Bone fixation device, particularly of the sacrum, for spinal osteosynthesis

The present invention relates generally to a fastening device, in particular the sacrum, used in osteosynthesis of the spine.

It is common practice of osteosynthesis spine using fasteners taking anchoring in the sacrum. It is thus possible to proceed, between floors attached to movements reduction that can be contractions, distractions or vertebrae recalls having slipped forwardly of the spine. The latter condition is known under the name of "spondylolisthesis".

In the case of a spondylolisthesis reduction, distraction is often practiced. A reduction partial product by the retightening of fibers of the ligament and disc unit of the patient. The reduction is complemented by the use of the equipment surgical technique associated with it. This operation is performed, except in exceptional cases, so bilateral. Throughout the description which follows, will describe a side processing.

Most plates or mounting blocks sacrum known in the prior art have some drawbacks. One of these drawbacks is that the orientation of the bone anchor screw is imposed, which gives the product a lack of flexibility Clearly taking account of changes in the configuration sacrum and its vicinity of a patient to another.

Another disadvantage of the plates or blocks fixation sacrum known is the risk of a unscrewing anchoring screws driven in particular Microwave relative movements occurring between the material and the sacrum. This then results in the failure of the fixation sacred.

Furthermore, osteosynthesis of the spine are achieved through hardware for attaching to often very rigid way, different functional units of the spine. This results in a variation brutal force distribution, and therefore states constraints and resulting deformations at the level of suspension discs and underlying fixing. This modification leads to more or less long term disc degeneration. This condition is known as the "hinge syndrome".

Are also known from EP-A-0625337 a device according to the preamble of claim 1 which allows to vary the inclination of the anchor screw by relative to an elongate connecting element, as well as the spacing between these screws.

It is known dispostif however disadvantageous in that the elongated connecting means are constituted of several components, namely an elongate shaped member bowl and a plurality of mounting blocks distributed along the elongate member and each receiving a screw head and, in the lower part, the corresponding area of ​​the body elongate.

It follows that the handling and laying of this device by the surgeon are extremely tedious, with in particular the need to drag on the elongate member a series of mounting blocks, and the y maintain in position.

The present invention therefore aims to overcome this disadvantage.

It proposes for this purpose a fastening device bone as defined in claim 1.

Preferred, but not limiting the device according to the invention are defined in the dependent claims.

Other aspects, objects and advantages of the present invention appear better on reading the description following detailed preferred embodiments of the latter, given by way of example and with reference to accompanying drawings, in which:<sl><li>Figure 1 is a longitudinal sectional view median of a fastening element according to the invention,</li><li>Figure 2 is a front view of the element of figure 1,</li><li>Figure 3 is a side view of the element and that of three bone anchorage screws and associated plugs,</li><li>Figure 4 is a front view of the element provided screws and plugs,</li><li>Figure 5 is a side elevational view of a plug designed to cooperate with the element of Figures 1 and 2 and a bone anchor screw ,,</li><li>Figure 6 is a view in side elevation of the screw bone anchor,</li><li>Figure 7 is a cross-sectional view of the fixing member, a bone anchor screw and associated plug after mounting</li><li>Figure 8 is a view partially in elevation and partially in section of a bone anchor screw auxiliary intended to cooperate with another portion of the fastener of Figures 1 and 2,</li><li>Figures 9 to 12 are sectional views similar cross in Figure 7, four variants of embodiment of the invention,</li><li>Figure 13 is a cross-sectional view of different components of a fifth variant of embodiment of the invention, and</li><li>Figure 14 is a cross-sectional view of this fifth embodiment in the assembled state.</li></sl>

Note the preliminary view that, from one figure to the other elements or parts identical or similar are designated as far as possible by the same reference signs, and will not be described each time.

Referring now to Figures 1 and 2, there is shows a fixing element to the sacrum, generally designated by reference numeral 1, which consists of three parts, namely an upper ring 4, a sacral plate 5 and a rod 6, for example cylindrical, connecting the grommet to the plate. The element 1 as a whole has, in profile, a curvature in lordosis illustrated in Figure 1.

In the plate 5 is formed a series of holes 7 aligned in the longitudinal direction of the element 1, for screw bone anchor 2.

