Using finite element analysis we have studied the pelvic bony socket and compared it with radiolo... more Using finite element analysis we have studied the pelvic bony socket and compared it with radiological imaging using threaded acetabular cups of three different shapes (parabolic, conical, hemispherical). The twodimensional model depicted a planar section through a left pelvic hemisphere. In all three cups the stress in the bony socket increased from lateral towards medial. Compressive stress was found on the superior and inferior parts of the cup, but mainly on the superior aspect, seen radiologically as new trabecular bone formation. The maximum compressive stresses were seen in the cranial curvature of the conical cup, with less in the parabolic form and least in the hemispheric form. The tensile stress at the bottom of the socket increased from the hemispheric to the conical shape. Radiological rarefaction gave an indication of lower stress. There was lower compressive stress between the teeth of the threads. This FE model uses computer simulation to predict bony changes with different designs of implant. The ability to simulate biological conditions is a valuable addition to the testing of mechanical strength. Résumé Par éléments finis nous avons étudié le cotyle osseux et l'avons comparé avec les images radiologiques faites avec des cupules vissées de trois formes différentes (parabolique, conique, hémisphérique). Le modèle à deux dimensions a représenté une section plane à travers une hémisphére pelvienne gauche. Pour les trois cupules la contrainte dans l'os augmente de dehors en dedans réalisant un toit osseux en pince. La contrainte de compression existe sur les parties supérieure et inférieure de la cupule, mais d'une manière prédominante sur le côté supérieur, radiologiquement représentée par une nouvelle formation osseuse trabeculaire. Les contraintes de compression maximales étaient présentes dans la courbure polaire crâniale des cupules coniques, avec une tendance décroissante de la forme parabolique à la forme hémisphérique. Des contraintes en tension ont été démontrées au fond du cotyle osseux, en augmentant de la cupule hémisphérique à la cupule conique. La raréfaction osseuse radiologiquement visible a représenté la contrainte calculée et moindre de contrainte de compression entre les filets. Ce modèle utilise la simulation informatique pour prédire les changements de l'os selon les différents dessins des implants. La possibilité de simuler des conditions biologiques complète utilement les essais de résistance mécanique.
analysis INTRODUCTION: Ruptures of the anterior and posterior cruciate knee ligament (ACL and PCL... more analysis INTRODUCTION: Ruptures of the anterior and posterior cruciate knee ligament (ACL and PCL), alone or combined, are among the most frequent joint injuries, especially in sports. The long-term unsatisfactory results and lack of systematic evaluation of surgical reconstructions have led us to make an evaluation on cadaver knees.
Acute mechanical failure of prosthetic heart valves is rare, but associated with high mortality w... more Acute mechanical failure of prosthetic heart valves is rare, but associated with high mortality when occurring. For convexo-concave Björk-Shiley prostheses only fractures of the outlet strut are reported. We present a case of lethal mechanical complication 5 years after implantation. By additional metallurgic analysis we were able to identify a sequential course of the outlet strut fracture. This could lead to new approaches for early detection of this complication.
The capsular and ligamentous structures as control system of a healthy knee-joint supported by th... more The capsular and ligamentous structures as control system of a healthy knee-joint supported by the muscular system are responsible for the rolling and gliding motion of the femoral condyles on the tibial plateau. Both the condyles and the tibial plateau have individually developed but to each other adjusted shapes and fine structures thereby. These structures consist of hyaline cartilage at their three-dimensional surfaces and of closely packed fibrils (lamina splendens) as the final gliding zone for tensile load. The orientation of the collagenous fibres can be made visible by split lines. The chondral surfaces are indirectly in contact to each other and orthogonally stressed at the particular point of contact. The indirect contact of the cartilaginous surfaces happens under interposition of the menisci. The meniscus serves to reduce and equalize the surface pressure by its own projected surface on the one hand and by maintaining of a hydraulic pressure of the synovial fluid on the...
