FR2771282A1 - Surgical support implant for spine - Google Patents

Abstract

The implant is inserted into an intravertebral gap from the rear. It has two arms (3) articulated around a transverse axis (4) at their introduction ends. A wedge screw (7,8,12) adjusts the spacing between the arms.

Description

 The present invention relates to a vertebral implant adapted to be introduced posteriorly into an intervertebral or intersomatic space.

 French patent 94 06 028 of May 11, 1994 describes an interbody implant made up of a single piece reproducing a pair of fins joined posteriorly and coming to apply against the corresponding vertebral plates, and whose angular spacing is adjustable by means of '' a needle introduced by the back of the part.

 Monoblock interbody devices called cages introduced posteriorly are difficult to extract if necessary.

Their introduction into this space also poses problems in particular by their bulk which imposes significant bone sacrifices made at the expense of the posterior arches of the vertebrae adjacent to this space. Under these conditions, some recommend a complementary posterior osteosynthesis, aimed at repairing the posterior columns damaged by the approach. Furthermore, the anchoring of these devices is made of cancellous bone. This presupposes collapsing the subchondral bone beforehand and can induce a depression in the vertebral body.

 In the specific case of the intervertebral wing implant, its geometry means that the compression forces are exerted on a cantilever on its anterior portion and determine, behind the implant, tensile forces compromising its structure and its stability between the vertebral plates.

 Certain cages provided with an internal sliding device make it possible to obtain a few degrees of asymmetry between the anterior and posterior portions of the implants. However, the latter remain in one piece, being simply provided with an openwork slot. The final angle obtained is far from corresponding to physiological lordosis, and is obtained by plastic or elastic deformation of the fins or their junction zone by creating stresses and micro-cracks, sometimes leading to rupture of the implant. , leading to complications and reoperation. Their geometry in the introduction phase has the same bulk drawbacks described above.

 Cages of cylindrical or parallelepiped shape are also known, the height of which is greater at the front in order to restore the lordosis of the disc space. Their size means that they can be implanted anteriorly. This approach destroys the anterior vertebral ligament which can no longer play its hinge function.

 The object of the invention is to produce a vertebral implant of the aforementioned type, so as to eliminate these various drawbacks.

 According to the invention, the vertebral implant comprises two arms articulated around a transverse axis situated in the vicinity of one end of said arms, opposite their free end of introduction into the intervertebral space, and means for adjusting the the angular opening of the arms, adapted to cooperate with the internal surface of the arms between their insertion end and the articulation axis.

 Thus the transverse articulation axis and the means for adjusting the angular opening of the implant make it possible to distribute the load on the two supports thus formed. Under these conditions, it follows that the two unfolded arms of the implant work only in compression, and not in tilting or tearing, like the fins of the implant of the aforementioned prior patent, which undergo compression forces in carrier false.

 Advantageously, the bearing zone of the means for adjusting the angular opening is situated beyond the middle of the distance between the geometric axis of articulation and the insertion ends or free ends of the arms. A better balancing of the compression forces on the arms is thus obtained.

 According to one embodiment, the two arms are identical and have an external curvature corresponding to the bone surface of the vertebral support plate, this curvature being preferably double, and the two arms have an overall wedge shape when they are closed one over the other.

 The wedge shape, combined with their conformation corresponding to that of the bone on which they come to rest, notably facilitates the insertion of the implant into the intervertebral space, while considerably limiting the necessary bone sacrifice, compared to monobloc cages with fixed geometry, having parallel or slightly asymmetrical bearing faces.

 Other features and advantages of the invention will appear during the description which follows, given with reference to the appended drawings which illustrate two embodiments thereof by way of nonlimiting example.

 Figure 1 is an exploded perspective view, on an enlarged scale, of a first embodiment of the intersomatic vertebral implant according to the invention.

 Figure 2 and an elevational view of the implant of Figure 1 assembled and placed in an intervertebral space, after the angular opening of its two arms.

 Figure 3 is an elevational view of the implant of Figure 2 assembled and with its two arms closed one on the other for their introduction.

 FIG. 4 is an end elevation view of the implant of FIG. 3.

 FIG. 5 is a view in longitudinal elevation, on an enlarged scale, of a second embodiment of an implant arm of FIGS. 1 to 4.

 FIG. 6 is a bottom view of the arm of FIG. 5.

