CA2264720C - Intervertebral implant - Google Patents

Abstract

A hollow cylindrical intervertebral implant with a longitudinal axis (3), a top surface (1) and a bottom surface (2), consisting essentially of a ceramic material displaying a maximum porosity of 30 vol. %, the pores of which are filled with air. The implant according to this invention is characterized in that upon primary fusion during the resorption process it equalizes the distance (corresponding to intervertebral disk height) between two vertebrae while providing adequate fusion and is resorbed by the body after a certain amount of time.

Description

CA 02264720 1999-03-031573 /PCT8/5/98Intervertebral ImplantThis invention relates to an intervertebral implant as specified in claim 1.Intervertebral implants of this type are inserted when, after removal of the intervertebraldisk between two vertebrae especially in the lumbar section of the vertebral column, thesevertebrae are to be fused. One or two such implants are used in each intervertebral space.In EP-B 346.269, FUHRMANN ET AL already describe an intervertebral implant whoseoutside front, end and lateral surfaces are coated with a layer of hydroxyl apatite or aceramic HIP material. The drawback of this earlier implant lies in the fact that the basicbody of the implant consists of typical nonceramic and hence nonresorbable materials.In VS—A—S 306.303, LYNCH describes an intervertebral implant which consists entirely ofa porous ceramic material. The drawback of that earlier implant concept lies, on the onehand, in its low pressure resistance attributable to the relatively high porosity and, on theother hand, in the fact that the implant cannot be filled with bone chips with which to obtainaccelerated bone integration.REPLACEMENT PAGECA 02264720 1999-03-032Another intervertebral implant has been described in EP 505 634 by OKA et al, consistingof a porous ceramic base element with hydrogel deposited in the pores. This earlier implantas well offers insufficient pressure resistance owing to the hydrogelfilled pores.In EP—A-493 698, HARLE describes a bone substitute for filling fault areas, consisting oftwo different, porous, ceramic materials the pores of which are evacuated.Finally, DE-A 44 23 826 by ASAHI describes an artificial ceramic vertebra the porosity ofwhich is maintained by means of a foaming agent.This invention is intended to solve the problem. Its objective is to provide an intervertebralimplant that can hold up to the various pressures to which the vertebral column is exposed,offering a sufficiently large contact surface at the end plates so as to prevent them fromsinking in. It is also designed to permit fastest possible fusion of the two vertebrae as wellas rapid incorporation of the implant with due allowance for the height of the intervertebraldisk prior to its removal. In a subsequent progression, the implant should be fully (or nearlyfully) capable of being replaced by the patient’s own bone growth.The characteristic features of the independent claim 1 provide the enhancements to theimplant referred to above that are necessary to solve the problem.REPLACEMENT PAGECA 02264720 1999-03-033Advantageously, this makes it possible for the implant according to this invention, uponprimary fusion during the resorption process, to equalize the distance (corresponding tointervertebral disk height) between two vertebrae while providing adequate fusion and to beresorbed by the body after a certain amount of time to a point where it is no longerdetectable.Another major advantage of this implant is its transparency to xrays, which avoids artifactsthat would interfere with a diagnosis of the surrounding bone structure.The intervertebral implant may be shaped as a prismatic or as a cylindrical element, with aporosity not to exceed 30% by volume. In one preferred enhanced embodiment of thisinvention, the porosity of the ceramic material is 9 vol.% at the most and preferably notmore than S vol.%. Reduced porosity of the implant provides greater pressure resistancewhich is a fundamental requirement especially in the lumbar section of the vertebralcolumn. In this area, particular importance is attributed to the largest possible contactsurface between the end plate and the implant. Therefore, the wall thickness of the ring-shaped intervertebral implant should be at least 4 mm and preferably at least 6 mm so as toinhibit any penetration, of the implant into the end plates.REPLACEMENT PAGECA 02264720 1999-03-03WO 98/09586 33 PCT/CH96/00303In another preferred embodiment of this invention, the ceramic material has a density value ofgreater than 2.8 and preferably greater than 3.1, which further enhances the pressure resistance ofthe implant.The implant is preferably configured as a hollow, circular cylinder which permits the insertion ofthe patient's own bone chips or similar biocompatible material, thus promoting rapid fusion ofthe implant.In another preferred embodiment of this invention, the top surface and/or the bottom surface ofthe implant is not planar but is provided with grooves and/or ridges extending perpendicular toCA 02264720 1999-03-03WO 98/09586 4 PCT/CH96/00303the axis of the cylinder. Such three-dimensional structuring of the top and bottom surface wouldpermit primary fastening of the implant immediately after its introduction in the intervertebralspace, thus enhancing the positional stability of the implant and the rotational stability of theadjoining vertebrae. The three-dimensional surface structure is preferably in the form of"undulations" (raised reinforcing ridges with distinct radii) in both the longitudinal andhorizontal directions.Depending on where the implant is applied, the top and/or bottom surface extend parallel or inwedge-like converging fashion in relation to each other so as to permit adequate following of thecurvature (lordosis, kyphosis).The implant is preferably provided with a convex top and/or bottom surface which matches theconcave shape of the natural end plates of the vertebrae, to achieve better contact between theimplant and the end plates.The jacket of the intervertebral implant is preferably provided with one or several perforationsprimarily for the purpose of engaging an instrument for manipulating the implant. Theperforations may be located both on the anterior side and in the lateral zone of the implant. Theperforations additionally serve to facilitate primary bone growth through the implant.The positional stability of the implant can be further improved by providing the jacket of theintervertebral implant with a fine, three-dimensional texture which promotes bonding with thebone at an early stage. This textural structure is preferably 0.5 - 1.0 mm deep, with grooves 0.5 to1.0 mm wide. The entire surface of the jacket may be textured in that fashion.For the implant according to this invention, suitable, ceramic materials may be used which havetypically and successfully been used in medicine, except with a porosity as defined by thisinvention, with preference given to polycrystalline ceramics with a foreign-phase content of lessthan 3 and preferably less than 2 % by weight. The pressure resistance of the ceramic materialshould be between 400 and 600 MPa and preferably between 450 and 550 MPa.CA 02264720 1999-03-03WO 98/09586 5 PCT/CH96/00303The following will describe the invention and its enhanced implementations in more detail withthe aid of a partly schematic illustration of an embodiment shown by way of example.Shown in the sole figure isa perspective view of the implant according to this invention.The intervertebral implant illustrated in this one figure consists essentially of a hollow cylinderwith an inner space 8, a longitudinal axis 3, a top surface 1 and a bottom surface 2. Theintervertebral implant is essentially produced from a polycrystalline ceramic material. Theceramic material has a porosity of 5 vol.%, the pores are filled with air. The width of the pores isless than 100 um and preferably less than 50 pm. The foreign-phase content of the ceramicmaterial is 1.5 % by weight. The pressure resistance of the ceramic material is 500 MPa.The top and bottom surfaces 1, 2 serve to provide bone contact with the surface plates of twovertebrae and are configured accordingly. The wall thickness of the intervertebral implant is 7mm, the density of the ceramic material is 3.2. The top surface 1 and the bottom surface 2 are notplanar but are provided with a number of grooves 4 and ridges 5 extending in a perpendicular(i.e. radial) direction relative to the longitudinal axis 3.The top surface 1 and the bottom surface 2 extend in wedge—1ike converging fashion in relation toeach other and have a slightly convex outward curvature.The anterior side of the jacket 6 of the intervertebral implant is provided with a perforation 7serving to accept a manipulating instrument. The jacket is further provided with a three-dimensional surface structure 9 having a depth of 0.75 mm.The following will describe in detail the clinical application of the intervertebral implantaccording to this invention.CA 02264720 1999-03-03WO 98/09586 6 PCT/CH96/00303The implant illustrated in the figure is filled with bone chips (bone grafi or bone substitutes),possibly compressed, grasped with a suitable instrument by insertion in the perforation 7 andintroduced into the appropriately cleared-out intervertebral space with the aid of a distractordevice.

