# Patent

## Title
Intervertebral implant

## Abstract

In an intervertebral implant, having an upper part that has a support face for a vertebra and a lower part that has a support face for an adjacent vertebra, on each of which parts engagement elements, which are accessible from one side of the intervertebral implant, for a manipulation instrument are disposed, in order to minimize the structural height of the intervertebral implant upon insertion into an intervertebral space, it is proposed that the upper part and lower part each have protrusions and recesses aimed at the respectively other part, which are offset laterally from one another in such a way that when the upper part has been brought close to the lower part they mesh with one another; and that the engagement elements on the upper part and on the lower part are each disposed in protrusions of these parts in such a way that the engagement elements of the upper part and lower part are located side by side and at least partly overlap in the direction of the height of the intervertebral implant.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 10/998,951, filed Nov. 30, 2004, now U.S. Pat. No. 8,506,634, which is in turn a continuation of U.S. application Ser. No. 10/018,402, now U.S. Pat. No. 6,936,071, which was a national stage application based on International Application Serial No. PCT/EP99/04628, filed Jul. 2, 1999.


BACKGROUND OF THE INVENTION
The invention relates to an intervertebral implant, having an upper part that has a support face for a vertebra and a lower part that has a support face for an adjacent vertebra, on each of which parts engagement elements, which are accessible from one side of the intervertebral implant, for a manipulation instrument are disposed, in order to minimize the structural height of the intervertebral implant upon insertion into an intervertebral space.
One such intervertebral implant is known for instance from U.S. Pat. No. 5,314,477. This intervertebral implant is used to replace a disk removed from the intervertebral space, and accordingly the intervertebral implant must have a relatively low structural height, since it has to fit into the gap between vertebrae. This is particularly difficult if an additional pivot insert is also embedded between the upper part and the lower part, as is the case in the known intervertebral implant of U.S. Pat. No. 5,314,477.
But even in two-piece intervertebral implants, difficulties also arise, especially if the implants also have pins and other protrusions on their support faces that are intended for anchoring the intervertebral implant in the bone. Often, these parts can be inserted only by widening the intervertebral space greatly. Not only is this difficult, but it also presents the risk of injuries.
Since the intervertebral space has a relatively low height, it is also difficult for engagement elements that a manipulation instrument can engage to be secured to both parts of the intervertebral implant. It is conventional to have such manipulation instruments engage the upper part and the lower part separately, for instance by means of pins that are inserted into bores on the upper part and lower part, so that with the manipulation instrument, the two parts of the intervertebral implant can be inserted into the intervertebral space and can optionally also be varied in terms of their spacing from one another, thereby allowing a certain spreading open of the intervertebral space. In this respect, reference is made to the pincerlike manipulation instrument of U.S. Pat. No. 5,314,477.
Because of the strong forces, it is necessary to provide a certain structural height for the engagement elements; for instance, the receiving bores must have a certain diameter. This dictates a minimum structural height for the upper part and for the lower part, and in conventional intervertebral implants, the structural heights of the upper part and lower part are thus added together, so that even if the upper and lower parts rest directly on one another, a relatively great structural height of the intervertebral implant is still unavoidable.
SUMMARY OF THE INVENTION
It is the object of the invention to embody an intervertebral implant of this generic type in such a way that the minimum structural height is reduced, to make it easier to insert the intervertebral implant into the intervertebral space.
In an intervertebral implant of the type described at the outset, this object is attained in accordance with the invention in that it is proposed that the upper part and lower part each have protrusions and recesses aimed at the respectively other part, which are offset laterally from one another in such a way that when the upper part has been brought close to the lower part they mesh with one another; and that the engagement elements on the upper part and on the lower part are each disposed in protrusions of these parts in such a way that the engagement elements of the upper part and lower part are located side by side and at least partly overlap in the direction of the height of the intervertebral implant.
In such an embodiment, a minimal structural height of the two intervertebral implant parts resting on one another can be attained, since the engagement elements, which cannot fall below a minimal structural height, are each disposed in protrusions of the upper part and lower part, or in other words in the parts of the upper part and lower part that have the greatest structural height. These regions of great structural height are embodied as protrusions, next to which are respective recesses, into which the protrusions of the respectively other part can dip. As a result, on the one hand, the engagement elements for the manipulation instruments are located side by side, and on the other, they can at least partly overlap, so that the total structural height of the parts resting on one another of the intervertebral implant can be reduced markedly compared to conventional intervertebral implants. The result is accordingly an internested arrangement of the upper and lower parts, with maximal exploitation of the available material height.
It is favorable if the engagement elements are insertion openings for pinlike retaining elements of a manipulation instrument; because of the described construction, these insertion openings can have a relatively large diameter and can thus receive strong retaining pins, and nevertheless a relatively low structural height of the intervertebral implant with parts resting directly on one another is obtained.
It is advantageous if the insertion openings extend substantially parallel to the support faces; once again, this prevents an increase in the structural height of the intervertebral implant parts.
In a preferred embodiment, it is provided that the lower part has a central indentation, opposite the lower support face, which indentation is surrounded by a U-shaped edge. Thus with the lower part and upper part resting directly on one another, the indentation serves to receive a protrusion on the upper part.
It is advantageous if the upper part has a central protrusion that fits substantially in complimentary fashion into the indentation; that is, the total volume of the indentation is utilized for the protrusion.
It is also advantageous if the engagement elements of the lower part are disposed on the two ends of the U-shaped edge, or in other words are located on the outside.
Conversely, the engagement elements of the upper part can be disposed on the central protrusion of the upper part, or in other words are located farther inward than the engagement elements of the upper part.
In particular, the engagement elements of the upper part can be disposed near the lateral edges of the central protrusion, so that for the upper part as well, the spacing of the engagement elements can be selected to be relatively great; as a result, both the upper part and the lower part can be reliably secured against skewing.
It should already be noted here that the words “lower part” and “upper part” do not necessarily say anything about the installed position of the intervertebral implant in the spinal column; the part called the “lower part” could in fact be above in the spinal column. Therefore, these parts may also be referred to as first and second parts having outer and inner surfaces. What is essential is merely that the upper part and lower part define the intervertebral implant on opposite sides of the implant.
It is especially advantageous if the upper part and/or the lower part is embodied in substantially platelike fashion; these parts naturally, in accordance with the design of the invention, have protrusions and recesses that are oriented toward the respectively other part. The platelike embodiment, however, leads as a whole to a very low structural height of the intervertebral implant.
In a preferred embodiment, the lower part and the upper part each have a respective receptacle for a pivot insert. This pivot insert, which is placed between the upper part and lower part after the insertion of the intervertebral implant, supports the upper part and lower part against one another; it takes on a resilient function, for instance, and furthermore leads to a certain pivotability of the two parts of an intervertebral implant relative to one another, so that a pivotability of the adjacent vertebra is thus attainable as well.
In particular, it is advantageous if the pivot insert has at least one spherical support face, which engages the correspondingly spherically shaped receptacle.
It is favorable if the spherical receptacle is disposed in the central protrusion of the upper part.
It is also advantageous if the central indentation of the lower part forms the receptacle for the pivot insert.
According to a preferred embodiment of the invention, it is provided that the pivot insert can be inserted from the side into the receptacle, which has the engagement elements for a manipulation instrument. This is the side from which the upper part and lower part are introduced into the intervertebral space, and it is also from this side that the pivot insert can then be thrust between the already-inserted parts of the intervertebral implant.
It is favorable if the pivot insert is insertable into the receptacle along a guide.
In that the insert as well is preferably embodied substantially in platelike fashion.
An especially favorable design is obtained if the insert substantially completely fills up the central receptacle and with its spherical support face protrudes from the receptacle.



