FR2904526A1 - Monoaxial bone anchoring element i.e. screw, for vertebral column e.g. scoliosis, deformation correction device, has head with receptacale receiving rods, and elastic element formed by portions of lateral arms limiting channel width - Google Patents

Abstract

The element i.e. screw (1), has a head (4) with a receptacle for receiving rods of a vertebral column deformation correction device. The receptacle opens towards a top by a channel (13) with a U-shaped section defined by lateral arms (14, 15). Internal surfaces of the lateral arms are provided with a thread for the insertion and blocking of a threaded stopper. An elastic element formed by the portions of the lateral arms of the head locally limits the width of the channel and stops expulsion of the rods outside the receptacle.

Description

 The invention relates to the field of spinal osteosynthesis devices.

It is known to use, to correct deformities of the spine such as scoliosis, spondylolisthesis, lordosis or kyphosis, devices comprising one or more rods, most generally a metal such as steel, s extending over at least a portion of the length of the spine, and which are secured to one or two rows of anchors (or implants) implanted on the spine. Such devices are described, for example, in US-A-5,005,562. These anchoring elements are often constituted by screws that are implanted in a vertebra, or by hooks which are provided a lamar, pedicle or transverse anchor point on a vertebra.

The head of these anchoring elements is shaped to support at least one channel U, perpendicular to the axis of the element, in which a rod is inserted. The U-shaped channel is delimited by two lateral branches. These are most often, on their surface facing the inside of the channel threads constituting a tapping for insertion and locking of a generally cylindrical plug. This cap has the function, during its tightening, to perform the plating of the rod at the bottom of the channel, and to maintain the rod after installation of the device.

During the installation of the correction device, the rod is inserted into the U-shaped channels of the heads of the anchoring elements previously fixed on the vertebrae, and the plugs are then screwed into the channels by means of a suitable screwdriver. In the case where it is necessary to correct a severe deformation of the spine, relatively large mechanical stresses, for example in bending and / or rotation, must be imposed on the rod when it is introduced into the channels of the heads of the elements. anchorage. In the zones where the deformation is maximal, the stem is removed from the implant, and it is necessary to use a heavy and bulky specific instrument to bring it between the branches of the channel U. This maneuver increases the operating time and sometimes requires an extension of the incisions made on the patient. The relatively high rigidity of the rod makes it difficult its deformation to insert it into the heads of the anchoring elements. In addition, the forces generated during the introduction of the rod are directly transferred to the bone anchoring elements, compromising their long-term behavior. It has been proposed in GB-A-2 294 394, WO-A-02/41

797 and WO-A-02/085 217 to replace the single rod of large diameter of these devices by a plurality of rods of small diameter that the surgeon inserts one after the other in channels defined by the heads of the anchoring elements . A threaded plug keeps the rods in their housing. These rods are inserted either longitudinally (GB-A-2 294 394 and WO-A-02/085 217), or laterally (WO-A-02/41 797) in the heads of the anchoring elements. Because of the small diameter of each rod, it is easier for the surgeon to conform them so as to be able to insert them into the heads of the anchoring elements, and experience shows that the added effects of these multiple rods of small diameter, pressed against each other inside the heads by the plugs, are comparable to those of the usual large diameter rods.

The Applicant has also proposed in WO-A2005 / 058173 to conform the heads of the anchoring elements so as to order the stacking of the stems in one or more columns, in order to give the surgeon the possibility of better modulating the properties of the correction device according to the specific needs of the patient.

A difficulty encountered by the surgeon during the installation of the device is that when the heads of the anchoring elements are shaped to allow longitudinal insertion of the rods, there is a risk that rods already inserted out of their housing before the plug Thread is not in place, especially when they undergo significant torsion. From this point of view, the lateral insertion of the rods proposed by WO-A-02/417797 with the preloaded cap on the head provides an improvement, but complicates the step of insertion of the rods due to the reduction of the width the insertion slot, and its lateral location on the head. In particular, it is necessary that at the location of insertion, the rod has a substantially straight configuration and, especially, parallel to the slot. The insertion is very difficult in areas where the stem has a significant curvature.

The object of the invention is to propose a configuration of the heads of the anchoring elements allowing easy insertion of the rods of small diameters and an effective limitation of the possibilities of exit of the rods of their housing after their insertion.

For this purpose, the subject of the invention is a bone anchoring element, such as a screw, for a device for correcting deformations of the spine of a patient, intended to be implanted on a vertebra, whose head comprises a receptacle. for one or more rods of said correction device, on which opens a channel opening on the upper edge of the head defined by two lateral branches whose inner faces are provided with a thread for the insertion and locking of a threaded cap, characterized in that it comprises at least one elastic element locally limiting the width of the channel and preventing or hindering the expulsion from the receptacle of the rods inserted in the head and not yet blocked by the plug.

