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Background We applied a previously established and validated numerical model to a novel short-stemmed implant for a ‘pre-launch’ investigation. Methods The implant system consists of two different implant geometries for valgus/varus-positioned proximal femurs with differences in volume distribution, head/neck angle, and calcar alignment. The aim of the design was to achieve a better adaption to the anatomic conditions, resulting in a favourable load transfer. The implant type G showed the best fit to our model, but both stem geometries were implanted; the implant type B was used to compute an ‘imperfection scenario’. Findings Apparent bone density decreased by 4.3% in the entire femur with the implant type G, and by 12.3% with the implant type B. Bone mass loss was pronounced in the proximal calcar region. Apparent bone density increased at the lateral cortical ring and in the minor trochanter. The apparent bone density in the imperfection scenario was very similar to that of a straight stem, indicating a distal load transfer. Interpretation No adverse effects of the A2 short-stemmed implant system on bone remodeling could be detected. The overall bone density reduction was acceptable, and wedge fixation was not observed, indicating that there was no distal load transfer. The simulation of an incongruous implant indicates the sensitivity of our model in response to modifications of implant positioning. Correct implant selection and positioning is crucial when using the A2 system.

Bone density measurements using computed tomography (CT) instead of dual-energy X-ray absorptiometry (DEXA) are currently of great interest in human and veterinary medical research as it would be beneficial to use CT scans obtained for other indications also for determining bone density. For Hounsfield units (HU) measured with CT in specific regions of interests (ROIs) in one or several slice/s a correlation with bone mineral density (BMD) measured by DEXA in humans and dogs of between 0.44 and 0.77 is reported in the literature. In the present study, instead certain volumes of interest (VOIs) obtained by CT scan and the corresponding HU to the respective VOIs were compared with the bone mineral density of the corresponding areas measured by DEXA. The aim of the study was to investigate whether this procedure gives more accurate information about bone density of the bones as three-dimensional objects of the respective patient. Correlation between measured HU in the respective VOI and BMD measured with DEXA in the corresponding ROI showed a very good correlation of 0.93. Linear regression with R2 = 0.85 (p = 0.0262) was calculated. Except for VOI5, similar distribution of values and significant differences (p

This paper presents the results and analysis of wear investigations carried out on a wear test bench with high strength sheet metal DP600+Z drawn over selectively oxidised α-Fe 2 O 3 tool steel surfaces. Wear investigations were carried out with several selectively oxidised specimens by varying the pulling and counter force, and thus the surface pressure on the samples. This allowed for a systematic study of the wear behaviour of the oxide layers under different loads. The specimens were characterised using microscopy (light microscopy, scanning electron microscopy and topography analysis) and scratch testing on a nanoindenter. The study shows that it is possible to realise a dry metal forming process while using α-Fe 2 O 3 oxide layers on the tool steel surface. The oxidised surface acts as a friction reducing separation layer and protects the tool against wear. Simultaneously, it was found that the surface of sheet metal drawn over oxidised specimens showed lower zinc abrasion than sheet metal drawn over non-oxidised reference specimens at the same surface pressure. In addition, the oxidised specimens have a reduced Zn pick-up affinity.

Mechanical joining processes provide various advantages over conventional fusion welding of metallic components such as shorter cycle times, little or no heat input and reduced need for subsequent surface finishing operations. Several investigations in the past have shown that joints between tubes and sheets or plates can be manufactured by upsetting operations. Under axial compression, the tube develops a plastic instability in form of bulge. In-between two such bulges, a force and form fit to sheet material can be created. Previous work concentrated on forming fully developed bulges, i.e., at the end of the bulging process, both hinges of the bulge are in contact. This paper presents a numerical and experimental study aiming at optimizing the bulge shape to increase the bearable limit loads. Two new bulge designs are investigated, an ‘arrow bulge’ and a ‘wave bulge’. The paper details the results of FE-simulations of the bulge shapes under bending and torsion loads. Forming tools were designed and both bulge shapes were produced experimentally. The results show that the material flow under compressive plastic instability can be controlled and that the resulting bulge shapes yield improved strength in various load cases.

