WO2000045750A1

WO2000045750A1 - Hip endoprosthesis in which at least the articular surface of the femoral head is replaced

Info

Publication number: WO2000045750A1
Application number: PCT/EP2000/000184
Authority: WO
Inventors: Hans-Georg Pfaff; Michael Debruyckere
Original assignee: Ceramtec Ag Innovative Ceramic Engineering
Priority date: 1999-02-03
Filing date: 2000-01-13
Publication date: 2000-08-10
Also published as: AU2796500A; DE19904126A1; TW527181B

Abstract

According to the invention, the femoral head is essentially replaced by an artificial head provided in the form of a sturdy ball (7) which is entirely comprised of the same biocompatible material. In addition, the dimensions of the ball (7) are matched to the dimensions of the articular surface (8) of the natural femoral head, and the ball (7) is anchored in the femoral neck bone (17) by means of a pin (22). An artificial socket (1) is implanted in the hip bone (15) if the acetabulum lacks a natural articular surface for the artificial femoral head, otherwise known as the ball (7).

Description

Hip endoprosthesis in which at least the articulation surface of the femoral head is replaced

The invention relates to a hip endoprosthesis according to the preamble of the first claim.

Depending on the degree of wear of a hip joint and the life expectancy of the patient, the bone substance of the joint partner is replaced by prostheses in order to restore the joint function. If the acetabular cup is still intact, the full or partial replacement of the femoral head may be sufficient. In the event of wear that affects both joint partners, a total replacement of both joint partners is required, both by implanting an artificial femoral head and by implanting an acetabular cup. A total replacement in particular leads to a profound intervention in the bone substance with corresponding bone loss. For this reason, attempts have always been made to preserve the bone substance and its viability as far as possible.

From US Pat. No. 3,521,302 it is known to insert a pan in the pelvic bone, which is held by means of a pin cemented in the pelvic bone. The articulation surface of the femoral head is replaced by a cap adapted to the femoral head, which is also fixed by means of a pin cemented into the remaining bone substance of the femoral head. When processing the femoral head to adapt a cap, the supply vessels of the femoral neck are generally largely destroyed. As a result, the supply of the stump of bone under the cap is no longer guaranteed. Particularly in the case of caps with a large coverage of the bone tissue, there is a risk that the bone tissue will regress and the cap will loosen. A prosthesis for the femoral head is known from DE-PS 1 164 019. It has the shape of a hollow sphere, consists of a biocompatible metal and is anchored in the thigh neck with pins welded to its inner surface. When fitting the cap, the pins must be aligned precisely and correctly in relation to the holes due to their position. The head prosthesis is adapted to the bone surface by means of hardenable plastic filled into the hollow sphere. Due to its insulating effect, the plastic is also intended to prevent any corrosive influences between the pin attachments, ie between the welds inside the ball. To fix the prosthesis, a device is required with which it is possible to drill the holes for anchoring the pins in the correct places in the femur neck. The holes penetrate the entire bone, which leads to a corresponding weakening of the bone substance in the three usually provided pins. The filling of the hollow sphere with plastic mass must be done carefully so that no voids are created. In addition, the amount of plastic must be such that the position of the cap, for example by lifting, does not change when it hardens.

The object of the present invention is to present a hip endoprosthesis, the use of which limits bone loss to a necessary minimum, in order to maintain a bone stock, in particular in young patients with a long life expectancy, which can be used in the event of a due reoperation.

The object is achieved with the aid of the characterizing features of the first claim, advantageous embodiments of the invention are claimed in the subclaims.

With the hip endoprosthesis according to the invention it is possible, depending on the stage of wear, to replace the joint partners accordingly. If the acetabulum is in a state that still permits its function as a joint partner, the femoral head becomes essentially replaced in the part that encompasses the articulation surface. The replacement takes place according to the invention by a solid ball which consists entirely of the same, biocompatible material. The dimensions of this sphere are adapted to the dimensions of the articulation surface of the natural femoral head. Compared to hollow balls or caps, a solid ball has the advantage that it cannot deform under loads. In addition, in contrast to caps, extensive coverage of the bone tissue with the disadvantages listed above is avoided. It is fastened with only one pin in the femur neck, so that the bone substance only has to be drilled at one point.

The ball is advantageously attached to the pin by means of a conical plug connection. The attachment of balls by means of conical plug connections in the hip endoprosthesis is easy to handle and has proven itself for years. The conical connector allows the pin to be implanted in the bone first and then the ball to be put on. In contrast to a cap, the ball does not need to be aligned. The pin consists of a cone-shaped pin for attaching the ball and a subsequent anchoring part, which is implanted in the bone.