H. Ef fen ber ger 1 • M. Im hof 2 • U. Wit zel 3 • S. Re hart 4 1 Gries kir chen, Ös ter reich • ... more H. Ef fen ber ger 1 • M. Im hof 2 • U. Wit zel 3 • S. Re hart 4 1 Gries kir chen, Ös ter reich • 2 Rot kreuz, Schweiz 3 For schungs grup pe für Bio me cha nik, In sti tut für Kon struk ti ons tech nik, Fa kul tät für Ma schi nen bau, Ruhr-Uni ver si tät, Bo chum 4 Or tho pä di sche Uni ver si täts kli nik und Po li kli nik Fried richs heim, Frank furt am Main Ze ment freie Hüft schäf te Ak tu el ler Stand Zu sam men fas sung Die op ti ma le Fi xie rung der ze ment frei en Hüft schäf te ist für eine dau er haf te Sta bi li tät unab ding bar. Da für sind Ver an ke rung, Sta bi li sa to ren, Ma te ri al und Ober flä che von ent scheiden der Be deu tung. Hin sicht lich der Pri mär sta bi li tät muss große Ro ta ti ons-, Axi al-und Ra di al sta bi li tät ge ge ben sein. Sta bi li sa to ren op ti mie ren die Sta bi li tät. CCD-Win kel und Hal sach sen län ge be stim men den Off set, die Bein län gen ver än de rung so wie die Lage des Ku gel kopf zen trums. Der Hüft stiel (Ver an ke rungs teil der Pro the se) hat die Auf ga be der Pro the sen fi xa ti on und der Ge lenk kraf tein lei tung in den Kno chen. Er wird epi phy sär (Femur kopf durch Scha len-bzw. Kap pen pro the sen um fasst), me ta phy sär (s. me ta dia phy sär, zu sätz lich Druck schei ben pro the se), me ta dia phy sär (ge ra de und ana to mi sche Pro the sen in Mo no block form mit un ter schied li cher Län ge, mo du la re und Cu stom-made-Pro thesen) und dia phy sär (mo du la re Sys te me) ver an kert. Als Ma te ri al für die ze ment frei en Hüftschäf te ha ben sich Ti t an schmie de le gie run gen durch ge setzt. Die Ober flä chen sind vor wiegend ko rund ge strahlt oder plas ma spray be schich tet. Me ta phy sär bzw. me ta dia phy sär veran ker te Schäf te er rei chen nach 15 Jah ren Über le bens ra ten von 95-98. Dia phy sär ver anker te Im plan ta te ha ben im mit tel fris ti gen Ver lauf Über le bens ra ten von 92-99. Schlüs sel wör ter Hüf ten do pro the tik • Ze ment freie Hüft schäf te • Klas si fi ka ti on • Ver an ke rung • Kon struk ti on Ce ment less stems of the hip. Cur rent sta tus Ab stract Op ti mal fix a tion of ce ment less stems is a pre con di tion for long-last ing sta bil i ty. Thus, anchor age, sta bi liz ers, ma te ri al and sur face are of es sen tial im por tance. To achieve pri mary sta bil i ty, good ro ta tion al, tilt ing and ax i al sta bil i ty is nec es sary. Sta bi liz ers such as fins and ribs op ti mize sta bil i ty. The CCD-an gle and length of neck-axis de ter mine the off set (lat er al i ty), leg-length and cen ter of ro ta tion. The stem, is re spon si ble for the fix a tion of the pros the sis and for trans mit ting forces to the bone. The types of fix a tion are epiph y se al (the fem o ral head is cov ered by a cup pros the sis), meta phy seal and meta-di a phy se al (with straight or anatom i cal ly shaped mono block-pros the ses of dif fer ent lengths, mod u lar and cus tom-made pros the ses) and di a phy se al (us ing pre dom i nant ly mod u lar sys tems). Ti ta nium al loys are the pre dom i nate ma te ri al for ce ment less stems. The sur faces are gen er al ly co run dum-blast ed or plas ma sprayed. For meta phy seal and meta-di a phy se al stems, survival rates from 95 to 98 have been reached af ter 15 years. Di a phy se al-fixed stems have mid-term sur vival-rates of 92-99.
