Damping element and device for stabilisation of adjacent vertebral bodies

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DESCRIPTION

Damping element and device for stabilization of adjacent vertebral bodies.

The invention relates to a shock absorbing element, according to the concept of claim 1, as well as to a device for stabilizing adjacent vertebral bodies, according to the concept of claim

25.

From document FR-A-2 799 949 a spinal column fixation device is known, which is composed of a set of tulip-shaped pedicle screws, which, unlike the common fixed spar, are joined together by different elements of coil springs The length of the coil springs is adjustable, but doing so only achieves a change in the spring force between two adjacent pedicle screws and in turn between two adjacent vertebral bodies. It is not described in this document whether the spring elements are implanted between the pedicle screws in a prestressed state.

From EP-A-0 516 567 another spinal column fixation device is known, which is composed of a set of tulip-shaped pedicle screws, which, unlike the common fixed spar, are joined together by different damping elements. A disadvantage of this device is that only pressure forces can be assimilated between the pedicle screws. Due to the fact that the damping elements have a fixed length, it is envisaged to have a greater number of these damping elements with different lengths, in order to then be able to fix a damping element with the appropriate length between two implanted pedicle screws. This is circumstantial and conditions a greater storage of shock-absorbing elements of different lengths. The concept of claim 1 is based on this disclosure.

From document EP-B-0 669 109 another spinal fixation device is known composed of a set of pedicle screws with a perforated head, which, unlike the common fixed spar, are joined together by a retractable elastic synthetic band through of the perforations of the pedicle screws. Between the different pedicle screws - flanged in the synthetic band - there are concave cylindrical support elements that can assimilate the possible pressure forces between the pedicle screws. The disadvantages of this device are manifold.

First, the synthetic band and the support elements have to be threaded - as with a pearl necklace in or between the holes of the already implanted pedicle screws, which is time consuming and complicated for the surgeon. Second, the elastic synthetic band shows no pre-tension to some extent. Because the length of the support bodies is also fixed in this device, the fixed fracture sites are subjected to the support body, so that it can be correctly cut during the operation by the surgeon at the effective distance between both screws. pedicle affected. This is time consuming and complicated for the surgeon and should usually lead to a bra that is too short so that its damping effect occurs only with a certain delay, which is obviously undesirable.

From US B 6267764 a damping element is known, the connecting elements of which are rod-shaped or sleeve-shaped, where the sleeve can be connected to a rod-shaped reinforcing element.

In this sense the invention will help. The purpose of the invention is to create a combined prestressed traction-pressure element, which can be fixed between two pedicle screws or pedicle hooks and which, on the one hand, when applying traction, acts as a spring element with a certain modulus of elasticity, and on the other hand When pressure is applied, it acts as a damping element with another modulus of elasticity.

The invention solves the problem posed with a shock absorbing element which has the characteristics of claim 1, as well as with a device for stabilizing the adjacent vertebral bodies which has the characteristics of claim 25.

In the preferred embodiment of the damping element according to the invention, one of the spring elements is positioned as a pressure spring. In the mounted damping element, the connecting elements located at the ends of the spring elements are convenient, which can be fixed at the ends of the spring element positioned as a pressure spring, so that the first spring element can be loaded and prestressed. .

The advantages achieved with the invention are essentially the following:

- by selecting inner cylinders of different lengths, the damping properties can be varied;

- the pre-assembled prestressing force in the state of the aforementioned shock absorbing element is clearly defined and can be made available to the surgeon in a selection that responds to the different body weights of the patients and to the different indications; Y

- after distraction of the vertebral bodies, the shock absorbing elements can be quickly and simply inserted between the pedicle screws and fixed to them.

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In another embodiment of the damping element according to the invention, the two connecting elements are freely connected to the spring elements. The connection between the connection elements and at least one of the spring elements preferably takes place via a threaded connection. In this way, it can be achieved that, according to the application, different connecting elements can be used according to the needs. For this, the damping element according to the invention forms a unified tension / pressure element, the length of which can be variable.

In another embodiment of the damping element according to the invention, at least one of the two connecting elements is made in one piece with at least one of the spring elements. With such a configuration, a compact construction of the damping element according to the invention can be achieved.

