HK1121665B - Intervertebral disc prosthesis - Google Patents

Description

Intervertebral disc prosthesis

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application serial No.60/696,882, filed on 6/7/2005 and U.S. patent application serial No.60/741,817, filed on 2/12/2005, and claims priority from european patent application EP06002765.3, filed on 16/2/2006. The entire disclosures of these earlier applications are incorporated herein by reference.

Technical Field

The present invention relates to an intervertebral disc prosthesis for insertion into an intervertebral disc compartment (intervertebral disc component) formed between a first and a second vertebra. More particularly, the present invention relates to intervertebral disc prostheses that restore the natural flexibility of the spine.

Background

Intervertebral disc prostheses generally comprise two constituent elements each having a support plate which rests with an abutment surface against the adjacent vertebrae when the prosthesis is inserted into the intervertebral disc compartment. The other side of the respective support plate bears a coupling member (joint member) which allows relative movement between the two support plates.

Us patent No.6,936,071, corresponding to WO01/07893a1, discloses an intervertebral disc prosthesis in which the upper support plate includes a hat-shaped recess. The lower support plate has a recessed cavity which receives a replaceable slide-in insert having a hat-shaped projection. The cap-shaped recess in the upper bearing plate and the cap-shaped projection of the insert form a ball-and-socket joint, so that the two bearing plates can be tilted relative to one another in all directions in space.

The cervical disc compartment is usually machined by means of abrasive material before the disc prosthesis is inserted into the cervical disc compartment. During this procedure, the bone material is abraded with a milling cutter to properly form large flat opposing surfaces for the abutment surfaces of the support plates on the adjacent vertebrae. Fins formed on the abutment surfaces of the support plates prevent the otherwise flat abutment surfaces from slipping on the adjacent vertebrae. Each fin engages a groove that has been previously recessed into the adjacent vertebra by a chisel. However, precision grinding of the grooves is a cumbersome process. For this reason, it is difficult to correctly position the prosthesis in the intervertebral disc compartment.

WO2005/004756a1 discloses an intervertebral disc prosthesis which does not comprise fins on the abutment surfaces. Instead, the abutment surfaces are slightly convexly curved in a manner adapted to the anatomical requirements of the intervertebral disc prosthesis. The geometrical data of a healthy intervertebral disc compartment, in particular its height, are determined by extrapolation of data obtained from three-dimensional (3D) scanning measurements performed on a diseased spinal column segment. The convex curvature of the abutment surfaces is said to result in a self-centering action of the bearing plate within the intervertebral disc compartment. The abutting surfaces are coated with Hydroxyapatite (HAK), ceramic or tricalcium phosphate (TCP) material. These coatings are usually porous and rough, which ensures that the support plate does not slide in the intervertebral-disc compartment.

With such abutment surfaces it is difficult to obtain the desired self-centering action and a permanent fixation of the prosthesis in the intervertebral disc compartment. If the abutment surfaces have a coating with a smooth surface, the support plate slides within the intervertebral disc compartment. If the abutment surfaces have a coating with a rough surface, the friction is too great to obtain a self-centering effect.

EP0754018B1 discloses a similar intervertebral disc prosthesis. The center of motion of the prosthesis, i.e. the center of curvature of the non-spherical ball-and-socket joint, is here located at the posterior part of the prosthesis, but still between the bearing plates.

WO03/090648A1 discloses another prosthesis in which each support plate is configured to receive an insert. Each insert has a cap-shaped recess. Both recesses typically accommodate a ball that allows for hinged movement between the support plates. Each bearing plate has a cylindrically curved abutment surface and a flat tab mounted at the side edge of the bearing plate. Before the prosthesis can be inserted, the adjacent vertebrae must be prepared by forming elongated recesses in the bone material. The shape of the recess corresponds to the cylindrical shape of the abutment surface of the support plate. To prevent the bearing plate from sliding along the axis of the cylinder relative to the vertebrae, each fin has a tooth that facilitates clamping of the fin against the bone material.

In addition, in the case of such a prosthesis, the positioning of the prosthesis in the intervertebral-disc compartment is determined solely by the skill of the surgeon preparing the cylindrical recess accommodating the abutment surface of the support plate.

Disclosure of Invention

A first object of the present invention is to provide an intervertebral disc prosthesis which is easy to implant in an intervertebral disc compartment and which remains fixedly in its implanted position.

According to a first aspect of the invention, this object is achieved by an intervertebral disc prosthesis for insertion into an intervertebral disc compartment formed between a first vertebra and a second vertebra. The prosthesis comprises a first bearing plate having a first coupling member on one side and a first abutment surface on the other side, which first abutment surface is pressed against a first vertebra when the intervertebral disc prosthesis is inserted into the intervertebral disc compartment. The second support plate has a second coupling member on one side and a second abutment surface on the other side, which second abutment surface presses against the second vertebra when the intervertebral disc prosthesis is inserted into the intervertebral disc compartment. At least one of the first and second abutment surfaces has a region of convex aspherical curvature. According to the invention, the curved region is completely surrounded by an annular flat region having a rougher surface than the curved region.

The convexly curved region has a relatively smooth surface so that the prosthesis adjusts itself relative to the dome by sliding when the intervertebral disc prosthesis is inserted into the intervertebral disc compartment. Such a smooth surface even allows the insertion of an intervertebral disc prosthesis through a lateral access, if the smooth surface is not rotationally symmetrical, but has long and short dimensions in orthogonal directions. Lateral access is often preferred because it does not require pushing away large sensitive vessels that block the anterior access canal (vascular access canal).

During insertion, the intervertebral disc prosthesis is preferably inserted with its long dimension parallel to the channel axis through the access channel. After the intervertebral disc prosthesis reaches a position between the adjacent vertebrae, the pressure exerted by the vertebrae on the polished surface allows the prosthesis to rotate about 45 ° to 90 ° (depending on the direction of the access passage) in the intervertebral disc space until it finally reaches its desired position with its long dimension extending laterally upwards. Alternatively, the prosthesis is rotated within the intervertebral disc compartment by means of a steering mechanism connected to the prosthesis.

The curved region is formed such that it penetrates further by a few millimeters into the porous and softer bone tissue (cancellous bone) between the tubes of the harder bone (cortical bone) after insertion into the intervertebral disc compartment from the anterior or lateral access canal. The annular end of this rigid tubular body will be referred to hereinafter as the "apophyseal ring" of the vertebra. The penetration is stopped when the flat and preferably rough area surrounding the convexly curved region rests on the apophyseal ring of the adjacent vertebra. This ensures a tight and reliable connection of the intervertebral disc prosthesis to the adjacent vertebrae.

In an advantageous embodiment, the curvature region of at least one abutment surface is formed with an apex or apex region which is configured such that the constituent element can be rotated by at least 10 °, preferably by at least 25 °, within the adjacent dome when the apex of the curvature region contacts the apex of the dome. In the case of abutment surfaces having precisely the shape of an arch, it is difficult for the surgeon to manually rotate the constituent elements with respect to the adjacent vertebrae, since the large curved surfaces are in direct contact. However, if the abutment surface has such an apex, only the apexes of both the abutment surface and the dome contact each other after the abutment surface has been pressed into the cartilaginous material in the dome before a tighter connection is achieved.

The shape of the convexly curved region may require that the shape of the dome is biometrically determined before the intervertebral disc prosthesis is inserted into the intervertebral disc compartment. This can be done by computer processing a high resolution image of the vertebrae. The curved region is then machined or molded according to the resulting biometric shape data of the dome. However, since the shape of the curved region is preferably similar to, rather than identical to, the geometry of the dome within the apophyseal ring, adaptation to this particular geometry of the patient may not be required in many cases. But a support plate manufactured from statistics obtained for the affected vertebrae of many patients may be used.

