FR2913328A1 - Intervertebral dynamic stabilization assembly for arthrodesis of adjacent vertebrae, has elastic units interacting until equilibrium point is found, where point is controlled by external forces e.g. patient weight of and muscle contraction - Google Patents

Abstract

The assembly has an extra-discal elastic unit (40) e.g. spring, arranged behind an intervertebral space (30) and limiting displacement between two adjacent vertebrae (10, 20) in a direction of intervertebral flexion. An intra-discal elastic unit (42) e.g. spring, ensures intervertebral spacing and compressed during lordosis of the vertebrae to control the lordosis. The elastic units mutually interact until an equilibrium point is found, where the equilibrium point is displaced in a dynamic manner and controlled by external forces e.g. weight of a patient and contraction of muscles.

Description

INTERVERTEBRAL DYNAMIC STABILIZATION ASSEMBLY FOR ARTHRODESIS

  The present invention relates to an intervertebral dynamic stabilization assembly for arthrodesis. The invention is in the field of arthrodesis, namely bone fusion between at least two adjacent vertebrae. The known state of the art uses an intra-disc cage, associated with a rod or a plate. The latter, connecting two adjacent vertebrae, is secured on pedicular screws that penetrate into the vertebral bodies opposite. This known solution, however, involves certain disadvantages. Indeed, it has been found that patients with these components, are subject to stiffness, as well as to poor positions, particularly related to deficiency of lordosis. Under these conditions, these patients suffer premature wear of the disk placed immediately above the upper vertebra, among those receiving the pedicle screws. That being said, the invention aims to remedy the various disadvantages mentioned above. It also aims to provide a dynamic type of stabilization assembly, which allows the absorption of shock and vibration. For this purpose, it relates to an intervertebral dynamic stabilization assembly for arthrodesis, intended to connect at least two adjacent vertebrae, comprising: - at least one extra-disc elastic member, intended to be arranged at the rear of the space intervertebral, which is adapted to limit a displacement between two adjacent vertebrae in the direction of the intervertebral flexion; and at least one intra-disc elastic member providing an intervertebral spacing function, this elastic intra-discal organ being capable of being crushed during the lordosis of the two adjacent vertebrae, so as to control this setting in lordosis, these two elastic members mutually interact to find a point of equilibrium, which can then be moved dynamically but controlled by external forces such as subject weight or muscle contraction.

  According to other features: - there is further provided an additional extra-disc elastic member, able to oppose the lordosis of the patient; - The intra-discal elastic member has an end adapted to deform preferentially, during the lordosis of the patient; - The intra-disc elastic member generally has a shape of C, seen from the side, in particular being constituted by a spring blade; - The intra-discal elastic member C-shaped has deformation limiting means, in particular a secondary spring extending between the flanges facing this elastic member; - The intra-discal elastic member comprises a median body, from which extend two pairs of deformable wings, this elastic member having generally a V-shape, seen from above; - The intra-discal elastic member is provided with a rigid body for maintaining the intervertebral spacing, this rigid body being provided at the front, namely the opposite of the extra-discal displacement limiting element. ; the intra-discal organ has an annular shape, in particular being formed by a folded spring blade on itself; - It is expected an incompressible body, able to move back and forth in the inner volume of the intra-discular annular organ; for at least one vertebral stage, at least one first extra-discal member and at least one second extra-discal member are provided, intended to be implanted on either side of the sagittal axis of the patient, as well as at least one first intra-disc elastic member and at least one second intra-disc elastic member intended to be placed on either side of said sagittal axis, the stiffnesses and / or the elasticities of said extra-disc and intra-disc elastic members can be set independently.

  The invention will be described hereinafter with reference to the accompanying drawings, given solely by way of non-limiting examples, in which: FIG. 1 is a schematic side view, illustrating two neighboring vertebrae associated with a dynamic stabilization assembly; according to the invention; FIG. 2 is a graph illustrating the variations of the voltage, as a function of the length or the angular spacing of the two elastic members involved in this stabilization assembly; - Figures 3A and 3B are side views illustrating two different configurations of the assembly according to the invention; - Figure 4 is a side view, similar to Figure 1, illustrating an alternative embodiment of the invention; - Figure 5 is a rear view, illustrating another embodiment of the invention; - Figures 6 and 7 are perspective views illustrating two alternative embodiments of the intra-disc elastic member; FIGS. 8 and 9 are respectively side and perspective views, illustrating two additional embodiments of this intra-disc elastic member; FIGS. 10 to 12 are perspective views, illustrating an additional alternative embodiment of this intradiscal elastic member, in three different configurations; and FIGS. 13 and 14 are side views, illustrating a last alternative embodiment of this intra-discal elastic member, in two different configurations. Figure 1 illustrates, schematically, two adjacent vertebrae 10 and 20 which are connected through a stabilization assembly according to the invention, which will be described in more detail in the following. In this FIG. 1, we find the respective vertebral bodies 12 and 22, as well as the intra-disc space 30. The front and the back of the patient correspond respectively to the left and to the right in the drawing.

