Intervertebral implant

p0001The present invention relates to an intervertebral implant for maintaining a desired space between two vertebral bodies of a spinal column. Such an implant is also known under the name of "interbody fusion cage". It is used to treat pathologies of the intervertebral disc.

p0002An intervertebral fusion cage is generally placed within an intervertebral disc including a partial discectomy has been previously achieved. The interbody fusion cage restores the height of the intervertebral disc and allows the vertebrae to fuse. Examples of interbody fusion cages are described in international patent applications<patcit id="pcit0001" dnum="WO02089712A"><text>WO 02/089712</text></patcit> and <patcit id="pcit0002" dnum="WO2005055869A"><text>WO 2005/055869</text></patcit>.

p0003There are several techniques of setting up an interbody fusion cage. The technique which is particularly interested in the invention is "TLIF" technique (transforaminal Lumbar Interbody Fusion) that the cage is introduced by a unilateral posterior open through tissue.

p0004An interbody fusion cage should be placed in a definite position in space of the intervertebral disc. The cage is more precisely positioned in the front part of said space. The interbody fusion cages that are used in the context of the TLIF technique generally have an arched shape with a convex face and a concave face. The convex side must be balanced against the front side of the intervertebral disc space and the concave face facing the posterior side. To do this, it is necessary to rotate the cage after its introduction into the intervertebral disc space. This positioning of the cage is quite difficult to perform and requires the use of a relatively large number of bent instruments.

p0005The patent application <patcit id="pcit0003" dnum="FR2861582"><text>French FR 2861582</text></patcit> describes an interbody fusion cage and an associated gripping means which are designed to ensure freedom of rotation of the cage relative to the instrument. To this end, the cage comprises at each of its ends of the vertical recesses oblong section formed over the entire height of the cage and horizontal notches découchant in vertical recesses. The instrument provides him a tooth rod end is provided with a cylindrical latching lug which can be coupled to the vertical recesses in the manner of a bayonet. The rod is within a mobile tube, said lock, which can be approached or moved away from the latching lug by means of a knob to tighten the shaft wall between the tube end and the latching lug, and thus temporarily fasten the cage and the instrument, or to release this wall in order to permit rotation of the instrument relative to the cage.

p0006By allowing rotation between the cage and the gripping instrument, the number of instruments required for the implementation of the cage is reduced. However, despite this freedom of rotation, rotate the cage to put it in its final position is a delicate operation. Furthermore, the binding mode between the cage and the gripping instrument has several disadvantages. Due to the oblong section of the vertical recesses, a horizontal translation match exists between the latching lug and the vertical recesses if the locking tube is not sufficiently tight against the wall of the cage. Such a game will hurt the cage running accuracy. Another disadvantage is that this binding mode requires the surgeon to perform Successive applications and releases and tedious blocking tube for the introduction of the cage.

p0007The present invention aims to provide an intervertebral implant designed to facilitate its rotation in its final position when it is in place between two vertebral bodies.

p0008To this end, there is provided an intervertebral implant comprising a body having upper and lower surfaces intended to be in contact with respective vertebral bodies to maintain a desired space between these vertebral bodies, characterized in that it comprises a pivot on the 'at least one of upper and lower faces. Such pivot is engageable with the corresponding vertebral body during installation of the implant to allow an easy rotation thereof around the imaginary axis defined by the pivot.

p0009To further facilitate its implementation, the intervertebral implant according to the invention further comprises, preferably, means for coupling to a gripping means arranged to allow a rotation of the instrument relative to the implant, these coupling means including a housing formed in the body and opening on a peripheral face of said body and a rotatable member in the housing, said moving member being adapted to mate with one end of the instrument. Such coupling means enable the use of a gripping instrument without locking tube and easy to handle.

p0010Preferably, to further facilitate the introduction of the implant according to the invention, the body comprises first and second parts articulated horizontally between a first relative position where the first and second portions are substantially aligned and a second relative position where the first and second portions form an angle therebetween. The first relative position gives the implant a straight temporary shape which allows it to move more easily in the portion or posterior route, generally narrow, which is practiced in the tissues. The second relative position is the final position, which gives the implant an arcuate shape adapted to its function.

p0011particular embodiments of the invention are defined in the appended dependent claims.

