Konstanty Skalski

Process of hip joint prosthesis design including bone remodeling phenomenon

The design of hip joint prostheses is very complex process which requires close co-operation between engineers and surgeons. To design a prosthesis of higher durability one has to take natural processes occurring in bone into consideration. In the paper a process of hip joint prosthesis design is described. The design process was performed for a particular patient who suffered from severe trauma of a hip joint. A set of three prostheses was created and then some numerical calculations were carried out with the use of ADINA system. The visco-elastic properties of bone and the bone remodeling phenomenon were taken into consideration, which is a novel approach in prosthesis design. The results of the numerical analyses allowed us to decide which one of the three designed prostheses is the most capable for the patient. This way the shape optimisation process is completed. As a result of it the load acting on the designed prosthesis will be anatomically adopted by the femur.

Methodology of off-line software compensation for errors in the machining process on the CNC machine tool

Abstract Off-line software machining accuracy enhancement has been suggested based on the prediction of the machining error Δ → =[ Δ x , Δ y , Δ z ] . It has been assumed that errors in the machine tool workspace can be analysed as a superposition of the components Δ → g , Δ → m , Δ → n where Δ → g results from the geometric surface description, Δ → m results from the limited machine tool stiffness and Δ → n results from the cutting tool deflection during machining. Geometric description error Δ → g =[ Δ xg , Δ yg , Δ zg ] arises from the surface geometric modelling phase in the CAD system. The NURBS (Non-Uniform Rational B-Spline) technique has been selected as the most effective for the complex shape surface description, supported by the least square principle. Then the distances between the measuring points and the calculated points on the described surface patch have been determined and a function representing the inaccuracy of the surface description has been defined. The Δ → m =[ Δ xm , Δ ym , Δ zm ] error has been calculated based on periodic measurements of the machine tool positions while applying static forces to the spindle endpoint. The points in the factor have been selected according to principles of mathematical experiment planning. The polynomial regression-based relationships have been derived for Δ → m error description. The results have been validated using statistical correlation analysis. A similar approach has been adopted for the estimation of the cutting tool deflection error Δ → n =[ Δ xn , Δ yn , Δ zn ] . The resulting Δx, Δy and Δz components have been introduced as compensation values adding up to the regular tool movements along the programmed tool path. A special postprocessing program has been developed for doing this job, herein called active task in order to differentiate it from standard postprocessing functions named as passive tasks.

Reverse engineering of free-form surfaces

Abstract Reverse engineering is used in different areas of design and manufacturing. In the automotive industry it is often necessary to change the shape of the prototype during the manufacturing process. The changes have to be then considered in the drawing and in the geometric model of some parts in CAD system. It is associated with the measurements of the part surface and its approximation. The authors of this paper have concentrated on presenting methods of measurement and of the geometric modelling of free-form surfaces. An integrated solution of these tasks will be proposed. The identification of the object with coordinate measurements is discussed. Measurement results are written in the format ready for use by the program of the surface approximation. This program was created by the authors of the paper. The NURBS method is used for surface description and the problem is solved by the least squares method. The results of calculations are written in the macrostatement format (for the definite CAD system) or in a way using the more universal IGES standard. Two integrated CAD/CAM systems are used in the research (Personal Machinist and Mastercam). In the CAD module, visualisation of the geometrical model is effected. The CAM module is used for generating the cutter path for CNC milling machines. The machined parts are measured for the purpose of determining of the manufacturing accuracy. This is carried out on the CNC milling machine with a special probe.

Design and manufacture of anatomical hip joint endoprostheses using CAD/CAM systems

Abstract This paper contains a methodology for the design and manufacture of implants in cases when the medical indications favour the application of an anatomic custom design implant. Methods of interpretation and identification of the anatomic shapes of the human bone system (marrow cavity, trochanter, etc.) are discussed on the basis of computer tomography (CT) data. Methods for the process of modelling implants using CAD systems are then presented. The advantages of the parametric modelling for typical CAD/CAM systems are discussed. A new possibility allowing surgeons to make the final decision as to the selection of a prosthesis from the standard set is explained, based on geometric modelling preceded by a CT-based process of identification. Methods of metallic prostheses manufacturing using numerically controlled machine tools are proposed. Specific difficulties arising in the integration process of CAD and CAM modules are presented and methods for improvement are proposed. Requirements for up-to-date CAM systems pertaining to driving the tool across the complex shape surfaces are summarised and the demand for additional software to bridge the gap between the CAD/CAM and the given CNC machine tool controllers is determined (postprocessing). Attention is paid to NC programs verification techniques using substitute materials for the machining process and rapid prototyping. Limitations of the proposed method due to its relatively low productivity and the shape problems are defined, and ways of overcoming them are suggested. The results of practical experiments leading to prototype manufacture are described. The areas of problems caused by the specific kinematics of the applied CNC machine tools, as well as problems of handling large amounts of data flowing into machine control units are mentioned.

Rapid prototyping in the intervertebral implant design process

Purpose – The purpose of this paper is to present the methodology of a design process of new lumbar intervertebral disc implants with specific emphasis on the use of rapid prototyping technologies. The verification of functionality of artificial intervertebral discs is also given. The paper describes the attempt and preliminary research to evaluate the properties of the intervertebral disc implant prototypes manufactured with the use of different rapid prototyping technologies, i.e. FDM – fused deposition modelling, 3DP – 3D printing and SLM – selective laser melting. Design/methodology/approach – Based on the computed tomography (CT) scan data, the anatomical parameters of lumbar spine bone tissue were achieved, which were the bases for the design-manufacture process carried out with the use of computer-aided designing/computer-aided engineering/computer-aided manufacturing systems. In the intervertebral disc implant design process, three RP technologies: FDM, 3DP and SLM were used for solving problems r...

