Intervertebral prosthesis

p0001The invention relates to an intervertebral implant comprising an elongate, elastic body. A prosthesis of this kind is known from<patcit id="pcit0001" dnum="EP0453393A"><text>EP-A-0453393</text></patcit> known. It is used to replace a damaged disc nucleus (nucleus pulposus). Here, the outer ring (annulus fibrosus) of a natural disc is largely maintained. The known prosthesis consists of a liquid-tight hollow body, which is filled with an incompressible, flowable medium. This prosthesis required for their implantation, a specially trained insertion instrument with which the hollow body can be intra-operatively wound into spiral shape, and then filled. This places high demands on the skill of the surgeon on the one hand, and to the manufacture of the insertion tool with respect to the take-up mechanism, as well as with respect to the filling device. Furthermore, the tightness criteria of the hollow body at rest in view of the high stresses in the spine in the long run a risk. After the body has been rolled up and filled in the intervertebral area, is located on the free end of the annulus fibrosus, if the auxiliary tool, which for filling and sealing in the center the spiral acts, is removable without causing cavities. Only if there is no migration of spiral parts can be done in other cavities can occur during loading, radially directed forces are compensated and the spiral is given the desired support function.

p0002In the <patcit id="pcit0002" dnum="FR2712486A"><text>FR-A-2712486</text></patcit> Showing that of shape memory alloys (memory metal) exist which deform due to a physical phenomenon of a stress-free state in another form with energized condition helical implants for the core area of ​​an intervertebral disc. As a physical phenomenon, the occurrence of a tensile stress and a change of temperature are listed, which modify the original physical conditions. Other examples show tick studded conveyor belts, which are drawn through a tube to wind an entrained, tick filled band into a spiral.

p0003<patcit id="pcit0003" dnum="US3867728A"><text>US 3,867,728</text></patcit> among other things, describes an intervertebral implant in the form of an oval disk, which shape is achieved by varying the thickness of a aufgewickelden elongated body.

p0004The object of the invention is to provide an implant, which allows easy handling.

p0005This object is achieved by an implant according to claim 1. The cross-section of the body is preferably rectangular, wherein the edges may also be rounded. It is also possible to use the body with a roundish cross-section, while under load a substantially form-fitting, tilt-up position of the spiral remains. The cross-section of the elastic body is not constant over its entire length, but the thickness decreases towards the outside. Such spiral has the advantage that they are self-stores, while pushing the conduit does not buckle and can be separated in a matching wound length.

p0006The implant can assume the shape of a cylinder as such disc so be flat, or else following the contours of the vertebral surfaces have bulges outwards and / or inwards. This ensures that distribute the forces generated under load evenly to the vertebral surfaces. The diameter of the spiral is preferably dimensioned so that the space within the annulus fibrosus is filled.

p0007To introduce the intervertebral disc, it has proved advantageous to attach stiffening means in the form of a plastic or metal strip at the free end of the spiral, through which a separation device can be guided up to an intended separation point. The band has the force-free state, preferably to no curvature. After implantation, the band is removed together with the unnecessary portion of the deposited spiral coil by means of the separating device.

p0008In order to control the position of the implant intra- and post-operatively, the provision of X-ray-positive marks in the form of beads or a thread recommends on or along within the elastic body.

p0009The material from which the elastic body is made substantially corresponds to the elastic properties of an intervertebral disc, so that the forces are transmitted as evenly as possible to the vertebral surface. An advantageous use of polyurethane or polyurethane-silicone mixtures has been found which have a Shore hardness in the range of approximately 80A. also possible to use foams of different plastics, provided they satisfy the elastic requirements.

p0010In a particularly preferred embodiment, the Spriale on a key centerpiece around which to create the other turns tightly. There arise only small gaps, which may optionally fill in the implanted state with disc liquid and do not allow tilting of the elastic body under the radial forces. A suitable Höhenzu width ratio canting of the elastic body is generally prevented. The center piece can basically have a circular cylindrical shape, but also forms such as spherical or ellipsoid have been useful. This is followed advantageously includes a short, thinner transition part, through which the connection is prepared for further spiral. This has the advantage that the spiral remains in the densest, surface-fitting package and the greatest possible surface distribution is achieved by reduction of power peaks. In a simpler embodiment of the implant, the central Centerpiece be omitted because its surface area relative to total contribution is small.

p0011The height of the spiral corresponds to the physiological intervertebral spacing substantially. From the elastic properties of the material used results in the preferred thickness, in which the elastic body is to be formed. At the periphery of the spiral, after about three to five turns, depending on the material and width of the winding, the thickness of the body may decrease, since the applied forces should be primarily taken centrally and partly since the body at the appropriate place will be deemed severable. In a further embodiment of the invention, it is possible to adjust the individual Wirbelanständen the height of the implant.

