Allan T. Dolovich

Accuracy of Intraoperative Assessment of Acetabular Prosthesis Placement

Anteversion and vertical tilt of the acetabular prostheses in 50 consecutive total hip arthroplasties were prospectively evaluated during surgery (by the surgeon, using an alignment guide) and radiographically (calculated). From postoperative standardized radiographs vertical tilt was measured directly and anteversion was calculated. The mean error of vertical tilt was 5 degrees (range, 0 degrees - 20 degrees). The mean error of version was 9 degrees (range, 0 degrees - 24 degrees). The reliability of prosthesis placement in a predetermined zone was examined. Although the surgeons believed that all 50 cups were inside this zone, radiographic measurements revealed that 21 of the cups were actually outside. It is concluded that vertical tilt can be reasonably assessed during surgery. Anteversion, however, cannot be accurately assessed during surgery, despite use of the alignment guide.

From the rhombic transposition flap toward Z-plasty: An optimized design using the finite element method

In this paper, an optimized design for rhombic transposition flaps is created using a reliable finite element model that assures convergence for stress and deformation results. Defining a general configuration for rhombic flaps, the surgical process of wound closure is simulated for a wide variety of patterns. To address the intrinsic uncertainties associated with modelling skins mechanical properties, four different sets of material parameters are considered, to investigate statistical measures. The results suggest that implementing the rhombic flap technique in a way similar to Z-plasty leads to an optimized surgical technique. The proposed flap, which can be employed for 60° to 90° rhombic defects, can reduce the maximum von Mises stress by 53% (on average) with respect to the Dufourmentel flap, and, in the case of a 60° defect, 43% with respect to the Limberg flap. To avoid any depressed area such as dog-ear formation, the maximum compressive principal stress is examined to assure that it remains within the limits of the stresses in the existing surgical techniques. The deformed configuration is also taken into consideration. Ease of implementation, in terms of both construction and orientation with respect to the relaxed skin tension lines, is another design feature offered by the proposed flap.

Toward a Unified Design Approach for Both Compliant Mechanisms and Rigid-Body Mechanisms: Module Optimization

Rigid-body mechanisms (RBMs) and compliant mechanisms (CMs) are traditionally treated in significantly different ways. In this paper, we present a synthesis approach that is appropriate for both RBMs and CMs. In this approach, RBMs and CMs are generalized into modularized mechanisms that consist of five basic modules, including compliant links (CLs), rigid links (RLs), pin joints (PJs), compliant joints (CJs), and rigid joints (RJs). The link modules and joint modules are modeled through beam elements and hinge elements, respectively, in a geometrically nonlinear finite-element solver, and subsequently a beam-hinge ground structure model is proposed. Based on this new model, a link and joint determination approach—module optimization—is developed for the type and dimensional synthesis of both RBMs and CMs. In the module optimization approach, the states (both presence or absence and sizes) of joints and links are all design variables, and one may obtain an RBM, a partially CM, or a fully CM for a given mechanical task. Three design examples of path generators are used to demonstrate the effectiveness of the proposed approach to the type and dimensional synthesis of RBMs and CMs.

Characterization of Mechanical Properties of Tissue Scaffolds by Phase Contrast Imaging and Finite Element Modeling

In tissue engineering, the cell and scaffold approach has shown promise as a treatment to regenerate diseased and/or damaged tissue. In this treatment, an artificial construct (scaffold) is seeded with cells, which organize and proliferate into new tissue. The scaffold itself biodegrades with time, leaving behind only newly formed tissue. The degradation qualities of the scaffold are critical during the treatment period, since the change in the mechanical properties of the scaffold with time can influence cell behavior. To observe in time the scaffolds mechanical properties, a straightforward method is to deform the scaffold and then characterize scaffold deflection accordingly. However, experimentally observing the scaffold deflection is challenging. This paper presents a novel study on characterization of mechanical properties of scaffolds by phase contrast imaging and finite element modeling, which specifically includes scaffold fabrication, scaffold imaging, image analysis, and finite elements (FEs) modeling of the scaffold mechanical properties. The innovation of the work rests on the use of in-line phase contrast X-ray imaging at 20 KeV to characterize tissue scaffold deformation caused by ultrasound radiation forces and the use of the Fourier transform to identify movement. Once deformation has been determined experimentally, it is then compared with the predictions given by the forward solution of a finite element model. A consideration of the number of separate loading conditions necessary to uniquely identify the material properties of transversely isotropic and fully orthotropic scaffolds is also presented, along with the use of an FE as a form of regularization.

Curved-ray technique to measure the stress profile in tempered glass

We present a new laser method that exploits curved-ray effects and that provides a practical method to investigate the stress profile in tempered glass. A feature of the technique is that the probing laser beam curves sufficiently that it exits on the same side as it enters; it does not reflect off or exit from the opposite side. The governing equations are formulated and studied using analytical methods and computer simulations. For a typical piece of tempered glass, the distance between the entry and exit points is of the order of a few tens of centimeters and is highly sensitive to details of the underlying stress distribution.

An iterative approach to curved ray reconstruction of birefringent fields

Abstract The transmission of polarized light through non-homogeneous birefringent fields is examined, and an iterative approach for incorporating ray curvature into the analysis of tomographic data is proposed. The method extends strain-gradient theory and applies iterative algorithms which have been used by other researchers to reconstruct fields which are non-homogeneous but optically Isotropic. Optical anisotropy is incorporated by using a light propagation model which includes both bending and separation of initially coincident light ray pairs. To illustrate the method, data are generated computationally and are analysed to determine the bending moment in a prismatic beam and the forces acting on a diametrically loaded disc.

A generalized iterative approach to curved-ray tomography

Abstract A generalized iterative approach to the tomographic reconstruction of strongly refracting fields is proposed. The mappings for existing iterative schemes are recognized to be special cases of a more general form, and this form is shown to possess an arbitrary operator which affects convergence but may be changed without altering the roots of the original mapping. This, therefore, provides the basis for defining new recursive sequences which may converge in cases where the standard iterative schemes are divergent. To illustrate the approach, two enhanced schemes are developed by making particular selections for the arbitrary operator, and a 1 -D boundary layer type field is reconstructed from numerically simulated interferometric data.