Preferably, the surgeon may propose several models of elements 1, including different lengths of rod 6, and in the plate 5, different numbers holes for bone anchor screw.

As shown in Figure 3, the plate 5 can receive, in a version with three holes 7, two screw 2 bone anchor and, in a version of five holes (not illustrated), three screws 2 bone anchor.

7 the holes 7 communicate with each other through a through groove 9 of oblong cross section, as be seen in Figure 2. This allows for groove easily pass a screw 2 from one position to another in During the reduction process. Each of these holes has in the region of its bottom, a spherical cup 7a adapted to cooperate with a bottom portion complementary to the head 21 of the screw 2, the head 21 being in its whole and having a spherical Tightening footprint 211 for example of the hexagon Hex.

This conformation of each hole 7 and the head associated screw 21 makes an angular movement of the screw in a solid angle, the half-angle at the apex is example of the order of 30 °.

Furthermore, each screw being stabilized in its housing during installation, two remote screws are fit maintaining bone distraction without requiring the use of a distractor instrument.

As particularly shown in Figures 1 and 7, each hole 7 has internally, away from the cup 7a, 8 tapping allowing it to receive a plug 3 shown in detail in Figure 5. This stopper has on its outer side a clamping footprint 302, preferably identical to that of the screw head 21 of so you can use the same clamping tool, and housing spherical cup 301 engaging the top also spherical head screw 21. The cap also includes at its periphery a thread 304 for cooperating with the thread 8 of the hole 7. The cap 3 has purpose, after screwing and tightening, ensure blocking of the screw 2 in the angular position determined by the surgeon.

The plate 5, the screw 2 and the cap 3 after assembly are illustrated in particular in Figure 7. The screw cap 3 provides a non-return function prevents accidental unscrewing the anchor screw 2 Associate especially under the conditions set by the preamble present application.

In addition, through the device of the present invention, spondylolisthesis may be reduced implanting into the pedicle of the vertebra is concerned an intermediate screw fixed on the connecting rod Intermediate 6, a screw placed in the eyelet 4.

In the first case, the intermediate shaft 6 can thus be used to perform a return vertebra. AT For this purpose, and as shown in Figure 8, one can associate a top loading screw overall Designated by reference numeral 10 and known per se, which has been previously implanted in the vertebra in question.

One can also attach the vertebra request to the intermediate shaft 6 by means of another type of device, not shown but known itself, into which the screw is offset relative to the axis of the stem 6 but connected thereto by a svstem of maintenance.

In the second case, it is the top eyelet 4 the element 1 which is used to receive an anchoring screw 2 bone in the vertebra to be processed, this screw 2 being preferably of the same type as that described above. In this Indeed, a hole 7 identical to that described with reference to plate 5 is formed in said grommet, to enable there yet angulation of the screw 2 and a non-return function allowing thanks to a plug 3 to prevent it loosens.

In order not to cause the hinge syndrome described in the preamble can be avoided to ensure strict Screw the lock 2 introduced into the upper 4 eyelet. then stored in this case a relative mobility of the screw 2 relative to the eyelet 4.

In this way, the position of the vertebra in which is anchored screw 2 inserted into the eyelet 4 is fixed, but the functionality of the underlying intervertebral disc is partly maintained. This creates a gradient of stiffness in the binding which has the effect of mitigating the sudden change of stress state at the disk level overlying.

This relative mobility of the screw 2 in the eyelet 4 can be achieved in different ways.

A first solution, not illustrated, is to resume the principle illustrated in Figure 7 using a screw cap 3 and by providing in the hole 7 of carnation a shoulder preventing the cap 3 from achieving a locking position of the screw 2 in angular position.

Alternatively, also not illustrated, such a shoulder can be formed on the screw cap 3.

In addition, or alternatively, can be reduced to render negligible friction between the plug 3 and the head 21 of the screw 2 by applying a thin layer low coefficient of friction, e.g. ceramic-carbon or diamond, on one or more of different contact surfaces, namely the screw head 21, the cup 7a of the hole 7 of the eyelet 4, and the cup 301 of screw cap 3.

For example, one can apply such a coating only on the head 21 of the screw 2.

Now with reference to Figures 9 to 14, there will describe a number of variants for attenuating the stiffness of the assembly of the screw 2 and the eyelet 4 in which it is introduced, so there yet avoid the hinge syndrome.