It may comprise at least one housing formed in the head facing the channel and the receptacle and a resilient U-shaped part insertable in said housing, comprising two vertical branches connected by a substantially semicircular lower portion whose shape and internal dimensions correspond substantially to those of the receptacle, said vertical branches each having a protuberance locally reducing the width of the space between the branches.

The upper lateral edges of said housing may be curved towards the interior of the housing so as to reduce its width at its entrance, and the upper parts of the branches of the U-shaped part include notches.

Said elastic element may consist of portions of the branches of the head.

The invention also relates to a spinal deformity correction device comprising bone anchoring elements such as screws implanted on vertebrae of the patient and a rod inserted into the heads. said screws, characterized in that at least one of said elements is of the preceding type.

Said rod may be composed of a plurality of rods of small diameter. As will be understood, the invention consists in integrating at the head of a longitudinally inserted bone anchoring element rods at least one elastic element locally limiting the width of the insertion slot.

This elastic element may be constituted in particular by a separate element in the general shape of U narrowing at its open end, insertable into the head of the anchoring element at one of its longitudinal openings for insertion of the rods.

It can also be constituted by the head of the anchoring element itself, whose configuration of at least one longitudinal insertion opening of the rods has said U-shape narrowed at its open end, and whose mechanical properties allow a elastic spacing of the edges of the opening when inserting a rod whose diameter slightly exceeds the nominal width of the opening.

The bone anchoring element according to the invention may be a monoaxial screw, as in the example which will be described and shown. But it can also be a polyaxial screw, or a hook, or any connector. It can be implantable in anterior approach or posterior approach.

The invention will be better understood on reading the description which follows, given with reference to the following appended figures:

- Figure 1 which shows a front view of an example of bone anchoring screw according to the invention, equipped with its resilient U-shaped piece for holding the rods after insertion;

- Figure 2 which shows a view from above said screw without its U-shaped part;

- Figure 3 which shows a perspective view said U-shaped part;

- Figures 4, 5 and 6 which show perspective view and in section along IV-IV the screw with the U-shaped part in three insertion positions;

- Figure 7 which shows schematically the operation of insertion of the rods in the screw; - Figure 8 which shows the state of the screw and the U-shaped part after insertion of the rods;

- Figure 9 shows a perspective view of the screw and the rods after tightening the plug holding the rods. FIG. 1 represents a monoaxial bone anchoring screw 1 of a device for correcting the deformations of the spine according to an exemplary implementation of the invention. This screw 1 comprises, as usually, a lower portion 2 externally threaded for fixing the screw 1 in a vertebra whose contour 3 is shown in broken lines. The screw 1 also comprises a head 4 in which are inserted independent rods 5, 6, 7, 8, 9, 10 of relatively small diameter, of the order, for example, from 1.3 to 3mm. These rods 5-10, which are typically (but not necessarily) metallic, constitute the longitudinal element of the correction device extending along the part of the spine whose curvature must be corrected, and pass to this effect in the heads. other screws similar to the screw 1 implanted in the vertebrae of the area of the spine to be treated. The rods 5-10 are received in a receptacle 11 formed in the head 4, and whose bottom 12 has a substantially cylindrical surface. The receptacle 11 opens upwards by a U-shaped channel 13 defined by lateral branches 14, 15 of the head 4 whose internal faces are provided with a thread 16 for the insertion and locking of a All of these features are customary for bone anchoring screws for receiving a single large diameter rod or multiple small diameter rods 5-10 of a spinal deformity correction facility. According to a form of the invention, the head 4 comprises facing the receptacle

11 and the channel 13 a housing 17 in which can be inserted a U-shaped elastic part 18. It consists of two vertical branches 19, 20 connected by a substantially semicircular lower portion 21.

FIG. 4 shows in more detail the head 4 in section along IV-IV, with the U-shaped elastic part 18 completely inserted into the housing 17. It can be seen that the lower part 21 of the elastic part 18 has an internal shape and dimensions which correspond substantially to those of the receptacle 11, so to leave free the entrance of the receptacle 11. It is also seen that the upper side edges 22, 23 of the housing 17 are slightly curved towards the interior of the housing 17 so as to reduce the width at its entrance. This feature cooperates with notches 24, 25 formed on the upper part of the outer face of the branches 19, 20 of the U-shaped part 18, as will be explained later.

The U-shaped part 18 bears on the upper parts of the internal faces 26, 27 of its branches 19, 20 beveled protuberances 28, 29 which reduce to their level the width of the space between the branches 19, 20 to a first li value. This feature allows, in accordance with the invention, to facilitate the installation of rods 5-10 of the device for correcting deformations of the spine, as will be described.