BRIEF DESCRIPTION OF THE DRAWINGS
The ensuing description of preferred embodiments of the invention serves in conjunction with the drawing to provide further explanation. Shown are:
FIG. 1: a perspective exploded view of an intervertebral implant with an upper part, a lower part, and a pivot insert that can be inserted between them;
FIG. 2: a perspective exploded view of the upper part and the lower part of the intervertebral implant, without an inserted pivot insert;
FIG. 3: a view similar to FIG. 2 with the pivot insert inserted into the lower part;
FIG. 4: a perspective view of the upper part and the lower part of the intervertebral implant with maximum mutual proximity;
FIG. 5: a front view of the intervertebral implant of FIG. 4;
FIG. 6: a perspective view of the intervertebral implant with the pivot insert inserted; and
FIG. 7: a cross-sectional view of the intervertebral implant of FIG. 6.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The intervertebral implant 1 shown in the drawing includes three parts, namely a platelike upper part 2, a platelike lower part 3, and a substantially platelike pivot insert 4. In plan view, the implant, although having rounded corners, is generally rectangular.
The upper part 2 is embodied flat on its top, thus creating a support face 5, on which various kinds of protrusions 6, 7 are disposed which serve the purpose of anchoring the upper part 2 in a vertebra that rests, with its end face toward an intervertebral space, on the support face 5. As is most evident from FIG. 5, the height of each smaller protrusion 7 is not greater than its width.
The upper part 2 is substantially rectangular in cross section; in the exemplary embodiment shown, a longitudinal edge 8 curves outward.
On the two short sides of this rectangle, the thickness of the platelike upper part 2 is less than in the central region, so that along the short sides of the upper part 2, downward-pointing recesses 9 each extending parallel to these edges are formed that are open toward the outside. The central region of the upper part 2 is located between the two recesses 9 and thus has a greater thickness or height and thus forms a downward-pointing protrusion 10 embodied between the two recesses 9. This protrusion is defined by an underside 11, which extends substantially parallel to the support face 5 and in which there is a spherical indentation 12, which forms a bearing plate for the pivot insert 4.
The lower part 3 of the intervertebral implant 1 is also platelike in embodiment and on its underside has a flat support face 13 with protrusions 14 and 15, which correspond to the protrusions 6 and 7 of the support face 5. On the side remote from the support face 13, the thickness of the lower part 3 is less in the central region than in an outer region. This outer region of greater thickness has the form of a U, with two parallel legs 16, 17, which extend parallel to the short edges of the lower part 3, which in cross section is embodied similarly to the upper part 2, and with a crosspiece 18 that connects the two legs 16 and 17 on one end. The region enclosed by the legs 16 and 17 and the crosspiece 18 forms a central indentation 19, whose area is substantially equivalent to the area of the central protrusion 10 of the upper part 2, while the disposition and length of the legs 16 and 17 correspond essentially to the disposition and length of the recesses 9 on the upper part 2. As a result, it is possible to place the upper 2 and lower part 3 on one another in such a way that the central protrusion 10 of the upper 2 dips into the central indentation 19, while the legs 16 and 17 of the lower part 3 dip into the recesses 9 of the upper part 2 (FIG. 4); in this position, the upper part 2 and lower part 3 have maximum proximity to one another and a minimal structural height.
The dimensions are selected such that the various recesses are essentially filled completely by the protrusions dipping into them.
Blind bores 20 and 21 are machined into the two legs 16 and 17 of the lower part 3, extending parallel to these legs 16, 17 from their free ends; the diameter of these bores is relatively great in proportion to the height of the legs 16, 17, and this diameter is in fact greater than the thickness or height of the lower part 3 in the region of the central indentation 19.
Blind bores 22 and 23, which extend parallel to the blind bores 20 and 21 in the lower part 3, are machined into the central protrusion 10 of the upper part 2, in the vicinity of its side edges. These blind bores 22 and 23 again have a relatively great diameter, which corresponds to a substantial portion of the height of the protrusion 10 and is greater than the thickness of the upper part 2 in the region of the recesses 9.
When the upper part 2 and lower part 3 rest tightly against one another in the manner described, the blind bores 20 and 21 of the lower part 3 and the blind bores 22 and 23 of the upper part 2 overlap at least partly in the direction of the height of the intervertebral implant 1, as is clearly shown in FIGS. 4 and 5.