 FIG. 7 is a view in axial longitudinal section on an enlarged scale, of a third embodiment of the intervertebral implant according to the invention.

 The intervertebral implant 1 illustrated in FIGS. 1 to 6 is adapted to be able to be introduced posteriorly into an intervertebral or intersomatic space 2 between two vertebrae V1, V2, in place of the corresponding intervertebral disc, destroyed or damaged and which has been previously extracted.

 The implant 1 comprises two identical arms 3 articulated around a transverse axis 4 located in the vicinity of one end 5 of the arms 3 opposite their free end 6 of introduction into the intervertebral space 2.

The implant 1 also comprises means for adjusting the angular opening A of the arms 3, adapted to cooperate with their interior surfaces facing one another, between their insertion end 6 and the axis of articulation 4.

 In the embodiment illustrated in the drawings, these adjustment means comprise a sphere 7 integral with one end of a threaded rod 8, the other end of which 9 can be screwed into a radial tapped hole 11 of the axis 4.

These adjustment means also comprise ramps 12 for sliding the sphere 7 formed in the interior surfaces facing the arms 3, the angular opening of the latter thus depending on the position of the sphere on the inclined ramps 12 Advantageously, each ramp 12 forms in the interior surface of each arm 3, a cylindrical imprint complementary to the sphere 7 and having an identical radius. This feature ensures the sphere 7 a linear contact with the ramps 12, and not a point contact. The pressures exerted by the arms 3 on the sphere 7 are thus distributed over a greater support area, which avoids a risk of crushing of the sphere.

 The sliding ramps 12 machined by oblique milling, are formed between a bearing 14 of the axis 4 and insertion end 6 of the arms 3; they are connected to the flat inner surface 15 of the arms 3 which extends to their free end 6. In the sphere 7 and in the end 9 of the threaded rod 8, drive means are arranged, constituted by example by respective slots 16, 17 for not shown screwing tools. Thus, the angular opening A of the arms 3 varies as a function of the position of the sphere 7 on the support ramps 12, itself linked to the degree of insertion of the threaded rod 8 into the through hole 11: on the Figure 3 the rod 8 is pressed as far as possible in the axis 4 and the sphere 7 is in its position closest to this axis, to which corresponds a closure of the implant, whose arms 3 are applied one on the 'other. In FIG. 2, the sphere 7 is in its position furthest from the axis 4, bearing on the ends of the ramps 12, a position which corresponds to an angular opening A maximum, restoring the natural lordosis.

 In this latter position, the sphere 7 is situated clearly beyond the middle M of the distance D between the geometric axis Xx of the axis 4 and the free ends 6 of the arms 3. On the other hand, when the latter are applied l one on the other, the opening A being zero (FIG. 3), the bearing zones 13 of the sphere 7 on the ramps 12 are located below the middle M, in the direction of the geometric axis Xx. The ramps 12 are profiled in such a way that when the arms 3 are open, the bearing zones 13 of the sphere 7 are located between the medium M and the free ends 6, which makes it possible to distribute the load exerted in a balanced manner by the arms 3 on the two supports constituted by the axis 4 and the sphere 7.

 The two arms 3 are identical and their outer surface 18 has a curvature corresponding to the bone surface of the vertebral plateau 19 of support. This curvature is advantageously double and therefore has two radii of curvature R1, R2, the radius of curvature R1 extending from the end 5 of the arm 3 over a certain length. This radius of curvature RI is connected to the second radius of curvature R2, less than R1, which ends at the free end 6. Thus when the two arms 3 are closed and applied one on the other (FIG. 3), L implant 1 has a general wedge shape with its thinned insertion end, constituted by the two free ends 6 of arms 3 applied to one another.

 The outer surfaces 18 of the arms 3 are each provided with at least one longitudinal rib 21, preferably extending from one end 5 to the other end 6. In the variant of FIGS. 5 and 6, the rib 21 is completed by at least one transverse rib 22, formed at the free end 6.

 The ribs 21 and 22 have the function of ensuring sufficient anchoring of the arms 3 in the vertebral plates 19.

 The articulation ends 5 of the arms 3 are provided with shapes adapted to allow lateral insertion of the axis 4 therein.