p0012Other characteristics and advantages of the present invention appear on reading the following detailed description made with reference to the accompanying drawings in which:<ul><li>Figures 1 to 3 are respectively a perspective view from above, a side view and a horizontal sectional view taken along the plane III-III of Figure 2, of an intervertebral implant according to a first embodiment of the invention;</li><li>Figures 4 and 5 are respectively a perspective view from above and a side view of an intervertebral implant according to a second embodiment of the invention;</li><li>Figures 6 to 8 are respectively a perspective view from above, a horizontal sectional view and a top plan view of an intervertebral implant according to a third embodiment of the invention;</li><li>Figures 9 and 10 are respectively a perspective view of two parts forming the body of the intervertebral implant according to the third embodiment of the invention;</li><li>Figure 11 is a plan view in horizontal section of the intervertebral implant according to the third embodiment of the invention coupled to two instruments for gripping and handling;</li><li>12 shows the intervertebral implant according to the third embodiment of the invention in its final position on a vertebra.</li></ul>

p0013Referring to Figures 1 to 3, an intervertebral implant or intersomatic fusion cage according to a first embodiment of the invention includes an arcuate shaped body 1 comprising a top side 2, an underside 3, a convex front face 4, a concave rear face 5 and two rounded end faces 6, 7 connecting the front walls 4 and rear 5. the front walls 4, 5 and rear end 6, 7 together define the periphery of the body 1.

p0014The upper and lower surfaces 2, 3 are intended to be in contact with two respective adjacent vertebral body, specifically with two endplates. The pins 8 are provided on these upper and lower surfaces 2, 3 to be anchored in the vertebral plates.

p0015Apertures 9 passing through the body 1 over its entire height allow the fusion of the vertebral bodies. vascularization of holes (not shown) may also be provided.

p0016According to the invention, the body 1 has on each of the upper and lower surfaces 2, 3, or at least on one of them, a pivot 10, 11. Pivots 10, 11 are located at one end of body 1 and are aligned relative to each other. In the illustrated example, the pivots 10, 11 have a hemispherical shape. They could still have another shape, for example conical or pyramidal.

p0017The cage can be implemented according to TLIF art. A way of unilateral posterior first opened to the right or left of the spine, the vertebral bodies between which should be introduced the cage are distractés, parts of the affected intervertebral disc is removed and the cage is introduced by said track. Distraction of the vertebral bodies must be sufficient so that the pivots 10, 11 must not impede the insertion of the cage. Once the cage inserted into the intervertebral disc space, the distraction of the vertebral bodies is released, the endplates then come into contact with pivots 10, 11, which form a depression in the endplates. The cage can then be easily rotated to its final position around a single imaginary axis passing through the pivots 10, 11. A impacting of the vertebral bodies on the cage enables the endplates to come in contact with the upper and lower surfaces 2, 3 and 8 pins to anchor in the vertebral endplates to secure the cage in position.

p0018According to another characteristic of the invention, the body 1 comprises at its end opposite that comprising the pivots 10, 11 a recess 12 opening on its periphery, specifically on the end face 7. In the example shown, the housing 12 is spherical and opens on the end face 7 by means of a frustoconical aperture 13 outwardly flared. A spherical coupling member 14 is disposed in the housing 12 so as to be movable in rotation on itself, without play, in the manner of a ball joint, while remaining captive of the housing 12. The body of coupling 14 is traversed along an axis thereof by a threaded bore 15 whose diameter is smaller than the smallest diameter of the frustoconical opening 13 and which communicates with the tapered opening 13 in order to receive through said opening 13 a threaded end of a rod of a gripping means (not shown).

p0019The movable coupling member 14 thus gives the cage freedom in rotation relative to the gripping means in the limits defined by the wall of the frustoconical opening 13, which wall serves as a bearing surface and a stop for the gripping instrument. This rotational freedom is exerted in all directions inside the cone defined by the wall of the opening 13, and therefore in particular in horizontal and vertical planes. Such an instrument grip can therefore be used both to enter the cage in the intervertebral disc space and rotating the cage horizontally to give it its final position. Freedom in vertical rotation of the cage relative to the instrument in turn facilitate the introduction and movement of the cage in the passage leading into the intervertebral disc space, a passage which is narrow and offers little visibility the surgeon. Alternatively, however, it can give the movable coupling member 14 is cylindrical rather than spherical, if such freedom in vertical rotation is not desired.

p0020When, as in the example illustrated, the coupling member 14 has a spherical shape, a pin 16 on the coupling member 14 cooperates with a housing 17 of larger size formed in the body 1 in block rotating the coupling member 14 in the direction of screwing and unscrewing the threaded end of the instrument into the bore 15 and thus permit the coupling and uncoupling of the cage and the instrument.

p0021Figures 4 and 5 show an intervertebral implant or intersomatic fusion cage according to a second embodiment of the invention. In this second embodiment, the cage comprises on each or at least one of its upper and lower faces 20, 21 in addition to the pivot 22, 23, here conical, and anchor pins 24, a projection 25, 26 of height less than that of the pivot 22, 23 but much greater than that of the anchor pins 24. the protrusions 25, 26 have an inclined planar surface 27 which defines, with a peripheral face of the protrusions 25, 26, a cutting edge 28. This edge 28 has in the plane of the face 27, a curved shape, preferably elliptical as shown, allowing the protuberances 25, 26 of progressively be anchored in the vertebral endplates during rotation of operating the cage around the imaginary axis through the pivots 22, 23 and raprochement of consecutive vertebrae to release distraction. This anchoring protrusions 25, 26 secures the final position of the cage before impacting.

