Abstract
The invention describes an implant for wear couples in endoprosthetics, the implant having an outer side, with an outer face, and an inner side, and a hemispherical wear region for accommodating a spherical wear partner being formed on the inner side. The aim of the invention is to reduce the height of the implant as much as possible and to ensure that, e.g., the pelvic bone does not have to be milled down as much. According to the invention, the implant is therefore designed in the form of a ring or annular structure and the outer face permits direct implantation in the body. In order to reduce friction between the spherical wear partner and the implant to a minimum, the implant has a specially designed inner geometry.
Claims
1. Ceramic bone implant for the tribological pairing comprising a spherical sliding partner, the bone implant being formed in a half shell or annular manner and comprising an inner surface which is formed as a sliding region for receiving a spherical sliding partner, wherein the sliding region corresponds to a portion of half a spindle of a spindle torus in the longitudinal extension, the maximum diameter D1 of the sliding region being larger than the diameter of the spherical sliding partner to be inserted, and the minimum diameter D2 of the sliding region being smaller than the diameter of the spherical sliding partner to be inserted, and the radius r of the circle describing the spindle torus, the clearance C, and the radius r.sub.P of the sphere of the prosthesis being in the relationship according to Formula I.
C=(r−r.sub.P)*2 (Formula I).
2. Implant according to claim 1, comprising a first region for introducing the sliding partner and having an end face which represents the transition from the inside to the outer surface in the first region, and a second region which limits the reception of the sliding partner, comprising a base surface which is located opposite the end face, and an outside which comprises an outer surface having a rough and/or structured surface for anchoring the implant in the bone.
3. Implant according to either claim 1, wherein the implant is formed as a half shell and the minimum diameter D2 of the sliding region is 0, or wherein the implant is formed as a half shell and is flattened, and the closed base surface does not touch the spherical sliding partner to be inserted.
4. Implant according to either claim 1, wherein the implant is annular.
5. Implant according to claim 1, wherein the height H.sub.G of the sliding region corresponds to 20% of the diameter of the sphere to be inserted, and/or 50-95% of the height H of the implant.
6. Implant according to claim 1, wherein the following applies: 10 μm<C<500 μm.
7. Implant according to claim 1, wherein the implant, preferably the sliding region, is elevated cranially, and/or the implant is annular and the sliding region is enlarged cranially.
8. Implant according to claim 1, wherein the rough surface is a coating.
9. Implant according to claim 1, wherein the rough surface is a porous surface.
10. Implant according to claim 1, wherein the porous surface has a porosity between 50% and 99%, preferably between 60% and 85%, and the pores have a pore size of between 100-1000 μm.
11. Implant according to either claim 7, wherein the porous surface is a porous ceramic.
12. Implant according to claim 9, wherein the porous ceramic is a porous ceramic foam.
13. Implant according to claim 1, wherein the implant is entirely ceramic.
14. Implant according to claim 11, wherein the implant consists of a porous ceramic foam.
15. Use of an implant according to claim 1 in hip, shoulder, elbow, finger joint or toe joint endoprosthetics.
Description
[0109] Selected embodiments of the annular implant according to the invention are described in the figures, in which:
[0110] FIG. 1a: is a side view of an implant,
[0111] FIG. 1b: is a cross section showing the implant according to FIG. 1a in the annular embodiment,
[0112] FIG. 2: shows an embodiment of an implant according to the invention comprising an inserted spherical KG,
[0113] FIG. 3a-c): show the contact points of the spherical sliding partner in a conventional insert (A), a conventional annular insert (B), and the implant according to the invention (C) in the annular embodiment thereof,
[0114] FIG. 4a-c): shows the geometry of the spindle,
[0115] FIG. 5: shows a preferred embodiment of the implant according to the invention,
[0116] FIG. 6: shows a preferred embodiment of the geometry of the cranial elevation,
[0117] FIG. 7: shows a preferred embodiment of the geometry of the cranial lengthening.
