ABSTRACT
BACKGROUND: Posterior long-segment (LS) fixation, short-segment (SS) fixation, and short segment fixation with intermediate screws (SI) have shown good outcomes for the treatment of thoracolumbar burst fractures. However, limited data compared the biomechanical properties between LS fixation and SI. The purpose of this study was to compare the von Mises stresses on the pedicular screw system and bone between posterior LS fixation, SS fixation, and SI for the treatment of thoracolumbar burst fracture. MATERIALS AND METHODS: The finite element model of thoracolumbar spines from T11 to L3 was created based on the computed tomography image of a patient with a burst fracture of the L1 vertebral body. The models of pedicular screws, rods, and locking nuts were constructed based on information from the manufacturer. Three models with different fixation configurations-that is, LS, SS, and SI-were established. The axial load was applied to the superior surface of the model. The inferior surface was fixed. The stress on each screw, rod, and vertebral body was analyzed. RESULTS: The motion of the spine in SS (0.5 mm) and SI (0.9 mm) was higher than in LS (0.2 mm). In all models, the lowest pedicle screws are the most stressed. The stress along the connecting rods was comparable between SI and LS (50 MPa). At the fracture level, stress was found at the pedicles and vertebral bodies in SI. There was relatively little stress around the fractured vertebral body in LS and SS. CONCLUSIONS: Posterior SI preserves more spinal motion than the LS. In addition, it provides favorable biomechanical properties than the SS. The stress that occurred around the pedicle screws in SI was the least among the 3 constructs, which might reduce complications such as implant failure. SI produces more stress in the fractured vertebral body than LS and SS, which could potentially aid in bone healing according to the Wolff law. CLINICAL RELEVANCE: SI has proved to be a biomechanically favorable construct and helps preserve the spinal motion segment. It could be an alternative surgical option for treating patients who present with thoracolumbar burst fractures.
ABSTRACT
Thin film sliding and friction phenomena of food bolus confined between tongue-palate surfaces during oral processing can be explored using tribological measurements. However, these measurements are still limited within the food industry due to the requirement of expensive commercial instruments which are not commonly used in the food industry. This work has designed and manufactured a modular "tribological cell" (tribo-cell) that can simulate lubricated soft-hard contact interfaces and can be mounted on a rotational rheometer to perform tribological measurements. The tribo-cell was validated by performing tribological measurements using a range of corn syrup solutions as model liquid foods. It was shown that the Stribeck curve describing the change in friction behaviour with entrainment speed or with the product of entrainment speed and liquid viscosity could be obtained. Since tribology deals with surface property, the cell was then used in the further studies to demonstrate the effects of applied normal load and surface wetting on the tribological response of lubricated hard-soft contact of the designed fixture. These parameters were shown to have a marked influence on in the boundary and mixed-lubrication regimes. The designed tribo-cell was also used to illustrate the impact of fat content on the lubrication properties of commercial liquid and semi-solid foods with different fat contents, thus, pointing out to the importance of tribology as a vital tool for product formulation designs in food and beverage industry.