  In a manner known per se, each vertebra is associated with a respective pedicle screw 14 and 24, implanted by any appropriate procedure. A first elastic member 40, said back or extra-disc, connects these two pedicle screws, while a second elastic member 42, called before or intra-discal, is placed in the intervertebral space. The extra-disc elastic member 40 is connected to the pedicle screws by any appropriate means, ensuring or not a hinge relative to these screws. In addition, the intra-disc elastic member 42 may be implanted by means of a posterior or posterolateral impaction. Finally, it should be noted that the stabilization assembly according to the invention can equip a number of vertebral stages greater than two, in particular equal to three or four. These members 40 and 42 are elastic, namely that they are adapted to deform under the action of a force that is exerted to them, in proportion to the intensity of this force, then to return to their initial shape if this force is deleted. This proportional deformation can be of linear type, or others, such as for example exponential, or asymptotic. In the context of the invention, these two members 40 and 42 have a constituent material and a structure of any type, to give them the elastic property described above.

  Each elastic member may be, for example, made in the form of a spring of any suitable type, or in the form of a combination of springs between them, any stiffness and any type of suitable material. This elastic member may also be different from a spring: it may then consist of an elastic material, such as a silicone or a simple biocompatible rubber, or of a composite material that can use elastic elements as well as to non-elastic elements. Finally, each elastic member in the sense of the invention can be of any type and use any material, so as to develop a force-deformation curve corresponding to the graph of Figure 2, which will be further explained in the following section. description. As will be seen in more detail in the following, the extra-disc elastic member 40 is adapted to limit a displacement between the two adjacent vertebrae 10 and 20, in the direction of the intervertebral flexion. Furthermore, the intra-disc elastic member 42 is able to control the lordosis of these two adjacent vertebrae while maintaining a spacer type effect. More specifically, the intra-disk elastic member has a front end 421 whose height is substantially invariant, as well as two opposite surfaces 422, respectively upper and lower, each of which bears against a respective vertebral body 12 or 22. note that these surfaces are likely to move closer or away from each other, so that the rear end 423 of this elastic member is adapted to deform, preferably, during the lordosis of the patient. Furthermore, the presence of the front end 421 substantially indeformable ensures an intervertebral spacer function spacer type. Thus, regardless of the type of elastic intra-discal member, it is suitable to have a minimum height, regardless of the forces applied to it, which ensures the spacer effect mentioned above. On the other hand, the profile of this organ is likely to vary, by decreasing its posterior height, or even increasing its anterior height, according to its elastic properties, in order to obtain a modification of the position of the vertebrae preferentially in the direction of the lordosis. . The operation of the intervertebral stabilization assembly, illustrated in this Figure 1, will now be described in the following. During the lordosis of the patient, the stress thus exerted tends to deform the elastic member 42, by mutual approximation of the surfaces 422. This body then exerts a restoring force, materialized by the arrows F. As a result, it opposes a permanent elastic counter-stress to the extra-discal organ 40. Furthermore, during the kyphosis of the patient, this extra-discal organ tends to oppose this movement, according to the arrows F ', while the intra-discal organ only performs an intervertebral spacer function, but without substantially deforming. It will be appreciated therefore that the intervertebral stabilization assembly of the invention provides different functions, depending on the point of application of the patient's gravity forces. Thus, if the patient leans forward, the extradiscal member 40 limits the setting in kyphosis, while distributing the forces on the intra-discal organ 42, without the height of the latter decreases significantly. In other words, this member 42 continues to perform its intervertebral spacing function. When the patient leans back, it deforms elastically and against resistance the elastic member 42, until the deformation in lordosis finds its counterpart in elastic resistance from this organ. A point of equilibrium between the forces applied is then reached. In this respect, it will be noted that the presence of the end 423 ensures a preferential deformation of this organ during the setting in lordosis, namely that the latter is deformed asymmetrically.

