ZA200304084B

ZA200304084B - Bone implant, in particular, and inter-vertebral implant.

Info

Publication number: ZA200304084B
Application number: ZA200304084A
Authority: ZA
Inventors: Robert Mathys Jr; Beat Lechmann; Beat Gasser
Original assignee: Synthes Ag
Priority date: 2003-05-27
Filing date: 2003-05-27
Publication date: 2004-05-26

Description

. r 1858/PCT 30.1.2001

English translation of the International Patent Application

No. PCT/CH01/00049 “Bone implant, in particular

S intervertebral implant” in the name of Synthes AG Chur

Bone implant, in particular intervertebral implant

The invention relates to a bone implant, in particular an intervertebral implant as claimed in the precharacterising part of claim 1 and to a method for fabricating said bone implant as claimed in the precharacterising part of claim 16.

A bone implant of this type is known from FR-A-2,703,580

ROBERT. This known intervertebral implant suffers from the disadvantages that

A) the surface smoothness of the implant's cover and base faces which are provided with coarse ribs and which will be in contact with the end plates of the adjoining vertebral bodies prevent the new bone tissue from optimally growing onto said surfaces, and that

B) in cases where a filling material is placed in the hollow space of the implant, this material may easily fall out as a result of the surface smoothness of the implant's inner walls.

The discussion of the state of the art as set out above is merely intended to illustrate the background of the invention and does not mean that at the moment of filing the present application or its priority the cited state of the art was actually published or otherwise known to the public.

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The invention is intended to provide a remedy for this. It is accordingly an object of the invention to create a bone implant, particularly an intervertebral implant, having a surface structure which is optimally adapted for permitting new bone to grow onto it.

According to the invention, this object 1s achieved by means of a bone implant which shows the features of claim 1 and of a method which shows the features of claim 16.

The surface roughness according to the invention of at least 2 pm enables a better adherence of the newly grown bone onto the implant, thus permitting a better bone integration.

According to a preferred improvement of the invention, the hollow body is subdivided by at least two partitions, said partitions being preferably braced against one another by ‘means of a transverse brace. These partitions contribute to increase the contact surfaces with the adjacent end plates of the vertebral bodies, thus reducing the surface pressure and preventing the implant from sinking into the adjacent vertebral bodies. In addition, the hollow spaces between the partitions permit the new osseous structure to grow through the implant.

According to another preferred improvement of the invention, the surface roughness is inferior to 10 um. An excessive surface roughness diminishes the efficiency of the remaining points, which in turn may lead to the occurrence of osteolysis and thus have a negative effect on arthrodesis.

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According to another improvement of the invention, the partitions are provided with perforations which preferably have a minimum surface of 3.5 mm2?. The perforations on the lateral walls serve for anchoring the newly grown osseous structure and also for keeping in place any filling material which may have initially been inserted.

According to another preferred improvement of the invention, the lateral segments of the hollow body's lateral area are provided with perforations which preferably have a minimum surface of 3.5 mm?2. The perforations on the lateral segments of the lateral area serve for anchoring and keeping in place the newly grown

Osseous structure and, above all, for holding the implant during the process of insertion.

According to another preferred improvement of the invention, the radiolucent material is selected from the following group: polyaryletherketone (PAEK), polyetherimide (PEI), polyoxymethylene (POM) , liquid crystal polymer (LCP), polymethylpentene (PMP), polysulfone (PSU), polyethersulfone (PESU or PES), polyethyleneterephthalate (PETP), polymethylmethacrylate (PMMA) , and ultra-high molecular weight polyethylene (UHMWPE).

All these preferred materials are resilient but have different mechanical properties such as elasticity (stiffness) and also resistance. Some of them have good creep properties as compared to other polymers or are characterised by a low water absorption. It is thus possible to choose for any application the most adequate material.

According to another preferred improvement of the invention, the radiolucent material is fibre reinforced, the reinforcement material being preferably carbon fibre or

PEEK fibre. The fibre reinforcement of the radiolucent material changes its mechanical properties and leads to a stiffening, said stiffening taking effect on the material either in a general or in a specific manner.

According to another preferred improvement of the invention, the ratio V:v between the total volume V of the bone implant and the volume v of the hollow body is in a range of between 1.9 and 2.3. Experience shows that this ratio is apt to combine the advantages of a mechanically stable implant with a maximum volume of newly grown,

Osseous structure.

