EP1924225A2

EP1924225A2 - Femoral head cap with combined cemented and cement-free anchoring face for surface replacement prostheses for the hip joint

Info

Publication number: EP1924225A2
Application number: EP06791373A
Authority: EP
Inventors: Joachim Schmidt
Original assignee: Biomet Deutschland GmbH
Current assignee: Biomet Deutschland GmbH
Priority date: 2005-09-12
Filing date: 2006-09-08
Publication date: 2008-05-28
Also published as: WO2007031063A3; DE102005043244A1; WO2007031063A2

Abstract

The invention relates to a femoral head cap (1) for surface replacement prostheses of the hip joint, with an inner anchoring face (6) for securing to the hip joint (2), characterised in that the inner anchoring face (6) has a first section (3) for the cemented anchoring of the femoral head cap (1) to the apical section of the hip joint (2) and a second section (4) for the cement-free anchoring of the femoral head cap (1) to the most cylindrical section of the hip joint. The invention also relates to a method for applying cement to a femoral head cap and to an applicator therefor.

Description

Hüftkopfkappe with combined cemented and cement-free anchoring surface for surface replacement prostheses of the hip joint

The invention relates to a femoral head cap for hip replacement surface prostheses according to the preamble of claim 1, a method of applying cement according to claim 15 and an applicator according to claim 17.

The replacement of a worn or destroyed hip joint (coxarthrosis) with an artificial joint (endoprosthesis) is a globally recognized procedure. Since the beginning of the 1990s, surface replacement prostheses have been used again, in which the machined femoral head is covered with a femoral head cap, which fits exactly into an artificial socket, which is anchored in the pelvic bone. Both partners are made of metal, one speaks of a metal-metal sliding pair. The most currently implanted in Germany surface replacement prosthesis is according to McMinn (Knecht et al., Surface replacement hip replacement, orthopedist 34, 2005, pp. 79-90), but many other similar prostheses are on the market.

Currently, femoral caps are anchored in most cases with bone cement on the machined femoral head. So far there is no standardized cementing technique, so that the anchoring quality of the femoral head cap is very changeable. In addition, it is known that the geometry of the machined femoral head and the Hüftkopfkappe virtually no homogeneous cement penetration can be achieved in the lateral, usually cylindrically shaped surfaces of the machined femoral head. The hematopoietic head failure cases analyzed so far are therefore in most cases based on a lack of cement quality (Morlock, M. et al., Biomechanical, morphological, and histological analysis of early failures in hip resurfacing arthroplasty, Proc.lMechE Vol. 220, Part H: J. Engineering in Median).

An alternative is the cementless anchoring of the femoral head cap with appropriate surface design of the inner anchoring surface of the femoral head cap, as they are also offered in the market.

One way of cementless attachment of a prosthetic element is the use of anchoring elements such as screws, pins, or nails. In DE 69634255 T2 prosthetic elements are described, the be anchored on the joint bone by means of a frusto-conical dome after prior resection of the articular surface.

Overall, however, shows a cementless anchoring of prosthetic elements u.a. in the form of a Hüftkopfkappe in clinical investigations poor results, which is probably related to the lack of blood flow to the femoral head, especially in the apical area by the disease itself (sclerosis, cyst formation, necrosis) and the deterioration of blood flow through surgically created vessel interruptions (McMinn, D. Development of Metal-Metal- Hip Resurfacing, Hip International 13, 1, supp 2, 2003, 41-53).

The invention is therefore based on the problem to provide a femoral head cap, which allows both a good anchorage of the femoral head cap on a machined femoral head and guarantees sufficient blood flow to the femoral head.

This object is achieved by a Hüftkopfkappe with the features of claim 1.

Thereafter, the hip cap according to the invention for surface replacement prostheses of the hip joint on an inner anchoring surface for attachment to the femoral head. The femoral head cap according to the invention is characterized in that the inner anchoring surface has a first region for cement-fixed anchoring of the femoral head cap on the apical portion of the femoral head and a second region for cementless anchoring of the femoral head cap on most cylindrical shaped portion of the femoral head.

The femoral head cap is thus anchored with a portion of the inner anchoring surface with bone cement on the femoral head, while another portion of the inner anchoring surface is anchored cementless on the machined femoral head.

