Validation of the RWD Precise Impactor for a Cervical Spinal Cord Injury Contusion Model

Introduction: Cervical spinal cord injuries are the most common human spinal cord injury (SCI). Various contusion models have been developed to mirror SCI pathology in humans but few have described cervical-level injuries. We utilized the RWD Precise Impactor which uses penetration depths and a controlled dwell time to generate three severities of cervical spinal cord contusion. The goal of this study is to determine an optimal penetration depth that produces a consistent and reliable graded SCI for testing potential new therapeutic modalities.

Methods: Hemi-contusion SCI was created with the RWD precise impactor on 14 rats, with 3 as uninjured controls. Penetration depths of 2.11mm (n=4), 2.24mm (n=4), and 2.36mm (n=3) were used to create mild, moderate, and severe injuries. Behavioral assessments on weeks 1, 2, 5, and 8 included a grooming test, forelimb asymmetry test, and the Irvine, Beatties and Bresnahan forelimb scale (IBB). After 8 weeks rats were euthanized and spinal cord histology was performed.

Results: Deficits in motor function were graded, with a significant difference between the mean IBB scores per injured group at week 8 (p < 0.0001). There were significant decreases in motor neuron counts and ipsilateral white and gray matter compared to controls. The remaining intact ipsilateral spinal cord area was correlated with motor function outcomes and was graded by injury severity.

Conclusion : Using the RWD Precise Impactor we were able to create a reproducible model of cervical SCI with severity of injury correlating with greater penetration depth. A penetration depth of 2.24mm appears to provide enough capacity to allow for differences to be seen with various treatment arms in future studies.