WO2009060388A1

WO2009060388A1 - Intervertebral implant to immobilize a vertebra relatively to another and instrument

Info

Publication number: WO2009060388A1
Application number: PCT/IB2008/054604
Authority: WO
Inventors: Paolo Mangione; Hervé Chataigner
Original assignee: Medicrea International
Priority date: 2007-11-05
Filing date: 2008-11-05
Publication date: 2009-05-14
Also published as: FR2923158B1; FR2923158A1

Abstract

This intervertebral implant (1) comprises a first intervertebral part (5) intended to be inserted between two vertebrae (100) to be immobilized. According to the invention, the implant (1) comprises two flexible strands (6a, 6b) connected to the first intervertebral part (5), the length of which is such that these strands (6a, 6b) jut out from the patient when the first intervertebral part (5) is placed between the vertebrae (100), these strands (6a, 6b) being capable of receiving between them in the intervertebral space, one or more grafts and/or cancellous bone chips (103) and of maintaining these graft(s) and/or chips (103) between the vertebrae (100).

Description

INTERVERTEBRAL IMPLANT TO IMMOBILIZE A VERTEBRA RELATIVELY TO ANOTHER AND INSTRUMENT

The present invention relates to an intervertebral implant with which a vertebra may be 5 immobilized relatively to another and to an instrument for setting up this implant.

The invention also relates to a surgical procedure with which a vertebra may be immobilized relatively to another.

Immobilization of two vertebrae relatively to each other by means of an

10 intervertebral implant in a rigid material, forming a cage which delimits the housing, is well known, this housing being intended to receive one or more bone grafts, and/or cancellous bone chips. In some cases, the bone grafts and/or the cancellous bone chips may also be placed around the implant. With the implant, adequate spacing of the vertebrae may be re-established and

15 crushing of the graft(s) by the latter may be prevented. Immobilization of the vertebrae relatively to the implant is achieved by growing bone cells on either side of the graft(s) and/or chips, but also on either side of the implant, leading to what is conventionally called a "fusion" of both vertebrae.

Certain intervertebral implants have a reduced width, so that they may be 20 placed by a posterior approach, on either side of the spinal cord. It is then generally necessary to place two implants, one on the left side of the spinal cord and the other one on the right side.

This technique has the drawbacks of being relatively risky to apply, implying that an adaptation of the vertebrae should be achieved by bone

25 resection close to the spinal cord, and forcing the use of hollow implants with reduced width, which only allow a small contact surface of the grafts with the vertebrae.

To find a remedy to these drawbacks, it is possible to place an intervertebral implant by an anterior approach. As the approach is wider than 30 by a posterior approach, such an implant may have a shape such that it extends over a major portion of the surface of a vertebral plate, and it may therefore contain one or more grafts with a significant contact surface with the vertebral plates, which is an essential condition for the vertebral fusion to be successful. An anterior approach however has the drawback of exposing certain anatomic structures (notably veins and arteries) which the orthopedist surgeon or neurosurgeon is not used to mobilize. This approach will therefore only be possible for a vertebral column surgeon if he/she is assisted by a colleague, whose specialty is vascular surgery for example.

An alternative, with which the drawbacks of both previous techniques may be overcome, consists in placing a single cage by a posterior approach, positioned in front of the vertebra in the front plane. Some graft is positioned in the cage but also behind or in front of the latter. This technique however has the drawbacks that the cage only provides a limited contact space between the graft(s) or chips and the bone, that these grafts or chips positioned behind the cage are not secured in the intersomatic space, that the grafts or chips positioned in front of the cage force the surgeon to place the cage in a relatively posterior position, thereby reducing its stabilizing potential, and that with a single cage positioned in the front plane, it is not possible under all circumstances to recover a sufficient and symmetrical discal height.

Further, the existing implants are relatively difficult to position between plates of two vertebrae.

The object of the present invention is to find a remedy to the drawbacks of the existing implants, and of the existing approaches, by providing an intervertebral implant both easy to place, notably in a position as anterior as possible of the vertebral plates, and by a not very invasive approach, and with which perfect "fusion" of the treated vertebrae may be obtained.

