# Patent

## Title
Intervertebral prosthesis or disk prosthesis

## Abstract

An intervertebral prosthesis or disk prosthesis comprising a front side, a rear side, an upper side which can be placed on the base plate of vertebral body, a lower side which can be placed on the base plate of a vertebral body, a right side, a left side, a cavity which can receive a fluid hydraulic osteocementum, an opening in the cavity and several outlets out from the cavity. The total of the transversal surfaces of the outlets SV on the front side, the total of the transversal surfaces of the outlets SH on the rear side, the total of the transversal surfaces of the outlets SR on the right side and the total of the transversal surfaces of the outlets on the left side satisfy the following conditions: SL>SR or SR>SL or SH>SV or SV>SH.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 14/638,196, filed on Mar. 4, 2015, which is a continuation of U.S. application Ser. No. 11/587,723, filed on Sep. 4, 2007, which is a national stage entry pursuant to 35 U.S.C. §371 of International Application No. PCT/CH04/00250. Each of the above applications is hereby incorporated herein by reference in its entirety.


FIELD
The invention relates to an intervertebral prosthesis or disk prosthesis, especially for arthrodesis surgery by means of dorsal access PLIF (posterior lumbar interbody fusion), TLIF (transforaminal lumbar interbody fusion), ELIF (extraforaminal lumbar interbody fusion), ALIF (anterior lumbar interbody fusion) and ACIF (anterior cervical interbody fusion. The objective of this surgical technique is the treatment of a degenerated or otherwise diseased intervertebral disk. The surgeon looks for access to the intervertebral disk through a centrally placed skin incision. Subsequently, he exposes the rear region of the movement segments, especially the laminae and the pedicle entry points. By means of a partial resection of the facettal and laminar components, the surgeon aims past the nerve roots and the medullary space in the direction of the diseased intervertebral disk.
BACKGROUND
For this surgical technique, only a limited amount of autologous spongiosa is available for filling the cavities of cage-like intervertebral or disk prosthesis and the spaces between individual implants and their surroundings. In the long term, the arthrodesis takes place not with the implant but between the bone and the bone replacement material. The individual implants therefore function only as place holders or spacers.
The intervertebral spaces, supplied with the known intervertebral implants, therefore frequently do not attain complete arthrodesis, that is, they end in a pseudoarthrosis. The situation is much the same also with cage-like intervertebral implants for the cervical spine, as well as for those, which were inserted through ventral entrances. Such intervertebral spaces are not stable mechanically, as would have been expected from a stiffening. The consequences then may be recurring pain with subsequent revision surgery.
For the implants and surgical techniques described above, the surgeon uses autologous bone material, which he obtains from the resected parts of the vertebral body or by means of an additional intervention in the crest of the ilium. Since dorsal accesses to the intervertebral disk space are very narrow, the applying of bone material is made difficult. The surgeon is unable to ensure that the whole of the intervertebral space is filled with autologous bone material. There is therefore the danger that empty spaces will result which, on the one hand, permits migration of the implant. On the other hand, the spaces, not filled with autologous bone material, are filled by a soft, fibrous tissue.
SUMMARY
It is an object of the invention to provide an intervertebral prosthesis or a disk prosthesis, which makes an asymmetric emergence of the osteocementum possible, so that individual regions between the vertebral bodies (for example the central and posteriors zones) are automatically supplied with more osteocementum than other regions.
This objective is accomplished by an intervertebral prosthesis or disc prosthesis, for which the outlet openings are dimensioned differently in size. The amount of osteocementum KL, emerging through SL is either larger or smaller than the amount of osteocementum KR emerging through SR; or the amount of osteocementum KH, emerging through SH, is larger or smaller than the amount of osteocementum KV emerging through SV.
In other words, the outlet openings are dimensioned so that, when flowable osteocementum is supplied through the inlet opening into the cavity, the amount of osteocementum KL emerging through SL is either larger or smaller than the amount of osteocementum KR emerging through SR or the amount of osteocementum KH, emerging through SH, is larger or smaller than the amount of osteocementum KV, emerging through SV.
The invention permits the intervertebral space to be filled with synthetic bone material (osteocementum) after the cage-like intervertebral prosthesis or disk prosthesis has been placed. The implant is secured by the emergence and subsequent curing of the flowable, hydraulic osteocementum. Due to the asymmetric arrangement of the outlet openings in the implant, the osteocementum can be spread selectively. The inventive prosthesis furthermore has the advantage that it makes superfluous the additional removal of bone at the crest of the iliac, which can cause long enduring pain.
In a special embodiment, the inlet opening is provided in the front side of the prosthesis and the cavity extends from the inlet opening in the direction of the rear side.
In the case of a further embodiment, the inlet opening is disposed in the left all right side of the prosthesis and the cavity extends from the inlet opening in the direction of the opposite right or left side.
In the case of a further embodiment, the cross section of the cavity decreases at least on a partial section as the distance from the inlet opening increases. Due to the tapering of the cavity, the liquid cement mixture flows more easily through the side openings of the implant. The wall of the implant in the opening opposite the injection point has a shearing-off edge, so that the liquid cement mixture is diverted.
