry of less than 1 mm gives a significant reduction of perception threshold and may result in unilateral paresthesiae.