FR2615095A1 - Osteosynthesis instrumentation for the correction of lumbar scoliosis through the posterior - Google Patents

Abstract

This instrumentation comprises, for each lumbar vertebra 1b, two pedicle screws 2, 3, with a double thread 4, 5 and two rods 8, 9, associated respectively with one screw 2, 3 and solidly attached therewith with corresponding clamps 11, 12; it comprises, for each vertebra, a plate 13 passed through by the said screws 2, 3 and adapted to hold the latter transversally. The presence of the transverse holding plate 13 ensures very solid vertical holding, making it possible to act on the vertebra in all directions and distribute the stresses over the whole of the latter between the pedicle screws 2, 3 and this joining plate 13, which prevents any risk of breakage or tearing of the vertebra.

Description

 The present invention relates to osteosynthesis instrumentation for the correction of lumbar scoliosis by the posterior route, of the type comprising for each lumbar vertebra, two pedicle screws with double thread and two rods associated respectively with a screw and secured to these by clips corresponding.

 We know that the surgical treatment of scoliosis aims to correct spinal deformation in the three planes of space. To this end, this treatment performs compression between all the structural anatomical elements which oppose the correction (discs, joints, ligaments, etc.) and this by means of instrumentation whose points of application and directions developed forces must go in the direction of correction.

To meet these requirements, the most recent known instrumentations carry out a segmental grip involving several vertebrae of the deformation
- either all the vertebrae, with grip on the vertebral bodies or on the posterior arches;
- or certain so-called strategic vertebrae, by instrumentation located at the level of the posterior column.

 The differences between these devices reside in their mode of action and in the type of vertebral "plug", the known prior instrumentations allowing an excellent vertebral grip by means of transverse body screws.

 In addition, the disc excision necessary for the graft, and which allows the direct approach of the vertebral bodies, allows a significant correction of the lateral clinion and rotation by shortening the anterior column. However, it has the drawback linked to the nature of its path itself, due to the proximity of noble organs. But above all, if this previous instrumentation has a "decyphosing" effect, it does not have a real lordosing effect because of its mode of action in antero-lateral compression.

 However, the restitution of a lordosis is particularly important at thoraco-lumbar level and especially lumbar for the sagittal balance of the patient.

 The posterior instruments provided on the posterior arches or at the level of the posterior column with hooks, allow a good frontal correction, saggital at the lumbar level, but unfortunately do not provide practically any effectiveness in the horizontal plane, that is to say that practically no vertebral derotation effect is obtained.

 This gap is largely linked to the mode of vertebral grip. In fact, at the lumbar level considered here, the articulars cannot be used because of their orientation, and the transverses are too fragile to allow a solid grip. Furthermore, it is essentially on the blades that the instrumentations are supported, either by means of wires (Luque), or by means of hooks (Cotrel-Dubousset). However, these lamar grips have the drawback of not ensuring a perfect vertebral grip allowing a small mobility of the vertebra with respect to the instrumentation. In addition, they are very badly placed mechanically to allow a vertebral derotation, because they are too close to the axis of rotation.

It follows in particular during the rotation of the rod in lordosis with Cotrel instrumentation
Dubousset, a loss of potential correction with absence of real vertebral derotation - which persists compared to the instrumentation - and less significant lordotization of the column compared to the rod.

In other words, it is relatively difficult to move the vertebra in three directions in space using this instrumentation.

 The object of the invention is to produce osteosynthesis instrumentation for the correction of lumbar scoliosis by posterior view, not having these drawbacks.

 According to the invention, the instrumentation comprises, for each vertebra, a plate crossed by the pedicle screws and adapted to hold them transversely.

 The presence of this connecting plate and transverse holding of the associated screws allows effective three-dimensional correction by the posterior route, thanks to a solid vertebral grip. In addition, the plate supports part of the force exerted on the vertebra, which avoids risks of breakage or tearing-of the latter.

 According to one embodiment of the invention, the plate is V-shaped, wide open and the concavity of which is directed towards a medular channel of the vertebra, and the ends of said plate are crossed by the corresponding screws, thanks to holes in preferably frustoconical formed in said ends.

 Thanks to this frustoconical profile, it is possible to position the pedicle screws with a large angular movement, for example of the order of 20 *.

Other features and advantages of the invention will appear during the description which follows, given with reference to the accompanying drawings which illustrate an embodiment thereof by way of non-limiting example
- Figure 1 is an elevational view in continuous lines of a lumbar vertebra of a spine affected by scoliosis and, in finer lines, of the same vertebra positioned after correction;
- Figure 2 is an exploded perspective view of an embodiment of the osteosynthesis instrumentation according to the invention;
- Figure 3 is a top view of the instrumentation of Figure 2 positioned on a straightened lumbar vertebra;
- Figure 4 is a half-sectional, partial half-elevation view on an enlarged scale, of the instrumentation of Figure 3;
- Figure 5 is an elevational view of all of the instrumentation according to Figures 2 to 4 arranged on lumbar vertebrae.