The increased use of high and ultra-high strength steel and materials with a high adhesion tendency leads to higher demands regarding the wear resistance of forming tools. A promising approach addressing both challenges is to apply MoS2 dry film lubricant coating systems to the tool surface. These coatings reduce friction and the use of drawing oils and can also be used as an abherent. Once these coatings are exhausted, they can be chemically removed and reapplied. However, the tool life of the coatings cannot be predicted properly, due to their inhomogeneous wear behavior which depends on the forming parameters and differs locally. Moreover, there are carryover effects of MoS2-particles to already ablated areas. Given the unpredictability of the wear of dry film lubricant coatings, it is not possible to plan the recoating cycles appropriately and thus, the potential of these coatings for commercial applications is limited. In this research, the wear behavior of MoS2-layers in deep drawing processes was investigated on a test stand with DP800+Z coil material which ensures realistic load conditions at the draw ring radius. Firstly, the wear pattern was determined and locally different contact pressures were recorded and assigned to respective wear areas. Due to bending effects of the sheet material, there are two major areas of wear on the draw ring radius. During wear tests, the wear-dependent coating thickness during wear initiation was determined by using 3D laser scanning microscopy and the friction force was evaluated.

Due to the limitations of other processes in joining different types of material, mechanical joining methods can be alternatively used. Joining by upset bulging can be employed for joining tubes with other structures such as sheets, plates, tubes or profiles as well as for joining different materials. In spite of successful industrial applications of this joining process, material damage is still a challenge. This damage affects the resistance of the created joint to service loads. Thus, in this paper, a local heating is studied, which aims at avoiding pre-damage or failure of the joint. A parametric FE model is developed to analyse the influence of local heating on the bulging process. It is found that the process window set by the bulge length suitable for joining is widened, but only to a minor extent. The marginal influence of local heating on the bulge geometry allows designing the process in the same way as room temperature processes. Metallographic investigations confirm the damage-free bulging of tubes by forming at elevated temperatures. Another important result is that tubes can be equipped with predefined bulge zones by local heating zones to 700 °C for 15 seconds for example. This enables bulging of tubes during joining by applying an axial load only, without using tools to define the location of the bulge or its length, thus enabling joining operations with limited access.

