Journal of biomechanics
-
The purpose of this study was to determine the correlation between the back shape of the lumbar region and the spinal loads during activities performed in the sagittal plane. Measurements were performed in four subjects who had suffered from a compression fracture of a lumbar vertebral body which was treated with a telemeterized vertebral body replacement that is able to measure six load components in vivo. An Epionics SPINE measurement system was used to determine the lumbar lordosis angle. ⋯ Correlation coefficients greater than 0.6 were found for exercises that involved both large back shape and load changes, such as upper body flexion. A strong increase in spinal load can be associated with an increase or a decrease of the lordosis angle. Only for considerable changes of the lordosis angle in an upright body position was a strong correlation between lordosis angle and implant force found.
-
Journal of biomechanics · May 2013
Cervical spine intervertebral kinematics with respect to the head are different during flexion and extension motions.
Previous dynamic imaging studies of the cervical spine have focused entirely on intervertebral kinematics while neglecting to investigate the relationship between head motion and intervertebral motion. Specifically, it is unknown if the relationship between head and intervertebral kinematics is affected by movement direction. We tested the hypothesis that there would be no difference in sagittal plane intervertebral angles at identical head orientations during the flexion and extension movements. ⋯ Further, data should be collected during both flexion and extension movements when investigating intervertebral kinematics with respect to global head orientation. Also, in vitro protocols that use intervertebral total range of motion as validation criteria may be improved by assessing model fidelity using continuous intervertebral kinematics in flexion and in extension. Finally, musculoskeletal models of the head and cervical spine should account for the direction of head motion when determining muscle moment arms because vertebral orientations (and therefore muscle attachment sites) are dependent on the direction of head motion.
-
Journal of biomechanics · Mar 2013
Viscoelastic properties of the ferret brain measured in vivo at multiple frequencies by magnetic resonance elastography.
Characterization of the dynamic mechanical behavior of brain tissue is essential for understanding and simulating the mechanisms of traumatic brain injury (TBI). Changes in mechanical properties may also reflect changes in the brain due to aging or disease. In this study, we used magnetic resonance elastography (MRE) to measure the viscoelastic properties of ferret brain tissue in vivo. ⋯ Estimated viscoelastic properties of white matter in the ferret brain were generally similar to those of gray matter and consistent between animals and scan dates. In both tissue types G' increased from approximately 3 kPa at 400 Hz to 7 kPa at 800 Hz and G″ increased from approximately 1 kPa at 400 Hz to 2 kPa at 800 Hz. These measurements of shear wave propagation in the ferret brain can be used to both parameterize and validate finite element models of brain biomechanics.
-
Journal of biomechanics · Feb 2013
Sensitivity, reliability and accuracy of the instant center of rotation calculation in the cervical spine during in vivo dynamic flexion-extension.
The instant center of rotation (ICR) has been proposed as an alternative to range of motion (ROM) for evaluating the quality, rather than the quantity, of cervical spine movement. The purpose of the present study was to assess the sensitivity, reliability and accuracy of cervical spine ICR path calculations obtained during dynamic in vivo movement. The reliability and sensitivity of in vivo cervical spine ICR calculations were assessed by evaluating the effects of movement direction (flexion versus extension), rotation step size, filter frequency, and motion tracking error. ⋯ In vivo, the path of the ICR can reliably be characterized within 0.5mm in the SI and 1.0mm in the AP direction. The inter-subject variability in ICR location averaged ±1.2mm in the SI direction and ±2.2mm in the AP direction. The computational experiment estimated the in vivo accuracy in ICR location was between 1.1mm and 3.1mm.
-
Journal of biomechanics · Feb 2013
Clinical and statistical correlation of various lumbar pathological conditions.
Current clinical evaluations often rely on static anatomic imaging modalities for diagnosis of mechanical low back pain, which provide anatomic snapshots and a surrogate analysis of a functional disease. Three dimensional in vivo motion is available with the use of digital fluoroscopy, which was used to capture kinematic data of the lumbar spine in order to identify coefficients of motion that may assist the physician in differentiating patient pathology. Forty patients distributed among 4 classes of lumbar degeneration, from healthy to degenerative, underwent CT, MRI, and digital x-ray fluoroscopy. ⋯ The classifier achieved 95% sensitivity and specificity using (C(FE), C(LB), ROM(LB)) as input features, and 40% specificity and 80% sensitivity using ROM variables. The new coefficients were better correlated with patient pathology than ROM measures. The coefficients suggest a relationship between pathology and measured motion which has not been reported previously.