EP1962728A1

EP1962728A1 - Endoprosthesis with intermediate part

Info

Publication number: EP1962728A1
Application number: EP06829523A
Authority: EP
Inventors: Arnold Keller; Hakon Kofoed
Original assignee: Waldemar Link GmbH and Co KG
Current assignee: Link America Inc
Priority date: 2005-12-12
Filing date: 2006-12-12
Publication date: 2008-09-03
Also published as: WO2007068440A1; RU2008127783A; US20100204799A1; AU2006326312A1; IL192127A0; BRPI0619626A2; RU2426520C2; KR20080085032A; AU2006326312A2; JP2009518156A; US20070173944A1

Abstract

The invention relates to an endoprosthesis for replacement of a joint, wherein an intermediate part (2) forms slide surfaces that are of different contours and accordingly define planes of movement for a respective bearing (1). According to the invention, a tensioning band encloses the intermediate part and its side faces and is arranged thereon in such a way that it is arranged free from the planes of movement defined by the slide surfaces of different contours. In this way, it is also possible to reinforce endoprostheses of the kind that have complex biomechanics with a plurality of degrees of freedom.

Description

Endoprosthesis with: intermediate part

The invention relates to an endoprosthesis for replacement of a joint comprising a component to be connected to a lower bone, which has an upper-side sliding surface, a component to be connected to an upper bone, which has a lower-side sliding surface, and an intermediate part which is attached to its lower part - And top each having a counter-sliding surface which forms a bearing with the sliding surfaces of the aforementioned components.

Such endoprostheses are used, for example, to replace the ankle. (FR-A-2 676 917, WO-A-03/075802, WO-A-2005/030098). The components and the intermediate part cooperate via sliding surfaces which allow flexion and extension in a sagittal plane. The sagittal plane is a plane defined by the AP direction and the vertical axis. The component on the tibia and the intermediate part form cooperating sliding surfaces that allow rotation about the vertical axis. They can be designed to allow compensating movements in the AP and LM (lateral-medial) directions. So that

Joint having the natural model corresponding degrees of freedom with respect to rotational, pivoting and / or pushing movements, the sliding surfaces are correspondingly contour different, for example, a flat sliding surface is combined with a cylindrical surface curved like a sliding surface. The stabilization happens through the natural ligaments. The entire load of the endoprosthesis rests on the intermediate part. It is highly charged. In practice, it has been shown that under high load "working" of the intermediate part usually made of polyethylene can occur. There is thus the risk that under increased loads, such as may occur, for example, as a result of movement dynamics (especially when climbing stairs or jumping), it can lead to overloading and thus uncontrolled deformation of the intermediate part. Excessive wear, cold flow or even failure of the prosthesis due to material failure can be the result. This is especially true when the intermediate part is made thin, as is usually the case as a result of the contour difference of the sliding surfaces.

Based on the cited prior art, the invention is based on the object of improving an endoprosthesis of the type mentioned at the beginning in such a way that, while retaining multiple degrees of freedom, it can safely carry high loads.

The solution according to the invention lies in a prosthesis with the features of claim 1. Advantageous developments are the subject of the dependent claims.

Thereafter, in an endoprosthesis for replacement of a joint comprising a component to be connected to a lower bone having an upper-side sliding surface, a component to be connected to an upper bone having a lower-side sliding surface and an intermediate portion attached to its lower and Each upper side has a sliding surface, which with the sliding surfaces of the vorge Designate components each have a movement plane for a bearing, the sliding surfaces of the intermediate part are contour different, provided according to the invention that a tensioning rim surrounds the intermediate part at the side surfaces and is arranged on the intermediate part free of the determined by the contour different sliding surfaces planes of movement. The term movement plane is to be understood broadly and also includes curved contours.