The relevant implant comprises a first intervertebral part intended to be inserted between two vertebrae to be immobilized.

According to the invention, the implant comprises two flexible strands connected to the first intervertebral part, the length of which is such that these strands jut out from the patient when the first intervertebral part is placed between the vertebrae. The first intervertebral part is thus introduced into the intervertebral space and carries along both strands; these strands may be used alone or combined with the instrument described later on, for directing and positioning this first part in the intervertebral space, or for removing this part out of this space in the case when the latter would not be in the desired position, which is a decisive advantage.

The strands are further capable of receiving between them in the intervertebral space, one or more grafts and/or cancellous bone chips and of maintaining these graft(s) and/or chips between the vertebrae.

Once the first intervertebral part is set into place, the strands are used more or less as a guide for introducing the graft(s) and/or the cancellous bone chips, and at the intervertebral space allow a receiving area to be delimited for these graft(s) and/or bone chips. When this introduction is completed, these graft(s) or bone chips may be surrounded by both strands in order to prevent them from moving out of the intervertebral space and to compact them so that they are well in contact with the vertebral plates.

The first intervertebral part therefore does not have the goal of containing some bone graft or achieving by itself the vertebral fusion but has the goal of assuming a position in the intervertebral space by carrying the flexible strands along with it. It also has the function of maintaining these graft(s) in position while one or more grafts and/or bone chips are being set into place. With this first intervertebral part, it is further possible to maintain a defined height between both vertebrae and therefore to avoid any crushing of the grafts and/or bone chips while said growth of bone cells is occurring.

Both flexible strands, as for them, have the function of allowing said first intervertebral part to be positioned or removed if necessary. When one or more grafts and/or bone chips are placed in the intervertebral space, they are used for guiding these grafts and/or bone chips in this space, and for maintaining and compacting them together. They may define a wide space between them, for introducing a significant amount of grafts and/or chips in said space, with which perfect vertebral fusion may be ensured.

The first intervertebral part preferably has a width such that it is able to be introduced into the intervertebral space to be treated by a posterior approach, by a side approach or by an intermediate approach between the posterior approach and the side approach.

The implant may thereby be placed by a not very invasive approach and the first intervertebral part only occupies a marginal surface of the intervertebral space, freeing a large surface for placing the graft(s) and/or bone chips.

Advantageously, said first intervertebral part has a curved shape substantially corresponding to the curvature exhibited by the front face of a vertebral body.

This first intervertebral part may thereby be positioned in the most anterior area of the vertebral plates.

The first intervertebral part may be devoid of one or more housings for receiving one or more grafts and/or cancellous bone chips; preferably it however comprises one or more of these housings and receives one or more grafts and/or cancellous bone chips before it is introduced into the intervertebral space.

This part may thereby be immobilized relatively to the vertebral plates by the growth of bone cells through the graft(s) and/or chips which it contains. Said first intervertebral part may also comprise raised features protruding from at least one of its faces intended to come into contact with the vertebral plates.

With these raised features, it is possible to promote immobilization of the first intervertebral part relatively to the vertebrae once this part is placed in the intervertebral space.

The first intervertebral part may be in any suitable rigid material, notably in a so-called "PEEK" (polyetheretherketone) material.

Advantageously, the flexible strands each have a width substantially corresponding to the height of the intervertebral space to be restored, or slightly less than this height, so that they provide perfect contention of the grafts and/or bone chips, without any risk of having these grafts and/or chips escape or leak out beyond them.

These strands may have a circular or flattened cross-section. They may notably be formed by a braid of fibrous material, notably of PEEK or polyester. The first intervertebral part preferably comprises a strand connected to it at one of its longitudinal ends and the other strand connected to it at the other of its longitudinal ends. When the first intervertebral part is placed in the anterior area of the vertebral plate, both strands may thereby be easily separated from each other and may define between them a wide space for receiving the graft(s) and/or bone chips. Further, during the positioning of said first intervertebral part between the vertebrae, both of these strands may be utilized for orienting and positioning this part in the best way as possible, being used like the strings of a kite, notably in combination with an instrument for introducing and positioning said first intervertebral part.

