WO1999011203A1

WO1999011203A1 - Prosthesis of the spinal column

Info

Publication number: WO1999011203A1
Application number: PCT/AT1998/000201
Authority: WO
Inventors: Ronald J. Sabitzer; Franz K. Fuss
Original assignee: Sabitzer Ronald J; Fuss Franz K
Priority date: 1997-08-28
Filing date: 1998-08-26
Publication date: 1999-03-11
Also published as: AT405237B; ATA144897A; EP1009339A1; AU8963698A

Abstract

In a spinal column prosthesis for insertion into the intervertebral space of the spinal column after surgical removal of the intervertebral disk, it is provided that the prosthesis (6), which in the inserted state is designed in a single piece, has a curved surface (9) at its top side, is movable relative to the cranial vertebra (1) and is fixed to the caudal vertebra (3) by anchoring and connecting means (11) arranged on the bottom side (10) of the prosthesis. The axis of rotation (7) between adjacent vertebrae (1, 3) when bending forwards and backwards (5) lies in the caudal vertebra (3). This makes it possible to preserve the natural mobility between adjacent vertebrae (1, 3) and to keep the natural centre of rotation in its physiological position.

Description

SPINE PROSTHESIS

The invention relates to a spinal prosthesis for insertion into the intervertebral space of the spine after surgical removal of the intervertebral disc.

The intervertebral disc (intervertebral disc, intervertebral disc) has two functions: ensuring the mobility of two vertebrae to one another and the effect of a shock absorber. It may be necessary to remove the disc (disc) for various medical reasons. First of all, there is no standard surgical therapy for or after disc removal. Three surgical methods are generally used as an operative option: A: fusion, B: neither disc replacement nor fusion, C: disc replacement (only available in the lumbar spine).

In Fusion, two adjacent vertebral bodies are connected to one another by means of various blocking options so that both the mobility and the shock absorber effect are lost.

Neither disc replacement nor fusion lead to abnormal mobility with no shock absorber effect.

The following types of prostheses or implants (only for the lumbar spine) are intended for insertion into the intervertebral space (intervertebral gap):

a) The implant consists of only one piece, which may have elastic properties and is not connected to the vertebral bodies. These implants ensure reduced mobility and possibly a certain shock absorber effect. The fulcrum of these implants lies in the implant itself and not in the lower vertebral body, as is physiologically the case. aa) no elastic properties: a steel ball is installed as an implant (Fernström ball-bearing prosthesis)

ab) elastic properties: implants with the following patent numbers: WO 94/23671, WO 93/16664, DE 37 41 493 AI, US-A

4,874,382, US-A 5 047 055, US-A 5 108 438, US-A 5 192 326, EP-A 0 304 305, US-A 5 320 644.

b) The implant consists of a single piece, which consists of hard cover plates and an elastic core. The cover plates may have connecting or anchoring means in relation to the vertebral bodies. These implants ensure reduced mobility and a certain shock absorber effect. The fulcrum of these implants lies in the implant itself and not in the lower vertebral body, as is physiologically the case. This relates to implants with the following patent numbers: CH 671 691 A5, WO 90/11740, US-A 4 911 718, US-A 5 071 437, US-A 5 171 281, EP 0 346 269 A2, EP 0 310 837 AI.

c) The implant is fixed to both vertebral bodies and consists of at least two parts that are movably connected to one another, as can be seen, for example, from FR-A 2 718 635. Each part is firmly connected to a vertebral body. Elastic elements can be installed between these parts. These two parts ensure reduced mobility and possibly a certain shock absorber effect. The fulcrum of these implants lies in the implant itself or on the edge of the implant and not - as is usually the case - in the lower vertebral body. “Edge” is to be understood as: top of the implant (= bottom of the upper vertebra; WO 93/10725), bottom of the implant (= top of the lower vertebra; US Pat. No. 5,314,477), rear side of the implant (US Pat. No. 4 759 769).

ca) no elastic properties: implants with the following patent numbers: US-A 5 314 477, EP 0 560 141 AI, US-A 5 258 031, US-A 5 246 458, EP-A 0 177 728, DE 35 29 761 AI, WO 93/10725.

cb) elastic properties: implants with the following patent numbers: WO 94/26213, EP 0 566 810 AI, DE 41 09 941 AI,

DE 42 13 771 Cl, US-A 4 309 777, US-A 5 002 576, US-A 4 759 769, US-A 4 946 378, US-A 4 873 477.

