WO1996015736A1 - Anisotropically elastic hip joint endoprosthesis - Google Patents
Anisotropically elastic hip joint endoprosthesis Download PDFInfo
- Publication number
- WO1996015736A1 WO1996015736A1 PCT/DE1995/001630 DE9501630W WO9615736A1 WO 1996015736 A1 WO1996015736 A1 WO 1996015736A1 DE 9501630 W DE9501630 W DE 9501630W WO 9615736 A1 WO9615736 A1 WO 9615736A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- hip joint
- elastic
- core
- shaft
- joint endoprosthesis
- Prior art date
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- A61F2250/00—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof
- A61F2250/0014—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof having different values of a given property or geometrical feature, e.g. mechanical property or material property, at different locations within the same prosthesis
- A61F2250/0026—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof having different values of a given property or geometrical feature, e.g. mechanical property or material property, at different locations within the same prosthesis differing in surface structures
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2250/00—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof
- A61F2250/0014—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof having different values of a given property or geometrical feature, e.g. mechanical property or material property, at different locations within the same prosthesis
- A61F2250/0036—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof having different values of a given property or geometrical feature, e.g. mechanical property or material property, at different locations within the same prosthesis differing in thickness
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2310/00—Prostheses classified in A61F2/28 or A61F2/30 - A61F2/44 being constructed from or coated with a particular material
- A61F2310/00005—The prosthesis being constructed from a particular material
- A61F2310/00011—Metals or alloys
- A61F2310/00023—Titanium or titanium-based alloys, e.g. Ti-Ni alloys
Definitions
- the invention relates to a special hip joint endoprosthesis for use in human medicine for the optional implantation with or without cement.
- Such hip joint endoprostheses are known in various embodiments. They usually consist of a shaft for insertion into the upper medullary cavity of the thigh (femur), an adjoining neck and a spherical joint head, with the joint head being attachable in modern designs via a standardized cone. There are also known designs which have a collar between the shaft and neck in order to realize a support on the resection surface of the femur.
- the known shafts of such hip joint endoprostheses are in their dimensions and shape the anatomical conditions of the upper medullary cavity of the femur more or less roughly approximated and usually consist of solid metal. It is customary to structure the surface of such shafts in order to achieve the most stable anchoring in the bony bearing.
- finer structures have a favorable influence on the primary fixation, while finer structures, for example by sandblasting or in the form of a coating made of porous metal, promote a so-called injection of bone substance the Improve secondary fixation of the implant.
- a hip joint shaft belonging to the second group mentioned is known, for example, from German patent application OS-DE 3737372 A1. It essentially consists of a helical spring-like element made of metal, which corresponds in its outer contour to the shape of known shafts. The shaft derives its elasticity from the geometry of the coil spring-like element, this elasticity due to the material, the material thickness, the pitch of the winding, etc. is adjustable.
- such a shaft has quasi-isotropic elastic properties, which are expressed both in terms of elastic flexibility and elastic extensibility, or, depending on the winding distance, also elastic compressibility. In fact, such behavior is only partially congruent with that of the bony femur.
- the hip joint shaft according to the above-mentioned patent application is moreover designed too elastic in the area of the main force introduction below the collar and at the start of the winding there is extremely prone to breakage due to the alternating bending load occurring during use. In the case of loosening, it should also be extremely difficult to remove such a resilient shaft from the medullary cavity.
- hip joint endoprostheses there was therefore the task of creating an implant with a characteristic that was better adapted to the femur in terms of its elasticity.
- the concept should also reliably rule out a risk of breakage of the artificial shaft and enable problem-free explanting in the event of loosening.
- the basic idea according to the invention is now to equip such a hip joint endoprosthesis, deviating from previous designs, with an anisotropically elastic characteristic which approximates that of the femur and thereby takes into account the alternating relationships between the shaft and the femur with regard to the transmitted forces and bending moments.
- the practical implementation of the invention concentrates on realizing the desired characteristic by means of a functional breakdown of the shaft. According to this, at least the lower area of the shaft consists of a slender core with an axial extension, which is firmly connected with a special elastic covering.
- the slender core is designed to take on the function of an elastic element with pronounced anisotropy, which is characterized by a very high degree of rigidity in the axial and radial directions and at the same time good elastic flexibility.
- the special elastic covering of the core is optimized in terms of its mechanical properties for greater axial elasticity with radial rigidity.
- the overall anisotropically elastic characteristic of the hip joint endoprosthesis according to the invention results from the summation of the properties of both functional elements.
- Fig.l shows a hip joint shaft according to the invention, in which the functional breakdown to achieve the desired anisotropic elasticity is realized by means of special processing.
- FIG. 1 The example of a shaft according to the invention presented in drawing FIG. 1 is a monoblock design which can be produced from a metallic blank, for example from titanium alloy.
- the upper end is provided with a collar 3. This merges into a cone-shaped neck 1 with a rounding.
- the neck in turn opens into a cone 2, onto which the conventional ball heads can be attached.