Both of the strands may be jointed to each other so as to maintain the graft(s) and/or chips between the vertebrae while growth of the bone cells occurs, achieving definitive immobilization of the vertebrae; they may also be removed after placing the graft(s) and/or chips. In the second case, both of the flexible strands may be formed by two portions of a same flexible bond connected to said first intervertebral part with possibility of sliding. Removal of the strands is thereby easy to perform, by sliding the flexible bond relatively to the first intervertebral part.

According to a preferred embodiment, in this case the first intervertebral part comprises, at one of these longitudinal ends, a first conduit for providing a passage for the flexible bond through it, and, at its other longitudinal end, a second conduit providing a passage for the flexible bond through it; the flexible bond passes through said first conduit, and then runs along the first intervertebral part and then passes through said second conduit. Both aforementioned strands are thereby formed by the portion of this flexible bond jutting out from said first conduit and from said second conduit. The joining of both strands may be achieved by any suitable means, notably by simple knotting. It may also be achieved by means of a joining part which may slide along the strands towards said intervertebral part and equipped with antireturn means preventing this joining part from sliding in the opposite direction. These anti-return means may be formed by teeth or claws capable of being supported on the material forming the strands. Said joining part may notably be in a bioresorbable material. The implant according to the invention may comprise at least one second intervertebral part capable of being inserted between two vertebrae to be immobilized, intended to be slidably engaged on at least one of the two strands and to be placed in proximity to the first intervertebral part, in the continuity of the latter.

This second intervertebral part allows a more complete restoration of the intervertebral height and allows the surface of the vertebrae bearing against the implant to be increased. Further, as it comes in the continuity of said first intervertebral part, the graft(s) and/or bone chips may be held in the intervertebral space securely by obstructing the entry point of the implant between the vertebrae. This securization is particularly useful when said strands are not left in place.

When it is engaged on only one of the two strands, said second intervertebral part may be inserted into the intervertebral space at the same time as the first part. When it is engaged on both strands, this second intervertebral part is set into place in the intervertebral space by sliding on both strands, after introducing the graft(s) and/or bone chips. It thereby allows these strands to be closed around this graft or these grafts and/or bone chips so that the latter is held and compacted. This second intervertebral part may then form said joining part.

Said first intervertebral part and said second intervertebral part may comprise reciprocal interengagement means allowing the second part to be positioned in a determined way relatively to the first part and this second part to come in close proximity to the first part.

These interengagement means may notably comprise a notably rounded protrusion laid out on one of said first and second parts, and a corresponding cavity laid out on the other of said first and second parts, capable of receiving this protrusion in it.

The invention also relates to an instrument for setting up the implant described above, comprising:

- a rigid rod for introducing said first intervertebral part between the vertebrae to be treated, by a posterior approach, a side approach and/or an intermediate approach between the posterior approach and the side approach; and - removable connecting means between this rigid rod and said first intervertebral part, this connection being able to be suppressed when said first intervertebral part is set into place between the vertebrae.

Preferably, the instrument comprises pivot means with which the first intervertebral part may be pivoted between a first position, in which this first intervertebral part is substantially found in the extension of said rigid rod, and a second position, in which this first intervertebral part is angled relatively to this rigid rod, notably substantially at right angles to this rod.

Said first position is a position for introducing said first intervertebral part between the vertebrae, and said second position is a position for setting into place this first intervertebral part between the vertebrae.

The change in orientation of the first intervertebral part relatively to said rigid rod may notably be achieved by means of either one of the aforementioned strands, when these strands are connected to the first intervertebral part at the longitudinal ends of the latter.

Preferably, the instrument comprises means for blocking/unblocking the pivoting allowed by said pivot means.

