Flexion Model Simulating Spinal Cord Injury Without Radiographic Abnormality in Patients With Ossification of the Longitudinal Ligament: The Influence of Flexion Speed on the Cervical Spine

Abstract

Background/Objective: It is suspected that the speed of the motion of the spinal cord under static compression may be the cause of spinal cord injury (SCI). However, little is known about the relationship between the speed of the motion of the spinal cord and its stress distributions. The objective was to carry out a biomechanical study of SCI in patients with ossification of the longitudinal ligament without radiologic evidence of injury. Methods: A 3-dimensional finite element spinal cord model was established. After the application of static compression, the model underwent anterior flexion to simulate SCI in ossification of the longitudinal ligament patients without radiologic abnormality. Flexion of the spine was assumed to occur at 1 motor segment. Flexion angle was 5u, and flexion speeds were 0.5u/s, 5u/s, and 50u/s. Stress distributions inside of the spinal cord were evaluated. Results: Stresses on the spinal cord increased slightly after the application of 5u of flexion at a speed of 0.5u/s. Stresses became much higher at a speed of 5u/s and increased further at 50us. Conclusions: The stress distribution of the spinal cord under static compression increased with faster flexion speed of the spinal cord. High-speed motion of the spinal cord under static compression may be one of the causes of SCI in the absence of radiologic abnormality.

Cervical ossification of the posterior longitudinal ligament: Biomechanical analysis of the influence of static and dynamic factors

“…Our first goal was to develop a 3D-FEM spinal cord model that simulates the clinical situation, while our second goal was to analyze the clinical condition of patients. Similar to previous studies by Kato et al, [14][15][16] Li and Dai, 17,18 and Nishida et al, [19][20][21] bovine spinal cord was used in the current analytical model since it was impossible to obtain fresh human spinal cord. The mechanical properties of the spinal cord used in our study were similar to earlier reports.…”

“…The mechanical properties of the spinal cord used in our study were similar to earlier reports. [15][16][17][18][19][20][21] Li et al noted that it was reasonable to use the mechanical properties of bovine spinal cord because the brain and spinal cord of cattle and humans show similar injury-induced changes. 17 For the purpose of this study, we therefore assumed that the mechanical properties of spinal cord from these two species were similar.…”

Biomechanical study of the spinal cord in thoracic ossification of the posterior longitudinal ligament

“…Similar to previous studies by Kato et al [12][13][14] and Xin-Feng, Li et al, [15][16] bovine spinal cord was used in the model for the current analysis since it was impossible to obtain fresh human spinal cord. The mechanical properties of spinal cord used in our study were similar to earlier reports.…”

Biomechanical performance of an ovine model of intradural spinal cord stimulation

“…From Table 2, the mean vertical flexion speed of the sheep was &21 s À1 , thus making it $4-times the normal rate of that in man. Kato et al [17] also found that flexion rates of 50 s À1 can cause high stress distributions in the spinal cord and, indeed, flexions at this angular speed and above have been used for many years to benchmark dynamical models of head and neck trauma in man [18][19][20]. Again from Table 2, the mean lateral angular speeds for the sheep were &54 s À1 , which is 10-times faster than (although orthogonal to) the normal flexional rate in man and comparable to the rates associated with traumatic injury.…”

“…As part of their study of spinal cord injury mechanisms associated with the angular speed of neck flexion, Kato et al [17] noted that cervical flexion rates of sÀ 1 were considered to be in the range of a person's normal physiologic movement. From Table 2, the mean vertical flexion speed of the sheep was &21 s À1 , thus making it $4-times the normal rate of that in man.…”