Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine
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Proc Inst Mech Eng H · Aug 2013
A biomechanical study of the recovery in spinal stability of flexion/extension and torsion after the resection of different posterior lumbar structures in a sheep model.
Posterior lumbar structures are vital for spinal stability, and many researchers thought that laminectomy and facetectomy would lead to severe spinal instability. However, because living organisms have compensatory repair capacities, their long-term condition after injuries may change over time. To study the changes in the lumbar biomechanical stability of flexion/extension and torsion at different time points after the resection of various posterior structures, as well as to assess the capacity for self-healing, sheep that had undergone laminectomy or facetectomy were used as an experimental animal model. ⋯ Torsional stiffness also recovered gradually over time. All injury groups demonstrated decreased intervertebral space and degeneration or even fusion in the small joints of the surgical segment or in adjacent segments. These results indicate that the body has the ability to repair the mechanical instability to a certain extent.
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Proc Inst Mech Eng H · Jul 2013
Towards a realistic in vitro experience of epidural Tuohy needle insertion.
The amount of pressure exerted on the syringe and the depth of needle insertion are the two key factors for successfully carrying out epidural procedure. The force feedback from the syringe plunger is helpful in judging the loss of pressure, and the depth of the needle insertion is crucial in identifying when the needle is precisely placed in the epidural space. ⋯ A pilot trial has been conducted to collect depth and pressure data with the devices on a porcine cadaver. These measurements are then combined to accurately configure a haptic device for creating a realistic in vitro experience of epidural needle insertion.
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Proc Inst Mech Eng H · Jun 2013
A meta-model analysis of a finite element simulation for defining poroelastic properties of intervertebral discs.
Finite element analysis is an effective tool to evaluate the material properties of living tissue. For an interactive optimization procedure, the finite element analysis usually needs many simulations to reach a reasonable solution. The meta-model analysis of finite element simulation can be used to reduce the computation of a structure with complex geometry or a material with composite constitutive equations. ⋯ The results showed that the in vitro disc experimental deformations were well fitted with limited finite element simulations and a quadratic response surface regression. The comparison of material properties of intact and degenerated discs showed that the hydraulic permeability significantly decreased but Poisson's ratio significantly increased for the degenerated discs. This study shows that the developed protocol is efficient and effective in defining material properties of a complex structure such as the intervertebral disc.
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The wear of a model metal-on-metal ball-and-socket total disc arthroplasty was measured in a simulator. The ball had a radius of 10 mm, and there was a radial clearance between ball and socket of 0.015 mm. The model was subjected to simultaneous flexion-extension, lateral bending, axial rotation (frequency: 1 Hz) and compression (frequency: 2 Hz, maximum load: 2 kN). ⋯ Wear occurred in two stages. In the first stage (duration about 1 million cycles), there was a linear wear rate of 2.01 ± 0.04 mm(3) per million cycles; in the second stage, there was a linear wear rate of 0.76 ± 0.02 mm(3) per million cycles. Surface roughness increased linearly in the first million cycles and then continued to increase linearly but more slowly.
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Proc Inst Mech Eng H · Mar 2013
Biomechanical comparison of supplemental posterior fixations for two-level anterior lumbar interbody fusion.
Posterior instrumentations have been used to supplement anterior lumbar interbody fusion with cages. Biomechanical studies on single-level anterior lumbar interbody fusion show that stand-alone cages supplemented with posterior translaminar facet or transfacet screw fixation exhibit comparable stability to those supplemented with pedicle screw/rod fixation, while stability of multilevel anterior lumbar interbody fusion remains mostly unknown. The objectives of this study are to compare the stabilization of three supplemental posterior fixations to two-level anterior lumbar interbody fusion, including translaminar facet fixation, transfacet screw fixation, and pedicle screw/rod fixation. ⋯ Supplemental posterior fixation significantly improved stability of two-level anterior lumbar interbody fusion when compared to the stand-alone cages. Pedicle screw/rod system is still the "gold standard" in providing supplemental stability. However, both translaminar facet screws and transfacet screws are good alternatives to provide adequate fixation.