By blocking this pivoting, introduction of the intermediate part between the vertebrae may notably be facilitated. According to a possible embodiment of the invention, the instrument comprises:

- a tube forming said rigid rod;

- an internal rod engaged in this tube;

- a pivotably mounted head on the distal end of said internal rod comprising a threaded pin capable of being screwed into a tapped hole made in said first intervertebral part, and

- tightenable means for displacing the internal rod/head assembly relatively to said tube, between a distal displacement position of the internal rod relatively to the tube, in which said head does not bear against said tube and is therefore mobile relatively to the internal rod, and a proximal displacement position of the internal rod relatively to the tube, in which said head bears against said tube so that it is immobilized relatively to this tube and to the internal rod. Said distal displacement position thus allows the head to be pivoted relatively to the internal rod and to the tube, and therefore corresponds to the position for unblocking the pivoting of the first intervertebral part relatively to said rigid rod of the instrument, whereas said proximal displacement position allows blocking of the pivoting of the head relatively to the internal rod and to the tube, and therefore corresponds to the position for blocking the pivoting of the first intervertebral part relatively to said rigid tube of the instrument.

Said tightenable means may be screwing/tapping means laid out on said internal rod on the one hand, and on said tube on the other hand, the screwing and unscrewing of which allow said internal rod to be moved relatively to said tube.

The invention also relates to a surgical method for immobilizing a vertebra relatively to another one, comprising the steps of:

- using a first intervertebral part as mentioned before; - introducing said intervertebral part and a portion of said strands between the vertebral plates of two vertebrae, the other portion of these strands jutting out on the outside of the patient;

- using the strands for directing and positioning said first part in the intervertebral space, or for removing this part out of this space in the case when the latter would not be in the desired position. The method may comprise the steps of:

- introducing one or more grafts and/or cancellous bone chips between the strands, in the intervertebral space, and

- using the strands so as to hold this graft or these grafts and/or chips between the vertebrae and compact them.

The method may comprise the step consisting of joining the strands to each other, when these strands are left in place, or the step consisting of removing these strands.

The method may comprise the step consisting of using said second intervertebral part and engaging this second part on at least one of the two strands right up to a position in which this second part is placed in proximity to said first part in the continuity of the latter. The method also comprises the steps consisting of using an instrument as mentioned before and of introducing said first intervertebral part into the intervertebral space to be treated by means of this instrument, by a posterior approach, a side approach or an intermediate approach between the posterior approach and the side approach.

In this case, the method advantageously comprises the step consisting of orienting said first intervertebral part relatively to the instrument by means of said strands.

The invention will be better understood and other characteristics and advantages thereof will become apparent, with reference to the appended schematic drawing, which illustrates as non-limiting examples, two possible embodiments of the intervertebral implant and of an instrument, to which it relates.

Fig. 1 is a top, partly sectional view of a first intervertebral part comprised by the implant according to a first embodiment;

Fig. 2 is a perspective view of the instrument;

Fig. 3 is a top, partly sectional view of the instrument, in the disassembled condition;

Fig. 4 is a view of the instrument similar to Fig. 3, in the assembled condition;

Fig. 5 is a perspective view of the distal portion of the instrument;

Fig. 6 is a side view of this distal portion in a position for unblocking a pivoting allowed by this distal portion;

Fig. 7 is a view of the distal portion, similar to Fig. 3, in a position for blocking the pivoting;

Figs. 8-14 are top views of the implant and of the instrument during various successive steps for the placement of the implant between the plates of two vertebrae;

Fig. 15 is a top, partially sectional view of first and second intervertebral parts comprised by the implant according to a second embodiment; and

Fig. 16 is a view of this implant during its placement between the plates of two vertebrae. Figs. 8-14 illustrate an intervertebral implant 1 with which a vertebra 100 may be immobilized relatively to the overlying vertebra 100 and an instrument 2 for placing this implant 1 between the plates 101 of both vertebrae.

The implant 1 comprises a first intervertebral part 5 intended to be inserted between the plates 101 of both vertebrae 100 to be immobilized and a bond or flexible ligament 6 forming two strands 6a, 6b jutting out from this part 5.