The connection elements, according to the application of the damping element according to the invention, can have the shape of a bar or a bushing, where at least one connecting element with a bushing is arranged in a circular cylindrical manner with at least one connecting element, and each joint element is positioned coaxial to the longitudinal axis at the end of the spring elements. The bushing has a central hole coaxial to the longitudinal axis and preferably comprises fixing means for fixing a bar inserted in the central hole. With this conformation of the damping element, it is possible to connect, coaxially to the longitudinal axis, a bar-shaped reinforcing element or a circular cylindrical connecting element of another damping element with the sleeve-shaped connecting element of the first damping element .

The fixing means preferably comprise at least one screw, which is screwed into the bushing transverse to the longitudinal axis and which serves to fix a bar-shaped element inserted in the central hole of the bushing. By using as a fixing means a threaded pin which does not protrude radially from the socket, a compact construction of the damping element can be achieved, which is advantageous when using the damping element within a device for stabilizing vertebral bodies.

The connecting elements at both ends of the spring elements can be, depending on the use of the damping element, both in the form of a rod, both in the form of a sleeve or one in the form of a sleeve and the other in the form of a rod.

In an application of one or more shock absorbing elements according to the invention within a device for the stabilization of adjacent vertebral bodies, one of the connecting elements is preferably fixed to a pedicle screw or a pedicle hook and is joined by means of the second element connecting to a bar-shaped stringer. For this, a configuration of the connecting elements is suitable such that one of the connecting elements is in the form of a sleeve while the second connecting element is in the form of a bar. The spar is inserted into the central hole of the bushing and is fixed to the bushing by the fixing means, while the rod-shaped connecting element can be inserted into the receiving means, which is usually channel-shaped, to the screws. pedicle or pedicle hooks and is also fixed there. Preferably, the rod-shaped connecting element has an axial length, which is greater than the length of the receiving means, so that the damping element can be axially displaced and adjusted as needed.

To facilitate a combined use of reinforcing elements in the form of bars, for example stringers, and shock absorbing elements according to the invention within a device for stabilizing adjacent vertebral bodies, the diameter D of the central hole of the connecting element in the form of bushing and the diameter d of the bar-shaped connecting element are selected such that D = d.

In an embodiment of the damping element according to the invention, the spring elements are designed such that they exhibit a constant modulus of elasticity. In this way, it can be achieved that the state of the spring elements is regenerated effortlessly when discharging the damping element.

In another embodiment of the damping element according to the invention, it shows a reniform profile orthogonal to the longitudinal axis. The advantages of an embodiment of this type are that with the implantation of one or more shock-absorbing elements, for example, within the fixation of a spinal column, these can be inserted in a more suitable way taking into account extensions of the vertebrae or other implanted parts.

In another embodiment of the damping element according to the invention, the second spring element is placed inside the first spring element. Preferably, the second spring element is in the form of a pressure spring, so that a pretension of at least the first spring element can be achieved in the assembled damping element. Furthermore, the arrangement of both spring elements is preferably concentric.

Again in another embodiment of the damping element according to the present invention, the second spring element placed inside the first spring element and having the shape of a pressure spring has a central hole coaxial with respect to the longitudinal axis, the diameter of which preferably corresponds to the diameter of the central hole of the bushing. This enables a greater axial passage of a rod-shaped element inserted into the central holes, whereby a greater stability of the joints between the damping element and the rod-shaped element can be achieved.

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In another embodiment of the damping element according to the invention, the first spring element is in the form of a spiral spring. The thread-shaped groove of the coil spring is preferably closed with a complementary, elastically deformable, thread-like elevation in the second spring element. The spring coil of the coil spring can also have multiple pitches. Preferably, the second spring element is made of a moldable material, so that the second spring element can be molded into the already manufactured first spring element.

In an embodiment of the damping element according to the invention, the spring element in the form of a pressure spring is made of a polymer, preferably polycarbonurethane (PCU).

In a further embodiment of the damping element according to the invention, the sleeve-shaped connecting element is produced in one piece with the spring element, whereby a simple construction of the damping element can be achieved. Conformations of the damping element are also possible in which both connecting elements are built in one piece with the first spring element.