There are many ways to obtain a smooth surface in the curved region. For example, the surface may be polished or provided with a coating having desired surface properties. Preferably, the surface has an arithmetic roughness Ra of less than 10 μm, preferably less than 1 μm, so as to ensure a coefficient of dynamic friction with respect to the bone material of less than 0.1.

These properties can be readily achieved by applying diamond-like carbon coatings (DLC) known in the art. Such coatings are biocompatible, very hard and have low friction.

In another aspect, the flat region can have a kinetic coefficient of friction greater than 1.0 with respect to the bony material of the apophyseal ring.

Of course, the two support plates can also be formed in the manner described above.

According to another aspect of the invention, the above object is achieved by an intervertebral disc prosthesis for insertion into an intervertebral disc compartment formed between a first and a second vertebra. The prosthesis comprises a first bearing plate having a first coupling member on one side and a first abutment surface on the other side, which first abutment surface presses against a first vertebra when the intervertebral disc prosthesis is inserted into the intervertebral disc compartment. The prosthesis further comprises a second support plate having a second coupling member on one side and a second abutment surface on the other side, which second abutment surface presses against a second vertebra when the intervertebral disc prosthesis is inserted into the intervertebral disc compartment. At least one of the first and second abutment surfaces has a convexly curved region. According to the invention, the convexly curved region may have (at least substantially) a chamfer.

It has been found that if a support plate with flexion zones is implanted, this shape is similar to the geometry of the dome containing the flexion zones. Because the ramps are not rotationally symmetric, a self-centering torque is generated if there is a compressive force applied between the vertebrae and the support plate. During implant surgery, this force is generated by ligaments extending along the spinal column. When the bearing plate rotates to a position where these compression forces are symmetrical, the torque disappears and the rotation is thus stopped. If the compressive force is still further applied, the ramp-shaped curved region will press into the bony material (cancellous bone) within the apophyseal ring, thus causing a partial deformation of the dome material. This ensures a very close contact between the bone material and the bending zone.

Even in the case where the implantation of an intervertebral disc prosthesis has been carried out without any complications, it may sometimes be necessary to change the coupling which determines the position of the center of motion. Typically the prosthesis is implanted through an anterior portal. However, re-creating such an anterior portal often increases the risk due to scarring from a previous surgical procedure.

It is therefore a further object of the present invention to provide an intervertebral disc prosthesis which reduces such risks.

According to the invention, this object is achieved by an intervertebral disc prosthesis for insertion into an intervertebral disc compartment formed between a first and a second vertebra. The prosthesis comprises: a first support plate having a longitudinal edge and a transfer edge; a first slide-in pocket located on a first support plate; a first coupling piece, which is separately connected to the first support plate and comprises a first slide-in plate, which can be inserted into the first slide-in cavity. The prosthesis also includes a second support plate supporting the second coupling member. According to the invention, the first slide-in plate and the first slide-in compartment are configured in such a way that the first slide-in plate can be inserted into the first slide-in compartment from the longitudinal side edge of the first carrier plate and from the transfer side edge.

This enables the first coupling piece to be replaced from the lateral inlet channel. Any risk associated with providing a reusable front side access passage is thus avoided.

The inventors have found that many of the problems encountered in the case of conventional intervertebral disc prostheses are the result of a mismatch between the anatomically possible movements of the vertebrae on the one hand and the movements which can be produced by the prosthesis. If this mismatch is significant, the muscles and ligaments supporting the spine naturally deform, causing tension and ultimately pain.

It is therefore another object of the present invention to provide an intervertebral disc prosthesis that significantly reduces this mismatch.

According to the invention, this object is achieved by an intervertebral disc prosthesis for insertion into an intervertebral disc compartment formed between an upper and a lower vertebra. The prosthesis includes a first coupling member associated with the superior vertebra. The second link is associated with the inferior vertebra and is configured such that the second link is rotatable relative to the first link about a point or axis of rotation. According to the invention, the rotation point or axis is arranged above the second coupling part, preferably above the first coupling part. In many cases it may even be advantageous to arrange this rotation point or axis above a support plate which supports the first coupling member on one side and has a first abutment surface on the other side, which first abutment surface presses against the first vertebra when the intervertebral disc prosthesis is inserted into the intervertebral disc compartment.

In conventional prostheses, the point of rotation is arranged in or below the lower link. It has been found, however, that the centre of motion is not below the lower link, but (far) above the lower link. For example, in the case of lumbar vertebrae, the center of motion is in the apex of the dome surrounded by the apophyseal ring of the upper vertebra. Only when the rotation point or axis of the prosthesis substantially coincides with the anatomical centre of motion does the elements of the prosthesis rotate to a certain extent, as is the case with a natural and healthy intervertebral disc in the intervertebral disc compartment. Thus, unnatural deformations of ligaments and muscles are avoided and no reinforcement of the prosthesis takes place.

In order to be able to arrange the rotation point or axis as close as possible to the natural center of motion of the adjacent vertebrae, the position and curvature of the coupling element must be carefully selected. For this reason, the prosthesis can be assembled like a kit with a plurality of components of the same kind but with different dimensions or curvatures. This allows the surgeon to assemble the prosthesis during the implantation surgery while the surgeon can determine how much material must be removed from the adjacent vertebrae. Of course, it is also advantageous to assemble the prosthesis with various components if, as is often the case with lumbar vertebrae, no or only a small amount of bone material has to be removed, or if it is known in advance how much bone material has to be removed. In these cases, the components are determined from the pre-surgical 3D scan so that the point of rotation or axis of rotation is as close as possible to the natural center of motion of the adjacent vertebrae.

Such a kit may include first and second connectors having different shapes (curvatures and/or spacings from the base surface), and/or different support plates and/or a different set of spaces having a disc or wedge shape that may be inserted between the support plate and the adjacent vertebrae.

Another problem in the case of the above-described known intervertebral disc prosthesis is that, in case the vertebrae are tilted laterally about a tilt axis parallel to the lateral sides of the support plates, the mobility of the support plates is limited in the case of larger tilt angles only by the mutual impact of the edges of the support plates. It is also sometimes desirable to selectively limit the forward and/or rearward tilt angle of the support plate.

For this reason, it is a further object of the invention to provide an intervertebral disc prosthesis in which the angle of inclination can be limited in a straightforward manner.

According to the invention, this object is achieved by an intervertebral disc prosthesis for insertion into an intervertebral disc compartment formed between a first and a second vertebra. The prosthesis includes a first bearing plate supporting a first coupling member and a second bearing plate supporting a second coupling member. The second link member is engaged with the first link member so as to be capable of performing a tilting or rotating motion between the first and second support plates. A projection is arranged on the first support plate, which projection serves as a stop for limiting the relative tilting or rotational movement between the first and second support plates. According to the invention, the projection is arranged on a replaceable guide plate which can be inserted into a guide plate slide-in compartment provided on the first carrier plate.

By providing one or more protrusions on the guide plates, the protrusions can be easily replaced by removing only one guide plate and inserting another guide plate having a different protrusion. Since the insertion into the slide-in compartment requires only a translational movement, such a change can be made with a very small access channel if the slide-in compartment direction is appropriately selected with respect to the possible access channel direction. Once the intervertebral disc prosthesis is implanted, a lateral access is often preferred. For this reason, the slide-in compartment should be oriented in such a way that the insertion plate supporting the projection can be pulled out of the slide-in compartment with a lateral movement.

The limitation of the lateral inclination angle is achieved if the first projection is arranged between the first coupling member and the lateral side of the first bearing plate. If the tilting angle of the bearing plate is to be limited in the forward and/or rearward direction, the projection should be arranged between the first coupling member and the longitudinal side edge of the first bearing plate.

Another problem with the known intervertebral disc prosthesis is that a larger anterior access canal has to be prepared for inserting the support plate.