In a further advantageous embodiment of the invention, the ball has a recess. With this recess, the ball is placed on the neck of the femoral head on the femur neck, which is adapted to the recess. The recess is designed so that when the joint is stressed, in particular perpendicular to the pin, the protruding bone tissue supports the ball against lateral displacement. The shear forces on the pin are reduced and local, one-sided force effects of the pin on the bone are avoided.

A simple to produce and effective shape of the recess is a conical recess in the ball. The attachment of the femoral head to the femur neck is milled accordingly. The cone angle can be the size of the Ball, in particular its diameter, and the available bone substance on which the ball is to be supported. It is in a range from 80 to 170 degrees. A range from 100 to 130 degrees is preferred the hole into which the pin is implanted, with which the ball is attached to the bone

By selecting the size of the ball and the shape of the pin, the prosthesis can be optimally matched to the geometry of the joint to be restored. The center of the ball can lie on the center line of a straight pin. The symmetry of the ball in relation to its recess can also be aligned with the Include an angle of up to 20 degrees between the center line of the anchoring part of the pin inserted in the bone. This deviation then also exists between the center line of the pin and the center line of the anchoring part of the pin

In order to facilitate the insertion and to apply a certain clamping force, the pin inserted into the bone tapers towards its end that faces away from the ball

When anchoring the ball in the femur, it is advantageous if the length and the diameter of the pin anchored in the bone are matched to the dimension of the bone so that the anchoring takes place essentially in the hard bone tissue. The diameter and length of the pin must therefore be based on that Age and body structure of the patient as well as the available bone tissue can be coordinated.Therefore, the dimensions of the pins in adolescents and short stature patients who are not yet fully grown may differ in diameter and length from the dimensions intended for adults with an adult bone structure and a strong stature

In a further advantageous embodiment of the invention, the ball is also made from a biocompatible material. All biocompatible materials can be used in the Prosthetics applicable metals and ceramic materials are called. Since the fastening pin for the ball does not have to be firmly connected to this ball, the choice of the material of the ball can be matched to the respective application, in particular to the material of a pan.

The use of ceramic has proven to be advantageous, particularly when a spherical head has an implanted socket as a joint partner. Endoprostheses in which ceramic is articulated by ceramic have the lowest abrasion rate. Ceramic balls are anchored in the bone with metal pins, since ceramic and metal do not interact with one another that cause corrosion.

In an advantageous embodiment of the invention, the ball can be roughened on its non-articulated surface. In addition or alone, it can carry an osteoconductive layer, for example made of hydroxylapatite, which enables the bone to grow into the ball and thus enable the ball to be anchored particularly well on the bone.

The hip endoprosthesis according to the invention enables the ball to articulate the acetabulum directly when it is still in a suitable state. However, if the acetabulum is also affected by wear or illness, then according to the invention, only the main load area of the acetabulum is replaced by an implanted pan, which then articulates the ball.

To ensure that as little bone as possible is lost and damaged during implantation, the socket is limited to a functional angle between 90 and 170 degrees.

In view of a long life span of the prosthesis, taking into account the age of the patient and the stage of wear, it is advantageous if the material of the surface of the socket articulated by the ball in each case corresponds to the

Ball material is matched that the material pairing is tribologically optimal. Tribologically possible are, for example, pairings between balls made of cobalt chrome and pan inserts made of polyethylene or between ceramic balls and pan inserts made of polyethylene. A tribologically optimal combination of ceramic pans with ceramic heads, as is already known from hip arthroplasty.

The fact that when the socket of the hip endoprosthesis according to the invention is removed from the pelvic bone only the bone substance that is absolutely necessary for an insert, it is advantageous if the surface of the socket inserted into the bone has elements for increasing the tilting stability. For example, webs can be provided for this purpose, which rise in the vertical or almost vertical direction from the plane of the pan inserted into the bones. They are inserted into a correspondingly milled recess in the hip bone.

As with the ball, the pan can also be roughened on the surface to be inserted into the bone. In addition to roughening or alone, it can also wear an osteoconductive layer to facilitate and accelerate waxing in the hip bones.

The invention is explained in more detail using exemplary embodiments.

Show it:

FIG. 1 shows a cup of the hip endoprosthesis according to the invention made of ceramic, cut,

FIG. 2 shows a ball as a prosthesis of the femoral head, cut, 3 shows a ball anchored in the thigh bone by means of a pin, which articulates a socket implanted in the hip bone, and

FIG. 4 shows a prosthesis with a composition of ball and pin as a conical plug connection, the center line of the pin and the axis of symmetry of the ball enclosing an angle of 10 degrees and the implanted ball articulating the acetabulum directly.

