WO2008033976A1

WO2008033976A1 - Element of a vertebral column stabilization device

Info

Publication number: WO2008033976A1
Application number: PCT/US2007/078356
Authority: WO
Inventors: Philippe Maxy; Philippe Lemaitre
Original assignee: Warsaw Orthopedic, Inc
Priority date: 2006-09-14
Filing date: 2007-09-13
Publication date: 2008-03-20
Also published as: KR20090068225A; EP2061389A1; FR2905847A1; JP2010518886A; CN101516283A; AU2007296418A1; FR2905847B1

Abstract

Element of a device for stabilizing the spine, designed to be implanted on a set of at least two vertebrae (V1, V2) in order to permit relative movements of limited amplitude of said vertebrae (V1, V2) in all spatial directions, comprising a rigid elastic plate (1) which, at each of its ends, has means for fixing it to one of said vertebrae (V1, V2), and, in its central part (4), has at least two transverse compartments (5, 6, 7) with an anterior wall and a posterior wall and at least one longitudinal orifice (8), each compartment (5, 6, 7) having, on one of its walls, an incision (9, 10, 11) that extends from one end of said wall to the other end and intersects a longitudinal orifice (8). Device for stabilizing the spine, characterized in that it comprises a pair of these elements and the means for fixing them to at least two vertebrae (V1, V2).

Description

ELEMENT OF A VERTEBRAL COLUMN STABILIZATION DEVICE

The invention concerns the field of surgical implants that are designed to limit the closing together of two vertebrae during the movements of the spine.

When intervertebral discs have become worn or have undergone considerable degeneration, they may become powerless to prevent excessive closing together of two successive vertebrae during flexion (forward movement) or extension (rearward movement) of the spine. Such closing together can result in crushing of the spinal nerves, which causes the patient great pain. In the most serious cases, this closing together can even result in contact between the vertebrae during extreme movements.

A first known method for addressing this problem consists in joining the affected vertebrae to one another so as to maintain between them a space that is sufficient on a permanent basis. This joining together can be effected by various devices in the form of plates or intravertebral disc implants. However, it entails a significant loss of mobility of the patient, because it prohibits any flexion or extension of the spine in the affected zone.

It is also known to ligate the spinous processes of the affected vertebrae by means of artificial ligaments. This preserves a freedom of movement in extension of the vertebrae, while limiting the amplitude of the permitted flexion movements, to the point of prohibiting contact between the front of the vertebrae. However, this does not prevent contact at the rear of the vertebrae, and it is this zone where compression of the spinal nerves is more likely to occur.

It is also known to insert wedges between the spinous processes, as in document EP-A-O 392 124. These wedges are made of a rigid material such as PTFE and prevent any contact between the separated spinous processes during extension of the spine. They are preferably maintained in place by artificial ligaments that pass through them and that are wound round the spinous processes. By virtue of these ligaments, it is also possible to limit the amplitude of the flexion movements of the spine in the affected zone.

However, placing a rigid element between the spinous processes leads to virtual suppression of the movements of extension of the spine in this area, or at least to a sudden interruption of such movements when the spinous processes come into contact with the wedge. It would be desirable to be able to use a device that more faithfully reproduces the normal behaviour of a vertebra — disc-vertebra assembly (functional unit) in which the action of blocking the movements of the spine is normally exerted only progressively, and in all spatial directions.

The object of the invention is to make available a device that responds to this need.

To this end, the subject matter of the invention is a device for stabilizing the spine, designed to be implanted on a set of at least two vertebrae in order to permit relative movements of limited amplitude of said vertebrae in all spatial directions, characterized in that it comprises a rigid elastic plate which, at each of its ends, has means for fixing it to one of said vertebrae, and, in its central part, has at least two transverse lateral orifices defining compartments with an anterior wall and a posterior wall and at least one longitudinal orifice, said compartments and longitudinal orifices passing right through the plate, each compartment having, on one of its walls, an incision that extends from one end of said wall to the other end and intersects a longitudinal orifice.

The incisions of two successive compartments are preferably arranged alternately on the anterior wall and on the posterior wall of the corresponding compartment.

