Dataset Information

A biomechanical model for estimating loads on thoracic and lumbar vertebrae.

ABSTRACT:

Background

Biomechanical models are commonly used to estimate loads on the spine. Current models have focused on understanding the etiology of low back pain and have not included thoracic vertebral levels. Using experimental data on the stiffness of the thoracic spine, ribcage, and sternum, we developed a new quasi-static stiffness-based biomechanical model to calculate loads on the thoracic and lumbar spine during bending or lifting tasks.

Methods

To assess the sensitivity of the model to our key assumptions, we determined the effect of varying ribcage and sternal stiffness, maximum muscle stress, and objective function on predicted spinal loads. We compared estimates of spinal loading obtained with our model to previously reported in vivo intradiscal pressures and muscle activation patterns.

Findings

Inclusion of the ribs and sternum caused an average decrease in vertebral compressive force of 33% for forward flexion and 18% in a lateral moment task. The impact of maximum muscle stress on vertebral force was limited to a narrow range of values. Compressive forces predicted by our model were strongly correlated to in vivo intradiscal pressure measurements in the thoracic (r=0.95) and lumbar (r=1) spine. Predicted trunk muscle activity was also strongly correlated (r=0.95) with previously published EMG data from the lumbar spine.

Interpretation

The consistency and accuracy of the model predictions appear to be sufficient to justify the use of this model for investigating the relationships between applied loads and injury to the thoracic spine during quasi-static loading activities.

SUBMITTER: Iyer S

PROVIDER: S-EPMC2949493 | biostudies-literature | 2010 Nov

REPOSITORIES: biostudies-literature

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Publications

A biomechanical model for estimating loads on thoracic and lumbar vertebrae.

Iyer Sravisht S Christiansen Blaine A BA Roberts Benjamin J BJ Valentine Michael J MJ Manoharan Rajaram K RK Bouxsein Mary L ML

Clinical biomechanics (Bristol, Avon) 20100723 9

<h4>Background</h4>Biomechanical models are commonly used to estimate loads on the spine. Current models have focused on understanding the etiology of low back pain and have not included thoracic vertebral levels. Using experimental data on the stiffness of the thoracic spine, ribcage, and sternum, we developed a new quasi-static stiffness-based biomechanical model to calculate loads on the thoracic and lumbar spine during bending or lifting tasks.<h4>Methods</h4>To assess the sensitivity of the ...[more]

PMID: 20655634

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Project description:BackgroundPedicle screw insertion in osteoporotic patients is challenging. Achieving more screw-cortical bone purchase and invasiveness minimization, the cortical bone trajectory and the midline cortical techniques represent alternatives to traditional pedicle screws. This study compares the fatigue behavior and fixation strength of the cement-augmented traditional trajectory (TT), the cortical bone trajectory (CBT), and the midline cortical (MC).MethodsTen human cadaveric spine specimens (L1 - L5) were examined. The average age was 86.3 ± 7.2 years. CT scans were provided for preoperative planning. CBT and MC were implanted by using the patient-specific 3D-printed placement guide (MySpine®, Medacta International), TT were implanted freehand. All ten cadaveric specimens were randomized to group A (CBT vs. MC) or group B (MC vs. TT). Each screw was loaded for 10,000 cycles. The failure criterion was doubling of the initial screw displacement resulting from the compressive force (60 N) at the first cycle, the stop criterion was a doubling of the initial screw displacement. After dynamic testing, screws were pulled out axially at 5 mm/min to determine their remaining fixation strength.ResultsThe mean pull-out forces did not differ significantly. Concerning the fatigue performance, only one out of ten MC of group A failed prematurely due to loosening after 1500 cycles (L3). Five CBT already loosened during the first 500 cycles. The mean displacement was always lower in the MC. In group B, all TT showed no signs of failure or loosening. Three MC failed already after 26 cycles, 1510 cycles or 2144 cycles. The TT showed always a lower mean displacement. In the subsequent pull-out tests, the remaining mean fixation strength of the MC (449.6 ± 298.9 N) was slightly higher compared to the mean pull-out force of the CBT (401.2 ± 261.4 N). However, MC (714.5 ± 488.0 N) were inferior to TT (990.2 ± 451.9 N).ConclusionThe current study demonstrated that cement-augmented TT have the best fatigue and pull-out characteristics in osteoporotic lumbar vertebrae, followed by the MC and CBT. MC represent a promising alternative in osteoporotic bone if cement augmentation should be avoided. Using the patient-specific placement guide contributes to the improvement of screws' biomechanical properties.

Dataset Information

A biomechanical model for estimating loads on thoracic and lumbar vertebrae.

Background

Methods

Findings

Interpretation

Publications

A biomechanical model for estimating loads on thoracic and lumbar vertebrae.

Similar Datasets

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