For this reason, it is a further object of the invention to provide an intervertebral disc prosthesis which can be inserted into an intervertebral disc compartment through a relatively small anterior access canal.

This object is achieved by an intervertebral disc prosthesis comprising a first support plate supporting a first coupling member and a second support plate supporting a second coupling member. According to the invention, the first carrier plate comprises a connecting element for detachably connecting the first carrier plate to an actuating element by means of which the first carrier plate can be rotated about an axis which is substantially perpendicular to the first carrier plate.

In this way, the first support plate can be inserted with its short transverse side facing forwards through the narrower front-side inlet channel, which has a diameter which is not specified by the length of the long side of the support plate, but by the length of its short and narrow transverse side. The support plate is first rotated by means of the actuating mechanism into a defined position in or near the intervertebral-disc compartment. The smaller the diameter of the access canal, the lower the risk of damaging the blood vessel that has to be displaced when forming the anterior access canal.

Drawings

The various features and advantages of this invention may be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a top plan view of an upper component element of an intervertebral disc prosthesis according to the invention;

FIG. 2 is a sectional view taken along line II-II of the upper constituent element shown in FIG. 1;

FIG. 3 is a bottom view of the upper constituent element shown in FIG. 1;

FIG. 4 is a sectional view taken along line IV-IV of the upper constituent element shown in FIG. 1;

FIG. 5 is a sectional view taken along line V-V of the upper constituent element shown in FIG. 1;

figures 6a-6e show the underside of the upper support plate in several states during assembly of the upper constituent element;

FIG. 7 is a top view of the lower component element of the intervertebral disc prosthesis according to the invention;

FIG. 8 is a sectional view taken along line VIII-VIII of the lower constituent element shown in FIG. 7;

FIG. 9 is a bottom view of the lower constituent element shown in FIG. 7;

FIG. 10 is a side view of an intervertebral disc prosthesis in an inserted state;

FIG. 11 is a side view of an intervertebral disc prosthesis corresponding to FIG. 10 but with the constituent elements inclined relative to one another;

FIG. 12 is a side view of an intervertebral disc prosthesis, which corresponds to FIG. 10, and which has been secured against lateral tilting movement;

fig. 13 is a view corresponding to fig. 2, without the projection serving as a stopper;

FIG. 14 is a schematic simplified cross-sectional view of the upper and lower lumbar vertebrae;

FIG. 15 shows a coupling of two constituent elements in a first configuration;

FIG. 16 shows a coupling of two constituent elements in a second configuration;

fig. 17 shows a coupling of two constituent elements in a third configuration;

fig. 18 shows a coupling of two constituent elements in a fourth configuration;

fig. 19 shows a coupling of two constituent elements in a fifth configuration;

fig. 20 shows a coupling of two constituent elements in a sixth configuration;

FIG. 21 is a side view of an intervertebral disc prosthesis inserted between two lumbar vertebrae according to another embodiment;

FIGS. 22a-22d show the underside of the upper support plate in several states during replacement of the coupling;

FIGS. 23a-23c are top views of the upper support plate rotated by means of the lever during insertion into the front inlet channel;

FIG. 24 is a schematic perspective view of a connecting member for the lever;

FIG. 25 is a side view of an intervertebral disc prosthesis inserted between two lumbar vertebrae according to another embodiment in a first state;

FIG. 26 shows the prosthesis of FIG. 25, but in a second state after rotation of the lower component member relative to the upper component member;

FIG. 27 is a side view of an intervertebral disc prosthesis according to another embodiment inserted between two lumbar vertebrae in a first state; and

fig. 28 shows the prosthesis of fig. 27, but in a second state after rotation of the lower constituent element relative to the second constituent element;

FIG. 29 is a top plan view of an upper component element of an intervertebral disc prosthesis according to another embodiment of the invention;

FIG. 30 is a sectional view taken along line XXX-XXX of the upper constituent element shown in FIG. 29;

FIG. 31 is an enlarged cross-sectional view through the cap-shaped insert member of the upper constituent element shown in FIGS. 29 and 30;

FIG. 32 is a cross-sectional view through the cap insert shown in FIG. 31 along line XXXII-XXXII;

FIG. 33 is an enlarged cross-sectional view through a cap insert element according to another embodiment;

FIG. 34 is a cross-sectional view through the cap insert shown in FIG. 33 along line XXXIV-XXXIV;

FIGS. 35a-35e are cross-sectional views through the cap insert of FIG. 33 and adjacent vertebrae in different configurations during an implantation procedure;

FIGS. 36a-36e are cross-sectional views through the cap insert shown in FIG. 34 and adjacent vertebrae in different configurations during an implantation procedure;

fig. 37 is an enlarged cross-sectional view through a cap insert element according to another embodiment.

Detailed Description

Fig. 1-5 show the upper constituent element of the intervertebral disc prosthesis in a top view, a sectional view along the line II-II, a bottom view, a sectional view along the line IV-IV, and a sectional view along the line V-V, respectively.

The upper constituent element, generally designated by the reference numeral 10, comprises an upper support plate 12, said upper support plate 12 having an approximately kidney-shaped periphery. A spherical cap insert 16 is inserted into the central recess 14 (see fig. 2) on the upper side of the upper support plate 12 and is secured there by a self-locking ring 18, which self-locking ring 18 is formed on the spherical cap insert 16. In the exemplary embodiment shown, the outward facing outer surface of the spherical cap insert 16, designated by reference numeral 20, is curved in a spherically convex manner. However, inserts having non-spherical convex caps may be used as well, as further described below with reference to FIGS. 24-27. The outer surface 20 of the spherical cap insert 16 supports a coating 22 having a high roughness.

In the exemplary embodiment shown, the spherical cap insert 16 is constructed of a softer, resilient material, such as an elastomer, while the surrounding upper bearing plate 12 is fabricated from a harder material, such as a metal, such as titanium. After the insertion of the upper constituent element into the intervertebral-disc compartment, the spherical cap insert 16 rests with its rough coating 22 on the softer material which is located in the apophyseal ring of the adjacent vertebra. The peripheral harder region, indicated by the numeral 23, on the outward facing side of the upper support plate 12 bears on the apophyseal ring of the adjacent vertebra.

On the underside of the upper support plate 12, which is located opposite the spherical cap insert 16, there is a coupling element 24, said coupling element 24 comprising a slide-in plate 26, said slide-in plate 26 having a convex spherical cap coupling 28 integrally molded thereon. Guide ribs 30, 32 extend parallel to the lateral sides of the upper support plate 12, said guide ribs 30, 32 being molded on the slide-in plate 26. Due to the convex curvature of the spherical cap-shaped coupling portion 28, the center of gravity of motion is located above the coupling portion. This has significant advantages at least for prostheses inserted in the lumbar intervertebral space, as will be explained in more detail below.

The coupling element 24 abuts the first 34 and the second 36 guide plate in a direction towards the lateral side of the upper support plate 12. The two guide plates 34, 36, which in principle have the same construction, have a first and a second projection 38, 40, respectively, which first and second projections 38, 40 are of parallelepipedal design and serve as stops for the purpose of limiting the movement of the coupling parts. In the direction of the coupling element 24, the guide plates 34, 36 have guide grooves 42, 44, which guide grooves 42, 44 engage with the guide ribs 30, 32 of the slide-in plate 26 of the coupling element 24.

As can be seen from the sectional view along the line V-V shown in fig. 5, the two guide plates 34, 36 likewise have guide grooves 46, 48 in the direction of the longitudinal side edges of the upper bearing plate 12, said guide grooves 46, 48 having a complementary design to the guide ribs 50, 52 formed on the upper bearing plate 12.

