MXPA99002345A - Expansive osteosynthesis sheath - Google Patents

Abstract

An expansive osteosynthesis implant comprises branches (5) connected by one of their ends to a tube cap (7) pierced by an orifice (8), which can be slid from the rear between the vertebral disks of two consecutive vertebrae, so as to maintain them at a set distance and restore the stability of the spinal column. Said branches (5) and said tube cap (7) define a hollow sheath which, in inoperative position, has a general cylindrical external shape with circular cross section and at least part of the internal volume (9) of the sheath (1) towards the distal ends of the branches (5), is in the shape of a revolving truncated cone with its larger base on the side of said tube cap (7). This implant comprises at least three branches (5) and at least one wedge (2) capable of passing into said orifice (8) and through the larger base of the truncated cone into said internal volume (9).

Description

COVER OF EXPANSIVE OSTEOSYNTHESIS The present invention relates to a cover of expansive osteosynthesis. The technical field of the invention is that of implantable bone implants or prostheses, and of the surgical techniques for using them. The main application of the invention is to provide implants designed to slide or insert from a posterior direction between the facing faces of two consecutive vertebrae, in order to maintain a given distance between them, and to restore stability of the spine, for example , after a failure of the corresponding joint, by fixing the two vertebrae together. Various techniques are known in the present for restoring a "normal" lumbar lordosis in this way, by implanting either a graft that eventually fixes them together immediately, while still making it possible over time to achieve fusion between them. the vertebrae. In the second technique mentioned above, use is made mainly of implants, also known as "covers", some of which are hollow, rigid and in one piece, with internal / external intercommunication slots, to receive a bone graft that, by means of these grooves, it subsequently fuses with the adjacent vertebrae on either side: in this field, reference can be made to Patent Application Number WO 96/08205 published on March 21, 1996 for "Intervertebral fusion cage of conical shape ", and to the European Application Number EP 637,440 published on February 8, 1995 for" Intersomatic implant for the spinal column ". However, covers of this type are of external dimensions that are given and fixed, while the distances between the pairs of vertebrae are not constant. In addition, the inclinations of the facing vertebral faces to which a given angular position must be imparted, do not make it possible to use the rigid covers from a posterior direction: they can be inserted only from a previous direction. As a result, other types of covers with two substantially parallel branches connected to a rigid body have been developed, through which it is possible to rotate a screw system which then moves to a wedge in screw engagement on this screw from a position initial near the distal ends of the branches towards the body, linking the branches to each other, thus deploying the two branches to separate them angularly. Then, it is possible to insert this cover in an initially flat manner between the vertebrae, and then, when rotating the pulse axis of the wedge, the desired angle between the branches is adjusted, or it is established from a later access. These covers or implants are described, for example, in European Patent Application Number EP 664,994 published on August 2, 1995, entitled "Vertebral intersomatic cage", or in the European Application Number EP-2,719,763 published on November 17, 1995 , and entitled "Vertebral implant". However, these devices that are covered more mechanically than hollow and rigid, and therefore more complex, leave a smaller internal volume for the fusion graft, and due to their flat shape, which is not circularly symmetric, even when they are better to ensure a given angle of support between the vertebrae, they require a preparation step of the same rectangular section to receive them, and this complicates the implementation. Therefore, the problem presented is to be able to have implants or covers available, making it possible simultaneously to make the form of a conventional rigid cover, first to facilitate the implantation, and second, to provide a larger internal volume, with the possibility of increasing the diameter from the distal end of the cover to a given value in relation to its end located adjacent to its surgical insertion point, after it has been put in place, and corresponding to the back face of the vertebrae, as long as as few mechanical elements as possible are kept. One solution to the problem presented is an expansive osteosynthesis implant having branches, each connected at one end with a seat pierced with a hole, such that these branches and the seat constitute a hollow cover which, in a position in "rest" ", has an external general shape that is cylindrical or almost cylindrical with the generating line that generates it, rotating around its axis of symmetry, which is a straight line, or else that has a curved middle portion, such as a convex circular arc of a large radius, and having a director curve around which runs the generating line, thus also defining the cross section of the cylinder, which is almost circular: this provides a cylinder that is a straight circular cylinder or otherwise is a cylinder that is referred to in the present case as "ovoid" or "oval", and which is referred to below as a cylinder or an almost cylinder; a portion at least of the internal volume of the cover and towards the distal ends of the branches, is in the shape of a truncated almost circular cone, whose large base is towards the seat, this implant having at least three branches and at least one spacer of dimensions compatible with the dimensions of the large base of the truncated cone in the internal volume in the resting position, and possibly suitable for passing through this hole. In an "active" position, the separator deploys the branches