WO2002064066A2

WO2002064066A2 - Implantable socket for a hip joint endoprosthesis

Info

Publication number: WO2002064066A2
Application number: PCT/EP2002/001422
Authority: WO
Inventors: Hans Ulrich STÄUBLI
Original assignee: Staeubli Hans Ulrich
Priority date: 2001-02-14
Filing date: 2002-02-12
Publication date: 2002-08-22
Also published as: WO2002064066A3; DE10106863A1; DE10106863C2

Abstract

The invention relates to an implantable socket for a hip joint endoprosthesis, comprising a ball socket-type surface (10) and an inner support (19) for a bearing shell that is inserted into the socket. For the purpose of anchoring the socket in the bone, the surface (10) has a pyramid tip-type structure (16) that is produced by incorporating by cutting right-handed thread profiles (12) and left-handed thread profiles (11). The profile height of said thread profiles (11, 12) decreases from the insertion plane (13) of the socket towards the pole region (15).

Description

description

Implantable cup for hip joint endoprostheses

The invention relates to an implantable cup for hip joint endoprostheses according to the preamble of claim 1.

In total hip replacement prostheses, the acetabular cup is also replaced by an artificial cup implanted in the pelvic bone. In most cases, a two-part socket is used today, which consists of a metal socket that is implanted in the bone and a bearing shell that can be inserted into this socket and holds the joint head. The bearing shell is made of a wear-resistant material that has good sliding properties when paired with the rod end.

For the cement-free fastening of the socket in the bone, it is known to provide the surface of the socket with a structure which serves to anchor the socket in the bone. In the so-called screw cups (e.g. EP 0 726 066 A2, DE 94 02 941 Ul) this structure consists of a thread which is formed on the surface of the cup and cuts into the bone substance when the cup is screwed in.

So-called press-in pans are also known, which are pressed into the correspondingly milled acetabulu. The press-in pans have, for example, a cord on the surface (EP 0 381 351 AI) or barb-like projections (US Pat. No. 5,755,799). To ensure that the socket is adequately anchored in the bone and in particular that there is sufficient primary anchoring To ensure the insertion of the pan into the bone, the pan must have a certain oversize compared to the milled acetabulum. As a result, a strong pressure, which is flat in the area of the cord or in the area of the barb-shaped projections, is exerted on the bone tissue, which in the long term can lead to damage to the bone tissue, which affects the growth of the bone on the pan or even to a later loosening of the pan can lead.

The invention has for its object to provide a socket for the hip joint endoprosthesis that can be pressed in with low pressure and ensures stable anchoring, especially primary anchoring.

This object is achieved according to the invention by an implantable cup with the features of claim 1.

Advantageous embodiments and developments of the invention are specified in the subclaims.

By incorporating a right-hand thread profile and a left-hand thread profile into the surface of the pan according to the invention, pyramid-shaped tips are formed which decrease in height from the entry side of the pan towards the pole. The height of the pyramid tips decreases so far that it has decreased to zero before reaching the pole. This leaves an area around the pole of the pan surface free from the pyramid tips. This pole area is preferably flattened, ie has a larger radius of curvature. The surface is thus characterized in particular by three different radii of curvature: the core radius in the area of the thread profiles, ie the radius of the surface J

before in the profile reason; the pyramid tip radius, i.e. the radius of the spherical surface in which the tips of the pyramids or the profile back lie and which is different from the core radius due to the decreasing profile height; the pole radius, i.e. the radius of the flattened pole area.

To insert the cup, the acetabulum of the bone is milled in the peripheral area with a radius that corresponds to the core radius of the surface of the cup. The pan can thereby be pressed in with a slight pressure, the pyramid-shaped tips anchoring themselves increasingly more strongly in the bone tissue against the entrance plane of the pan due to their height decreasing towards the pole. The pyramid tips formed by the opposing threads are offset from one another in the initial direction with a gap, so that there is a strong fixation of the socket against rotation. Likewise, the pyramid tips have a strong asymmetry in the meridian direction due to the opposite thread profiles and the decreasing profile height, so that there is also a strong axial anchoring, which counteracts a loosening of the pan and also causes a high tilt stability of the pan. This good anchoring against rotation, axial movement and tilting occurs directly when the pan is pressed in, so that good primary anchoring is ensured. This stable primary anchoring represents sufficient fixation of the socket when inserting it, so that additional fixation screws can generally be dispensed with.

The formation of the pyramid tips by means of milled or screwed-in thread profiles creates a large structured surface of the cup without the total volume of the cup and thus the required bone resection being significantly increased. The large textured surface and the relatively little bone resection required favors a quick and good ingrowth of the socket in the bone.

The surface of the pan can optionally be coated or surface-treated after machining. A coating is possible, for example, with hydroxyapatite ceramic or titanium plasma. Surface processing can e.g. be carried out by titanium corundum blasting.