In Figure 1, 1 denotes an acetabular cup. In the present exemplary embodiment, it consists of ceramic, for example of high-purity aluminum oxide. However, it can also consist of another biocompatible material such as metal, for example cobalt-chrome, or plastic, for example polyethylene. The choice of material depends on the material of the other joint partner, the prosthesis of the femoral head. It is made in such a way that there is a tribologically optimal material pairing, for example ceramic pan with ceramic head or polyethylene pan with ceramic or metal. The socket 1 has a recess, the functional surface 2, in the form of a spherical cap for receiving the prosthesis of the femoral head, a ball. In the present exemplary embodiment, there are two elements on the surface 3 of the pan 1 inserted into the bones, two webs 4 in the form of circular arcs, which are inserted into correspondingly milled recesses in the hip bone in order to increase the tilting stability of the pan 1.

The surface 3, as shown here in the left half of the figure, can be roughened, as designated by the reference number 5, in order to allow the bone tissue to grow in and thus to better anchor it in the bone. In addition to the rough surface or even without roughening, the surface 3 can be coated with an osteoconductive layer, not shown here, for example hydroxylapatide, which also promotes the ingrowth of the bone tissue. The functional angle 6, which includes the functional surface 2, lies at 100 degrees at the lower end of the claimed angular range.

The prosthesis of the femoral head shown in FIG. 2 is a solid ball 7, which in the present exemplary embodiment consists of ceramic, for example of high-purity aluminum oxide. Other biocompatible materials are also possible, whereby their selection depends on whether the prosthesis of the femoral head articulates the acetabulum directly or a cup. In the latter case, as already mentioned above, attention should be paid to a tribologically optimal material pairing.

The shape of the femoral head prosthesis 7 corresponds to that of the known ball head prostheses. The dimensions of the articulation surface 8 are adjusted to the dimensions of the natural femoral head. It is attached to the thigh bone with a pin. The ball 7 is fastened on this pin by means of a conical plug connection, as is already known from hip arthroplasty. A slightly conical bore 9 is provided for plugging onto the pin.

The ball 7 has a recess 10 which is conical in the present case. It connects to the bore 9 and is arranged symmetrically to this. The imaginary tip 12 of the recess 10 thus lies on the line of symmetry 11 of the ball 7. The Kegeiwinkel 12 can be adjusted to the size of the ball, in particular its diameter, and the available bone substance on which the ball is to be supported. It is in the range of 80 to 170 degrees. A range of 100 to 130 degrees is preferred.

In order to achieve an optimal connection between the ball 7 and the bone tissue, the surface of the recess 10, comparable to the surface of the socket 1, which is anchored in the bone tissue, can be roughened 14 and additionally or instead of the roughening, an osteoconductive layer, not shown here wear. FIG. 3 shows a ball anchored in the femur neck by means of a pin, which articulates with a socket 1 implanted in the hip bone 15. As the following exemplary embodiment shows, compared to a total resection of the femoral neck, only the femoral head is removed except for its conically milled attachment. It is anchored using a pin that is embedded in the hard tissue of the femur. The hole and pin can also penetrate the femur completely. If a new operation is necessary due to bone regression or progressive pathological changes in the bone, there is sufficient bone material available, at least for conventional prosthetics with a shaft inserted into the femur.

As can be seen from FIG. 3, the femoral head on the thigh bone 16 has been severed at the level of its shoulder on the thigh neck 17. A slightly conical bore 21 is made in the femur neck 17 through the tip 19 of the conical milled bone contour 18, centered on its center line 20. A pin 22 is implanted in it, the conically tapered anchoring part 23 is inserted in the bore 21. The end of the pin 22 protruding from the bone is a conical pin 24 on which the ball 7 with its bore 9 is placed.

When the femoral head prosthesis is implanted, the anchoring part 23 of the pin 22 is first driven into the bore 21. Because of its taper, there is a tight fit in the bone. Then the ball 7 with its conical bore 9 is placed on the pin 24 and a slight fit with the pin 24 is achieved by light impacts on the ball. The surface of the recess 10 is supported on the conically milled stump 18 of the femoral neck 17. In particular in the case of loads in which the force acting on the ball 7 is essentially perpendicular to the center line 20 of the pin 22, the force is better introduced into the bone. as if the ball and the bone meet in a plane perpendicular to the center line of the pin. - 10 -

FIG. 4 shows a prosthesis of a femoral head in which the femoral head prosthesis, the ball, articulates the acetabulum 26 directly. The center line 120 of the pin 122 and the line of symmetry 11 of the ball 7 enclose an angle of 10 degrees. In the present exemplary embodiment, the ball 7 corresponds to the ball shown in FIGS. 2 and 3. The shape of the pin 122 implanted in the femur 17 differs from the pin 22 of FIG. 3. The center line 120 of the conical anchoring part 123 forms an angle 25 of 10 degrees with the line of symmetry 11 of the ball 7. The center line of the pin 124, which carries the ball 7, coincides with the line of symmetry 11 of the ball.