- the entire area of the implantable length has been cut open in order to better illustrate the structural design.
- the shaft has a more or less central core 8, which increases in cross-section at the top and smoothly merges into the solid body 9, or tapers increasingly towards the bottom.
- This geometry is matched to the mechanical load on the shaft and the load-bearing capacity of the material used and is designed so that the core is extraordinarily rigid on the one hand, but on the other hand is increasingly flexible towards the bottom by being there over a very long length / Diameter ratio.
- a sheath 10, 11 with special elastic properties is superimposed on the core 8 of the shaft.
- this has the function of a placeholder by realizing the desired outer shape of the shaft with its outer surface. It is intended to transmit forces between the core 8 and femur. On the other hand, it must not impair the elastic flexibility of the core too much and must therefore have a high degree of axial elasticity. In addition, it must be sufficiently strong and unbreakable.
- these properties were achieved in that a helical groove was machined from the solid shaft with the desired outer contour. This begins at 4 below the collar 3 and continues to 5, or via 6 to its outlet 7. The beginning of the groove can be moved further up, for example to structure the body by means of the turning ice.
- the depth of this groove, as well as its width and slope, has an impact on the rigidity of the overall system and the anisotropy of its elasticity. It is designed in such a way that a sufficiently large cross section of the core is retained and at the same time an adapted increase in this cross section results from the shaft end to the collar.
- the dimensions selected in the drawing figure have more symbolic meaning because there is a certain constructive range for the actual definition.
- the spiral groove with multiple threads, to change its slope smoothly, or to plunge eccentrically in order to achieve a certain elasticity characteristic of the shaft.
- the hip joint endoprosthesis according to the invention is primarily intended for cementless implantation.
- the bony bearing in the medullary canal is prepared in the usual way by means of suitable rasps and the shaft is driven in with slight pretension until the collar is put on.
- Collarless variants can be introduced in a similar manner.
- a piping or piping-like flexible hose made of a physiologically harmless material, e.g. made of PEEK (polyether ether ketone) or the like to prevent the bone cement from penetrating.
- the inventive basic idea of an axially stiff, but over a defined extension of relatively flexurally elastic shaft, consisting of the corresponding functional construction elements core and casing can be put into practice in a variety of configurations and is not limited to the above-mentioned embodiment.
- the desired anisotropically elastic characteristic is achieved by modifying the turning tion, for example adjustment of the pitch, number of gears, depth, width and penetration angle of the groove, or the fluid change in the various parameters can be set within a wide range and realized using known manufacturing processes at low costs.
- the hip joint endoprosthesis made available with the invention promises a substantially improved adaptation to the elastic characteristics of the bone system involved and thus good prerequisites for long-term and symptom-free usability of such an implant.
Landscapes
- Health & Medical Sciences (AREA)
- Orthopedic Medicine & Surgery (AREA)
- Cardiology (AREA)
- Oral & Maxillofacial Surgery (AREA)
- Transplantation (AREA)
- Engineering & Computer Science (AREA)
- Biomedical Technology (AREA)
- Heart & Thoracic Surgery (AREA)
- Vascular Medicine (AREA)
- Life Sciences & Earth Sciences (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Prostheses (AREA)
Abstract
The invention relates to a special hip joint endoprosthesis for artificial joint replacement in the human body. Prior art hip joint endoprostheses are either rigid or isotropically elastic to a greater or lesser extent. Their elastic behaviour does not correspond to that of the bone system involved. The bone may subsequently be distorted and the implant may loosen. The invention provides an isotropically elastic hip endoprosthesis which is much closer to the behaviour of the upper tigh bone. To obtain the anisotropically elastic prosthesis it is proposed to divide at least the lower section of the shaft of the hip joint endoprosthesis into the two functional regions core (8) and jacket (10, 11), in which the core (8) is relatively elastic in bending while having high axial and radial rigidity and the jacket (10, 11) surrounding the core (8) is axially flexible while being radially rigid. The hip joint endoprosthesis of the invention is expected to have a substantially longer useful life and to be less painful.
Description
Anisotrop elastische Hüftgelenk-EndoprotheseAnisotropic elastic hip joint endoprosthesis
Die Erfindung betrifft eine spezielle Hüftgelenk-Endoprothese zur Anwendung in der Humanmedizin für die wahlweise Implantation mit oder ohne Zement.The invention relates to a special hip joint endoprosthesis for use in human medicine for the optional implantation with or without cement.
