INTERSOMATIC FUSION CAGE

Abstract

An interbody fusion cage comprising a hollow body of revolution (1) provided with a thread (3) and capable of being rotated by means of a tool for inserting the cage by screwing it between two vertebral discs. According to the invention, the thread (3) is self-tapping. It is interrupted by flats (3A) tangent to the hollow body (1) which, by notching, form cutting edges (3B) of the vertebral discs during screw insertion. The hollow body (1) is closed at one end by a base (7) and at the opposite end by a removable cap providing a grip for the cage screwing tool. The self-tapping thread allows the cage to penetrate between the vertebral discs with minimal preparation and reduces the risk of migration. The cage reduces the number of surgical steps while allowing for filling with the graft before insertion. It thus contributes to reducing the duration of the procedure and increasing the safety of the surgical intervention.

Description

MELTING CAGEINTERSOMATIC The invention relates to an intersomatic fusion cage, and in particular to a cage which comprises a hollow body of revolution provided with a thread and which can be actuated in rotation using a tool for inserting cage by screwing between two vertebral discs. By interbody fusion cage is meant a hollow implant pierced with openings to allow a graft placed inside to fuse with the vertebral discs. As is well known, the cage provides the graft with mechanical protection during the interbody fusion phase, and also prevents premature wear of the graft by maintaining a constant intervertebral space. To insert the cage between the vertebral discs, a reception housing is first of all arranged, most often by drilling. Then the practitioner performs a tapping of the housing to allow the screwing of the cage. Whether in insertion by an anterior or posterior route, the tapping operation is particularly tricky to perform, given the fact that the tapping tool must be introduced and then withdrawn, which increases the risk of mishandling. moreover, this operation inserted between the drilling and the screwing increases the duration of intervention of the practitioner and of anesthesia of the patient. The question of the safety of the operative gestures and the duration of the intervention also arises with regard to the filling of the cage. meets cages which must be filled by the graft after having been screwed into the receiving housing between the two vertebral discs. The cage must indeed remain empty to allow the practitioner to introduce a tool inside the hollow body via an open end and as far as a closed opposite end providing a grip for the tool. At the end of screwing, the practitioner places the graft in a cage and closes the open end of the hollow body using a cap. The filling operation performed after insertion again increases the risk of improper handling. There are also cages which, although they can be filled before their insertion, require relatively complicated handling. After filling with the graft, the cage must indeed be closed by a cap forming a front part, that is to say which appears first in the receiving housing. The insertion by screwing the cage is carried out from a rear part adjoining the hollow body and provided with a socket for a tool. With this arrangement, the practitioner must necessarily disengage from the cap the tool which he used to close the cage and engage in the rear part of the hollow body the tool which he will use for screwing the cage. In other words, the closing of the hollow body and the insertion of the cage require a sequence of two operating steps concerning respectively the front and then the rear part of the cage. One of the aims of the invention is to provide the practitioner with an interbody fusion cage which allows him to simplify the operative gestures and to reduce the duration of the intervention both when filling the cage with a graft during the insertion of the cage between two vertebral discs. To this end, the subject of the invention is an interbody fusion cage for a graft placed inside the cage with vertebral discs between which the cage is inserted, comprising a hollow body of revolution provided with a thread and which can be actuated in rotation using a tool to insert the cage by screwing between the two vertebral discs, characterized in that the thread is self-tapping. The self-tapping thread makes it possible to eliminate the operation of tapping the receiving housing, or to replace it with a lighter operation of priming the tapping of the housing. It also makes it possible to insert the cage by direct priming between the vertebral discs, that is to say without prior drilling of a receiving housing. This results in a reduction in the duration of the intervention and a simplification of the operating procedures. According to a particular embodiment of the invention, the thread is interrupted by gougeures or flats tangent to the hollow body of revolution. The interruption of the thread at the intersection with a flat makes it possible to form, by offsetting, a cutting edge of the vertebral discs during insertion by screwing. Preferably, the flats are offset, for example by 120 degrees, angularly around the axis of revolution of the hollow body.This arrangement distributes the screwing force and allows better penetration of the hollow body into the receiving housing. This results in greater ease of installation of the cage. Advantageously, the thread has, in the direction opposite to insertion, an inclination of the hollow body with respect to a direction perpendicular to the axis of revolution. thus prevents a recoil of the cage after its insertion between vertebral discs. In other words, the cage has no possibility of migrating along the reception housing. According to another advantage, the hollow body is closed at one end by a bottom and, at the opposite end, by a removable cap providing a grip for the tool for screwing the hollow body during the insertion of the cage between the two discs vertebral. By this arrangement, the filling of the cage by the graft is carried out by the end opposite the bottom, the cap being removed. The practitioner then closes the cage by the same end which he will use to introduce the tool and screw the hollow body into the receiving housing. It can advantageously use the same tool in engagement with the cap that will then use during screwing. We thus observe a reduction in the operating gestures in the sequence of closing and inserting the cage between the vertebral discs, as well as a reduction in the material to be used, while allowing the cage to be filled before insertion. Other advantages of the invention are highlighted with the detailed description