Background: In recent years, the use of hip prostheses has become a routine procedure. Despite this experience and good clinical results different complications arise which have a negative influence on the lifetime of prostheses. Especially the migration or loosening of the hip cup prosthesis due to strain adaptive bone remodelling is still a problem. Patient-individual prostheses represent a possible solution to this problem. Individual hip cups, however, are just implanted for the treatment of massive deformities or tumours. This study aimed at developing an innovative concept for the production of patient-specific human hip prostheses made of titanium plates by sheet metal forming. Methods: For the realisation of this innovative concept, a reproducible design method for the generation of standardised human hip cup prosthesis was generated based on 13 original human geometries. By means of this methodology a hip cup was designed. Based on this design a human hip cup was produced by a developed high-pressure sheet metal forming process. The development of the process was accompanied by a numerical preliminary design. Results: A comparison between the simulation and the fabricated hip cup leads to a standard deviation of 0.404 mm. Furthermore, an implantation of the prosthesis in a synthetic bone model shows a satisfactory fit accuracy at the edge of the prosthesis. Conclusion: The high-pressure sheet metal forming process is suitable to manufacture the designed standardised hip cup. However, further optimisation is necessary. Hintergrund: In den letzten Jahren ist die Implantation der Huftprothesen ein Routineverfahren geworden. Trotz der langjahrigen Erfahrung und den guten klinischen Ergebnissen treten verschiedene Komplikationen auf, die einen negativen Einfluss auf die Lebensdauer der Prothese haben. Vor allem stellen die Lockerung der Huftpfannenprothese sowie die Prothesenmigration aufgrund des beanspruchungsadaptiven Knochenumbaus nach wie vor ein groses Problem dar. Patientenindividuelle Prothesen bieten eine mogliche Losung fur dieses Problem. Einzelne individualisierte Huftpfannen werden jedoch nur fur die Behandlung von massiven Deformitaten oder Tumoren eingesetzt. Ziel dieser Studie ist ein innovatives Konzept fur die Herstellung von patientenspezifischen Huftprothesen aus Titanblechen zu entwickeln. Methoden: Zur Realisierung des innovativen Konzepts, wurde eine reproduzierbare Designmethode basierend auf 13 ursprunglichen menschlichen Geometrien entwickelt. Mit Hilfe dieser Methode wurde eine standardisierte menschliche Huftpfannenprothese erzeugt. Beruhend auf diesem Entwurf wurde eine Huftpfanne mittels eines entwickelten Hochdruck-Blechumformungsverfahrens hergestellt. Die Entwicklung dieses Verfahrens wurde mit Hilfe der Finite-Elemente-Methode konzeptioniert. Ergebnisse: Der Vergleich der Simulationsergebnisse mit der geometrischen Vermessung der hergestellten Huftpfannen fuhrt zu einer Standardabweichung von 0,404 mm. Weiterhin zeigt die Implantation der Prothese in ein synthetisches Knochenmodell eine zufriedenstellende Passgenauigkeit am Rand des Acetabulum. Fazit: Das Hochdruckblechumformungsverfahren ist fur die Herstellung der entworfenen, standardisierten Huftpfannenprothesen geeignet. Jedoch ist eine weitere Optimierung weiterhin notwendig.

Die aseptische Lockerung der Prothese stellt immer noch ein Problem bei der Huftgelenkprothese dar. Die Lockerung kann u. a. durch den Knochenumbau um die Prothese aufgrund von Stressabschirmung verursacht werden. Ein numerisches Modell wurde am Institut fur Umformtechnik und Umformmaschinen der Leibniz Universitat Hannover entwickelt, um den Knochenumbauprozess nach der Belastungsabschirmung abzubilden. Diese Studie wird durchgefuhrt, um das Modell mittels DEXA- sowie CT-klinischen Studien an Patienten mit verschiedenen Arten von Prothesen zu validieren. Ferner wurde das Modell verwendet, um die Pfannenmigration abzubilden. Das Modell wurde auf den periprothetischen Femur und das Becken angelegt. In beiden Fallen zeigen die numerischen Berechnungen sehr gute Ergebnisse im Vergleich mit den klinischen Studien. Mit einer durchschnittlichen Differenz von 12 % im Falle des Femurs und 6,8 % im Falle des Beckens wurde das numerische Knochenumbaumodell erfolgreich validiert. Daruber hinaus wurde eine neue Methode entwickelt, um die Prothesenmigration in das Becken abzubilden. Durch mechanische Gleichungen und Neuvernetzungsmethoden ist die Finite-Elemente-Analyse (FEA) in der Lage, die mogliche Prothesenmigration im Becken zu berechnen. Diese Methode wurde an Polyethylen-Pfannen angewendet und zeigt gute Ergebnisse im Vergleich mit der klinischen Studie von Kadar et al. Um die Genauigkeit der numerischen Berechnung zu erhohen, wird der Unterschied des durch die Pfannenmigration hervorgerufenen Huftlastkollektivs mittels Mehrkorpersimulation mitberucksichtigt und in die FEA mittels einer von unserer wissenschaftlichen Gruppe entwickelten Kopplungssoftware integriert. Aseptic loosening of the prosthesis is still a problem in artificial joint implants. The loosening can be caused by, among other factors, resorption of the bone surrounding the prosthesis owing to stress shielding. A numerical model was developed at the Institute of Forming Technology and Machines, Leibniz Universitat Hannover, in order to anticipate the bone remodelling process according to the stress shielding. This study is carried out to validate this model by means of DEXA- as well as CT-clinical studies on patients with different kinds of prostheses and use it to map the cup migration. The model was applied to the periprosthetic femur and pelvis. In both cases it shows very good results. With a mean difference of 12% in case of the femur and 6.8% in case of the pelvis the numerical bone remodelling model is successfully validated. A new method is developed to map the prosthetic migration in the pelvis. Using mechanical relationships and remeshing regulations the finite-element-analysis (FEA) calculates the possible migration of the cup in pelvis. This method was applied to polyethylene cup and showed good results in comparison with a clinical study. In order to increase the accuracy of the numerical model, the difference in hip contact forces caused by the migration of the cup is calculated by multi body simulation and embedded in the FEA using online coupling software developed by our scientific group.