The material of the pen consists of a high-strength, biocompatible metal, such as a titanium alloy or an alloy of cobalt, chromium and molybdenum. As with the stems known in hip arthroplasty, which are inserted into the femur itself, the anchoring part 123 of the pin can also be roughened and / or provided with an osteoconductive layer in order to enable better ingrowth in the bones.

Claims

claims

1. Hip endoprosthesis, in which at least the articulation surface of the femoral head is replaced by a spherical prosthesis, the prosthesis being supported outside its articulation surface on the femur neck, characterized in that the femoral head is essentially made up of an artificial head in the form of a solid one , biocompatible material existing ball (7) is replaced, that the dimensions of the ball (7) match the dimensions of the articulation surface of the natural femoral head and that the ball (7) is anchored in the femur neck (17) by means of a pin (22; 122) .

2. Hip endoprosthesis according to claim 1, characterized in that the pin (22; 122) consists of a pin (24; 124) for attaching the ball (7) and an anchoring part (23; 123) for anchoring in the femur (17) and that the ball (7) is attached to the pin (22; 122) by means of a conical plug connection (9, 24).

3 hip endoprosthesis according to claim 1 or 2, characterized in that the ball (7) has a recess (10) and that the ball (7) with its recess (10) on the recess (10) of the femur neck (17) is put on.

4. Hip endoprosthesis according to one of claims 1 to 3, characterized in that the recess (10) in the ball (7) is conical.

5. hip endoprosthesis according to one of claims 1 to 4, characterized in that the recess (10) in the ball (7) includes a cone angle (13) of 80 to 170 degrees, preferably from 100 to 130 degrees.

6. Hip endoprosthesis according to one of claims 1 to 5, that the line of symmetry (11) of the ball (7) and the center line (20) of the pin (22) coincide.

7. Hip endoprosthesis according to one of claims 1 to 5, characterized in that the line of symmetry (11) of the ball (7) and the center line (120) of the anchoring part (123) of the pin (122) enclose an angle of up to 20 degrees.

8. Hip endoprosthesis according to one of claims 1 to 7, characterized in that the anchoring part (23; 123) of the pin (22; 122) tapers conically.

9. hip endoprosthesis according to one of claims 1 to 8, characterized in that the dimensions of the pin (22; 122) so to the dimensions of the

Bone (17) are coordinated and that the anchoring takes place essentially in the hard bone tissue.

10. Hip endoprosthesis according to one of claims 1 to 9, that the ball (7) is made of a biocompatible material.

11. Hip endoprosthesis according to claim 10, characterized in that the material of the ball (7) is ceramic.

12. Hip endoprosthesis according to one of claims 1 to 11, characterized in that the ball (7) is roughened (14) on its non-articulated surface (10).

13. Hip endoprosthesis according to one of claims 1 to 12, characterized in that the ball (7) on its non-articulated surface (10) carries an osteoconductive layer. - 13 -

14. Hip endoprosthesis according to one of claims 1 to 13, characterized in that the ball (7) articulates the acetabulum (26) directly.

15. Hip endoprosthesis according to one of claims 1 to 13, characterized in that the main load area of the acetabulum is replaced by an implanted cup (1) which articulates the ball (7).

16. Hip endoprosthesis according to claim 15, characterized in that the cup (1) has a functional angle (6) of 90 to 170 degrees.

17. Hip endoprosthesis according to claim 15 or 16, characterized in that the material of the ball (7) articulated functional surface (2) of the socket (1) is matched to the material of the ball (7) in such a way that the

Material pairing is tribologically optimal.

18. Hip endoprosthesis according to one of claims 15 to 17, characterized in that the surface (3) of the socket (1) used in the hip bone (15) has elements (4) for increasing the tilting stability.

19. Hip endoprosthesis according to one of claims 15 to 18, characterized in that the surface (3) of the socket (1) used in the hip bone (15) is roughened (5).

20. Hip endoprosthesis according to one of claims 15 to 19, characterized in that the surface (3) of the socket (1) used in the hip bone (15) carries an osteoconductive layer.