apart, the internal volume tends towards a circular cylinder, and the external shape of the cover tends towards an approximate truncated cone, and once the separator has been placed in the desired position , there is no internal part inside the space defined by the branches, the separator, and the hole. The definitions of positions in "rest" and "active" are shown by way of example, respectively, in Figures 1, 3A, 4A, 5A, 9, 10, and 11, and in Figures 2, 3B, 3C, 4B, and 5B. The "at rest" position is the position of the implant before it is put in place, and while it is being put in place, that is, without the spacer placed between its branches inside the cover, in such a way that the cover has a cylindrical external volume of a constant section. The "active" position is the final position of the implant, for example between two vertebrae, with its branches deployed apart by means of the spacer that is placed in its final adjustment position, the general external shape of the cover being approximately truncated, bending towards outside from the seat, which corresponds to the end of the implant located towards its point of surgical insertion, towards its distal end that is placed deeper between the vertebrae. To provide better anchoring in the bone, and to avoid any subsequent migration of the cover, the external surfaces of the branches preferably have knots, are grooved, or are threaded, using a thread profile having projecting ridges, and so on. . Also, in order to reduce any risk of rotation after implantation, and consequently, reduce any risk of displacement of the cover, while simultaneously increasing the contact area with the faces of the vertebrae, at least the seat of the implant, and preferably also the sides of the branches, have at least two optionally parallel planes, each arranged symmetrically about the axis of the implants between two successive branches. These planes, optionally assisted by the generally ovoid shape of the cover, make a better possible retention after expansion, by reducing any risk of implant rotation. In addition, this ovoid shape can make it possible, better than if the external generating line of the basic cylindrical shape of the cover at rest were a straight line, return after expansion to an external profile that is conical and without curvature, providing this way a better distributed thrust against the body of the vertebrae, therefore helping to implant the bone graft better. To reinforce the cover at its rear end, particularly if there is a large hole in the seat, thereby making it easier to fill the cover with the bone material after the cover has been put in place and expanded, the hole of this seat is suitable to receive a plug to close the internal volume of the cover. As an example, the plug can be screwed into the hole, in which case the hole is also threaded. Under these circumstances, the plug prevents the bone material from escaping, and, depending on the material it is made of, it can also reinforce the cover. Different particular modalities are described below in the accompanying Figures. The result is that of novel expansive osteosynthesis implants that satisfy the presented problem, in particular for the main application previously defined. The presence of at least four branches, and possibly four to eight branches, makes it possible to obtain a bilateral expansion, and in this way, a better fit against the two facing faces of the vertebrae, and the absence of a part or link rod between the separator that maintains the expansion, and the hole or plug in the end seat, guarantees a larger internal volume to receive a large amount of bone material, thereby improving consolidation and fusion bonding, in particular between vertebrae that will be kept together. This filling operation is made much easier by having a large hole in the rear end of the cover through the seat. In addition, the hole makes it possible to scrape the faces of the vertebrae through the slots located between the branches on the lower and upper faces of the cover. Furthermore, the expansion system defined above is very simple, since it comprises only two parts, namely the separator and the cover (which optionally has a stopper located at its end, and which possibly also has an intermediate separator, as mentioned below), but no linkage member remaining after installation, since any rod or arrow is subsequently removed to place the spacers and plug. Accordingly, the present invention provides numerous advantages over existing implants or covers, of the kind already mentioned, and other advantages may also be provided, but those given above are sufficient to demonstrate the novelty and utility of the invention. The description and the Figures below show two embodiments of the invention with four branches, but are not limiting in any way: other embodiments are possible in the context of the scope of this invention, for example three-branched modes, or modes with more than four. Figure 1 is a perspective view of an example of an implant in the "at rest" position, with its different parts aligned on a common installation axis XX '. Figure 2 is a perspective view of the implant of Figure 1 in its "active" position, with the three anterior parts assembled together. Figures 3A, 4A, and 5A are respectively a sectional view, and two views of axial end, one of the front face and the other of the rear face of a cover, showing another embodiment of an implant of the invention in the position "Resting" . Figures 3B, 4B, and 5B show the same views shown in Figures 3A, 4A, and 5A, of the same cover, but with their complementary elements assembled together in the "active" position. Figure 3C is a side view perpendicular to the axis of the implant of the embodiment shown in Figures 3, 4, and 5, in the "active" position. Figures 6, 7, and 8 are Figures showing modality details of the implant cover of the invention. Figures 9, 10, and 11 are respectively a fragmentary side view, and two axial views, showing the anterior face and the posterior face of the embodiment of the implant shown in perspective in Figures 1 and 2. Figures 12, 13, and 14 are side views