Der Einsatz von Huftendoprothesen hat sich in den letzten Jahren als Routineeingriff entwickelt. Trotz dieser Erfahrung kommt es immer wieder zu Komplikationen. Besonders die Migration oder Lockerung der kunstlichen Huftpfannenkomponente aufgrund des belastungsadaptiven Knochenumbaus ist immer noch ein aktuelles Problem. Dies ist auf die veranderte mechanische Situation nach der Implantation der Prothese zuruckzufuhren. Eine weitere Problematik stellt der hohe Knochenverlust wahrend der Implantation dar, der eine Revision der Prothese erschwert. Eine Losung stellt der Einsatz von patientenindividuellen Prothesen dar. Aufgrund der zeitaufwandigen und kostenintensiven Herstellung ist der Einsatz dieser Prothesen bisher begrenzt. Das ubergeordnete Ziel des im Rahmen dieser Veroffentlichung vorgestellten Projektes ist die Erarbeitung und Etablierung eines innovativen Konzeptes zur Herstellung von patientenindividuellen Huftprothesenpfannen aus Titanblechen mit dem Einsatz eines Blechumformverfahrens. Die Idee dieses Konzeptes beinhaltet die Entwicklung eines zweistufigen Prozesses, bei dem zunachst standardisierte Huftprothesenpfannen mittels Hochdruckblechumformung gefertigt werden und anschliesend im zweiten Schritt individualisiert werden. Diese Veroffentlichung beinhaltet die Ableitung der standardisierten Prothese. Hierfur wurde eine Konstruktionsmethodik generiert, die auf dem sogenannten Agglomerative Clustering basiert. Des Weiteren werden im Zuge dieser Veroffentlichung die Ergebnisse der numerischen Vorauslegung der ersten Prozessstufe sowie das entwickelte Werkzeugkonzept vorgestellt. In recent years, the use of hip prostheses has become a routine procedure. The use of total hip replacement has evolved in recent years to a routine procedure. Despite this experience, it always comes back to complications. Especially the migration or loosening of the acetabular component because of the artificial load adaptive bone remodeling is still a current problem. This is due to the changing mechanical situation after the implantation of the prosthesis. Another problem is the high bone loss during implantation, which complicates a revision of the prosthesis. One solution is the use of patient-specific prostheses. So far, the use of these prostheses is limited due to the time-consuming and cost-intensive production. The overall objective of the presented project in this publication is the development and establishment of an innovative concept for the production of patient-specific hip prosthesis made of titanium plates by sheet metal forming. The idea of this concept involves the development of a two-stage process. First of all a standardized hip prosthesis is made by high-pressure sheet metal forming and then individually in the second step. This publication contains the derivation of the standard prosthesis. For this purpose, a design methodology was generated, based on the so-called agglomerative clustering. In addition, presents the results of the numerical preliminary design of the first stage of the process and the tool developed concept in the course of this paper.

