MXPA99004541A - Osteosynthesis system with elastic deformation for spinal column - Google Patents

Abstract

The osteosynthesis system comprises two anchoring members (2) adapted for being fixed to two vertebrae (4), and a connecting member (6;106) adapted for connecting the two anchoring members by exerting stresses preventing the two anchoring members from coming together in translation. The connecting member (6;106) is capable of flexural elastic deformation about a deformation axis (45, 47, 49). It comprises two fixing portions (16) adapted for being fixed to the two anchoring members (2) and an intermediate portion (40). The intermediate portion is offset relative to an axis (18) aligning the two fixing portions (16). The connecting member (6;106) comprises two stops (39) arranged so as to be urged in support when the connecting member is deformed about the axis.

Description

SYSTEM OF OSTEOS1NTES1S WITH ELASTIC DEFORMATION FOR SPINAL COLUMN DESCRIPTIVE MEMORY The invention relates to osteosynthesis systems for spinal column. From FR-2 659 546, an osteosynthesis system for spine or spine is known, which includes anchoring elements designed to be fixed to a series of vertebrae of the spine, and at least one rigid connecting element designed to join the anchoring elements between them. After the system has been fixed to a series of vertebrae and assembled, it constitutes a rigid device that immobilizes the vertebrae to each other. This rigidity allows the device to restrict all or part of the forces to the place of the series of vertebrae in question. However, the first vertebra adjacent to the series is totally free to move with respect to the series of stiffened vertebrae. Then, between the last vertebra of the series and the first free vertebra a great discontinuity in the distribution of the forces along the column can appear. As a consequence, the disc interposed between those two vertebrae is very required, and an abnormal increase in the forces at the level of the disc is also observed. In addition, an acceleration of the degeneration of that disc is very frequent. Then, we talk about a neo-hinge syndrome.

WO 94/21185 presents an osteosynthesis device for spinal column in which two pedicle screws are joined by a joining element having a central "U" shaped flexible portion and laterally displaced. Thus, when the two vertebrae are subjected to forces which tend to relatively displace the two anchoring elements in rotation around a forming axis, the joining element is subjected to a bending moment and is bent elastically around the deformation axis. Then, partially restrict the forces. The system again partially recreates the biomechanics of the functional unit composed of two fixed vertebrae as well as the intervertebral disc. However, this device has the disadvantage that the possibility of the relative rotation between the two pedicle screws is essentially a function of the elasticity of the intermediate portion. In other words, it is under this elasticity that the ability of the intermediate portion to deform rests. Therefore, when this elasticity is high in order to limit the relative displacements, the vertebrae can be induced to suffer important demands that can be harmful. On the contrary, when the elasticity is low, the maintenance of the vertebrae is medium. A purpose of the invention is to provide an osteosynthesis system that allows to control the ability of the intermediate portion to deform without limiting the choice of elasticity. In view of the modality of this purpose, according to the invention, an osteosynthesis system is provided for the vertebral column containing at least two anchoring elements adapted to be fixed to the two vertebrae of the spine, and an element adapted to join the two anchoring elements by exerting forces that prevent the two anchoring elements from coming together during the translation, the joining element being elastically deformable in flexure around at least one axis of deformation, the connecting element containing at least two fixing portions adapted to be fixed to the two anchoring elements and at least one intermediate portion such that the two fixing portions are joined to each other only by the intermediate portion being displaced with respect to the axis of alignment defined by the two fixing portions. For each intermediate portion, the connecting element also contains two stops that extend one with respect to the other and arranged so that they bear against each other when the connecting element is deformed about the axis or at least one of the axes of deformation in a direction of rotation provided over an equal angle or a predetermined limit value. A) Yes, the amplitude of the deformation of the joint element in this direction of rotation is limited. By means of the stops the capacity of the joint element to be deformed is then controlled without influencing the choice of the elasticity of the intermediate portion. When the system contains three anchoring elements with two anchoring elements rigidly joined to each other and two anchoring elements joined together by the deformable joining element and meeting at one end of the series, a transition or gradient of stiffness is formed between the rigid part of the column and the free part. As a result, a better distribution of the forces along the column is obtained. The appearance of a great discotinuity in the distribution of forces between the last vertebra of the rigid series and the first free vertebra is avoided, and a harmonious distribution of the forces along the column is favored, on the contrary. On the other hand, when the system does not concern the two vertebrae, an accommodating arthrodesis is made between these two vertebrae. Advantageously, the axis or at least one of the deformation axes extends perpendicularly to a longitudinal direction of each anchoring element and to a longitudinal direction of the joining element. Advantageously, the axis or at least one of the deformation axes extends mainly parallel to a longitudinal direction of each anchoring element. Advantageously, the axis or at least one of the deformation axes extends parallel to a longitudinal direction of the joining element. Thus, each of these axes corresponds to an axis of displacement relative to the rotation of two anchoring elements one with respect to the other, due to the movement of the vertebrae. Depending on the case, the vertebral disc is then aligned at least partially with the forces corresponding to these respective displacements. Advantageously, the alignment axis extends between the intermediate portion on the one hand and the two stops on the other part.