and a sectional view, respectively, of: a screwless end spacer for the embodiment of Figures 1, 2, 9, 10, and 11; an end and / or intermediate screw separator, for a mode of Figures 3, 4, and 5, and a closure plug for any of the embodiments of the invention. Whatever the mode, the expansive osteosynthesis implant comprises, in a conventional manner, the branches 5, each connected at one end to a seat 7 pierced by a hole 8. In accordance with an essential feature of the invention, the branches 5 and the seat 7 constitute a hollow cover 1, which, in a "resting" position, as shown for the embodiments of Figures 1, 3A, 4A, and 5A, and of Figures 9, 10, and 11, it is of a general external form that is cylindrical or almost cylindrical, having a cross section that is also the director curve of the cylinder that is circular or almost circular, being the generating line that is coupled with the director curve, and that generates the cylinder or almost cylinder when moving around its axis of symmetry XX ', either a straight line, or a circular, convex arc of a large radius: this provides a circular cylinder symmetrical straight, as shown in solid lines 201 in Figure 3A, or otherwise a pseudo-cylinder, referred to herein as "oval" or "ovoid", ie, which is of an externally slightly bulging shape, as shown in the dashed lines long and short 202 in Figure 3A. at least a portion of the internal volume 9 of the cover 1 towards the distal ends of the branches 5 is in the shape of a truncated cone that is almost circularly symmetrical with its larger base that is closer to the seat 7, whose implant has when minus four branches 5, and at least one spacer 2 suitable for passing through the hole 8, and by the large base of the truncated cone inward of the internal volume 9. In Figures 2, 3B, 4B, 5B, and 3C, it is to say, in the "active" position, the end separator 2 extends the branches 5 apart, the internal volume 9 then extending towards a circular cylinder, while the external shape of the cover 1 tends towards an approximately truncated cone. In Figure 3B, for example the solid lines 201 show the slightly concave shape obtained from a regular base cylinder in the idle position, while the short and long line lines 202 show the straightest shape obtained from a cylinder that was initially ovoid, as shown in Figure 3A. Once the separator 2 has been placed in the desired position, no internal part has been used to place the implant, and the spacers in place are within the space defined by the branches 5, the separator 2, and the hole 2 Whatever the embodiment, at least a portion of the outer surface of the branches 5 is threaded with a thread profile 11 having flanges projecting as shown in detail in Figure 7. In particular, by way of example , for a cover that has a length L of approximately 20 millimeters to 25 millimeters, the length 1 of the threaded portion of the branches 5 can be in the scale of 13 millimeters to 16 millimeters, with a separation jp_ of 1.5 millimeters to 2 millimeters , being the outer diameter D of the circular cylinder of the cover of 9 millimeters to 16 millimeters, and the height of 1 tooth being 11- | _ of the thread of the order of 0.7 millimeters to 0.9 millimeters for a thread angle ß between the successive teeth of approximately 60 °, and with an internal profile 112 of the thread having a radius of approximately 0.4 mm. This rounded shape of the profile minimizes stress concentrations, thus making it possible to withstand large forces and impacts. This external thread, with flanges that project, therefore, facilitates the installation, since it is not traumatizing, since there is no impact shock while inserting the implant, because it is screwed in a hole previously drilled by any tool compatible with hole 8 of the implant, and once in place, this thread also provides an anchor in the bone, thus eliminating any subsequent emigration. The seat 7 may include at least two planes 6 that are parallel or slightly inclined one relative to the other, to fit the profile of the vertebrae more closely, each arranged between two successive branches 5, as shown in the embodiments of the drawings. Figures 1, 2, 9, 10, and 11. Alternatively, the seat 7 may have four planes that form a square or pseudo-square section, as shown in the embodiment of Figures 3, 4, and 5. In addition to the seat, the branches 5 themselves can also have respective planes at least in line with those of the seat, as shown in the embodiment of Figures 3 to 5, particularly if the section of the implant is almost circular, or alternatively it may not have planes at all, as in the embodiment of Figures 1, 2, and 9 to 11. These planes can be replaced, or at least associated with a longitudinal implant section having a slightly oval shape or voide, as mentioned above. The hole 8 of the seat 7 can be threaded with a thread profile 15, as shown by way of example in Figure 6, with a thread separation that is rounded both in its flanges and in its grooves, and to associate with the dimensions given above by way of example, an opening 8 can have an internal diameter d of 7 millimeters to 10 millimeters, a spacing p 'of 1 millimeter to 1.5 millimeters, a depth of thread of approximately 0.6 millimeters, and a screw angle? between the walls of the thread of approximately 30 °. A plug 3 is then screwed to close the internal volume 9 in the hole 8, either to serve as an anchor point for an implant installation rod, or otherwise after the implant has been put in place and the ramifications have been spread apart by the end separator 2 for the purpose of closing the internal volume 9, in order to first reinforce the cover, and secondly, to prevent any bony matter that has been implanted inside the cover from escaping by the back end. This plug shows in a front view in Figure 14A, and in a side view in Figure 14B, having a thread 152 of the type shown in Figure 6, and a central hole 17 of a polygonal shape, which is square, hexagonal etc., or is replaced by any suitable element for securing therein the end of a rod having a compatible end for the purpose of making it possible to screw and unscrew the cap.

