WO2019057434A1

WO2019057434A1 - Replacement prosthesis for natural femur head

Info

Publication number: WO2019057434A1
Application number: PCT/EP2018/072721
Authority: WO
Inventors: Markus FLOHR; Maren FREUTEL; Kim Lars Häussler; Thomas Pandorf; Roman Preuss
Original assignee: Ceramtec Gmbh
Priority date: 2017-09-21
Filing date: 2018-08-23
Publication date: 2019-03-28

Abstract

The invention relates to a replacement prosthesis (1) for the natural femur head (2) having a base body (7), which comprises an outer spherical surface (5) and an inner receiving space (3) having an inner surface (10) and an elongate guide element (4) that extends starting from the inner surface (10) away from same. To ensure a secure, permanent holding of the replacement prosthesis (1), the guide element (4) has features that ensure a secure, permanent attachment to the femur head (2) and make removal difficult or practically impossible. To this end, features in the form of reductions in the direction of the guide element (4) are provided.

Description

Replacement prosthesis for the natural femoral head

The invention relates to a replacement prosthesis for the natural femoral head having a base body having an outer spherical surface and an inner receiving space having an inner surface and an elongated guide member which extends away from the inner surface thereof away from the inner surface. In order to ensure a secure, lasting retention of the replacement prosthesis, the guide element features that ensures a secure, permanent attachment to a bone and removal difficult to almost prevented. This ensures permanent attachment in a human or animal bone, preferably a femur.

Replacement prostheses, for example, surface replacement prostheses, are also called resurfacing head, hip cap or cap prosthesis. When wear of the natural femoral head or femoral head (caput femoris), it is known in the prior art to set up a surface replacement prosthesis made of metal or ceramic on the femoral head and anchored with bone cement. The surface replacement prosthesis replaces only the articular cartilage of the femoral head and is used when the femur bone under the articular cartilage is not substantially damaged in shape or structure.

Previous ceramic surface replacement prostheses are largely based on known metallic designs and can be implanted cemented or cementless. In the cemented version, the internal receiving space is connected to the corresponding prepared bone by bone cement. For secure permanent attachment, or for better anchoring WO 2009/1 1 1624 discloses a joint implant with a pin having a wavy contour. The diameter of the pin is continuously reduced, starting from the inside of the implant to the end of the pin. This diameter reduction facilitates centering for the user and inserting the joint implant into the bore of the bone structure. The wavy contour extends along the surface of the pin. It has been found that it is difficult to fill all undercuts along the wave structure with cement, which is necessary for a secure anchoring of the implant. For this, a deep cement entry into the bore of the bone, a cancellous bone structure, would be required. As a result, the implantation is complicated and expensive and for the patient longer and thus riskier.

DE 102015205583 proposes a non-radially symmetrical design of the cross section of the guide pin (pin) of a resurfacing head. This should be a relaxation of the resurfacing head, due to rotational stress about its longitudinal axis, prevented. All disclosed in DE 102015205583 guide pins, regardless of their cross-sectional shape, taper in the direction away from the inner circumferential surface of the inner receiving space towards the end of the guide pins. This guide pin shape facilitates the user centering and inserting the joint implant into the bore of the bone structure.

The IT 471394 discloses various cross-sections of a pin of an implant, wherein along the edges of the pin tooth-like recesses and projections are provided. Such a structure creates undercuts which likewise support the axial fixing of the pin and counteract the removal of the implant from the femur. However, even in this solution, similar to WO 2009/1 1 1624, a very deep introduction of cement into the femoral bore is required. In addition, the sharp-edged tooth-like structure poses a significant risk of dislocation of the cementum structure under cyclic loading, which is accompanied by loosening and possible withdrawal of the head from the femur. Also, the pin of IT 471394 has a cross-sectional reduction, from the receiving space of the implant to the end of the pin, for ease of insertion and implementation.

It is also known to produce a large roughness of the inner surfaces (receiving space and tenon) of metal alloy resurfacing heads intended for cementing, for example by sand blasting. As a result, the cement adhesion is increased - bone cement has no adhesive Function. It can thus be made only a positive connection between the replacement prosthesis and the cement. In order to improve this positive connection, it is also known to provide the surfaces of the insides of resurfacing heads of metal alloys with recesses, for example in the form of pockets (cement pockets). These recesses are filled with cement upon insertion of the prostheses and improve the fixed attachment of the prostheses.