Claims (36)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An intervertebral implant for fusion of vertebrae, the implant being made of a substantially pure porous ceramic material and having a longitudinal axis, the implant comprising:
top and bottom surfaces configured and dimensioned to contact end plates of the vertebrae; and an outer side surface extending substantially from the top surface to the bottom surface, and having a three-dimensional texture for promoting initial stability.

2. An implant as defined in claim 1, wherein the implant has a substantially cylindrical shape extending along its longitudinal axis.

3. An intervertebral implant for fusion of vertebrae, the implant comprising a body made of a substantially pure porous ceramic material, the body having top and bottom surfaces configured and dimensioned to contact end plates of the vertebrae, and the body having an outer side surface extending substantially from the top surface to the bottom surface, the outer side surface having a three-dimensional texture with a depth from 0.5 mm to 1 mm.

4. An implant as defined in claim 1, 2 or 3, wherein the ceramic material has a porosity of less than about 30 vol.%.

5. An implant as defined in any one of claims 1 to 4, wherein pores of the ceramic material are open to air.

6. An implant as defined in claim 5, wherein the pores have a width of less than about 100 µm.

7. An intervertebral implant for fusion of vertebrae, the implant being made of a substantially pure ceramic material having a porosity of less than about 30 vol.% and pores which are open to air, the implant comprising:

top and bottom surfaces configured and dimensioned to contact end plates of the vertebrae, at least one of the top and bottom surfaces being not planar; and an outer side surface extending substantially from the top surface to the bottom surface, and having a three-dimensional texture for promoting initial stability.