In the case of a further embodiment, the cavity tapers, at least on a partial section, either in wedge-shaped or conical fashion. In the case of a further embodiment, the upper and lower sides converge in the direction of the front side at least on a partial section. In yet another embodiment, the prosthesis is filled at least partially with a cured hydraulic osteocementum, which extends at least partially beyond the outlet opening.
In the case of a further embodiment, the implant may consist of two intervertebral prostheses, which are disposed next to one another, the right side of the intervertebral prosthesis disposed on the left being oriented in the direction of the left side of the intervertebral prosthesis disposed on the right. For the intervertebral prosthesis disposed on the left, the condition SL>SR applies and for the intervertebral prosthesis on the right, the condition SR>SL.
Moreover, the intervertebral prosthesis may be varied in many ways, for example, by using flat, concave, convex or also spherical side walls.
Calcium phosphate cements, which, after the two components are mixed, may be injected in liquid form into the implant and are subsequently cured hydraulically, are suitable as flowable hydraulic osteocementum.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention and further development of the invention are described in even greater detail by means of several examples and partially diagrammatic drawings, in which
FIG. 1 shows a perspective view of an inventive, lens-shaped intervertebral implant,
FIG. 2 shows a longitudinal section through the intervertebral implant of FIG. 1 along the central plane VIII-VIII,
FIG. 3 shows a side view from the right of the intervertebral implant of FIG. 1,
FIG. 4 shows a side view from the left of the intervertebral implant of FIG. 1,
FIG. 5 shows a perspective view of an inventive intervertebral prosthesis, which is secured by means of cured osteocementum,
FIG. 6 shows a plan view of the intervertebral prosthesis of FIG. 5,
FIG. 7 shows a perspective view of a variation of the embodiment, using two intervertebral implants, the osteocementum securing the implant in their position relative to one another as well as to prevent migrating apart,
FIG. 8 shows a plan view of the two intervertebral implants of FIG. 7,
FIG. 9 shows a front view of a variation of the embodiments, in which the perforated intervertebral implant has a rectangular cross section and
FIG. 10 shows a front view of a variation of the embodiment, in which the perforated intervertebral implant has a circular ring-shaped cross section.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The intervertebral prosthesis 1, shown in FIGS. 1 and 2, consists of a rectangular hollow body and has a front side 2, a rear side 3, an upper side 4 suitable for positioning against the baseplate of a vertebral body, a lower side 5 suitable for positioning against the baseplate of a vertebral body, a right side 6, a left side 7, a cavity 8 suitable for accommodating a flowable, hydraulic osteocementum, an inlet opening 9 into the cavity 8 and several outlet openings 10; 11; 12; 13 from the cavity 8. The upper side 4 and the lower side 5 converge toward the front side 2 as well as toward the rear side 3, so that a lens-like configuration of the intervertebral prosthesis results.
As can be seen from FIG. 2, the cross section of the cavity 8 decreases in the shape of a cone as the distance from the inlet opening 9 increases.
As shown in FIG. 3, there are three outlet openings 12 with areas F1, F2 and F3 in the right side 6 of the intervertebral prosthesis 1, so that the sum SR of the cross sectional surfaces of the outlet openings emerging the right side 6 is SR=F1+F2+F3.
As shown in FIG. 4, there are two outlet openings 13 with the areas F4 and F5 in the left side 7 of the intervertebral prosthesis 1, so that the sum SL of the cross-sectional surfaces of the outlet openings emerging for the left side 7 is SL=F4+F5.
It is important that the sum SL>SR, so that more osteocementum can emerge on the left side 7 of the intervertebral prosthesis 1 from the cavity 8 through the outlet opening 13 into the intervertebral space than from the right side 6.
FIGS. 5 and 6 show how the osteocementum 20, emerging from the right side 6 and the left side 7 of the intervertebral prosthesis 1, is distributed. Because the sum SL of the cross sectional areas of the outlet openings 13 emerging on the left side 7 is larger, the amount of osteocementum 20, emerging on the left side 7 and curing, is also larger than that emerging on the right side 6 and curing.
FIGS. 7 and 8 show a further embodiment, which consists of two inventive intervertebral prosthesis 1, which are disposed next to one another. The two intervertebral prostheses are positioned in such a manner, that the right side 6 of the intervertebral prosthesis 1, which is disposed on the left, is oriented in the direction of the left side 7 of the intervertebral prosthesis 1, which is disposed on the right. For the intervertebral prosthesis 1, disposed on the left, the condition SL>SR applies, whereas, for the intervertebral prosthesis 1, which is disposed on the right, the reverse applies, namely SR>SL. Due to this measure, less osteocementum 20 emerges in the space between the two intervertebral prostheses 1 than emerges to the right side of the intervertebral prosthesis 1 disposed on the right and to the left side 7 of the intervertebral prosthesis 1 disposed on the left.
FIG. 9 shows a variation of the embodiment of an inventive intervertebral implant 1, which has a rectangular cross section and from which a larger amount of osteocementum 40 has emerged on the right side than on the left side.
FIG. 10 shows a further variation of an embodiment of an intervertebral prosthesis 1, which has a circular cross section and for which the amount of osteocementum 40 emerging on the right side through the outlet openings 12 is larger than that emerging on the left side through outlet openings 13.