The blind bores 20, 21, 22 and 23 serve as receptacles for pinlike extensions of a manipulation instrument, not shown in the drawing, and thus form engagement elements for this manipulation instrument, which in this way separately engages the upper part 2 and the lower part 3. With this manipulation instrument, it is possible to introduce the upper part 2 and the lower part 3 of the intervertebral implant 1 into an intervertebral space; the very low structural height of the intervertebral implant 1 facilitates this introduction, which can be done essentially without major widening of the intervertebral space.
After the introduction of the upper part 2 and lower part 3 in this way, the two parts of the intervertebral implant 1 can be spread apart; that is, their spacing is increased, for instance with the aid of the manipulation instrument that is holding the upper 2 and the lower part 3. Thus, in accordance with the method of operation, the upper and lower parts (or the first and second parts) are first inserted together into the intervertebral space, after which these parts are separated from each other and the insert is inserted between them. Thereafter, these parts are allowed to come together towards each other to engage the insert.
In this spread-open position of the upper part 2 and lower part 3, it is possible to thrust the pivot insert 4 between the upper part 2 and the lower part 3.
This pivot insert is constructed essentially in the shape of a plate, which has a flat underside 24 and a spherically upward-curved top side 25. The outer dimensions of the platelike pivot insert correspond to those of the central indentation 19 in the lower part 3, so that the pivot insert 4 can be thrust into this indentation, filling it up, specifically from the side toward which the blind bores 20, 21, 22, 23 open. Guide strips 26 on the side edges of the pivot insert 4 engage corresponding guide grooves 27 in the legs 16, 17, so that an insertion guide for the pivot insert 4 is formed that fixes it in the lower part 3 after its insertion. The inserted pivot insert 4, after insertion, fills up the indentation 19 and protrudes with its spherically curved top side 25 upward past the top side of the lower part 3; the spherical top side 25 dips in complimentary fashion into the spherically curved indentation 12 on the underside of the protrusion 10, where with the upper part 2 it forms a ball joint, which enables a certain pivotability of the upper part 2 relative to the lower part 3 (FIG. 7).
The pivot insert 4 can have a detent protrusion 28 on its flat underside 24; when the pivot insert 4 is inserted into the lower part 3, this protrusion locks elastically into a detent recess 29 that is located on the bottom of the indentation 19; as a result, the pivot insert 4 is also fixed in the insertion direction in the indentation 19.
The upper part 2 and lower part 3 are preferably made of physiologically safe metal, such as titanium, while the pivot insert 4 preferably comprises a likewise physiologically safe plastic material, such as polyethylene. These support faces 5 and 13 can be embodied in an especially bone-compatible way; for instance, this surface can be roughened by a coating, so that optimal anchoring to the adjacent bone material is obtained.
The invention may also be described as follows, which description is the full equivalent of the preceding discussion. An upper part 2 has an upper surface 5 for engaging a vertebrae and a lower surface which comprises a downward pointing protrusion 10 between side recesses 9 and a rounded portion, preferably in the form of a concave spherical indentation 12. A lower part 3 has a lower surface 13 for engaging a vertebrae. A pivot insert 4, when joined to the lower part 3, as shown for example in FIG. 3, provides a convex upper surface portion 25, preferably spherical, in operational engagement with the rounded portion 12 of the upper part.
The lower part 3 and pivot insert 4 may, taken together, be described as a lower part formed in two pieces, namely the elements 3 and 4, wherein the element 3 may be referred to as a lower piece and the element 4 may be referred to as an upper piece.
The upper and lower parts include on their upper surface and lower surface, respectively, protrusions 6 and 14 which may also be referred to as anchors, which anchor the upper and lower parts, respectively, into the adjacent vertebrae that form the intervertebral space and rest against the respective upper and lower surfaces.
As shown in the figures, the anchors 6 and 14 are each single anchors, preferably extending perpendicular to the respective outer surfaces from which they extend. The anchors may also be referred to as anchor portions and the plane or line along which the anchor or anchor portions extend may be referred to as an anchor line. Each of the anchors 6 and 14 has a zigzag edge which comprises a series of teeth. As best shown in the cross-sectional view of FIG. 7, anchor 6 has at least one section that is greater in height than the remainder of the upper part 2, i.e., from surface 5 to the bottom of protrusion 10, at the section of the upper part where the anchor section meets the surface of the part. Similarly, at least one section of anchor 14 is greater in height than the remainder of the lower part 3 exclusive of its convex portion, i.e., from lower surface 13 to the top