Increasing the breaking load of ceramic cup inserts for hip joint prostheses by a defined back side collision of the cup insert and acetabular cup

Abstract

The invention relates to an acetabular cup (4) and a cup insert (3) for a hip joint prosthesis (12), wherein the cup insert (3) is coupled to the acetabular cup by means of a clamping cone (5) of a conical clamping device in the equatorial region (7) of the two components (3, 4) and, in the unloaded state of the cup insert (3), a gap (8) is provided between the two components (3, 4) below the clamping cone (5) to the pole (6), said gap being delimited by the radial contours of the two components (3, 4). In order to reduce the tensile stresses in the cup insert, the radial contours of the two components (3, 4) have identical geometric elements in the same order, starling front the lower cone end (9) to the pole (6), and tangential or substantially tangential transitions exist between the geometric elements.

Claims

1. A hip joint prosthesis comprising: a hip socket comprising metal walls; a socket insert comprising a ceramic, said socket insert having a back side; a ball sphere; and a conical clamping connection; wherein the conical clamping connection couples the socket insert to the hip socket in an equatorial region of the socket insert and the hip socket; wherein in an unloaded state there is a gap between the a hip socket surface and a surface of the socket insert facing said hip socket surface; and wherein the metal walls of the hip socket are of a thickness such that when a load is applied to the socket insert the hip socket is flexible and expands, wherein the socket insert on the clamping cone may slide into an interior of the hip socket; and wherein at a transition between a clamping cone and the ball sphere, in each case a rounding radius is present, and R.sub.insert back side (R.sub.ER) is approximately the same as R.sub.socket pole (R.sub.PP), and R.sub.insert rounding (R.sub.EV) is larger than R.sub.socket rounding (R.sub.PV).

2. A hip joint prosthesis according to claim 1, wherein the width of the initial gap between the hip socket and the socket insert in the unloaded state of the socket insert in the region near the conical clamping connection is less than or equal to the width of the gap in the region of a pole thereof.

3. A hip joint prosthesis according to claim 1, wherein the width of the initial gap between the hip socket and the socket insert in the unloaded state of the socket insert continuously increases, starting from the region near the conical clamping connection to a pole thereof.

4. A hip joint prosthesis according to claim 1, wherein the ceramic comprises at least one member selected from the group consisting of aluminum oxide ceramic, zirconium oxide and silicon-nitride.

5. A hip joint prosthesis according to claim 1, wherein the ceramic is a mixed ceramic.

6. A hip joint prosthesis according to claim 5, wherein the mixed ceramic comprises at least one ceramic selected from the group consisting of aluminum oxide and silicon-nitride.

7. A hip joint prosthesis according to claim 1, wherein contact between the hip socket and the socket insert occurs in the back side.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is hip joint prostheses have a modular design according to the prior art.

(2) FIG. 2 illustrates a socket insert according to the present invention.

(3) FIG. 3 illustrates a socket insert according to the present invention.

DETAILED DESCRIPTION

(4) In one preferred embodiment, the gap is an initial gap which is largest in the unloaded state of the socket insert, and which decreases when load is applied to the socket insert, and which is at least partially closed above a certain load, so that contact of the components also occurs beneath the clamping cone. The breaking load of the socket insert is thus significantly increased by a controlled backside contact.

(5) The width of the initial gap between the components in the unloaded state of the socket insert in the region near the cone is preferably less than or equal to the width of the gap in the region of the pole.

(6) Alternatively, the width of the initial gap between the components in the unloaded state of the socket insert continuously increases, starting from the region near the cone to the pole.

(7) The hip socket is preferably made of metal and has thin walls, and thus has a particularly flexible design. As a result, when load is applied to the socket insert the hip socket may expand, and the socket insert on the clamping cone may slide into the interior of the hip socket until, above a certain load, contact of the components also occurs beneath the clamping cone.

(8) The socket insert is advantageously made of ceramic, and is preferably made of an aluminum oxide ceramic or mixed ceramics based on aluminum oxide or zirconium oxide, or a silicon-nitride ceramic.

(9) In one embodiment of the invention, the back side of the socket insert, exactly the same as the internal geometry of the hip socket, has the design of a portion of a ball sphere.

(10) In one embodiment, except for on the clamping cone, the radius R.sub.insert back side (R.sub.ER) of the back side of the socket insert is greater than or equal to the radius R.sub.socket pole (R.sub.PP) of the internal geometry of the hip socket.

(11) At the transition between the clamping cone and the ball sphere, the rounding radius (R.sub.insert rounding) of the back side of the socket insert is preferably equal to the rounding radius (R.sub.socket rounding) of the internal geometry of the hip socket.

(12) One preferred embodiment is characterized in that, at the transition between the clamping cone and the ball sphere, in each case a rounding radius is present, and R.sub.insert back side (R.sub.ER) is approximately the same as R.sub.socket pole (R.sub.PP), and R.sub.insert rounding (R.sub.EV) is larger than R.sub.socket rounding (R.sub.PV), the socket insert is made of aluminum oxide-mixed ceramic, and the hip socket is a thin-walled metal socket.

(13) The following approach is proposed to avoid the above-described problems and to achieve a so-called controlled back-side contact, or also a “controlled base contact”:

(14) The back-side geometry of the socket insert and the internal geometry of the hip socket are coordinated with one another in such a way that on a radial contour, starting from the lower cone end to the pole of the particular component, only tangential or substantially tangential transitions occur between geometric elements the radial contours of the associated components, starting from the lower cone end to the pole, have only identical geometric elements, wherein the dimensions do not have to be the same the initial gap between the components, i.e., in the unloaded state, in the region near the cone is less than or equal to the gap in the region of the pole.

(15) The invention is explained in greater detail below with reference to three figures.

(16) FIG. 1 shows a hip joint prosthesis 12 according to the prior art, having a modular design. The hip joint prosthesis 12 is composed of a shank 1 which is coupled to a ball head 2, and a hip socket 4 which is coupled to a socket insert 3. The shank 1 and the hip socket 4 are generally made of metal alloys, and are joined to the body by ingrowth into the femur and the pelvic bone, respectively. The shank and the hip socket are supports for the ball head 2 and the socket insert 3, respectively. The ball head 2 is rotatably supported in the spherical recess of the socket insert 3 with a degree of freedom of one.

(17) FIGS. 2 and 3 illustrate one preferred embodiment of a socket insert and a hip socket according to the invention for a hip joint prosthesis 12 (see FIG. 1). The socket insert 3 is anchored in the hip socket 4 by means of a damping cone 5. The equatorial region is denoted by reference numeral 7, and the pole is denoted by reference numeral 6. In this embodiment, the back-side geomentry of the socket insert 3 and the internal geometry of the hip socket 4 are designed as ball spheres or portions of ball spheres. At the transition to the damping cone 5, in each case there is a rounding R.sub.EV and R.sub.PV. The radius R.sub.insert back side R.sub.ER of the ball sphere of the back side 11 of the socket insert 3 is slightly larger than the radius R.sub.socket pole R.sub.PP of the internal geometry of the hip socket 4. The rounding radius R.sub.insert rounding R.sub.EV at the socket insert 3 is equal to the rounding radius R.sub.socket rounding R.sub.PV of the internal geometry of the hip socket 4. The resulting gap 8 between the components 3, 4 increases starting from region dose to the lower cone end 9 to the pole 6 of the components 3, 4. The width of the gap 8 is denoted by refence numeral 10.