Thus, with the present invention, the advantages of cement fixation are combined with the advantages of cementless fixation. The femoral head cap according to the invention is fixed in the poorly perfused apical area with cement and at the same time ingrowth in the well-perfused lateral, mostly cylindrical portion of the femoral head without cement (osteointegration). Advantageously, the first region of the inner anchoring surface comprises the apical, ie the tip portion of the Hüftkopfkappe located at the tip, while the second region comprises the lateral, cylindrically expiring portion of the femoral head cap.

Thus, therefore, preferably the apical portion of the inner anchoring surface with bone cement and the lateral, mostly cylindrical portion of the inner anchoring surface anchored cementless on the processed femoral head.

Preferably, the first region is bounded by at least one limiting means for cement, in particular a separating strip, coupled to the inner anchoring surface. Advantageously, the at least one limiting means for cement is formed as a closed curve, in particular as a ring, in order to be able to form a seal against the cement compound.

It is also advantageous if the first region is delimited by the second region by the separating strip coupled to the inner anchoring surface as limiting means.

The at least one limiting means is advantageously integrally formed at least partially integrally with the inner anchoring surface, the limiting means preferably being both part of a coating in the first, apical region and in the second, lateral region of the femoral head cap. The at least one limiting means is, however, also advantageously fastened to the inner anchoring surface.

Advantageously, the at least one limiting means is at least partially formed as a separate from the femoral head cap part, which is placed directly on the femoral head before applying the femoral head cap.

The at least one limiting means advantageously has at least partially a round or pointed cross-section. This means that the cross section of the at least one limiting means can be variable over its circumference.

It is also advantageous if the separating strip is designed in the form of a prefabricated ring of polymethyl methacrylate (PMMA) or another material. This separating strip or other structure on the inner anchoring surface between the cement anchoring subarea and the cementless anchoring subarea serves in particular to limit the spread of cement.

It is advantageous if the first region has a shape specially designed for cement anchoring, e.g. is spherical, conical or rounded and / or has surface enlargements. It is likewise advantageous if the first region has a surface structure or coating designed especially for cement anchoring.

The second region of the inner anchoring surface, that is to say the lateral part, likewise advantageously has a shape specially designed for cementless anchoring, such as e.g. a cylindrical or conical shape, and / or anchoring grooves, anchoring bars or surface enlargements of different construction.

Furthermore, the second region of the inner anchoring surface, that is to say the lateral part, advantageously has a surface structure designed especially for cementless anchoring.

In particular, it is preferred if the second region or lateral portion of the inner anchoring surface has a coating designed especially for the cementless anchoring, in particular hydroxylapatite.

On the inner anchoring surface a guide pin is advantageously arranged, which also acts as a centering aid during the operation. The guide pin is preferably installed in the center of the apical portion of the inner anchoring surface and stands out from the inner anchoring surface.

It is also advantageous if, in the first region, in the form of the apical portion of the inner anchoring surface for the cement-fixed anchoring of the femoral head cap, low-viscosity or highly viscous cement, e.g. PMMA, is arranged.

The quality of cement fixation in the apical part can be standardized by means of a special cement applicator and design of the anchoring surface. The osteointegration in the lateral portion can be achieved by special surface design and optionally coating with z. B. hydroxyapatite be optimized. Cement fixation in the apical region ensures immediate stable anchoring of the femoral headcap. This primarily stable anchoring allows for secure bone (osteointegration) growth on the inner surface of the femoral head cap in the cementless anchoring area. If, after 10 to 15 years, there is a cement disruption due to cement aging, the bony, stable, cementless anchoring region provides secure stabilization of the femoral head cap.

To adapt the femoral head cap to the femoral head, the femoral head is first machined using standard milling machines. In this case, the processing of the femoral head with special milling, which are tailored to the partial area of the cement fixation and the partial area of the cementless fixation.

The desired amount of cement for the cement fixation section is then applied to the machined femoral head using a specially designed applicator. Also, the desired amount of cement for the cement fixation subset is introduced into the anchorage surface, particularly the first region of the inner anchorage surface, of the femoral head cap with a specially adapted applicator.