The part 5 has a curved shape substantially corresponding to the curvature which is exhibited by the anterior face of the body of a vertebra and a length which it occupies, once placed between the plates 101 , the major portion of the area of these plates bordering this anterior face (cf. Figs. 11 -14).

Moreover it has a width so that it may be introduced into the intervertebral space to be treated by a posterior approach, by a side approach or by an intermediate approach between the posterior approach and the side approach (cf. Figs. 8 and 9).

As this is seen more particularly in Fig. 1 , the part 5 has faces 10 intended to come into contact with the plates 101 , provided with series of ribs 11 with a triangular section. These ribs 11 provide a support without any sliding of the part 5 against the plates 101. The part 5 also comprises an interior housing 12 emerging out in the faces 10. This housing 12 is intended to receive one or more grafts and/or cancellous bone chips 102 before its introduction into the intervertebral space.

It also comprises a circular wall 15 protruding from one of its ends, according to an angle of the order of 120-130 degrees relatively to its longitudinal axis. This wall 15 surrounds a rounded cavity 16, with a more or less hemispherical shape, in the bottom of which a tapped bore 17 coaxial with the cavity 16 emerges.

The part 5 moreover comprises internal conduits 18, 19 allowing the ligament 6 to be slidably engaged at one of its longitudinal ends, this ligament to pass along its convex face and the ligament 6 to be then slidably engaged at the other of its longitudinal ends. The ligament 6 may notably consist of a braid of implantable fibrous material for example polyester. It is preferably flattened and has a width substantially corresponding to the height of the intervertebral space to be restored or slightly smaller than this height. With reference to Figs. 2-7, it is apparent that the instrument 2 comprises a body 20 in two portions 21 , 22 and a jointed head 23.

The portion 21 comprises a portion 25 forming a grip handle, a threaded portion 26 and a portion 27 forming a rod. At its distal end, this rod 27 is pierced with a transverse conduit 28. The portion 22 is tubular; it comprises a tapped portion 30 capable of being engaged on the portion 26 of the part 21 by screwing and a portion 31 capable of slidably receiving the rod 27.

As shown in Figs. 3 and 4, the conduit 28 receives in itself a spindle 32 for mounting the head 23 on the end of the rod 27. This spindle 32 may notably be retained in the conduit 28 by force-fitting it into the latter.

With reference to Figs. 5-7, it is apparent that the head 23 comprises a base portion 35 connected to the rod 27 and a threaded pin 36 protruding from this base portion 35 on the side opposite to the one through which this portion 35 is connected to the rod 27. The base portion 35 is of a general partially spherical shape. It is hollow inside so that it may be engaged onto the end of the rod 27 and comprises two transverse diametrically opposite lumens 37 for receiving the ends of the spindle 32. These lumens 37 have their lengths directed parallel to the axis of the pin 36. The base portion 35 also comprises two diametrically opposite notches

38 made along an axis perpendicular to the one along which the lumens 37 are laid out. These notches 38 provide mobility of the head 23 relatively to the remainder of the instrument 2, upon pivoting around the ends of the spindle 32. The portion 31 has a length such that, when the portion 30 is completely screwed onto the portion 26 and when the portion 22 is in contact with the handle 25 (cf. Figs. 4 and 6), the distal end of this portion 31 is set back from the base portion 35 of the head 23 and is not an obstacle to the pivoting of the head 23 relatively to the remainder of the instrument 2. This length of the portion 31 however is such that, when the portion 22 is moved away from the portion 25 by partly unscrewing the portion 30 relatively to the portion 26, the distal end of the portion 31 may be tightened against the base portion 35 so as to fix the head 23 in a determined angular position (cf. Fig. 7).

The lumens 37 have a length of the order of twice the diameter of the spindle 32. In the position in which pivoting of the head 23 is possible (cf. Fig. 6), they allow a play of this head 23 relatively to the spindle 32 so that the assembly forms a universal joint allowing unscrewing of the pin 36 by rotation of the body 20 along its axis, notwithstanding angulation of this pin 36 relatively to this body 20.