 FIG. 1 shows a lumbar vertebra 1a of a vertebral column affected by lumbar scoliosis, and in fine lines this same vertebra 1b positioned after correction by means of the instrumentation targeted by the invention.

 As shown by the three series of arrows F, G, H, this deviation of the position of the vertebra la is three-dimensional, so that the correction of its positioning must be able to be carried out in the three planes of space, in particular by means a lateral derotation indicated by angle A.

 The osteosynthesis instrumentation targeted by the invention is therefore intended to allow this correction of scoliosis by posterior route. This instrumentation includes (Figures 2 to 4), for each lumbar vertebra, two pedicle screws 2, 3 with double thread 4, 5 separated by a body 6 and by a frustoconical part 7. The part 2a external to the vertebra carries a thread 4 at low screw pitch, while the part 2b of the screw 2, 3 carries a thread 5 with a large pitch and is intended to sink into the vertebral body. These screws are said to be of the spondylolisthesis type.

 The instrumentation also includes two knurled rods 8, 9 with diamond points, respectively associated with a pedicle screw 2, 3 and secured to them by corresponding pliers 11, 12 as well as, for each vertebra, a plate 13 traversed by the part 2b of the screws 2, 3 carrying the thread 5 and adapted to hold it transversely.

 The plate 13 is profiled in a V wide open and whose concavity is directed towards a medular channel 14 (Figure 3) of the vertebra lb. The ends 15 of the plate or bar 13 are folded in the same plane relative to the two branches of the V, and pierced with frustoconical holes 16 adapted to receive the threaded part 2b of the screws 2, 3.

 The plate 13 is provided, in its middle part, with gripping means by a tool not shown such as a forceps, in order to allow the vertebra to be displaced in the desired directions.

In the embodiment shown, these gripping means consist of a boss 17 projecting towards the outside of the V, that is to say in the direction opposite to the medular channel 14, and in which a tapped hole is formed. 18 intended to receive the corresponding end of the tool.

 Of course, each transverse holding plate 13 can be produced according to different lengths, so as to be able to adjust to all the morphologies of the vertebrae.

 Each clamp 11, 12 for connection between the knurled rod 8, 9 and the associated screw 2, 3 consists of two half-hooks or semi-hooks 19, 21 each having at one end a semi-circular opening 22, 23. The half-hooks 19, 21 are arranged relative to each other so that the openings 22, 23 complement each other to receive the corresponding rod 8 or 9. Each half-hook 19, 21 is pierced with a hole 24 , 25 for passing the threaded part 2a of the screw 2 (or 3) carrying the thread 4. Each hole 24, 25 has a frustoconical flare 24a, 25a adapted to receive respectively a nut 26 for tightening the two half-hooks 19, 21 on the rod 8 (or 9), and the frustoconical part 7 of the screw (Figure 4).

 The implementation of the instrumentation which has just been described is as follows.

 First, each transverse plate 13 is mounted on the two corresponding pedicle screws 2, 3, the threaded parts 2b of which are driven into the vertebral bodies. Then we thread each knurled rod 8, 9 previously curved to the desired curvature in two extreme hooks 27 and 28 (Figure 5) pedicle and lamar. (The hooks 27 and 28 are known per se and therefore do not require any particular description).

 Then mounted on the threaded part 2a of each screw 2, 3 the half hooks 19, 21, at a height determined by the deformation of the vertebra, so that the rod 8, 9 is trapped in the openings 22, 23 between the half-hooks 19, 21. The latter therefore bear on the rod 8 or 9 blocked by its ends in a fixed position, the screws 2, 3 being on the other hand blocked in the vertebra.

The nut 26 is then screwed onto the thread 4 until it sinks into the frustoconical flare 24a (the frustoconical flare 25a receiving the frustoconical part 7). The upper half-hook 19 rests on the fixed rod 8 or 9, this tightening of the nut 26 raises the vertebra until the rod 8 (or 9) comes into contact with the lower half-hook 21, which itself # is in contact with the upper cone 7. The tightening of the nut 26 is completed and the vertebra is then straightened.

 There was thus produced a monobloc assembly comprising the grip of the rod 8 or 9 by the two half-hooks 19t 21 locked by the conical part 7 and by the nut 26, the screw 2 or 3 being itself taken by the vertebra .