Durch eine systematische Vorgehensweise und den konsequenten Abgleich der Ergebnisse aus experimentellen und numerischen Untersuchungen konnte zunachst ein tiefgreifendes Verstandnis fur die beim Knickbauchen wirksamen Mechanismen entwickelt und daraus abgeleitete Verfahrensgrenzen ermittelt und in Form eines Arbeitsdiagrammes fur den Werkstoff E235+N dargestellt werden. Im Hinblick auf eine breite industrielle Nutzung des Knickbauchens als Fugeverfahren wurde auserdem eine sowohl aus technologischer als auch aus fertigungstechnischer und wirtschaftlicher Sichtweise geeignete Methode entwickelt und anhand praktischer und numerischer Versuche validiert.

We developed a numerical model to describe the bone remodeling process in periprosthetic bone tissues and validated it by means of dual energy X-ray absorptiometry methods with different types of hip implants. In this paper, we applied the numerical model to investigate the influence of implant size and of the size of the porous coated area on bone remodeling in a periprosthetic human femur in an effort to define properties of implants, which would reduce bone remodeling after total hip arthroplasty. Two different sizes of a newly designed implant and three different coating area sizes were investigated in this paper. The results show that the smaller the implant, the less bone remodeling occurs. Reducing prosthesis size by 2mm from all sides has decreased bone remodeling by 14.4%. Extending the coating area on both, lateral and medial parts of the implant, has decreased bone remodeling in the lateral part of the femur and increased it in the medial part. In conclusion, depending on these results, the oversized hip replacement would cause more bone resorption in the femur. Concerning the coating area, the manufacturer must find a compromise between the small coating area with less bone remodeling in the medial part of the femur as well as less primary stability and the bigger coating area with less bone remodeling in the lateral part of the femur, but with higher bone remodeling in its medial part and more primary stability.

Background The history of total ankle arthroplasty (TAA) has different evolution steps to improve the outcome. The third generation implants show an overall 8-year survival rate up to 93%. The main reported reason for early failure of TAA is aseptic loosening, cyst formation is also frequently reported. The aim of the present study is to use the finite element (FE) method to analyze the adaptive bone remodeling processes, including cyst formation after TAA. Methods Bone characteristics applied to the model corresponded to information obtained from computed tomography. Finite element models for the tibia and the talus were developed and implant components were virtually implanted. Results The calculated total bone loss is 2% in the tibia and 17% in the talus. Cysts and areas of increased bone density were detectable dependent on prosthesis design in the tibia and talus. Conclusion Our FE simulation provides a theoretical explanation for cyst formation and increasing bone density depending on implant design. However, cysts are not mono-causal, histo-chemical reactions should also be considered. Further clinical studies are necessary to evaluate the relevance of cyst formation and therapeutic strategies.

Joining by upset bulging is a mechanical joining method where axial load is applied to a tube to form two revolving bulges, which clamp the parts to be joined and create a force and form fit. It can be used to join tubes with other structures such as sheets, plates, tubes or profiles of the same or different materials. Other processes such as welding are often limited in joining multi-material assemblies or high-strength materials. With joining by upset bulging at room temperature, the main drawback is the possible initiation of damage (cracks) in the inner buckling zone because of high local stresses and strains. In this paper, a method to avoid the formation of cracks is introduced. Before forming the bulge the tube is locally heated by an induction coil. For the construction steel (E235+N) a maximum temperature of 700 °C was used to avoid phase transformation. For the numerical study of the process the mechanical properties of the tube material were examined at different temperatures and strain rates t...

In the present study, the surface conditions of workpieces used for dry-metal forming experiments were analyzed. Specifically, the effectiveness of different cleaning approaches was evaluated using x-ray photoelectron spectroscopy, infrared spectroscopy and wetting experiments. The best cleaning results were obtained using a CO2-based approach. CO2 acts as an effective solvent and as a result of the mechanical impact, it removes material from the surface. In fact, cleaning results were similar to those achieved by plasma cleaning. However, even simple cleaning with a towel and acetone left only a surface film of less than 100 nm. A residual oil film thickness below 100 nm on the work piece appears sufficient to mimic true dry-forming conditions in most cases. In order to determine cleanliness of surfaces used in dry-metal forming, an infrared spectroscopy-based oil film gauge along with a customized extended calibration curve turned out to provide for sufficiently accurate data.