The flattening of the surface of the socket in the pole region offers the advantage that a smaller amount of bone has to be removed in this region, which does not contribute to the fixation of the socket.

The inner receptacle of the pan for the bearing shell is designed in a manner known per se with a conical surface, the cone angle of which can be selected in accordance with the material pairing of the pan and the bearing shell in such a way that a self-retaining wedge effect holds the bearing shell in the pan.

In an advantageous embodiment, the inner receptacle of the socket is designed with an anti-rotation device which enables the bearing shell to be inserted in any continuously adjustable rotational position and which fixes the bearing shell in the inserted position against rotation. This is particularly advantageous if the bearing surface of the bearing shell receiving the joint head is not rotationally symmetrical to the central axis of the socket and must be used in a certain orientation, as may be necessary in the case of dysplasia, for example. In this case, too

Pan can be used in any rotational position without having to take into account the later orientation of the bearing pan. Since the bearing shell has no preferred orientation in relation to the pan, the required orientation tion without restriction when inserting the bearing shell into the socket of the pan. The stepless anti-rotation protection of the bearing shell against rotation is preferably effected by circular multiple teeth on the bottom of the inner receptacle of the cup.

The invention is explained in more detail below on the basis of an exemplary embodiment shown in the drawing. Show it

1 schematically shows a side view of the machining of the surface of the pan,

2 in a schematic pole top view of the socket, the arrangement of the thread profiles,

3 is an outline side view of the surface shape,

4 is a pole top view of the pan,

5 is a side view of the pan,

6 shows a plan view of the input side of the cup with a detailed representation of the circular multiple toothing at the bottom of the internal receptacle of the cup and

Fig. 7 an axially cut in the left half

Side view of the pan.

In Fig. 1, the production of the surface of the pan is shown schematically. A pan blank, the surface of which has the shape of a hemisphere or spherical cap, serves as the exit. The surface of this blank is designated 10 in FIG. 1. Left-hand thread profiles 11 and right-hand thread profiles 12 are machined, for example milled, into this surface 10 of the hemispherical blank. The profiles 11 and 12 are worked in with a depth decreasing from the input plane 13 towards the pole 14. The profiles 11 and 12 thus have the greatest profile height in the area of the entrance level 13. The profile height decreases until it has decreased to zero at a certain distance from the pole 14. This results in a pole region 15 in which there are no more profiles 11 and 12. For clarification, only one left-hand thread profile 11 and one right-hand thread profile 12 are shown in FIG. 1. As can be seen from Fig. 2, however, a plurality of threads of such left-hand thread profiles 11 and right-hand thread profiles 12 are incorporated, which are distributed in a uniform division over the circumference of the surface of the pan. The intersecting left-hand thread profiles 11 and right-hand thread profiles 12 each produce pyramid tips 16, the height of which decreases in accordance with the decrease in the profile height from the input plane 13 towards the pole region 15.

This type of machining of the profiles 11 and 12 results in the profile backs and thus the tips of the pyramid tips 16 lying on a spherical surface with a pyramid tip radius, this surface corresponding to the original surface 10 of the blank. The profile base of the profiles 11 and 12 lies on a surface 17 which corresponds to the core of the thread profiles 11 and 12. This

Surface 17 has a core radius which is smaller than the pyramid tip radius of surface 10 due to the profile height decreasing towards the pole. The pole region 15, in which there are no profiles 11 and 12, is then turned off so that this pole region 15 is flattened and has a pole radius which is larger than the radius of the original surface 10 of the blank.

In one embodiment of the pan according to the invention, e.g. about 20 gears of the left-hand thread profiles 11 and 20 gears of the right-hand thread profiles 12 incorporated. These thread profiles 11 and 12 each have a pitch angle of approximately 18 °. The height of the profiles 11 and 12 and thus the height of the pyramid tips 16, i.e. The radial distance between the spherical surfaces 10 and 17 is approximately 0.8 to 1.5 mm in the region of the input plane 13 and decreases continuously to zero up to the pole region 15.

An opening 18 is preferably provided on the pole 14. When inserting the socket, it can be checked through this opening 18 whether the socket with the pole region 15 is seated on the base of the acetabulum. The recess in the opening 18 also has an advantageous medullary decompression effect.

As can be seen from Figures 6 and 7, the pan has an inner receptacle in which the bearing shell, not shown, can be inserted. The receptacle initially has the shape of an inner cone 19 adjacent to the input plane 13. This inner cone 19 serves to hold and axially and radially position the bearing shell, which has a corresponding outer cone for this purpose.

If the bearing shell consists of a hard material, for example ceramic or metal, the bearing shell is preferably held in the inner cone 19 in a self-locking manner. The cone angle of the inner cone 19 and the outer cone of the bearing shell are selected in this case so that self-locking occurs according to the material pairing of the pan and the bearing shell. If the bearing shell consists of a plastic which has a certain elasticity, then an undercut groove 20 is preferably inserted into the inner edge of the inner cone 19, into which the bearing shell engages with a corresponding bead or corresponding projections.