A similar surface preparation to increase the roughness is not possible for resurfacing heads made of ceramic materials. Roughening the surfaces to be cemented would reduce the fracture toughness of the ceramic implant component.

In addition, especially in the case of ceramic resurfacing heads, the design of recesses, so-called cement pockets, has narrow limits on the inside of the heads. Due to the thin-walled nature of the component, very high stresses occur under mechanical loads, which can be increased by introducing recesses and thus further weakening the wall thickness. could reach critical levels. This increases the risk of breakage of resurfacing heads made of ceramic.

The smooth surface in comparison to metallic prostheses in conjunction with the missing recesses results in that the axial pull-off force of the ceramic component is lower compared to a metal component.

The implantation, the setting process of a resurfacing head is done inter alia by hammer blows with the aim of making optimal contact between milled bone geometry and the inside of the head of the prosthesis. The prosthesis is first placed on the bone and centered by means of the pin in the bone bore. The cement between the inside of the prosthetic head and the bone cement is driven a few millimeters deep when driving the implant into the spongy structure of the prepared femur bone. The tapering pin away from the prosthetic head, which aids in centering, potentially introduces cement into the dynamic setting process along the pin is transported particularly deep into the cylindrical bore and is pressed by conical portions even along the hole in the spongy structure of the femur. This may affect the stability of the cancellous femur and possibly have a negative effect on the biological tissue. As a result, it can lead to a thermal overload in the polymerization of the cement as well as to a reduction in the supply and death of the tissue.

It has been found that with the means disclosed in the prior art the anchoring of a prosthesis in the bone tissue is improved, whereby loosely, loosened prostheses are becoming known again and again. As a result, further medical intervention is required, which is known to be a burden on the organism.

Based on the prior art, the invention is based on the object to improve a replacement prosthesis so that an axial release of the prosthesis difficult, ideally prevented, or almost impossible.

This object is achieved by a prosthesis according to the features of claim 1.

A replacement prosthesis according to the invention for the natural femoral head comprises a base body with an outer rounded surface, which is designed as a sliding partner, and an inner receiving space with an inner circumferential surface and a guide element in the form of a pin or pin. The guide element extending in the longitudinal direction away from the lateral surface or surface has a diameter which varies over the length of the guide element. The diameter of the guide element rises, starting from the inner circumferential surface of the receiving space. This increase may be a continuous, steady, or non-linear, non-steady increase. As a result, this leads to a mushroom-shaped guide element whose diameter is smaller at the connection point than at its first end. Surprisingly, it has not been confirmed that the prevailing It is true that the guiding element for the centering of the prosthesis is decisive and therefore has to be thinner at its first end remote from the receiving space than at the connection point. It has been found, even refuting the general prejudice, that prostheses with the largest diameter at the first end of the guide element can be fixed just as securely as prostheses with conventional guide elements. If the largest diameter of the guide element adapted to the diameter of the bore in the femoral head, it can be prevented that when inserting cement unintentionally introduced into the depth of the bore. According to the invention, it is proposed that the largest diameter of the guide element is adapted to the diameter of the bore of the femoral head so that when driving the prosthesis only a small gap, ideally no gap is present and thus prevents cement far into the bore of the femur is driven. According to the invention, the shape of the guide element is formed such that, in the case of a resultant force in the longitudinal direction of the guide element, in the pulling direction, the movement in this direction obstructs the principle of self-locking, ideally completely prevented. For this purpose, the guide element, starting from its origin, ie, from its connection point on the inside of the resurfacing head on the surface of the receiving space over a limited section in diameter or in cross-section increasingly designed, ie D1 <D2, where D1 at the joint or the origin and D2 is measured at a distance X to the connection point, at the first end of the guide element. By the first end towards increasing diameter of the guide member increase in tensile forces occurring, the radial forces that lead to jamming of the guide element in the bore of the femur. Preferably, the diameter increase may be tapered, performed as a cone having a self-locking cone angle. The cone angle may have a value between 0 ° and 20 °, preferably a value around 5 °. The value between the smallest and largest diameter or cross section of the self-locking portion of the guide element may have a value between 0.1 and 2 mm, preferably between 0.3 and 1 mm or 0.03 and 12 mm ² , preferably between 0.28 and 3.14 mm ² .

