Abstract
The invention describes an implant for wear couples in endoprosthetics, comprising at least one shell, into which an insert, preferably a ceramic insert, is introduced. The insert has 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 insert is therefore designed in the form of a ring or annular structure. 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. Insert for the tribological pairing comprising a spherical sliding partner, the insert 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 height H.sub.G of the sliding region corresponding to 20-80% of the diameter of the sphere to be inserted and/or 50-95% of the height H of the implant, and the maximum diameter D1 of the sliding region being larger than the diameter of the spherical sliding partner to be inserted.
2. Insert according to claim 1 for the tribological pairing, comprising an outside (6), wherein a clamping surface is arranged on the outside, at least in part, by means of which the annular insert can be fastened in a shell, and a first region for introducing the sliding partner, and a second region which limits the reception of the sliding partner.
3. Insert according to either claim 1, wherein the insert is annular and the minimum diameter D2 of the sliding region is smaller than the diameter of the spherical sliding partner to be inserted.
4. Insert according to claim 1, wherein the insert has an axis of rotation R, and wherein the clamping surface of the annular insert is arranged at an acute angle of 10°-20° relative to the axis of rotation R, such that the outside dimensions of the insert in the second region are smaller than in the first region.
5. Implant according to claim 4, wherein the angle of the clamping surface is 18°-18.5°.
6. Insert according to either claim 4, wherein the axis of rotation R is arranged so as to be in parallel with the axis of rotation L, preferably corresponds to the axis of rotation L.
7. Insert according to claim 2, wherein the clamping surface (3) comprises recesses in the form of notches or tangential cuts.
8. Insert according to claim 1, wherein the radius of the circle r describing the spindle torus, the clearance C, and the radius of the sphere of the prosthesis r.sub.P are in the relationship according to Formula I.
C=(r−r.sub.p)*2 (Formula I)
9. Insert according to claim 1, wherein the following applies: 10 μm<C<500 μm.
10. Insert according to claim 1, wherein the insert is ceramic.
11. Insert according to claim 1, wherein the annular insert, preferably the sliding region, is enlarged cranially.
12. Implant comprising at least one shell and an insert according to claim 1.
13. Implant according to claim 12, wherein the shell is made of metal and has a wall thickness of from at least 1 mm to less than 3 mm, preferably less than 2 mm.
14. Implant according to either claim 12, comprising at least two shells, wherein the insert is inserted into a second shell and the second shell is inserted into the first shell.
15. Implant according to claim 13, wherein the second shell is made of plastics materials, preferably polyethylene.
Description
[0104] Advantageous embodiments of the annular insert according to the invention are described in the figures, in which:
[0105] FIG. 1a: is a side view of an annular insert,
[0106] FIG. 1b: is a cross section showing the annular insert according to FIG. 1a,
[0107] FIG. 2: shows an embodiment of an annular insert according to the invention,
[0108] FIG. 3: is a cross-sectional view of an implant according to FIG. 2
[0109] FIG. 4a: shows an embodiment of an annular insert
[0110] FIG. 4b: shows a further embodiment of an annular insert
[0111] FIG. 5: is a cross-section of an example of an implant according to the invention
[0112] FIG. 6: is a cross-section of a further embodiment of an implant
[0113] FIG. 7: is a cross-section of a further embodiment of an implant according to the invention
[0114] FIG. 8: shows 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,
[0115] FIG. 9a-c): shows the geometry of the spindle,
[0116] FIG. 10: shows a preferred embodiment of the implant according to the invention,
[0117] FIG. 11: shows a preferred embodiment of the geometry of the cranial elevation,
[0118] FIG. 12: shows a preferred embodiment of the geometry of the cranial lengthening.
LIST OF REFERENCE SIGNS AND ABBREVIATIONS
[0119] 1 insert [0120] 2 sliding region [0121] 3 outer surface, surface, clamping surface [0122] 4 shell [0123] 5, 109 head, sphere of the prosthesis [0124] 6 outside [0125] 7 clamping surface [0126] 8 implant [0127] 9 base surface [0128] 10 end face [0129] 13 recess [0130] 14 second shell, bipolar shell [0131] 15 receiving chamber, pocket [0132] 16 first pivot point [0133] 17 second pivot point [0134] 18 surface [0135] 19 free space [0136] 20 elevation [0137] 100 contact point [0138] 101, 112 annular contact, contact line [0139] 105 spindle [0140] 106 outer surface of the spindle [0141] 107 portion of the spindle [0142] 108 circle describing the spindle torus [0143] 110 tangent point [0144] 111 sectional plane of the contact line [0145] 112 contact line [0146] 201 region of the cranial elevation of the sliding region [0147] 202 region of the cranial lengthening of the insert [0148] 205 region of the clamping surface (shown in dashed lines) [0149] 212, 212′ circle line (orientation aid) [0150] 214 infeed zone [0151] 216 discharge zone [0152] A distance between the axis of rotation and the center point M of the circle describing the spindle torus [0153] C clearance [0154] D1 maximum diameter of the sliding region, arranged in the first region [0155] D2 minimum diameter of the sliding region, arranged in the second region [0156] E, E′ point of intersection of the spindle outer surface with L [0157] F cross-sectional surface [0158] H height of the insert [0159] H.sub.G height of the sliding region [0160] K straight line describing the cranial elevation [0161] K.sub.G straight line describing the cranial elevation of the sliding region [0162] K′ straight line describing the cranial lengthening [0163] KG spherical sliding partner [0164] L longitudinal axis of the spindle, axis of rotation [0165] L′, L″ axis, in parallel with L, of the circle, describing the spindle torus, through the center point [0166] M center point of the spindle [0167] M′, M″ center point of the circle describing the spindle torus [0168] M.sub.P center point of the spherical sliding partner [0169] r radius of the circle describing the spindle torus [0170] r.sub.P radius of the spherical sliding partner (KG, prosthesis head) [0171] R axis of rotation of the clamping surface [0172] S, S′ planes normal to L [0173] S1, S2 points of intersection of the normal planes S, S′ on the longitudinal axis L [0174] X maximum of the insert or cranial elevation in the direction of the end face [0175] X.sub.G maximum of the sliding region without a cranial elevation in the direction of the end face [0176] X′ maximum of the insert without a cranial lengthening in the direction of the base surface [0177] x height difference of the cranial elevation [0178] Y maximum of the insert of the cranial elevation [0179] Y.sub.G maximum of the sliding region of the cranial elevation [0180] Y′ maximum of the insert of the cranial lengthening [0181] y height difference of the cranial lengthening
[0182] An insert 1 according to the invention is shown in FIG. 1a and FIG. 1b, which insert is part of an implant according to the invention. FIG. 1a is a view of said insert 1 and FIG. 1b is a cross-section thereof along an axis of rotation L according to FIG. 1a. The insert 1 comprises an inner portion of a spindle, 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. An outer surface, preferably clamping surface, 3 is arranged on the outside 6 of the insert 1, by means of which surface the insert can be anchored in a shell 4, 14. The height H of the insert is shown by dashed lines and extends from the end face 10, the first region, to the base surface 9, the second region. The height is between 5 and 20 mm. The axis of rotation is denoted by L.