With all these types of implants according to the state of the art mentioned above, the mobility is generated within the prosthesis; only with the Fernström ball-bearing prosthesis does the movement between the implant and both vertebrae take place. There is no implant that is movable with respect to one vertebral body and immovable with respect to the other.

The problems that arise after operative care are as follows:

a) The mobility is eliminated: This causes the neighboring segments (adjacent intervertebral discs) to be overloaded insofar as they have to take over the lost mobility.

b) the shock absorber effect is eliminated: this does not put any strain on the neighboring segments, since there are other structures that take on this shock absorber effect (ligaments, muscles); in addition, there are no devices that act as shock absorbers for the large joints of the lower extremity (hip, knee, ankle).

c) There is mobility and the implant is not connected to the vertebrae: the pivot point is in the wrong place, namely in the middle of the implant. This leads to an unnatural strain on the other facilities of the spine (ligaments, joints, muscles) and pain in these structures, so that they can no longer function optimally. Furthermore, see pivot point to shear forces that can force the implant out of the intervertebral gap.

d) there is mobility and the implant is firmly connected to both vertebrae: the fulcrum is right there! in the wrong place, in the middle of the implant or on its edge. Because parts of the implant are firmly connected to the vertebrae, the (non-physiological) kinematics of the implant prescribe the kinematics to the vertebrae. This in turn leads to an unnatural strain on the other spinal devices (ligaments, joints, muscles) and to shear forces between the implant and vertebra. Due to the fixed connection of the implant to both vertebrae, the implant cannot be forced out of the intervertebral space due to the unnatural kinematics. As a result, the fasteners and the bone are overstressed, so that there is a risk of implant loosening. This is the only way for the bone to react to the unnatural kinematics, since it has no further possibility of adaptation due to the fixed connection.

Further disadvantages result from the fact that implants consisting of two or more parts cannot be installed on the cervical spine due to the small size.

The object of the invention relates to a prosthesis that maintains the physiological or natural mobility and maintains the center of rotation in its physiological position. To achieve this object, the spinal prosthesis according to the invention is essentially characterized in that the prosthesis, which is formed in one piece in the installed state, has a curved surface on the upper side of the prosthesis and is movable relative to the cranial vertebral body, in that the prosthesis by means of anchoring and connecting means on the underside of the prosthesis is immovably connected to the caudal vertebral body and that the axis of rotation between the neighboring vertebral bodies lies in the caudal vertebral body when bending forwards and backwards. The prosthesis must be inserted into the intervertebral space during operations in which the disc (disc) is removed. The implant or the prosthesis is constructed according to the invention in such a way that the cranial (upper [standing person]) vertebral body is movable relative to the one-piece prosthesis and the prosthesis is not movable relative to the caudal (lower) vertebral body. The inventive design of the spinal prosthesis not only succeeds in reliably anchoring the prosthesis in the caudal vertebral body, but it can also provide the physiological or natural mobility of the adjacent vertebral bodies by providing the mobility of the prosthesis, which is designed in one piece when installed, in accordance with the invention the axis of rotation between the adjacent vertebral bodies in the caudal vertebral body, as corresponds to the natural axis of rotation between adjacent vertebral bodies, are maintained.

In the event of limited space, it is provided according to a preferred embodiment that the prosthesis consists of two equally large, essentially symmetrical, parts that can be put together, but this embodiment also results in a one-piece prosthesis in the installed state, which is relative to the cranial vertebral body is movable along the curved surface, while the prosthesis according to the invention is immovably anchored in the caudal vertebral body.

In order to achieve a corresponding number of degrees of freedom of movement between the adjacent vertebral bodies when the prosthesis according to the invention is installed, it is furthermore provided according to a further preferred embodiment that the curved surface of the prosthesis facing the cranial vertebral body is at least one section of a spherical surface. , Ellipsoid, saddle or cylinder surface is formed, with the appropriate choice of the curved surface and a corresponding orientation when Installation of the prosthesis allows different degrees of freedom of movement to be achieved between the adjacent vertebral bodies. A different selection of degrees of freedom can be achieved in that the curved surface has a different curvature or curvature along two essentially normal intersection lines, as corresponds to a preferred embodiment of the prosthesis according to the invention.