p0012The separation should preferably be carried out within the cavity, for which the corresponding forces must be applied by means of an instrument to be described later.

p0013This also provides a process for the preparation of an intervertebral implant in a spiral shape will be described. As a manufacturing method, an injection molding method is used, wherein the helical mold is cast in the coil interior. The implant thus obtained has a spiral shape with strongly positive turns.

p0014Further, a device for the introduction of the implant is described, which comprises essentially a tube of rectangular cross-section, in which the elastic body may be recovered and preferably so far that the middle piece or protrudes from the distal end of the tube. The cross-section of the tube substantially corresponds to the cross section of the elastic body. The feed of the body can take place by hand. Preferably however the feed means are provided in the form of a plunger with a corresponding cross-sectional enlargement of the pipe, can be activated via a lever mechanism for example. The plunger has at its distal, operatively connected with the elastic body or the stiffening end to agents which facilitate an advancing of the body. The means may consist roughen the surface, or even in tooth-like projections with preferential orientation in the distal direction. This ensures that the extensions engage in advancing the plunger in the elastic body or the stiffening and they set it / with it while sliding over the surface with retraction of the ram to the rear. Thereby, a controlled feed of the elastic body is possible. Of additional advantage is to design the tube at its distal end with a unilateral cross-sectional constriction, which only can absorb the elastic body at its narrow end. This causes the plunger during advancement is simultaneously pressed down and thus enhances the adhesion between stem and body.

p0015The tube of the insertion device can advantageously be curved, since the introduction of the implant into the disc space is preferably carried out from the side dorsally. The curvature can be performed both upwards or downwards, and optionally to the left or right depending on which side is to take place of the access. Here, the introduction device also forwards expire wedge-shaped to adequately space neighboring vertebrae after entstandenem spacing loss again with the wedge-shaped part.

p0016Described is further an apparatus for separating the unnecessary spiral end. After the intervertebral prosthesis has been implanted, the insertion is along the stiffening, which at least partially remains outside the disc area, withdrawn and postponed the severing. This instrument preferably has a mechanism of action similar to pliers, comprising two handle parts that are available through a link with each other. One jaw of the cutting part is hollow so that it can accommodate the stiffener. The other jaw has a cutting edge which is transverse to the longitudinal axis of the chuck substantially. The length of the jaws as well as the arrangement of the cutting in a distal direction are preferably chosen so that on the one hand, a cut in the intervertebral area is possible, on the other hand even the necessary Abtrennkräfte can be safely applied. Here, the elastic body is enclosed so that when separating the unneeded spiral end any foreign tissue parts are recorded. Of course, according to the invention can also find use pliers, are their grip parts at an angle to the longitudinal axis.

p0017In a particularly preferred embodiment, the introducer also include a cutting instrument. This is for example realized by that another ram is provided at its distal end with a cutting blade which is transverse to the longitudinal axis of the device. The cutting action is generated by the distal cross-sectional constriction of the pipe, similarly to the feed.

p0018The implant has the advantage of being simple in construction as possible and to secure a supporting effect uniformly over a large part of its surface. The implant also has not be fixed by additional means in a spiral shape to have the advantage, but can be introduced with relatively simple and safe to use instruments.

p0019In the following the invention will be explained in more detail with reference to a particularly preferred embodiment in connection with the drawings.<dl id="dl0001"><dt>Fig. 1</dt><dd>schematically and greatly enlarged the elastic body in the form of a spiral;</dd><dt>FIG. 2</dt><dd>shows a cross section through the spiral <figref idrefs="f0001">Fig. 1</figref>; </dd><dt>Fig. 3</dt><dd>shows a schematic representation of a delivery device;</dd><dt>Fig. 4</dt><dd>shows a schematic representation of a separation and</dd><dt>Fig. 5</dt><dd>schematically shows a plan view of the separating device according to <figref idrefs="f0003">Fig. 4</figref>,</dd></dl>

p0020The figures act of an implant, in particular an intervertebral prosthesis, consisting of an elongated elastic body which is elastic in shape and in the force-free state in the form of a spiral S assumes. The spiral can be collected by Rückwärtsaufziehen in an introducer, which is only slightly larger than the cross section of the elongated elastic body in the insertion to achieve through a small opening in the annulus fibrosus the interior of an intervertebral disc and insert the self-coiling spiral and separate, if the interior is filled. This has the advantage that different size interiors with the same spiral can be filled.