At least one of the ends of the plate is a flat zone traversed by an orifice for the passage of a bone-anchoring screw.

At least one of the ends of the plate can be a rod.

The device preferably comprises at least three compartments and three incisions.

The device can be made of polyetheretherketone, carbon fibres, polyethylene, a superelastic shape-memory metal alloy, titanium, or stainless steel.

The invention also relates to a device for stabilizing the spine, characterized in that it comprises a pair of elements of the above type, and the means for fixing them to at least two vertebrae.

As will have been understood, the invention consists first of a plate designed to be fixed straddling two or more vertebrae and made of a rigid material, but designed to have a limited deformability in all spatial directions. This plate is used in pairs, with two possible types of implantation: an implantation in which the ends of each plate are each connected to a pedicle; an implantation in which the ends of each plate are each connected to a face of a spinous process; the two plates than face each other, separated by the spinous process. This construction gives the plate a non-linear deformation behaviour. In a first stage, the deformation takes place with relatively moderate resistance on the part of the plate. Then, when the edges of at least one incision come into abutment, the plate offers greater resistance to its deformation. The plate thus has several successive levels of rigidity.

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

Figure 1 shows an example of a plate for stabilizing the spine according to the invention;

Figure 2 shows a first mode of implantation of the plates according to the invention;

Figure 3 shows a second mode of implantation of the plates according to the invention;

Figure 4 shows a variant of the plate according to the invention and an example of the way in which it is fixed.

The plate 1 for stabilizing the spine according to the invention is designed to be implanted straddling two consecutive vertebrae Vl, V2 that are separated by a disc D whose degeneration, through trauma or disease, does not allow it to perform its function of absorbing the relative movements of the vertebrae Vl and V2. This plate 1 is made of a rigid material, but one that still has limited possibilities of elastic deformation. To this end, it is possible in particular to use PEEK (polyetheretherketone), carbon fibres, polyethylene, a superelastic shape-memory metal alloy, titanium, or stainless steel. It is advantageous, but not essential, for this material to be radiotransparent. The plate 1 has, for example, a total length of 40 to 50 mm and a width of 10 to 15 mm.

At each of its ends, the plate 1 has a design allowing it to be fixed to one of the vertebrae Vl, V2. As is shown, this can be achieved by shaping each of these ends with a flat zone 2, 2' of relatively low thickness (for example 3 to 5 mm), traversed by an orifice 3, 3' for passage of a bone-anchoring screw that penetrates into the vertebra Vl, V2. Another way of shaping the ends of the plate 1 is to give them the form of rods 19, 19', for example cylindrical rods, that are each designed to fit in a corresponding recess formed either in the head of a bone-anchoring screw or in an orifice of a connector 20 which is itself fixed on the head of a bone-anchoring screw 17 (see Figure 4). It is conceivable for the two ends of the plate 1 to be configured differently, for example with one of them flat and the other shaped like a rod. The ends can also be configured to allow the use of other anchoring means, such as hooks.

The plate 1 has a central part 4 of relatively large thickness (of the order of 10 mm for example) so as to permit the formation of a plurality of transverse lateral orifices (preferably at least three, as shown) that extend right through the plate 1 and define compartments 5, 6, 7. The central part 4 also has at least one longitudinal orifice 8 that also extends right through the plate 1. The walls of the compartments 5, 6, 7 can have a thickness of the order of 1 to 2 mm, for example, and this thickness may be non-uniform in order to provide the plate 1 with a particular deformability in the thinner zones. These compartments 5, 6, 7 each have an anterior face (intended to face the spine when the plate 1 is in place) and a posterior face lying opposite the anterior one.

Each compartment 5, 6, 7 has, on one of its anterior and posterior walls, an incision 9, 10, 11 that extends from one end of said wall to the other end. These incisions have a width of the order of 1 mm, for example. The incisions 9, 10, 11 of two successive compartments 5, 6, 7 are preferably arranged alternately on the anterior wall and the posterior wall of the corresponding compartment 5, 6, 7. The incisions 9, 10, 11 must all intersect the longitudinal orifice 8 (or one of such longitudinal orifices if there are several of them).

