Jean-Marc Linares

Aide in decision-making: contribution to uncertainties in three-dimensional measurement

Abstract The authorities of the standards organization International Organization of Standardization (ISO) advocate mastering any uncertainties in all parts of the industrialization process. In the three-dimensional (3D) measurement process, uncertainty is usually obtained at the end of a battery of tests. It is defined as a whole because it includes several types of errors, known systematic components, unknown systematic components and random components. Automated calculations of uncertainty can be made based on statistics. This method is based on statistical concepts, which are in accordance with “The Guide to the expression of the uncertainty in measurement” (GUM). It also enables us to generate uncertainties on the verification of ISO specifications (or specs in the ISO directives). In the course of this article, a usage will be presented that takes the knowledge of uncertainties into account: this usage will help the operator to take a decision on the conformance of a mechanical part in reference to its conformance to geometric tolerance.

Machining dispersions based procedures for computer aided process plan simulation

Among the whole manufacturing cycle of a product, a sequence of manufacturing stages needs to be optimized using the increasingly available computing resources. Computer aided process planning is seen as the missing link between CAD and CAM, which relates to the translation of design tolerances into manufacturing tolerances to be executed in the shop floor. A computerized module for process plan simulation, taking into account the manufacturing dispersions, has been developed. The process plan simulation program, which consists of three procedures, uses a combination of the minimal transfer method and a modified form of the dispersions method. The first procedure performs a verification of the feasibility of the projects process plans through tolerance transfer. The second procedure performs an optimization of the tolerance distribution using the process capability data. The third procedure computes the manufacturing dimensions, which ensure the quality of the components and products. The simulation module has been validated on complex problems and shows that it gives good results in a short time. The manual work requires several days to solving this manufacturing problem.

Posterior tibial slope accuracy with patient-specific cutting guides during total knee arthroplasty: A preliminary study of 50 cases.

BACKGROUND Patient-specific cutting guides were recently introduced to facilitate total knee arthroplasty (TKA). Their accuracy in achieving optimal implant alignment remains controversial. The objective of this study was to evaluate postoperative radiographic outcomes of 50 TKA procedures with special attention to posterior tibial slope (PTS), which is difficult to control intraoperatively. We hypothesized that patient-specific cutting guides failed to consistently produce the planned PTS. MATERIAL AND METHODS The Signature™ patient-specific cutting guides (Biomet) developed from magnetic resonance imaging data were used in a prospective case-series of 50 TKAs. The target PTS was 2°. Standardised digitised radiographs were obtained postoperatively and evaluated by an independent reader. Reproducibility of the radiographic measurements was assessed on 20 cases. The posterior cortical line of the proximal tibia was chosen as the reference for PTS measurement. Inaccuracy was defined as an at least 2° difference in either direction compared to the target. RESULTS The implant PTS was within 2° of the target in 72% of knees. In the remaining 28%, PTS was either excessive (n=10; maximum, 9°) or reversed (n=4; maximum, -6°). The postoperative hip-knee-ankle angle was 0° ± 3° in 88% of knees, and the greatest deviation was 9° of varus. CONCLUSION These findings support our hypothesis that patient-specific instrumentation decreases PTS accuracy. They are consistent with recently published data. In contrast, patient-specific instrumentation provided accurate alignment in the coronal plane.

Influence of the optical system and anatomic points on computer-assisted total knee arthroplasty

BACKGROUND For over a decade, computer-assisted orthopaedic surgery for total knee arthroplasty has been accepted as ensuring accurate implant alignment in the coronal plane. HYPOTHESIS We hypothesised that lack of accuracy in skeletal landmark identification during the acquisition phase and/or measurement variability of the infrared optical system may limit the validity of the numerical information used to guide the surgical procedure. METHODS We built a geometric model of a navigation system, with no preoperative image acquisition, to simulate the stages of the acquisition process. Random positions of each optical reflector center and anatomic acquisition point were generated within a sphere of predefined diameter. Based on the virtual geometric model and navigation process, we obtained 30,000 simulations using the Monte Carlo statistical method then computed the variability of the anatomic reference frames used to guide the bone cuts. Rotational variability (α, β, γ) of the femoral and tibial landmarks reflected implant positioning errors in flexion-extension, valgus-varus, and rotation, respectively. RESULTS Taking into account the uncertainties pertaining to the 3D infrared optical measurement system and to anatomic point acquisition, the femoral and tibial landmarks exhibited maximal alpha (flexion-extension), beta (valgus-varus), and gamma (axial rotation) errors of 1.65° (0.9°); 1.51° (0,98°), and 2.37° (3.84°), respectively. Variability of the infrared optical measurement system had no significant influence on femoro-tibial alignment angles. CONCLUSION The results of a Monte Carlo simulation indicate a certain level of vulnerability of navigation systems for guiding position in rotation, contrasting with robustness for guiding sagittal and coronal alignments. LEVEL OF EVIDENCE Level IV.

A stochastic concept for the optimization of manufacturing tolerances in computer aided process plan simulation

In order to integrate tolerance synthesis for manufacturing dimensions in CAPP systems, an automated process plan simulation module has previously been developed. This module permits the verification of the manufacturing pre-projects and the optimization of the manufacturing dimensions. The module used an optimization procedure which was realized through an equal distribution of the excess tolerance which is that of the design functional requirement. However in reality, this distribution should take into account the stochastic aspects of the dispersions and the complexity or cost of the manufacturing dimensions. In the present work, in order to overcome these drawbacks, a statistical and cost based tolerance synthesis model has been developed. It is shown that this model performs an objective and global distribution of the residual (excess) tolerances of the design functional dimensions on all the manufacturing dimensions of the process plan. The dispersions method is used in the modelling process to determine the variables of the objective function and to automatically extract the manufacturing tolerance chains. These chains are then used to construct the functional constraints of the optimization model. The whole process has been programmed as an automated tolerancing tool for manufacture and validated for several examples.