According to another preferred improvement of the invention, the surface of the implant is at least partially provided with a radiolucent coating or with a thin coating which does not affect the radiolucency. The advantage of the radiolucent coating is that it gives the surgeon a possibility of observation during the formation of arthrodesis. While pure PEEK is by itself characterised by an excellent biocompatibility, an additional coating with a suitable material may optimise the mechanical properties and the interfaces between the newly grown bone and the implant. Suitable coating materials preferably include metals (with a very small thickness which does not substantially affect the radiolucency of the implant) ,

Particularly suitable metals are titanium, gold or platinum, as well as any other suitable implant metals.

According to another preferred improvement of the invention, the coating consists of a ceramic material, preferably of hydroxyapatite or tribasic calcium phosphate.

Both ceramics, hydroxyapatite and tribasic calcium 5 phosphate, are suitable coating materials and are characterised by the additional advantage that they may be completely integrated into the bone and are even replaced by new, natural bone tissue.

According to another preferred improvement of the invention, the hollow body is at least partially filled with a filling material consisting of calcium phosphate, preferably hydroxyapatite or tribasic calcium phosphate.

This permits to achieve a better, more undisturbed control of the process of arthrodesis. The hollow body may also be filled with a filling material consisting of calcium sulphate, demineralised bone, autologous bone or coralline substances.

According to another preferred improvement of the invention, the hollow body is at least partially filled with a radiopaque filling material consisting of a resorbable, preferably porous polymer. In order to render the filling material radiopaque, X-ray contrast media may be added to the polymer. In the case of PLA, a marker such as zirconium dioxide may be added, whereas PEEK may be treated by the addition of barium sulphate.

According to another preferred improvement of the invention, the perforations which may be present in the implant are at least partially filled with the radiopaque filling material. This prevents the filling material from falling out of the implant.

The method for fabricating a bone implant according to the invention consists in that the annular, hollow body is fabricated by means of an injection moulding, a hot forming or a hot pressing technique. The hot forming process leads to a compacting of the polymer in all its form elements, which results in particular in an improved fatigue resistance.

In the following, the invention and improvements of the invention will be illustrated in greater detail with reference to the partially diagrammatic representation of one embodiment.

In the drawings:

Fig. 1 shows a perspective view of an intervertebral implant according to the invention;

Fig 2 shows a top plan view of the implant of Fig. 1;

Fig. 3 shows a front view of the implant of Fig. 1; and

Fig. 4 shows a side view of the implant of Fig. 1.

The intervertebral implant shown in Figs. 1 to 4 consists of a radiolucent material (PEEK, optionally reinforced with carbon fibres or glass fibres) which is fabricated by injection moulding and shaped in the form of an annular, hollow body 1. It comprises a lateral area 6 shaped in the form of a segment of a hollow cylinder which has a front segment 9, a rear segment 10, as well as two lateral segments 11, and which defines a cylinder axis 7.

The hollow body 1 is subdivided into individual cavities by means of two partitions 3 extending substantially parallel to the cylinder axis 7 and connecting the front segment 9 with the rear segment 10 of the lateral area. The two partitions 3 are braced against each other by means of a transverse brace 4. The partitions 3 are provided with perforations 5 having a surface of about 10 mm2?. The lateral segments 11 of the lateral area 6 are equally provided with perforations 8 having a surface of about 10 mm2.

The surface 2 of the bone implant has a surface roughness of 6 ym and is provided with a thin, radiolucent gold coating.

The ratio V:v between the total volume V of the bone implant and the volume Vv of the hollow body 1 is approximately 2.1.

The hollow body 1 may be filled with a radiopaque hydroxyapatite filling material, special attention being paid to assure that preferably also the perforations 5 and 8 are filled with said radiopaque filling material.

Claims

Co 040037 +24 R 1858/pCT

3.9.2002 English translation of the amendments as annexed to the International Preliminary Examination Report of the International Patent Application No. PCT/CH01/00049 “Bone implant, in particular intervertebral implant” in the name of Synthes AG Chur Claims

1. A bone implant, in : .rticular an intervertebral implant which consists of a radiolucent material and is shaped in the form of an annular, hollow body (1) including a lateral area (6) in the form of a segment of a hollow cylinder which comprises a front segment (9), a rear segment (10), as well as two lateral segments (11), and which defines a cylinder axis (7), whereby the hollow body (1) being subdivided by at least two partitions (3) extending substantially parallel to the cylinder axis (7) and connecting the front segment (9) with the rear segment (10) of the lateral area, characterised in that A) the surface (2) of the bone implant has a surface roughness of at least 2 um; and B) the partitions (3) are provided with perforations (5).