For proper anchoring of the prosthesis in the lower or caudal vertebral body, it is preferably provided according to the invention that the anchoring and connecting means are formed by at least one web or extension, which in particular has a granular, porous, ribbed, toothed or roughened surface. In addition, for adaptation to different purposes or for using different anchoring or connecting means with a base body of the prosthesis, it is preferably provided that the connecting and anchoring means are releasably fixed to the prosthesis via a plug-in or threaded connection.

The advantages of the invention result from the fact that a) the implant can be used in all spine sections (cervical, thoracic and lumbar spine), since it takes into account the individual kinematics of each section and can be produced in any necessary size; b) it can be installed from the ventral (front) and dorsal (rear); c) it consists of one part (or from two parts, left and right part) which is only connected to the lower vertebral body; d) because of its shape it guarantees a maximum of three degrees of freedom of movement and maintains the physiological axes of movement in their natural position, the pivot point in the case of ante- and retroversion being in the middle of the caudal vertebral body; e) the cranial vertebral body is movable relative to the prosthesis, so that the bone tissue of the prosthesis can adapt through physiological remodeling processes; and f) due to points d) and e) the structures associated with the movement segment (ligaments, joints, muscles) are not overused.

The invention is described in detail below with reference to the accompanying drawing using schematically illustrated exemplary embodiments, in which:

Fig. 1 shows an intact spine segment in a side view;

2 shows a spinal movement segment from the side with a spinal prosthesis according to the invention (kinematic spinal prosthesis);

Fig. 3 shows a sagittal section (section viewed from the side) through an embodiment of a prosthesis according to the invention; and FIG. 4 shows a frontal section (sectional area seen from the front) through further modified embodiments of the prosthesis according to the invention with different curvature of the surface in accordance with arrows IV of FIGS. 2 and 3, FIG. 3 showing a view in the direction of arrow III 4 is.

A natural, intact spinal movement segment (Fig. 1) from the side (front to left, back to the right, standing person) consists of the cranial (upper) vertebral body 1, the caudal (lower) vertebral body 3 and the discus in between ( 2, intervertebral disc). The direction of movement 5 of the upper vertebra 1 during forward and backward bending (ante / retro version) takes place around a pivot point 4 which lies in the lower vertebra 3.

During the operation, the prosthesis or the implant 6 (FIG. 2) is inserted between the vertebral bodies 1, 3. The direction of movement 5) of the upper vertebra 1 during forward and backward bending (ante / retro version) is now carried out by one rotation. Point 7, which lies in the lower vertebra 3 and is predetermined by the shape of the prosthesis and corresponds essentially to the natural pivot point 4 according to FIG. 1.

The one-piece prosthesis 6 (FIG. 3) is divided into an upper side 8 and a lower side 10. On the upper side 8 there is the surface 9 relevant for mobility. The curvature of the surface determines the pivot point 7 for forward and backward bending (center of curvature = Center of rotation for circular geometry). On the underside 10 there are anchoring and connecting means 11 for anchoring the prosthesis 6 in the lower vertebral body 3, so that the immobility of the prosthesis 6 with respect to the lower vertebral body 3 is ensured. In Fig. 3 and also in Fig. 2, a sinking of the prosthesis 6 in the lower vertebral body 3 is drawn as anchoring means.

The frontal section (section viewed from the front) through the prosthesis (FIG. 4) shows modified embodiments of possible different curvatures of the surface of the prosthesis 6: spherical surface 9a, ellipsoid surface 9b, saddle surface 9c, cylinder surface 9d.

When using a prosthesis 6, the following conditions result for mobility:

-A) The top 8 has a curved surface 9. The curvature defines the kinematics in the direction of movement 5 of the upper or cranial vertebral body. With forward and backward bending (ante- and retroversion) of the spine, the fulcrum 7 of the movement lies in the lower vertebral body 3.

