Influence of a posterior ligamentous complex injury on the mechanical condition of the spinal cord during flexion
1Eric W, 1Hagen J, 1Beauséjour M, 2Mac-Thiong J, 3Arnoux P, 1Petit Y
1École de technologie supérieure, Montreal, Quebec, Canada; 2University of Montreal, Montreal, Quebec, Canada; 3Aix-Marseille University, Marseille, Provence, France
Spinal instability following posterior ligamentous injuries can lead to devastating neurological consequences. Recent finite element (FE) studies on spinal trauma have mostly focused on high velocity traumas [1,2] and surgical instrumentation . Few studies have investigated the post-traumatic mechanical condition of the spinal cord under physiological movements. This study investigated how the spinal cord may be mechanically affected under a physiological motion after posterior ligamentous injury using FE analysis.
The C2-T1 segment was isolated from the Spine Model for Safety and Surgery (SM2S) , a detailed FE model of the spine developed jointly by the Laboratory of Applied Biomechanics of IFSTTAR/Aix-Marseille University, Ecole de Technologie Superieure and Ecole Polytechnique de Montreal. It includes vertebrae, intervertebral disks and spinal ligaments. The nervous system contained gray (GM) and white matter (WM) as well as membranous structures (dura, pia matter and dentate ligaments) with material properties derived from literature . First, a baseline simulation was conducted with intact ligaments by applying a pure flexion moment on C2 (T1 being fixed). A stepwise posterior reduction was then performed at three different levels (C2-C3, C4-C5 and C6-C7). The protocol consisted of removing step-by-step the supraspinous, interspinous and flavum ligaments. Between each step, the flexion moment was re-applied. Von Mises stresses were computed in the white and gray matter at full flexion and compared with the baseline model.
Simulations showed no significant change in spinal cord maximum stress when the supraspinous and interspinous ligaments were successively cut. However, when the ligamentum flavum was also disrupted, the maximum stress in both the white and grey matter increased by 80% compared to the normal flexion.
The finite element analysis showed that posterior ligamentous injury could influence stresses in the spinal cord components. It also pointed out that immobilisation and stabilisation should receive special care when managing injured patients. However, specific injury criteria for the spinal cord should be developed to further analyze these results.
This research was funded by: the Investissements d’Avenir French Government program, managed by the French National Research Agency (ANR), the Natural Science and Engineering Council (NSERC) and the Canada Research chair Program (CRC).
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