Conception d'un dispositif de contusion antérieure de la moelle épinière d'un modèle porcin

Abstract

The use of animal models to reproduce spinal cord injuries (SCI) are especially useful to close the gap between experimental models and SCI observed in clinical reality. In burst fractures, spinal injuries are caused by the disruption of the vertebral body and the retropulsion of posterior bone fragments into the spinal canal, leading to acute anterior compression of the spinal cord. Current experimental studies are able to reproduce the acute SCI, but don’t emphasize enough on the consequences of secondary injury mechanisms on the damage to the spinal cord tissues. This project focuses on the design of an experimental device and methodology to study the effects of the residual compression observed in burst fractures on the severity of an anterior SCI. The specific objectives of the study are to: 1. Design, build, and validate an experimental motorised test bench able to reproduce a Spinal Cord Injury in vivo on a large animal model (porcine); 2. Design and build a functional device that reproduces an anterior spinal cord acute compression and that is able to maintain a residual compression over time; 3. Validate the device by fixing it on an in vitro porcine spine and by recreating experimental tests under different injury degrees. The technical specifications of the device were written to guide the design process in order to best answer the research problem. A few potential solutions were suggested and put through a scale of assessment to output the most promising concept. The final solution, made of four distinct components, was first evaluated with a finite element analysis to show it could withstand moments of magnitude ±5 N-m in flexion/extension, and lateral inflexion, mimicking the anatomic movements of a live pig model. Before the experimental evaluation of the device, a surgical test bench was designed to study spinal cord injuries on in vivo animal models. The initial concept was taken from the proposition of a previous project at the Imagery and Orthopaedic Research Laboratory, realized by Mr. Francis Cliche who started the design of this surgical table during his master degree. Major modifications were implemented following his recommendations and the observations at beginning of the current project. The test bench was then assembled and tested on a live pig model. The surgery showed the potential of the test bench and demonstrated the relevance of a motorised impactor, which is able to reproduce acute spinal cord compression at an impact speed close to 750 mm/s and to hold it for a few minutes. Then, the functional prototype of the device was submitted to experimental tests in flexion/extension and lateral inflexion to observe both its mechanical resistance and the precision of the residual compression imposed. Due to technological limitations, we chose an indirect measurement of the residual compression, using a distance sensor aimed at the bottom of the spinal canal. The tests performed on 12 in vitro pig vertebral segments revealed that the distance between the device and the bottom of the spinal canal could vary from 1 to 3 mm in height, meaning it may be difficult to hold a residual compression for several hours on a live pig. Nevertheless, this innovative device offers an interesting approach to study experimentally the effects of residual compression on the severity of SCI on a live animal model. It is designed to allow wound closure immediately after surgery and it is biocompatible, therefore limiting the risks of infection and surgical complications.

Date	18 Mar 2019
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Yvan Petit (Supervisor) & Éric Wagnac (Co-supervisor)