Introduction: Acute traumatic spinal cord injury (SCI) leads to debilitating dysfunction and has recently been observed in injured warfighters after the introduction of newer blast resistant vehicles (MRAP). Researchers have made strides in understanding SCI and identifying treatments, but clinical benefit remains sparse. This may be due to interspecies differences and technical limitations of weight drop devices, in which impact events are variable and brief. Here, we describe the design and development of a controlled spinal cord impactor for use in large animal models of SCI.
Methods: A custom designed spinal cord impactor and mounting platform were fabricated from machined parts and commercially available components. The impactor consisted of a voice coil actuator capable of 89 N of force with a stroke length of 19mm. A voice coil was selected because it is capable of rapid acceleration with precise control of output force. Force and displacement were measured with a 25-lb button load cell and linear potentiometer respectively. Labview (National Instruments, Austin, TX) software was used to control the impact cycle and import force and displacement data. Software finite impulse response (FIR) filtering was employed for all input data. Silicon tubing was used a surrogate for spinal cord in order to test the device; repeated impacts were performed at 15, 25, and 40 Newtons.
Results: Repeated impacts demonstrated predictable results with less than 10% variability at each target force. The average duration of impact was 71.2 +/- 6.1 msec. At a target force of 40 N, the output force was 41.5 N +/- 1.7%. With a target of 25 N, the output force was 23.5 N +/- 2.7%; a target of 15 Newtons revealed an output force of 15.2 N +/- 9.3%.
Conclusions: This custom spinal cord impactor reliably delivers precise impacts to the spinal cord and will aid future research of traumatic SCI.
Patient Care: This impactor will be used in future large animal studies of the physiology and treatment of acute spinal cord injury. It is also capable of delivering anterior impacts to the spinal cord and will be used in the first known study of ventral spinal cord injury in a burst fracture model.
Learning Objectives: 1. Weight drop impactor devices introduce variability in the creation of laboratory SCI.
2. A controlled impactor, like the one described, can reliably produce consistent impacts to the spinal cord.