PubMed Health⌕ Search

Biomedical subjects

L Voo

Publications and source records attributed to L Voo.

6 recordsLinked to original sources
PubMed1998

Effect of age and loading rate on human cervical spine injury threshold.

STUDY DESIGN: Statistical analysis of human cadaver cervical spine compression experiments. OBJECTIVES: To quantify the cervical spine compressive injury threshold as a function of the person's age, gender, and external loading rate. SUMMARY OF BACKGROUND DATA: Results of epidemiologic studies have indicated that most survivors of cervical spinal cord injury have spinal column fractures and dislocations that result from a compression or compression-flexion force vector. Cervical spinal column injury thresholds are dependent on many factors. Delineation of the injury thresholds according to age, gender, and loading rate is necessary to improve clinical assessments and prevention strategies. METHODS: Twenty-five human cadaver head-neck compression tests were included in the analysis. Two statistical models were used to quantify the effects of age, gender, and loading rate on the force required to induce failure in the cervical spine. A multiple linear regression model provided a direct equation that quantified the effects of the variables, and a proportional hazards model was used to quantify probability of injury with each factor. RESULTS: The regression model had a correlation coefficient of 0.87. There was an interactive effect between age and loading rate: Increasing age reduced the effect of loading rate and at approximately 82 years, loading rate had no effect. Men were consistently 600 N stronger than women. The 50% probability of failure for a 50-year-old man at a 4.5-m/sec loading rate was approximately 3.9 kN. Differences in probability curves followed the same trends as seen in the regression model. CONCLUSIONS: The effects of age on cervical spine injury threshold are coupled with the rate of loading experienced through the external force vector that causes the trauma. Assessment of injury mechanisms and thresholds should be based on the person's age, gender, and loading rate to determine treatment and prevent injuries.

Adult↗
PubMed1997

Finite element model of the human lower cervical spine: parametric analysis of the C4-C6 unit.

In this study, a three-dimensional finite element model of the human lower cervical spine (C4-C6) was constructed. The mathematical model was based on close-up CT scans from a young human cadaver. Cortical shell, cancellous core, endplates, and posterior elements including the lateral masses, pedicle, lamina, and transverse and spinous processes, and the intervertebral disks, were simulated. Using the material properties from literature, the 10,371-element model was exercised under an axial compressive mode of loading. The finite element model response agreed with literature. As a logical step, a parametric study was conducted by evaluating the biomechanical response secondary to changes in the elastic moduli of the intervertebral disk and the endplates. In the stress analysis, the minimum principal compressive stress was used for the cancellous core of the vertebral body and von Mises stress was used for the endplate component. The model output indicated that an increase in the elastic modulii of the disk resulted in an increase in the endplate stresses at all the three spinal levels. In addition, the inferior endplate of the middle vertebral body responded with the highest mean compressive stress followed by its superior counterpart. Furthermore, the middle vertebral body produced the highest compressive stresses compared to its counterparts. These findings appear to correlate with experimental results as well as common clinical experience wherein cervical fractures are induced due to external compressive forces. As a first step, this model will lead to more advanced simulations as additional data become available.

Aging↗
PubMed1996

Finite element applications in human cervical spine modeling.

The authors present a comprehensive state-of-the-art and critical review of the finite element models of the human cervical spine. They also focused on the developments in model construction (geometry generation), constitutive law (material property) identification, loading and boundary condition details, and validation, the most important phase. A data base of available experimental sources is also provided, which can be used by the modeler for validating the finite element model. The potential developments in finite element modeling of the human cervical spine are discussed.

Biomechanical Phenomena↗
PubMed1996

Finite element modeling of the C4-C6 cervical spine unit.

This study was conducted to develop a detailed, three-dimensional, anatomically accurate finite element model of the human cervical spine structure using close-up computed tomography scans and to validate against experimental data. The finite element model of the three vertebra segment C4-C6 unit consisted of 9178 solid elements and 1193 thin shell elements. The force-displacement response under axial compression correlated well with experimental data. Because of the inclusion of three levels in the spinal structure, it was possible to determine the internal mechanics of the various components at each level. The applicability of the model was illustrated by adopting appropriate material properties from literature. Results indicated that, the stresses in the anterior column were higher compared to the posterior column at the inferior level, while the opposite was found to be true at the superior level. The superior and inferior endplate stresses were higher in the middle vertebral body compared to the adjacent vertebrae. In addition, the stresses in the cancellous core of the middle, unconstrained vertebral body were higher. The present three-dimensional finite element model offers an additional facet to a better understanding of the biomechanics of the human cervical spine.

Adult↗
PubMed1995

An experimental technique to induce and quantify complex cyclic forces to the lumbar spine.

The human spine is a complex, heterogeneous nonlinear and viscoelastic structure. In addition, in vivo loading is not uniaxial. Although many studies on the mechanical behavior of the spine under "pure" forces and single cycle load applications exist, little research is conducted with complex cyclic loads. In this study, we developed a technique to induce and quantify controlled complex physiological loads to the lumbar spinal column under cyclic (chronic) conditions. The methods described include specimen preparation and mounting to induce controlled complex loading (cyclic compression-flexion vector was chosen as an example), instrumentation, and biomechanical data to achieve the objectives. The results indicated that the specimen sustained the external load in a combined compression-flexion mechanism without considerable off-axis forces (lateral shears) and moments (lateral bending and torsion). By mounting the anchoring bolt in appropriate places (such as an anterolateral placement to induce compression-flexion-lateral bending), this technique can be used to apply and continuously quantify complex physiological acute or cyclic loads to describe the biomechanics of the spine. This procedure of inducing complex loads eliminates the difficulty in applying the principles of superposition, using the response from individual "pure" forces to account for the nonlinearity and viscoelasticity of the human lumbar spinal column.

Biomechanical Phenomena↗