In fig. 5, it can also be seen that the second guide plate 36 is accommodated in a second guide plate slide-in pocket 54, which second guide plate slide-in pocket 54 opens only in the direction towards the middle of the upper bearing plate 12. The second guide plate 36 can thus be inserted into the second guide plate slide-in pocket 54 from the side, while the guide grooves 46, 48 of the second guide plate 36 engage with the guide ribs 50, 52 of the upper support plate 12. The front side of the second guide plate 36, on which the guide groove 44 is formed, finally hits a stop 55 (see fig. 3) formed on the upper support plate 12. Thus, the position of the second guide plate 36 in the second guide plate slide-in pocket 54 is defined by abutment in all directions except the slide-in direction.

To prevent the second guide plate 36 from unintentionally sliding out of the second guide plate slide-in pocket 54, the second guide plate 36 is preferably made of a material having resilient properties. For example, polyvinyl chloride can be envisaged for this purpose. The frictional resistance between the second guide plate 36 and the upper support plate 12 should be such that the second guide plate 36 can be inserted into the second guide plate slide-in compartment 54 by hand or with the aid of a tool, but cannot be removed again from the second guide plate slide-in compartment 54 without the aid of a tool after the insertion of the intervertebral disc prosthesis into the intervertebral disc compartment.

As shown in fig. 1 to 3, the upper constituent element 10 is formed symmetrically with respect to a plane of symmetry passing through the middle of the spherical cap insert 16 and the spherical cap coupling portion 28. The first guide plate 34 is therefore manufactured in the same way as the second guide plate 36, and therefore the above description applies correspondingly to the second guide plate 36.

The lateral surfaces of the two guide plates 34, 36 facing the middle define a slide-in cavity 56 for the coupling element 24 along the lateral sides of the upper supporting plate 12. Along the longitudinal side of the upper bearing plate 12, the slide-in compartment 56 is delimited on one side by a step 58 (see fig. 3) formed on the upper bearing plate 12 and on the opposite longitudinal side by a third guide plate 60. The third guide plate 60 is inserted into a third guide plate slide-in pocket 62 formed on the underside of the upper support plate 12. As can be seen in fig. 4, the side of the front guide 60 facing the middle of the support plate 12 likewise has a guide groove 63, said guide groove 63 engaging with a guide rib 65 having a complementary shape, said guide rib 65 being attached to the slide-in plate 26 of the coupling element 24.

In this way, the slide-in plate 26 of the coupling element 24 bears on three sides against the guide plates 34, 36 and 60 and on the fourth side against the step 58 and is thus fixed in all directions to the underside of the upper supporting plate 12.

In fig. 6a-6c, the assembly of the upper constituent element 10 in several stages is illustrated in simplified schematic form.

In fig. 6a, the underside of the support plate 12 is shown without the guide plates 34, 36, 60 and the coupling element 24. In this view, the side guide plate slide-in pockets 64, 66 for the first and second guide plates 34, 36, respectively, and the third guide plate slide-in pocket 62 for the third guide plate 60 can be seen. The first and second guide plates 34, 36 are now inserted into the guide plate slide-in pockets 64 and 66, respectively, from the side, as indicated by arrows 68, 70, until they encounter the stops 55, 59.

This state is shown in fig. 6 b. The side guides 34, 36 now form, together with the step 58, a slide-in recess 56 for the slide-in plate 26 of the coupling element 24. The slide-in plate 26 is now inserted into the slide-in cavity 56 from the front, as indicated by arrow 72. In order to secure the coupling element 24 against unintentional slipping out of the slide-in compartment 56, the third guide plate 60 is now also inserted into the slide-in compartment 56 from the front, as indicated by arrow 74 in fig. 6C.

The above-described assembly structure of the upper constituent element 10 allows the coupling element 24 to be arbitrarily assembled with the first and second guide plates 34, 36 with the projections 38, 40, respectively, serving as stoppers, in a manner of a mating construction tool. Moreover, the replacement of the guide plates 34, 36 and the coupling element 24 is possible even after the intervertebral disc prosthesis has been surgically inserted into the intervertebral disc compartment. This will be explained in more detail below with reference to fig. 12-19.

Fig. 7-9 show, in a view similar to fig. 1-3, a top view, a cross-sectional view along line VIII-VIII, and a bottom view of a lower component element 10 ', which lower component element 10' together with an upper component element forms an intervertebral disc prosthesis. The lower constituent element 10 'differs from the upper constituent element 10 only in that the convex spherical cap-shaped coupling portion 28 has been replaced by a concave spherical cap-shaped coupling portion 28'. The curvature of the convex spherical-cap coupling 28 is numerically equal to the curvature of the concave spherical-cap coupling 28 ', so that the two spherical-cap couplings 28, 28' together form a ball-and-socket coupling.

Since the two constituent elements 10, 10' otherwise have the same construction, reference may be made to the description of the upper constituent element 10 in this context. In order to distinguish the corresponding parts of the upper constituent element 10 and the lower constituent element 10 ', the parts of the lower constituent element 10' are indicated by prime notation.

Fig. 10 shows the intervertebral disc prosthesis made of two constituent elements 10, 10' after it has been placed in the intervertebral disc compartment. In fig. 10, it can be readily seen that the softer, resilient spherical cap insert 16 with rough coating 22 is pressed against the same soft material located within the apophyseal ring of upper vertebra V1. In this way, a very tight connection is obtained between the spherical cap insert 16 and the soft material of the vertebra V1. The roughness of the coating 22 has the effect that the upper constituent element cannot slip in the intervertebral-disc compartment.

The harder region of the upper support plate 12 surrounding the spherical cap insert 16 bears on the apophyseal ring 71 of vertebra V1. By virtue of the stiffer regions, large longitudinal forces are transmitted between the vertebra V1 and the upper constituent element 10.

There is a corresponding description of the inferior component element 10 ', which inferior component element 10' rests against the inferior vertebra V2.

In the inserted state, the convex spherical cap-shaped coupling part 28 of the upper constituent element 10 rests on the concave spherical cap-shaped coupling part 28 ' of the lower constituent element 10 ', so that the two constituent elements 10, 10 ' can be rotated relative to one another about a rotation point 80 in all directions, the meaning of which will be explained in more detail below. Since the rotation of the vertebrae V1, V2 in the lateral direction is generally only possible to a limited extent, the projections 38, 40 on the guide plates 34, 36 of the upper constituent element 10 and the corresponding projections 38 ', 40' on the guide plates 34 ', 36' of the lower constituent element 10 'are additionally produced in such a way that the two constituent elements 10, 10' can only be rotated through a few degrees about an axis perpendicular to the plane of the paper. In fig. 11 it is shown how the protrusions 38, 38' limit the rotational movement to a maximum rotational angle of about 4 °. It should be noted that it may be sufficient that only one of the constituent elements 10, 10' has a projection.

As can be seen in fig. 3 and 9, the projections 38, 40 and 38 ', 40' all have a rectangular bottom cross-sectional area, with the long sides extending in the front-rear direction. This shape also ensures that forward and backward rotational movement is limited. The length of the long side determines the maximum rotation angle in this direction, which may be in the range between 6 ° and 12 °. Where the projections 38, 40 and 38 ', 40' have a substantially square bottom cross-sectional area, there is no restriction to such rotational movement, which may be desirable in some circumstances.

If the maximum angle of rotation of one or both axes of rotation is to be changed, it is sufficient to replace the upper guide plate 34, 36, the lower guide plate 34 ', 36' or all 4 guide plates 34, 36, 34 ', 36' with guide plates having different projections. In this case, the projections 38, 40 and 38 ', 40' are either of different height, different bottom cross-sectional area, or may be mounted, for example, closer to the coupling elements 24, 24 'or farther from the coupling elements 24, 24'. It should be noted that such a variation of the rotation angle is possible even after the intervertebral disc prosthesis has been inserted into the intervertebral cavity. This is due to the fact that each guide plate 34, 36, 34 ', 36' can be replaced by a lateral access without having to remove the entire prosthesis.