In addition, it is possible to form, on the rear face of the implant and on the periphery of the hole 8 in the seat 7, poles or grooves that serve to secure a portion of the "auxiliary" installation apparatus around the rod, making it possible to drive the cover 1, the spacers and / or the plug 3 in order to more securely fix the implant placement while it is being put in place, and to facilitate the dismantling of the auxiliary apparatus without moving the implant. In the embodiments shown with four branches 5, the cover 1 has four slots 10 forming inter-ram spaces, as shown in Figure 8 looking along the arrow VIII of Figure 9, for example. These grooves serve firstly to improve the fusion of the bone graft, which can be housed in the internal volume 9 with the adjacent intervertebral discs, and second, to obtain a better deformation of the branches 5 during the installation of the implant, the branches being in this particular portion of a section that is smaller than at its ends. In addition, these grooves may be of an oblong shape, with their ends located towards the distal ends of the branches 5 narrower than their opposite ends, as shown in Figure 8, and ending in a narrow slit 101 between the distal ends. of the adjacent pairs of branches.

This shape, at least for the main slot 10, makes it possible to have a slot with parallel edges, once the cover is expanded. In addition, the choice of a profile of this shape instead of an initial groove of a constant width, as shown in Figure 3A, makes it possible to increase the support surface area between the separator 2 and the distal ends of the branches 5. of the cover, thus providing greater strength. In the embodiments of Figures 1, 2, 9, 10, and 11, the internal surfaces of the branches 5 that define the internal volume 9 of the cover 1, are smooth, so that the volume includes, at its distal end , an axial housing 12 suitable for receiving the separator 22, as shown in Figure 12, and for stopping it by means of a shoulder 13 of a larger diameter than that of the internal volume 9 of the cover in its active position, as shown in Figure 1. The spacer 22 has a threaded axial bore 14 suitable for receiving a rod whose end is at least in the same manner threaded and is compatible for the purpose of putting the spacer in place merely by applying a thrust, and being moved. in translation, this rod being subsequently removable. In Figures 1 and 2, in order to avoid any risk of the body of the cover 1 deforming at its anterior end near the distal ends of the branches 5 under the great stresses due to the pressure of the adjacent vertebrae, which could have the effect of moving the branches towards one another by sliding around the separator 2, it is possible to provide the separator with at least two teeth 18 or other elements that are arranged symmetrically around the axis XX 'of the implant. This spacer is put in place inside the cover 1 before the implant is put in place when engaged therein from the ends of the branches, or otherwise, the seat 7 has at least two compatible grooves 19 which they allow the two teeth 18 to slide along them when the spacer 12 is put in place if it needs to be inserted by means of the seat, the width e of the teeth being not greater than the distance and the spacing between the distal ends of two adjacent branches 5. The device may include additional systems, such that the branches do not deform after they have expanded, for example, an outer ring received in a groove at the ends of the branches and deformable by the branches . In the embodiment shown in Figures 3, 4, and 5, the internal surfaces of the branches 5 defining the internal volume 9 of the cover 1 are threaded with a spacing equivalent to that of the hole 8 in the seat 7, for example, as shown in Figure 6, and the separator 2- ^ is threaded in a compatible manner, as shown in Figures 13A and 13B. In this embodiment with an internal thread, the cover 1 can also include at least one intermediate spacer 4 threaded as the end spacer 2, and which can be screwed behind it, in order to compress first the bone material that has been inserted in the space defined between the two separators, and second, to reinforce the central portion of the cover. These end and intermediate separators 2 and 4 have respective polygonal axial holes 16 suitable for receiving a removable rod having a male end in a compatible manner for propelling them while they are being installed. The trunco-conical shape of the internal volume 9 of the cover 1 can have a half-angle of the inclination. leaving the range from 6th to 9th, for example.