Derartige Hüftgelenk-Endoprothesen sind in verschiedenen Ausfüh¬ rungsformen bekannt. Sie bestehen üblicherweise aus einem Schaft zur Einbringung in die obere Markhöhle des Oberschenkelkochens (Femur) , einem sich anschließenden Hals und einem kugelförmigen Gelenkkopf, wobei der Gelenkkopf bei modernen Konstruktionen über einen genormten Konus aufsteckbar ist. Es sind auch Ausführungen bekannt, welche zwischen Schaft und Hals einen Kragen besitzen, um eine Auflage auf der Resektionsfläche des Femurs zu realisie¬ ren. Die bekannten Schäfte solcher Hüftgelenk-Endoprothesen sind in ihren Abmessungen und ihrer Formgebung den anatomischen Gege¬ benheiten der oberen Markhöhle des Femurs mehr oder weniger grob angenähert und bestehen in der Regel aus massivem Metall. Es ist üblich, die Oberfläche derartiger Schäfte zu strukturieren, um eine möglichst stabile Verankerung im knöchernen Lager zu erzie¬ len. Dabei geht man davon aus, daß gröbere Strukturierungen vor allem einen günstigen Einfluß auf die Primärfixation haben, wäh¬ rend feinere Strukturierungen, z.B. durch eine Sandstrahlbehand¬ lung oder in Form einer Beschichtung aus porösem Metall, ein so¬ genanntes Einspriessen von Knochensubstanz begünstigen, um die
Sekundärfixation des Implantats zu verbessern.Such hip joint endoprostheses are known in various embodiments. They usually consist of a shaft for insertion into the upper medullary cavity of the thigh (femur), an adjoining neck and a spherical joint head, with the joint head being attachable in modern designs via a standardized cone. There are also known designs which have a collar between the shaft and neck in order to realize a support on the resection surface of the femur. The known shafts of such hip joint endoprostheses are in their dimensions and shape the anatomical conditions of the upper medullary cavity of the femur more or less roughly approximated and usually consist of solid metal. It is customary to structure the surface of such shafts in order to achieve the most stable anchoring in the bony bearing. It is assumed that coarser structures have a favorable influence on the primary fixation, while finer structures, for example by sandblasting or in the form of a coating made of porous metal, promote a so-called injection of bone substance the Improve secondary fixation of the implant.
Trotz derartiger Vorkehrungen kann jedoch eine dauerhafte Veran¬ kerung solcher Starrschaft-Endoprothesen kaum garantiert werden. Es hat sich nämlich gezeigt, daß vor allem durch das Einbringen des künstlichen Schaftes in den Femur in die elastischen Verhält¬ nisse des beteiligten Knochensystems eingegriffen wird. In der Folge sind daher Umbauvorgänge im Knochen und teilweise auch Lockerungen des Implantats zu beobachten. In diesem Zusammenhang ist von Interesse, daß rein geometrisch betrachtet, der natürli¬ che Kugelkopf des Hüftgelenks beim Menschen genau senkrecht ober¬ halb der Kondyläen des Kniegelenks positioniert ist. Der Femur stellt nun allerdings nicht die kürzeste Verbindungslinie zwi¬ schen diesen beiden Punkten dar. Vielmehr ergibt sich aus dem Verlauf des Oberschenkelhalses vom Kugelkopf weg zum Trochanter ajor hin und weiter nach unten zurück zum Kniegelenk eine aus¬ gelenkte Linie, welche entfernt an einen Bogen erinnert. Diese Formgestalt bewirkt beim Einleiten von vertikaler Last auf den natürlichen Hüftkopf ein geringes Ausfedern des Femurs, weil der Femur zum Teil mit axialen Kräften und zum Teil mit Biegemomenten beansprucht wird. Dieses elastische Verhalten ist in Verbindung mit den Dämpfungseigenschaften des Knochens vorteilhaft, da es bei dynamischer Beanspruchung des Knochenapparats, z.B. beim Lau¬ fen, zu einer Abschwächung der in das Becken geleiteten Lastspit¬ zen führt.Despite such precautions, however, permanent anchoring of such rigid shaft endoprostheses can hardly be guaranteed. It has been shown that, above all, the insertion of the artificial shaft into the femur interferes with the elastic relationships of the bone system involved. As a result, remodeling processes in the bone and in some cases loosening of the implant can be observed. In this context it is of interest that, viewed purely geometrically, the natural spherical head of the hip joint in humans is positioned exactly perpendicularly above the condyles of the knee joint. The femur does not, however, represent the shortest connecting line between these two points. Rather, the course of the femoral neck from the ball head to the trochanter ajor and further down to the knee joint results in a deflected line, which is removed from an arch remind. This shape causes a slight rebound of the femur when vertical load is applied to the natural femoral head, because the femur is partially loaded with axial forces and partially with bending moments. This elastic behavior is advantageous in connection with the damping properties of the bone, since it is subject to dynamic loading of the bone apparatus, e.g. when running, leads to a weakening of the load peaks conducted into the basin.