It is essential that a cement wetting of the guide pin is reliably avoided when using the applicator, which is achieved by the special design of the applicator.

The invention will be explained below with reference to the figures in several embodiments. Show it:

Figure 1 is a schematic sectional view of a preferred embodiment of the femoral head cap according to the invention;

Figure 1A is a schematic sectional view of a modification of the embodiment of FIG. 1A;

FIG. 1B shows a schematic sectional view of a modification of the embodiment according to FIG. 1B; Figure 1 C is a schematic sectional view of a modification of the embodiment of Figure 1 with two separator strips.

Figure 2 is a schematic representation of the use of an applicator according to the invention

First embodiment

Figure 1 shows the schematic structure of a preferred embodiment of the inventive Hüftkopfkappe 1 and a schematic frontal section through the hip joint.

The femoral head cap 1 according to the invention is applied to a processed femoral head 2. Hüftkopfkappe 1 has a cap edge 7 and an outer sliding surface 8, which with another prosthetic element, such. an anchored in the pelvic bone art pan, can interact. The inner anchoring surface 6 is divided into the first, apically shaped region 3 and the second, cylindrically expiring region 4.

Only in the apical portion of the femoral head cap 1 as the first region 3 is located between the femoral head 2 and femoral head cap 1 of the bone cement.

In the lateral, second region 4 of the femoral head cap 1 there is a direct contact between the femoral head cap 1 and the femoral head 2 with the second region 4 of the cementless anchoring 4.

Both areas 3, 4 are delimited from one another by the separating strip 5, whereby a spread of the cement from the first area 3 into the second area 4 is prevented. In the described embodiment, the separating strip 5 is integrally formed on the inner anchoring surface 6. Variations of this detail are shown in Figs. 1A and 1B. In the illustrated embodiment, the separator bar 5 has a sharp, here triangular cross-section. The cross section is the same here over the entire circumference of the separating strip. Alternatively, however, the cross section may also be variable, ie the triangular contour may have different angles. It is also possible that the separating strip 5 at least partially has a round cross section, for example the cross section of a circle segment. By this technique, the cement 3 is pressed in the final compression of the femoral head cap 1 on the femoral head 2 in the open Spongiosawaben 10 of the bone and ensures the stable anchorage.

The embodiment according to FIG. 1A essentially corresponds to the embodiment according to FIG. 1, so that reference can be made to the corresponding description.

However, here is the parting strip 5 is not integrally formed on the inner anchoring surface 6, but is designed as a separate component which is inserted in the anchoring surface 6 or placed on the anchoring surface. It is also possible that the separator strip 5 partially inserted and partially hangs up. The separator strip 5 has a round cross section here.

Alternatively or additionally, the separating strip 5 can also be designed as a separate part from the femoral head cap, which is applied to the femoral head 2. This is shown in FIG. 1B. Again, the separator bar 5 has a round cross-section.

In principle, it is also possible for the embodiments of the separating strip 5 according to FIG. 1, FIG. 1A and FIG. 1B to be combined with one another, ie. the separator strip 5 is formed differently at different locations or that two embodiments are combined with each other. Thus, it is possible to provide a first separator strip 5A, which is integrally formed on the inner anchoring surface 6, a second separator strip 5B, which is applied to the femoral head 2 with a larger circumference. Such a combination of separating strips 5A, 5B is shown in FIG. 1C.

At least one of the non-integrally molded separator strips 5 may e.g. be made of PMMA.

Second embodiment

FIG. 2 shows the femoral head cap 1 when filling with bone cement. An adapted to the size of the femoral head cap 1 applicator 11 is placed in the inner surface of the femoral head cap on the separator strip 5 and a precisely defined amount of cement with a cement syringe 12 in the first region 3 of the inner Anchoring surface Hüftkopfkappe 1 injected. It is important to ensure that the guide pin 9 is not wetted with cement.

Subsequently, the applicator 11 and the cement syringe 12 is removed and the filled with bone cement Hüftkopfkappe 1 applied to the machined femoral head 2.