With the Spannreif as a relative to the polyethylene tensile strength Umgürtung increases the resulting total modulus of elasticity of the intermediate part. Conveniently, the Spannreif is of such a material that it has at least fifty times, preferably at least two hundred times higher elastic modulus than the polyethylene. With the Spannreif as a high tensile Umgürtung an elastic or plastic deformation of the intermediate part is counteracted under load. The intermediate part can thus withstand even higher loads without deforming. This can with the Spannreif invention

Reinforcement of the intermediate part can be achieved. Thanks to the inventive arrangement of Spannreifs the movement surfaces, as determined by the sliding surfaces of the upper and lower bearing remain free. Thus, despite the reinforcement by the hoop, the mobility of the endoprosthesis in all joint functions is maintained. This applies not only to the normal range of motion of the endoprosthesis, but also in more extensive movements, as they can occur in buckling (for example, buckling of the foot).

Although it has been known as a component of knee joint endoprostheses acting plateaus made of polyethylene to reinforce that on its resting on the tibia underside a metal plate is provided. Thus, the polyethylene plateau was strengthened from its back so that it yielded less under bending stress. However, this reinforcement measure known from EP-A-0 829 243 is exclusively applicable to prostheses which have a sliding surface on only one side. In a generic endoprosthesis, the intermediate part has sliding surfaces both on its upper side and on its underside, so that the use of such a reinforcing plate is eliminated. The same applies to a reinforcing ring, as it is known from US-A-5,766,256. This ring is also located at the bottom, which does not serve as a joint surface.

Preferably, the hoop is made of a two-zone, with a circumferentially circumferential belt zone and a Spreizschutzzone, which adjoins the belt zone. In this case, the expansion protection zone need not be provided circumferentially, but it is generally sufficient if it is provided on two opposite sides. The expansion protection zone additionally counteracts diverging of the outer sections of the intermediate part under high bending stress.

Preferably, the upper and lower edge of the Spannreifs is adapted to the contour of the respective adjacent sliding surface. Under adapted here is understood that seen in the side view, the edge of the Spannreifs has a constant distance from the edge of the adjacent sliding surface. If, for example, the one sliding surface is a plane, then its edge is a straight line and the corresponding edge of the clamping rim is likewise a straight line; is the corresponding arched sliding surface, so the edge is circular arc and the corresponding edge of Spannreifs also a circular arc with a circular arc-shaped edge. By each adapted to the contour upper and lower edges of the Spannreifs even with endoprostheses with complex joint function, such as those with contour different sliding surfaces, a reinforcement of the particularly loaded intermediate part can be achieved and yet ensure that the gain-causing element, the Tight, free from the complex, contour-different sliding surfaces certain levels of motion remains.

Expediently, the clamping strip has at its lower edge at least on two sides a chamfer, which is designed such that it smoothly merges into the intermediate part. Next, the clamping ring on its inside preferably has a bead-like protrusion, which engages in a corresponding recess on the intermediate part. Thus, the Spannreif is secured against undesired displacement from its intended position. But it can also be provided other attachment techniques, such as a bond or a clamp, which is generated in particular by shrinking the Spannreifs on the intermediate part. It may also be provided a positive connection, such as pinning or screwing.

In order to give the hoop a defined position on the intermediate part, it has on its upper or lower side a flange on which the clamping ring rests. This simplifies the assembly of the hoop, since the intended

Position is clearly defined. Furthermore, it is achieved that the sliding surface of the intermediate part does not need to be downsized because of the hoop. This is the area burden tion no higher than in the conventional design of the intermediate part without Spannreif.

Conveniently, the clamping strip is dimensioned such that its upper edge and its lower edge around it have a distance of at least 1 mm, preferably between 1.5 and 2.5 mm, to the edge of the respective sliding surface. This ensures that even at high, leading to a compression of the intermediate part of the load or wear of the intermediate part, an undesirable contact between the clamping ring and the sliding surfaces of the components of the prosthesis can be prevented.

