Intervertebral nucleus prosthesis and surgical procedure for implanting the same.

p0001The invention relates to an intervertebral nucleus prosthesis, whose job it is, the mobility in the area of ​​a disc to restore. This mobility is physiologically produced by the nucleus, which can be regarded as a mechanical joint element of the vertebral bodies.

p0002Physiologically, the nucleus is formed by a generally spherical, non-stretchable, but deformable body which is used as a ball between two Wirbelendflachen, and while allowing substantially in the center thereof, and the movements in the form of tilt, rotation and shift ,

p0003The Wirbelendflachen in turn are surrounded by concentric layers of fibers, which are called the annulus and containing fibers which are crossed diagonally from one layer to another.

p0004In this arrangement moves the nucleus, which is really a malleable but not stretchable capsule, which is filled with a hydrophilic, jelly-like substance (mucopolysaccharides) during flexion of the spine forward or backwards even backwards or forwards, which movement of the nucleus is restricted by the rear and the front fibers of the annulus and through different longitudinal bands.

p0005In a lateral inclination of the spinal column, the displacement of the nucleus stretches the fibers on the convex side. The displacement is limited by the intervertebral ligaments.

p0006During a rotation of the spine the intervertebral disc is subjected to shear forces.

p0007The nucleus, which represents a hydrophilic body has at rest a certain osmotic pressure. Under load, the nucleus loses water. The thickness of the disc decreases as the pressure is reduced again, rehydration occurs.

p0008The pathological conditions that interfere with the reciprocal movements of the different vertebrae, thereby essentially overloading or excessive and frequent exposure or natural aging processes.

p0009With too strong, too frequent or prolonged exposure rehydration does not occur and hence the pressure exerted by the nucleus on the various concentric layers of the annulus forming fibers are no longer built, so no longer plays even this pressure the role of the provision in the movements. In this case occurs instability and an accompanying osteoarthritis.

p0010It is an object of the invention to prevent the development of this instability, characterized in that a nucleus prosthesis is inserted, which can take place in vivo implantation and with less trauma than has hitherto been possible with known prostheses of this type.

p0011These known prostheses, the principles of which are considered below, show drawbacks, which can be understood if one knows the mutual movements and the role of the nucleus in these movements.

p0012These disadvantages occur both during use and during insertion of these known implants.

p0013First is simply proposed to remove the discs, which are located in the traumatized area. Then you have a bony grafting used, some with and some without osteosynthesis.

p0014The achieved thereby blocking two adjacent vertebral bodies, however, only transfer the loads on the intervertebral discs of the directly adjacent vertebral bodies, which were characterized overstressed and damaged quickly, the problem is therefore only moved and has not been resolved.

p0015It has been further proposed a complete spinal disc prosthesis comprising both annulus and nucleus.

p0016This practice has the major disadvantage that to complete removal of the damaged disc is necessary and that the total prosthesis must then be inserted between two adjacent vertebrae.

p0017For both phases of this intervention must be cut through the common vertebral longitudinal bands, namely the anterior longitudinal ligament (LVCA) and the posterior longitudinal ligament (LVCP) so that you can not restore the natural movements of the spine, this lost thus a reliability.

p0018In order to avoid these disadvantages, it is considered within the scope of the present invention from the fact that a nucleus prosthesis is used without resecting the entire intervertebral disc. In this way can be achieved by replacing the nucleus already developing the instability limit, which is the cause of the deterioration.

p0019The nucleus prosthesis allows without damaging the annulus or the longitudinal straps (LVCA and LVCP) by the displacement of the replaced nucleus to exert pressure on the annulus and therefore to tension it in the movement of the spine so that it restores the equilibrium position.

p0020The center of rotation, which has been restored in this manner, actually remains movable and to adapt the location to the various bending movements forwards and backwards of stretching movements and lateral inclination movement.

p0021The document <patcit id="pcit0001" dnum="EP0621020A"><text>EP 0621020</text></patcit> discloses a Zwischenwirbei-nucleus prosthesis to replace a portion of the core portion of an intervertebral disc, capable of transmitting compressive forces. of at least three movable, in particular spherical, bodies of a non-oxidizing material, the volume of which is matched to that of the biological nucleus

p0022The nucleus prosthesis of the present invention is defined in Claim first This prosthesis can be accommodated in the volume, which is released after the removal of the nucleus between two Wirbelendflächen. The <figref idrefs="f0001">figure 1</figref> shows a top view of a vertebral body with the respective positions of the nucleus, the annulus and the anterior and posterior longitudinal ligaments. The <figref idrefs="f0001">figure 2</figref> is a perspective view of a vertebra showing the annulus and the nucleus surrounded by him, which is supported on the vertebral body. The <figref idrefs="f0001">figure 3</figref> is a perspective schematic view of a diametrically sectioned annulus and showing the concentric, intersecting layers of fibers.