FIG. 5 shows the head 4 in section along IV-IV with the U-shaped elastic part 18 incompletely inserted in the housing 17, but in such a way that the upper lateral edges 22, 23 of the housing 17 are facing the external indentations 24 19, 20 of the U-shaped part 18. In this configuration, the space between the branches 19, 20 has the same minimum width li, at the protuberances 28, 29, as when the U-shaped part 18 is completely inserted in the housing 17. FIG. 6 shows the head 4 in section along IV-IV with the U-shaped elastic part 18 incompletely inserted in the housing 17, so that the upper lateral edges 22, 23 of the housing 17 are located below the indentations 24, 25 of the branches 19, 20 of the U-shaped part 18. They thus exert a pressure against the branches 19, 20, which tends to decrease to a second value I ₂ smaller than the minimum width of the space separating the branches 19, 20, at the protuberances 28, 29.

The establishment of the device for correcting deformations of the spine according to the invention is carried out as follows.

The surgeon implants on the vertebrae 3 of the patient the various screws 1 serving to fix the device then he inserts one by one the rods 5-10 of diameter d in the heads 4 of the screws 1. For this purpose, as shown in FIG. 7, it can place the U-shaped pieces 18 in the position of FIG. 5, so as to give the spaces separating the branches 19, 20 of the U-shaped pieces 18 the first minimum width h mentioned above. , h must be greater than the diameter d of rods 5-10, to allow the insertion of rods 5-10, but by little, in order to make the exit of the rods 5-10 difficult after their insertion, in case the deformations 5-10 rods would tend to cause this output. The bevels of the protuberances 28, 29 facilitate the entry of the rods 5-10 into the interior space of the U-shaped part 18.

The output of the rods 5-10 can be totally prevented if, after having all inserted (or only some of them), as represented in FIG. 8, the U-shaped pieces 18 are placed in the position of FIG. 6, so as to give the spaces separating their branches 19, 20 the aforementioned second minimum width, being less than the diameter d of rods 5-10. In fact, in many cases, the rods 5-10 will tend to emerge from the receptacle 11 under the effect of their own energy due to their elastic deformation. In doing so, they tend to drive themselves the U-shaped part 18 upwards, thus bringing its branches 19, 20. There is thus an effect of autocapture of the rods 5-10 by the U-shaped part 18.

Once all the rods 5-10 are placed in the head 4, where they are held by the U-shaped piece 18, the surgeon can place a threaded plug 30 between the limbs 14, 15 of the head 4 and tighten it securely. to press the rods 5-10 against the bottom 12 of the receptacle 11. The pressure exerted on the rods 510 by the plug 30 during tightening also causes the U-shaped part 18 to come down inside the housing 17, so that end tightening it no longer emerges above the upper edge of the head 4. It is then found in the situation of Figure 9. In the example shown, the plug 30 comprises, as is known, a top breakable portion 31 which will separate from the lower part at the end of the tightening, when the applied force exceeds a predetermined value. The plug 30 thus tightened will no longer protrude above the head 4. It is generally preferable to proceed with the establishment and tightening of the plugs 30 of the screws 1 of the device after the rods 5-10 have have been inserted into the heads 4 in all the screws 1 of the device. In this way, the establishment of the rods 5-10 is easier to achieve, the rods 5-10 advantageously preserving for this purpose the possibilities of movement and bending which would become more limited after the tightening of the cap 30. The presence of U-shaped parts 18 prevents precisely during this establishment, rods 5-10 already inserted into a head 4 come out when the surgeon manipulates them to insert them in another head 4.

Alternatively, it could be provided in the head 4 two housings 17, namely one face each inlet of the receptacle 11, so as to insert two U-shaped elastic parts 18 in the head 4 and thus further ensure the maintenance of the rods 5 -10 when installing the correction device.

The invention has been described in its preferred application framework, which is the installation of correction devices whose stem consists of multiple rods 5-10 of small diameter. But it goes without saying that it can also be used for devices having a single rod of larger diameter, if using a U-shaped piece 18 of suitable dimensions for this purpose.

As the heads 4 of the screws 1 according to the invention are substantially identical in shape and dimensions to those of the usual screws (apart from a possible slight excess thickness of the head 4 in the region of the housing 17), they can be used on any device correction instead of the usual screws. If the surgeon does not want to use the possibility of maintaining the rods 5-10 in the heads 4 of the screws 1, it is sufficient for him not to insert U-shaped parts 18 in the housings 17. The manufacturing range of the elements Bone anchoring can therefore be simple, the housing elements 17 according to the invention can easily replace the conventional elements that are lacking.