The increasing portion of the guide element, the self-locking portion of the guide member may be formed in the axial sectional view as a contour, which is defined by one or more mathematical functions such that the mechanical stresses acting in the application in the guide element are minimized. In this case, the contour train or its descriptive mathematical function may be a so-called baud curve, or the mathematical function may be an exponential function or a logarithm function or a combination thereof. In the inserted state exists between the wall of the bore in

Bone and the guide element in the area of diameter reduction a distance. This distance is filled in a cemented application with cement paste, wherein the cement paste in the bore of the bone has a connection with the cement paste in the interior of the receiving space of the prosthesis. In a possible trigger movement, the guide element presses with its extended area against the existing in the bore of the bone cement there. It creates a very high contact voltage and thus the movement is inhibited, ideally prevented. The length of the tapered portion of the guide element, the self-locking guide element portion can be varied system specific. Thus, it is possible to influence the possibly occurring mechanical stresses in the guide element and to optimize the size of the resulting undercut (clearance between guide element and bore in the bone).

The inventive design of the guide element causes the dynamic setting process of the prosthesis that the cement preferably remains in the region of the origin of the guide element and in the receiving space. The cement enters the free space between the cylindrical bore of the bone and the reduced diameter of the guide element and reaches at most as far as the second end of the guide element. During the setting process, there is no pressure build-up between the pin and the spongy bore wall, as the volume of the free space increases when the prosthesis is inserted. In a modified embodiment according to the invention, a second section adjoins the self-locking guide section. This means that the guide element has a second end. The second portion is disposed between the first end and the second end. The transition between the self-locking guide portion and the second portion is rounded, so that the insertion of the prosthesis is not hindered by this transition. A smooth transition of the two sections allows a bone-friendly insertion of the prosthesis. The second section may have a cylindrical cross-section. The second portion may be formed of a plurality of regions that may have different diameters. Thus, according to the invention, the second section can be formed from a region with a constant diameter, wherein this diameter can be equal to or smaller than the diameter at the first end of the guide element. Alternatively, the second portion may be formed of a tapered portion. This means that the largest diameter of the guide element is arranged at the first end and reduces in the direction of the second end and also in the direction of the origin of the guide element. The second portion may also consist of a combination of a cylindrical and a tapered region. The cylindrical portion forms a guide during insertion and facilitates insertion of the prosthesis. In addition, it seals the bore in the bone against cement penetration. A second section, which tapers in the direction of the second end, decouples the guide element from the bone at its tip. As a result, the guide element in the region of the second end has no contact with the bone, whereby a force transmission to the bone at the tip of the guide element is avoided. In an embodiment in which the second portion of the guide member consists of two regions, a cylindrical portion and a tapered portion, the diameter of the cylindrical portion may even be made excessively large relative to the diameter of the bore in the bone, thereby creating a slight interference fit. As a result, an effective seal between the guide member and the bore is formed. Thus, it is almost impossible for cement to reach the region between the first and second ends of the guide element. A prosthesis according to the invention with a mushroom-shaped guide element can also be used without cement, ie without cement. The free area between the hole in the bone and the guide element in the area near the origin, the undercut, can be filled by tissue growth, the so-called remodeling process of the bone. The prosthesis according to the invention can, so to speak, grow firmly. In the cementless application, the replacement prosthesis, the implant, is preferably provided with a textured and / or rough and / or porous outer surface / coating to assist in "growing" in the tissue Such a prosthesis may be formed by a porous ceramic foam.

The interlocking principle of self-locking according to the invention can be used independently of the prosthesis material used. A positive connection between the guide element and the femur can be achieved with both ceramic and metallic resurfacing heads. Even with metallic resurfacing heads, it would be possible to increase the cement anchorage and thus the resistance to pull-off forces.

A ceramic replacement prosthesis according to the invention may consist of oxidic ceramic material systems, comprising:

• zirconia-reinforced alumina (ZTA) and all ZTA systems or systems developed on this basis

Zirconia ceramic, in particular yttrium-stabilized zirconia (3Y-TZP) or

• Ce-stabilized zirconia (Ce-TZP), which stabilizes the tetragonal phase of the zirconia with cerium oxide, or · All other composites based on zirconia, the dispersoid composite component being based on aluminates and also other rare earth stabilizers can be used, such as Gd and Sm, be formed. The invention relates to a replacement prosthesis for the natural femoral head having a base body having an outer spherical surface and an inner receiving space having an inner surface and an elongated guide member which extends away from the inner surface thereof away from the inner surface. In order to ensure a secure permanent retention of the replacement prosthesis, the guide element features that ensures a secure, permanent attachment to a bone and removal difficult to almost prevented. For this purpose, features in the form of reductions in the direction of the guide element are provided. The invention will be further explained with reference to figures. It shows