Advantageously, the intermediate portion has an external face of spherical shape. Advantageously, the two stops each have an outer face of spherical shape. Thus, in both cases, the system is designed to be inside the body; the number of edges is limited and the sharp edges are arranged to reduce the danger risks created by the presence of the system in the patient's body. Advantageously, the spherical face of the intermediate portion and the spherical face of the two stops have the same center of curvature. Advantageously, for each pair of fixing portions, the joining element comprises a joining portion adjacent to the two fixing portions, the joining portion associated with the pair or at least one of the pairs of fixing portions is of a single piece. Advantageously, for each pair of fixing portions, the joining element comprises a joining portion adjacent to the two fixing portions, the joining portion associated with the pair or at least one of the pairs of fixing portions comprises a first and a second joining elements distinct from one another, and two means for fixing the first and second connecting elements to each other. Thus, the joining element will be both easier to manufacture than the joining part than the joining part that will have two pieces or that the connecting element that contains a large number of joining parts in two pieces in relation to the total number of the joining parts. Advantageously, these fixing means are adapted to allow regulating the distance between the two associated anchoring elements, following the longitudinal direction of the joining element. Thus, the length of the connecting element is adjustable. During the installation of the system, the distance between the two anchoring elements can be adapted to the desired position for the two vertebrae associated with these anchoring elements. Advantageously, the second connecting element comprises a rod and the first connecting element has a housing adapted to receive the rod, the first connecting element comprising means for locking the rod inside the housing in many positions, following the longitudinal direction of the rod. joining element. Advantageously, the system is adapted so that the axis of alignment extends between the intermediate portion and the vertebrae. Thus, when the two vertebrae are subjected to forces that tend to approximate the two anchoring elements in translation along the axis of alignment, this arrangement induces an increase in the lifting arm that intervenes in the moment of bending during the bending that follow one of the deformation axes. The intermediate portion is then subjected to a more important bending moment and suffers an accumulated elastic deformation. This allows to increase the flexing capacity of the arthrodized spinal segment around that axis and create a better transition of forces with the unfixed layers. Other features and advantages of the invention will become apparent from the following description of the preferred embodiments that are given as non-limiting examples. In the attached drawings: Figure 1 is an elevation view of a first embodiment of the osteosynthesis system according to the invention fixed to two vertebrae; Figure 2 is a cross-sectional view following the plane ll-ll of the joining element of Figure 1; Figure 3 is a partial elevation view of a second embodiment of the osteosynthesis system according to the invention attached to the vertebrae; and Figure 4 is an elevation view partially in axial section of the joining element of Figure 3. With reference to Figures 1 and 2, a first embodiment of the invention of the osteosynthesis system according to the invention for spinal column allows constitute the osteosynthesis device represented. The system consists only of a first and a second anchoring elements or pedicle screws 2 adapted to be fixed respectively to two vertebrae 4 adjacent to each other of the vertebral column of a patient. The system further comprises a connecting element 6 adapted to join the two anchoring elements 2 together.

Each of the anchoring elements 2 comprises an elongate body and the longitudinal axis 10 having a slightly conical shaped threaded foot 12 of the axis 10 tapering towards the free end of the foot, adapted to be anchored in the associated vertebrae. The bodies 10 consist of a head opposite longitudinally to the free end of the foot 12 and designed to extend to the outside of the vertebrae 4 in the patient's body. The connecting element 6 is here in one piece. It contains first and second fixing portions 16 each comprising a rectilinear cylindrical rod 17. The two rods 17 are aligned with one another and have a common longitudinal axis 18 which is the longitudinal axis of the connecting element and the axis of alignment of the two rods 17. Each fixing portion 16 is adapted to be fixed to the head of one of the anchoring elements according to the known means. The axis 18 of the joining element is mainly perpendicular to the axis 10 of the anchoring element. During the installation of the osteosynthesis system, each anchoring element 2 is anchored in the associated vertebra 4, then the anchoring elements 2 are fixed rigidly to the joining element 6. The joining element 6 includes another joining part 28 adjacent to the two fixing portions 16, at one end of each rod 17 and extending on the longitudinal axis 18 between the two rods.