Fig. 12 shows a view corresponding to fig. 10 and 11, in fig. 12 the guide plate 134, 136, 134 ', 136 ' has been inserted into the upper and lower support plates 12, 12 ', respectively, the projections 138, 140 and 138 ', 140 ', respectively, of said guide plate all fixing the intervertebral disc prosthesis. To this end, each projection 138, 140, 138 ', 140' may have a large area and a flat bearing surface in order to achieve a good distribution of forces. If the intervertebral disc prosthesis is only fixed in the lateral direction, while a rotational movement forwards and backwards is still possible, the projections 138, 140, 138 ', 140' may take the shape of a laterally seated hemi-cylinder. The semicylindrical bodies can thus roll on one another, so that a rotation of the two constituent elements 10, 10' about the axis of rotation indicated by the numeral 73 in fig. 12 is possible.

In order to limit the maximum angle of rotation of the rotary movement in the forward direction, one or both third guides 60, 60' may also have a projection which acts as a stop. However, the provision of the third guide plate 60, 60' with a projection is not preferred if the projection is replaceable. This is because the guide plates 60, 60' can only be replaced through the front side access channels, and it is often a difficult and risky process to prepare such channels again.

Of course, the stop element defining the movability may also be omitted altogether. In this case, guide plates 234, 236 are utilized that do not have protrusions. Fig. 13 shows such an embodiment in a sectional view similar to fig. 2.

It will be understood that the intervertebral disc prosthesis described above may also be inserted in the intervertebral disc compartment in reverse so that the upper constituent element 10 engages the lower vertebra V2 and the lower constituent element 10' engages the upper vertebra VI.

Since the coupling elements 24, 24 'of the two constituent elements 10, 10' can be interchanged in a straightforward manner, the intervertebral disc prosthesis can be adapted in a wide range to the corresponding shape of the intervertebral disc compartment and to the possible movements of the vertebrae V1, V2 adjoining the prosthesis.

The shape of the intervertebral-disc compartment generally varies with the longitudinal position of the adjacent vertebrae in the human spine. Often, however, the size of the cavity must be significantly exaggerated by, for example, abrasion methods used to remove pathological deformities near the apophyseal ring of one or both adjacent vertebrae.

The possible movements of the vertebrae are anatomically predetermined by facet joints (facet joints), joint capsules (joint capsules), annulus fibrosus and ligament strands extending along the spinal column. The inventors have found that many of the problems that conflict with conventional intervertebral disc prostheses are, on the one hand, the result of a mismatch between the anatomically possible movements of the individual vertebrae and the movements that the prosthesis may produce. If this mismatch is significant, the muscles and ligaments supporting the spine strain unnaturally, which can produce strain and ultimately pain. In addition, it has been found that the motion of a pair of adjacent vertebrae can be described at least very closely as rotational motion in which the lower vertebrae rotates about a point of rotation associated with the upper vertebrae.

For the purpose of illustrating possible movements, the following term "center of motion" is used, said center of motion representing the point of rotation of such a movement. For the cervical column bone, the center of motion of the vertebrae is a few millimeters away from the upper vertebral level that defines the intervertebral disc compartment. However, recent studies conducted by the present inventors have shown that this is not generally applicable to the lumbar spine. Because of this, the center of motion is almost precisely located in the apex of the lower vault of the upper lumbar spine.

Figure 14 shows in schematic simplified cross-sectional view upper and lower lumbar vertebrae LV1 and LV2, respectively, both of which have a dome, shown approximately in cross-sectional view by the angle formed by the straight lines LV1 and LV 2. The possible movement of the upper lumbar LV1 is indicated in figure 14 by different dashed lines. In this representation, the center of motion, designated by reference numeral 8, is located in the angle formed by the two straight lines at the lower corner of the upper lumbar vertebra LV 1. This angle corresponds to the apex of the curved vault of the actual upper lumbar spine. From the above it is clear that an intervertebral disc prosthesis for the lumbar intervertebral disc compartment should be configured such that its centre of motion is located as close as possible to the apex of the lower vault of the upper lumbar vertebra. In the case of the prosthesis described above, this can be easily achieved by inserting coupling elements 24, 24' having the desired shape.

How almost any arbitrary center of motion can be obtained with the prosthesis described above will be described in more detail below with reference to fig. 15-18.

In fig. 15, the two coupling elements 24, 24 'of the two constituent elements 10, 10' are shown in isolation, respectively. The center of motion, indicated by the reference numeral 80, is the center of a dashed circle 82, the dashed circle 82 having a length that coincides with the spherical surface 25 of the spherical cap-shaped coupling portion 28 of the coupling element 24.

Especially in the case of the cervical spine, it may be necessary to clear the pathological deformations in the vicinity of the apophyseal ring. Removing such deformations means that the surgeon has to remove a larger part of the vertebrae adjacent to the intervertebral-disc compartment. This clearance increases the height of the intervertebral disc compartment. For example, if it is necessary to clear a greater part of the lower part of the upper vertebra V1, this can be compensated by replacing the coupling element 24 of the upper constituent element 10 with a coupling element 124 in which the spherical cap-shaped surface 125 is further away from the slide-in plate 126 of the coupling element 124.

This design is shown in fig. 16 with a view similar to that of fig. 15. It can be seen therein that the slide-in plates 126, 126 'of the two coupling elements 124, 124' are now arranged further apart in order to take account of the greater height of the intervertebral-disc compartment. However, the coupling element 124 'of the lower constituent element 10' remains unchanged compared to the design shown in fig. 15.

As best seen in fig. 16, although the spherical cap surface 125 is now further away from the slide-in plate 126, the location of the center of motion 180 remains at an anatomically predetermined optimum position fixed relative to the upper vertebra V1.

Often, it is not possible for the surgeon to accurately estimate how much bone material of the adjacent vertebrae must be removed prior to implantation surgery. This is usually only known during surgery. The surgeon can then measure the height of the final intervertebral disc compartment, for example by using an adjustable template, and then decide where the support plate should lie against the vertebrae. Additional spacers may be provided between the vertebrae and the support plate. If the position of the support plate is determined, the surgeon selects a pair of slide-in plates having a geometry that ensures that the center of motion of the prosthesis coincides with the position of the anatomical center of motion that has been previously determined from three-dimensional (3D) biometric measurements.

Fig. 17 shows a different situation than that shown in fig. 16, in which not the greater part of the upper vertebra V1, but the greater part of the lower vertebra V2, has to be removed. One way to compensate for this is to use an upper coupling element 224 with a larger distance between the slide-in plate 226 and the spherical surface 225. This also requires increasing the radius of curvature of the spherical surface 225 in order to maintain the position of the center of motion 280 at its optimal anatomically determined position. The radius r is thus a prescribed function r (r) (a) of the distance a between the slide-in plate 226 and the spherical surface 225. In this case, both the coupling pieces 224, 224' are different as compared with the case shown in fig. 15.

Fig. 18 shows a combination of couplings 324, 324 'that can be used in place of the couplings 224, 224' shown in fig. 17. The radius of curvature of the spherical surface 325 is not increased here, but only the distance between the slide-in plate 326 ' and the spherical surface 325 ' of the lower link 324 ', similar to that shown for the upper link 124 in fig. 16. In addition, the center of motion 380 remains at an anatomically predetermined location despite the shifting of the abutment surface positions of the adjacent vertebrae V1, V2.

As an alternative to replacing the coupling, the same effect can be obtained by replacing support plates having different thicknesses. This is due to the following reasons: with regard to the location of the center of motion, it is ultimately effected that the spherical surface is not spaced from the slide-in plate, but rather that the spherical surface is spaced from the abutment surfaces of the adjacent vertebrae V1, V2. Thus, in this manner it may not even be necessary to replace parts of the prosthesis if additional spacers of different thickness are inserted between each support plate and the abutting side faces of the adjacent vertebrae. The spacer may have a disc or wedge shape. A disadvantage of such spacers is that they have to be held in place, in addition to which the intervertebral-disc compartment is often too small to insert additional spacers.