An advantage of this situation is that the screws 1 according to the invention can be reused if a modification of the correction device of which they form part is useful at a later stage of the treatment of the patient. For example, if the surgeon wants to change the initial single rod for a 5-10 multi-strand rod better adapted to correct spinal deformity in a specific area that may be required after a first rough correction provided by the initial stem, then it suffices to carry out the substitution of the stems and the addition of U-shaped pieces 18 to the heads 4 of the screws 1. The reverse passage of a multi-strand rod 5-10 to a single rod would also be possible by removing the U-shaped pieces 18.

With respect to the configuration of the screws of the document WO-A-02/41797 which have an inlet channel for the rods in the receptacle formed on the lateral part of the heads, the invention has the advantage in particular of not requiring that the rod 5-10 which is inserted has a relatively straight portion over a length corresponding to approximately the diameter of the head 4. The insertion of the rods 5-10 is simpler and requires fewer instruments. In addition, the screw 1 according to the invention is of more universal use since its inlet channel 13 accepts rods of very different diameters. In the screws of WO-A-02/41797, the width of the slot limits the diameter of the rods that can be inserted while benefiting from the holding function inside the head prior to locking. In the screws 1 of the invention, the same screw 1 can receive and hold rods 5-10 of various diameters; it suffices to change the U-shaped part 18 by choosing a width of the space separating its branches 19, 20 adapted to the diameter of the rods 5-10 used.

A variant of the invention would be to remove the housing 17 and the U-shaped elastic part 18, and to give the branches 14, 15 of the head 4, in their portions defining one of the inputs (or both inputs) of the channel 13 a configuration and elasticity comparable to those of the U-shaped piece 18 as described. In doing so, it deprives the advantages associated with the interchangeability of the U-shaped part 18, but it nevertheless provides its essential functions of maintaining the rods 5-10 by reducing the number of parts of the device.

By way of non-limiting example, it is possible to design a screw 1 and a U-shaped part that would have the following main characteristics. For a head 4 of 13.4 mm width, it is possible to provide a U-shaped piece with a maximum width of 8 mm and a thickness of 0.9 mm. h can vary between 1, 5 and 6.35 mm depending on the diameter of the rods 5-10 used. The bottom 12 of the receptacle 11 has a radius of 3.4 mm which is also that of the inner edge of the semicircular portion 21 of the U-shaped part 18. This can be made of any biocompatible elastic material: titanium, steel austenitic stainless steel, Cr-Co shape memory alloy, polymer such as PEEK ...

It is also possible to apply the invention to the case of WO-A2005 / 058173 wherein the head of the bone anchoring element comprises several compartments ordering the rods in separate columns, at the cost of adaptations obvious to those skilled in the art.

It is not necessarily essential for all the bone anchoring elements of a spinal deformity correction installation according to the invention to be of the type according to the invention. It may sometimes be sufficient to provide such elements only in one or certain areas where the rod or rods of the installation are the most strongly deformed.

Claims (6)

u Bone anchoring element, such as a screw (1), for a device for correcting deformations of the spine of a patient, intended to be implanted on a vertebra (3), whose head (4) comprises a receptacle (11) for one or more rods (5-10) of said correction device, on which opens a channel (13) opening on the upper edge of the head (4) defined by two lateral branches (14, 15) of which the inner faces are provided with a thread (16) for the insertion and locking of a threaded plug (30), characterized in that it comprises at least one elastic element locally limiting the width of the channel (13) and preventing or hindering the expulsion from the receptacle (11) rods (5-10) inserted into the head (4) and not yet blocked by the plug (30). 2. bone anchoring element according to claim 1, characterized in that it comprises at least one housing (17) formed in the head (4) facing the channel (13) and the receptacle (11) and an elastic part in U (18) insertable in said housing (17), comprising two vertical branches (19, 20) connected by a substantially semicircular lower portion (2) whose shape and internal dimensions substantially correspond to those of the receptacle (11), said vertical legs (19, 20) each having a protuberance (28, 29) locally reducing the width of the space between the legs (19, 20). Bone anchoring element according to claim 2, characterized in that the upper lateral edges (22, 23) of said housing (17) are curved towards the inside of the housing (17) so as to reduce its width to its inlet, and in that the upper portions of the legs (19, 20) of the U-shaped piece (18) have notches (24, 25). 4. bone anchoring element according to claim 1, characterized in that said elastic member is constituted by portions of the branches (14, 15) of the head (4). 5. Device for correcting deformations of the spine comprising bone anchoring elements implanted on vertebrae (3) of the patient and a rod inserted in the heads (4) of said elements, characterized in that at least one of said elements is of the type according to one of claims 1 to 4. 6. Device according to claim 5, characterized in that said rod ée a plurality of rods (5-10) of small diameter.