LIST OF REFERENCE NUMBERS

1 femoral head cap

2 femoral head

3 first region of the inner anchoring surface 6

second area of the inner anchoring surface 6

Disconnection Module

inner anchoring surface

cap edge

outer sliding surface

guide pin

10 cancellous honeycombs

11 applicator

12 cement syringe

Claims

claims

1. Hüftkopfkappe (1) for surface replacement prostheses of the hip joint with an inner anchoring surface (6) for attachment to the femoral head (2),

characterized in that

the inner anchoring surface (6) has a first region (3) for cement-anchoring the femoral head cap (1) at the apical portion of the femoral head (2) and a second region (4) for cementless anchoring of the femoral head cap (1) at the most cylindrically shaped portion of the femoral head having.

2. femoral head cap according to claim 1, characterized in that the first region (3) is arranged on the apical portion of the femoral head cap.

3. femoral head cap according to claim 1 or 2, characterized in that the first region (3) by at least one with the inner anchoring surface (6) coupled limiting means (5) for cement, in particular a separating strip is limited.

4. Hüftkopfkappe according to claim 3, characterized in that the at least one limiting means (5) for cement forms a closed curve, in particular a ring.

5. femoral head cap according to claim 3 or 4, characterized in that the at least one limiting means (5) is at least partially integrally formed in the inner anchoring surface (6).

6. femoral head cap according to one of claims 3 to 5, characterized in that the at least one limiting means (5) at least partially on the inner anchoring surface (6) is attached.

7. femoral head cap according to one of claims 3 to 6, characterized in that the at least one limiting means (5) at least partially as one of the femoral head cap (1) separate part is formed.

8. femoral head cap according to one of claims 3 to 7, characterized in that the at least one limiting means (5) has a round and / or pointed cross section.

9. femoral head cap according to one of claims 3 to 8, characterized in that the at least one limiting means (5) in the form of a prefabricated ring of polymethylmethacrylate (PMMA) and / or another material is formed.

10. femoral head cap according to one of claims 3 to 9, characterized in that the at least one limiting means (5) is part of a coating in the first region (3) and / or second region (4).

11. femoral head cap according to one of the preceding claims, characterized in that the first region (3) is shaped specifically for cement anchoring spherical, conical or rounded and / or surface enlargements.

12. Hüftkopfkappe according to any one of the preceding claims, characterized in that the first region (3) has a specially designed for cement anchoring surface structure or coating.

13. femoral head cap according to one of the preceding claims, characterized in that the second region (4) in the lateral, expiring portion of the femoral head cap (1) is arranged.

14. Hüftkopfkappe according to any one of the preceding claims, characterized in that the second region (4) to the first region (3) by the with the inner anchoring surface (6) coupled at least one Begrenzungsmitte! (5) is limited.

15. Hüftkopfkappe according to any one of the preceding claims, characterized in that the second region (4) is cylindrical or conical shaped specifically for the cementless anchoring, and / or anchoring grooves, anchoring bars or surface enlargements of different construction.

16. Hüftkopfkappe according to any one of the preceding claims, characterized in that the second region (4) has a specially designed for the cementless anchoring surface structure.

17. femoral head cap according to one of the preceding claims, characterized in that the second region (4) has a specially designed for the cementless anchoring coating, in particular hydroxyapatite having.

18. femoral head cap according to one of the preceding claims, characterized in that on the inner anchoring surface (6) a guide pin (9) is arranged.

19. femoral head cap according to claim 18, characterized in that the guide pin (9) in the apical portion of the inner anchoring surface (6) is arranged.

20. femoral head cap according to claim 18 or 19, characterized in that the guide pin (9) from the inner anchoring surface (6) protrudes.

21. Hüftkopfkappe according to any one of the preceding claims, characterized in that in the first region (3) for cement-fixed anchoring of the Hüftkopfkappe (1) is arranged low-viscosity or highly viscous cement.

22. A method for applying the cement for cement fixation in a femoral head cap according to one of the preceding claims, characterized in that a defined amount of cement in the first region (3) of the femoral head cap (1) is introduced with a specially adapted applicator.

23. The method according to claim 22, characterized in that no cement wetting of the guide pin (9).

24. Applicator (11) for introducing a defined amount of cement into the first region (3) of the inner anchoring surface (6) of a femoral head cap (1) according to one of claims 1 to 18.