FIG. 1 shows a cross-section of a natural femoral head with an implanted replacement prosthesis, in extracts and in a schematic representation,

FIG. 2 shows the guide element of the replacement prosthesis according to FIG. 1 enlarged, in excerpts and in a schematic representation,

Figure 3 shows an alternative embodiment of the guide element of

Replacement prosthesis according to Figure 1, in extracts and in a schematic representation and

FIG. 4 shows a further alternative embodiment of the guide element of FIG

Replacement prosthesis according to Figure 1, extracts and in schematic

Presentation.

FIG. 1 shows a replacement prosthesis 1 according to the invention arranged on a natural femoral head 2. The replacement prosthesis 1 comprises a main body 7 which is delimited by a surface 5 which is designed as a sliding surface and a surface 10 of a receiving space 3. On the main body 7, a guide element 4 is arranged. The sliding partner (not shown) of the surface 5, may be natural bone tissue or even a prosthesis. The surface 5, the receiving space 3 and its surface 10, and the guide member 4 are integrally connected to each other, wherein the transitions of the individual surfaces or components are rounded, tissue-friendly design.

For the purpose of implantation, the replacement prosthesis 1, also called the resurfacing head, has a guide element 4. This guide element 4 is in a Bore 8 introduced in the femoral head 2. In the intra-operative procedure, the guide element 4 forms an aid, a centering aid, for the user. This makes it possible to insert the replacement prosthesis 1 in the cylindrical bore 8, which is usually produced by means of a drilling jig. Starting from its origin 9, on which the guide element 4 is connected to the main body 7 and the surface 10 of the receiving space 3, according to the invention the cross section A1 (marked as a diameter in FIG. 1) rises steadily up to its first end 14. This rising or conically shaped first section 26 forms the first region 26 of the guide element 4. The cross section A2 at the first end 14 has a larger amount than the cross section A1 at the origin 9 of the guide element 4. Depending on the application, the cross section of the guide element 4th cylindrical, elliptical, square, polygonal or have a different shape. Regardless of the shape of the cross section of the guide element, the larger amount of the cross section A2 is arranged according to the invention at the first end 14 of the guide element 4.

Due to the inventive design of the guide element 4 of the replacement prosthesis 1 is formed between the guide member 4 and the wall of the bore 8 of the femur head 2, a free space 17, which may also be referred to as an undercut. When inserting a replacement prosthesis 1, which is attached by means of cement, not only the space between the surface 10 of the receiving space 3, but also the free space 17 or undercut fills with the cement. This creates a fastener 20, which may consist of two areas. A first region of the fastening element 20 is formed in the region of the bore 8 in the form of a wedge 19. A second region of the fastening element 20 extends between the surface 10 of the replacement prosthesis and the femoral head 2. Both regions of the fastening element are connected to one another in a material-locking manner. The fastening element 20, in particular the wedge 19, counteracts a withdrawal force F (see arrow). The existing bone cement fastener 20 adjusts itself not only in the area of the surface 10 of the receiving space 3 to the femoral head 2, but also in the area of the bore 8, in particular in the region of the origin 9, in which the guide element 4 with the base body 7 of the replacement prosthesis 1 is connected. Thus, a permanent, secure attachment of the replacement prosthesis 1 guaranteed. The fastener 20, which is formed of cement, in particular its wedge 19, may extend from the first end 14 to the origin 9.

As can be seen in FIG. 2, the wedge 19 of the fastening element 20 extends around the guide element. It can be rotationally symmetrical. Its length L is at least as large as the width, for example, the diameter D1 of the opening, or the bore 8. The length of the wedge 19 may be up to four times (4) as large as the width D1. The length can also be in the range of once (1) to four times (4), for example, 1, 5 or 2 or 3 times the width D1. The manner of representation selected in FIG. 2 with the different hatchings of the fastening element 20 has been selected in order to clarify the region of the wedge 19. Regardless of this representation, the fastener 20 consists of two areas, which form a single part cohesively. In the application, the fastening element 20 counteracts positively a withdrawal force F.