p0022Figures 6 to 11 show an intervertebral implant or intersomatic fusion cage according to a third embodiment of the invention. In this third embodiment, the body 30 consists of two parts 31, 32 hinged horizontally to one another between a first relative position, called open position, where the parts 31, 32 are aligned (Figure 8) and a second relative position, called closed position, where the parts 31, 32 form an angle therebetween (Figure 6) and impart to the shaft a conventional arcuate shape.

p0023The joint between the portions 31, 32 is made by engaging a male joint member 33, of cylindrical shape, the portion 32 with a female articulation organ or cavity 34, of cylindrical shape corresponding to the part 31 . the male member 33 comprises a horizontal rib 35 along its periphery, rib which cooperates with a corresponding horizontal groove 36 in the wall of the cavity 34 to position and lock the vertically housing parts 31, 32 one by relative to each other. Alternatively, of course, the rib could be located on the wall of the cavity 34 and the corresponding groove in the male member 33.

p0024The cavity 34 defines two laterally guiding and stop 37, 38 which cooperate with corresponding recesses 39, 40 of the portion 32 situated on either side of the male joint member 33 for guiding and limiting the stroke relative portions 31, 32. the guide member and abutment 37, respectively 38, is in abutment against the bottom of the cavity 39, respectively 40, where the portions 31, 32 are in their open relative position, respectively closed.

p0025That of the cavities 39, 40 nearest the rear side of the cage, namely the cavity 40, has on its side wall opposite the mate member 33 a vertical locking rib 41 (see Figure 8). This vertical rib 41 slides over the guide member and stop 38 holding the side walls of the cavity 40 resiliently apart when the parts 31, 32 move between their open and their closed relative position relative position. The rib 41 fits into a vertical groove corresponding detent 42 formed in the guide member and stop 38 when the latter comes into abutment in the bottom of the cavity 40, that is to say when the parts 31, 32 reach their closed relative position. In this position, the cavity 40 returns to its resting shape, undeformed, and the body portions 31, 32 are locked. Alternatively, of course, the vertical rib 41 could be located on the guide member and stop 38 and the corresponding groove 42 in the wall of the cavity 40.

p0026The closed relative position of the body parts 31, 32 is particularly adapted to the insertion of the cage in the intervertebral disc space. Indeed, as already indicated, the posterior route or passageway formed through the tissue through which the cage is inserted is narrow. Illustratively, this passage has been shown schematically in Figure 12 by dotted lines designated by the reference VP, the intervertebral disc space it being designated by the mark ED. The arched shape of a conventional cage interbody fusion does not facilitate the introduction and movement of the cage in the VP pass. The hinged cage according to this third embodiment of the invention is introduced and moved longitudinally in the VP path while the body portions 31, 32 are in their open relative position, where the cage is straight (Figure 8). To this end, the body portions 31, 32 include in their thickness respectively a longitudinal blind hole 43 and a longitudinal through hole 44 which are aligned when the body portions 31, 32 are in their open relative position. These holes 43, 44 for receiving a rod 45 of a first gripping tool (Figure 11) which holds the body portions 31, 32 in their open relative position. This instrument is withdrawn progressively as soon as the cage has penetrated into the space of the intervertebral disc ED.

p0027Open relative position of the body portions 31, 32 corresponds, in turn, to the final implantation position of the cage, as shown in Figure 12. In order to manipulate the cage and put in its final position after that it has penetrated into the space of the intervertebral disc ED, the cage according to this third embodiment includes coupling means 46-51 identical to the means 12 to 17 of the first embodiment. These coupling means 46 to 51 receive a second instrument for grasping, designated in Figure 11 by the numeral 52, which, thanks to its rotational freedom relative to the cage, allows to rotate the cage as a whole for the place in the anterior part of the space of the intervertebral disc and ED to rotate the body portions 31, 32 relative to each other until the locking of these parts 31, 32 in their closed relative position. As the first instrument 45, the second instrument 52 is coupled to the cage before its introduction into the path VP. It is unscrewed and removed from the cage when the cage has been put into its final position.

p0028The interbody fusion cage according to this third embodiment may also include a pivot 50 and a corresponding cutting protuberance (not shown) on one or each of the upper and lower faces of the body 30, as in the first embodiment, for facilitate the rotation and positioning of the cage.