An electromechanical spinal injury technique with dynamic sensitivity.

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 dural surface. This also allows a known biomechanical starting point. This combination of improvements in sensitivity and ability to measure all components 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.