According to a particularly preferred embodiment, which may deserve independent protection for endoprostheses with contour-like sliding surfaces, the tensioning strip has a convex projection on at least one outer side. By means of the projection, during a rotation, as well as during a linear movement, the joint and thus also the intermediate part, together with the tensioning ring, can be pushed back laterally next to the endoprosthesis, growing undesired tissue material. Penetration of this tissue material, the so-called fibrosis, can be counteracted or even prevented in this way. The risk that the joint is limited with the endoprosthesis according to the invention by an excessive formation of fibrosis in its mobility, can be met with it. Pain, as can occur conventionally in such a fibrosis due to the tissue material growing in the movement region of the intermediate part, is avoided thanks to the development according to the invention. Any otherwise required surgical removal of this tissue structure terials is not required thanks to the design of the invention.

A particular advantage of this development is that with the preferably made of metal strapping basically a touch of the bone or the fabric material can be done, while in the conventional alone consisting of a polyethylene material intermediate parts contact with the bone or the fabric material was not desirable because this leads to unwanted polyethylene abrasion. Thus, the design according to the invention uses the hoop in two ways, namely its structure for forming the convex projection to push back the fibrosis and its material, which permits contact with the fibrotic tissue in the first place.

The crowning of the projection need only be one-dimensional, so that therefore results in a substantially cylinder shell-like shape; however, it may preferably also be two-dimensional, so that a substantially spherical design results, wherein the curvature may be different in the plane of the hoop and perpendicular thereto.

Conveniently, the spherical projection extends over the entire length of the respective outer side. Although in principle can be achieved with only over a part of the length of an outer extending projection of the desired effect, however, arise in an embodiment over the entire length larger and thus more favorable radii of curvature for the projection. Particularly expedient is an arrangement of the spherical projection on a medial longitudinal side of the Spannreifs. In this area is located, for example, in an implantation of the endoprosthesis according to the invention on the ankle of Malleolus media lis. Especially in this area can lead to unwanted fibrosis, whose harmful effects are prevented thanks to the development of the invention. The arrangement extending over the entire length also has the advantage that the desired effect of restraining can be achieved even in the case of a nonrotatory, for example linear, forward and backward movement of the intermediate part.

Conveniently, the contour of the crowned projection is chosen so that it is circular arc in plan view. Such a contour is favorable in the production and results in a uniform curvature of the projection without major changes in the course of curvature. It is not necessary here that the circular center on which the circular arc is based is in the center of the hoop. Conveniently, it is offset in the direction of the opposite lateral side. This results in an eccentricity, due to which a greater repression of the fibrotic tissue material is achieved at larger rotational deflections of the intermediate joint piece.

The outer surface of the crowned projection is preferably made smooth. Preferably, it may be polished. This results in a low-slip behavior, especially under the influence of tissue fluid. The risk of tearing or shearing tissue material is thus effectively countered.

The spherical projection can be expediently also provided on the adjacent outer sides. In a rectangular design, this means that at the anterior, the posterior and the medial side of the Spannreifs such a spherical projection is formed.

The invention will be explained below with reference to the accompanying drawing, in which an advantageous embodiment of the invention is shown. Show it:

1 shows a sagittal section through a supplied with the prosthesis according to the invention

ankle;

Fig. 2 fanned the prosthesis of Figure 1 in a perspective view.

Fig. 3 a), b) a frontal and a side view of a hoop of the prosthesis;

4 is a partial cross-sectional view of the hoop with an intermediate part of the prosthesis;

5 shows a front view of a lower region of the tibia with a part of a variant of the endoprosthesis according to FIGS. 1 to 4;

FIG. 6 shows a view from below of the variant according to FIG. 5; FIG. and

Fig. 7 a), b) a front and side view of the in Fig.

6 shown Spannreifs. In the illustrated embodiment of the prosthesis according to the invention is an ankle prosthesis. It should be noted that the invention can also be applied to other types of endoprostheses, for example intervertebral endoprostheses. It is essential that the endoprosthesis has two bearings whose planes of motion are determined by contour-different sliding surfaces.