The pin 36, as for it, is conformed so that it may be screwed into the bore 17 of the part 5.

In practice, the part 5 is connected to the ligament 6 by engaging this ligament into the conduits 18 and 19 and it is fitted out with one or several grafts and/or bone chips 102 in its housing 12; it is then connected to the instrument 2 by screwing the pin 36 into the bore 17. The portions 21 and 22 are then actuated so as to block the head 23 in the position in which the part 5 is in the extension of the body 20. The implant 1 is then introduced into the intervertebral space by means of the instrument 2, by a posterior, side or intermediate approach, the part 5 carrying along with it both strands 6a, 6b of the ligament (cf. Figs. 8 and 9).

The portions 21 and 22 are then actuated so as to unblock the pivoting of the head 23, so that the part 5 may be brought into an angulation position relatively to the body 20 (cf. Fig. 10), until it assumes a position at the anterior area of the vertebral plates 101 , along the anterior face of these plates (cf. Fig. 11 ). The strands 6a, 6b may be used for directing and positioning the part 5 in the intervertebral space in the manner of strings of a kite.

The instrument 2 is then separated from part 5 by unscrewing the pin 36, and is then removed (cf. Fig. 12). If it turned out that the part 5 is not perfectly positioned, the strands 6a, 6b might be used for removing this part 5 out of the intervertebral space and for starting to introduce it again. Once the part 5 is set into place, the strands 6a, 6b are more or less used as a guide for introducing into the intervertebral space, one or several grafts and/or cancellous bone chips 103, and allowing, at this intervertebral space, an area to be delimited for receiving this graft or these grafts and/or bone chips 103 (cf. Fig. 13). When this introduction is completed, both of the strands 6a, 6b allow this graft or these grafts and/or bone chips 103 to be encircled so as to avoid their moving out of the intervertebral space, and compacted so that they are properly brought into contact with the vertebral plates 101. The ligament 6 may be left in place as shown in Fig. 14; the strands 6a,

6b are in this case joined to each other by knotting, as illustrated; they may also be joined by means of a joining part slidably engaged on them and comprising anti-return means, these means preventing this joining part from sliding in the direction opposite to its engagement direction. The practitioner may also choose to remove the ligament 6, which is easily achieved by pulling on a strand 6a or 6b of the latter and by sliding it relatively to the part 5.

In this implantation position, with the part 5, it is possible restore the height of the intervertebral space and to prevent crushing of the grafts or chips 103, by only occupying a marginal surface of the intervertebral space and therefore by freeing a large surface for placing the graft(s) and/or bone chips 103. With the ligament 6, a large amount of these grafts and/or chips 103 may be introduced and maintained, allowing them to be compacted.

In the embodiment shown in Fig. 15, the implant 1 comprises a part 5 and a ligament 6 (not shown) in all points identical with those described earlier. It further comprises a second intervertebral part 40, intended to be slidably engaged on both strands 6a, 6b until it is placed in proximity to the part 5, in the continuity of the latter (cf. Fig. 16).

For this purpose, this part 40 comprises on one of its sides a longitudinal conduit 41 and on its opposite side, a conduit 42, the conduit 41 being intended to receive the strand 6a emerging from the conduit 18 of the part 5 whereas the conduit 42 is intended to receive the strand 6b emerging from the conduit 19 of this part 5. The conduit 41 is substantially rectilinear and extends over the major portion of the length of the part 40 whereas the conduit 42 is curved and exclusively extends at the proximal portion of this part 40. These conduits 41 and 42 are thereby conformed in order to fit the travel of the strands 6a and 6b after placing the graft(s) and/or bone chips 130, as visible in Fig. 16.