p0023The <figref idrefs="f0001">Figures 4 and 5</figref> are schematic side views of two adjacent vertebral bodies at a flexion movement forward or back.

p0024The <figref idrefs="f0001">figure 6</figref> is a schematic front view of two adjacent vertebrae during a lateral flexion of the spine.

p0025The <figref idrefs="f0002">figure 7</figref> is a top view of a vertebral body during a rotation movement.

p0026The <figref idrefs="f0002">Figures 8, 9 and 10</figref> are schematic views from the side, from above and from the front of a Nucleus prosthesis with only one ball, not according to the present invention.

p0027The <figref idrefs="f0002">figure 11</figref> is a schematic, exemplary longitudinal sectional view along line AA in <figref idrefs="f0002">figure 8</figref>,

p0028The <figref idrefs="f0002">Figures 12, 13 and 14</figref> are schematic views from above, from the front and from the side of a nucleus prosthesis with a plurality of balls.

p0029The <figref idrefs="f0002">Figures 15, 16 and 17</figref> are schematic views from above, from the front and from the side of a nucleus prosthesis with a damping device.

p0030The <figref idrefs="f0001">Figures 1 and 2</figref> show good an intervertebral plane formed by a plurality of concentric layers of intersecting fibers 1 and 2, clearly visible in <figref idrefs="f0001">figure 3</figref>, And in the center of each of the Nucleus 3 is arranged, while (LVCP) 5 are arranged on the outside of the anterior longitudinal ligament (LVCA) 4 and the posterior longitudinal ligament.

p0031The <figref idrefs="f0001">Figures 4 and 5</figref> show the compressive forces exerted by the nucleus 3 on the concentric Annuluslagen, in each case on the outer side of the bending angle at a bend forwards or backwards.

p0032The nucleus 3 exerts in the same way a pressure on the rings of the annulus, on the outside of the seit1ichen inclination angle (<figref idrefs="f0001">figure 6</figref>).

p0033Each of these displacements of the nucleus 3 ensures a return to the equilibrium position.

p0034At a rotation in a horizontal plane, it is the joint capsules 6 which lie along a fictive circle on the outside, which allow the circular displacement and which limit the rotational movement (<figref idrefs="f0002">figure 7</figref>), The nucleus 3 is thereby subjected to shear forces.

p0035Thus, the nucleus plays in all these cases, the role of a motion damper and provides in this movement, the return to the equilibrium position safely. It can be seen from the consequences which are established when the nucleus is altered.

p0036It can be seen from this also, that a restoration of reciprocal movements of adjacent vertebrae can be achieved already in that one uses a nucleus prosthesis, the implant is a very large surgical advantage.

p0037The existing surgical techniques, surgical vertebral fusion leads to a permanent fusion of adjacent vertebrae, which are located on either side of the damaged disc. To this end, the disc is completely removed.

p0038When the fusion of two vertebrae is achieved by arthrodesis, then the problems of degeneration of the adjacent discs are wearing (up or down) exceeded, these problems are heightened by the strength of the vertebral block thus generated.

p0039However, if the merger succeeds, what is the reason for frequent failures and resulting in a continuation of the complaints, then you can often nachoperieren very difficult.

p0040In the case of implantation of a total prosthesis of the intervertebral disc, it has been found that this makes a complicated and difficult surgical procedure necessary which requires a large opening to remove the natural disc and to be able to use the full denture.

p0041This includes the need to cut through and the displacement of large abdominal vessels (aorta and vein) and the nerve bundle of the sexual organs.

p0042This results in the risk of major vascular bleeding that are difficult to control.

p0043This can also lead to serious sexual problems: impotence and retrograde ejaculation.

p0044In addition, the total resection of the disc leads to a destruction of the entire annulus, and the front and rear intervertebral longitudinal bands 4 and 5, thereby creating serious instability risks.

p0045There is also in this case no return, it remains only the way of spinal fusion with the disadvantages described above.

p0046The invention nucleus prosthesis does not have these disadvantages. It makes it possible to replace the damaged nucleus in both the form and the function to. It is suitable to stop the degeneration of the intervertebral disc in that it stabilizes this again.

p0047The surgical implantation procedure is extremely simple.

p0048Initially, the implantation can be performed endoscopically. It is quickly and gently.

p0049In case of failure can be prepared by removing the nucleus prosthesis to its original state again.

p0050It is not connected with vascular risk and even with risks for the sexual organs.

p0051It suffices in fact, endoscopically incorporate an opening between two vertebrae through the annulus through which is just large enough to reach the injured nucleus and to remove and to then introduce the same way the artificial nucleus, which automatically centers itself in the original chamber , then the opening is closed by a seam produced.

p0052Regardless of that, this intervention is fast, can the Faserk6rper, which is only slightly damaged by the incision, recover spontaneously and quickly and virtually painless. The front and rear longitudinal bands are traumatized in any way, so that you can restore the original flexibility of the spine.