8. An implant as defined in any one of claims 1 to 7, wherein the implant has a bore extending from the top surface to the bottom surface and forming an interior for receiving a bone-grafting material.

9. An implant as defined in any one of claims 1 to 8, wherein the ceramic material has a porosity of less than about 5 vol. %.

10. An implant as defined in any one of claims 1 to 9, wherein at least one of the top and bottom surfaces has a plurality of grooves and ridges for promoting initial stability of the implant.

11. An implant as defined in any one of claims 1 to 10, wherein the implant has at least one hole for receiving a surgical instrument for manipulating the implant.

12. An implant as defined in any one of claims 1 to 11, further comprising a jacket having walls with a thickness of at least about 6 mm, for preventing penetration of the implant through the end plates.

13. An implant as defined in any one of claims 1 to 12, wherein the ceramic material has a density of greater than about 2.8 g/cm3.

14. An implant as defined in any one of claims 1 to 13, wherein the ceramic material is polycrystalline.

15. An implant as defined in any one of claims 1 to 14, wherein the ceramic material has an impurity content of less than about 3% by weight.

16. An implant as defined in any one of claims 1 to 15, wherein the ceramic material has a compressive strength from about 400 MPa to about 600 MPa.

17. An implant as defined any one of claims 1 to 16, wherein the ceramic material is radiolucent.

18. An intervertebral implant for fusion of vertebrae, the implant formed of a resorbable material and comprising:
top and bottom surfaces configured and dimensioned to contact end plates of the vertebrae; and an outer side surface extending substantially from the top surface to the bottom surface and having an additional three-dimensional texture added thereto for promoting initial stability, the three-dimensional texture comprising openings on the outer side surface having a depth from about 0.5 mm to about 1 mm.

19. An intervertebral implant for fusion of vertebrae, the implant comprising:
a body made of a resorbable material and having top and bottom surfaces configured and dimensioned to contact end plates of the vertebrae, and the body having an outer side surface extending substantially from the top surface to the bottom surface, the outer side surface having additional three-dimensional texturing added thereto for promoting initial stability comprising openings with a depth from 0.5 mm to 1 mm.

20. An implant as defined in claim 18 or 19, wherein the resorbable material has a porosity of less than about 30 vol.%.

21. An intervertebral implant as defined in claim 18 or 19, wherein at least one of the top and bottom surfaces is not planar, and the implant is formed of a resorbable material having a porosity of less than about 30 vol.%.

22. An implant as defined in any one of claims 18 to 21, wherein the implant has a substantially cylindrical shape extending along a longitudinal axis.

23. An implant as defined in any one of claims 18 to 22, wherein the implant has a bore extending from the top surface to the bottom surface that forms an interior for receiving a bone-grafting material.

24. An implant as defined in any one of claims 18 to 22, further comprising a bore extending from the top surface toward the bottom surface and forming an inner surface, with a wall defined between the outer side surface and the inner surface having a thickness of at least about 6 mm.

25. An implant as defined in any one of claims 18 to 24, wherein the resorbable material has a porosity of less than about 5 vol.%.

26. An implant as defined in any one of claims 18 to 25, wherein the resorbable material has pores that are open to air.

27. An implant as defined in claim 26, wherein the pores have a width of less than about 100 µm.

28. An implant as defined in any one of claims 18 to 27, wherein the three dimensional texture further comprises grooves having a width of 0.5 mm to 1 mm.

29. An implant as defined in any one of claims 18 to 28, wherein at least one of the top and bottom surfaces comprises a plurality of grooves and ridges for promoting initial stability of the implant.

30. An implant as defined in any one of claims 18 to 29, further comprising at least one hole for receiving a surgical instrument for manipulating the implant.

31. An implant as defined in any one of claims 18 to 30, wherein the resorbable material has a density of greater than about 2.8 g/cm3.

32. An implant as defined in any one of claims 18 to 31, wherein the resorbable material is a ceramic.

33. An implant as defined in claim 32, wherein the resorbable material is a polycrystalline ceramic.

34. An implant as defined in claim 33, wherein the ceramic has an impurity content of less than about 3% by weight.

35. An implant as defined in claim 33 or 34, wherein the ceramic has a compressive strength from 400 MPa to 600 MPa.

36. An implant as defined in any one of claims 18 to 35, wherein the resorbable material is radiolucent.