Die oben genannten Überlegungen waren in der Vergangenheit be¬ reits Grundlage für die Entwicklung von sogenannten iso-elasti- schen Schaft-Implantaten, bzw. auch solchen mit quasi isotrop elastischen Eigenschaften. Ein zur zweiten genannten Gruppe ge¬ hörender Hüftgelenkschaft ist z.B. aus der Deutschen Patentanmel¬ dung OS-DE 3737372 A 1 bekannt. Er besteht im wesentlichen aus einem schraubenfederartigen Element aus Metall, welches in sei¬ ner äußeren Kontur der Formgestalt bekannter Schäfte entspricht. Der Schaft bezieht dabei seine Elastizität aus der Geometrie des schraubenfederartigen Elements, wobei diese Elastizität durch den Werkstoff, die Materialstärke, die Steigung der Wicklung usw.
einstellbar ist. Aufgrund seiner Konstruktion besitzt solch ein Schaft quasi isotrop elastische Eigenschaften, welche sowohl in einer elastischen Biegsamkeit, als auch elastischen Dehnbarkeit, bzw. je nach Wickelabstand auch elastischen Kompressibilität zum Ausdruck kommen. Tatsächlich ist jedoch ein derartiges Verhalten dem des knöchernen Femurs nur teilweise kongruent. Der Hüftge¬ lenkschaft gemäß der oben genannten Patentanmeldung ist darüber hinaus im Bereich der Hauptkrafteinleitung unterhalb des Kragens viel zu elastisch ausgelegt und am dortigen Windungsanfang auf¬ grund der im Gebrauch auftretenden Biegewechselbelastung extrem bruchgefährdet. Es dürfte ferner im Falle von Lockerungen ausge¬ sprochen schwierig sein, einen derartig federnden Schaft aus der Markhöhle zu entfernen.In the past, the above-mentioned considerations were already the basis for the development of so-called iso-elastic shaft implants, or also those with quasi-isotropic elastic properties. A hip joint shaft belonging to the second group mentioned is known, for example, from German patent application OS-DE 3737372 A1. It essentially consists of a helical spring-like element made of metal, which corresponds in its outer contour to the shape of known shafts. The shaft derives its elasticity from the geometry of the coil spring-like element, this elasticity due to the material, the material thickness, the pitch of the winding, etc. is adjustable. Because of its construction, such a shaft has quasi-isotropic elastic properties, which are expressed both in terms of elastic flexibility and elastic extensibility, or, depending on the winding distance, also elastic compressibility. In fact, such behavior is only partially congruent with that of the bony femur. The hip joint shaft according to the above-mentioned patent application is moreover designed too elastic in the area of the main force introduction below the collar and at the start of the winding there is extremely prone to breakage due to the alternating bending load occurring during use. In the case of loosening, it should also be extremely difficult to remove such a resilient shaft from the medullary cavity.
Tiefer gehende Überlegungen über die elastischen Mikrobewegungen des Femurs unter Last führen zu der Erkenntnis, daß aufgrund der axialen Steifigkeit des Femurs und seiner insgesamt bogenähnli- chen Geometrie die mittels vertikaler Last induzierten Kräfte im wesentlichen in Biegung und nur indirekt in Längenänderungen um¬ gesetzt werden. Die auftretende Biegung wiederum baut im zur Kör¬ permitte zeigenden Sektor des Femurs Druckspannungen, bzw. im nach außen zeigenden Sektor Zugspannungen auf, welchen noch in beiden Sektoren eine geringe axiale Druckspannungskomponente überlagert ist. Aus den genannten Zusammenhängen kann auf ein stark anisotrop elastisches Verhalten des Femurs geschlossen werden.Deeper considerations about the elastic micro-movements of the femur under load lead to the realization that due to the axial rigidity of the femur and its overall arch-like geometry, the forces induced by vertical load are essentially converted into bending and only indirectly into changes in length. The bending which occurs in turn builds up compressive stresses in the sector of the femur pointing towards the center of the body, or tensile stresses in the outward-pointing sector, to which a small axial compressive stress component is still superimposed in both sectors. A strong anisotropic elastic behavior of the femur can be concluded from the above-mentioned relationships.
Eigene Untersuchungen des Anmelders mittels Finite-Elemente-Ana- lysen deuten nun überraschenderweise darauf hin, daß die vom Hüftgelenkschaft bei festem Sitz auf den Femur übertragenen Bie¬ gemomente von dem Maximalwert in der Nähe der Resektionsfläche zum distalen Bereich, also nach weiter unten hin, quasi exponen- tiell so abnehmen, daß ab einer Entfernung von etwa zwischen 6 und 8 cm praktisch kaum noch Biegemomente übertragen werden. Bei geeigneter Ankopplung des darunter befindlichen Schaftbereiches an den knöchernen Hohlraum des Femurs sind hier allenfalls noch axial wirkende Kräfte übertragbar. Andererseits stellt dieser
Schaftbereich für Biegemomente einen Widerstand dar, wobei wegen des langen Hebelarms auslockernd wirkende Bewegungen auf das obe¬ re Schaftende übertragen werden.Analyzes its own investigations the applicant by means of finite element analog now pointing surprisingly out that the data transmitted from the hip joint stem with a fixed seat on the femur Bie ¬ gemomente from the maximum value in the vicinity of the resected surface of the distal region, so after further downward, quasi-exponentially decrease so that from a distance of about 6 to 8 cm practically hardly any bending moments are transmitted. With a suitable coupling of the shaft area underneath to the bony cavity of the femur, axially acting forces can at best be transmitted here. On the other hand, this represents Shaft area for bending moments represents a resistance, with loosening movements due to the long lever arm being transmitted to the upper end of the shaft.