By varying the radius of curvature of the spherical cap surface and/or the spacing of the spherical cap surface from the support plate, it is thus possible to adapt the intervertebral disc prosthesis to virtually any arbitrary geometry of the intervertebral disc compartment, while at the same time maintaining an anatomically predetermined center of motion. If the surgeon is equipped with a construction kit comprising two support plates and a set of differently shaped coupling elements, the adaptation to the anatomically predetermined center of motion can be accomplished by a suitable choice of coupling elements by the surgeon.

Alternatively, the inserted coupling element may be specially machined for a particular patient. This allows to maintain the centre of motion even in the case of drastic pathological deformations of the vertebrae, for example due to accidents. In this case, the upper and lower constituent elements may each be machined as a unitary element from a single piece of suitable material, such as titanium.

Fig. 19 shows an embodiment in which the activity center 482 has been moved in the longitudinal direction. This is accomplished by moving the spherical surfaces 425, 425 'of the slide-in plates 426, 426' relative to the bottom areas of the plates.

The same effect can be obtained by providing the spherical surfaces 525, 525 'with a shape that is not also rotationally symmetrical with respect to the central axis of the slide-in plates 526, 526'. This embodiment is shown in fig. 20.

Fig. 21 shows, in a view similar to fig. 10, an intervertebral disc prosthesis made up of two constituent elements 210, 210', in a position between two lumbar vertebrae LV1, LV 2. The constituent element 210, 210 'differs from the constituent element 10, 10' shown in fig. 1 to 11 only in that the spherical surface 625 of the spherical cap-shaped coupling portion 628 and the spherical surface 625 'of the groove 625' have a large radius of curvature. As a result, the center of motion 680 is precisely located in its anatomically optimal position, i.e., in the apex 690 of dome 692 formed within apophyseal ring 694 of upper lumbar vertebra LV 1.

Returning again to the first embodiment shown in fig. 1-11, it should be noted that the first and second guide plates 34, 36 on the lateral sides of the upper constituent element 10 make it possible to slide the coupling element 24 of the upper bearing plate 12 not only from the front through the third guide plate into the cavity 62, but also from the side through one of the lateral guide plate slide-in cavities 64, 66 to a central position of the slide-in cavity 56. Of course, the corresponding description also applies to the coupling element 24 'of the lower constituent element 10'.

In particular, the coupling element 24 can be laterally replaced even when an intervertebral disc prosthesis has been inserted into the intervertebral disc compartment. The possibility of being able to replace the coupling element 24 from the side in this case is advantageous, since an access channel is required due to the front side access. However, forming such a passage again increases the risk. For example, a blood vessel that is displaced outward through the anterior portal during the first procedure may scar. Due to scarring, the blood vessel loses a portion of its elasticity, and serious complications may occur if the blood vessel is displaced again during the second operation. In order to be able to access an already inserted intervertebral disc prosthesis, the only possibility is to form a lateral access canal.

Such access may be necessary, for example, if it turns out that the intervertebral disc prosthesis is not optimally adapted to the geometry of the centre of motion and the intervertebral disc compartment. Moreover, in rare cases, symptoms may arise due to wear and tear of the coupling elements, which impair the mobility of the intervertebral disc prosthesis.

How the coupling element 24 of the upper constituent element 10 can be replaced by a lateral access in this case will be described below on the basis of fig. 22a to 22 d. Of course, the corresponding description also applies to the coupling element 24 'of the lower constituent element 10'.

Fig. 22a shows, in a representation based on fig. 6a, that the underside of the upper supporting plate 12 points towards the lower constituent element 10'. Through the lateral access canal leading to the intervertebral disc compartment, first the second guide plate 36 is withdrawn from its sliding into the compartment 66, as indicated by arrow 84 in fig. 22 a. To this end, for example, a wire can be placed around the projection 40 on the guide plate 36, with which the second guide plate 36 can be pulled out of the second guide plate slide into the cavity 66. The now exposed second guide plate pocket 66 shows the lateral access of the coupling element 24. The coupling element 24 is now also pulled out through the second guide plate sliding into the cavity 66, as indicated by arrow 85 in fig. 22 b. For this purpose, the slide-in plate 26 of the coupling element 24 can be provided with a hole 86. The surgeon can insert a hook-shaped instrument into the bore 86, with which the coupling element 24 is pulled laterally.

Another coupling element 424 is now inserted into the slide-in cavity 56 as indicated by arrow 88 in fig. 22 c. Finally, the second guide plate 36 is inserted into the second guide plate slide-in cavity 66, as indicated by arrow 90 in FIG. 22 d.

Of course, it is also possible in the manner described above to replace not only the coupling element 24 but also one or both of the guide plates 34, 36 by means of a lateral access, for example in order to completely fix the intervertebral disc prosthesis in the lateral direction as shown in fig. 12.

In order to keep the diameter of the anterior access canal small when inserting the intervertebral disc prosthesis, the lateral sides of the support plates 12, 12' may first be inserted anteriorly into the access canal and may only be rotated into their defined position in or near the intervertebral disc space.

This will be illustrated below with reference to fig. 23a, 23b and 23c, which fig. 23a, 23b and 23c show the upper support plate 12 in a top view in an exemplary manner. On the underside of the support plate 12, connecting elements 94, 96 are mounted, by means of which connecting elements 94, 96 the upper support plate 12 can be connected separately and in an articulated manner to operating levers 98, 100. The connecting elements 94, 96 can be designed as simple (small) bores into which actuating levers 98, 100 can be inserted. Fig. 24 shows a lever 98, which lever 98 is bent at one end to an angle of about 90 ° to form a short spike 97. The peg 97 has a diameter adapted to provide a loose fit with the hole 99 provided in the first bearing plate 12. In this way, an easily separable hinged connection is obtained between the upper support plate 12 and the operating rods 98, 100.

The connecting members 94, 96 are mounted at diagonally opposite corners of the upper support plate 12. If the upper support plate 12 is now connected to the operating levers 98, 100 by means of the connecting elements 94, 96, the upper support plate 12 can be rotated about an axis extending perpendicular to the plane defined by the upper support plate 12 as a result of the movement of the operating levers 98, 100.

If the actuating elements 98, 100 are moved, for example, in the direction of the arrows 104, 106, the upper supporting plate 12 is rotated in the direction of the arrow 108. This rotation will continue until such time as the upper support plate 12 reaches the orientation shown in figure 23 b. In this orientation, the upper support plate 12 requires a front side inlet channel, the diameter of which must correspond only to d ', where d' is the maximum width of the upper support plate 12. Indicated by d in fig. 23b is the diameter that the front inlet channel must have if the upper support plate 12 is inserted into the inlet channel with its longitudinal side forward, instead of its lateral side.

Once the upper support plate 12 is inside the intervertebral-disc compartment, it is turned back again to the position shown in fig. 23 a. For this purpose, the levers 104, 106 are moved in the direction indicated by the arrows 110, 112, and as a result of this movement the upper support plate 12 is rotated in the direction indicated by the arrow 114 into the final position shown in fig. 23 c. The actuating elements 98, 100 can now be separated from the connecting elements 94, 96 and the actuating elements 98, 100 can be pulled out of the front access duct.

Fig. 25 shows an intervertebral disc prosthesis according to a further embodiment in a side view similar to fig. 21. The prosthesis is inserted in the intervertebral-disc compartment between the two lumbar vertebrae LV1, LV 2. In contrast to the embodiment shown in fig. 21, the prosthesis does not have a ball-and-socket joint between the two constituent elements 610, 610 ', but rather a needle-like coupling comprising a recess 728 and a cone 728' with a rounded tip. Thus, cone 728' has a shape similar to a cone of tagatose.