Further, the part 40 comprises a rounded distal protrusion 43, capable in the implantation position of being engaged into the cavity 16 of the part 5. With this engagement, the part 40 may be positioned in a determined way relatively to the part 5 and this part 40 may come in close proximity to this part 5. As this is apparent, said second intervertebral part 40 provides a more complete restoration of the intervertebral height and an increase in the surface of the vertebrae 100 bearing against the implant 1. Further, as it comes in the continuity of part 5, the graft(s) and/or bone chips 103 may be held in the intervertebral space securely by obstructing the entry point of the implant 1 between the vertebrae 100. This securization is particularly useful when the ligament 6 is not left in place. The part 40 alternatively may comprise anti- return means at its conduits 41 and 42, notably as teeth or claws capable of being supported in the material forming the strands 6a, 6b, and of thereby forming said joining part. It is apparent from the foregoing that the invention provides an intervertebral implant 1 with which a vertebra may be immobilized relatively to another, which as compared with homologous implants of the prior art, has determining advantages of being easy to place, notably in a position of the vertebral plates as anterior as possible, by a not very invasive approach, and by which perfect "fusion", of the treated vertebrae may be obtained.

The invention was described above with reference to embodiments only given as examples. It is obvious that it extends to all the other embodiments covered by the claims appended herein.

Claims

1 - Intervertebral implant (1) with which a vertebra (100) may be immobilized relatively to another, comprising a first intervertebral part (5) intended to be inserted between two vertebrae (100) to be immobilized, characterized in that it comprises two flexible strands (6a, 6b) connected to the first intervertebral part (5), the length of which is such that these strands (6a, 6b) jut out from the patient when the first intervertebral part (5) is placed between the vertebrae (100).

2 - Intervertebral implant (1 ) according to claim 1 , characterized in that the first intervertebral part (5) has a width such that it is able to be introduced into the intervertebral space to be treated by a posterior approach, by a side approach or by an intermediate approach between the posterior approach and the side approach.

3 - Intervertebral implant (1 ) according to claim 1 or claim 2, characterized in that said first intervertebral part (5) has a curved shape substantially corresponding to the curvature exhibited by the front face of a vertebral body.

4 - Intervertebral implant (1 ) according to any of claims 1 to 3, characterized in that the first intervertebral part (5) is devoid of one or more housings (12) for receiving one or more grafts and/or cancellous bone chips (102).

5 - Intervertebral implant (1 ) according to any of claims 1 to 4, characterized in that the first intervertebral part (5) comprises raised features (11 ) protruding from at least one of its faces (10) intended to come into contact with the vertebral plates (101 ).

6 - Intervertebral implant (1 ) according to any of claims 1 to 5, characterized in that the flexible strands (6a, 6b) each have a width substantially corresponding to the height of the intervertebral space to be restored, or slightly less than this height. 7 - Intervertebral implant (1 ) according to any of claims 1 to 6, characterized in that the first intervertebral part (5) comprises a strand (6a) connected to it at one of its longitudinal ends and the other strand (6b) connected to it at the other of its longitudinal ends. 8 - Intervertebral implant (1 ) according to any of claims 1 to 7, characterized in that both of the flexible strands (6a, 6b) are formed by two portions of a same flexible bond (6).

9 - Intervertebral implant (1 ) according to any of claims 1 to 8, characterized in that the first intervertebral part (5) comprises, at one of these longitudinal ends, a first conduit (18) for providing a passage for the flexible bond (6) through it, and, at its other longitudinal end, a second conduit (19) providing a passage for the flexible bond (6) through it; the flexible bond (6) passes through said first conduit (18), and then runs along the first intervertebral part (5) and then passes through said second conduit (19). Both aforementioned strands (6a, 6b) are thereby formed by the portion of this flexible bond (6) jutting out from said first conduit (18) and from said second conduit (19).

