Yeditepe spine mesh: Finite element modeling and validation of a parametric CAD model of lumbar spine.

Finite element analysis is a powerful tool that is often used to study the biomechanical response of the spine. The primary objective of this study was to illustrate the mechanical behavior of a previously proposed parametric CAD spine model in comparison with a segmented FSU model and the literature. In this study, two finite element models of the L4-L5 spinal level were developed from the same patient's CT scan data. The first was developed using well-known segmentation methods, whereas the second was developed from the new by using a novel parametric CAD model. Both models were subjected to the same loading and boundary conditions to perform flexion, extension, lateral bending and axial rotation motions. The segmented finite element model was observed to be in good agreement with the literature. The parametric finite element model results were also observed to be in good agreement with the segmented finite element model and with the literature except under extension.

[The contribution of locked screw-plate fixation with varying angle configurations to stability of osteoporotic fractures: an experimental study]. / Osteoporotik kemikte kilitli plak ve açili vida kullaniminin stabilizasyonun dayanikliligina katkisi: Deneysel çalisma.

OBJECTIVES: This experimental study was designed to find new ways of improving stabilization of fractures in osteoporotic elderly patients through alterations made in the configuration and geometry of locked screw-plate fixation used in the conventional plate technique. METHODS: Four screw configurations with varying angulations were used for plate-bone construction. Forty iron plates of high quality (100x35x3 mm) were divided into four groups and two screw holes, 3 mm in diameter, were drilled on each plate at a distance of 15 mm. In group A, the holes were drilled so that the screws would be vertically sent to the bone interface. In the remaining groups, the holes were drilled for convergent (group B, 15 degrees ) and divergent (group C, 15 degrees ; group D, 30 degrees ) screw orientation. Screw-plate fixation was tested in a modified osteoporotic bone (Osteoporotic Generic Bone, Synbone) on an Instron materials testing system with an axial pullout force of 0.1 mm/sec. Failure loads were read from load-displacement curves and the type of failure was noted. RESULTS: Screws placed in divergent orientations showed the highest axial pull-out strength (group C, 83.3 N/mm; group D, 80.8 N/mm), followed by convergent placement (72 N/mm) and vertical placement (66.7 N/mm). The type of failure was breakage of the bone sample in divergent configurations, and screw pull-out in convergent and vertical configurations. CONCLUSION: Divergent constructs may be a promising alternative to conventional screw placement in treating osteoporotic fractures.