WO2013014590A1

WO2013014590A1 - Vertebral osteosynthesis equipment

Info

Publication number: WO2013014590A1
Application number: PCT/IB2012/053718
Authority: WO
Inventors: Nicholas Birch
Original assignee: Medicrea International
Priority date: 2011-07-25
Filing date: 2012-07-20
Publication date: 2013-01-31
Also published as: FR2978347A1; FR2978347B1

Abstract

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

Description

VERTEBRAL OSTEOSYNTHESIS EQUIPMENT

The present invention relates to vertebral osteosynthesis equipment.

It is well known to treat the degeneration of an intervertebral disc by immobilizing two vertebrae relative to one another using a bone junction between said two vertebrae, such a junction being called "spinal fusion." This bone junction is generally done using vertebral osteosynthesis equipment comprising an intervertebral implant, designed to be inserted between the plates of two vertebrae, and screws for immobilizing the implant relative to the bodies of the vertebrae. The implant is generally hollow and contains one or more natural or synthetic grafts intended to be colonized by growing bone cells. The screws are designed to be engaged through holes formed in the front wall of the implant, then inserted into the bodies of the vertebrae; the axis of the holes forms, in the sagittal plane, an angle of substantially 45° with the horizontal median plane of the implant, i.e. a plane of symmetry of the implant extending parallel to the vertical plates when the implant is placed between the vertebrae. These screws serve to immobilize the implant relative to the vertebrae for the time necessary for the bone cells to grow through the graft(s).

It will be understood that the spatial reference terms such as "front," "sagittal" or "horizontal" used above, or "upper," "lower," etc. used in the rest of this description, refer to the body of the patient and must therefore be understood in reference to the position of the implant when it is placed on a patient.

The aforementioned type of equipment has a significant risk of the anchor screw, and therefore the implant, coming loose relative to the vertebrae over time, which may lead to a forward expulsion of the implant. This risk results from:

the anatomical angulation (lordosis) of the vertebrae of the joints most often affected by degeneration of the intervertebral disc (fourth lumbar vertebra (L4) and fifth lumbar vertebra (L5)); fifth lumbar vertebra and first sacral vertebra (S1 ));

the weight of the patient borne by said vertebrae, and

repeated stresses exerted by movements of the vertebrae on said anchors.

Such loosening impedes, or even prevents, the accomplishment of a good bone fusion of the vertebrae, and the present invention aims to resolve this essential drawback.

One known means for increasing the strength of the anchoring of the equipment to the vertebrae consists of providing not two, but four anchor screws for the implant, two screws being inserted into the overlying vertebra and the other two being inserted into the underlying vertebra. Such equipment nevertheless has the drawback of being relatively difficult to place, given the presence of the aortic bifurcation at L4-L5. This bifurcation hinders access to the engagement holes of the screws as well as the work to place those screws, and its mobilization involves a delicate and lengthy operation. The present invention also aims to resolve this drawback.

Le docu m ents GB 2 454 229, US 2010/106249, WO 2010/054181 and

EP 1 247 503 show various devices according to the prior art that do not overcome the drawbacks indicated above.

Therefore, to date, there is no existing vertebral osteosynthesis equipment as cited above that can be placed under optimal conditions, either at L4-L5 or at L5-S1 .

The primary aim of the invention is to provide vertebral osteosynthesis equipment allowing completely resistant anchoring of the implant to the vertebrae.

Another aim of the invention is to provide such equipment, allowing placement of the implant at L4-L5 with a mobilization as reduced as possible of the aortic bifurcation.

One additional aim of the invention is to provide such equipment allowing optimized anchoring of the implant both at L4-L5 and at L5-S1.

The equipment in question comprises, in a known manner, an intervertebral implant, designed to be inserted between the bodies of two vertebrae, and screws for immobilizing the implant in relation to the vertebrae, the implant forming two respective bearing surfaces for the bodies of the vertebrae and comprising engagement holes adjusted to at least one first screw and at least one second screw; the axis of at least one first hole, oriented on the side of a first of said bearing surfaces, forms a first angle in the sagittal plane 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 on the side of the second of said bearing surfaces, forms a second angle in the sagittal plane with that same horizontal median plane of the implant.

According to the invention,

- said first angle is from 30° to 50°, and

- said second angle is from 10° to 30°.