  The intra-discal organ 42 thus performs a dual function, namely first the intervertebral spacing, a spacer effect and, secondly, the setting intervertebral lordosis due to its asymmetric anteroposterior deformation. Due to the nature of the elastic members 40 and 42, an equilibrium is obtained between the mechanical effects of these two components, which advantageously corresponds to the therapeutic neutral position. The interaction between the elastic members 40 and 42 is more particularly illustrated in the graph of FIG. 2. On the abscissa, there is the tension T exerted on each of these members and, on the ordinate, the variations of the characteristic dimension of each of these organs. In the case of the intra-discal organ 42, this characteristic dimension is materialized by the angle α, that is to say the intervertebral angle which merges with the angle of the two upper and lower flats 422 of the intra-discal organ. Thus, with reference to FIG. 3A, when this member 42 is placed between the vertebrae, without being associated with the extra-discal member 40, these surfaces define an angle denoted ao, denoted in FIG. 2, which corresponds to a position of kyphosis. Then, as deformation of this member 42, the surfaces 422 tend to approximate and then become parallel. If this deformation continues, these surfaces tend to get closer to each other. There is, in Figure 3B, an angle a f, which corresponds to a deformation in lordosis. This angle a f is also plotted on the graph of Figure 2. It is noted on the latter, a lower zone denoted I, which corresponds to kyphosis, and an upper zone denoted Il, which corresponds to the lordosis. As illustrated in Figure 2, the value of the angle a varies, depending on the voltage T, between the values a o and a f, according to the curve C42. This variation, which is here linear, can also be of any other type, for example exponential or asymptotic. Furthermore, FIG. 2 also shows the variations, as a function of the tension that is applied to the extra-discal organ 40, of the length L of the interpedicular distance, which merges with that of this organ 40. in the absence of voltage, this length is maximum, namely that it has a value denoted Lo, for a kyphosis corresponding to the value a 0 for the intra-discal organ 42 (Figure 3A). On the other hand, for a position of maximal lordosis, corresponding to the value a f of the deformation of the intra-discal organ 42, the length of the extra-discal organ has on the contrary a minimum value, denoted Lf (FIG. 3B). The variation of the length as a function of the voltage, between these values Lo and Lf, is materialized by the curve C40 of FIG. 2. This variation, which is illustrated in a linear manner in this FIG. 2, may also be of any other type. as exponential, asymptotic or otherwise. These curves C40 and C42, which are respectively strictly decreasing and strictly increasing as a function of the voltage T, intersect at a point noted E, corresponding to the mechanical equilibrium provided by the two elastic members 40 and 42. It is conceivable that It is possible to adjust the mechanical characteristics of these two members 40 and 42 so that this point of equilibrium is as close as possible to the neutral physiological position. These characteristics can also be such that this point E is relatively close to the ordinate axis, namely that it can be reached for a relatively low voltage value T. We denote at E and LE the values corresponding to this point of equilibrium. It will also be noted that this equilibrium point E can vary according to various parameters, particular to the patient. It is thus the action of the weight, according to whether the patient leans forward or backwards, as well as the action of the muscles, according to whether the latter are released or contracted. Under these conditions, this equilibrium point E is likely to move on the graph of Figure 2, within a zone Z, called dynamic equilibrium zone.

  This graphic zone Z may itself be controlled in its extent by the chosen stiffness of the various elastic bodies thus kept in equilibrium because of their mutual interaction. Thus, the more the organs are stiff, and the more the weight forces of the patient and the forces of the muscles have difficulty moving the equilibrium point E. In the context of the arthrodesis, it is advantageous to use elastic members whose stiffness is such that the surface of the zone Z is relatively small, that is to say, compatible with bone fusion. In this respect, it will be noted that the invention finds its essence in the combination of these two elastic members 40 and 42, the interaction of which provides a mechanical balance. It should also be emphasized that each of these elastic members 40 or 42 can not be used as such, regardless of its association with the other of these elastic members. Such an isolated use would be even proscribed, since it would lead to placing the patient in an anatomically dangerous position. Thus, the use of the extra-discal organ alone would lead to excessive lordosis, while the use of the intra-discal organ alone would induce kyphosis too pronounced. FIG. 4 illustrates a first variant embodiment of the invention, in which the intra-disc elastic member 142 has a shape of C. The latter thus has a core 1421 provided at the front, namely the opposite of the elastic extra-discal member 40. This soul is extended by two wings 1422, each bearing against a respective vertebral body 12 or 22.