2. A bone implant as claimed in claim 1, characterised in that the hollow body (1) is subdivided by at least two partitions (3), said partitions (3) being preferably braced against one another by means of a transverse brace (4).

3. A bone implant as claimed in claim 1 or 2, characterised in that the surface roughness is inferior to 10 pm.

4. A bone implant as claimed in any of the claims 1 to 3, characterised in that the perforations in the partitions (3) have a minimum surface of 3.5 mm?2.

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5. A bone implant as claimed in any of the claims 1 to 4, characterised in that the lateral segments (11) of the lateral area (6) are provided with perforations (8) which preferably have a minimum surface of 3.5 mm?2.

6. A bone implant as claimed in any of the claims 1 to 5, characterised in that the radiolucent material is selected from the following group: polyaryletherketone (PAEK), polyetherimide (PEI), polyoxymethylene (POM), liquid crystal polymer (LCP), polymethylpentene (PMP), polysulfone (PSU), polyethersulfone (PESU or PES), polyethyleneterephthalate (PETP), polymethylmethacrylate (PMMA), and ultra-high molecular weight polyethylene (UHMWPE).

7. A bone implant as claimed in any of the claims 1 to 6, characterised in that the radiolucent material is fibre reinforced, the reinforcement material being preferably carbon fibre or PEEK fibre.

8. A bone implant as claimed in any of the claims 1 to 7, characterised in that the ratio V:v between the total volume V of the bone implant and the volume v of the hollow body (1) is in a range of between 1.9 and 2.3.

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6. A bone implant as claimed in any of the claims 1 to 5, characterised in that the lateral segments of the lateral area are provided with perforations.

7. A bone implant as claimed in claim 5 where the perforations have a minimum surface of 3.5 mm?.

8. A bone implant as claimed in any of the claims 1 to 7, characterised in that the radiolucent material is selected from the following group: polyaryletherketone (PAEK) , polyetherimide (PEI), polyoxymethylene (POM) , liquid crystal polymer (LCP), polymethylpentene (PMP), polysulfone (PSU), polyethersulfone (PESU or PES), polyethyleneterephthalate (PETP), polymethylmethacrylate {PMMA , and ultra-high molecular weight polyethylene (UHMWPE) .

9. A bone implant as claimed in any of the claims 1 to 8, characterised in that the radiolucent material is fibre reinforced.

10. A bone implant as claimed in claim 9 where the reinforcement material is carbon fibre or PEEK fibre.

11. A bone implant as claimed in any of the claims 1 to 9, characterised in that the ratio V:v between the total volume V of the bone implant and the volume v of the hollow body is in a range of between 1.9 and 2.3.

12. A bone implant as claimed in any of the claims 1 to 11, characterised in that its surface is at least partially provided with a radiolucent coating or with a thin coating which does not substantially affect the radiolucency. AMEDD SHEET

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13. A bone implant as claimed in claim 12, characterised in that the coating consists of a metal, preferably of titanium, gold or platinum.

14. A bone implant as claimed in claim 12, characterised in that the coating consists of a ceramic material, preferably cf hydroxyapatite or tribasic calcium phosphate.

15. A bone implant as claimed in any of the claims 1 to 14, characterised in that the hollow body is at least partially filled with a filling material consisting of calcium phosphate, preferably of hydroxyapatite or tribasic calcium phosphate.

16. A bone implant as claimed in any of the claims 1 to 14, characterised in that the hollow body is filled with a filling material consisting of calcium sulphate, demineralised bone, autologous bone or coralline substances.

17. A bone implant as claimed in any of the claims 1 to 14, characterised in that the hollow body is at least partially filled with a filling material consisting of a resorbable, preferably porous polymer.

18. A bone implant as claimed in any of the claims 5 to 17, characterised in that the perforations which may be present in the implant are at least partially filled with the radiopaque filling material.

19. A method for fabricating a bone implant as claimed in any of the claims 1 to 18, characterised in that the

‘ — J . rd 12 annular, hollow body 1s fabricated by means of an injection moulding, a hot forming or a hot pressing technique.

20. A bone implant substantially as herein described with reference to the drawings. AMENDED SHEET