AU708593B2

AU708593B2 - Femur component for a hip endoprosthesis

Info

Publication number: AU708593B2
Application number: AU57577/96A
Authority: AU
Inventors: Lutz Claes; Andre Gaechter; Lothar Kinzl; Robert Jun Mathys; Peter Studer
Original assignee: Mathys Medizinaltechnik AG
Current assignee: Synthes Bettlach GmbH
Priority date: 1996-06-03
Filing date: 1996-06-03
Publication date: 1999-08-05
Anticipated expiration: 2016-06-03
Also published as: EP0910315A1; AU5757796A; WO1997046179A1

Description

Femur component for a hip endoprosthesis The invention concerns a femur component for a hip endoprosthesis according to the generic part of patent claim i.

The problem of non-cemented femur components is the poor primary stability, i.e. the initial poor firm anchoring and the lack of the fast bony joining between the surface of the prosthesis and the bones.

Standard non-cementing systems lead to a poorly aimed introduction of the force into the femur since the introduction of the force takes place over the entire, yet mostly distal, 15 prosthesis shaft and thus it is non-physiological. This may lead to a proximal bone resorption and a subsequent instability of the prosthesis.

The present invention provides a femur component for a hip endoprosthesis with a distal end intended for the introduction into the medullary space of the femur, a proximal collar 20 section with a neck, on which a spherical head can be fastened, a shaft section situated between the collar section and the end having a longitudinal axis and a length of L, an anterior lateral surface, a posterior lateral surface, a medial side and a lateral side, wherein A) on the anterior and/or posterior lateral surfaces at least one pocket-shaped depression is provided, which is situated in the proximal third of the shaft section blending into the collar section; B) the anterior and the posterior lateral surfaces converge tapered towards the end; C) the medial side converges tapered towards the end, D) the at least one depression is joined with the proximal zone of the collar section via a groove extending on the surface of the collar section; and E) the individual volume of the at least one depression is 320 to 800 mm C:\WNWORD\JANELLE\SPECI 57577.DOC I I I I Thanks to its geometry and the pocket-shaped depressions, the femur component according to the invention has an improved primary stability and consequently an initial good form-locking and a proximal anchoring. This leads finally to a physiological loading of the femur.

By means of a suitable operating technique or implantation bed preparation an optimum fitting can be achieved with the femur component according to the invention, thus permitting a minimum removal of the femur. The filling of the anterior and/or 1 posterior pocket-shaped depression with spongiosum provides the S S

S

S.

S

0

S

s

*SS@

0 C:\WINWORDUANELLE\SPECI57577.DOC I I J II r possibility of a rapid osseous joining between the surfaces of the prosthesis and the bones. This produces manifold possibilities for the correction and optimising of the initial seating of the prosthesis. The possibility of filling for the purpose of bridging over the missing spongiosum is particularly valuable in the case of osteoporosis.

Further advantageous developments of the invention are characterised in the dependent claims.

The advantages achieved by the invention are essentially that by virtue of the femur component according to the invention a good positive locking fit with proximal anchoring and primary stability is achieved.

The invention and developments of the invention are explained in detail in the following based on partly schematic illustrations of several embodiments. They show in: Fig.l a perspective illustration of a femur component according to the invention; Fig.2 a lateral view of the femur component according to Fig.l with the surrounding femur, and Fig.3 a cross-section along the line III-III in Fig.2.

The femur component illustrated in Figs.l and 2 for a hip endoprosthesis to be secured cement-free has a distal end 1 which is introduced into the medullary space 18 of the femur 19, a proximal collar section 2 with a neck 3 on which a spherical head can be fastened, a shaft section 4 situated between the collar section 2 and the end 1 having a longitudinal axis 5 and a length of L, an anterior lateral surface 12, a posterior lateral surface 13, a medial side 14 and a lateral side 15. On each of the anterior and posterior lateral surfaces 12, 13 a pocket-shaped depression 6 is provided for the purpose of accommodating the spongiosum, which R,4, 2 7 T -r depression is situated in the proximal third of the shaft section 4 blending into the collar section 2.