The connecting part 28 has an outer face 30 of generally spherical shape having a center of curvature located on the longitudinal axis 18, half the distance of the two end portions 16. The connecting part 28 has a cylindrical hollow. 32 that crosses from one side to another following a diameter of the sphere. The cylindrical recess 32 has a cylinder axis 34 that intercepts the longitudinal axis 18 of the joining element at half the distance of the two end portions 16 and extending perpendicularly to that longitudinal axis 18. The connecting part 28 further has a recess 36 in the shape of a sphere segment, delimited by two flat faces 38 of the connecting part extending one with respect to the other and each passing through the axis 34 of the cylindrical hollow. The recess 36 extends along a radial direction to the axis of the cylinder 34, then the spherical outer face 30 to the cylindrical recess 32. The angle of this recess, defined around the axis 34 of the cylindrical recess by the two flat faces 38, is of approximately 15 °. One of the flat faces 38 is perpendicular to the longitudinal axis 18, so that the recess extends from one side of the median plane transverse to the axis 18 of the joining element. The cylindrical hollow 34 and the notch 36 allow to distinguish two portions of the joining part 28 extending from one part to another of the longitudinal and alignment axis 18. Likewise, the joining part includes two stops 39 that extend from a first side of the longitudinal axis 18 associated with the recess 36. Each stop 39 is then extended to one of the respective fixing portions 16 to the recess 36, the faces 38 forming two end faces of the stops. The connecting part 28 also includes an intermediate portion 40 extending from a second side of the longitudinal axis 18 opposite the recess 36. Likewise, the two stops 39 extend from a same side of the intermediate portion 40 as the longitudinal axis 18. This axis 18 extends between the intermediate portion 40 of a part and the two stops 39 of the other part. The spherical face 30 constitutes an external face of the stops 39 and of the intermediate portion 40. The spherical faces of the intermediate portion and of the stops have the same center of curvature. The cylindrical hollow 32 defines a cylindrical internal face of the stops 38 and of the intermediate portion 40. The intermediate portion 40 is displaced laterally in relation to the longitudinal axis 18 which is the axis of alignment of two fixing portions 16. The intermediate portion 40 has a neutral fiber 42. The displacement has an estimated measure "d" between the neutral fiber 42 and the longitudinal axis 18 and extending perpendicularly to that axis. This measure is here equal to approximately the diameter of the rods 17 of the end portions 16. The two end portions 16 are joined to each other only by the intermediate portion 40. This exerts forces opposite to the approach and elongation in the translation following the longitudinal axis 18 of the two fixing portions 16 one of the other, and then the two anchoring elements 2 one from the other. The intermediate portion 40 is elastically deformable about a first deformation axis 45 parallel to the axis 34 of the recess 32 and traversing the intermediate portion at the level of the neutral fiber 42. Also, said intermediate portion is around a second deformation axis 47. perpendicular to the longitudinal axis 18 and to the first axis 45, passing through the center of the sphere and intercepting the axes 45 and 18. It is also around a third deformation axis 49 parallel to the longitudinal axis 18 and perpendicular to the first axis 45 intercepting it to the neutral fiber of the intermediate portion. The second and third axes 47 and 49 pass through the intermediate portion 40. The three axes 45, 47, 49 are perpendicular to each other, intersect at the same point and form a trihedral. During the installation of the system, the connecting element 6 is oriented around its longitudinal axis 18 so that the stops 39 are on the side of the vertebrae 4, the intervening portion 40 is on the opposite side of the vertebrae 4. Thus, the first deformation axis 45 extends perpendicularly to the longitudinal axis 10 of the anchoring elements 2 and the second deformation axis 47 is mainly parallel to the axes 10. The intermediate portion 40 is adapted to be bent following each of the three axes of deformation to enclose at least a part of the forces that are normally exerted on the disc between the two vertebrae 4. This bending is carried out following a single axis at a time or many of those axes at the same time. The two stops 39 abut one against the other when the intermediate portion 40 is bent around the first deformation axis 45, over an angle equal to a predetermined limit value, adopting the shape of the body 28, in the direction of rotation corresponding to a Approximation of two stops to each other. Thus, deformation of the joint element at an angle greater than the predetermined value is not allowed. This system performs a flexible arthrodesis between the two vertebrae. Figures 3 and 4 represent a second embodiment of the osteosynthesis system according to the invention in which the different elements have the reference numbers increased by one hundred. In addition, this time the system includes a third anchoring element, not shown, and extends to the right of the device visible on Figure 3. The three anchoring elements are each identical to those of the first embodiment. The connecting element 106 includes a connecting part 128 which contains a different connecting element 106a and a second connecting element 106b this time. The second connecting element 106b includes a rigid, elongate, rectilinear rod 144 of the longitudinal axis 18 and a circular section. The fixing on the second connecting element 106b of the second and third anchoring elements is carried out in the same manner as in the first embodiment. The second attachment element 106b mainly includes the second attachment portion 16. The first attachment element 106a includes a first attachment portion 16 identical to the first attachment portion of the first embodiment.