Claims (12)

1. An expansive osteosynthesis implant comprising branches (5), each connected at one end with a seat (7) pierced by a hole (8) characterizing the implant because these branches (5) and the seat (7) constitute a hollow cover (1) which, in a "resting" position, has a general external shape that is almost cylindrical, of an almost circular section, and a portion at least of the internal volume (9) of the cover (1) toward the distal ends of the branches (5), is in the form of a truncated cone almost circular whose large base is towards the seat (7), whose implant has at least three branches (5), and inside internal volume (9), at least a separator (2) compatible with the dimensions of the large base of the truncated cone, and in such a way that once the separator (2) has been placed in the desired position, no internal part remains in the space defined by the branches (5) the separator (2) and the hole (8). An implant according to claim 1, characterized in that, in an "active" position, the separator (2) deploys the branches (5) apart, the internal volume (9) tending towards a circular cylinder, while the shape outer of the cover (1) tends towards an approximate truncated cone. An implant according to claim 1 or 2, characterized in that at least a portion of the external surfaces of the branches (5) is threaded with a thread profile (11) having a projection flange. An implant according to any of claims 1 to 3, characterized in that the seat (7) has at least two planes (6) each arranged between two successive branches (5). An implant according to any of claims 1 to 4, characterized in that the hole (6) of the seat (7) is suitable for receiving a plug (3) to close the internal volume (9) of the cover (1) . An implant according to any of claims 1 to 5, characterized in that the internal surfaces of the branches (5) defining the internal volume - (9) of the cover (1) are smooth, whose volume has an axial housing (12) at its distal end suitable for receiving the separator (2) and for stopping it by means of a shoulder (13) of a diameter greater than the diameter of the internal volume (9) of the cover in the "active" position. An implant according to claim 6, characterized in that the spacer (22) includes a threaded axial hole (14) suitable for receiving an installation rod that is removable, at least the end of the rod being also threaded and compatible. An implant according to claim 6 or 7, characterized in that the separator (2) includes at least two teeth (18) arranged symmetrically around the axis of the implant, the width e of the teeth being not greater than the distance of the gap desired between the distal ends of two adjacent branches (5). An implant according to any of claims 1 to 5, characterized in that the internal surfaces of the branches (5) defining the internal volume (9) of the cover (1) are threaded, the separator also being. { 2- ^) threaded, in a compatible way. An implant according to claim 9, characterized in that the cover (1) has at least a second intermediate spacer (4) threaded as the end spacer. { 2- ^). 11. An implant according to claim 9 or 10, characterized in that the spacers. { 2l r 4) have respective axial holes (16) of a polygonal shape suitable for receiving a removable rod having at least one end of a compatible male shape, to urge them and put them in place. 1

2. An implant according to any of claims 1 to 11, characterized in that the general external shape of the cover (1) is a cylinder whose generating line that generates it by rotation about its axis of symmetry XX ', has a middle curve portion, such as a circular arc of a large radius, which gives the cover a longitudinal ovoid shape.