A recess 728 is formed in the cap insert 716 of the upper component element 710. The upper bearing plate 712 has a central opening 713 through which the tip of the cone 728' passes into the groove 728.

The base of the cone 728 'is fixedly received in a groove 717 formed in the slide-in plate 726 of the lower component element 710'. A disc-shaped damping element 715 made of an elastomer or other resilient material is sandwiched between the base of the cone 728' and the base of the recess 717.

The needle-like coupling allows the lower constituent element 710' to rotate about a point of rotation located in the apex of the recess 728 formed in the constituent element 710. Fig. 26 shows the state of the intervertebral disc prosthesis of fig. 25 after the lower constituent element 710' has been rotated by a few degrees. Because the groove 728 is formed in the cap 716 of the upper component element 710, the point of rotation is directly adjacent to the center of anatomical motion represented by point 780.

The embodiment shown in fig. 25 and 26 differs from the embodiments described above in that the outer surface 720 of the cap insert 716 is not spherical. Instead, this outer surface 720 is specifically adapted to the shape of the dome 723 formed between the apophyseal rings 771 of the upper lumbar vertebra LV 1. More specifically, outer surface 720 is formed as a complement to dome 723 and there is no significant gap between one side of outer surface 720 and the other side of dome 723. Preferably, this gap has a width of less than 1mm and at least more than half the area of the inner surface of dome 723.

This fit of the outer surface 720 to the dome requires that the shape of the dome 723 be biometrically determined prior to insertion of the intervertebral disc prosthesis into the intervertebral disc compartment. To determine the shape of dome 723, a high resolution image of upper vertebra L1 may be computer processed. Outer surface 720 is then machined or molded according to the resulting biometric shape data of dome 723.

Adapting the shape of outer surface 720 to the shape of adjacent dome 723 has the following advantages: the upper component element 710 is more firmly attached to the upper vertebra L1. Since the dome is not only non-spherical but generally non-rotationally symmetrical, the cap insert 716 and the upper component element 710 as a whole cannot rotate within the intervertebral disc compartment if the surrounding ligaments exert sufficient pressure on the intervertebral disc prosthesis.

In addition, as was the case in the embodiments described above, it is not necessary to provide an additional rough coating to ensure a tighter connection between the cap insert and dome 723. Further, it may be advantageous to polish the outer surface 720 to reduce its roughness. This is due to the fact that the smooth outer surface 720 enables the cap-shaped insert 716, and therefore the entire upper constituent element 710, to adjust itself with respect to the dome 723 by means of a sliding movement when the intervertebral disc prosthesis is inserted into the intervertebral disc compartment. By applying slight longitudinal pressure, the constituting elements 710 will rotate slightly about the longitudinal axis of the lumbar vertebrae VL1, VL2 until they reach a position in which the outer surface 720 and the dome 723 are perfectly matched.

Of course, the same considerations apply to the underlying cap insert 716 'and its outer surface 720'. It should also be understood that, not only in the present embodiment, but also in other embodiments, very generally, in all the embodiments of the prosthesis having at least one convex protrusion reaching into the vault of the adjacent vertebra, it is advantageous to specifically modify the shape of the convex protrusion of the constituent elements of the intervertebral disc prosthesis.

Fig. 27 and 28 show an embodiment of an intervertebral disc prosthesis in two different rotation states in a view similar to that of fig. 25 and 26. In this embodiment, an annular damping disk 819 having elastic properties is filled in the space between the upper and lower constituent elements 810, 810'. The dampening disk 819 is preferably sufficiently rigid to carry a portion of the substantial forces that exist between the adjacent vertebrae LV1, LV 2. On the other hand, the damping disc 819 must be sufficiently elastic to allow the lower constituent element 810' to perform a rotary motion with respect to the upper constituent element 810.

Accordingly, damping disk 819 has the following advantages: on the one hand, it reduces the forces exerted on the cone 828' and the groove 828, and on the other hand, it effectively limits the rotational movement. The damping disk 819 ensures that the rotational movement is restricted smoothly, because the elastic force increases as the rotational angle increases, as compared with the protrusions 738, 738' serving as stoppers in the foregoing embodiment.

As can also be seen in fig. 26 and 27, the anatomical center of motion 880 is now located precisely in the apex of the trough 828. This is achieved by abrading a portion of the upper lumbar vertebra LV1 to the extent indicated in figures 27 and 28 by dashed line 821, which dashed line 821 represents the shape of the upper lumbar vertebra LV1 prior to abrasion. The height of the removed bone volume corresponds at least substantially to the thickness of the upper support plate 812 at the apex of the groove 828. The height may be in the range between 1mm and 5mm, preferably between 1.5mm and 2.5 mm.

Fig. 29 and 30 show an upper constituent element 910 of an intervertebral disc prosthesis according to another embodiment in top view and in cross-sectional view along line XXX-XXX, respectively. The upper constituent element 910 differs from the other upper constituent elements described above mainly in that it comprises a cap insert 916, said cap insert 916 having a shape specifically adapted to the inner groove of the apophyseal ring of the adjacent vertebra. More specifically, the cap insert 916 has a shape that is at least substantially complementary to the recess. This means that the gap between the cap insert 916 and the bone tissue located between the apophyseal rings is small, preferably not more than 1 or 2 mm. Preferably, the largest portion of the convex surface of the cap insert 916 is in direct contact with the bone tissue. However, this does not mean that the cap insert 916 must take on the large forces exerted by the adjacent vertebrae. Instead, the upper constituent element 910 comprises a support plate 912, said support plate 912 having a flat top annular region 923, against which the apophyseal ring of the adjacent vertebra rests. The support plate 912 is preferably made of a hard material having a rough surface.

In the embodiment shown, the upper constituent element 910 is assembled by inserting the cap insert 916 into the support plate 912 from below until it abuts against the annular protrusion 913. The cap insert 916 is then secured by a plate 915, the plate 915 having threads (not shown) on its circumference so that it can be screwed into the support plate 912. On the underside of the plate 915, a slide-in plate 926 with a convex spherical cap coupling is inserted in a similar manner to that shown in fig. 1 and 2.

Fig. 31 and 32 show the cap insert 916 in an enlarged view and a cross-sectional view along line XXXII-XXXII, respectively. The cap insert 916 has, in a cross-sectional view along its longitudinal axis, a substantially horizontal portion 931, the horizontal portion 931 being centrally located between two inclined portions 933, 935. The cap insert 916 has, in a cross-sectional view along its transverse axis, a first portion 937 with a steep incline and a second portion 939 with a gentler incline. The shape of this bevel corresponds to the dome shape formed between the apophyseal rings of the adjacent vertebrae.

Fig. 33 and 34 show, in a view similar to fig. 31 and 32, respectively, a cap insert 1016 in accordance with another embodiment. In addition, the convex region of the cap insert 1016 has a shape similar to the bevel of the embodiment shown in fig. 31 and 32. However, in this embodiment, the convex region of the cap insert 1016 has a shape that is slightly different from the shape of the dome between the apophyseal rings of the adjacent vertebrae. This will be explained in more detail below with further reference to fig. 35a-35c and 36a-36 c.

Referring back to fig. 33 and 34, the cap insert 1016 has a major side 1060, the major side 1060 being inclined at a major side angle δ relative to the base area 1062₁Said main flank angle δ₁At least for most vertebrae, may be in the range between 5 ° and 20 °. The opposing side 1064 is disposed opposite the major side 1060 and forms an opposing side angle δ with the base area 1062₂. Relative flank angle delta₂At least for most vertebrae, may be in the range between 25 ° and 50 °. In the illustrated embodiment, there is a transition area 1066 between the major side 1060 and the opposing side 1064, the transition area 1066 being free of any edges and thus smoothly connecting the major side 1060 and the opposing side 1064. As can be seen in fig. 33, the sloped surface of the cap insert 1016 has sides 1068, 1070, the sides 1068, 1070 smoothly sloping downward toward the base area 1062.