10 - Intervertebral implant (1 ) according to any of claims 1 to 9, characterized in that it comprises one second intervertebral part (40) capable of being inserted between two vertebrae (100) to be immobilized, intended to be slidably engaged on at least one of the two strands (6a, 6b) and to be placed in proximity to the first intervertebral part (5), in the continuity of the latter. 11 - Intervertebral implant (1 ) according to claim 10, characterized in that said first intervertebral part (5) and said second intervertebral part (40) comprise reciprocal interengagement means (16, 43) allowing the second part (40) to be positioned in a determined way relatively to the first part (5) and this second part (40) to come in close proximity to the first part (5). 12 - Assembly comprising the implant according to any of claims 1 to 11 and an instrument (2) for setting up the implant (1 ), characterized in that the instrument (2) comprises:

- a rigid rod (31) for introducing said first intervertebral part (5) between the vertebrae (100) to be treated, by a posterior approach, a side approach and/or an intermediate approach between the posterior approach and the side approach; and

- removable connecting means (17, 36) between this rigid rod (31 ) and said first intervertebral part (5), this connection being able to be suppressed when said first intervertebral part (5) is set into place between the vertebrae (100).

13 - Assembly according to claim 12, characterized in that the instrument (2) comprises pivot means (32, 37, 38) with which the first intervertebral part (5) may be pivoted between a first position, in which this first intervertebral part (5) is substantially found in the extension of said rigid rod (31 ), and a second position, in which this first intervertebral part (5) is angled relatively to this rigid rod (31 ), notably substantially at right angles to this rod (31 ). 14 - Assembly according to claim 13, characterized in that the instrument (2) comprises means for blocking/unblocking the pivoting allowed by said pivot means (32, 37, 38).

15 - Assembly according to claim 14, characterized in that the instrument (2) comprises - a tube forming said rigid rod (31 );

- an internal rod (27) engaged in this tube (31 );

- a pivotably mounted head (23) on the distal end of said internal rod (27) comprising a threaded pin (36) capable of being screwed into a tapped hole (17) made in said first intervertebral part (5), and - tightenable means (26, 30) for displacing the internal rod (27)/head (23) assembly relatively to said tube (31 ), between a distal displacement position of the internal rod (27) relatively to the tube (31 ), in which said head (23) does not bear against said tube (31 ) and is therefore mobile relatively to the internal rod (27), and a proximal displacement position of the internal rod (27) relatively to the tube (31 ), in which said head (23) bears against said tube (31 ) so that it is immobilized relatively to this tube (31 ) and to the internal rod (27).

16 - Surgical method for immobilizing a vertebra (100) relatively to another one, characterized in that it comprises the steps of:

- using a first intervertebral part (5) according to any of claims 1 to 11 ; - introducing said intervertebral part (5) and a portion of said strands (6a, 6b) between the vertebral plates of two vertebrae (100), the other portion of these strands (6a, 6b) jutting out on the outside of the patient; - using the strands (6a, 6b) for directing and positioning said first part in the intervertebral space, or for removing this part out of this space in the case when the latter would not be in the desired position.

17 - Surgical method according to claim 16, characterized in that it comprises the steps of:

- introducing one or more grafts and/or cancellous bone chips (103) between the strands (6a, 6b), in the intervertebral space, and

- using the strands (6a, 6b) so as to hold this graft or these grafts and/or chips (103) between the vertebrae (100) and compact them. 18 - Surgical method according to claim 16 or claim 17, characterized in that it comprises the step consisting of joining the strands (6a, 6b) to each other, when these strands (6a, 6b) are left in place, or the step consisting of removing these strands (6a, 6b).

19 - Surgical method according to any of claims 16 to 18, characterized in that it comprises the step consisting of using said second intervertebral part (40) and engaging this second part (40) on at least one of the two strands (6a, 6b) right up to a position in which this second part (40) is placed in proximity to said first part (5) in the continuity of the latter.

20 - Surgical method according to any of claims 16 to 19, characterized in that it comprises the steps consisting of using an instrument (2) according to any of claims 12 to 15 and of introducing said first intervertebral part (5) into the intervertebral space to be treated by means of this instrument (2), by a posterior approach, a side approach or an intermediate approach between the posterior approach and the side approach. 21 - Surgical method according to claim 20, characterized in that it comprises the step consisting of orienting said first intervertebral part (5) relatively to the instrument (2) by means of said strands (6a, 6b).