In all embodiments of the damping element according to the invention, the spring constant F of the first spring element and the spring constant f of the second spring element differ from each other. Both constants F; f can be differentiated by a factor of at least 1.2, preferably at least 5. In this way, the advantage can be achieved that the elastic forces of the damping element when receiving a tensile or pressure load differ from one another. Depending on the field of application of the damping element, the spring constants can also differ by a factor of around 10 N / mm and 100 N / mm.

In other embodiments of the damping element according to the invention, the modulus of elasticity f of the second damping element reaches between 50 N / mm and 5000 N / mm, preferably between 100 N / mm and 2000 N / mm.

Other advantageous embodiments of the invention are characterized in the appended claims.

The device according to the invention for stabilizing adjacent vertebral bodies essentially comprises several pedicle screws or hooks attached with fixators. Between two pedicle screws or pedicle hooks, for example, rod-shaped spars, springs or damping elements according to the invention can be placed as a fixator.

In the device according to the invention, the pedicle screws or pedicle hooks comprise reception means, which allow the reception (preferably axially displaceable) of reinforcing elements, for example bar-shaped beams, respective of the connecting elements in rod-shaped in the damping elements according to the invention. For fixing the reinforcing elements to the receiving means, the pedicle screws or pedicle hooks can comprise locking means, which, for example, can be placed last and can consist of studs or cage nuts. The stability of the device according to the invention can be adjusted to the corresponding conditions by using rigid elements, such as stringers, on the one hand, and shock-absorbing elements on the other.

In one embodiment, the device according to the invention comprises at least one receiving means with a pedicle screw or a pedicle hook, which simultaneously allows the assimilation of two parallel longitudinal fixation elements. In this way, it is possible that a spring-acting element, for example a damping element according to the invention, can be used to effect a fixation between at least one pedicle screw or hook provided with receiving means and another pedicle screw or hook. adjacent.

Pedicle screws or pedicle hooks with receiving means that allow two parallel longitudinal fixation elements to simultaneously be attached to the pedicle screw or pedicle hook, are known, for example, from US-A-4 653 481 HOWLAND. The damping elements according to the invention, analogously to the beams shown in the aforementioned patent, with the help of the rods mounted parallel to the longitudinal axis in the connecting elements, can be fixed on the screw heads. The possible displacement capacity of the damping element parallel to the longitudinal axis in the channels, by means of a configuration of this type, makes it possible to introduce a damping element according to the invention prestressed to a desired spring force before its implantation in the means for receiving the pedicle screws without having to manipulate the damping element again. The compensation of lengths with different distances between adjacent pedicle screws or pedicle hooks takes place through the axial displacement capacity of the connecting elements constituted in the form of a bar and arranged at the ends parallel to the longitudinal axis on the damping elements according to the invention. that are in the channels equally parallel to the longitudinal axis.

The pretensioning of the damping element makes it possible, for example, to consider various instabilities, the indication or the weight of the patient. The shock absorbing element is loaded by pressure as the parts of the spine attached to it extend, while it is loaded by traction as the portions of the spine attached to it flex. The selection of the spring material, for example a polymer, preferably polycarbonate urethane (PCU) for the pressure-loaded spring element and a metal for the tension-loaded spring element, the selection of the geometric dimensions, as well as the graduated pretension of the tensile-loaded spring element,

ES 2 296 901 T3 allow an optimal adaptation of the device according to the invention to the biomechanical particularities of a patient.

The advantages of the device according to the invention are essentially the following:

- harmonic transition of the stiffness of the stabilized segment of the spine to the healthy segments of the spine.

- The damping elements can optionally be combined with segmentally rigid rods.

The invention and modifications thereof are explained in more detail below in part by way of schematic representations of various representative examples.