The endoprosthesis according to the illustrated embodiment has essentially three components. The first component is a tibial component 1, which is designed to be located at the lower end of a tibial bone 91. It has a plate-shaped part 10, whose underside forms a flat sliding surface 11. On the upper side of the plate-shaped part 10 there is provided an anchoring body 12 provided with projections, which serves for fastening the tibial component 1 in corresponding resection recesses of the tibia 91.

The prosthesis further comprises an ankle bone component 4.

It is saddle-shaped and has on its upper side a convex curved sliding surface 44. It can be designed like a cylinder jacket, as shown; but it can just as well be executed cone-like. On her a guide rib 46 is arranged, which lies in the AP direction. It serves as a guide during a bending and stretching movement of the ankle.

Between the tibial component 1 and the ankle component 4, an intermediate part 2 is arranged. It has on its upper side a flat sliding surface 21, which is formed to match the sliding surface 11 of the tibial component 1. On its underside, the intermediate part 2 a Congruent to the sliding surface 44 of the ankle component 4 trained sliding surface 24. It also has a groove 26 which is formed for longitudinally displaceable receiving the rib 46. Thus, the intermediate part 2 is guided laterally in relation to the ankle component 4. Only bending and stretching movements are possible. In contrast, the flat sliding surfaces 11, 21 allow any movement in a horizontal plane, both longitudinal and transverse movements as well as in particular a rotation about the vertical axis.

The tibial component 1 and the talar component 4 expediently consist of metal, for example a cobalt-chromium alloy, which are provided on their respective outside with a bone growth-promoting coating (for example calcium phosphate). The intermediate part 2, however, preferably consists of a sliding plastic material, in particular polyethylene. However, it should not be excluded that other materials with sufficient strength and lubricity can be used.

In the implanted state, the joint and in particular the intermediate part 2 is exposed to a high axial load (symbolized by an arrow 95) along the vertical axis. Due to the resulting compression arises in the polyethylene material of the intermediate part 2, a horizontally outward diverging force (symbolized in Fig. 1 by the arrows 96). Due to the convex design of the sliding surface 44 of the anklebone component 4, this diverging force is additionally reinforced. This can lead to undesirable deformation of the intermediate part 2 under high load. In order to counteract this, a clamping strip 3 according to the invention is provided. It consists of a cobalt chromium alloy with a modulus of elasticity about four hundred times that of the polyethylene material of the intermediate part 2. It is also possible to use titanium which has an approximately 200 times higher modulus of elasticity. The clamping strip 3 is made of a flat strip material. It has a thickness of, for example, 1 mm. The clamping strip 3 has a contour in horizontal section corresponding to the outer contour of the intermediate part 2. In the illustrated embodiment, this is a square contour. But it could just as well be provided another contour, z. B. round for a version as an intervertebral prosthesis. Its dimensions are chosen so that it tightly encloses the intermediate part 2.

The hoop 3 has a circumferential belt zone 36 in its upper portion. It counteracts a deformation of the intermediate part 2 under load in all lateral directions (in the longitudinal and in the transverse direction). In addition, at the bottom of the belt zone 36 still includes an expansion protection zone 37. The expansion protection zone 37, which also includes the chamfer 32, additionally stabilizes the outer regions of the concave sliding surface 24 and thus counteracts in a particularly effective manner the divergent force component 96 resulting from the convex design of the sliding surface 44. Thus, the intermediate part 2 is reinforced thanks to the invention Spannreifs. As a result, an undesirable deflection is counteracted even under high load.