BMD_GV_ml1_ml2.docx. Results BMD and GV. Measured bone mineral content (DEXA) and gray scale values (X-ray) for the regions of interest 1–5 (ROI1 – ROI5) in ml1 and ml2: mean value (M) ± standard deviation (SD), coefficient of variation [CV]. (DOCX 25 kb)

Background Aseptic loosening due to bone remodelling processes after total hip replacement is one common cause for revision surgery. In human medicine, dual-energy X-ray absorptiometry (DEXA) is the gold standard for quantitative evaluation of bone mineral density, whereas in veterinary medicine conventional radiography is used for follow-up studies. Recently, a method has been described using digital X-ray images for quantitative assessment of grey scale values of bone contrast. Therefore, the aim of the present study was to evaluate the correlation of bone mineral density (BMD) measured by DEXA with grey scale values (GV) measured in digital X-ray images (RX50, RX66) ex vivo. Results The measured GV in the chosen X-ray settings showed on average a good correlation (r = 0.61) to the measured BMD with DEXA. Correlation between the two X-ray settings was very good (r = 0.81). For comparisons among regions of interests (ROIs) a difference of 8.2% was found to be statistically significant, whereas in the case of RX50 and RX66 differences of 5.3% and 4.1% were found to be statistically significant. Conclusions Results indicate that measuring absolute changes in bone mineral density might be possible using digital radiography. Not all significant differences between ROIs detectable with DEXA can be displayed in the X-ray images because of the lower sensitivity of the radiographs. However, direct comparison of grey scale values of the periprosthetic femur in one individual patient during the follow-up period, in order to predict bone remodelling processes, should be possible, but with a lesser sensitivity than with DEXA. It is important that the same X-ray settings are chosen for each patient for follow-up studies. Electronic supplementary material The online version of this article (doi:10.1186/s12917-017-1047-y) contains supplementary material, which is available to authorized users.

The increased use of high and ultra-high strength steel and materials with a high adhesion tendency leads to higher demands regarding the wear resistance of forming tools. A promising approach addressing both challenges is to apply MoS2 dry film lubricant coating systems to the tool surface. These coatings reduce friction and the use of drawing oils and can also be used as an abherent. Once these coatings are exhausted, they can be chemically removed and reapplied. However, the tool life of the coatings cannot be predicted properly, due to their inhomogeneous wear behavior which depends on the forming parameters and differs locally. Moreover, there are carryover effects of MoS2-particles to already ablated areas. Given the unpredictability of the wear of dry film lubricant coatings, it is not possible to plan the recoating cycles appropriately and thus, the potential of these coatings for commercial applications is limited. In this research, the wear behavior of MoS2-layers in deep drawing processes was investigated on a test stand with DP800+Z coil material which ensures realistic load conditions at the draw ring radius. Firstly, the wear pattern was determined and locally different contact pressures were recorded and assigned to respective wear areas. Due to bending effects of the sheet material, there are two major areas of wear on the draw ring radius. During wear tests, the wear-dependent coating thickness during wear initiation was determined by using 3D laser scanning microscopy and the friction force was evaluated. © 2017 The Authors. European Research Association for Sheet Metal Working (EFB) German Federation of Industrial Research Associations (AiF) Federal Ministry of Economic Affairs and Energy (BMWi)