of walls 16, 17 and 18. As can be seen from the perspective view of these same parts shown in FIG. 6, anchor 6 is aligned along a single anchor line across surface 5 to form a single anchor plane, this anchor plane having an anchor plane height at least a portion of which is greater than the height of the remainder of the upper part 2 at the section of the upper part where the anchor plane portion meets the surface. Alternatively, or additionally, as best shown in the front view of the parts depicted in FIG. 5, at least a portion (here, at least the facing portion) of anchor 6 is at least substantially equal in height to the overall height of the remainder of the upper part 2, i.e., from surface 5 to the bottom of protrusion 10 with its longitudinal edge 8. Furthermore, as can be seen in the perspective view of these same parts shown in FIG. 4, by virtue of the sloping edge of the anchor 6 at least a portion of the anchor plane height of anchor 6 may be less than the overall height of the remainder of the upper part 2. As also shown in the figures, in the preferred embodiment, the length of the anchors 6 and 14, i.e., in the direction from the anterior to the posterior thereof, is greater than one half of the overall dimension of its respective part from its anterior to its posterior (as defined with reference to the part's anterior posterior orientation in the body upon implantation), passing through that anchor. As also noted in the figures, the vertical height of each anchor 6 and 14 is greater than its width which is the dimension taken horizontally in FIG. 5 or 7. Furthermore, in the illustrated embodiment as shown in FIGS. 5 and 7 the anchors 6 and 14 lie essentially in a common vertical plane in the assembled implant. As best shown in FIG. 7, pivot insert 4 enables a certain pivotability, or articulating motion, of the upper part 2 relative to the lower part 3. Midlines are lines on the outer surfaces passing essentially through the center of the outer surfaces of parts 2 and 3. Such midlines may divide the part into two separate symmetrical halves. In the illustrated embodiment, the common vertical plane of anchors 6 and 14 is located essentially at a midline of the implant which lies in an anterior to posterior plane of the implant, again as defined with reference to the intended orientation of the implant upon implantation. Each anchor 6 and 14 is elongated along the anterior to posterior midline and the width of each anchor straddles the midline.
The lower part comprises three walls including parallel side walls 16 and 17 and a rear wall 18. These walls form between them a central indentation 19 which comprises a recess with a generally flat surface. The fourth side of the recess is open. The pivot insert 4 has a detent 28 that snap-fits into a detent recess 29 formed in the generally flat surface of recess 19.
As best shown in FIGS. 2, 4 and 5, in the absence of pivot insert 4, the protrusion 10 of upper part 2 can fit down between walls 16, 17 and 18 of the lower part 2. This fitting of protrusion 10 within the recess 19, surrounded by walls 16, 17 and 18 may be referred to as “nesting” since the protrusion 10 essentially “nests” within recess 19. With the upper and lower parts in this nested condition, as shown in FIGS. 4 and 5, the combined height of the upper and lower parts 2 and 3, i.e., the height from surface 13 to surface 5, is less than the total additive height of the upper and lower parts, taken separately, i.e., less than the total of the height from surface 13 to the top of walls 16, 17 and 18 plus the height from surface 5 to the bottom of protrusion 10.
To reach its final destination within an intervertebral space, the implant must of course be moved along a path, i.e., an insertion direction from outside of the patient, into the patient, and then into the intervertebral space. In the illustrated embodiment, as described above, instruments would engage apertures 20, 21, 22 and 23 to move implant along a path in an insertion direction. The anchors 6 and 14 are parallel to this path and each defines a single anchor line parallel to this path as the implant is moved into an intervertebral space. Each anchor is thus adapted to enter a corresponding groove in the adjacent vertebra as the implant is inserted. As a point of reference, lateral planes parallel to the direction of this path pass through the outermost boundaries of the implant which, in the preferred embodiment, would be the opposed side surfaces of the parts. Each anchor 6 and 14 lies at a midline at the center of the outer surface of each part 2 and 3 in between and parallel to the lateral parallel planes. Thus, in the illustrated embodiment, the path would be parallel to the front to rear (anterior to posterior) direction, wherein, during insertion, the rear (posterior) of the implant would constitute the lead end and the front (anterior) thereof would constitute the trailing end.
Although the invention has been described in detail with respect to preferred embodiments thereof, it will be apparent that the invention is capable of numerous modifications and variations, apparent to those skilled in the art, without departing from the spirit and scope of the invention.