The Spannreif 3 is just executed at its upper edge 31. This results in a constant distance to the Kan te the upper sliding surface 21. At its lower edge 34, the clamping strip on its longitudinal sides 33 (which are aligned parallel to the rib 46) an arcuate configuration. It is designed so that there is a constant distance of the lower edge 34 of the clamping ring 3 to the edge of the lower sliding surface 24 in this area. At its transverse sides 35, the clamping strip 3 has a straight lower edge. This in turn results in a constant distance from the corresponding edge of the sliding surface 24. In the region of the transverse sides, the lower edge of the Spannreifs apron-like pulled down and also has a chamfer 32. The latter is designed so that it forms a continuous plane with the corresponding side surface 22 of the intermediate part 2. Thanks to the beveling, an additional reinforcement results, especially in a region which is particularly stressed by the divergent forces (see arrow 96), without this resulting in an undesirable limitation of the mobility.

The intermediate part 2 has a flange 20 in the region of its upper sliding surface 21. Against the underside of the clamping strip 3 is pushed flush, so that there is a smooth transition on the outside between the flange 20 and the outer surface of the clamping ring 3.

Thanks to the inventive design of the Spannreifs 3, the upper and lower sliding surfaces 21, 24 remain free, so that they are not affected in their storage function.

In FIGS. 5 to 7, a variant of the ankle endoprosthesis according to FIGS. 1 to 4 is shown as a further exemplary embodiment. 5 shows the endoprosthesis at its intended implantation location at the distal end of the implant. bia-bone 91. For reasons of clarity, only the tibial component 1, the intermediate part 2 and a varied tensioning rim 3 'are represented by the endoprosthesis. The fibular bone 90 runs parallel to the tibia bone 91. The tibia bone 91 forms a plateau at its distal end, on which the tibial component 1 of the endoprosthesis according to the invention is arranged. This plateau is bounded medially laterally by an extension of the tibial bone 91, the so-called malleolus medialis 93, and laterally by a corresponding extension of the fibular bone 90, namely the malleolus lateralis 94. They include the plateau of the tibial bone 91 and thus the tibial component 1 of the endoprosthesis fork-like. This can be clearly seen in FIG.

It has been found that, some time after implantation, formation of tissue material (fibrosis) 99 occurs frequently in the area between the malleolus medialis 93 and the intermediate part 2 or the tether 3 'arranged around it. This can cause pain that could not only be very uncomfortable for the patient, but in many cases also require surgery to remove the tissue material 99. In order to avoid or reduce the fibrotic tissue material 99, a projection 39 is formed on at least one longitudinal side 33 of the clamping rim 3 ', expediently on the medial side. The projection protrudes with respect to a congruent to the intermediate part 2 contour. Such a protrusion projecting beyond the congruent contour can also be provided on endoprostheses which have contact surfaces which have the same shape. The projection preferably has an arcuate outer contour, wherein the arc extends over the entire length. The projection 39 is suitably curved two-dimensionally, that is to say it has a spherical surface shape (see Fig. 7a). The radii of curvature are different in size, a slight curvature in the horizontal plane (as shown in Fig. 6) and a greater curvature in a frontal plane (as shown in Fig. 7a). In order to obtain the largest possible radius of curvature in the horizontal plane, the center 30 of the circle defined by the radius of curvature is preferably not centrally located in the clamping rim 3 ', but eccentrically laterally and preferably also offset from the front. The outside of the projection 39 is smooth.

In the illustrated embodiment, an option is realized, namely that the frontal side and the back of the Spannreifs 3 'are each provided with a projection 39 ^f and 39''. They are expediently designed in accordance with the projection 39, but may also be deviating in shape (for example, in the shape of a cylinder jacket rather than in the manner of a sphere, as shown in FIG. A curvature-like transition between the projections 39, 39 ', 39''is not required, but expediently the geometries are chosen such that the transition is step-free. The lateral longitudinal side of the clamping rim 3 'expediently has no projection. This serves to ensure the clearance of the hoop. Furthermore, this has the advantage that an unambiguous orientation of the hoop 3 'is predetermined so that the risk of installation in a wrong position is reduced.

