High-Speed Fluoroscopy to Measure Dynamic Spinal Cord Deformation in an In Vivo Rat Model

A Sensitive and Fast Fiber Bragg Grating-Based Investigation of the Biomechanical Dynamics of In Vitro Spinal Cord Injuries

To better understand the real-time biomechanics of soft tissues under sudden mechanical loads such as traumatic spinal cord injury (SCI), it is important to improve in vitro models. During a traumatic SCI, the spinal cord suffers high-velocity compression. The evaluation of spinal canal occlusion with a sensor is required in order to investigate the degree of spinal compression and the fast biomechanical processes involved. Unfortunately, available techniques suffer with drawbacks such as the inability to measure transverse compression and impractically large response times. In this work, an optical pressure sensing scheme based on a fiber Bragg grating and a narrow-band filter was designed to detect and demonstrate the transverse compression inside a spinal cord surrogate in real-time. The response time of the proposed scheme was 20 microseconds; a five orders of magnitude enhancement over comparable schemes that depend on costly and slower optical spectral analyzers. We further showed that this improvement in speed comes with a negligible loss in sensitivity. This study is another step towards better understanding the complex biomechanics involved during a traumatic SCI, using a method capable of probing the related internal strains with high-spatiotemporal resolution.

In vitro assessment of the role of the nucleus pulposus in the mechanism of vertebral body fracture under dynamic compressive loading using high-speed cineradiography

Traumatic Spinal Cord Injuries (TSCI) have a disastrous effect on the physical and mental health of both the patients and their relatives. Around 15 % of these injuries are caused by burst fractures, a sub-type of compressive fractures of the vertebral body. The transient dynamics of these fracture have been studied through in vitro experiments coupled with numerical simulations, but no direct observation have ever been made of their genesis and evolution and the behaviour of the nucleus pulposus under compressive loading has only been hypothesized. The purpose of this study was to evaluate the interactions between the vertebral body and the nucleus pulposus under dynamic compressive loading using high-speed cineradiography. A radiopaque agent was injected into the nuclei pulposi of 4 young porcine thoraco-lumbar and lumbar cadaveric segments, and a dynamic compressive load was applied to them using a servo-hydraulic bench-test. The compression process was filmed with a custom high-speed fluoroscope. The nucleus pulposus loaded the vertebral endplate up to 14,142 ± 486 N, before fracturing it and diffusing into the vertebral body. Then, internal pressure seemingly built up until an outward projection of the nucleus pulposus, at an antero-posterior velocity up to 2.9 m.s^-1, or until retroprojection of bony fragments into the spinal canal. These results directly corroborate the hypotheses previously made by other studies and stress the unprecedented advantages of using high-speed cineradiography for the study of complex fractures genesis and evolution.Clinical Relevance- Methodology and results from this study would provide an unprecedented insight on the genesis and transient evolution of complex spinal fractures.