JOURNAL OF NEUROTRAUMA Volume 9, Number 3, 1992 Mary Ann Liebert, Inc., Publishers
An Electromechanical
Spinal Injury Technique with Dynamic Sensitivity
BRADFORD T.
STOKES,1'2 DAVID H. NOYES,1 and DONALD L. BEHRMANN,2'3
ABSTRACT Over the past decade, our laboratory has attempted to create a simple, accurate device that could be used to produce reliable and quantifiable spinal cord injuries in the rodent. We report here on our latest of several modifications of a spinal cord impactor that has allowed us to meet these design criteria. The impactor uses the dynamic capacity of an electromagnetic driver (Ling shaker) and a unique pattern generator to briefly compress the dorsal surface of the spinal cord at velocities that may mimic compression injuries seen in the human. Calibrated, independent transducer systems provide open-loop output of the precise movement (displacement) of the impactor probe and the force necessary to achieve a given displacement. Touch sensitivity is accomplished by vibrating the probe slightly as it approaches the durai surface. This also allows a known biomechanical starting point. This combination of improvements in sensitivity and ability to measure all componenets of the dynamic compression has allowed us to determine detailed biomechanical descriptors of these impact injuries with low coefficients of variation. Furthermore, such descriptors correlate highly with histopathologic and behavioral outcome measures in animal populations with a variety of injury severities.
INTRODUCTION advances have been made in the development of devices that allow reproducible and quantifiable methods of experimental spinal cord injury in rodents (Noyes, 1987a; Noble and Wrathall, 1987; Beattie et al., 1988; Kearney et al., 1988; Anderson and Stokes, 1991; Anderson et al., 1992). The use of sensitive monitoring devices that permit the evaluation of biomechanical variables during the injury process has been a major development in this regard (Noyes, 1987a; Panjabi and Wrathall, 1988; Anderson and Stokes, 1991). As such devices evolve, it has become apparent that one can avoid the use of such terms as "gram-centimeter" (i.e., a weight dropped a through a frictionless tube from a given height) to characterize the physical nature of the injury (Noyes, 1987a, 1987b; Bresnahan et al., 1987; Somerson and Stokes, 1987; Beattie et al., 1988). The inadequate nature of such descriptors has been assessed previously (Molt et al., 1979; Noyes, 1987a;
Recent
Departments of ' Physiology and 2Surgery and 3Cell Biology, Neurobiology and Anatomy, The Ohio State University, College of Medicine, Columbus, Ohio. 187
STOKES ET AL. Beattie et al., 1988; Kearney et al., 1988; Panjabi and Wrathall, 1988), and the use of more precise measures of the physical events that occur during the injury process has been advocated (Noyes, 1987a; Beattie et al., 1988; Panjabi and Wrathall, 1988; Anderson and Stokes, 1991; Michel et al., 1992). After several design modifications in our spinal injury device, we report here on recent improvements in design and the subsequent results. In this and the next article, we characterize the design of the new electromechanical device, contrast its construction and use with other recent designs, and evaluate the precision of the biomechanical predictors in creating a variety of animal groups injured at different intensities. In the new design, we have improved the delivery of force to the spinal compartment and added new sensitive transducer systems to increase the precision of measurement. In addition, we have provided a predetermined mechanical starting point from which the injury can subsequently be made and provided simple calibration techniques to ensure reliability of the measured variables. By using such sensitive instrumentation and controlling our biomechanical variability, we have been able to create experimental groups that have sufficient behavioral sensitivity to various injury paradigms to be used in preclinical modeling with various experimental therapeutic protocols (Behrmannetal., 1991; Anderson et al., 1992).
MATERIALS AND METHODS General Protocol As described in detail in the next article, this injury device is used to make brief contusive injuries to the rodent spinal cord (
An Electromechanical
Spinal Injury Technique with Dynamic Sensitivity
BRADFORD T.
STOKES,1'2 DAVID H. NOYES,1 and DONALD L. BEHRMANN,2'3
ABSTRACT Over the past decade, our laboratory has attempted to create a simple, accurate device that could be used to produce reliable and quantifiable spinal cord injuries in the rodent. We report here on our latest of several modifications of a spinal cord impactor that has allowed us to meet these design criteria. The impactor uses the dynamic capacity of an electromagnetic driver (Ling shaker) and a unique pattern generator to briefly compress the dorsal surface of the spinal cord at velocities that may mimic compression injuries seen in the human. Calibrated, independent transducer systems provide open-loop output of the precise movement (displacement) of the impactor probe and the force necessary to achieve a given displacement. Touch sensitivity is accomplished by vibrating the probe slightly as it approaches the durai surface. This also allows a known biomechanical starting point. This combination of improvements in sensitivity and ability to measure all componenets of the dynamic compression has allowed us to determine detailed biomechanical descriptors of these impact injuries with low coefficients of variation. Furthermore, such descriptors correlate highly with histopathologic and behavioral outcome measures in animal populations with a variety of injury severities.
INTRODUCTION advances have been made in the development of devices that allow reproducible and quantifiable methods of experimental spinal cord injury in rodents (Noyes, 1987a; Noble and Wrathall, 1987; Beattie et al., 1988; Kearney et al., 1988; Anderson and Stokes, 1991; Anderson et al., 1992). The use of sensitive monitoring devices that permit the evaluation of biomechanical variables during the injury process has been a major development in this regard (Noyes, 1987a; Panjabi and Wrathall, 1988; Anderson and Stokes, 1991). As such devices evolve, it has become apparent that one can avoid the use of such terms as "gram-centimeter" (i.e., a weight dropped a through a frictionless tube from a given height) to characterize the physical nature of the injury (Noyes, 1987a, 1987b; Bresnahan et al., 1987; Somerson and Stokes, 1987; Beattie et al., 1988). The inadequate nature of such descriptors has been assessed previously (Molt et al., 1979; Noyes, 1987a;
Recent
Departments of ' Physiology and 2Surgery and 3Cell Biology, Neurobiology and Anatomy, The Ohio State University, College of Medicine, Columbus, Ohio. 187
STOKES ET AL. Beattie et al., 1988; Kearney et al., 1988; Panjabi and Wrathall, 1988), and the use of more precise measures of the physical events that occur during the injury process has been advocated (Noyes, 1987a; Beattie et al., 1988; Panjabi and Wrathall, 1988; Anderson and Stokes, 1991; Michel et al., 1992). After several design modifications in our spinal injury device, we report here on recent improvements in design and the subsequent results. In this and the next article, we characterize the design of the new electromechanical device, contrast its construction and use with other recent designs, and evaluate the precision of the biomechanical predictors in creating a variety of animal groups injured at different intensities. In the new design, we have improved the delivery of force to the spinal compartment and added new sensitive transducer systems to increase the precision of measurement. In addition, we have provided a predetermined mechanical starting point from which the injury can subsequently be made and provided simple calibration techniques to ensure reliability of the measured variables. By using such sensitive instrumentation and controlling our biomechanical variability, we have been able to create experimental groups that have sufficient behavioral sensitivity to various injury paradigms to be used in preclinical modeling with various experimental therapeutic protocols (Behrmannetal., 1991; Anderson et al., 1992).
MATERIALS AND METHODS General Protocol As described in detail in the next article, this injury device is used to make brief contusive injuries to the rodent spinal cord (
