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Since the biomechanical aspects were beyond the scope of their study, they were not discussed in detail.In our clinic, we also observed new compression fractures in vertebrae adjacent to augmented vertebrae (4). On the basis of our previous experience in arthroplasty and vertebroplasty, we hypothesized that an altered load transfer resulting from rigid cement fixation may induce degenerative changes in adjacent bone (5,6), especially because cement-filled bone is much stiffer than cancellous bone. In trying to explain adjacent fractures, we focused on the biomechanical aspects of vertebroplasty (5-9). In particular, we investigated the effect of the increased stiffness in the augmented vertebra on loading in the adjacent vertebrae by using theoretical and experimental models. Therefore, the purpose of this letter is to complement the article of Dr Uppin and colleagues by elaborating on the biomechanical effect of load shift and by discussing its clinical implications.We developed (theoretical) finite-element models of a lumbar motion segment to examine the effect of rigid cement augmentation on the loading in adjacent vertebrae (6 -8).The analysis of the model illustrated that the cement in the augmented vertebra acts as an upright pillar that reduces the physiologic inward bulging of the endplates of the augmented vertebra. As a result of this pillar effect, the pressure in the adjacent intervertebral disk increases substantially by approximately 19%. Subsequently, adjacent vertebrae experience a higher loading in the same range (6 -8). On the basis 606 ⅐ Radiology ⅐

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The low-velocity impact response of foam-core sandwich composites with fiberglass/epoxy face sheets is treated by a combination of computational and experimental methods. Linear elastic constitutive models are used for the face sheets and epoxy bond layer in conjunction with a foam constitutive model that includes nonlinear hardening plasticity and coupling between volumetric and deviatoric deformation. A transient finite- element code, utilizing four-noded uniform strain quadrilaterals, is used to explicitly solve the equations for balance of mass and momentum. The resulting deformation histories are compared to the experimental results and show qualitative agreement. The computed transverse shear stresses are used to correlate ultrasonic measurement of damage in the core/epoxy interface. Comparison of the plate stiffness prior to and after impact illustrates the effect of damage on subsequent behavior.