Identification and geometrical modelling of complex shape surfaces using coordinate measuring machine and CAD/CAM systems

Abstract Two similar methods for the geometric identification of complex shape surfaces using the scanning measurement technique on a coordinate measuring machine (CMM) will be presented in this work. The first method employs the surfaces defined by the CAD system parametric technique based on the set of measurement points. The coordinates of points in space are determined by measurement in successive scanning planes with a given measuring step. The second method employs the surfaces defined by the analytically generated orthogonal curve meshes given by Newtons interpolation function. The interpolation points are the measurement points in the Cartesian space for a given measuring step. The generation technique of the interpolation function is then applied by using the interpolation method to define the arbitrary coordinate point set of the range of the measured net. Following this method of identification, some corrective procedure for measuring the results of surface coordinate points are proposed. These correction procedures result from use of the probe end in the coordinate technique. As a consequence of the presented corrective procedures, the authors propose useful software (numerical programmes) for the applied CMM during measuring of the complex shape surfaces. In the final part of the work, the sets of points obtained from these measurements are used to the develop 3D geometrical models of surfaces in the CAD system. The discussed techniques of identification and modelling are adopted in the design of a TV tube and the shape surface of the radial bone in bioengineering as practical examples.

New lumbar disc endoprosthesis applied to the patient’s anatomic features

PURPOSE The paper describes the process of designing, manufacturing and design verification of the intervertebral of a new structure of lumbar disc endoprosthesis - INOP/LSP.1101. METHODS Modern and noninvasive medical imagining techniques, make it possible to record results of tests in a digital form, which creates opportunities for further processing. Mimics Innovation Suite software generates three-dimensional virtual models reflecting the real shape and measurements of components of L4-L5 spinal motion segment. With the use of 3D Print technique, physical models of bone structures of the mobile segment of the spine as well as the INOP/LSP.1101 endoprosthesis model were generated. A simplified FEA analysis of stresses in the endoprosthesis was performed to evaluate the designed geometries and materials of the new structure. RESULTS The endoprosthesis prototype was made of Co28Cr6Mo alloy with the use of selective laser technology. The prototypes were subject to tribological verification with the use of the SBT-03.1 spine simulator. CONCLUSIONS The structure of the endoprosthesis ensures a full reflection of its kinematics, full range of mobility of the motion segment in all anatomical planes as well as restoration of a normal height of the intervertebral space and curvature of the lordosis. The results of the tribological tests confirmed that SLM technology has the potential for production of the human bone and jointendoprostheses.

Computer-aided reconstruction of hip joint in revision arthroplasty

Geometric revision reconstruction of the hip joint of a female patient is presented. Because of extensive bone resorption and strong bone obstruction, we decided to employ a custom–made prosthesis not only in the pelvis but also in the femur. The custom prosthesis design and manufacturing processes were carried out with the aid of computed tomography (CT), a system of tomographic image processing, a computer–aided design (CAD) system and a computer–aided manufacturing (CAM) system. The process included tomographic measurements of the patient’s hip joint, conversion of the CT images, geometrical modelling of the femur and pelvis in the CAD system, prostheses design, virtual simulation of the reconstructed acetabulum, determination of prosthesis matching, and manufacturing on a CNC machine. The outcome of this engineering process was a total hip arthroplasty (THA) surgical operation.

The influence of the cumulated deformation energy in the measurement by the DSI method on the selected mechanical properties of bone tissues

PURPOSE The goal of the study was to determine the influence of DSI test conditions, i.e., loading/unloading rates, hold time, and the value of the maximum loading force on selected mechanical properties of trabecular bone tissue. METHODS The test samples were resected from a femoral head of a patient qualified for a hip replacement surgery. During the DSI tests hardness (HV, HM, HIT) and elastic modulus (EIT) of trabecular bone tissue were measured using the Micro Hardness Tester (MHT, CSEM). RESULTS The analysis of the results of measurements and the calculations of total energy, i.e., elastic and inelastic (Wtotal, Welastic, Winelastic) and those of hardness and elasticity made it possible to assess the impact of the process parameters (loading velocity, force and hold time) on mechanical properties of bone structures at a microscopic level. CONCLUSIONS The coefficient k dependent on the EIT/HIT ratio and on the stored energy (ΔW = Wtotal - Welastic) is a measure of the material reaction to the loading and the deformation of tissue.

Structure and mechanism of the deformation of Grade 2 titanium in plastometric studies

ABSTRACT In this paper, the results of plastometric and material studies on grade 2 titanium are presented. Cylindrical titanium samples were compressed at elevated temperatures on a Gleeble thermo-mechanical simulator. The process was captured in the form of stress-strain diagrams. Then, for the chosen-deformed samples, structural studies were performed on a digital light microscope. On the basis of the results, it was possible to determine the plastometric processing conditions that are most suitable for the fragmentation of the grains of the tested titanium. In order to find optimal processing parameters, it was also important to describe the plastometric process through the appropriate constitutive equations. Material constants in this equation were determined on the basis of a hyperbolic sinusoidal equation. This paper is part of a thematic issue on Titanium.