## Claims

1. An intervertebral implant configured to be inserted into an intervertebral space between a first vertebra and a second vertebra, the intervertebral implant having a height extending in a first direction, a width extending in a second direction, and a depth extending in a third direction from a front end that leads into the intervertebral space upon insertion to a rear end opposite the front end, wherein the first, second, and third directions are each perpendicular to each other, comprising:
a first part having a first support face facing in the first direction for engaging the first vertebra and a downward pointing protrusion having opposing protrusion side walls with protrusion side wall surfaces extending in the third direction and the first part having an inner surface oppositely facing the first support face and the inner surface of the first part having a spherically curved indentation;
a second part having a second support face facing oppositely the first support face for engaging the second vertebra, a rear wall, and a central indentation opposite the second support face, the central indentation partially formed between two opposing inner surfaces of two side walls extending in the third direction, the second part further having an inner surface of a front wall adjacent the front end, the inner surfaces of the side walls and front wall each extending up from a bottom surface facing the first direction and opposite the second support face, the central indentation also including a side opening located at the rear wall of the second part, the downward pointing protrusion of the first part being positionable within the central indentation in a nested condition, such that a combined height of the first and second parts in the nested condition is less than an additive height of the first and second parts separately, and the protrusion side wall surfaces and the inner surfaces of the two side walls of the second part are designed to be parallel when the first and second parts are in the nested condition;
an insert having a spherically curved top side for engaging the spherically curved indentation of the first part in an installed position, the insert being insertable into the central indentation through the side opening; and
wherein the first part has a midline on an outer surface of the first part and the second part has a midline on an outer surface of the second part, the midlines extending parallel to the third direction and passing essentially midway across the width of the outer surfaces and being generally parallel to each other, the first part having a first anchor on the midline of the first part and the second part having a second anchor on the midline of the second part, the first and second anchors having a height in the first direction, a length in the third direction, and a width in the second direction, wherein the height and the length of the first anchor being greater than the width of the first anchor and the height and the length of the second anchor being greater that the width of the second anchor.