Advanced Microsystems for Automotive Applications Yearbook 2002, 2002
This paper presents a new measurement concept for brake-pedal force in brake-by-wire systems by m... more This paper presents a new measurement concept for brake-pedal force in brake-by-wire systems by means of micromechanical pressure sensors. Differing from the conventional approach, the applied force is not measured indirectly via the pedal travel or angle, but directly at the point of application itself. First, the “driver - brake pedal” interface is analyzed so that the results can then
Sowa et al. haben insgesamt 24 Kreuzbandprothesen aus Poly~ithylenterephthalat unterschiedlicher ... more Sowa et al. haben insgesamt 24 Kreuzbandprothesen aus Poly~ithylenterephthalat unterschiedlicher Konstruktion, die wegen Ruptur oder Lockerung nach einer Verweildauer bis zu 40 Monaten explantiert werden muf3ten, histologisch untersucht.
Archives of orthopaedic and traumatic surgery. Archiv für orthopädische und Unfall-Chirurgie, 1981
The stability of external distance osteosynthesis for complete tibia and femur defects rests sole... more The stability of external distance osteosynthesis for complete tibia and femur defects rests solely on the rigidity of the external support. The rigidity of the external support is an function of the mechanical data of its individual elements, of the hold between the bone and the other system, as well as of the individually optimized construction form. The response of an osseous contact area which is not resistant to compression when external osteosynthesis is applied is mechanically similar to the response to distance osteosynthesis in the presence of a defect. The basic application rules for distance osteosynthesis of the lower limbs are given. The symmetric frame fixator applied in a three-dimensional arrangement is indicated for tibia defects. External distance osteosynthesis of femur defects can only be recommended when plate osteosynthesis alone or plate osteosynthesis in conjunction with a bracket fixator are out of the question. The various application forms for external ost...
The anatomy of the hip must be taken into account in order to ensure primary stability of cementl... more The anatomy of the hip must be taken into account in order to ensure primary stability of cementless acetabular implants. In this study we analyzed the shapes of osteoarthritic acetabula and compared these to normal non-degenerative acetabula and to pressfit implants. We measured 92 acetabula with osteoarthritic deformations and 35 non-degenerative acetabula. Bone tissue samples from 50 osteoarthritic acetabula were microradiographically analyzed. Furthermore, the size of the entrance plane of 37 pressfit cups was determined. The craniocaudal and ventrodorsal diameters of osteoarthritic acetabula correlate strongly ( r=0.87). In craniocaudal direction, the acetabular diameter correlates significantly to both the radius of the lunate surface ( r=0.42) and the acetabular base ( r=0.54). Osteoarthritic acetabula have a deeper shape as degeneration increases and the entrance plane becomes significantly more circular ( p<0.05). When comparing osteoarthritic and non-arthrotic acetabula...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca, 2003
Over a period of three generations, threaded cups were developed and have become viable contempor... more Over a period of three generations, threaded cups were developed and have become viable contemporary cementless hip implants. A few implants already have a high success rate over the mid and long term. Aim of this study was to evaluate contemporary threaded cups. 30 of the second and third generation cups were systematically analyzed and measured using by a no-touch light section technique. Construction of inner form was determined with half sections. Approximately 50% have a conical shape, although there is a trend towards a more anatomical shape. 83% of the cups have a height up to 23% smaller than the radius. Only conical threaded cups have a relatively thin and constant wall thickness (1 mm-1.8 mm). Corundum blasted pure titanium, titanium alloys or HA coated implants are considered the standard materials. The insert is pre-assembled in two implants, otherwise the cups have modular inserts. Total ceramic inserts are found in four cups. Ceramic inserts with a sandwich constructio...
To enable a comparison of different pressfit acetabular cups objective criteria are essential. Th... more To enable a comparison of different pressfit acetabular cups objective criteria are essential. The aim of this study is to describe the design features of this type of cup and to analyse currently available cups. 30 implants were systematically measured and analysed. The mean surface roughness (Ra) was determined and configurations established with the light section technique. For further evaluation the cups were transversely sectioned. The cups are made of pure titanium, titanium alloy or polyethylene coated with titanium. Five implants take the form of monoblocks. The configuration is predominately (n = 25) flattened spherical. The size of eight cups corresponds to the outer diameter, 19 cups have a larger outer diameter (overdimensioning), 3 cups have a smaller outer diameter (underdimensioning). The magnitude of overdimensioning is, on average, 1.9%. 9 cups are provided with plugs, hollow cylinders, fins or rings as outer stabilizers. Surface roughness achieved with corundum bla...