The top surface of the cap insert 1016 has a top coating 1073. The top coating 1073 provides a low friction effect against the cartilaginous material (cancellous bone) within the apophyseal ring of the adjacent vertebra. In an advantageous embodiment, the top coating 1073 is made of Diamond Like Carbon (DLC). Such a coating may be applied to the surface of the cap insert 1016 using ion beam deposition techniques or sputtering deposition techniques, and is not only biologically compatible, but also hard and provides a smooth surface with very low friction. With this coating 1073, an arithmetic roughness Ra of less than 10 μm or even less than 1 μm can be easily achieved, which results in a very low friction against adjacent bone material.

Instead of applying a low friction coating to the cap insert 1016, its surface may be polished by conventional means. For example, a polished surface made of titanium also ensures a very low friction value.

Fig. 35a shows the cap insert 1016 in a cross-sectional view similar to fig. 33, and shows the lower dome D1 of the adjacent upper vertebra V1 in the same cross-sectional view. As can be readily seen from fig. 35a, the shape of the dome D1 is slightly different from the shape of the cap insert 1016.

If the cap insert 1016 is inserted into the dome D1 of the upper constituent element 910 in the longitudinal direction indicated by the arrow 1074, only a small area near the apex of the cap insert 1016 comes into contact with the apex of the dome D1. This configuration is shown in fig. 35 b. Because the low-friction coating 1073 is applied to the surface of the cap insert 1016, the cap insert 1016 can be easily rotated at least 10 °, preferably at least 25 °, within the dome D1 until it reaches its final rotational position. The rotational capability is indicated by double arrow 1076 in fig. 35 b. Ease of rotation is particularly important if the prosthesis is inserted through a narrow access passage while its longer dimension is aligned along the conduit axis. This is valid even for ventral lateral access canals (ventral access canals) since even there the constituent elements of the prosthesis have to be rotated by about 20 ° before they reach the implant where they are positioned last.

Rotation may be achieved by the rods 98, 100 shown in fig. 23a-23c or by any other suitable mechanism that is detachably connected to the upper constituent element 910. In some cases, no active manipulation is required at all, or at least no manual fine-tuning is required, because of the self-centering action that occurs due to the low-friction coating 1073 and the rotationally asymmetric shape of dome D1 and cap insert 1016. The term "self-centering" means that if a compressive force is applied between the support plate 912 and the adjacent vertebrae, the cap insert 1016, and thus the entire upper constituent element 910, rotates. During implant surgery, this force is generated by ligaments extending along the spinal column. When the support plate is rotated to a position where these compression forces are symmetrical, the moment that generates the rotation disappears, and thus the rotation is stopped.

If the dynamic coefficient of friction observed between coating 1073 and dome D1 is as low as 0.1, the self-centering effect becomes significant.

If the movement of the upper constituent element 910 in the direction 1074 continues due to the tension exerted by the ligaments on the adjacent vertebrae V1, V2, the vertex region of the cap-like insert 1016, which is first in contact with the dome D1, deforms the dome D1 by displacing a portion of the cartilaginous tissue (cancellous bone). This process continues until the hard apophyseal ring 1079 of the adjacent vertebra V1 rests on the annular region 923 of the support plate 912. This final configuration is shown in fig. 35c, in which a larger area or even a large portion of the cap insert 1016 is in intimate contact with the cartilaginous tissue (cancellous bone) of the upper vertebra V1. Thin dashed line 1078 represents the shape of dome D1 before it is deformed by cap insert 1016.

Due to the rough surface of the annular region 923 and the intimate contact between most of the cap insert 1016 and the adjacent dome D1, the upper constituent element is rigidly secured to the upper vertebra V1, and therefore no additional securing mechanisms, such as screws, are required to hold the upper constituent element 910 in its final position.

Fig. 36a-36c show views similar to fig. 35a-35c, except for the cross-sectional view shown in fig. 34.

Although the shape of the cap insert 1016 is slightly different from the shape of the dome D1, it may be advantageous to manufacture the cap insert 1016 separately for each vertebra based on the biometric data obtained for a particular patient. This ensures on the one hand an optimal rotatability and on the other hand a good intimate contact between the cap insert 1016 and the dome D1. However, since the corresponding vertebrae of the human spine often have a similar shape, it may be sufficient to provide the surgeon with a set of different cap members, from which the surgeon selects the one that best fits the shape of the dome, which has been biometrically determined before.

In the above embodiments, it is assumed that the cap insert is a separate component having different material and/or surface properties. However, it may also be advantageous to prepare a separate cap insert in case a cap insert is manufactured that is individually adapted to the biometric data of the patient. In this case, only a separately manufactured cap insert can be inserted into one or more different support plates having the same standard recess for receiving the cap insert.

It is of course also possible to make the support plate and the modular cap together as a single piece. Fig. 37 shows an upper constituent element 1110 in a view similar to fig. 30, the upper constituent element 1110 having a support plate 1112 with a modular cap 1116. The surface 1173 of the cap 1116 is polished so that the arithmetic roughness Ra is less than 10 μm0.1, while producing a kinetic coefficient of friction with respect to the cartilage material (cancellous bone) of less than 0.1.

In this embodiment, a slide-in plate 1126 with a convex spherical cap coupling is placed in a plate 1115 having elastomeric properties. The material may have a thickness of greater than 1500N/MM²The modulus of elasticity of (a), which yields good damping properties. In addition to being resilient, the plate 1115 also allows for translational movement of the slide-in plate 1126. As a result, the constituent elements of the prosthesis can be moved in translation relative to one another, at least to a small extent. The superposition of the translational and rotational movements provided by the ball-and-socket joint best reproduces the movements of the healthy vertebrae of the spine. It should be appreciated that it may also be advantageous to provide the plate 1115 with elastomeric properties in any of the other embodiments described above.

The foregoing description of the preferred embodiments is given by way of example, and it is believed that one skilled in the art will readily appreciate from the disclosure provided that the present invention and its attendant advantages, as well as many other variations and modifications in the structure and methods disclosed herein may be resorted to. Accordingly, it is intended that the applicant include all such alterations and modifications as fall within the spirit and scope of the invention as defined by the appended claims and equivalents thereof.

Claims (3)

1. System for assembling different intervertebral disc prostheses, comprising:

a) a first support plate (12), the first support plate (12) having a socket (56) for removably securing a first coupler (24);

b) a second support plate (12 '), said second support plate (12') having a socket (56 ') for removably securing a second coupling (24');

c) at least two first couplings (24, 124, 424), the at least two first couplings (24, 124, 424) having different shapes;

d) at least two second couplings (24 ', 124'), the at least two second couplings (24 ', 124') having different shapes,

the first coupling members (24, 124, 424) each include a spherical cap-shaped protrusion (28), and the second coupling members (24 ', 124 ') each include a spherical cap-shaped recess (28 '), the spherical cap-shaped protrusions (28, 25, 125, 225) of the first coupling members (24, 124, 424) having different radii of curvature corresponding to the different radii of curvature of the spherical cap-shaped recesses (225 '; 325 ') of the second coupling members (24 ', 124 ').

2. The system of claim 1,

a) the first couplers each include a first base surface for attaching the first coupler to the first support plate; and

b) the spherical cap-shaped protrusion of the first coupling (24, 124, 424) is spaced from the first base surface (26'; 126; 226; 326) with different pitches.

3. The system of claim 1,

a) the second couplers each include a second base surface for attaching the second coupler to a second support plate; and

b) the spherical cap-shaped recess of the second coupling member (24 ', 124') is spaced from the second base surface (26 ', 126'; 226'; 326') have different pitches.