Es bestand daher im Hinblick auf Hüftgelenk-Endoprothesen die Aufgabe zur Schaffung eines Implantates mit einem in Bezug auf seine Elastizität besser an den Femur angepaßten Charakteristik. Das Konzept sollte ferner eine Bruchgefahr des künstlichen Schaf¬ tes sicher ausschließen und die problemlose Explantation im Falle der Lockerung ermöglichen.With regard to hip joint endoprostheses, there was therefore the task of creating an implant with a characteristic that was better adapted to the femur in terms of its elasticity. The concept should also reliably rule out a risk of breakage of the artificial shaft and enable problem-free explanting in the event of loosening.
Die erfinderische Grundidee ist nun, eine derartige Hüftgelenk- Endoprothese abweichend von bisherigen Konstruktionen mit einer anisotrop elastischen Charakteristik auszustatten, welche der des Femurs nahekommt und dabei die zwischen Schaft und Femur beste¬ henden wechselweisen Beziehungen bezüglich der übertragenen Kräf¬ te und Biegemomente berücksichtigt. Dabei konzentriert sich die praktische Ausführung der Erfindung darauf, die angestrebte Cha¬ rakteristik mittels einer funktionellen Aufgliederung des Schaf¬ tes zu realisieren. Danach besteht mindestens der untere Bereich des Schaftes aus einem schlanken Kern mit axialer Erstreckung, welcher mit einer speziellen elastischen Umhüllung fest verbunden ist. Der schlanke Kern ist dazu ausgelegt, die Funktion eines elastischen Elements ausgeprägter Anisotropie zu übernehmen, wel¬ che durch eine sehr hohe Steifigkeit in axialer und radialer Richtung bei gleichzeitig guter elastischer Biegsamkeit gekenn¬ zeichnet ist. Dagegen ist die spezielle elastische Umhüllung des Kernes in ihren mechanischen Eigenschaften auf eine stärkere axi¬ ale Elastizität bei radialer Steifigkeit hin optimiert. Die an¬ isotrop elastische Charakteristik der erfindungsgemäßen Hüftge¬ lenk-Endoprothese insgesamt ergibt sich aus der Summierung der Eigenschaften beider Funktionselemente.The basic idea according to the invention is now to equip such a hip joint endoprosthesis, deviating from previous designs, with an anisotropically elastic characteristic which approximates that of the femur and thereby takes into account the alternating relationships between the shaft and the femur with regard to the transmitted forces and bending moments. The practical implementation of the invention concentrates on realizing the desired characteristic by means of a functional breakdown of the shaft. According to this, at least the lower area of the shaft consists of a slender core with an axial extension, which is firmly connected with a special elastic covering. The slender core is designed to take on the function of an elastic element with pronounced anisotropy, which is characterized by a very high degree of rigidity in the axial and radial directions and at the same time good elastic flexibility. In contrast, the special elastic covering of the core is optimized in terms of its mechanical properties for greater axial elasticity with radial rigidity. The overall anisotropically elastic characteristic of the hip joint endoprosthesis according to the invention results from the summation of the properties of both functional elements.
Für die praktische Ausführung der Erfindung wird ein Vorschlag gemacht, welcher anhand der einzigen Zeichnungsfigur näher erläu¬ tert werden soll. Fig.l zeigt einen erfindungsgemäßen Hüftgelenk¬ schaft, bei welchem die funktioneile Aufgliederung zur Erzielung
der angestrebten anisotropen Elastizität mittels einer speziellen Bearbeitung realisiert ist.A proposal is made for the practical implementation of the invention, which will be explained in more detail with reference to the single drawing figure. Fig.l shows a hip joint shaft according to the invention, in which the functional breakdown to achieve the desired anisotropic elasticity is realized by means of special processing.