of the invention illustrated by the drawings. FIG. 1 shows a longitudinal profile of an interbody fusion cage according to the invention. FIG. 2 is a view in longitudinal section of the cage of FIG. 1. FIG. 3 is a top view of the cage of FIG. 1 showing more particularly zones where the thread is interrupted by tangential flats. Figure 4 is a detail view of the net of the cage of Figure 1. Interbody fusion cage comprises, Figure 1, a hollow body 1 which extends in an axial direction of revolution A. The hollow body 1 is provided with a thread 3 which allows, when the hollow body is rotated using a tool, to insert the cage by screwing between two vertebral discs. A graft placed inside the cage fuses with the vertebral discs by growth through openings 5 ​​drilled in the hollow body 1 between the helix pitch of the net 3. During the interbody fusion, the cage provides the graft with protection mechanical. The cage also contributes to the prevention of premature wear of the graft by maintaining a constant intervertebral space. According to the invention, the thread 3 is self-tapping to dispense with prior tapping of the receiving housing. As indicated above, the self-tapping thread 3 makes it possible to eliminate the tapping operation of the receiving housing, or to replace it with a lighter thread-priming operation. It also makes it possible to insert the cage by direct priming between vertebral discs, that is to say without prior drilling of a reception housing. In the embodiment represented by FIG. 3, the thread 3 is interrupted by gougeures or flats 3A which are tangent to the hollow body of revolution 1. The interruption of the thread 3 at the intersection with a flat 3A makes it possible to form a recessed 3B cutting edge. During the insertion by screwing the cage between the vertebral discs, each cutting edge 3B progresses by removing a small quantity of material from the vertebral body in contact with it to dig a furrow corresponding to the thread 3. Preferably, the thread is interrupted by several flats 3A offset by an angle [3, for example 120 degrees, around the axial direction of revolution A. The furrow in correspondence to the thread 3 is thus dug progressively by the successive action of several cutting edges 3B. The 120-degree arrangement makes it possible to distribute the force symmetrically around the axial direction A of the hollow body 1 and leads to better penetration of the cage into the reception housing. Although the hollow body 1 of revolution can be cylindrical, it is preferred, as shown in Figure 1, a slightly tapered shape, for example having a taper of a few degrees.The reduction in diameter of the trunk orients the hollow body 1 so that the smallest diameter constitutes the part by which the cage is inserted first between the two vertebral discs. By convention, this part forms the front of the cage, while the rear is made up of the part with the largest diameter. Compared to the cylindrical shape, the frustoconical shape ensures all along the helix of the net a more intimate contact between the furrow dug in the vertebral discs and the net. Hence a better immobilization of the cage. Advantageously, in FIG. 4, the thread 3 has, in the opposite direction to insertion, an inclination a of the hollow body 1 of approximately 10 degrees with respect to a direction perpendicular to the axis of revolution A. Thanks to this inclination, it prevents retraction of the cage after its insertion in the vertebral discs, and any possibility of migration is blocked. It is possible to choose the inclination between 8 and 12 degrees. In the embodiment illustrated by FIGS. 1 and 2, the hollow body 1 is closed at one end by a bottom 7 and, at the opposite end, by a cap 9 fixed reversibly. The cap 9 is for example screwed into the internal thread 1A of the hollow body 1 until it comes into abutment against the latter. socket 9A formed in the cap 9 to allow the cage to be rotated using a tool at the time of insertion between the two vertebral discs. According to the convention adopted previously, the bottom 7 constitutes the front part of the cage, while the cap is fixed reversibly to the rear. this arrangement, the cap 9 makes it possible both to close the hollow body and to actuate the cage in rotation during insertion. The practitioner also retains the possibility of filling the hollow body before insertion, which contributes to the simplification of the operative gestures and to the reduction of the duration of the intervention. The reversible fixing of the cap in the internal thread 1A of the hollow body 1 has the advantage for the practitioner of using the same tool for screwing on the cap 9 then for screwing on the cage. In this way, less intervention equipment is used. As can be seen in FIG. 1, to facilitate the interbody fusion of the graft with the vertebral discs, the hollow body 1 is pierced with two diametrically opposed oblong openings 11 extending in the axial direction A. It is noted that the arrangement of the two parallel openings to the axis of revolution does not weaken the rigidity of the hollow body 1. The two openings 11 are diametrically opposed to provide a growth zone in contact with each of the two vertebral discs, in addition to the openings 5 ​​pierced between the net Advantageously, FIG. 2, a mark 13 is formed on the cap 9 screwed into abutment in the hollow body 1 to indicate the angular position of the two openings 1 . A mark is also formed on the cage-holder tool which aligns with that of the cap before insertion. Then the cage is screwed in an angular position for which the mark of the cage holder is vis-à-vis with the vertebral discs, to guarantee the vis-à-vis the two oblong openings 11 with the latter. cage is made from a biocompatible material, for example titanium, using a machining process that does not tolerate burrs. fusion cage according to the invention provides a simplification of operating procedures both for filling with the graft and for its insertion by screwing between the vertebral discs. It thus contributes to reducing the duration of the intervention and to increasing the safety of the surgical act. Penetration into the vertebral discs is facilitated and the risk of migration reduced. The material to be used for manipulation is also unimportant. Interbody fusion is facilitated without prejudice to the mechanical protection of the graft. cage according to the invention is intended for use in human-animal surgery. The dimensions of the hollow body are related to the region of the spine to be treated. In humans, for cervical vertebrae, the length of the cage is typically of the order of 8 to 10 millimeters. It may be greater, for example for the lumbar vertebrae.