In the embodiment illustrated in Figures 1 to 4, these shapes are constituted, for each arm 3, by two pairs of parallel curved legs 23a 23b matching the cylindrical profile of the axis 4. These circular legs 23a, 23b extend on angular sectors substantially greater than a half circumference, so that the axis 4 can be introduced between the legs 23a 23b only laterally (according to arrow F (Figure 1). After its introduction it is retained by the legs 23 in a direction perpendicular to its lateral direction of introduction.

 When the threaded rod 8 is screwed into the hole 11, the axis 4 can no longer be removed from the lugs 23a 23b. The bearing 14 extends parallel to the axis 4 and perpendicular to the general plane of the shapes 23a 23b which it connects together.

 The arms 3 being identical, can be applied one on the other with mutual interlocking of the shapes 23a 23b (FIG. 4): for this purpose one 23a of each pair of shapes is flush with a lateral face 25 of the arm 3 , while the second form 23b is offset laterally from the corresponding lateral face 25 in the direction of the first form 23a. It is clearly seen in Figure 4 that this arrangement allows an interlocking of the two pairs of shapes 23a 23b.

 In the second embodiment, illustrated in FIG. 5, the shapes making it possible to retain the axis 4 consist of parallel and circular eyelets 26, dimensioned to match the cylindrical profile of the axis 4. Of course, these eyelets 26 can be made with or without the rib 22, and vice versa.

 The assembly of the elements making up the implant 1 which has just been described is done in the following way: the two arms 3 are fitted one on the other so as to nest the shapes 23a 23b or 26 of retaining the axis 4 (figure 4). Then the latter is introduced laterally (arrow F, FIG. 1) in the shapes 23 or 26, by sliding it on its bearing 14. The arms 3 are angularly opened so as to allow the introduction of the end 9 of the rod 8 in the hole 11 of the axis 4, and by means of a screwdriver engaged in the slot 16, the rod 8 is screwed in the axis 4. Depending on the depression of the rod 8 in the axis, the sphere 7 takes a position which adjusts the angular opening A between the closed position of FIG. 3 and the maximum open position of FIG. 2. Once the rod 8 is introduced into the axis 4, the various constituents of implant 1 can no longer be separated.

 The implant 1 having its arms 3 applied one on the other (FIG. 3) so as to present an overall wedge shape, the surgeon introduces posteriorly the tapered ends 6 of the wedge into the intervertebral space 2, the disc has been previously extracted. As already indicated, this general wedge shape facilitates the introduction of the implant into the intervertebral space.

 Thanks to the double curvature R1, R2 of the external surface 18 of the arms 3, and the possibility of adjusting the angular opening A to the appropriate value, the implant 1 advantageously restores the local physiological lordosis of the intersomatic space of the vertebrae V1, V2. As a result, the bone sacrifice required is much less than with the previously known implants. Therefore, the surface 18 of the arms 3 is in contact with the dense subchondral bone of the plates 19, which avoids the risks of osteolysis.

 - The shape of the implant, restoring the natural lordosis in situ, also makes it possible to obtain tensioning of the peripheral ligaments, because the height of the implant 1, that is to say the spacing between its outer surfaces 18, can be adjusted so as to be equal to the anterior disc height.

In total, the stability of the implant results from:
- on the one hand, edges ensuring the guiding of the implant at its introduction and once unfolded, its transverse stability,
- on the other hand, the fact that dynamic distraction creates the conditions for stability by restoring tension to dynamic and peripheral stabilizing elements, namely, the ligaments,
Finally, the implant is pressurized due to the loading of the operated patient.

When the implant 1 is in place in an intervertebral space (FIG. 2), the compressive forces exerted on the support zones 13 of the sphere 7 and on the axis 4 block in place the various constituent elements of
the implant, the axis 4 acting as a nut for the threaded rod 8. The position of the sphere 7 on the ramps 12 regulates the angular opening A and the lordosing force, resulting from the asymmetry of the implant 1. These compression forces are balanced on either side of the medium M, which eliminates the risks of deformation of the arms 3.

 - This implant is easy to introduce, because it only requires a limited resection of the posterior arch thanks to its reduced size when introduced in the form of a wedge. It is also easy to extract, because the fins formed by the arms 3 close one on the other during the extraction of the implant in the posterior zone.