Instead of such anterior and posterior depressions 6 one depression 6 only may be provided on the anterior lateral surface 12 or only on the posterior lateral surface 13. In any case, several such depressions 6 may be provided anterior and/or posterior. The depressions 6 have an average depth of 0.1 to 6.0 mm, preferably 0.2 to 4.0 mm and extend, measured in the direction of the longitudinal axis 5, on an average 5 to mm, preferably 8 to 50 mm. The volume of the depressions 6 is 320 to 800 mm 3 preferably 330 to 600 mm 3 Laterally measured the proximal boundary 10 of the depression 6 is at a distance of 5 to 60 mm, preferably 8 to 50 mm to the proximal boundary 11 of the proximal zone 8 of the collar section 2.

The depression 6 has a proximal boundary length of 8 to 45 mm, preferably 10 to 35 mm, situated at right angle to the longitudinal axis 5, and a distal boundary length of 4 to mm, preferably 8 to 30 mm, also situated at right angle to the longitudinal axis Both the anterior and the posterior lateral surfaces 12, 13 and the medial and lateral sides 14, 15 converge tapered towards the end 1 of the femur component, resulting in a diminishing cross-section.

The depression 6 is joined with the proximal zone 8 of the collar section 2 via a groove 7 extending on the surface of the collar section 2.

In Fig.2 an anterior groove 7 can be seen. A corresponding groove is provided also for the non-visible posterior depression 6. The grooves 7 have an average cross-sectional area of 4 to 120 mm 2 preferably 8 to 50 mm 2

III

In the proximal third of the shaft section 4, which blends into the collar section 2, in addition to the grooves 7 splines or ribs 9 may be also provided. The advantage of these additional splines or ribs 9 is the form-locking connection between the prosthesis and the femur which can be achieved by this for the purpose of improving the stability. The increase of the surface results in a further macroscopic spongious anchoring. The formlocking leads to an increase of the torsional loading capacity (rotational stability, rotational safety) of the prosthesis.

The additional splines or ribs 9 provide also an additional guiding and consequently an accurate positioning of the prosthesis during the setting process. The splines or ribs 9 converge both in the antero-posterior and in the medio-lateral directions tapered towards the end 1. The ribs may be interrupted by horizontal or oblique notches. During the setting process they serve as cutting teeth and prevent the expansion or bursting of the femur.

In the proximal half of the femur component, containing the collar section 2 and the proximal section of the shaft section 4, a microstructure 16 is provided, which has an average surface roughness of 5 Mm to 1000 gm, preferably of 10 Mm to 600 Mm.

In the distal half of the femur component a microstructure 17 is provided, which has an average surface roughness of 0.5 Mm to 600 gm, preferably of 1 Mm to 400 Mm.

The microstructure 16 in the proximal half is different from the microstructure 17 in the distal half and preferably its structure is coarser.

Since the entire proximal part is used to introduce the force by the implant into the bones and a proximal zone in the region of the depression 6 is provided for support and guiding, an optimisation of the osseous growth behaviour and consequently an osseous integration takes place particularly in this zone I II I due to an appropriate constitution of the surface. This proximal half of the femur component, preferably the collar section 2 and the pocket-shaped depression 6 contained therein, may be coated with a bioactive material, preferably hydroxylapatite. The additional microscopic anchoring achievable by this, in a manner similar to the coarser surface structure in the proximal half, as a superimposition to the macroscopic anchoring, improves the adhesion of the implant and the osseous integration and consequently the long-term stability. The coating with bioactive material leads to an improvement of the secondary stability.

A spherical head can be fastened to the head 3 in a known manner.

The average cross-section of the shaft section 4 in its distal third, containing the end 1, is 25 to 120 mm 2 preferably 40 to mm 2 The femur component may be made from titanium, a titanium alloy, a cobalt-chromium based alloy or a Fe-based alloy.