2. The intervertebral implant of claim 1, further comprising:
guide grooves in the side walls of the second part facing into the central indentation; and
the insert further comprising a bottom side oppositely facing the spherically curved top side, a first side and a second side both connecting the insert bottom side to the spherically curved top side, and guide strips extending from the first and second sides of the insert, the guide strips adapted to engage the guide grooves.

3. The intervertebral implant of claim 2, wherein the insert includes a detent protrusion and the bottom surface of the second part includes a detent recess, the detent protrusion positionable in the detent recess.

4. The intervertebral implant of claim 1, further comprising:
one blind bore extending into each side wall of the second part.

5. The intervertebral implant of claim 1, further comprising:
two blind bores extending into the downward pointing protrusion at a rear end of the first part.

6. An intervertebral implant configured and dimensioned to replace a disc removed from an intervertebral space and insertable between a superior vertebra and an adjacent inferior vertebra, the intervertebral implant having a height in a first direction, a width in a second direction, and a depth in a third direction, the first, second, and third directions being perpendicular to each other, the width of the intervertebral implant being greater than the depth, the intervertebral implant comprising:
a first part having a substantially planar outer surface facing in the first direction configured to engage the superior vertebra and an inner surface facing oppositely the substantially planar outer surface, the inner surface including a concave portion, the first part outer surface having a front edge and a back edge located opposite the front edge, the first part having a first depth in the third direction between the front and back edges;
a second part having an outer surface facing oppositely the first part outer surface configured to engage the inferior vertebra, an inner surface facing in the first direction and having a spherical portion adapted to operatively engage the concave portion of the first part, a sidewall located between and connecting the second part outer surface and second part inner surface, and the second part inner surface having a second portion not adapted to operatively engage the concave portion of the first part, the second portion located between the second part sidewall and the spherical portion;
the intervertebral implant being constructed to be a sole implant in the intervertebral space;
the intervertebral implant having lateral planes extending in the first and third directions and passing through outermost boundaries of the width of the intervertebral implant, and a midline on the outer surface of each of the first and second parts where the midline extends in the third direction essentially midway between the lateral planes, and
an anchor on each of the outer surface of the first part and the outer surface of the second part, each said anchor having a height in the first direction, a length extending along the midline, and a width perpendicular to the height and the length, wherein each said anchor has a maximum height at a first position that is greater than a first width measured at the first position and a maximum length greater than the maximum height, each said anchor being adapted to enter a groove in one of the superior vertebra or the inferior vertebra as the intervertebral implant moves along a path into the intervertebral space, to anchor the first or second part to the superior vertebra or the inferior vertebra;
wherein a first center height of the anchor on the outer surface of the first part at a center position located at approximately a center of the midline of the first part is greater than a height of a remainder of the first part measured between the outer surface and the inner surface of the first part at the center position and wherein the midline of the first part is the only location on the first part outer surface having an anchor having a height equating to the first center height.

7. An intervertebral implant configured and dimensioned to replace a disc removed from an intervertebral space and configured to be inserted into the intervertebral space between a first vertebra and an adjacent second vertebra, the intervertebral implant having a height in a first direction, a width in a second direction, and a depth in a third direction, the first, second, and third directions being perpendicular to each other, the width of the intervertebral implant being greater than the depth, the intervertebral implant comprising:
a first part having a substantially planar outer surface facing in the first direction adapted to engage the first vertebra and an inner surface facing oppositely the outer surface that includes a concave portion, the first part outer surface having a front edge and a back edge located opposite the front edge, the first part having a first depth in the third direction between the front and back edges;
a second part having a substantially planar outer surface facing oppositely the first part outer surface and adapted to engage the second vertebra, and an oppositely facing inner surface that has a spherical portion adapted to operatively engage the concave portion of the first part, a sidewall located between and connecting the second part outer surface and inner surface, and the second part inner surface having a second portion not adapted to operatively engage the concave portion of the first part where the second portion is located between the second part sidewall and the spherical portion;
the first and second parts being adapted for engagement with each other;
the intervertebral implant having a leading end that leads as the intervertebral implant is inserted along an insertion path into the intervertebral space and a trailing end opposite the leading end and lateral planes extending in the first direction and passing through outermost boundaries of the width of the intervertebral implant and parallel to the insertion path;
wherein the first part has a midline on the outer surface of the first part and the second part has a midline on the outer surface of the second part, where the midlines are located essentially midway between the lateral planes and parallel to the insertion path and wherein the midlines extend transverse to the width of the intervertebral implant;
a first anchor located on the outer surface of the first part and having a height in the first direction, a length extending along the first part midline and a width in the second direction, where the first anchor has a maximum height and a mid-anchor width measured at half the maximum height where the maximum height is greater than the mid-anchor width and the first anchor has a maximum length greater than the maximum height, and wherein the first anchor extends less than the first depth, and wherein the first anchor being adapted to anchor the first part in the first vertebra; and
a second anchor located on the outer surface of the second part and having a height in the first direction and a length extending along the second part midline, and a width in the second direction, where the second anchor has a maximum height and a mid-anchor width measured at half the maximum height where the maximum height is greater than the mid-anchor width, the second anchor being adapted to anchor the second part in the second vertebra and having a maximum length greater than the maximum height;
wherein the first and second part midlines are the only locations on the first and second part outer surfaces where an elongated anchor extends lengthwise where the elongated anchor has a height extending in the first direction, a width extending in the second direction and a length extending in the third direction and wherein the elongated anchor has a maximum length greater than a maximum height of the elongated anchor and where the elongated anchor maximum height is greater than a maximum width of the elongated anchor, and
wherein the second part spherical portion is adapted to operatively engage the first part concave portion in a position with the anchors on the first part and the second part vertically oriented to be parallel to the first direction such that the spherical portion of the inner surface of the second part that is adapted to engage the concave portion of the first part is located in a different horizontal plane than the outer surface of the second part.