Shows:

Fig. 1 is a longitudinal section of a damping element not according to the invention;

Fig. 2 is a view of the device not according to the invention for stabilizing adjacent vertebral bodies;

Fig. 3 is an enlarged representation of a damping element not in accordance with the invention;

Fig. 4 is a view of a damping element not according to the invention;

Fig. 5 is a perspective representation of a damping element not according to the invention;

Fig. 6 is an inspection of a damping element not in accordance with the invention;

Fig. 7 is a longitudinal section of an embodiment of the damping element according to the invention;

Fig. 8 is a view of an embodiment of the device according to the invention during its application for the stabilization of adjacent vertebral bodies; Y

Fig. 9 is a perspective view of an embodiment of the device according to the invention.

Fig. 1 shows a damping element 1 with two spring elements 2; 4 positioned concentrically to the longitudinal axis 3. The first spring element 2 is represented as a helical spring with a central cavity 15, while the second spring element 4 is in the form of a bar and is positioned inside the cavity

fifteen. The connecting elements 5; 6 that are at the ends are also positioned coaxially to the longitudinal axis 3 and show in comparison with the spring elements 2; 4, a threaded piece 16; 17 coaxial to longitudinal axis 3 with an external thread 18. The first spring element 2 is provided at its axial ends 21 with internal threads 24 mounted in the cavity 15, which are positioned complementary to the external threads 18, so that the threaded parts of the connecting elements 5; 6 can be screwed onto the spring element

2. Each connecting element 5; 6 further comprises a groove 23 in the inner end 19 of the connecting element 5; 6 and positioned coaxially to the longitudinal axis 3, so that the second spring element 4 in the form of a bar at its axial ends 22 can be assimilated in the grooves 23. The connecting elements 5; 6 at their outer ends 20 are furthermore formed coaxially in the form of a bar. In the mounted damping element 1, the ends 22 of the second spring 4 lie on the front surfaces 25 of the grooves 23 orthogonal to the longitudinal axis 3, so that the connecting elements 5; 6 have a distance L between these front surfaces

25. This distance L, as well as the length of the first undeformed spring element 2, are so limited that when threading the threaded pieces 16; 17 in the internal thread 24, the first spring element 2 is axially expanded by a desired length, through which the damping element 1 receives a pre-tension.

A device for stabilizing adjacent vertebral bodies (not shown) is shown in Figure 2. Several pedicle screws or hooks 12 are fixed to the pedicles of the vertebral bodies to be joined in such a way that their central axes 28 are positioned transversely with respect to the axis of the vertebral column. The receiving means 13 on the pedicle screws or hooks 12 are positioned perpendicular to the central axes 28 and formed as channels 26. In these channels 26 the outer bar-shaped ends 20 of the connecting elements 5 can be inserted; 6 (Figure 1), so that the damping elements 1 can be displaced axially to the channels 26, before being fixed by screws 27 relatively with pedicle screws or hooks 12. The reception means 13 in the pedicle screws or hooks 12 each comprise two parallel channels

26, so that in addition to a damping element 1, also, for example, a bar-shaped damping element 7 can be attached to a hook or pedicle screw 12.

Fig. 3 shows a damping element 1 according to a first spring element 2 designed as a helical spring, a second spring element 4 designed in the form of a rod and two connecting elements 5; 6 positioned coaxially with respect to the longitudinal axis 3.

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Figures 4 and 5 show a damping element 1 with a first spring element 2 designed as a helical spring and two connecting elements 5; 6 linked with the first spring element 2 coaxially with respect to the longitudinal axis 3.

In Fig. 6 an embodiment of the damping element 1 according to the invention is shown, which has a circular profile orthogonal to the longitudinal axis 3. Other shapes of transverse profiles, for example, oval or elliptical profiles are also possible and favor the implantation of the shock absorbing element 1.