It also contains, adjacent to one end of the fixing portion, an intermediate portion 40 and two stops 39. The first connecting element 106a further includes a cylindrical sleeve 146 having a cylindrical outer face 148 of the same radius as the radius of curvature of the same. the spherical face 30 and a cylindrical internal face 150. The fixing portion 16 and the sleeve 146 have as axis the longitudinal axis 18 of the joining element. The outer face 148 extends in the extension and continuity of the spherical face 30 to the end opposite longitudinally to the fixing portion 16. Thus, the outer face of one of the stops 39 and a part of the outer face of the intermediate portion 40 have a cylindrical. The inner face 150 of the sleeve 146 has a radius slightly greater than the radius of the rod 144 of the second element 106b. This internal face 150 defines a housing adapted to receive that rod. The wall of the sleeve 146 is traversed by a cylindrical conduit of the axis 151 perpendicular to the longitudinal axis 18 of the sleeve and opens into the external 148 and internal 150 faces of the sleeve. That conduit 151 is threaded, the second connecting element 106b including a screw 152 adapted to be screwed in that conduit to bear against the rod 144 received in the housing 150 due to the locking of the rod in the housing in many positions to be chosen along the axis longitudinal 18. The rod 144, the housing 150 and the screw 152 thus forming means for attaching two connecting elements 106a and 106b to each other, allowing to regulate the distance between the two fixing portions 16 following the longitudinal axis 18. For the installation of the osteosynthesis device, the three anchoring elements are fixed to the vertebrae 4, the rod 144 of the second element 106b engages in the housing 150 of the first joint element 106a without tightening the screw 152 so that the rod 144 remains free to slide in the housing along the longitudinal axis 18. Instead the connecting element 106 is put and each of the three anchoring elements is attached to the connecting element 106. The position of the rod 144 is then chosen in the housing 150 as a function of the desired position along the longitudinal axis 18 for the adjacent vertebra 4 associated with the first connecting element 106a in relation to the vertebra 4 associated with the second connecting element 106b . The two connecting elements are then immobilized relatively tightening the screw 152 against the rod 144. The rod 144 constitutes a part of the connecting element 106 adapted to rigidly join the third anchoring element to the second anchoring element. The three anchoring elements are joined together by the connecting element 106. The different parts of the osteosynthesis system will be, for example, a biocompatible alloy. In each of these two modes, the patient's spine will be provided with two osteosynthesis systems arranged symmetrically on the one hand, and on the other with a median longitudinal plane of the spine extending fixed to the same vertebrae. The maximum amplitude of the bends will typically be 2 ° around the third axis of deformation 49 (torsion) and 5 to 6 ° around the second axis of deformation 47 (lateral flexion). Of course, numerous modifications can be made to the invention without departing from the scope thereof. The connecting element 6 of the first embodiment, of fixed length, may be adapted to be associated to at least three anchoring elements. On the other hand, the connecting element 106 of the second variable length mode can be adapted to be associated only with two anchoring elements. This system may also include three anchoring elements. The same joining element may mainly include one or many connecting parts 28 (in one piece) and / or one or many connecting parts 128 in two distinct elements, each joining part being designed to extend between two anchoring elements. Advantageously, the joining element will include a joining part 28 in one piece at one end, followed by many joining parts 128 to the two elements. The center of curvature of the spherical face of the intermediate portion and / or the center of curvature of the spherical face of the stops may be located elsewhere on the axis 34 of the cylindrical hollow 32. Irrespective of the presence or absence of the stops, an osteosynthesis system for the spinal column, including at least one first, second and third anchoring elements adapted to be fixed to the first, second and third respective vertebrae of the spine, and a element of union (in one or several pieces) adapted to rigidly join the second and third anchoring elements to one another, and adapted to join the first and second anchoring elements to each other, exerting forces against the approach of the first and second anchoring elements in translation , one towards the other and being elastically deformable in flexure around at least one axis of deformation between the first and second anchoring elements. Thus, when the first and second vertebrae are subjected to forces tending to displace relative to the first and second anchoring elements in rotation about the axis of deformation, the joint member is subjected to a bending moment and elastically bent around the deformation axis. Restricts the forces partially. The system partially recreates the biomechanics of the functional unit composed of the first and second fixed vertebrae, as well as the intervertebral disc and thus allows attenuating the sum of the forces on the disc adjacent to the fixation. The system includes three anchoring elements with two of the anchoring elements rigidly joined to each other and two of the anchoring elements joined together by the deformable part of the joining element and located at one end of the series, forming an transition or stiffness gradient between the rigid part of the column and its free part. A better distribution of forces is therefore obtained along the column.