  This leaf spring 142 thus has an open end 1423, turned towards the back of the patient, which is adapted to be deformed preferentially when setting lordosis. Furthermore, there is an additional extra-disc elastic member, designated by the reference 44, which is provided in the vicinity of the main extra-discal member 40. This additional elastic member 44, which is for example secured to the pedicle screws 14 and 24, is capable of exerting a force F ", tending to move these pedicle screws away from each other, in other words, this additional member 44 exerts a force, the meaning of which is opposite to that exerted by the main organ 40. This makes it possible to reinforce the elasticity of the intradiscal organ 142, in the direction of the intervertebral extension, which is advantageous for example in the absence of an articular facet. this additional member 44 tends to oppose a lordosis which would be made easier because of the absence of anatomical stop lordosis, in combination with the action of the intra-discal organ 142. As mentioned above, it is possible to adjust from independent of the mechanical characteristics of these three members 40, 44 and 142. Note also that, if the additional member 44 is separate from the main member 40 in FIG. 4, these two members may alternatively be combined into one only element. It is also possible, with reference to Figure 5, to use two extra-disc organs 40a and 40b, and two leaf springs 242a and 242b, placed on either side of the sagittal axis A of the patient. This is advantageous since it is possible to separately adjust the mechanical characteristics of each pair of elastic members, respectively intra-disc and extra-disc, in order to take into account a possible lateral dissymmetrical collapse of the disc. FIG. 6 illustrates an alternative embodiment of the spring blade, in which the latter is associated with a secondary spring 243, connecting the opposite wings 242'2. Thus, during the deformation of the leaf spring 242 'due to the lordosis of the patient, the spring 243 opposes a controlled intensity resistance.

  In this respect, it will be noted that it is possible to vary the mechanical characteristics of this spring 243, as a function of the pathology that is to be treated, and in particular if the collapse of the disc is asymmetrical of right-left type. As a variant not shown, the spring 243 can be replaced by a spring blade, similar to that 242 ', which has smaller dimensions and a lower resistance. FIG. 7 illustrates a further variant embodiment of the intra-disc elastic member of the preceding figures. In this embodiment, the leaf spring 242 is replaced by a solid body 242 ", also generally having a shape of C, which is provided with a core 2421" from which extend two wings 2422 ". the core is hollowed out with an indentation 244, allowing the deformation of this massive body in the manner of a clothespin Fig. 8 illustrates a further variant embodiment of the intra-discal elastic organ, which is affected in its 342, differs from the one 142 of FIG 4 in that it comprises a rigid non-deformable body 345, for example in the form of a transversely extending cylindrical axis, which rigid body 345, which is fixed by any appropriate means against the core 3421 of the spring blade 342, allows to maintain substantially constant the height of the blade 342, at least in the vicinity of the body 345, regardless of the imposed stress level. , this blade 342 is able to reliably ensure its intervertebral spacing function. In this regard, it should be noted that this elastic member 342 can be divided into two regions. The first region 342A, located at the front, namely opposite the ligament 40, is substantially rigid with respect to a vertical compression force, so that it more particularly ensures the intervertebral spacing function. . Furthermore, the second region 342B, facing the ligament 40, is adapted to be crushed during the lordosis, while providing a controlled resistance as has been explained in the foregoing.

  Note that the rigid body 345 can equip the implant of Figures 6 and 7. In particular, in the case of Figure 7, it can be housed in the notch 244. With reference to Figure 5, we note that the two spring blades 242a and 242b are placed substantially parallel to one another, on either side of the sagittal axis A. However, as a variant, it is possible for these two spring blades to be placed obliquely, so as to form views from above globally V, whose tip is facing forward, namely opposite the ligament 40.

  As a further variant, illustrated in FIG. 9, these two leaf springs can be grouped into a single intradiscal elastic member, generally designated by the reference 442. The latter comprises first of all a median rigid body 445 made by example in the form of a sphere, providing the effect of spacing, similarly to the rigid body 345 of Figure 8. This rigid body 445 is for example placed in the vicinity of the sagittal axis A of the patient. In addition, two pairs of elastic wings 44221 and 44222 extend from the median body 445, namely on either side of the sagittal axis A, respectively to the left and to the right thereof. Thus, seen from above, the elastic member 442 has a shape of V, the tip is turned forward. Each pair of wings 44221 and 44222 is of elastic and deformable nature, so that they provide resistance to the extra-disc ligament, similarly for example to the wings 2422 equipping the implant of Figure 4. As in the case of Figure 5, it can be provided that these two pairs of wings have different mechanical characteristics, so as to oppose variable resistances, especially in the case of a lateral dissymmetrical collapse of the disc. FIGS. 10 to 12 illustrate a further alternative embodiment of the intra-discal organ, which is assigned reference 542. In this embodiment, this member 542 is constituted by a spring blade, folded back on itself at the way of a ring.