To prevent rotation of the bearing shell in the socket, a circular multiple toothing 22 is formed in a section 21 which adjoins the groove 20 against the base of the receptacle. This circularly arranged multiple toothing 22 preferably consists of a multiplicity of pointed teeth projecting slightly inward and distributed over the circumference in the same division. A flattened bottom 23 of the receptacle adjoins section 21.

The bearing shell can be inserted into the socket of the pan in any continuously rotatable position. If the bearing shell is pressed so far into the receptacle that it engages in the groove 20, the teeth of the toothing 22 press radially into the circumference of the bearing shell and fix it against rotation without play.

In this embodiment, the bearing shell is not fixable on the peripheral edge of the inner receptacle, but at the bottom thereof in the pan. A weakening of the maximum thickness of the bearing shell in the direction of the hip-resulting forces therefore does not occur.

It is obvious that the shape of the pyramid tips 16 formed by the threaded profiles 12 and 13 is determined by the profile cross section of the profiles 11 and 12. If the profiles 11 and 12 have a symmetrical profile cross-section, this results in a pyramid shape that is symmetrical in axial section. If the profiles 11 and 12 have an asymmetrical profile shape, there are different pyramid shapes of the pyramid tips 16. If the profiles 11 and 12 have, for example, a flat profile flank facing the pole 14 and a steep profile flank facing the input plane 13, the result is Pyramid tips 16, which are barb-shaped. The flat profile flanks make it easier to press the socket into the acetabulum, while the steep profile flanks promote the hooking of the socket in the bone and thus, in particular, the primary anchoring.

In order to enable positioning of the pan in a simple manner and with high anatomical precision, the pan can be connected to a navigation or target device. For this purpose, markers (eg light emitting diodes) are arranged on the pan in order to record their position and spatial orientation by means of a detection unit and to evaluate them with the aid of a computer and to display them on a monitor. Using the C-arm modules, the pan can be navigated two-dimensionally and three-dimensionally and brought into the planned position.

LIST OF REFERENCE NUMBERS

10 surface of the blank

11 Left-hand thread profile 12 Right-hand thread profile

13 entrance level

14 pin

15 pile rows

16 pyramid tips 17 surface of the base of the profile

18 opening

19 inner cone 20 groove

21 Section 22 Circular Multiple Teeth 23 Bottom

Claims

claims

1. Implantable cup for hip joint endoprostheses, with a spherical shell-shaped surface and preferably an inner receptacle for one that can be inserted into the cup

Bearing shell, the surface for anchoring in the bone having a structure, characterized in that the structure of the surface is produced by machining left-hand thread profiles (11) and right-hand thread profiles (12), these thread profiles (11, 12) have the same thread pitch and decrease in profile height from the entrance plane (13) of the pan against the pole (14) of the surface.

2. Pan according to claim 1, so that the profile height of the thread profiles (11, 12) decreases towards zero towards the pole (14), whereby a pole region (15) without thread profiles (11, 12) remains free.

3. Pan according to claim 2, so that the surface of the pan is flattened in the pole region (15).

4. Pan according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that depending on the size about 20 threads of the left-hand thread profile (11) and 20 threads of the right-hand thread profile (12) are available.

5. Pan according to one of the preceding claims, characterized in that the thread profiles (11, 12) have a thread pitch angle of approximately 18 °.

6. Pan according to one of the preceding claims, characterized in that the thread back of the thread profiles (11, 12) on a surface (10) with a tip radius, the bottom of the thread profiles (11, 12) on a surface (17) with a Core radius lie and the pole area (15) is flattened with a polar radius, the pole radius being larger than that

Tip radius and the core radius is smaller than the tip radius.

7. Pan according to one of the preceding claims, characterized in that the left-hand thread profiles (11) and the right-hand thread profiles (12) have an asymmetrical thread profile, the flank of this thread profile facing the pole (14) in particular being flatter than that of the input plane (13) facing edge.

8. Pan according to one of the preceding claims, that the surface has a coating or surface treatment.

9. Pan according to one of the preceding claims, that the bearing shell can be inserted into the inner receptacle of the pan in any rotational position and is fixed in a rotationally secure manner.

10. Pan according to claim 9, dadurchgekennzeic hn et that Circular multiple toothing (22) is provided on the inner circumference of the receptacle and engages in the bearing shell to prevent rotation.

11. Pan according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that in the region of the pole (14) a central opening (18) for

Control and medullary decompression is provided.

12. Pan according to one of the preceding claims, d a d u r c h g e k e n n e e c h n e t that the pan is coupled to a navigation device for anatomical positioning.