Determination of trunk muscle forces for flexion and extension by using a validated finite element model of the lumbar spine and measured in vivo data.
ABSTRACT Muscle forces stabilize the spine and have a great influence on spinal loads. But little is known about their magnitude. In a former in vitro experiment, a good agreement with intradiscal pressure and fixator loads measured in vivo could be achieved for standing and extension of the lumbar spine. However, for flexion the agreement between in vitro and in vivo measurements was insufficient. In order to improve the determination of trunk muscle forces, a three-dimensional nonlinear finite element model of the lumbar spine with an internal fixation device was created and the same loads were applied as in a previous in vitro experiment. An extensive adaptation process of the model was performed for flexion and extension angles up to 20 degrees and -15 degrees, respectively. With this validated computer model intra-abdominal pressure, preload in the fixators, and a combination of hip- and lumbar flexion angle were varied until a good agreement between analytical and in vivo results was reached for both, intradiscal pressure and bending moments in the fixators. Finally, the fixators were removed and the muscle forces for the intact lumbar spine calculated. A good agreement with the in vivo results could only be achieved at a combination of hip- and lumbar flexion. For the intact spine, forces of 170, 100 and 600 N are predicted in the m. erector spinae for standing, 5 degrees extension and 30 degrees flexion, respectively. The force in the m. rectus abdominus for these body positions is less than 25 N. For more than 10 degrees extension the m. erector spinae is unloaded. The finite element method together with in vivo data allows the estimation of trunk muscle forces for different upper body positions in the sagittal plane. In our patients, flexion of the upper body was most likely a combination of hip- and lumbar spine bending.
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ABSTRACT: Osteoporotic vertebral fractures represent major cause of disability, loss of quality of life and even mortality among the elderly population. Decisions on drug therapy are based on the assessment of risk factors for fracture, from bone mineral density measurements. The combination of biomechanical models with clinical studies could better estimate bone strength and support the specialists in their decision. A model to assess the probability of fracture, based on the Damage and Fracture Mechanics has been developed, evaluating the mechanical magnitudes involved in the fracture process from clinical bone mineral density measurements. The model is intended for simulating the degenerative process in the skeleton, with the consequent lost of bone mass and hence the decrease of its mechanical resistance which enables the fracture due to different traumatisms. Clinical studies were chosen, both in non-treatment conditions and receiving drug therapy, and fitted to specific patients according their actual bone mineral density measures. The predictive model is applied in a finite element simulation of the lumbar spine. The fracture zone would be determined according loading scenario (fall, impact, accidental loads, etc.), using the mechanical properties of bone obtained from the evolutionary model corresponding to the considered time. Bone mineral density evolution in untreated patients and in those under differentAdvances in Bioscience and Biotechnology 01/2014;
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ABSTRACT: Das neuartige transsakrale Fusionssystem AxiALIF erlaubt die Stabilisierung des lumbosakralen Übergangs. Das System besteht aus einer Schraube, die 2 unterschiedliche Durchmesser hat. Durch zusätzliche Facettenschrauben oder Fixateure kann eine 360°-Fusion erreicht werden. Die Einflüsse verschiedener Parameter wie Länge, Durchmesserkombination und Material der transsakralen Schraube, Art der zusätzlichen Fixierung sowie Steifigkeit des Knochens sind nicht bekannt.In einer probabilistischen Finite-Elemente-Studie wurden die Eingabeparameter zufällig variiert. Berechnet wurden die Rotationswinkel und die Axialkräfte in den verschiedenen Implantaten für 4 verschiedene Lastfälle. In einer anschließenden Sensitivitätsanalyse wurden die Einflüsse der einzelnen Eingabeparameter auf die Ergebnisvariation berechnet. Durch die transsakrale Schraube wird die Beweglichkeit im behandelten Segment deutlich reduziert, außer bei der axialen Rotation. Eine zusätzliche Fixierung hat einen großen Einfluss auf die Variation der Rotation. Die anderen Parameter erklären üblicherweise weniger als 10% der Ergebnisstreuung.Das lumbosakrale Fusionssystem erlaubt eine gute Stabilisierung des Segments, besonders in Verbindung mit einer zusätzlichen Fixierung.Der Orthopäde 01/2011; 40(2). · 0.67 Impact Factor
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ABSTRACT: Constructing models based on computed tomography images for finite element analysis (FEA) is challenging under pathological conditions. In the present study, an innovative method was introduced that uses Siemens syngo(®) 3D software for processing models and Mimics software for further modeling. Compared with the slice-by-slice traditional manual margin discrimination, the new 3D modeling method utilizes automatic tissue margin determination and 3D cutting using syngo software. The modeling morphologies of the two methods were similar; however, the 3D modeling method was 8-10 times faster than the traditional method, particularly in cases with osteoporosis and osteophytes. A comparative FEA study of the lumbar spines of young and elderly patients, on the basis of the models constructed by the 3D modeling method, showed peak stress elevation in the vertebrae of elderly patients. Stress distribution was homogeneous in the entire vertebrae of young individuals. By contrast, stress redistribution in the vertebrae of the elderly was concentrated in the anterior cortex of the vertebrae, which explains the high fracture risk mechanism in elderly individuals. In summary, the new 3D modeling method is highly efficient, accurate and faster than traditional methods. The method also allows reliable FEA in pathological cases with osteoporosis and osteophytes.Experimental and therapeutic medicine 06/2014; 7(6):1583-1590. · 0.94 Impact Factor