p0053The easy implantation of this nucleus prosthesis and the fact that no risks occur in this engagement, resulting in its application is always displayed when primary or secondary disc damage have occurred, namely already at the first appearance of the disease before definitive damage of the bone and joints may occur.

p0054The nucleus prosthesis consists essentially of at least one movable body 8, of a solid, non-oxidising, bio-compatible material, which can move in two axes of a plane (for example, a stainless steel ball or a ball made of titanium), the volume of which is adapted that of the biological nucleus. This movable body or these ball B is mounted in a cage as described in the following recorded body 7 which comprises a housing 14 (by way of example in<figref idrefs="f0002">figure 11</figref> shown) which consists of a lightweight, strong, non-oxidizing and biocompatible material (for example titanium), said housing 14 contains a mass 15 of a material having a minimum coefficient of friction (for example polyethylene). Inside there is a receiving space for the movable body or ball 8, this is captured in this receiving space, however freely around its center point rotated and so mounted that it on two opposite sides (top and bottom) of the cage 7 in the form a spherical cap leaking, the amount of which corresponds to about 1/10 of the diameter of the movable body or ball 8, this value does not have to be strictly adhered to.

p0055The volume of the cage 7, which receives the mobile body 8 is, for its part, as closely as possible adapted to the volume of the biological nucleus, is of course taken into account that the cage 7 must serve as a bearing for the ball eighth Thus, the prosthesis can position itself, she is thus possible to always be in the anatomical position, thereby restoring the natural movement between two vertebrae.

p0056The ball 8 overlapping cage 7 can in top view (<figref idrefs="f0002">figure 8</figref>have) a more or less curved shape which is symmetrical with respect to a transverse mid-plane. In cross section (<figref idrefs="f0002">figure 10</figref>), Preferably, the cage has the shape of a trapezium, the small end face receives the ends of the more or less strongly curved shape.

p0057This trapezoidal front oriented backward asymmetry of the cage 7 causes thereof that rotation is prevented between the two vertebrae when the in this way formed, the artificial nucleus (ball 8) receiving the prosthesis moves.

p0058When the <figref idrefs="f0002">Figures 12, 13 and 14</figref> illustrated modified embodiment, the cage 7, which has substantially the shape of a cross section having an isosceles trapezium s (<figref idrefs="f0002">figure 13</figref>), A number of identical balls 8 (<figref idrefs="f0002">figure 14</figref>) Record the touch on the outside of a common imaginary plane, which are arranged on both sides of the horizontal center plane of the cage. The balls are located on both sides of the cage 7 at the three corners of an equilateral triangle.

p0059To increase comfort, the cage 7 can according to embodiments of the <figref idrefs="f0002">Figures 15, 16 and 17</figref> consist of two identical individual bodies 10, 11, the test, are not formed oxidizable and biocompatible and having the shape of an isosceles trapezoid. They are so arranged that their perpendicular on the parallel base faces, along the center lines extending center planes are substantially parallel to each other and that the large base faces of the trapeze-shaped individual bodies 10 and 11 lie substantially in the same vertical plane.

p0060The two thus formed single body are interconnected by two resilient bearing members 12 and 13 which are perpendicular to the center planes of the individual bodies run 10 and 11 and disposed near the end of a major axis, which in turn have a common tangent of the sets of balls 8 forms, which are arranged at each outer side of the assembly so that the balls are arranged at the three corners of an isosceles triangle, which in turn have on opposite sides of the assembly in opposite direction.

p0061If a prosthesis in accordance with the <figref idrefs="f0002">Figures 8 to 17</figref> is used, then it is understood that the prosthesis already takes over immediately after the insertion into the cavity of the nucleus, the role of the biological nucleus, and sets the intersecting fibers of the annulus at a side or at a movement forward or backwards under tension and thereby produces a return to the equilibrium position. The rapid engagement, which is necessary for the insertion, avoids any Traumatisierungsrisiken and leads to a rapid healing of only the necessary opening.

p0062The final selection of the proposed models, which all have the same advantages in terms of onset and with regard to the physiological results will arise due to the clinical results over time.

p0063Of course, the cage 7, containing a ball 8 or several balls 8 and for the several embodiments are described above has been proposed, without departure from the inventive idea also have other equivalent forms, it is important only that he the ball or balls 8 superimposed that they are free to rotate with it and that its volume is adapted to the volume that is available after removing the biological nucleus.

p0064The described nucleus prosthesis can in all embodiments described above spontaneously in the anatomical environment take their own position, so that all the natural movements between two vertebral bodies can be recovered (lateral inclination, tilt forward and backward rotation). The conical shape (in cross section a trapezoidal shape) of the cage 7 facilitates the shift in the plane of Wirbelendflächen while preventing the rotation of the cage about its central axis, as well as the sinking of the implant in the Wirbelendflächen.