LIST OF REFERENCE SIGNS AND ABBREVIATIONS
[0118] 1 implant [0119] 2 sliding region [0120] 3 outer surface, rough and/or structured surface [0121] 4 biological coating [0122] 5, 109 head, sphere of the prosthesis [0123] 6 outside [0124] 9 base surface [0125] 10 end face [0126] 100 contact point [0127] 101, 112 annular contact, contact line [0128] 105 spindle [0129] 106 outer surface of the spindle [0130] 107 portion of the spindle [0131] 108 circle describing the spindle torus [0132] 110 tangent point [0133] 111 sectional plane of the contact line [0134] 112 contact line [0135] 201 region of the cranial elevation of the sliding region [0136] 202 region of the cranial lengthening of the implant [0137] 205 region of the bone contact [0138] 212, 212′ circle line (orientation aid) [0139] 214 infeed zone [0140] 216 discharge zone [0141] A distance between the axis of rotation and the center point M of the circle describing the spindle torus [0142] C clearance [0143] D1 maximum diameter of the sliding region, arranged in the first region [0144] D2 minimum diameter of the sliding region, arranged in the second region [0145] E, E′ point of intersection of the spindle outer surface with L [0146] F cross-sectional surface [0147] H height of the implant [0148] H.sub.G height of the sliding region [0149] K straight line describing the cranial elevation [0150] K.sub.G straight line describing the cranial elevation of the sliding region [0151] K′ straight line describing the cranial lengthening [0152] K.sub.G spherical sliding partner [0153] L longitudinal axis of the spindle, axis of rotation [0154] L′, L″ axis, in parallel with L, of the circle, describing the spindle torus, through the center point [0155] M center point of the spindle [0156] M′, M″ center point of the circle describing the spindle torus [0157] M.sub.P center point of the spherical sliding partner [0158] r radius of the circle describing the spindle torus [0159] r.sub.P radius of the spherical sliding partner (K.sub.G, prosthesis head) [0160] R axis of rotation of the outer surface [0161] S, S′ planes normal to L [0162] S1, S2 points of intersection of the normal planes S, S′ on the longitudinal axis L [0163] X maximum of the implant or cranial elevation in the direction of the end face [0164] X.sub.G maximum of the sliding region without a cranial elevation in the direction of the end face [0165] X′ maximum of the implant without a cranial lengthening in the direction of the base surface [0166] x height difference of the cranial elevation [0167] Y maximum of the implant of the cranial elevation [0168] Y.sub.G maximum of the sliding region of the cranial elevation [0169] Y′ maximum of the implant of the cranial lengthening [0170] y height difference of the cranial lengthening
[0171] An annular implant 1 according to the invention is shown in FIG. 1a and FIG. 1b. FIG. 1a is a view of said implant 1 and FIG. 1b is a cross-section thereof along an axis of rotation L according to FIG. 1a. The implant 1 comprises an inner annular portion of a spindle which is also referred to as a (non-hemispheric, covalent) sliding region 2 or inner surface. In the case of hip joint prosthesis the prosthesis head 5 is articulated thereon (see FIG. 2). In a preferred embodiment an outer surface 3 having a rough and/or structured surface is arranged on the outside 6 of the implant 1, by means of which surface the implant can be anchored in the bone. The height H of the implant is shown by the dashed lines and extends from a first region, having the end face 10, over a second region, to the base surface 9. The axis of rotation is denoted by L. F denotes the cross-sectional surface of the annular implant.
[0172] FIG. 2 is a cross-sectional view of the implant 1 according to the invention. A prosthesis head 5 is inserted into the implant 1. A biological coating 4 can additionally be applied to the outside 6 or the outer surface 3.
[0173] FIG. 3a) schematically shows the most likely locations of friction of a conventional insert, FIG. 3b) shows this for a conventional annular insert, and FIG. 3c) shows this for an implant according to the invention in an annular embodiment. In the case of a known semicircular insert, the contact point 100 is positioned between the insert and K.sub.G, on the base of the insert. In the case of a known annular insert, the contact between the insert and the K.sub.G (FIG. 3b) takes place on a contact line 101. This is preferably a linear contact, and linear friction. This line 101 is arranged in the region close to the base surface 9. In the implant according to the invention, the correspondingly designed geometry means that the contact line is arranged on the plane 111, at a distance from the base surface 9 in the direction of the end face 10 (FIG. 3c).
[0174] FIG. 4 shows the determination of the sliding region 2 of the implant according to the invention. The spindle torus 105 in FIG. 4a) is described by a circle 108 having a radius r that has a center point M′/M″ and rotates about the axis of rotation that corresponds to the longitudinal axis L of the spindle. The axes L′ and L″ are in parallel with L and extend through M′, M″. The distance between L′/L″ and L is smaller than the radius r. The spindle intersects the longitudinal axis L in the points E and E′.
