FR2978347A1 - MATERIAL OF VERTEBRAL OSTEOSYNTHESIS - Google Patents

Abstract

This material (1) comprises an intervertebral implant (2) intended to be inserted between the bodies of two vertebrae (100) and screws (3) immobilizing the implant (2) relative to the vertebrae (100), the implant (2) forming two respective bearing surfaces (6, 7) for the bodies of the vertebrae (100) and comprising holes (8, 9) for fitting engagement of at least a first screw (3) and at least one second screw (3); the axis of at least one first hole (8), oriented towards a first of said bearing surfaces (6), forms in the sagittal plane a first angle with a horizontal median plane (P) of the implant (2), and the axis of at least one second hole (9), oriented towards the second of said bearing surfaces (7), forms in the sagittal plane a second angle with the same horizontal median plane (P ) of the implant. According to the invention, said first angle is 40 ° to 50 °, and said second angle is 20 ° to 30 °.

Description

The present invention relates to a vertebral osteosynthesis material. It is well known to treat the degeneration of an intervertebral disk by immobilizing the two vertebrae relative to each other by means of a bone junction between these two vertebrae, such a junction being referred to as "vertebral fusion". . This bone junction is generally performed by means of a vertebral osteosynthesis material comprising an intervertebral implant, intended to be inserted between the trays of the two vertebrae, and screws for immobilizing the implant relative to the bodies of the vertebrae. The implant is usually hollow and contains one or more natural or synthetic grafts intended to be colonized by the growing bone cells. The screws are intended to be engaged through holes formed in the anterior wall of the implant and then to be inserted into the bodies of the vertebrae; the axis of the holes forms, in the sagittal plane, an angle of substantially 45 ° with a horizontal median plane of the implant, that is to say a plane of symmetry of the implant extending parallel to the vertebral plates when the implant is placed between the vertebrae. These screws serve to immobilize the implant with respect to the vertebrae while the growth of bone cells takes place through the graft or grafts. It will be understood that terms of reference in space such as "sagittal" or "horizontal" earlier employed above or "higher", "lower", etc. Employed in the remainder of this specification, refers to the patient's body and should therefore be understood with reference to the position of the implant when placed on a patient. The aforementioned type of material proves to present a significant risk of play of anchoring screws, and therefore of the implant, with respect to the vertebrae over time, possibly leading to anterior expulsion of the implant. This risk results from: - the anatomical angulation (lordosis) of the vertebrae of the joints most often concerned by a degeneration of the intervertebral disc (fourth lumbar vertebra (called "L4") and fifth lumbar vertebra (called "L5")); fifth lumbar vertebra and first sacral vertebra (so-called "SI")); the weight of the patient supported by these vertebrae, and repeated urges exerted by the movements of the vertebrae on said anchorages.

Such play frustrates or even prevents the achievement of good bone fusion vertebrae, and the present invention aims to overcome this essential disadvantage. One known way to increase the resistance of the anchoring of the material to the vertebrae is to provide not two but four screws anchoring the implant, two screws being inserted into the overlying vertebra and the other two screws being inserted in the underlying vertebra. Such a material, however, has the disadvantage of being relatively difficult to implement in view of the presence, at L4-L5, of the aortic bifurcation. This bifurcation hinders access to the screw engagement holes and the work of setting up these screws, and its mobilization involves a delicate and time-consuming intervention to implement. The present invention also aims to overcome this disadvantage. In addition, there is currently no vertebral osteosynthesis material as mentioned above adapted to be placed under optimal conditions, either L4-L5 or L5-S1. The main objective of the invention is therefore to provide a vertebral osteosynthesis material allowing a perfectly resistant anchoring of the implant to the vertebrae. Another object of the invention is to provide such a material, allowing placement of the L4-L5 implant with as little mobilization as possible of the aortic bifurcation. A further object of the invention is to provide such a material, allowing optimized anchoring of the implant both L4-L5 and L5-S1. The material concerned comprises, in a manner known per se, an intervertebral implant intended to be inserted between the bodies of two vertebrae and immobilizing screws of the implant relative to the vertebrae, the implant forming two respective bearing surfaces. for the bodies of the vertebrae and comprising fixed engagement holes of at least a first screw and at least a second screw; the axis of at least one first hole, oriented towards a first of said bearing surfaces, forms in the sagittal plane a first angle with a horizontal median plane of the implant, i.e. a plane of symmetry of the implant extending substantially between said bearing surfaces, and the axis of at least one second hole, oriented towards the second of said bearing surfaces, forming in the sagittal plane a second angle with this same median horizontal plane of the implant. According to the invention, said first angle is 30 ° to 50 °, and said second angle is 10 ° to 30 °. The inventor has indeed found that a conventional angulation of the screws, 45 ° on the upper and lower sides of the implant led to orient these screws substantially along a tangent to the curvilinear path that follows each vertebra during the game of the game. vertebral articulation, this game being made around a point of articulation lying behind the vertebrae, near the facets; he was thus able to determine that this orientation greatly solicited the anchoring of the screws along the longitudinal axis of these screws, and this, simultaneously on the anchor screw (s) inserted in the overlying vertebra and on the screw (s). anchorage inserted into the underlying vertebra. These simultaneous axial stresses, exerted on the cancellous bone of the vertebral bodies, could be identified as being at the origin of the aforementioned risk of screw play and, consequently, the risk of previous displacement of the implant, even previous expulsion from it. The inventor was then led to design the equipment according to the invention, wherein said first hole has a relatively conventional angulation, which allows, during the introduction of the equipment, to achieve by means of a first screw an immobilization effective intervertebral implant with respect to the vertebrae in the anterior direction; once this immobilization has been performed, a second screw can be placed in said second hole, without risk of anterior displacement of the implant, which would otherwise occur, this displacement resulting from the support of the screw in the hard bone and low retention of the implant in the anterior direction produced by such angulation of 20 ° to 30 °. This angulation thus makes it possible at the same time to support the screw in hard bone and to orient the screw at a non-tangent angulation to said curvilinear trajectory, thus producing a very strong anchoring of the implant, compensating for largely a possible weakening of the anchoring of said first screw. Such a weakening occurs to a much lesser degree than with a material according to the prior art, so that a progressive play of the anchors is perfectly contained.