  Thus, compared to the embodiment of the preceding figures, this intra-discal organ does not have an open end towards the rear, namely on the right of the sheet. Note however that it is not closed laterally, namely towards the front or back of the sheet. Under uniformly distributed body weight pressure, as shown in FIG. 11, the annular spring blade 542 tends to flatten, while having a height that is substantially constant from back to front. On the other hand, in the case of an asymmetrical pressure exerted by the weight of the body, as in FIG. 12, this organ is deformed in the direction of the lordosis, by decreasing the radius of curvature of its rear part, combined with an increase the radius of curvature of its front part. FIGS. 13 and 14 illustrate a last variant embodiment of the invention, in which the intra-disc elastic member 642 differs from that 542 of the previous figures, in that it is provided with a rigid sphere 644, movable by relative to the blade spring back and forth thereof. In this respect, it will be noted that the spring blade 642 is advantageously closed on its sides, namely towards the front and the rear of the sheet, so as to prevent this sphere from escaping from its interior volume. In addition, this interior volume can be filled with a fluid to facilitate the movement of this sphere. As shown in Figure 13, when the weight of the body exerts a substantially distributed action along the intra-discal organ, the sphere is substantially in the middle position. On the other hand, in case of an asymmetrical action of the weight of the body, exerted on the back of the member 642, the sphere tends to move forward, as shown in FIG. the intervertebral spacing function, while creating a lordosis effect.

Claims (10)

  An intervertebral dynamic stabilization assembly for arthrodesis, for connecting at least two adjacent vertebrae (10, 20), comprising: at least one extra-disc resilient member (40; 40a, 40b) to be disposed at the rear of the intervertebral space (30), which is adapted to limit a displacement between two adjacent vertebrae in the direction of the intervertebral flexion; and - at least one intra-disc elastic member (42; 142; 242a, 242b; 242 '; 242 "; 342; 442; 542; 642) providing an intervertebral spacing function, this elastic intra-discal member being adapted to to be crushed during the lordosis of the two adjacent vertebrae, so as to control this setting in lordosis, 1.5 these two elastic members interacting mutually to find a point of equilibrium (E), which can then be moved a dynamic but controlled by external forces such as the weight of the subject or the contraction of the muscles.   2. Stabilization assembly according to claim 1, characterized in that there is further provided an additional extra-disc elastic member (44), adapted to oppose the lordosis of the patient.   3. The assembly of claim 1 or 2, characterized in that the intra-disc elastic member (42; 242) has an end (423; 2423) adapted to deform preferentially, during the lordosis of the patient.   4. Assembly according to any one of the preceding claims, characterized in that the intra-disc elastic member (242; 242a, 242b; 242 '; 242 "; 342) generally has a shape of C, seen from the side, being constituted in particular by a spring blade.   5. The assembly of claim 4, characterized in that the intra-discal elastic member C-shaped (242 ') has deformation limiting means, in particular a secondary spring (243) extending between the wings facing each other. of this elastic member (242 ').   6. The assembly of claim 1 or 2, characterized in that the intra-discal elastic member comprises a median body (445), from which extend two pairs of deformable wings (44221, 44222), this elastic member. generally having a shape of V, seen from above.   7. Assembly according to any one of the preceding claims, characterized in that the intra-disc elastic member (342; 442) is provided with a rigid body (345; 445) for maintaining the intervertebral spacing, this body rigid being provided at the front, namely the opposite of the extra-discal displacement limiting element (40).   8. Assembly according to one of claims 1 or 2, characterized in that the intra-discal member (542; 642) has an annular shape, being formed in particular by a spring blade folded on itself.   9. An assembly according to claim 6, characterized in that there is provided an incompressible body (644) capable of moving back and forth in the internal volume of the intra-disk annular member (642).   10. Assembly according to any one of the preceding claims, characterized in that, for at least one vertebral stage, there is provided at least one first extra-discal member (40a) and at least one second extra-discal member (40b). , intended to be implanted on either side of the sagittal axis (A) of the patient, as well as at least one first intra-disc elastic member (242a) and at least one second intra-disc elastic member (242b) intended to be placed on either side of said sagittal axis, the stiffness and / or elasticity of said extra-disc and intra-disc internal elastic members can be adjusted independently.