Das in Zeichnungsfigur 1 vorgestellte Beispiel eines erfindungs¬ gemäßen Schaftes ist eine Monoblock-Ausführung, welche aus einem metallischen Rohling, z.B. aus Titanlegierung herstellbar ist. Das obere Ende ist mit einem Kragen 3 versehen. Dieser geht mit einer Verrundung in einen zapfenförmigen Hals 1 über. Der Hals mündet seinerseits in einen Konus 2, auf welchen die üblichen Ku¬ gelköpfe aufsteckbar sind. Der gesamte Bereich der implantierba¬ ren Länge wurde aufgeschnitten dargestellt, um die konstruktive Gestaltung besser verdeutlichen zu können. Der Schaft verfügt über einen mehr oder weniger zentral stehenden Kern 8, welcher in seinem Querschnitt nach oben hin stark zunimmt und weich in den massiven Korpus 9 übergeht, bzw. sich nach unten hin zunehmend verjüngt. Diese Geometrie ist auf die mechanische Belastung des Schaftes und die Belastbarkeit des verwendeten Werkstoffs abge¬ stimmt und dabei so ausgelegt, daß der Kern einerseits axial aus- serordentlich steif, andererseits jedoch nach unten hin zunehmend biegeelastisch ist, indem er dort über ein sehr großes Längen/ Durchmesserverhältnis verfügt. Dem Kern 8 des Schaftes ist eine Umhüllung 10,11 mit speziellen elastischen Eigenschaften überla¬ gert. Diese hat einerseits die Aufgabe eines Platzhalters, indem sie mit ihrer Außenfläche die gewünschte äußere Formgestalt des Schaftes verwirklicht. Dabei soll sie der Übertragung von Kräften zwischen Kern 8 und Femur dienen. Andererseits darf sie die ela¬ stische Biegsamkeit des Kerns nicht zu sehr beeinträchtigen, und muß daher eine hohe axiale Elastizität besitzen. Daneben muß sie ausreichend fest und bruchsicher sein. Diese Eigenschaften wurden am gezeigten Beispiel dadurch verwirklicht, daß aus dem massiven Schaft mit der gewünschten äußeren Kontur eine schraubenlinienar¬ tige Nut herausgearbeitet wurde. Diese beginnt bei 4 unterhalb des Kragens 3 und verläuft weiter nach 5, bzw. über 6 bis zu ih¬ rem Auslauf 7. Der Nutanfang kann noch weiter nach oben verlegt werden, z.B. um den Korpus mittels des Wendeis zu strukturieren. Die Tiefe dieser Nut, ebenso wie im übrigen ihre Breite und ihre Steigung, hat Auswirkungen auf die Steifigkeit des Gesamtsystems
und die Anisotropie seiner Elastizität. Sie ist so gestaltet, daß ein genügend großer Querschnitt des Kerns erhalten bleibt und gleichzeitig eine angepaßte Zunahme dieses Querschnitts vom Schaftende zum Kragen hin resultiert. Dabei haben die in der Zeichnungsfigur gewählten Dimensionierungen mehr symbolische Be¬ deutung, weil hier eine gewisse konstruktive Bandbreite für die eigentliche Festlegung besteht. So besteht z.B. die Möglichkeit, die gewendelte Nut mehrgängig vorzusehen, ihre Steigung fließend zu ändern, oder auch exzentrisch einzustechen, um eine bestimmte Elastizitätscharakteristik des Schaftes zu erzielen. Es wird je¬ doch vorgeschlagen, den Kernquerschnitt vom relativ massiven Kor¬ pus zum Ende des Schaftes hin mindestens um den Faktor 15 zu re¬ duzieren, weil unterhalb dieses Wertes die bezüglich der aniso¬ tropen Elastizität angestrebte Charakteristik praktisch kaum zum Tragen kommt.The example of a shaft according to the invention presented in drawing FIG. 1 is a monoblock design which can be produced from a metallic blank, for example from titanium alloy. The upper end is provided with a collar 3. This merges into a cone-shaped neck 1 with a rounding. The neck in turn opens into a cone 2, onto which the conventional ball heads can be attached. The entire area of the implantable length has been cut open in order to better illustrate the structural design. The shaft has a more or less central core 8, which increases in cross-section at the top and smoothly merges into the solid body 9, or tapers increasingly towards the bottom. This geometry is matched to the mechanical load on the shaft and the load-bearing capacity of the material used and is designed so that the core is extraordinarily rigid on the one hand, but on the other hand is increasingly flexible towards the bottom by being there over a very long length / Diameter ratio. A sheath 10, 11 with special elastic properties is superimposed on the core 8 of the shaft. On the one hand, this has the function of a placeholder by realizing the desired outer shape of the shaft with its outer surface. It is intended to transmit forces between the core 8 and femur. On the other hand, it must not impair the elastic flexibility of the core too much and must therefore have a high degree of axial elasticity. In addition, it must be sufficiently strong and unbreakable. In the example shown, these properties were achieved in that a helical groove was machined from the solid shaft with the desired outer contour. This begins at 4 below the collar 3 and continues to 5, or via 6 to its outlet 7. The beginning of the groove can be moved further up, for example to structure the body by means of the turning ice. The depth of this groove, as well as its width and slope, has an impact on the rigidity of the overall system and the anisotropy of its elasticity. It is designed in such a way that a sufficiently large cross section of the core is retained and at the same time an adapted increase in this cross section results from the shaft end to the collar. The dimensions selected in the drawing figure have more symbolic meaning because there is a certain constructive range for the actual definition. For example, it is possible to provide the spiral groove with multiple threads, to change its slope smoothly, or to plunge eccentrically in order to achieve a certain elasticity characteristic of the shaft. However, it is proposed to reduce the core cross-section from the relatively solid body toward the end of the shaft by at least a factor of 15, because below this value the characteristic sought with regard to the anisotropic elasticity is practically of no consequence.