[0175] In FIG. 4b) the determination of the portion 107 is made clear. The portion 107 is located in half the spindle 105 and is formed by the planes normal to L (S and S′). Said planes intersect L in points S1 and S2 and in this case the following applies: S1=M or S1 is located between M and S2, S2=E′ or S2 is located between S1 and E′. Both the points of intersection S1, S2 are therefore located in half of the spindle and do not exceed the center thereof. The diameter D1 in the first region is larger than the diameter D2 in the second region, D1 being larger than the diameter of the K.sub.G to be inserted. D2 is smaller than the diameter of the K.sub.G to be inserted, as a result of which (in the case of an annular implant) the K.sub.G is prevented from falling out.
[0176] FIG. 4c) schematically shows the sectional plane 111 of the contact line 112 between the K.sub.G 109 and the implant 1, on the sliding region 2 thereof, according to the outer surface of the spindle 106. The contact line 112 corresponds to a sectional line 111 on the spherical sliding partner 109. Owing to the spindle shape, the region of the end face 10 is inclined towards the spherical sliding partner 109 or towards the longitudinal axis L. As a result, the diameter D1 has a smaller value compared with a diameter of a comparable hemispheric sliding region measured at the same point. As a result, the contact line 112, on which the spherical sliding partner 109 moves, is displaced towards the end face 10 of the implant and away from the base surface 9.
[0177] FIG. 5 shows the height H.sub.G of the non-hemispherical sliding region 2, shown on an annular implant 1 having K.sub.G inserted having a center point M.sub.P and a radius r.sub.P. The sliding region 2 corresponds to a portion 107 of half a spindle of a spindle torus, in the longitudinal extension. The circle lines 212, 212′ are used merely for orientation. The portion 107 is limited by the infeed zone 214 in the region of the end face 10, and by the discharge zone 216 in the region of the base surface 9. The infeed zone 214 and the discharge zone 216 are not part of the sliding region 2 and therefore do not necessarily follow the spindle geometry. The clearance C corresponds to the formula C=(r−r.sub.P)*2. The K.sub.G slides on the sliding surface 2 on the circle line described by the plane 111.
[0178] FIG. 6 shows the region of the cranial enlargement of the sliding region 201. The height y.sub.G of the cranial enlargement extends between a point of intersection of the normal plane S with the end of the sliding region 2 in the direction of the infeed zone 214 and the point Y.sub.G. In this case, the point Y.sub.G lies on a straight line K.sub.G that intersects L. The straight line K.sub.G extends between the point of intersection X.sub.G of the normal plane S with the end of the sliding region 2 on the outer surface of the spindle 106 and the point Y.sub.G. In this case, the points X.sub.G and Y.sub.G are arranged on a plane which extends through the end points of the sliding region 2. The two points X.sub.G and Y.sub.G are mutually spaced. If the cranial elevation is symmetrical, i.e. the ascent and fall are of the same length and each extend over 180°, then the point X.sub.G is arranged opposite the point Y.sub.G. It is then 180° away from the point Y.sub.G. In the case of an embodiment of this kind, a gentle ascent of the cranial elevation can be achieved. If the ascent or the fall of the cranial elevation are steeper, two points X.sub.G may be provided. The slope of the cranial elevation begins and ends at these points. Between these two points X.sub.G, where no cranial elevation is formed, the implant can be formed so as to be planar and flat, without any elevation or depression. In the preferred embodiment shown, the straight line K.sub.G also intersects the center point of the spindle, and Y.sub.G lies on the outer surface of the spindle. For the height H.sub.G of the sliding region of an implant having a cranial elevation, the following applies: H.sub.G′=H.sub.G+y. The same relations can be created for the cranial enlargement of the implant, proceeding from the height of the implant.
[0179] FIG. 7 shows the region of the cranial lengthening 202 of the implant. The region results between the point Y′ on a straight line K′ and the sectional plane S′. The straight line K′ extends from point X′, which is located on the plane S′ and the outer surface of the spindle 106, to a further point Y′ which is located opposite X′ and represents the maximum of the cranial elevation. In this case, X is located on the opposite side from Y′, i.e. a straight line from X′ to Y′ intersects L. For the height of the implant the following applies: H′=H+x. The region 205 corresponds to the bone contact surface of the outside of the implant in the inserted state. As shown, this region is preferably in parallel with the straight line K′ which shows the maximum dimension of the implant in the region of the base surface. The axis of rotation R of these bone contact surfaces is therefore perpendicular to the straight line K′. An implant of this kind then appears as an implant having a cranial elevation, the inside geometry of which is tilted away from the cranial elevation in the form of a portion of a spindle.