Claims

CLAIMS 1. An interbody fusion cage for a graft disposed inside the cage with vertebral discs between which the cage is inserted, comprising a hollow body of revolution (1) provided with a thread (3) and capable of being actuated (9A) in rotation by means of a tool for inserting the cage by screwing between the two vertebral discs, characterized in that the thread (3) is self-tapping.

2. An interbody fusion cage according to claim 1, characterized in that the thread is interrupted by grooves or flats (3A) tangent to the hollow body of revolution (1).

3. An interbody fusion cage according to claim 2, characterized in that the flats (3A) are angularly offset about the axis of revolution (A) of the hollow body (1).

4. An interbody fusion cage according to claim 2 or 3, characterized in that the thread (3) is inclined at an angle (a).) between 8 and 12 degrees relative to a direction (R) perpendicular to the axis of revolution (A), to prevent migration of the hollow body (1) relative to the vertebral discs.

5. Interbody fusion cage according to claim , characterized in that the hollow body (1) is closed at one end by a base (7) and, at the opposite end, by a removable cap (9) providing a grip (9A) for the tool used to rotate the hollow body.

6. Interbody fusion cage according to claim 5, characterized in that the cap (9) is screwed butted into a thread (1A) of the hollow body (1).

7. Interbody fusion cage according to claim 1 or 5, characterized in that two diametrically opposed oblong openings (11) extend along the direction of revolution (A) of the hollow body (1).

8. Interbody fusion cage according to claim 7, characterized in that a marker (13) is formed on the cap (9) corresponding to one of the oblong openings (11). 9.Interbody fusion cage according to claim 1 or 5, characterized in that the hollow body (1) is frustoconical.

10. Interbody fusion cage according to claim 1 or 5, characterized in that openings (5) are drilled in the hollow body (1) between the threads (3).