 This "derotation" movement is carried out, which makes it possible to give tension to the lumbar vertebrae V1, V2, V3 (Figure 5) for each of these successively. Each of these successive operations is facilitated by the presence of the connecting plate 13 previously threaded on the threaded part 2b and then on the body 6 of the screw before screwing it into the vertebral body.

 The presence of the plates 13, anchored on one of the screws 2, 3 driven into the vertebra, makes it possible to tighten the nut 26 on the other screw (3 or 2) and to force on the thread 4, avoiding any risk of fracture or tearing of the vertebra. In fact, each plate 13 receives part of the force exerted on the vertebra.

 Once the first series of half-hooks 19, 21 thus put in place on the screws and the corresponding rod 8 or 9, we start again with the second series of half-hooks 19, 21 on the second rod 9 or 8. As in the previous sequence, the fixed support provided by the extreme grips of the pedicle hooks 27 and the lamary 28 allows, by screwing and tightening the nuts 26, to complete the straightening of the vertebrae in the three dimensions of the space, to reposition them correctly (Figure 1).

We see in Figure 5 all the instrumentation obtained after successive placement of the various elements thereof according to the sequences described above, on three lumbar vertebrae V1,
V2, V3.

 In addition to the technical advantages previously mentioned, the instrumentation according to the invention has the other advantages below.

 The interpedicular plate 13 joining the corresponding screws 2, 3 constitutes a very solid vertebral "bipedicular grip" making it possible to act on the vertebra in all directions, the stresses being distributed over the whole of the vertebra between the converging screws 2, 3 towards the vertebral body and their connection by the plate 13.

 The gripping of the latter during the assembly sequence is made possible by the boss 17 pierced with the threaded hole 18 for receiving a forceps, which allows the surgeon to move and correctly orient the vertebrae during the sequences described above. above. The tapered holes 16 make it possible to position the plates 13 on the bodies 6 of the screws with a wide angular clearance, for example of the order of 20 (Figure 3) depending on the geometry of the conical holes 16. The positioning of the plates 13 is thus adapted to the morphology of each vertebra.

 Furthermore, the fact of replacing the simple hooks of the previous instrumentations with two complementary half-hooks or semi-hooks 19, 21 significantly improves the stability of the knurled rod 8, 9, which in fact is no longer housed in an open jaw and therefore no longer risks slipping into it. On the convex side, the rod 8 or 9 grows in lordosis on the anterior half-hooks 19, the stabilization being favored by the tightening of the posterior half-hooks 21. The convex pedicle is thus pushed forward. Conversely on the concave side, the posterior semi-hooks 21 allow, by progressive screwing, to increase the derotation by posterior recall of the concave pedicle. The set of two semi-hooks 19, 21, which are not fully locked, makes it possible to exert tensile and compressive forces.

  it should also be noted that the posterior articular structure has been previously minimized as much as possible by a wide articular excision in other words, the ligaments and the muscles of maintenance of the vertebra have been reduced by the surgeon in order to facilitate the displacement of that -this.

 Finally, as already indicated, the V-shaped middle part of the plates or bars 13 allows, thanks to its threaded hole 18, the grip of the plate by an instrument making it possible to act on it.

 Many variations can be made to the invention within the scope of the claims below.

Claims (6)

 1 - osteosynthesis instrumentation for the correction of lumbar scoliosis by posterior route comprising, for each lumbar vertebra (V1, V2, V3), two pedicle screws (2, 3) with double thread (4, 5) and two rods (8 , 9) respectively associated with a screw (2, 3) and secured to them by corresponding clamps (11, 12), characterized in that it comprises, for each vertebra, a plate (13) crossed by said screws (2, 3) and adapted to hold them transversely.  2 - instrumentation according to claim 1, characterized in that the plate (13) is profiled in a V wide open and whose concavity is directed towards a medular channel (~ 4) of the vertebra, and the ends (15) of said plate (13) are crossed by the corresponding screws (2, 3).  3 - instrumentation according to one of claims 1 and 2, characterized in that the plate (13) is provided, in its middle part, with gripping means by a tool such as a forceps, in order to allow the vertebra to be moved in the. desired directions.  4 - instrumentation according to claim 3, characterized in that the gripping means comprise a boss (17) projecting towards the outside of the V and in which is formed a tapped hole (18).  5 - instrumentation according to one of claims 2 to 4, characterized in that the ends (15) of the plate (13) are pierced with frustoconical holes (16).  6 - instrumentation according to one of claims 1 to 5, characterized in that each clamp (11, 12) connecting between the rod (8, 9) and the associated screw (2, 3) consists of two half-hooks (19, 21) complementary, each having a semi-circular opening (22, 23), the rod (8, 9) can be received and locked in said openings by means of a nut (26) for tightening the half hooks (19, 21) with which the screw (2, 3) is provided.