Effect of fatigue load on internal mechanical properties of the intervertebral disc / Efecto de la carga de fatiga en las propiedades mecánicas internas del disco intervertebral

SUMMARY: Lumbar disc herniation is considered to be the main pathological factor for the common clinical disease of low back pain. Biomechanical factor is an important cause of lumbar disc herniation, so it is urgent to analyze the stress/strain behavior of intervertebral disc under different loading condition. Slow repetitive loading is considered to be an important factor of spine and disc injuries, and the effect of fatigue load on internal displacement in the intervertebral disc was investigated by applying the optimized digital image correlation technique in this study. The first finding was that fatigue load had a significant effect on the displacement distribution in the intervertebral disc under compression. Superficial AF exhibited the largest axial displacements before fatigue load, while it exhibited the smallest axial displacements after fatigue load. Inner AF exhibited slightly smaller radial displacements than outer AF before fatigue load, while it exhibited significantly greater radial displacements than outer AF displacements after fatigue load. The second finding was that fatigue load had a certain effect on the internal displacement distribution in the flexed intervertebral disc under compression. Middle AF exhibited the smallest axial displacements before fatigue load, while deep AF exhibited the smallest axial displacements after fatigue load. The radial displacement distribution did not change before and after fatigue load, as the radial displacement in outer AF was the smallest, while the radial displacement in inner AF was the largest. The third finding was that with the increase in fatigue time and amplitude, the Young's modulus of the intervertebral disc increased significantly. This study can provide the basis for clinical intervertebral disc disease prevention and treatment? and is important for mechanical function evaluation of artificial intervertebral disc as well.

RESUMEN: La hernia de disco lumbar se considera el principal factor patológico para la enfermedad clínica común del dolor lumbar. El factor biomecánico es una causa importante de hernia de disco lumbar, por lo que es urgente analizar el comportamiento de esfuerzo / tensión del disco intervertebral bajo diferentes condiciones de carga. La carga repetitiva lenta se considera un factor importante de lesiones de columna y disco, y en este estudio el efecto de la carga de fatiga sobre el desplazamiento interno en el disco intervertebral se investigó mediante la aplicación de la técnica de correlación de imagen digital optimizada. El primer hallazgo fue que la carga de fatiga tuvo un efecto significativo en la distribución del desplazamiento en el disco intervertebral bajo compresión. El AF superficial exhibió los desplazamientos axiales más grandes antes de la carga de fatiga, mientras que exhibió los desplazamientos axiales más pequeños después de la carga de fatiga. El AF interno exhibió desplazamientos radiales ligeramente más pequeños que el AF externo antes de la carga de fatiga, mientras que exhibió desplazamientos radiales significativamente mayores que los desplazamientos AF externos después de la carga de fatiga. El segundo hallazgo fue que la carga de fatiga tenía un cierto efecto sobre la distribución del desplazamiento interno en el disco intervertebral flexionado bajo compresión. El AF medio exhibió los desplazamientos axiales más pequeños antes de la carga de fatiga, mientras que el AF profundo exhibió los desplazamientos axiales más pequeños después de la carga de fatiga. La distribución del desplazamiento radial no cambió antes ni después de la carga de fatiga, ya que el desplazamiento radial en la FA externa fue el más pequeño, mientras que el desplazamiento radial en la FA interna fue el más grande. El tercer hallazgo fue que con el aumento del tiempo de fatiga y la amplitud, el módulo de Young del disco intervertebral aumentó significativamente. Este estudio puede proporcionar la base para la prevención y el tratamiento clínico de la enfermedad del disco intervertebral, y también es importante para la evaluación de la función mecánica del disco intervertebral artificial.

OpenSim-Based Biomechanical Analysis of Lumbar Musculoskeletal System under Forward Flexion / 医用生物力学

Objective Based on OpenSim platform, an improved musculoskeletal model was developed to analyze the force of lumbar muscle groups under forward flexion. Methods The existing lumbar musculoskeletal model was improved via modifying constraints of lumbar vertebrae to restore them into 6 degrees of freedom (DOF). The 30 year-old and 70 year-old muscle models were established respectively by adjusting muscle parameters according to Thelen’s model, adding stiffness matrixes and abdominal pressure (AP) characterized by concentrated force to investigate the effects of arm swing, movement velocity, varying AP and muscle aging on the force distribution of 9 lumbar muscle groups during forward flexion. Results A multi-body musculoskeletal model with 9 lumbar muscle groups was developed. Based on the computations of 0°-70° flexion, the results showed that arm swing reduced the force of psoas and external oblique abdominis, while under the movement of forward flexing to 70° and returning up-right, the force of psoas, erector spinae, rectus and external oblique abdominis obviously increased, when the time of flexing-returning process was reduced from 5 s to 2.5 s, and in the 5 s case, increasing AP reduced the force of psoas but increased the force of transversus, internal and external oblique abdominis. In the 2.5 s case, there was no obvious difference between the 30 year-old and 70 year-old muscle models under different conditions. Conclusions The developed model provides an effective method to analyze the force of lumbar spine and muscles, and it certainly shows a potential application in the fields of kinematic mechanics and rehabilitation engineering with further development of basic theory.

Positional perception in forward or backward flexion of the trunk while standing / 体力科学

We carried out three measurements on 12 healthy men to investigate the positional perception in forward or backward flexions of the trunk while standing. In measurement (I), the subjects reproduced the target angle perceived by forward flexion (FF) or backward flexion (BF) of the trunk with their eyes blindfolded. In measurement (II), the subjects first visually perceived the angle shown by an angular, indicator, and then reproduced it by manually by operating the indicator with their eyes open. In measurement (III), the subjects first visually perceived the angle shown by an angular indicator, and then expressed the target angle by FF or BF with their eyes blindfolded. In measurements (I) and (III), indication of the target angle was set at in 5° increments from 5° to 60° in FF, and from 5° to 30° in BF, and in measurement (II) from 5° to 60°. The ability of positional perception was evaluated using the constant error (CE) and the absolute error (AE) of the reproduced or expressed angle.<BR>In measurement (I), CE was small for all target angles, ranging from -0.2°to 2.6°in FF and from 0.3°to 1.6°in BF. However, CE from 5° to 25°in FF was significantly positive. In BF, significant CE was not recognized for any target angles, and AE at each target angle was smaller than that in FF. These results suggest that the sensitivity of positional perception of the trunk in FF is relatively low for small target angles which are close to the quiet standing position.<BR>In measurement (II), CE was very small for all target angles, ranging from -1.2° to 0.9°. Significant CE was recognized only at 10°, 20°and 55°. AE was also small for all target angles, ranging from 0.5° to 1.8°, and no significant difference in AE was recognized among the target angles. These results suggest that visual perception, memorization and recall of the target angle is well retained.<BR>In measurement (III), a relationship between the target angle and the CE was shown on a negative regression line in both FF and BF. As viewed from the regression line, the angle at which the CE became zero was 36°in FF and 18° in BF. AE in target angles close to these angles was also small. This indicates that angles smaller than these are perceived as smaller than they actually are, while angles larger than these are perceived as larger than the actual ones.