Die erfindungsgemäße Hüftgelenk-Endoprothese ist primär für die zementfreie Implantation vorgesehen. Hier wird das knöcherne Lager im Markraum in üblicher Weise mittels geeigneter Raspeln vorbereitet und der Schaft mit leichter Vorspannung bis zum Auf¬ setzen des Kragens eingetrieben. In ähnlicher Weise sind kragen¬ lose Varianten einbringbar. Für die Verwendung der erfindungsge¬ mäßen Hüftgelenk-Endoprothese mit schraubenlinienförmig umlaufen¬ der Nut in Verbindung mit einer Zementierung wird vorgeschlagen, in die Nut einen Keder bzw. kederartigen nachgiebigen Schlauch aus einem physiologisch unbedenklichen Werkstoff, z.B. aus PEEK (Polyätherätherketon) oder dergleichen einzulegen, um das Ein¬ dringen des Knochenzementes zu unterbinden.The hip joint endoprosthesis according to the invention is primarily intended for cementless implantation. Here, the bony bearing in the medullary canal is prepared in the usual way by means of suitable rasps and the shaft is driven in with slight pretension until the collar is put on. Collarless variants can be introduced in a similar manner. For the use of the hip joint endoprosthesis according to the invention with a helical circumferential groove in connection with a cementation, it is proposed to insert a piping or piping-like flexible hose made of a physiologically harmless material, e.g. made of PEEK (polyether ether ketone) or the like to prevent the bone cement from penetrating.
Die erfinderische Grundidee eines axial steifen, jedoch über eine definierte Erstreckung relativ biegeelastischen Schaftes, beste¬ hend aus den entsprechenden funktionellen Konstruktionselementen Kern und Umhüllung ist in vielfältiger Ausgestaltung in die Pra¬ xis umsetzbar und nicht auf das oben genannte Ausführungsbeispiel beschränkt. In Bezug auf eine Herstellung als Monoblock mit einer schraubenlinienförmig umlaufenden Nut ist die angestrebte aniso¬ trop elastische Charakteristik durch Modifikationen der Wende-
lung, z.B. Anpassung der Steigung, Gangzahl, Tiefe, Breite und Einstichwinkel der Nut, oder die fließende Änderung der verschie¬ denen Parameter in einem weiten Rahmen einstellbar und mit be¬ kannten Herstellverfahren zu günstigen Kosten zu realisieren.The inventive basic idea of an axially stiff, but over a defined extension of relatively flexurally elastic shaft, consisting of the corresponding functional construction elements core and casing, can be put into practice in a variety of configurations and is not limited to the above-mentioned embodiment. With regard to production as a monoblock with a helical circumferential groove, the desired anisotropically elastic characteristic is achieved by modifying the turning tion, for example adjustment of the pitch, number of gears, depth, width and penetration angle of the groove, or the fluid change in the various parameters can be set within a wide range and realized using known manufacturing processes at low costs.
Aus medizinischer Sicht verspricht die mit der Erfindung zur Ver¬ fügung gestellte Hüftgelenk-Endoprothese eine wesentlich verbes¬ serte Anpassung an die elastische Charakteristik des beteiligten Knochensystems und damit gute Voraussetzungen für eine langandau¬ ernde und beschwerdefreie Benutzbarkeit eines derartigen I plan- tates .
From a medical point of view, the hip joint endoprosthesis made available with the invention promises a substantially improved adaptation to the elastic characteristics of the bone system involved and thus good prerequisites for long-term and symptom-free usability of such an implant.
Claims
Anisotrop elastische Hüftgelenk-EndoprotheseAnisotropic elastic hip joint endoprosthesis
PatentansprücheClaims
01. Hüftgelenk-Endoprothese zur Implantation in den Markraum des Oberschenkelknochens, bestehend aus einem an die Markraumkonturen anpaßbaren Schaft, wahlweise mit einem am oberen Ende des Ober¬ schenkelknochens z.B. auf der Resektionsfläche abstützbaren Kra¬ gen, und mit einem sich anschließenden Hals als Verbindungsglied zu einem wahlweise fest verbundenen oder aufsteckbaren Kugelkopf , dadurch gekennzeichnet, daß der Schaft mindestens in einem unte¬ ren Teilbereich eine deutlich anisotrop elastische Charakteristik mit einer hohen axialen und radialen Steifigkeit bei relativer Biegeelastizität besitzt, welche durch seine funktionelle Auf¬ gliederung in einen Kernbereich 8 mit hoher axialer und radialer Steifigkeit bei gleichzeitig hoher elastischer Biegsamkeit und einen Mantelbereich 10,11 mit einer gegenüber der radialen Stei¬ figkeit reduzierten axialen Steifigkeit bei relativer Biegeela¬ stizität verwirklicht ist, wobei Kern- und Mantelbereich stoff- schlüssig fest miteinander verbunden sind und das elastische Ver¬ halten des Gesamtsystems mittels mindestens einer im Mantelbe¬ reich schraubenförmig umlaufenden Nut 4,5,6,7 eingestellt ist.01. Hip joint endoprosthesis for implantation in the medullary canal of the thigh bone, consisting of a shaft that can be adapted to the contours of the medullary canal, optionally with one at the upper end of the upper leg bone, e.g. Collars that can be supported on the resection surface, and with an adjoining neck as a connecting link to an optionally firmly connected or attachable spherical head, characterized in that the shaft has a clearly anisotropic elastic characteristic with a high axial and radial rigidity at least in a lower partial region with relative bending elasticity, which is realized by its functional division into a core area 8 with high axial and radial rigidity with simultaneous high elastic flexibility and a jacket area 10, 11 with an axial rigidity reduced compared to the radial rigidity with relative bending elasticity is, the core and jacket area are firmly bonded to one another and the elastic behavior of the overall system is set by means of at least one groove 4, 5, 6, 7 that extends helically in the jacket area.