The guide element 4 according to FIG. 3 has a second end 21 following its first end 14. Between the first end 14 and the second end 21, a second portion 22 is arranged. The guide element 4 thus forms from the second section 22 and the first section 26 already described above in FIG. 1. The definitions relating to the length of the first section 26 apply correspondingly to what has been described above. According to the exemplary embodiment according to FIG. 3, the second section 22 has a constant cross-section A3, a constant diameter. If the guide element 4 is formed in a cylindrical shape, its diameter in the second section 22 is constant and can correspond to the diameter D1 of the bore 8 (not shown in FIG. 3). The diameter A3 of the guide element 4 may be matched to the diameter D1 of the bore 8 so that a fit, preferably a press fit is formed. As a result, the attachment of the replacement prosthesis 1 is improved. In addition, in the process of introducing the replacement prosthesis 1, the guide member 4 in the bore 8, the risk that cement enters deep into the bore 8, reduced, ideally completely prevented. In an alternative embodiment (FIG. 4), the guide element 4 has a centering aid 23 within the second section 22. By means of the tapered in the direction of the second end 21 centering 23, the replacement prosthesis 1 can be easily inserted into the bore 8 of the femur 2. Same features bear the same reference numerals, the already described applies accordingly.

All embodiments of a replacement prosthesis according to the invention have a guide element 4 with a first section 26 which, starting from its origin 9 to its first end 14, has a rising cross section.

LIST OF REFERENCE NUMBERS

1 replacement prosthesis

2 femoral head

3 recording room

4 guide element

5 surface

7 basic body

8 opening, bore

9 origin

10 lateral surface, surface of 3

14 first end of 4

17 free space

19 wedge

20 fastener

21 second end of 4

22 second section of 4

23 centering aid

26 first section of 4

A1 cross-section, diameter of 4 at the origin

A2 cross-section, diameter of 4 at the first end 14th

A3 cross-section, diameter of 4 at the second end 21st

F Withdrawal force

L length of 19

D1 width, diameter of 8

Claims

claims

1 . Replacement prosthesis (1) with a base body (7) of a surface (5) as

Sliding surface having a receiving space (3) having a surface (10), with a guide element (4) which is connected at an origin (9) with the base body (7), the guide element (4) has a first

Section (26), which in the region of the origin (9) has a diameter or cross section A1 and away from the origin (9) at its first end (14) has a diameter or cross section A2, characterized

in

that the amount of the diameter A2 is greater than the amount of

Diameter A1 is.

2. Replacement prosthesis according to claim 1, characterized in that the first portion (26) is formed in the shape of a cone, wherein the amount of

Cone angle in the range of 0 ° to 20 °, preferably in the range of 5 °.

3. Replacement prosthesis according to claim 1 or 2, characterized in that the difference between the amount of the diameter A2 and the diameter A1 has a value between 0.1 and 2 mm, preferably between 0.3 and 1 mm.

4. Replacement prosthesis according to claim 1 or 2, characterized in that the difference between the amount of the cross section A2 and the cross section A1 is between 0.03 and 12 mm ² , preferably between 0.28 and 3.14 mm ² .

5. replacement prosthesis according to one of claims 1 to 4, characterized in that the first portion (26) is formed in the axial sectional view as a contour, which follows one or more mathematical functions.

6. replacement prosthesis according to claim 5, characterized in that the

mathematical function of the contour of the first section (26) is a so-called baud curve.

7. replacement prosthesis according to claim 5, characterized in that the

mathematical function of the contour of the first section (26) is an exponential function or a logarithm function.

8. replacement prosthesis according to one of the preceding claims, characterized

characterized in that the guide element (4) has a second end (21) and between the first end (14) and the second end (21)

additional second section (22).

9. replacement prosthesis according to claim 8, characterized in that the

additional second section (22) has a constant diameter or

Cross section (A3) has.

10. replacement prosthesis according to claim 8 or 9, characterized in that the second portion (22) has a cylindrical shape.

1 1. Replacement prosthesis according to one of claims 8 to 10, characterized in that the second portion (22) has a in the direction of the second end (21) tapered centering aid (23).

12. Substitute prosthesis according to one of the preceding claims, characterized

characterized in that the guide element (4) is rounded.

13. Replacement prosthesis according to one of the preceding claims, characterized

characterized in that it is formed of ceramic.

14. Replacement prosthesis according to one of the preceding claims, characterized

characterized in that it is formed of a ceramic foam.

15. Replacement prosthesis applied to a natural femoral head (2), the one

Bore (8), characterized in that the diameter A2 at the first end (14) of the guide element (4) of the replacement prosthesis (1) is equal to or greater than the diameter (D1) of the bore (8) in the femoral head (2).