In Fig. 7 an embodiment of the damping element according to the invention 1 is shown, which comprises as a first spring element 2 a circular cylindrical spiral spring positioned coaxial to the longitudinal axis 3. This first spring element 2 has a notch 34 which forms helical lines and is provided with a cavity 15 open only at one end 21 of the first spring element 2 and coaxial to the longitudinal axis 3. At each of the two axial ends 21 a connecting element 5 is placed; 6, where both elements 5; 6 in this embodiment form a single piece with the first spring element 2. The first connecting element 5 is shaped like a bushing 30 with a central hole 32 coaxial to the longitudinal axis 3, while the second connecting element 6 is shaped like a rod equally coaxial to the longitudinal axis 3. The connecting segment 6 in the form of a bar is placed at the end 21 of the first spring element 2, where the cavity 15 is axially closed. The central hole 32 in the first connecting element 5 has a diameter D. The joint 6 is also of a circular cylindrical shape and has a diameter d, which in the embodiment represented in the present document of the damping element 1 is equal to the diameter D of the central hole 32 in the first joint element 5. Thus, for example, a longitudinal rod belonging to a device for stabilizing vertebral bodies or the second rod-shaped connecting element 6 of a second damping element 1 can be inserted into the central hole 32. By means of fixing means 31, which in the embodiment shown in this document of the damping element 1 have the shape of a stud transverse to the longitudinal axis 3 that can be screwed into the bushing 30, such a bar inserted in the central hole can be fixed. 32. The second spring element 4 is positioned coaxial to the longitudinal axis 3 in the cavity 15 of the first spring element 2 and has an elastically deformable and spiral shaped elevation 35 complementary to the spiral groove 34 in the first spring element 2. Said elevation 35 closes the slit 34 in the first spring element 2. Furthermore, the second spring element is provided with a central hole 33 coaxial to the longitudinal axis 3, which has the same diameter as the central hole 32 in the bushing 30.

Fig. 8 shows an embodiment of device 38 according to the invention in an application for stabilization of adjacent vertebral bodies 37. In four vertebral bodies 37 adjoining each other, a pedicle screw 12 is screwed into each one. The device 38 comprises, in each case, an element 14 that acts as a spring placed coaxial to the longitudinal axis 3 between one of the four outer adjacent vertebral bodies 37 and the inner adjacent vertebral body 37, as well as a bar-shaped spar 8 between the two internal adjoining vertebral bodies 37. The elements 14 that act as a spring consist of damping elements 1, which comprise 21 at one of their ends (Fig. 7) a connecting element 6 in the form of a bar and at the other end 21 a bushing 30 (Fig. 7). The rod-shaped connecting elements 6 serve as fixation elements 7, which are inserted into the receiving means 13 of the two pedicle screws 12 that are located at the end with respect to the device 38 and there are freely joined to the screws. pedicular through the closing means 29 made in the form of screws. The connecting elements 5 of the shock absorbing element 1 made in the form of bushings 30 (Fig. 7) are directed against the two inner vertebral bodies 37 of the four vertebral bodies that must be stabilized. Between the two shock absorbing elements 1 a bar-shaped stringer 8 is used, where the stringer 8 is constructed in such a way that the fixing elements 7 are created in the reception means of the two inner pedicle screws 12 by means of the stringer segments 8. The beam 8 is joined, on the one hand, with the device 38 by means of the closing means 29 constructed as screws of both inner pedicle screws 12 and, on the other hand, it is inserted with its two ends 39; 40 in the central holes 32; 33 in the connecting elements and the second spring elements 4 (Fig. 7) and once there the fixing means 31 (Fig. 7) locks it freely. Depending on the application, other combinations of the beam 8 and the damping elements 1 coaxial to the longitudinal axis 3. are also possible. Instead of one beam 8, several beams 8 can be used or the beams 8 can be replaced by connecting elements 6 into one or more. damping elements 1, which in this case must have a sufficient axial length. The longitudinal axis 3 can also be inclined or bent in different applications of the device 38 according to the invention.

Fig. 9 shows an embodiment which differs only in that it comprises two devices 38 parallel to the longitudinal axes 3 each with two axially positioned damping elements 1 and each one a spar 8 positioned between them. In addition, five pedicle screws 12 are provided each.

Documents mentioned in the description

This list of documents mentioned by the applicant has been compiled exclusively for the information of the reader and does not form an integral part of the European patent document. It was made with great care; but EPA assumes no responsibility for any errors or omissions.

ES 2 296 901 T3

Patent documents mentioned in the description • FR 2799949 A [0002] • EP 0516567 A [0003] • EP 0669109 B [0004] • US 6267764 B [0006] • US 4653481 A [0031]