During the movements of the spine, the existence and relative arrangement of the incisions 9, 10, 11 and of the longitudinal orifice 8 means that the plate 1 is able to deform in all spatial directions. However, the amplitude of these deformations in each direction is limited by the dimensional characteristics and mechanical properties of the plate 1.

Figure 2 shows a first mode of implantation of a device for stabilizing the spine according to the invention, comprising a pair of plates 1, 1 ' according to the invention. The upper flat zone 2 of the plate 1 is fixed by means of a pedicle screw 17 and a nut 18 to a left-hand pedicle Pl of the vertebra Vl, and the lower flat zone 2' of the plate 1 is fixed by means of a pedicle screw 17' and a nut 18' to a left-hand pedicle P2 of the vertebra V2. The other plate 1 ' is fixed, symmetrically with respect to the plate 1 , on the right-hand pedicles P' l, P'2 of the vertebrae Vl, V2. The manner of deformation of the plate 1 will now be described.

When the spine works in flexion (that is to say when the person leans forward) according to the arrow 12 in Figure 1, the anterior incision or incisions 10 facing the spine tend to narrow and the opposite posterior incisions 9, 11 tend to widen. The plate 1 at first offers only slight resistance to the movement of the spine until the edges of the anterior incision 10 come into contact with one another, thus acting as abutments. At this moment, continuation of the flexion movement of the spine is possible but is dependent on the capacity of elastic deformation of the plate 1. This deformation is thus limited in terms of its amplitude and kinetics on account of the resistance offered by the material of the plate 1.

When the spine works in extension (that is to say when the person leans back) according to the arrow 13 in Figure 1, the deformations are the reverse of the preceding ones. It is the edges of the posterior incisions 9, 11 that act as abutments and limit the amplitude and kinetics of the subsequent extension of the spine.

When the person leans to the right (or left) according to the arrow 14, the incisions 9, 10, 11 tend to widen on the left (or right) and narrow on the right (or left) until the right- hand edges (or left-hand edges) of the incisions come into contact with one another. Thereafter, as for the movements described above, the continuation of the movement is governed by the capacity for deformation of the material of the plate 1.

When the person makes a rotation movement of the spine according to the arrow 15, the amplitude and kinetics of the movement are limited essentially by the capacity for elastic deformation of the material of the plate 1 according to the invention. It is mainly to permit these movements of rotation that the longitudinal orifice or orifices 8 are provided, which increase the possibility of torsional deformation of the plate 1.

Finally, the plate can also work in pure traction or in pure compression, according to the arrow 16.

In practice, the movements of the spine are a combination of the types of movements that have just been described, and the device according to the invention deforms in all the spatial directions as permitted by its mechanical and dimensional characteristics. From this point of view, it is sufficient to form two compartments, but it is often preferable for the plate 1 to comprise at least three compartments 5, 6, 7 and three incisions 9, 10, 11 associated with them. Multiplying the number of compartments and incisions enhances the ability to limit the amplitude of the movements by abutment effects and not exaggerate the resistance to the deformation of the material of the plate 1.

Figure 3 shows a second mode of implantation of a device for stabilizing the spine according to the invention. This time, the upper flat zone 2 of the plate 1 is fixed by means of a screw 17 and a nut 18 to the left face of the spinous process El of the vertebra Vl, and the lower flat zone 2' of the plate 1 is fixed by means of a screw 17' and a nut 18' to the left face of the spinous process E2 of the vertebra V2. The other plate 1 ' of the device (not visible in Figure 3) is fixed symmetrically to the right-hand faces of the spinous processes El, E2. In this configuration, the various possible movements of the spine cause deformations of the plates 1, 1 ' different than those of the preceding variant, but these can be readily deduced, particularly in light of Figure 1 and the comments regarding Figure 2 above.

The choice between the two modes of implantation that have just been described will be made in particular depending on the types of movements that are to be permitted or prohibited, and on the state of the vertebrae on which the device is to be implanted.