8. An intervertebral implant configured and dimensioned to replace a disc removed from an intervertebral space and configured to be inserted into the intervertebral space between a first vertebra and an adjacent second vertebra, the intervertebral implant having a height in a first direction, a width in a second direction, and a depth in a third direction, the first, second, and third directions being perpendicular to each other, the width of the intervertebral implant being greater than the depth, the intervertebral implant comprising:
a first part having a substantially planar outer surface facing in the first direction and adapted to engage the first vertebra and an oppositely facing inner surface that includes a concave portion, the first part outer surface having a front edge and a back edge located opposite the front edge, the first part having a first depth in the third direction between the front and back edges;
a second part having a substantially planar outer surface facing oppositely the first part outer surface and adapted to engage the second vertebra, and an oppositely facing inner surface that has a spherical portion adapted to operatively engage the concave portion of the first part, a sidewall located between and connecting the second part outer surface and the second part inner surface, and the second part inner surface having a second portion not adapted to operatively engage the concave portion of the first part where the second portion is located between the sidewall of the second part and the spherical portion;
the first and second parts being adapted for engagement with each other;
the intervertebral implant having a leading end that leads as the intervertebral implant is inserted along an insertion path into the intervertebral space and a trailing end opposite the leading end and lateral planes extending in the first direction and passing through outermost boundaries of the width of the intervertebral implant and parallel to the insertion path;
wherein the first part has a midline on the outer surface of the first part and the second part has a midline on the outer surface of the second part, wherein the midlines are located essentially midway between the lateral planes and parallel to the insertion path and wherein the midlines extend transverse to the intervertebral implant width;
a first anchor having a height in the first direction, a length extending along the first part midline, and a width in the second direction, the first anchor being adapted to anchor the first part in the first vertebra; and
a second anchor having a height in the first direction, a length extending along the second part midline, and a width in the second direction, the second anchor being adapted to anchor the second part in the second vertebra;
wherein the first and second anchors each have a maximum height greater than a mid-anchor width measured at half the maximum height of the anchor and where each of the first and second anchors have a maximum length greater than the maximum height and are adapted to enter a groove in one of the first vertebra or the second vertebra as the intervertebral implant is inserted into the intervertebral space;
wherein the first and second part midlines are the only locations on the first and second part outer surfaces where an elongated anchor extends lengthwise where the elongated anchor has a height extending in the first direction, a width in the second direction and a length in the third direction and wherein the elongated anchor has a maximum length greater than a maximum height of the elongated anchor and where the maximum height is greater than a maximum width of the elongated anchor and where the elongated anchor is adapted to enter the groove in one of the first vertebra or the second vertebra as the intervertebral implant is inserted into the intervertebral space.