Total hip arthroplasty (THA) is a routine procedure for the treatment of advanced hip joint damage. The long-term result of the prosthesis is mainly determined by migration or aseptic loosening caused by bone remodelling. Especially the migration of the artificial hip cup as a consequence of the remodelling process is a major problem. Patient-specific hip cups can be used to counteract this. However, individual hip cups are currently only implanted for the treatment of great deformations or tumours in the hip joint due to the cost-intensive manufacturing. The aim of this project is the development and establishment of a concept for the economical production of patient-individual prosthetic hip cups out of titanium sheets. This process consists of two steps. First, undersized cups of a universal acetabulum geometry are produced. In the second step a true-to-size enlargement of the produced universal cup prothesis is carried out by means of a modified adaptive rubber-die forming process. The development of this process is accompanied by a simulationbased planning of the production process as well as by a realization of a metal forming adapted design method. For the examination of the feasibility of the concept, CT-data of canine pelvis geoemtries are used because of the large number of CT data, which were aviable for the project. Furthermore it is planned, that the first manufactured prototypes will be tested using canine cadaver. In this study the planning of the manufacturing of the standardized titanium sheet metal components is carried out. For this two methods of producing the standardized hip cup were compared. The first method is a hydraulic forming; the second is a normal pressing process with a bunch die and a binder. Pure titanium was introduced in the simulation, which shows the same mechnical properties like the in prosthetics normally used titanium alloy TiAl6V5. The results of the process simulation of both methods showed that the reducing of the blank thickness is a problem of the manufacturing of the prosthesis. Because of that an adaption of the tool geometry was executed and the influence of the increase of the forming temperature at 200 C was examined. These simulations indicated, that the hydraulic forming seems to be a convenient method to produce the prosthetic acetabulum. The first part of the metal forming adapted design method is the deduction of a universal acetabulum geometry, which has to be designed for the production of the standardized component. This deduction shall be realized by means of a superposition of 3D models of pelvis geometries. For this, two different superposition methods were compared and the Best Fit method was determined as the suitable method. By means of the Best fit method a first universal geometry was created.

Bone density measurements using computed tomography (CT) instead of dual-energy X-ray absorptiometry (DEXA) are currently of great interest in human and veterinary medical research as it would be beneficial to use CT scans obtained for other indications also for determining bone density. For Hounsfield units (HU) measured with CT in specific regions of interests (ROIs) in one or several slice/s a correlation with bone mineral density (BMD) measured by DEXA in humans and dogs of between 0.44 and 0.77 is reported in the literature. In the present study, instead certain volumes of interest (VOIs) obtained by CT scan and the corresponding HU to the respective VOIs were compared with the bone mineral density of the corresponding areas measured by DEXA. The aim of the study was to investigate whether this procedure gives more accurate information about bone density of the bones as three-dimensional objects of the respective patient. Correlation between measured HU in the respective VOI and BMD measured with DEXA in the corresponding ROI showed a very good correlation of 0.93. Linear regression with R

Aseptic loosening of the prosthesis is still a problem in artificial joint implants. The ýloosening can be caused by the resorption of the bone surrounding ýthe prosthesis according to stress shielding. A numerical model was developed and validated by means of DEXA-studies in order to ýanalyse the bone remodelling process in the periprosthetic bone. A total loss of about 3.7% of the bone density in the periprosthetic Femur with NANOS is computed. The bone remodelling calculation was validated by means of a DEXA-study with a 3-years-follow-up. The model was further developed in order to be able to calculate and consider the migration of the implants. This method was applied on the ýNANOS-implant with a computed total migration of about 0.43 mm. These calculations showed good results in comparison with a 2-year-follow-up clinical study, whereby a RSA-method was used to determine the stem migration in the bone. In order to ýstudy the mutual influence between the implant migration and the hip contact forces ý, a software is developed by our scientific group to couple a multi body simulation (MBS) of human lower limps with the FEA of the periprosthetic Femur.