Anthropologischer Anzeiger; Bericht über die biologisch-anthropologische Literatur, 2002
Using the FEM-program ANSYS 5.4, we have shaped a model of the human skull in which the flow of f... more Using the FEM-program ANSYS 5.4, we have shaped a model of the human skull in which the flow of forces and the relative location and magnitudes of stresses are investigated. Forces are applied from below through the tooth row of the upper jaw. An ample volume is provided for the transmission of these bite forces upward to the roof of the braincase, where bearings counteract the forces from below. Within this volume, no other morphological features are considered than two cone-shaped orbits and a nasal channel which has a rounded, triangular cross section, extending upward between the orbits. Under loads (= bite forces) acting simultaneously in the directions and relative sizes of realistic bite- and chewing forces, there occurred stress concentrations inside the model which resemble closely the morphological characteristics of the human skull. The most remarkable pathways of stresses correspond to Toldt's and Benninghoff's nasal, zygomatic and pterygoid pillars. Aside from t...
Anthropologischer Anzeiger; Bericht über die biologisch-anthropologische Literatur, 2002
The earliest attempts to understand the "pneumatized spaces" in the skulls of primates ... more The earliest attempts to understand the "pneumatized spaces" in the skulls of primates in general were focussed on the hollow spaces and the epithelium which covers their surfaces. More recent approaches consider the sinuses as a means to optimise skull architecture. Still, many attempts to get hold of the meaning of the intriguing pneumatized spaces circle around the air filled volumes they enclose. Here, we would like to reverse the approach and focus our biomechanic interpretation on the walls surrounding the big, empty, or at least not mechanically resistant spaces, and their mechanical properties. As a working hypothesis, we consider not only the walls of the more or less closed cavities, or sinuses, but also the braincase, the orbits, and the nasal channel as thin-walled shells of which we know that they can carry surprisingly large loads with a minimum of material. Details of the wall's profiles fit with this approach. From the same viewpoint, the bubble-like, a...
Using finite element analysis we have studied the pelvic bony socket and compared it with radiolo... more Using finite element analysis we have studied the pelvic bony socket and compared it with radiological imaging using threaded acetabular cups of three different shapes (parabolic, conical, hemispherical). The twodimensional model depicted a planar section through a left pelvic hemisphere. In all three cups the stress in the bony socket increased from lateral towards medial. Compressive stress was found on the superior and inferior parts of the cup, but mainly on the superior aspect, seen radiologically as new trabecular bone formation. The maximum compressive stresses were seen in the cranial curvature of the conical cup, with less in the parabolic form and least in the hemispheric form. The tensile stress at the bottom of the socket increased from the hemispheric to the conical shape. Radiological rarefaction gave an indication of lower stress. There was lower compressive stress between the teeth of the threads. This FE model uses computer simulation to predict bony changes with different designs of implant. The ability to simulate biological conditions is a valuable addition to the testing of mechanical strength. Résumé Par éléments finis nous avons étudié le cotyle osseux et l'avons comparé avec les images radiologiques faites avec des cupules vissées de trois formes différentes (parabolique, conique, hémisphérique). Le modèle à deux dimensions a représenté une section plane à travers une hémisphére pelvienne gauche. Pour les trois cupules la contrainte dans l'os augmente de dehors en dedans réalisant un toit osseux en pince. La contrainte de compression existe sur les parties supérieure et inférieure de la cupule, mais d'une manière prédominante sur le côté supérieur, radiologiquement représentée par une nouvelle formation osseuse trabeculaire. Les contraintes de compression maximales étaient présentes dans la courbure polaire crâniale des cupules coniques, avec une tendance décroissante de la forme parabolique à la forme hémisphérique. Des contraintes en tension ont été démontrées au fond du cotyle osseux, en augmentant de la cupule hémisphérique à la cupule conique. La raréfaction osseuse radiologiquement visible a représenté la contrainte calculée et moindre de contrainte de compression entre les filets. Ce modèle utilise la simulation informatique pour prédire les changements de l'os selon les différents dessins des implants. La possibilité de simuler des conditions biologiques complète utilement les essais de résistance mécanique.
analysis INTRODUCTION: Ruptures of the anterior and posterior cruciate knee ligament (ACL and PCL... more analysis INTRODUCTION: Ruptures of the anterior and posterior cruciate knee ligament (ACL and PCL), alone or combined, are among the most frequent joint injuries, especially in sports. The long-term unsatisfactory results and lack of systematic evaluation of surgical reconstructions have led us to make an evaluation on cadaver knees.