Titanium implant impairment and surrounding muscle cell death following neuro-myoelectrostimulation: An in vivo study

Electrical currents have deleterious effects on biomedical metallic implants. However, following arthroplasty, neuro-myoelectrostimulation (NMES) is often used in patient rehabilitation. Such a rehabilitation technique could compromise patient recovery through deleterious effects on metallic alloys and biological tissues. The purpose of our study was to assess the effects of NMES on a Ti6Al4V implant placed in a rat tibial crest and the surrounding muscle tissues. This in vivo study allowed to bring to the fore the prosthesis behavior under mechanical and electromagnetic loads induced by NEMS stimulation. After 3 weeks, implant-to-bone adhesion significantly decreased in stimulated animals compared with nonstimulated animals. Surface mapping indicated titanium implant degradation after NMES. Furthermore, NMES alone did not induce muscle damage contrary to that found in implanted animals. The muscle damage rate was significantly higher in implanted and stimulated animals compared with implanted-only animals. It seems obvious that rehabilitation programs using the NMES technique could induce early deterioration of biomaterial employed for surgical implants. Clinicians should reconsider the use of NMES as a rehabilitation technique for patients with titanium prostheses.

Titanium Implant Impairment and Surrounding Muscle Cell Death Following High-Salt Diet: An In Vivo Study

Aim of the study High-salt consumption has been widely described as a risk factor for cardiovascular, renal and bone functions. In the present study, the extent to which high-salt diet could influence Ti6Al4V implant surface characteristic, its adhesion to rat tibial crest, and could modify muscle cell viability of two surrounding muscles, was investigated in vivo. These parameters have also been assessed following a NMES (neuro-myoelectrostimulation) program similar to that currently used in human care following arthroplasty. Results After a three-week diet, a harmful effect on titanium implant surface and muscle cell viability was noted. This is probably due to salt corrosive effect on metal and then release of toxic substance around biologic tissue. Moreover, if the use of NMES with high-salt diet induced muscles damages, the latter were higher when implant was added. Unexpectedly, higher implant-to-bone adhesion was found for implanted animals receiving salt supplementation. Conclusion Our in vivo study highlights the potential dangerous effect of high-salt diet in arthroplasty based on titanium prosthesis. This effect appears to be more important when high-salt diet is combined with NMES.

Biocompatibility of Four Common Orthopedic Biomaterials Following a High-Salt Diet: An In Vivo Study

Nowadays, salt consumption appears to be drastically above the recommended level in industrialized countries. The health consequences of this overconsumption are heavy since high-salt intake induces cardiovascular disease, kidney dysfunction, and stroke. Moreover, harmful interaction may also occur with orthopaedic devices because overconsumption of salt reinforces the corrosive aspect of biological tissues and favors bone resorption process. In the present study, we aimed to assess the in vivo effect of three weeks of a high-salt diet, associated (or not) with two weeks of the neuro-myoelectrostimulation (NMES) rehabilitation program on the biocompatibility of four biomaterials used in the manufacture of arthroplasty implants. Thus, two non-metallic (PEEK and Al2O3) and two metallic (Ti6Al4V and CrCo) compounds were implanted in the rat tibial crest, and the implant-to-bone adhesion and cell viability of two surrounded muscles, the Flexor Digitorum (FD) and Tibialis Anterior (TA), were assessed at the end of the experiment. Results indicated lower adhesion strength for the PEEK implant compared to other biomaterials. An effect of NMES and a high-salt diet was only identified for Al2O3 and Ti6Al4V implants, respectively. Moreover, compared to a normal diet, a high-salt diet induced a higher number of dead cells on both muscles for all biomaterials, which was further increased for PEEK, Al2O3, and CrCo materials with NMES application. Finally, except for Ti6Al4V, NMES induced a higher number of dead cells in the directly stimulated muscle (FD) compared to the indirectly stimulated one (TA). This in vivo experiment highlights the potential harmful effect of a high-salt diet for people who have undergone arthroplasty, and a rehabilitation program based on NMES.

Study of Bearing Modelling in the Helicopter Gearbox

In trying to incessantly reduce gearboxes weight, designers can negatively impact the service reliability, particularly in the aeronautic industry, where a weight reduction is often linked with stiffness decrease. Looking for weight savings, gearbox casings are classically made of magnesium or aluminium alloy. In addition, helicopter gearbox design is included the integration of several functions within the same part (like the shafts which gather one or more gears, splines and integrated bearings raceways). These particularities in the design are requiring some specific methodologies for Power Transmission bearing modelling. In this paper, a comparison between tests and simulations results of the aforementioned gearboxes is presented. The first section of the article focuses on the helicopter gearbox description and associated finite elements modelling. Then, the second section provides a comparison between the experimental observations with the results of both FEM simulation and classical analytical simulation. This comparison demonstrates the interest of using FEM simulation to analyze gearboxes behaviour.

Quality Measurement on CMM

In the first section we wile discuss the sources of errors and uncertainties of the Coordinate Measuring Machine (CMM) [1]. The mastery of this process depends on a good knowledge of the initialisation methodology of the CMM.