The inventor has in fact noted that a traditional angulation of the screws, of 45° on the upper and lower sides of the implant, led to orienting said screws substantially along a tangent to the curvilinear path that each vertebra follows during the play of the vertebral articulation, that play taking place around an articulation point located behind the vertebrae, near the facets; he was therefore able to determine that this orientation was significantly stressing the anchoring of the screws along the longitudinal axis of said screws, simultaneously on the anchor screw(s) inserted into the overlying vertebra and on the anchor screw(s) inserted in the underlying vertebra. These simultaneous axial stresses, exerted on the cancellous bone of the vertebral bodies, were able to be identified as being at the source of the aforementioned risk of loosening of the screws and, as a result, the risk of forward movement of the implant, or even forward expulsion thereof.

The inventor was consequently led to design the equipment according to the invention, in which said first hole has a relatively traditional angulation, which makes it possible, when the equipment is placed, to achieve an effective immobilization of the intervertebral implant relative to the vertebrae in the forward direction using at least one first screw; once this first immobilization is done, a second screw can be placed in said second hole, without risk of forward movement of the implant, which would occur otherwise, that movement resulting from the bearing of the screw in the hard bone and the weak maintenance of the implant in the forward direction produced by such an angulation of 20° to 30°.

This angulation thus simultaneously allows bearing of the screw in the hard bone and orientation of the screw in an angulation that is not tangent to said curvilinear trajectory, therefore the production of a very strong anchoring of the implant, greatly offsetting any weakening of the anchoring of said first screw. Such weakening occurs to a much lesser degree than with equipment according to the prior art, such that gradual loosening of the anchoring is completely contained.

This results in the obtainment of very resistant anchoring of a vertebral implant to the bodies of the two vertebrae between which that 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, therefore two first screws and two seconds screws.

These two pairs of screws make it possible to obtain an even further strengthened anchoring.

Preferably, in that case, said first holes are positioned on either side of said second holes.

When used in L4-L5, this arrangement allows easy access to said second holes, this access being easy in the space delimited in the lower portion by the aortic bifurcation, without mobilizing the aortic bifurcation or with limited mobilization thereof. Advantageously, said two second holes are formed relative to one another such that their axes diverge in the frontal plane, from the front side of said holes toward the rear side thereof, forming an angle of 6° to 12° with one another.

This divergence is favorable to the achievement of bone anchoring that is completely resistant to the forces transmitted by the vertebra to the screws engaged in said second holes, notwithstanding said angulation of those holes relative to said reference plane.

Said divergence angle is preferably 8°.

Preferably, said two first holes are arranged such that their axes are parallel to one another in the frontal plane.

The same piece of equipment, configured in this way, is completely adapted to placement either at L4-L5, with said second holes oriented toward L4 and said first holes oriented toward L5, or, by reversing the implant 180°, in L5-S1 , said second holes than being oriented toward S1 and said first holes being oriented toward L5.

The invention will be well understood, and other features and advantages thereof will appear, in reference to the appended diagrammatic drawing, showing, as a non- limiting example, one preferred embodiment of the equipment to which it relates.

Figure 1 is a perspective view of the intervertebral implant it comprises;

figure 2 is a side view of one of the anchor screws for anchoring the implant to the vertebrae;

figure 3 is a frontal view of the equipment placed between the fifth lumbar vertebra (L5) and the first sacral vertebra (S1 );

figure 4 is a sagittal view, referencing a median plane of the implant and the extension axes of the screws; and

figure 5 is a front view of the equipment placed between the fourth lumbar vertebra

(L4) and the fifth lumbar vertebra, diagramming the aortic bifurcation in dotted lines.

Figures 3 to 5 illustrate vertebral osteosynthesis equipment 1 , comprising an intervertebral implant 2, designed to be inserted between the plates 1 01 of two vertebrae 100, and screws 3 for immobilizing the implant 2 relative to the bodies of the vertebrae 100.

In reference more particularly to figure 1 , the implant 2 is shown in the form of a single-unit piece, comprising a front wall 2a, a rear wall 2b, two side walls 2c, and an anteroposterior intermediate wall 2d. These different walls delimit two compartments 5 for natural or synthetic grafts between them, intended to be colonized by the growing bone cells, and jointly form a bearing surface 6 for the vertebral plate 101 of one of the vertebrae 100 and a bearing surface 7 for the vertical plate 101 of the other vertebra 100. The walls 2b to 2d have anchoring spurs or ribs at these bearing surfaces 6 and 7.

The front wall 2a has four adjusted engagement holes 8, 9 for the screws 3. Two first holes 8 are situated on the lateral sides of the front wall 2a and are oriented toward the surface 6, in which they emerge; as shown in figure 4, the axes of these holes 8 form an angle in the sagittal plane in the vicinity of 45° with a horizontal median plane P of the implant 2, i.e. a plane of symmetry of that implant extending substantially between said bearing surfaces 6 and 7. The two second holes 9 are situated on the inner portion of the wall 2a, between the holes 8, and are oriented toward the surface 7, in which they also emerge, the axes of said holes 9 forming an angle in the sagittal plane in the vicinity of 25° with the horizontal median plane.