Acute mechanical failure of prosthetic heart valves is rare, but associated with high mortality w... more Acute mechanical failure of prosthetic heart valves is rare, but associated with high mortality when occurring. For convexo-concave Björk-Shiley prostheses only fractures of the outlet strut are reported. We present a case of lethal mechanical complication 5 years after implantation. By additional metallurgic analysis we were able to identify a sequential course of the outlet strut fracture. This could lead to new approaches for early detection of this complication.
The capsular and ligamentous structures as control system of a healthy knee-joint supported by th... more The capsular and ligamentous structures as control system of a healthy knee-joint supported by the muscular system are responsible for the rolling and gliding motion of the femoral condyles on the tibial plateau. Both the condyles and the tibial plateau have individually developed but to each other adjusted shapes and fine structures thereby. These structures consist of hyaline cartilage at their three-dimensional surfaces and of closely packed fibrils (lamina splendens) as the final gliding zone for tensile load. The orientation of the collagenous fibres can be made visible by split lines. The chondral surfaces are indirectly in contact to each other and orthogonally stressed at the particular point of contact. The indirect contact of the cartilaginous surfaces happens under interposition of the menisci. The meniscus serves to reduce and equalize the surface pressure by its own projected surface on the one hand and by maintaining of a hydraulic pressure of the synovial fluid on the...
H. Ef fen ber ger 1 • M. Im hof 2 • U. Wit zel 3 • S. Re hart 4 1 Gries kir chen, Ös ter reich • ... more H. Ef fen ber ger 1 • M. Im hof 2 • U. Wit zel 3 • S. Re hart 4 1 Gries kir chen, Ös ter reich • 2 Rot kreuz, Schweiz 3 For schungs grup pe für Bio me cha nik, In sti tut für Kon struk ti ons tech nik, Fa kul tät für Ma schi nen bau, Ruhr-Uni ver si tät, Bo chum 4 Or tho pä di sche Uni ver si täts kli nik und Po li kli nik Fried richs heim, Frank furt am Main Ze ment freie Hüft schäf te Ak tu el ler Stand Zu sam men fas sung Die op ti ma le Fi xie rung der ze ment frei en Hüft schäf te ist für eine dau er haf te Sta bi li tät unab ding bar. Da für sind Ver an ke rung, Sta bi li sa to ren, Ma te ri al und Ober flä che von ent scheiden der Be deu tung. Hin sicht lich der Pri mär sta bi li tät muss große Ro ta ti ons-, Axi al-und Ra di al sta bi li tät ge ge ben sein. Sta bi li sa to ren op ti mie ren die Sta bi li tät. CCD-Win kel und Hal sach sen län ge be stim men den Off set, die Bein län gen ver än de rung so wie die Lage des Ku gel kopf zen trums. Der Hüft stiel (Ver an ke rungs teil der Pro the se) hat die Auf ga be der Pro the sen fi xa ti on und der Ge lenk kraf tein lei tung in den Kno chen. Er wird epi phy sär (Femur kopf durch Scha len-bzw. Kap pen pro the sen um fasst), me ta phy sär (s. me ta dia phy sär, zu sätz lich Druck schei ben pro the se), me ta dia phy sär (ge ra de und ana to mi sche Pro the sen in Mo no block form mit un ter schied li cher Län ge, mo du la re und Cu stom-made-Pro thesen) und dia phy sär (mo du la re Sys te me) ver an kert. Als Ma te ri al für die ze ment frei en Hüftschäf te ha ben sich Ti t an schmie de le gie run gen durch ge setzt. Die Ober flä chen sind vor wiegend ko rund ge strahlt oder plas ma spray be schich tet. Me ta phy sär bzw. me ta dia phy sär veran ker te Schäf te er rei chen nach 15 Jah ren Über le bens ra ten von 95-98. Dia phy sär ver anker te Im plan ta te ha ben im mit tel fris ti gen Ver lauf Über le bens ra ten von 92-99. Schlüs sel wör ter Hüf ten do pro the tik • Ze ment freie Hüft schäf te • Klas si fi ka ti on • Ver an ke rung • Kon struk ti on Ce ment less stems of the hip. Cur rent sta tus Ab stract Op ti mal fix a tion of ce ment less stems is a pre con di tion for long-last ing sta bil i ty. Thus, anchor age, sta bi liz ers, ma te ri al and sur face are of es sen tial im por tance. To achieve pri mary sta bil i ty, good ro ta tion al, tilt ing and ax i al sta bil i ty is nec es