Figure 4 shows a plate 1 according to the invention in which, as has been envisaged above, the holed flat zones 2, 2' of the plate 1 are replaced by cylindrical rods 19, 19'. These are each clamped inside a connector 20 provided with a slit 21 and engaged on a pedicle screw 17 and tightened by a nut 18 (only one screw and connector unit has been shown in Figure 4, and the other plate 1 ' of the device, arranged symmetrically with respect to the plate 1 on the spine, is also not shown). Of course, other types of connectors could be used. It will be noted that in the example shown the plate 1 has been given an orientation similar to that of Figure 3 and not to that of Figure 2, that is to say with the anterior face directed towards the spinous processes El, E2. This variant thus gives the surgeon additional possibilities of permitting or prohibiting precise movements of the spine, for a given type of implantation.

The device according to the invention is particularly simple to produce. Its implantation is easier than that of the ligaments and wedges of the prior art. Its size is smaller. The dimensions that have been indicated above can be modified depending on the site of implantation of the plate. If the plate 1 is intended to be implanted in the region of the cervical vertebrae, it must be smaller than if it were intended to be implanted in the dorsal or lumbar region, because of the sizes of the vertebrae concerned. The above description and the figures concern a case where the plates 1, 1 ' are implanted on a set of two consecutive vertebrae Vl, V2, but it is possible to make the plates 1, 1 ' longer so that they extend over a greater number of vertebrae. They can be fixed to each vertebra or only to the two endmost vertebrae of the vertebral unit concerned.

An important advantage of the invention is that, by acting on the characteristics of the material from which the plate 1 is made and on the dimensions of the compartments 5, 6, 7, the orifices 8 and the incisions 9, 10, 11, and on the thickness of the walls delimiting the compartments 5, 6, 7, it is easy to set very precise and predictable deformation capacities of the plate 1 in all spatial directions. It is possible to verify that the desired properties will indeed be obtained, simply by deforming the plate 1 before its implantation and checking that the maximum amplitudes of these deformations in the different directions do not exceed those that the patient is able to tolerate. With the devices of the prior art that use ligaments, it is much more difficult to ensure such precision in terms of the permitted amplitudes, and this precision is largely dependent on the skill of the surgeon implanting the device. The invention therefore affords a reliability hitherto unknown in this type of device.

Claims

1. Element of a device for stabilizing the spine, designed to be implanted on a set of at least two vertebrae (Vl, V2) in order to permit relative movements of limited amplitude of said vertebrae (Vl, V2) in all spatial directions, characterized in that it comprises a plate (1) of rigid elastic material which, at each of its ends, has means for fixing it to one of said vertebrae (Vl, V2), and, in its central part (4), has at least two transverse lateral orifices defining compartments (5, 6, 7) with an anterior wall and a posterior wall and at least one longitudinal orifice (8), said compartments (5, 6, 7) and longitudinal orifices (8) passing right through the plate, each compartment (5, 6, 7) having, on one of its walls, an incision (9, 10, 11) that extends from one end of said wall to the other end and intersects a longitudinal orifice (8).

2. Element according to Claim 1, characterized in that the incisions (9, 10, 11) of two successive compartments are arranged alternately on the anterior wall and on the posterior wall of the corresponding compartment.

3. Element according to Claim 1 or 2, characterized in that at least one of the ends of the plate (1) is a flat zone (2, 2') traversed by an orifice (3, 3') for the passage of a bone- anchoring screw.

4. Element according to one of Claims 1 to 3, characterized in that at least one of the ends of the plate (1) is a rod (19, 19').

5. Element according to one of Claims 1 to 4, characterized in that it comprises at least three compartments (5, 6, 7) and three incisions (9, 10, 11).

6. Element according to one of Claims 1 to 5, characterized in that it is made of polyetheretherketone.

7. Element according to one of Claims 1 to 5, characterized in that it is made of carbon fibres.

8. Element according to one of Claims 1 to 5, characterized in that it is made of polyethylene.

9. Element according to one of Claims 1 to 5, characterized in that it is made of a superelastic shape-memory metal alloy.

10. Element according to one of Claims 1 to 5, characterized in that it is made of titanium.

11. Element according to one of Claims 1 to 5, characterized in that it is made of stainless steel.

12. Device for stabilizing the spine, characterized in that it comprises a pair of elements according to one of Claims 1 to 11 , and the means for fixing them to at least two vertebrae (Vl, V2).