This results in obtaining a very strong anchorage of a vertebral implant to the bodies of the two vertebrae between which this implant is inserted. Preferably, said first angle is 45 °, and said second angle is 25 °.

Preferably, the intervertebral implant comprises two first holes and two second holes, thus two first screws and two second screws. These two pairs of screws make it possible to obtain an even stronger anchorage. Preferably, in this case, said first holes are arranged on either side of said second holes. This arrangement makes it possible, during use at L4-L5, easy access to said second holes, this access being easy in the space delimited in the lower part by the aortic bifurcation, without mobilization of the aortic bifurcation or with a limited mobilization of it.

Advantageously, said two second holes are arranged relative to each other so that their axes diverge in the frontal plane, from the front side of these holes to the posterior side thereof, forming one with the other an angle of 6 ° to 12 °. This divergence is favorable to the realization of a bone anchorage perfectly resistant to the forces transmitted by the vertebra to the screws engaged in these second holes, notwithstanding said angulation of these holes relative to said reference plane. Said angle of divergence is preferably 8 °. Preferably, said first two holes are arranged so that their axes are, in the frontal plane, parallel to each other. The same material, thus shaped, is perfectly suitable for placement in either L4-L5, with said second holes oriented towards L4 and said first holes facing L5, or, by a 180 ° reversal of the implant. at L5-S1, said second holes then facing SI and said first holes facing L5. The invention will be better understood, and other features and advantages thereof will become apparent, with reference to the appended schematic drawing, showing, by way of non-limiting example, a preferred embodiment of the material it relates.

Figure 1 is a perspective view of the intervertebral implant that it comprises; Figure 2 is a side view of one of the anchor screws of the implant to the vertebrae; Figure 3 is a front view of the material set up between the fifth lumbar vertebra (called "L5") and the first vertebra of the sacrum (called "SI"); Figure 4 is a sagittal view, with identification of a median plane of the implant and extension axes of the screws; and Figure 5 is a front view of the material placed between the fourth lumbar vertebra (called "L4") and the fifth lumbar vertebra, with dotted schematization of the aortic bifurcation. FIGS. 3 to 5 represent a vertebral osteosynthesis material 1, comprising an intervertebral implant 2, intended to be inserted between the plates 101 of the two vertebrae 100, and screws 3 immobilizing the implant 2 relative to the bodies of the vertebrae 100. Referring more particularly to Figure 1, it appears that the implant 2 is in the piece-piece form, comprising an anterior wall 2a, a posterior wall 2b, two side walls 2c and an anteroposterior intermediate wall 2d. These different walls delimit between them two compartments 5 with natural or synthetic grafts, intended to be colonized by the growing bone cells, and together form a bearing surface 6 of the vertebral plateau 101 of one of the vertebrae 100 and a surface 7 resting the vertebral plate 101 of the other vertebra 100. The walls 2b to 2d have pins or anchoring ribs at these bearing surfaces 6 and 7. The front wall 2a has four holes 8, 9 d The first two holes 8 are located on the lateral sides of the front wall 2a and are directed towards the surface 6, into which they open; as it appears in FIG. 4, the axes of these holes 8 form in the sagittal plane an angle of the order of 45 ° with a horizontal median plane P of the implant 2, that is to say a plane of symmetry of this implant extending substantially between said bearing surfaces 6 and 7. The two second holes 9 are located on the inner part of the wall 2a, between the holes 8, and are directed towards the surface 7, in which they also open, the axes of these holes 9 forming in the sagittal plane an angle of the order of 25 ° with the horizontal median plane P. It further appears that said second holes 9 are arranged relative to the other so that their axes diverge in the frontal plane (see FIGS. 3 and 5) from the anterior side of these holes 9 towards the posterior side thereof, forming with each other an angle of 8 °.