It also appears that said second holes 9 are arranged relative to one another such that their axes diverge in the frontal plane (cf. figures 3 and 5) from the front side of said holes 9 towards the rear side thereof, forming an angle of 8° with one another.

Said holes 8 are on the other hand arranged such that their axes are parallel to one another in the frontal plane.

Said front wall 2a also has a central opening and cavity, for mounting a tool for handling and impacting the implant 2.

The screws 3 serve to immobilize the implant relative to the vertebrae 100 for the time necessary for the bone cell growth to occur through said grafts. Figure 2 shows that they can be qualified as traditional, except that they have proximal portions with diameters adjusted to the diameters of the holes 8 and 9, such that they may be precisely guided by the latter.

Figures 3 and 4 show a use of the equipment 1 at L5-S1. In that case, the surface 6 receives the plate 101 of L5 and the surface 7 bears against plate of S1.

In practice, after the implant 2 is inserted 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 forward direction; the other two screws 3 are then placed in the holes 9 without any risk of forward movement of the implant 2.

The angulation of 25° of these other two screws 3 simultaneously allows bearing of said screws in the hard bone and orientation of the screws following an angulation that is not tangent to the curvilinear trajectory followed by the vertebra S1 during play of the joint, said play occurring around an articulation point situated behind the vertebral bodies, at the facets. This results in very resistant anchoring of the implant 2, reinforced by the divergence of said second screws relative to one another, making it possible to substantially offset any weakening of the anchoring of the two screws 3 engaged in the holes 8. Such weakening occurs to a lesser degree, such that gradual loosening of the anchoring of said first screws 3 is completely contained.

The equipment 1 can also be used at L4-L5, as shown in figure 5. The inner arrangement of the two holes 9 allows easy access to those holes, in the space delimited in the lower portion by the aortic bifurcation 102, therefore without mobilization, or with limited mobilization, of said bifurcation.

The invention therefore provides vertebral osteosynthesis equipment having the decisive advantages of allowing completely resistant anchoring of the implant 2 to the vertebrae 100, placement of the implant 2 at L4-L5 with as reduced a mobilization as possible of the aortic bifurcation 102, and optimized anchoring of the implant 2 both at L4-L5 and L5-S1 .

The invention has been described above in reference to one embodiment provided as an example. It is of course not limited to that embodiment, but encompasses all embodiments covered by the appended claims.

Claims

1 . Vertebral osteosynthesis equipment (1 ) comprising an intervertebral implant (2) designed to be inserted between the bodies of two vertebrae (100), and screws (3) for immobilizing the implant (2) in relation to the vertebrae (100), the implant (2) forming two respective bearing surfaces (6, 7) for the bodies of the vertebrae (100) and comprising engagement holes (8, 9) adjusted to at least one first screw (3) and at least one second screw (3); the axis of at least one first hole (8), oriented on the side of a first of said bearing surfaces (6), forms a first angle in the sagittal plane with a horizontal median plane (P) of the implant (2), i.e. a plane of symmetry of th e i m p l a nt (2) extending substantially between said bearing surfaces (6, 7), and the axis of at least one second hole (9), oriented on the side of the second of said bearing surfaces (7), forms a second angle in the sagittal plane with that same horizontal median plane (P) of the implant;

characterized in that

- said first angle is from 30° to 50°, and

- said second angle is from 10° to 30°.

2. Equipment (1 ) according to claim 1 , characterized in that

- said first angle is 45°, and

- said second angle is 25°.

3. Equipment (1 ) according to claim 1 or claim 2, characterized in that the intervertebral implant (2) comprises two first holes (8) and two second holes (9), therefore two first screws (3) and two seconds screws (3).

4. Equipment (1 ) according to claim 3, characterized in that said first holes (8) are positioned on either side of said second holes (9).

5. Equipment (1 ) according to claim 3 or claim 4, characterized in that said two second holes (9) are formed relative to one another such that their axes diverge in the frontal plane, from the front side of said holes (9) toward the rear side thereof, forming an angle of 6° to 12° with one another.

6. Equipment (1 ) according to claim 5, characterized in that said divergence angle is 8°.

7. Equipment (1 ) according to anyone of claims 1 -6, characterized in that said two first holes (8) are arranged such that their axes are parallel to one another in the frontal plane.