 In the embodiment illustrated in FIG. 7, the sphere 27 is pierced with a diametral hole 28 crossed by the threaded rod 29. The latter is only threaded on its part crossing the axis 4 of articulation, its second part 31, passing through the sphere 27, being smooth, the sphere being slidably mounted thereon. Elastic return means are provided to return the sphere 27 towards the end of the rod 29 opposite the axis 4. These return means can be constituted by a helical spring 32, enveloping the rod 29 and bearing on the axis 4. The end of the smooth part 31 is equipped with a head 33 forming a stop for retaining the sphere 27. The spring 32 allows the sphere 27 to be moved back on the ramps 12 thanks to the thrust exerted on this sphere, which ensures variability of the interval corresponding to the disc height (displacement of the natural nucleus of a disc), as a function of the compression forces during an anterior flexion movement of the spine. The compression-distraction forces exerted from top to bottom, are transmitted and absorbed by the implant, along an anteroposterior axis.

 The outer surface 18 of the arms 3 can advantageously be treated to facilitate bone attachment, for example by corundum. As a variant, the slots 16, 17 can be replaced by other drive means, such as squares, hexagons, half-moons, etc.

Claims (11)

 1. Vertebral implant (1) adapted to be introduced posteriorly into an intervertebral space (2), characterized in that it comprises two arms (3) articulated around a transverse axis (4) located in the vicinity of a end (5) of said arms opposite their end (6) for introduction into the intervertebral space, and means (7, 8, 12) for adjusting the angular opening of the arms, adapted to cooperate with the inner surface of the arm between their insertion end and the hinge pin.  2.lmplant according to claim 1, characterized in that the two arms (3) are identical and have an external curvature corresponding to the bone surface of the vertebral plateau (19) of support, this curvature being preferably double (R1, R2 ), and the two arms have an overall wedge shape when they are closed one on the other, facilitating the introduction into an intervertebral space (2).  3. Implant according to claim 1, characterized in that the outer surfaces (18) of the arms (3) are provided with at least one longitudinal rib (21) and at least one transverse rib (22) for anchoring the arm in the vertebral plateau (19).  4.lmplant according to claim 1, characterized in that the ends (5) of articulation of the arms (3) are provided with forms (23a, 23b; 26) adapted to allow lateral introduction of the axis (4) into these and to retain and this axis in a perpendicular direction.  5.lmplant according to claim 4, characterized in that said shapes are constituted by pairs of parallel curved legs (23a, 23b) matching a cylindrical profile of the axis (4).  6.lmplant according to claim 4, characterized in that the forms are constituted by a pair of parallel circular eyelets (26) matching a cylindrical profile of the axis (4).  7.lmplant according to one of claims 5 and 6, characterized in that the forms (23a, 23b, 26) are offset laterally to be able to fit together.  8.lmplant according to claim 1, characterized in that the means for adjusting the angular opening (A) of the arms (3) comprise a sphere (7) integral with one end of a threaded rod (8), the other end (9) can be screwed into a radial tapped hole (11) of the hinge pin (4), and inclined ramps (12) for sliding the sphere, formed in the inner surface of the arms ( 3), the angular opening of the arms depending on the position of the sphere on the inclined ramps.  9. implant according to claim 8, characterized in that the ramps (12) form complementary cylindrical imprints of the sphere (7) with which they cooperate.  10.lmplant according to claim 9, characterized in that the sliding ramps (12) are arranged so that the bearing zones (13) of the sphere lie beyond the middle (M) of the distance (D ) between the geometric axis (xX) of the articulation axis (4) of the arms (3), and the ends (6) of introduction of the arms, when the latter are open.  11. Implant according to claim 9, characterized in that the cylindrical ramps (12) have a radius identical to that of the sphere (7).  implant according to one of claims 8 to 10, characterized in that in the sphere (7) and the end (9) of the threaded rod (8) are arranged drive means (16,17) for a tool of screwing.  13.lmplant according to claim 8, characterized in that the sphere (27) is pierced with a diametral hole (28) traversed by the threaded rod (29) on which the sphere is slidably mounted, and elastic return means are designed to return the sphere towards the end of the rod opposite the articulation axis (4), for example a helical return spring (32) enveloping the rod and bearing on the axis (4).  14.lmplant according to claim 1, characterized in that the outer surface (18) of the arms (3) is treated to facilitate bone attachment, for example by corundum.