The tightening collar 3 ', like the tightening collar 3 of the exemplary embodiment illustrated in FIGS. 1 to 4, is preferably made of a metal material, in particular titanium or a cobalt Chromium alloy manufactures. It can thus come into contact with the fibrotic tissue material 99, without any fear of impairing the surrounding tissue. During the movement of the endoprosthesis, in particular during the rotation but also during a movement in the longitudinal direction to the front or the rear, a retraction of the fibrotic tissue material 39 is achieved thanks to the projection 39. An ingrowth of the fibrotic tissue material 99 in the area of the endoprosthesis is thus effectively counteracted.

The projection 39 is usually made in one piece with the clamping strip 3 '. However, it should not be excluded that a multi-part construction is selected, in which the projection 39 is designed as a separate part and is attached to the clamping ring 3 'by suitable fastening means. The latter offers the advantage that a particularly slippery and especially suitable for contact with the fibrotic fabric material 99 material may be selected for the projection 39, without it on the mechanical strength as a reinforcing element, as they are for the selection of the material for the hoop 3 of Meaning, arrives.

It should finally be noted that the inventive

Design of a hoop with a projection 39 is not limited to ankle endoprostheses.

Claims

claims

An endoprosthesis for replacement of a joint comprising a component (1) to be connected to a lower bone (91), which has a lower-side sliding surface (11), a component (4) to be connected to an upper bone (92), which is an upper-side Sliding surface (44) and an intermediate part (2) having at its bottom and top each have a sliding surface (21, 24) with the sliding surfaces (11, 44) of the aforementioned components (1, 4) each have a movement plane for determine a bearing, wherein the sliding surfaces (21, 24) of the intermediate part (2) are contours different, characterized in that

a tensioning strip (3) surrounds the intermediate part (2) on its side surfaces and is arranged on the intermediate part (2) free of the movement planes determined by the contour-different sliding surfaces (11, 44).

2. Endoprosthesis according to claim 1,

characterized in that

Upper and lower edge of the Spannreifs (3) are adapted to the contour of the respective adjacent sliding surface (21, 24).

3. Endoprosthesis according to claim 1 or 2,

characterized in that the tensioning hoop (3) has a two-zone design, with a circumferential belt zone (36) and an expansion protection zone (37) adjoining the belt zone (36).

4. Endoprosthesis according to one of the preceding claims,

characterized in that

the intermediate part (2) has on its upper or lower side a flange (20) on which the clamping strip (3) rests.

5. Endoprosthesis according to one of the preceding claims,

characterized in that

the clamping strip (3) has at its lower edge (34) at least on two sides a chamfer (32), which is formed so that it smoothly merges into the intermediate part (2).

6. Endoprosthesis according to one of the preceding claims,

characterized in that

the lower and upper edges (34, 31) of the Spannreifs (3) have a distance of at least 1 mm, preferably 1.5 to 2.5 mm.

7. Endoprosthesis according to one of the preceding claims, characterized in that

the tensioning collar (3) has on its inside a bead-like protrusion (38) which engages in a corresponding recess on the intermediate part (2).

8. Endoprosthesis according to one of the preceding claims,

characterized in that

the tensioning tire (3) has an elasticity modulus at least 50 times, preferably at least two hundred times, higher than that of the intermediate part (2).

9. Endoprosthesis according to one of the preceding claims,

characterized in that

the tensioning strip (3 ') has a convex projection (39) on at least one outer side.

10. endoprosthesis according to claim 9,

characterized in that

the spherical projection (39) extends over the entire length of the respective outer side.

11. Endopoprosthesis according to claim 9 or 10,

characterized in that

the projection (39) on a medial longitudinal side of the Intermediate part is formed.

12. Endoprosthesis according to one of claims 9 to 11,

characterized in that

the spherical projection (39) has an arc-shaped in plan view contour.

13. Endoprosthesis according to claim 12,

characterized in that

the arcuate contour follows a circular arc whose center (30) is offset towards the opposite side of the clamping rim (3 ').

14. Endoprosthesis according to one of claims 9 to 13,

characterized in that

on an anterior and a posterior side of the Spannreifs (3 ') additional spherical projections (39', 39 '') are formed.