## Claims

1. A surgical method, comprising:
inserting an intervertebral implant into a disc space between upper and lower vertebrae; and
delivering a flowable material into a cavity of the implant to cause the flowable material to flow asymmetrically out of the implant and into the surrounding disc space through openings formed in the implant;
wherein the implant includes:
a first lateral side being substantially straight and having at least one of the openings formed therein, the at least one opening of the first lateral side having a combined cross-sectional area A1;
a second lateral side being substantially straight and having at least one of the openings formed therein, the at least one opening of the second lateral side having a combined cross-sectional area A2;
wherein A1 is greater than A2 such that delivering the flowable material comprises delivering a greater amount of flowable material through the at least one opening of the first lateral side than through the at least one opening of the second lateral side.

2. The method of claim 1, wherein:
a greater amount of flowable material emerges from a right side of the implant than from a left side, or
a greater amount of flowable material emerges from the left side of the implant than from the right side.

3. The method of claim 1, wherein delivering the flowable material comprises delivering a greater amount of flowable material to a portion of the disc space on one side of the implant than to a portion of the disc space on an opposite side of the implant.

4. The method of claim 1, wherein delivering the flowable material comprises filling the disc space with the material.

5. The method of claim 1, wherein the openings in the implant are dimensioned to automatically supply more of the flowable material to a central zone of the disc space than to other regions of the disc space.

6. The method of claim 1, wherein the openings in the implant are configured to automatically supply more of the flowable material to a posterior zone of the disc space than to other regions of the disc space.

7. The method of claim 1, wherein the implant has a first end for engaging an insertion tool and a closed second end opposite the first end.

8. The method of claim 1, wherein the flowable material comprises osteocementum.

9. The method of claim 1, wherein delivering the flowable material comprises passing the material through an inlet opening of the implant after the implant is inserted into the disc space.

10. The method of claim 1, wherein the intervertebral implant comprises a first intervertebral implant and wherein the method further comprises:
inserting a second intervertebral implant into the disc space between the upper and lower vertebrae;
delivering a flowable material into a cavity of the second implant to cause the flowable material to flow asymmetrically out of the second implant and into the surrounding disc space through openings formed in the second implant.

11. The method of claim 10, wherein the first and second implants are configured such that a lesser amount of flowable material emerges from the first and second implants in a portion of the disc space disposed between the first and second implants than in portions of the disc space not disposed between the first and second implants.

12. The method of claim 10, wherein:
the first implant is configured to deliver an amount of material from a left side thereof and an amount of material from the right side thereof that is greater than the amount of material delivered from the left side;
the second implant is configured to deliver an amount of material from a left side thereof and an amount of material from the right side thereof that is less than the amount of material delivered from the left side; and
the first and second implants are inserted into the disc space such that they are spaced a distance apart from one another and such that the left side of the first implant faces the right side of the second implant.

13. A surgical method, comprising:
inserting an intervertebral implant into a disc space between upper and lower vertebrae; and
delivering a flowable material into a cavity of the implant to cause the flowable material to flow asymmetrically out of the implant and into the surrounding disc space through openings formed in the implant;
wherein the openings in the implant are configured to automatically supply more of the flowable material to a posterior zone of the disc space than to other regions of the disc space.

14. The method of claim 13, wherein delivering the flowable material comprises delivering a greater amount of flowable material to a portion of the disc space on one side of the implant than to a portion of the disc space on an opposite side of the implant.

15. The method of claim 13, wherein the implant has a first end for engaging an insertion tool and a closed second end opposite the first end.

16. The method of claim 13, wherein delivering the flowable material comprises passing the material through an inlet opening of the implant after the implant is inserted into the disc space.

17. A surgical method, comprising:
inserting an intervertebral implant into a disc space between upper and lower vertebrae; and
delivering a flowable material into a cavity of the implant to cause the flowable material to flow asymmetrically out of the implant and into the surrounding disc space through openings formed in the implant;
wherein the implant is configured to automatically supply more of the flowable material in a posterior direction than in other directions.

18. The method of claim 17, wherein delivering the flowable material comprises delivering a greater amount of flowable material to a portion of the disc space on one side of the implant than to a portion of the disc space on an opposite side of the implant.

19. The method of claim 17, wherein the implant has a first end for engaging an insertion tool and a closed second end opposite the first end.

20. The method of claim 17, wherein delivering the flowable material comprises passing the material through an inlet opening of the implant after the implant is inserted into the disc space.