02. Hüftgelenk-Endoprothese gemäß Anspruch 1, dadurch gekenn¬ zeichnet, daß der Kern des Schaftes vom Korpus zum Schaftende hin
- 9 -02. hip joint endoprosthesis according to claim 1, characterized gekenn¬ characterized in that the core of the shaft from the body to the shaft end - 9 -
verjüngt ist, bzw. die Nuttiefe in umgekehter Richtung abnimmt, wobei die Querschnittsfläche des Kernes im Bereich des Schaften¬ des höchstens ein Fünfzehntel derjenigen im Bereich des Korpus- ses beträgt.is tapered, or the groove depth decreases in the opposite direction, the cross-sectional area of the core in the region of the shank being at most one fifteenth of that in the region of the body.
03. Hüftgelenk-Endoprothese gemäß Anspruch 2, dadurch gekenn¬ zeichnet , daß die Querschnittsfläche des Kernes im Bereich des Schaftendes höchstens ein Zwanzigstel derjenigen im Bereich des Korpusses beträgt.03. hip joint endoprosthesis according to claim 2, characterized gekenn¬ characterized in that the cross-sectional area of the core in the region of the shaft end is at most one twentieth of that in the region of the body.
04. Hüftgelenk-Endoprothese gemäß einem oder mehreren der vorge¬ nannten Ansprüche, dadurch gekennzeichnet, daß in die schrauben¬ förmig umlaufende Nut über ihre längenmäßige Erstreckung und min¬ destens in einem Teilbereich ihrer Tiefe ein elastischer bzw. nachgiebiger Füllkörper in Gestalt z.B. eines Keders oder Schlau¬ ches aus einem physiologisch unbedenklichen Werkstoff (z.B. einem Silikonkautschuk oder einem Polyarylatherketon) eingelegt ist, um das Eindringen von Knochenzement mindestens einzuschränken.
04. hip joint endoprosthesis according to one or more of the preceding claims, characterized in that in the helical circumferential groove over its length and at least in a portion of its depth an elastic or resilient filler body in the shape of e.g. a piping or hose made of a physiologically harmless material (e.g. a silicone rubber or a polyaryl ether ketone) is inserted in order to at least restrict the penetration of bone cement.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE4441695A DE4441695A1 (en) | 1994-11-23 | 1994-11-23 | Anisotropically elastic hip joint endoprosthesis for implantation in narrow space of upper leg bone |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DEP4441695.4 | 1994-11-23 | ||
DE4441695A DE4441695A1 (en) | 1994-11-23 | 1994-11-23 | Anisotropically elastic hip joint endoprosthesis for implantation in narrow space of upper leg bone |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1996015736A1 true WO1996015736A1 (en) | 1996-05-30 |
Family
ID=6533956
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/DE1995/001630 WO1996015736A1 (en) | 1994-11-23 | 1995-11-22 | Anisotropically elastic hip joint endoprosthesis |
Country Status (2)
Country | Link |
---|---|
DE (1) | DE4441695A1 (en) |
WO (1) | WO1996015736A1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE29810818U1 (en) * | 1998-06-17 | 1999-10-28 | Trumpf GmbH + Co., 71254 Ditzingen | Cementless implantable metal endoprosthesis |
WO2001064139A3 (en) * | 2000-02-29 | 2002-02-07 | Hammill Mfg Co | Joint prosthesis having variable flexibility |
US7033399B2 (en) | 2003-08-22 | 2006-04-25 | Ortho Innovations, Inc. | Welded hip prosthesis |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE19619166C2 (en) * | 1996-05-11 | 1999-06-02 | Heraeus Kulzer Gmbh | Semi-finished product for the precise manufacture of an implantable prosthesis |
PL219087B1 (en) | 2009-07-06 | 2015-03-31 | Leszek Tadeusz Olbrzymek Ledo P P H U | Flexible endoprosthesis, especially of the hip joint |
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WO2001064139A3 (en) * | 2000-02-29 | 2002-02-07 | Hammill Mfg Co | Joint prosthesis having variable flexibility |
US7033399B2 (en) | 2003-08-22 | 2006-04-25 | Ortho Innovations, Inc. | Welded hip prosthesis |
Also Published As
Publication number | Publication date |
---|---|
DE4441695A1 (en) | 1996-06-13 |
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