[0183] FIG. 2 is a cross-sectional view of the insert according to the invention which is formed as an annular insert 1 and is inserted into a shell 4. A prosthesis head 5 is inserted into the annular insert 1. The free space 19, in the form of a recess 13, is visible between the sphere 5, or the sliding partner, and the shell 4.
[0184] FIG. 3 is a cross-section of an annular insert 1 according to the invention inserted in a metal shell 4. The annular insert comprises an inner annular portion, a sphere or a hemispherical sliding region 2. A clamping surface is denoted by reference sign 3. The clamping surface 3 can be designed so as to be circumferential, and thus correspond to the size of the outside 6 of the annular insert 1. In a manner deviating therefrom, the clamping surface 3 can include only portions of the outside 6 and be of different shapes. It is also possible for recesses or interruptions (not shown) to be present in the clamping surface 3.
[0185] FIG. 4a) shows an annular insert 1 having a cranial elevation which is achieved a continuous incline of the first region, the end face 10 of the annular insert 1, and which is of height x. In this case, the center point of the sliding surface 2 is located on the plane formed by the end face 10.
[0186] FIG. 4b) shows an annular insert 1, the cranial elevation of which is achieved by a balcony-like protrusion or a shaped projection of height x, the inside of the cranial elevation being a continuation of the sliding region 2, of the hemispherical receiving chamber or the inside 2 of the annular insert 1.
[0187] FIG. 5 shows an annular insert 1 which is introduced into a receiving chamber 15, a pocket of a second shell 14. The inside shape of the receiving chamber 15 corresponds to the outside shape of the annular insert 1. Both shapes are matched to one another such that the annular insert 1 can be received in the receiving chamber 15 of the second shell 14 in a force-fitting and/or anti-turn manner. In this case, the receiving chamber 15 comprises a surface 18 which limits the introduction of the annular insert 1. In the mounted state, the surface 18 of the receiving chamber 15 and the base surface 12 adjoin one another.
[0188] FIG. 6 shows an annular insert 1 which is introduced into a second shell 14 in a force-fitting manner, said second shell 14 not comprising any means for limiting the insertion depth of the annular insert 1.
[0189] FIG. 7 shows an implant according to the invention which comprises an annular insert 1, a second shell 14, and a shell 4. The center point 16 of the inside 2 of the sliding region of the annular insert 1, the first pivot point 16, is arranged so as to be at a distance from the second pivot point 17 of the shell 14.
[0190] FIG. 8a) schematically shows the most likely locations of friction of a conventional insert, FIG. 8b) shows this for a conventional annular insert, and FIG. 8c) shows this for an implant according to the invention comprising an annular insert. In the case of a known semicircular insert, the contact point 100 is positioned between the insert and KG, on the base of the insert. In the case of a known annular insert, the contact 101 (FIG. 8b) is located between the insert and the KG, on a 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 insert 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. 8c).
[0191] FIG. 9 shows the determination of the inside geometry of the insert according to the invention. The spindle torus 105 in FIG. 9a) 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 in the points E and E′.
[0192] In FIG. 9b) the determination of the portion 107 is made clear. The portion 107 of the spindle is located in a half 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 E′, 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 KG to be inserted. D2 is smaller than the diameter of the KG to be inserted, as a result of which (in the case of an annular insert) the KG is prevented from falling out.
[0193] FIG. 9c) shows the sectional plane 111 of the contact line 112 between the KG 109 and the implant 1, on the sliding surface 2 thereof, according to the outer surface of the spindle 106.
[0194] The contact line 112 corresponds to a sectional plane 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 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 insert and away from the base surface 9.
[0195] FIG. 10 shows the height H.sub.G of the non-hemispherical sliding region 2, shown on an annular insert 1 having KG 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 KG slides on the sliding surface 2 on the circle line described by the plane 111.
[0196] FIG. 11 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 insert 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 insert 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 insert, proceeding from the height of the insert.
[0197] FIG. 7 shows the region of the cranial lengthening 202 of the insert. 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 clamping surface of the insert. As shown, this region is preferably in parallel with the straight line K′ which shows the maximum dimension of the insert in the region of the base surface. The axis of rotation R of this clamping surface is therefore perpendicular to the straight line K′. An insert of this kind then appears as an insert 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.