sary. Sta bi liz ers such as fins and ribs op ti mize sta bil i ty. The CCD-an gle and length of neck-axis de ter mine the off set (lat er al i ty), leg-length and cen ter of ro ta tion. The stem, is re spon si ble for the fix a tion of the pros the sis and for trans mit ting forces to the bone. The types of fix a tion are epiph y se al (the fem o ral head is cov ered by a cup pros the sis), meta phy seal and meta-di a phy se al (with straight or anatom i cal ly shaped mono block-pros the ses of dif fer ent lengths, mod u lar and cus tom-made pros the ses) and di a phy se al (us ing pre dom i nant ly mod u lar sys tems). Ti ta nium al loys are the pre dom i nate ma te ri al for ce ment less stems. The sur faces are gen er al ly co run dum-blast ed or plas ma sprayed. For meta phy seal and meta-di a phy se al stems, survival rates from 95 to 98 have been reached af ter 15 years. Di a phy se al-fixed stems have mid-term sur vival-rates of 92-99.
Advanced Microsystems for Automotive Applications Yearbook 2002, 2002
This paper presents a new measurement concept for brake-pedal force in brake-by-wire systems by m... more This paper presents a new measurement concept for brake-pedal force in brake-by-wire systems by means of micromechanical pressure sensors. Differing from the conventional approach, the applied force is not measured indirectly via the pedal travel or angle, but directly at the point of application itself. First, the “driver - brake pedal” interface is analyzed so that the results can then
Sowa et al. haben insgesamt 24 Kreuzbandprothesen aus Poly~ithylenterephthalat unterschiedlicher ... more Sowa et al. haben insgesamt 24 Kreuzbandprothesen aus Poly~ithylenterephthalat unterschiedlicher Konstruktion, die wegen Ruptur oder Lockerung nach einer Verweildauer bis zu 40 Monaten explantiert werden muf3ten, histologisch untersucht.
Archives of orthopaedic and traumatic surgery. Archiv für orthopädische und Unfall-Chirurgie, 1981
The stability of external distance osteosynthesis for complete tibia and femur defects rests sole... more The stability of external distance osteosynthesis for complete tibia and femur defects rests solely on the rigidity of the external support. The rigidity of the external support is an function of the mechanical data of its individual elements, of the hold between the bone and the other system, as well as of the individually optimized construction form. The response of an osseous contact area which is not resistant to compression when external osteosynthesis is applied is mechanically similar to the response to distance osteosynthesis in the presence of a defect. The basic application rules for distance osteosynthesis of the lower limbs are given. The symmetric frame fixator applied in a three-dimensional arrangement is indicated for tibia defects. External distance osteosynthesis of femur defects can only be recommended when plate osteosynthesis alone or plate osteosynthesis in conjunction with a bracket fixator are out of the question. The various application forms for external ost...
The anatomy of the hip must be taken into account in order to ensure primary stability of cementl... more The anatomy of the hip must be taken into account in order to ensure primary stability of cementless acetabular implants. In this study we analyzed the shapes of osteoarthritic acetabula and compared these to normal non-degenerative acetabula and to pressfit implants. We measured 92 acetabula with osteoarthritic deformations and 35 non-degenerative acetabula. Bone tissue samples from 50 osteoarthritic acetabula were microradiographically analyzed. Furthermore, the size of the entrance plane of 37 pressfit cups was determined. The craniocaudal and ventrodorsal diameters of osteoarthritic acetabula correlate strongly ( r=0.87). In craniocaudal direction, the acetabular diameter correlates significantly to both the radius of the lunate surface ( r=0.42) and the acetabular base ( r=0.54). Osteoarthritic acetabula have a deeper shape as degeneration increases and the entrance plane becomes significantly more circular ( p<0.05). When comparing osteoarthritic and non-arthrotic acetabula...
Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca, 2003
Over a period of three generations, threaded cups were developed and have become viable contempor... more Over a period of three generations, threaded cups were developed and have become viable contemporary cementless hip implants. A few implants already have a high success rate over the mid and long term. Aim of this study was to evaluate contemporary threaded cups. 30 of the second and third generation cups were systematically analyzed and measured using by a no-touch light section technique. Construction of inner form was determined with half sections. Approximately 50% have a conical shape, although there is a trend towards a more anatomical shape. 83% of the cups have a height up to 23% smaller than the radius. Only conical threaded cups have a relatively thin and constant wall thickness (1 mm-1.8 mm). Corundum blasted pure titanium, titanium alloys or HA coated implants are considered the standard materials. The insert is pre-assembled in two implants, otherwise the cups have modular inserts. Total ceramic inserts are found in four cups. Ceramic inserts with a sandwich constructio...
To enable a comparison of different pressfit acetabular cups objective criteria are essential. Th... more To enable a comparison of different pressfit acetabular cups objective criteria are essential. The aim of this study is to describe the design features of this type of cup and to analyse currently available cups. 30 implants were systematically measured and analysed. The mean surface roughness (Ra) was determined and configurations established with the light section technique. For further evaluation the cups were transversely sectioned. The cups are made of pure titanium, titanium alloy or polyethylene coated with titanium. Five implants take the form of monoblocks. The configuration is predominately (n = 25) flattened spherical. The size of eight cups corresponds to the outer diameter, 19 cups have a larger outer diameter (overdimensioning), 3 cups have a smaller outer diameter (underdimensioning). The magnitude of overdimensioning is, on average, 1.9%. 9 cups are provided with plugs, hollow cylinders, fins or rings as outer stabilizers. Surface roughness achieved with corundum bla...
Anthropologischer Anzeiger; Bericht über die biologisch-anthropologische Literatur, 2002
Using the FEM-program ANSYS 5.4, we have shaped a model of the human skull in which the flow of f... more Using the FEM-program ANSYS 5.4, we have shaped a model of the human skull in which the flow of forces and the relative location and magnitudes of stresses are investigated. Forces are applied from below through the tooth row of the upper jaw. An ample volume is provided for the transmission of these bite forces upward to the roof of the braincase, where bearings counteract the forces from below. Within this volume, no other morphological features are considered than two cone-shaped orbits and a nasal channel which has a rounded, triangular cross section, extending upward between the orbits. Under loads (= bite forces) acting simultaneously in the directions and relative sizes of realistic bite- and chewing forces, there occurred stress concentrations inside the model which resemble closely the morphological characteristics of the human skull. The most remarkable pathways of stresses correspond to Toldt's and Benninghoff's nasal, zygomatic and pterygoid pillars. Aside from t...
Anthropologischer Anzeiger; Bericht über die biologisch-anthropologische Literatur, 2002
The earliest attempts to understand the "pneumatized spaces" in the skulls of primates ... more The earliest attempts to understand the "pneumatized spaces" in the skulls of primates in general were focussed on the hollow spaces and the epithelium which covers their surfaces. More recent approaches consider the sinuses as a means to optimise skull architecture. Still, many attempts to get hold of the meaning of the intriguing pneumatized spaces circle around the air filled volumes they enclose. Here, we would like to reverse the approach and focus our biomechanic interpretation on the walls surrounding the big, empty, or at least not mechanically resistant spaces, and their mechanical properties. As a working hypothesis, we consider not only the walls of the more or less closed cavities, or sinuses, but also the braincase, the orbits, and the nasal channel as thin-walled shells of which we know that they can carry surprisingly large loads with a minimum of material. Details of the wall's profiles fit with this approach. From the same viewpoint, the bubble-like, a...
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