9. An intervertebral implant configured and dimensioned to replace a disc removed from an intervertebral space and configured to be inserted into the intervertebral space between a first vertebra and an adjacent second vertebra, the intervertebral implant having a height in a first direction, a width in a second direction, and a depth in a third direction, the first, second, and third directions being perpendicular to each other, the width of the intervertebral implant being greater than the depth, the intervertebral implant comprising:
a first part having a substantially planar outer surface facing in the first direction and adapted to engage the first vertebra and an inner surface facing oppositely the outer surface and that includes a concave portion, the first part outer surface having a front edge and a back edge located opposite the front edge, the first part having a first depth in the third direction between the front and back edges;
a second part having a substantially planar outer surface facing oppositely the first part outer surface and adapted to engage the second vertebra, and an oppositely facing inner surface that has a spherical portion adapted to operatively engage the concave portion of the first part, a sidewall located between and connecting the second part outer surface and the second part inner surface, and the second part inner surface having a second portion not adapted to operatively engage the concave portion of the first part where the second portion is located between the sidewall and the spherical portion;
the first and second parts being adapted for engagement with each other;
the intervertebral implant having a leading end that leads as the intervertebral implant is inserted along an insertion path into the intervertebral space and a trailing end opposite the leading end and lateral planes extending in the first direction and passing through outermost boundaries of the width of the intervertebral implant and parallel to the insertion path;
wherein the first part has a midline on the outer surface of the first part and the second part has a midline on the outer surface of the second part, wherein the midlines are located essentially midway between the lateral planes and parallel to the insertion path and wherein the midlines extend transverse to the width of the intervertebral implant;
a first anchor located on the outer surface of the first part and having a height extending in the first direction, a length extending along the first part midline, and a width extending in the second direction, the first anchor being adapted to anchor the first part in the first vertebra; and
a second anchor located on the outer surface of the second part and having a height extending in the first direction, a length extending along the second part midline, and a width extending in the second direction, the second anchor being adapted to anchor the second part in the second vertebra;
wherein the first and second anchors each have a maximum height greater than a mid-anchor width measured at half the maximum height of the anchor and where each of the first and second anchors have a maximum length greater than the maximum height and wherein the first anchor has a first center height at a center position located at approximately a center of the midline of the first part that is greater than a height of a remainder of the first part measured between the outer surface and the inner surface of the first part at the center position; and
wherein the first anchor midline is the only location on the outer surface of the first part having an anchor having a height equating to the first center height.

10. An intervertebral implant configured and dimensioned to replace a disc removed from an intervertebral space and configured to be inserted into the intervertebral space between a first vertebra and an adjacent second vertebra, the intervertebral implant having a height in a first direction, a width in a second direction, and a depth in a third direction, the first, second, and third directions being perpendicular to each other, the width of the intervertebral implant being greater than the depth of the intervertebral implant, the intervertebral implant comprising:
a first part having a substantially planar outer surface facing in the first direction and adapted for engaging the first vertebra and an oppositely facing inner surface that includes a concave portion, the first part outer surface having a front edge and a back edge located opposite the front edge, the first part having a first part depth in the third direction between the front and back edges;
a second part having a substantially planar outer surface facing oppositely the first part outer surface and adapted for engaging the second vertebra, and an inner surface facing in the first direction and consisting essentially of a substantially flat portion and a spherical portion, the second part having a sidewall located between and connecting the inner and outer surfaces, the spherical portion being adapted to operatively engage the concave portion of the first part and being located inwardly from the side wall such that the substantially flat portion surrounds the spherical portion;
the first and second parts being adapted for engagement with each other;
the intervertebral implant having a leading end that leads as the intervertebral implant is inserted along an insertion path into the intervertebral space and a trailing end opposite the leading end and lateral planes extending in the first direction and passing through outermost boundaries of the width of the intervertebral implant and parallel to the insertion path;
wherein the first part has a midline on the outer surface of the first part and the second part has a midline on the outer surface of the second part, wherein the midlines are located essentially midway between the lateral planes and parallel to the insertion path and wherein the midlines extend transverse to the width of the intervertebral implant;
a first anchor located on the outer surface of the first part and having a height extending in the first direction, a length extending along the first midline, and a width extending in the second direction, the first anchor being adapted to anchor the first part in the first vertebra, and wherein the first anchor extends less than the first part depth; and
a second anchor located on the outer surface of the second part and having a height extending in the first direction, a length extending along the second part midline, and a width extending in the second direction, the second anchor being adapted to anchor the second part in the second vertebra;
wherein the first and second anchors each have a maximum height greater than a mid-anchor width measured at half the maximum height of the anchor and a maximum length greater than the maximum height and the mid-anchor width and are adapted to enter a groove in one of the first vertebra or the second vertebra as the intervertebral implant is inserted into the intervertebral space; and
wherein the midlines are the only locations on the first and second part outer surfaces where an elongated anchor extends lengthwise where the elongated anchor has a height extending in the first direction, a width extending in the second direction, and a length extending in the third direction and wherein the elongated anchor has a maximum length greater than a maximum width for the elongated anchor and greater than a maximum height for the elongated anchor and adapted to enter the groove in one of the first vertebra or the second vertebra as the intervertebral implant is inserted into the intervertebral space.