The center of curvature of the prosthesis (in the case of a sagittally cut prosthesis, cutting surface viewed from the side; FIG. 3) must therefore lie at the same point. If the curvature corresponds to the circular geometry, then the center of curvature is equal to pivot point 7 (center of rotation). if the implant is viewed from the front (frontal cut, cut surface viewed from the front; Fig. 4), then the curvature can be different. If the curvature from the side view 9 is identical to that from the front view 9a, then the top of the prosthesis corresponds to the circular geometry. The prosthesis therefore guarantees three degrees of freedom of movement:

-a) forward / backward bending around a horizontal axis -b) side bending around a sagittal axis, and -c) rotation around a vertical axis.

If the curvature from the side view 9 is not identical to the curvature from the front view but is either curved in the same direction 9b or curved in the opposite direction 9c, then the top of the prosthesis corresponds either to the ellipsoid geometry or the saddle geometry. The prosthesis 6 then ensures only two degrees of freedom of movement: -a) forward / backward bending about a horizontal axis -b) lateral bending about a sagittal axis

If the curvature from the side view 9 is not identical to that from the front view and the latter is not curved 9b, then the top of the prosthesis corresponds to the cylinder geometry. The prosthesis then only guarantees one degree of freedom of movement: -a) Forward / backward bending around a horizontal axis

The different curvatures of the surfaces from the front view (FIG. 4) are necessary in order to take into account the different movement behavior of the individual functional spinal column sections.

-B) The underside 10 of the one-piece prosthesis 6 must be designed in such a way that it cannot move relative to the lower or caudal vertebral body 3 (be it rotation or translation). This immobility is given by the anchoring and connecting means 11. These can be: webs or one or more extensions 11 which are sunk into the lower vertebral body 3; a granular, porous, ribbed, serrated or roughened surface surface 13 into which the bone tissue can grow; Bone cement for connecting the prosthesis and bone. The connecting means do not necessarily have to be permanently connected to the prosthesis, but can also be fastened to the prosthesis for easier installation by means of a plug connection or thread, as is indicated in FIG. 4 by a detachable connection 14.

-C) As a variant, the prosthesis can also consist of two parts of the same size (right part and left part), as indicated in Fig. 4 when the prosthesis is formed with the curvature 9a by the parts 6 and 6 ', the Division takes place essentially along the section line 12. This is the case when tightly dimensioned surgical access routes require easier insertion of the prosthesis (here: smaller parts of the prosthesis). According to the composition of the parts in the intervertebral gap, however, the one-piece form of the prosthesis 6 described above results in the installed state. The advantage in this case is that the prosthesis can also be installed from the back (dorsal), particularly on the lumbar spine.

Claims

Patent claims

1. Spinal prosthesis for insertion into the intervertebral space of the spine after surgical removal of the intervertebral disc, characterized in that the prosthesis (6), which is formed in one piece in the installed state, has a curved surface (9, 9a, 9b, 9c, 9d) on the prosthesis. Top (8) and is movable relative to the cranial vertebral body (1), that the prosthesis (6) is immovably connected to the caudal vertebral body (3) by anchoring and connecting means (11) on the underside of the prosthesis (10) and that the axis of rotation (7) between the adjacent vertebral bodies (1, 3) when bending forward and backward (5) lies in the caudal vertebral body (3).

2. Spinal prosthesis according to claim 1, characterized in that the prosthesis (6) consists of two equal, substantially symmetrical, parts that can be assembled together.

3. Spinal prosthesis according to claim 1 or 2, characterized in that the curved surface of the prosthesis (6) facing the cranial vertebral body (1) in at least one sectional view of a ball (9a), ellipsoid (9b), saddle - (9c) or cylinder surface (9d) is formed.

4. spinal prosthesis according to claim 1, 2 or 3, characterized in that the anchoring and connecting means are formed by at least one web or extension (11), which in particular a granular, porous, ribbed, toothed or roughened surface (13) having.

5. spinal prosthesis according to one of claims 1 to 4, characterized in that the connecting and anchoring means (11) on the prosthesis (6) via a plug or thread connection (14) are releasably fixed.

6. Spinal prosthesis according to one of claims 1 to 5, characterized in that the curved surface (9, 9a, 9b, 9c, 9d) have a different curvature or curvature along two substantially normal cutting lines.