The demand for customized products has increased in recent years and will become even more important in the future. This trend is mainly observed for the medical technology sector influenced by the increasing manufacturing of patient-individual prostheses. In particular the manufacturing of customized hip cups is gaining in importance. Over 800,000 total hip replacements are performed worldwide each year. Despite this experience, the migration and loosening of the hip prosthesis especially of the cup due to the bone resorption caused by stress shielding is a current problem. Patient-specific hip cups can be used to counteract this. However, individual hip cups are only implanted for the treatment of great deformations or tumours because of the cost-intensive manufacturing. Within this project the remodelling process is calculated with a conventional prosthesis via finite element method (FEM) coupled with multi-body simulation (MBS). A migration of the cup in the proximal direction can be suggested. Based on these results an innovative and economic concept for the design and production of patient-individual hip cups for primary surgery by means of sheet metal forming is developed. In this two-stage process first standardized titanium sheet metal components are produced. Then a true-size enlargement of these components is executed by a modified adaptive rubber-die forming process. The development is accompanied by an FE simulation-based planning as well as a metal forming adapted design method. In this study the first part of the design method is demonstrated, which contains the deduction of a universal acetabular geometry, necessary for the production of the standardized component. Furthermore, high pressure sheet metal forming (HPF) will be introduced for the manufacturing of standardized components. Therefore an FE-simulation of the process is carried out for the design of the forming tool.

Fragestellung: Das Design des Nanos® Kurzschaftes (Smith & Nephew) wurde anhand einer Durchschnittsgeometrie der lateralen und medialen Kortikalis von 565 Computertomographien von physiologischen proximalen Femura erstellt. Ziel ist eine physiologische Lasteinleitung über eine gute Anpassung[for full text, please go to the a.m. URL], Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2014)

The revision of an hip prosthesis can have diffrent reasons. One frequent cause, especialley after implantation of a conventional cup, is the so called stress-shielding ef- fect which can lead to a migration or loosening. Patient- specific hip cups can be used to counteract this. However, individual hip cups are only implanted for the treatment of great deformations or tumours because of the cost-intensive manufacturing. Within this project a patient-specific hip cup prosthesis has to be developed and manufactured. Be- sides the numerical design by means of a coupling between multi-body simulation (MBS) and finite element method (FEM), an inovative concept for the production of patient- individual hip prosthesis out of titanium sheets is introduced in this study. Patient-individual hip cups, bone remodelling, reverse en- gineering, process planning, sheet metal forming

For further development of better bone-preserving implants in total hip arthroplasty (THA), we need to look back and analyse established and clinically approved implants to find out what made them successful. Finite element analysis can help do this by simulating periprosthetic bone remodelling under different conditions. Our aim was thus to establish a numerical model of the cementless straight stem for which good long-term results have been obtained.We performed a numeric simulation of a cementless straight stem, which has been successfully used in its unaltered form since 1986/1987. We have 20 years of experience with this THA system and implanted it 555 times in 2012. We performed qualitative and quantitative validation using bone density data derived from a prospective dual-energy X-ray absorptiometry (DEXA) investigation.Bone mass loss converged to 9.25% for the entire femur. No change in bone density was calculated distal to the tip of the prosthesis. Bone mass decreased by 46.2% around the proximal half of the implant and by 7.6% in the diaphysis. The numeric model was in excellent agreement with DEXA data except for the calcar region, where deviation was 67.7%.The higher deviation in the calcar region is possibly a sign of the complex interactions between the titanium coating on the stem and the surrounding bone. We developed a validated numeric model to simulate bone remodelling for different stem-design modifications. We recommend that new THA implants undergo critical numeric simulation before clinical application.

Bone remodelling around a femoral prosthesis is one of the main reasons of aseptic loosening of the implant’s stem. The difference in stiffness between the bone tissue and the prosthesis leads to unload the periprosthetic bone and thus to decrease the bone mineral density (BMD), which is known as stress shielding. This paper represents a comparison between measured changes in (BMD) in a periprosthetic Femur with a cementless Bicontact stem by prospective dualenergy X-ray absorptiometry study (DEXA)and calculated changes of the (BMD) using a finite element method (FEM). As a result, it is determined that the total deviation between the two investigations is about 18%. DFG