Said holes 8 are instead arranged so that their axes are, in the frontal plane, parallel to each other. Said anterior wall 2a furthermore has a central opening and a cavity for mounting a tool for manipulating and impinging the implant 2.

The screws 3 serve to immobilize the implant with respect to the vertebrae 100 while the growth of the bone cells takes place through said grafts. Referring to Figure 2, it appears that they can be described as conventional, except that they have proximal portions of diameters adjusted to the diameters of the holes 8 and 9, so that they can be precisely guided by those this.

Figures 3 and 4 show a use of hardware 1 at L5-S1. In this case, the surface 6 receives the plate 101 of L5 and the surface 7 abuts against the SI plate. In practice, after insertion of the implant 2 between the vertebrae 100, two screws 3 are placed in the holes 8, making it possible to effectively immobilize the implant 2 relative to the vertebrae 100 in the anterior direction; the other two screws 3 are then placed in the holes 9 without any risk of anterior displacement of the implant 2. The angulation of 25 ° of these two other screws 3 simultaneously allows a support of these screws in hard bone and an orientation of the screws in a non-tangent angulation to the curvilinear trajectory that follows the vertebra SI during the game of the joint, this game being around a hinge point located behind the vertebral bodies, the level of facets. This results in the production of a very strong anchoring of the implant 2, reinforced by the divergence of these second screws relative to each other, making it possible to compensate widely for any weakening of the anchoring of the two screws 3 8. Such a weakening occurs in a reduced degree, so that a progressive play of the anchors of these first screws 3 is perfectly contained. The material 1 can also be used at L4-L5, as shown in FIG. 5. The internal arrangement of the two holes 9 allows easy access to these holes, in the space delimited at the bottom by the aortic bifurcation 102, hence without mobilization, or with limited mobilization, of this bifurcation. The invention therefore provides a vertebral osteosynthesis material having the decisive advantages of allowing a perfectly resistant anchoring of the implant 2 to the vertebrae 100, an implantation of the implant 2 into L4-L5 with a mobilization as small as possible aortic bifurcation 102, and optimized anchoring of the implant 2 both L4-L5 and L5-S1. The invention has been described above with reference to an embodiment provided by way of example. It goes without saying that it is not limited to this embodiment but that it extends to all other embodiments covered by the appended claims.

Claims (7)

CLAIMS1 - Spinal osteosynthesis equipment (1), comprising an intervertebral implant (2) intended to be inserted between the bodies of two vertebrae (100) and screws (3) for immobilizing the implant (2) relative to at the vertebrae (100), the implant (2) forming two respective bearing surfaces (6, 7) for the bodies of the vertebrae (100) and having holes (8, 9) of engagement adjusted by at least one first screw (3) and at least one second screw (3); the axis of at least one first hole (8), oriented towards a first of said bearing surfaces (6), forms in the sagittal plane a first angle with a horizontal median plane (P) of the implant (2), i.e., a plane of symmetry of the implant (2) extending substantially between said bearing surfaces (6, 7), and the axis of at least one second hole ( 9), oriented towards the second of said bearing surfaces (7), forms in the sagittal plane a second angle with the same horizontal median plane (P) of the implant; characterized in that - said first angle is 30 ° to 50 °, and - said second angle is 10 ° to 30 °. 2 - Material (1) according to claim 1, characterized in that - said first angle is 45 °, and - said second angle is 25 °. 3 - Material (1) according to claim 1 or claim 2, characterized in that the implant (2) intervertebral comprises two first holes (8) and two second holes (9), so two first screws (3) and two second screws (3). 4 - Material (1) according to claim 3, characterized in that said first holes (8) are arranged on either side of said second holes (9). 5 - Material (1) according to claim 3 or claim 4, characterized in that said two second holes (9) are arranged relative to each other so that their axes diverge in the frontal plane, since the anterior side of these holes (9) towards the posterior side thereof, forming with each other an angle of divergence of 6 ° to 12 °. 6 - Material (1) according to claim 5, characterized in that said divergence angle is 8 °. 7 - Material (1) according to one of claims 1 to 6, characterized in that said first two holes (8) are arranged so that their axes are, in the frontal plane, parallel to each other .