This system of osteosynthesis avoids, when the system concerns at least three vertebrae joined together, the appearance of a great continuity in the distribution of forces between the last vertebra of the rigid series and the second free vertebra, and favors instead a harmonious distribution of forces along the column.

Claims (13)

NOVELTY OF THE INVENTION CLAIMS

1. - An osteosynthesis system for vertebral column, consisting of at least two anchoring elements (2) adapted to be fixed to two vertebrae (4) of the spine and a connecting element (6; 106) adapted to connect the two anchoring elements when exerting forces that prevent the two anchoring elements from coming together in translation, the connecting element (6; 106) can undergo elastic deformation upon flexure around at least one axis of deformation (45, 47, 49), the connecting element (6; 106) containing at least two fixing portions (16) adapted to be fixed to the two anchoring elements (2) and at least one intermediate portion (40) in such a way that the two fixing portions are connected to each other only by the intermediate portion, the intermediate portion being offset in relation to an alignment axis (18) defined by the two fixing portions (16), characterized in that for each inter portion half (40), the connecting element (6; 106) further contains two stops (39) that extend one with respect to the other and are arranged so that they rest against each other when the connecting element is deformed about the axis or at least one (45) of the axes of deformation in a direction of rotation provided at an angle (a) equal to a predetermined limit value.

2. - The system according to claim 1, further characterized in that the axis or at least one (45) of the deformation axes extends perpendicular to a longitudinal direction (10) of each anchoring element (2) and a longitudinal direction (18) of the connection element (6; 106).

3. The system according to claim 1 or 2, further characterized in that the axis or at least one (47) of the deformation axes extends substantially parallel to a longitudinal direction (10) of each anchoring element (2).

4. The system according to any of claims 1 to 3, further characterized in that the axis or at least one (49) of the deformation axes extends parallel to a longitudinal direction (18) of each element of deformation. connection) (6; 106).

5. The system according to any of claims 1 to 4, further characterized in that the alignment axis (18) extends between the intermediate portion (40) on the one hand and the two stops (39) on the other hand.

6. The system according to any of claims 1 to 5, further characterized in that the intermediate portion (40) has an outer face (30) of spherical shape.

7. The system according to any of claims 1 to 6, further characterized in that the two stops (39) each have an outer face (30) of spherical shape.

8. - The system according to claim 6 and 7, further characterized in that the spherical face (30) of the intermediate portion and the spherical face (30) of the two stops are the same center of curvature.

9. The system according to any of claims 1 to 8, further characterized in that, for each pair of fixing portions (16), the connecting element (6) contains a connection portion (28) contiguous to both fixing portions, the connection portion associated with the pair, or at least one of the pairs of fixing portions being in one piece.

10. The system according to any of claims 1 to 9, further characterized in that, for each pair of fixing portions (16), the connection element (106) contains a connection portion (128) contiguous to both fixing portions, the connection portion associated with the pair, or at least one of the pairs of fixing portions containing a first and a second connection element (106a, 106b) different from one another, and two means for fixing the first and second connecting elements to each other.

11. The system according to claim 10, further characterized in that said fixing means are adapted to allow adjusting the distance between the two associated anchoring elements (2), following the longitudinal direction (18) of the connecting element (106).

12. The system according to claim 11, further characterized in that the second connection element (106b) contains a rod (144) and the first connection element (106a) has a length (150) adapted to receive the rod, the first connection element (106b) contains locking means (152) in many positions following the longitudinal direction (18) of the connecting element (106).

13. The system according to any of claims 1 to 12, further characterized in that it is adapted so that the axis of alignment (18) extends between the intermediate portion (40) and the vertebrae.