And Figure 9 describes a solution in which contact between the rigid parts to adopt relative movement is prevented by the use of a first O-ring 401, lower, and a second O-ring 402, above. These two rings are preferably made of a cushioning material such as silicone, and are illustrated in Figure 9 in the state deformed after tightening.

Thus, when the rings 401, 402 are brought into pressure and deformed when tightening, they provide link attenuated stiffness between the screw 2 and the eyelet 4.

Advantageously provides the surgeon rings with different shades of hardness, while retaining the same dimensions, which allows it to modulate the stiffness of the assembly without having to play on the torque of the screw cap 3, which would prove very tricky to implement reliably.

In addition, to minimize friction between the rings 401, 402 and the head 21 of the screw, it can be advantageous to carry on the screw surface treatment by ion bombardment with nitrogen, which improves the tribological characteristics of the screw head.

Still referring to Figure 9, it is observed the cap 3 has again a spherical cup 303, intended only to allow the angle of the screw 2, but without support blocking on the head 21 of said screw.

Figure 10 depicts a variant in which the plug 31 differs from that of Figure 5 in that its cup, indicated at 311, is no longer complementary to the spherical head 21 of the screw 2, but is flared, while a ball 411 of damping material is interposed 311 between the cup and said head 21 and pressurizing and defor Mee during tightening.

yet here it provides attenuation of stiffness assembly.

11 depicts a variant in which the screw cap 32 has a flat work surface, and wherein the direct contact between the stopper 32 and the screw head 21 is suppressed by the use of a ring ring 412 made of a damping material, setting pressure and deformed during tightening.

Figure 12 depicts a variant in which the plug, designated by the reference 33, has on its face working a conical recess 331, and wherein the contact between the plug 33 and the screw head is 21 deleted by injection, during the laying operation, a thixotropic fluid 413 performing a function amortization.

In addition, in the three embodiments figures 10, 11 and 12 contact the friction between the spherical head 21 and the cup 7a formed in the hole 7 the eyelet 4 can also be reduced by using a coating such as mentioned above. In this regard, the coating used in the variant of Figure 12 will chosen so that the contact between the base of the spherical head 21 and the cup 7a seals the thixotropic fluid under pressure when screwing.

Figures 13 and 14 describe another variant of embodiment in which the eye is changed. More Specifically, the eyelet 4 has a generally bowl 421 whose cylindrical remote part of the base is threaded 8 for receiving the screw cap 3, identical to that of Figure 5.

Between the cup 421 and the screw head 21 is interposed a ring 422. It can be either a ring rigid, eg made of coated titanium alloy a ceramic, or titanium alloy treated by ion bombardment, or massive ceramic or yet an O-ring similar to the ring 401 used in the alternative embodiment of Figure 9, carried out even in a damping material, for example silicone:

In the case where the ring 422 is rigid, it may be advantageous to provide the radius of curvature of its scope spherical inner slightly below the radius of the screw head 21, so as to ensure a set constraint of said screw head upon tightening. In this case, the version of Figures 13 and 14 may advantageously also be used when a complete blockage of the screw desired.

According to another variant, the ring 422 can be split, again with a stress-up head 21 and a blocking ability.

Naturally, the parts such as the element 1, the screw 2, the caps 3 are made of any material biocompatible appropriate mechanical properties, such as a titanium alloy.

Below we give some to finish additional comments.

Firstly, the shape and dimensions of the element 1 are chosen so as to allow to withstand the torsional stress with the support plane generated between the base part 5 in the form of plate and the adjacent bone.

This form also helps limit translatory movements longitudinqale on screws intermediaries.

Next, the attenuation means of the rigidté described above provide such attenuation both in the sagittal plane and in the transverse plane.

Finally the invention to provide a system osteosynthesis having high modularity: thus, for example, different versions of the ring 422 can be proposed to the practitioner to manage the contact zone anterior (vertebra side), while a means amortization described above can be offered with different degrees of stiffness to manage damping posterior (cap side). In practice, one can and cover the range between the flexible connections and the rigid connections.

In this regard, it will be observed that the means of the above-described rigidity reduction can be used both at the screw at the eyelet 4 level of the plate screw 5.