Claims

2. A femur component according to claim 1, the average depth of the depression being 0.1 to
3. A femur component according to claim 2, the average depth of depression being 0.2 to
4. A femur component according to any one of claims 1 to 3, the average extension of the depression measured in the direction of the longitudinal axis being 5 to 70 mm. A femur component according to claim 4, the average extension of the depression measured in the direction of the longitudinal axis being 8 to C:\WlNWORDUANELLE\SPECIM67577.DOC
6. A femur component according to any one of the claims 1 to 5, the individual volume of the at least one depression being 330 to 600 mm 3
7. A femur component according to any one of the claims 1 to 6, the depression having a proximal boundary length of 8 to 45 mm, situated at right angles to the longitudinal axis, and a distal boundary length of 4 to 40 mm, also situated at right angles to the longitudinal axis.
8. A femur component according to claim 7, said proximal boundary length of the depression being 10 to
9. A femur component according to claim 7 or claim 8, said distal boundary length of the depression being 8 to o. 15 10. A femur component according to any one of the claims 1 to 9, the anterior as well as the posterior lateral surface being provided with a pocket-shaped depression each.
11. A femur component according to any one of the claims 1 to 10, wherein, in 9 20 the proximal third of the shaft section, blending into the collar section, in addition to the grooves splines or ribs are also provided.
12. A femur component according to claim 11, the splines or ribs converging both in the antero-posterior and in the medio-lateral directions tapered towards the end.
13. A femur component according to claim 12, said ribs being provided with horizontal or oblique notches.
14. A femur component according to any one of the claims 1 to 13, the proximal half of the femur component being provided with a microstructure. C:\WINWORDUANELLE\SPECI\57577.DOC A femur component according to claim 14, the collar section and the pocket-shaped depression contained therein being provided with a microstructure.
16. A femur component according to any one of the claims 1 to 15, the distal half of the femur component being provided with a microstructure.
17. A femur component according to claim 16, the microstructure in the proximal half being different from that in the distal half.
18. A femur component according to claim 17, the microstructure in the proximal half having a coarser structure than that in the distal half.
19. A femur component according to claim 14 or 15, the average surface o 15 roughness of the microstructure in the proximal half being 5 pm to 1000 pm. i 20. A femur component according to claim 19, said average surface roughness being 10 pm to 600 im. S 20 21. A femur component according to any one of the claims 1. to 20, the average surface roughness of the microstructure in the distal half being 0.5 gm to 600 lm. *o
22. A femur component according to claim 21, said average surface roughness being 1 jpm to 400 im.
23. A femur component according to any one of the claims 1 to 22, the proximal half of the femur component being coated at least partially with a bioactive material, such as hydroxylapatite. C:\WINWORDUANELLE\SPECI\575 7 7 .DOC 9
24. A femur component according to claim 23, the collar section and the pocket-shaped depression contained therein of the proximal half of the femur component being coated at least partially with the bioactive material.
25. A femur component according to any one of the claims 1 to 24, the average cross-section of the shaft section in its distal third, containing the end, being 25 to 120 mm 2
26. A femur component according to claim 25, said average cross-section being 40 to 80 mm 2
27. A femur component according to any one of the claims 1 to 26, the ,o grooves having an average cross-sectional area of 4 to 120 mm 2 15 28. A femur component according to claim 27, said groove average cross- sectional area being 8 to 50mm 2
29. A femur component according to any one of the claims 1 to 28, wherein, laterally measured, the proximal boundary of the depression is at a distance of to 60 mm to the proximal boundary of the proximal zone. A femur component according to claim 29, said distance being 8 to
31. A femur component according to any one of the claims 1 to 30, the distal boundary of the depression being at a distance of 10 to 100 mm to the proximal boundary of the proximal zone.
32. A femur component according to claim 31, said distance being 15 to
33. A femur component according to any one of the claims 1 to 32, made from titanium, a titanium alloy, a cobalt-chromium based alloy or a Fe-based alloy. C:\WINWORD\JANELLE\SPECI\57577.DOC
34. A femur component according to any one of the claims 1 to 33, the lateral side converging tapered towards the end.
35. A femur component according to any one of the claims 1 to 34, the cross- section of the shaft section diminishing towards the end.
36. A femur component substantially as hereinbefore described with reference to the accompanying drawings. DATED: 8 June, 1999 PHILLIPS ORMONDE FITZPATRICK Attorneys for: 15 MATHYS MEDIZINAL TECHNIK AG C C *p C:\WINWORDUANELLESPECIl57577.DOC