p0021<figref idrefs="f0001">Fig. 1</figref> shows the spiral-shaped implant with a central middle piece 1, which has the form of a cylinder substantially. It laterally includes a thinner region 2 which a strong bending and thus a positive transition to the adjoining spiral winding 3, substantially without intermediate spaces allows.

p0022For the case where the center piece is omitted, it is recommended the inner end of the spiral in such a way that under load can no surges. This can be achieved for example by a rounded end.

p0023The adjoining the transition region scroll wraps are positively and have a constant width in the range of 2 to 5 mm, so that tilting is ruled out as far as possible under the load to be expected. The implant preferably includes at 2-4 tilt-safe turns. By this includes a transition region 4 on, in which the width of the elastic body is reduced such that approximately in the range of 5<figref idrefs="f0001">Fig. 1</figref> easy separation becomes possible. By the number of turns of the spiral is intra-operatively adjusted to the desired size. The supporting effect with respect to tipping in the outer narrow windings decreases as such, but in conjunction with the dimensionally stable inner turns sufficiently large.

p0024The thickness of the elastic body forming the spiral, but may also decrease steadily from the inside, so that no specially trained transition region is necessary. In<figref idrefs="f0001">FIG. 2</figref> is shown in cross-section the spiral. It has a diameter in the range of 20 to 30 mm, preferably in the range of 23 to 25.5 mm. The amount is preferably 5-10 mm. The amount may be increased continuously in a central direction and take the center up to 10 mm. The height can also be the individual course of the vertebral surfaces to be adjusted, which may be in vertebral deformations of interest in particular.

p0025To the free end of the coil 6 a band-shaped stiffener 7 is fixed, which protrudes beyond the free end and serve as an extension of the spiral during handling. The transition should be as smooth as possible. The tape should be to transfer shear forces capable of and is preferably made of biocompatibility and sterilization reasons of titanium. Its length is a practical way about 20 cm and enables management of Abtrenninstrumentes to separation point of the spiral.

p0026The elastic body is made of plastic, such as polyurethane, wherein the spiral turns come to lie largely förmschlüssig in the force-free state. The elastic properties of the material must be such that even after rolling out, again the spiral form is ingested. The deformation properties of the material to be largely similar to those of the disc and in the Shore hardness of 70A to 90A, preferably 80A lie.

p0027The elastic body can be cut to its manufacture from the material, which is possible in particular with computer controlled lasers. Cutting operations, which are thermally not strain the material preferred because toxic by-products are avoided and taken no influence on the elastic properties of the material. It must be noted that the material should be sterilizable as such.

p0028In order to control the position of the implant intra- and post-operatively, the provision of X-ray-positive marks in the form of points 8 or a thread not shown in the pictures is recommended to or along and within the elastic body. As marker material can be found barium, tantalum or similar use.

p0029The device for the introduction of the elastic body is in <figref idrefs="f0002">Fig. 3</figref> shown in more detail. It comprises a square tube 10 for receiving the at least so far rolled spiral that you still protruding portion S can be easily inserted through the surgically created opening in the intervertebral area. The hollow tube 10 preferably has a one-sided cross-sectional constriction 11 at the distal end on which is conical or beak-like. The tube may also have a curvature that is the access to the intervertebral area of ​​laterally off the dorsal facilitated and on the handedness of the user. The curvature can also be directed in a caudal or cranial, depending on requirements.

p0030The feed of the body can also be done by hand. Here handle means are supporting around the pipe helpful. They can be formed coaxially with the tube in the form of a thickening or extend radially to the tube axis. Preferably however the feed means are provided in form of an elastic plunger 12, can be operated via a lever mechanism 13 for example. The plunger has at its distal, standing with the elastic body or the stiffening operatively connected end to means 14 that facilitate advancement of the body. The means may consist roughen the surface, or even in tooth-like projections with preferential orientation in the distal direction. This ensures that the extensions engage in advancing the plunger in the elastic body or the stiffening and they set it / with it while sliding over the surface with retraction of the ram to the rear. In this case, a controlled feed of the elastic body is possible. The unilateral cross-sectional constriction 11 of the rectangular tube 10 causes the ram when advanced is simultaneously pressed down and thus enhances the adhesion between stem and body. The fact that the plunger very far forward to engage the unwound spiral, this is practically pulled through the hollow tube, so they can not be blocked even under their own power, as it could easily be in thrust from behind the case.

p0031<figref idrefs="f0003">FIGS. 4 and 5</figref> show a device for separating the superfluous spiral end. After the intervertebral prosthesis has been implanted, the insertion device along the stiffener 7, which remains outside the disc area, withdrawn and postponed the severing 20th This instrument preferably has a mechanism of action similar to pliers, comprising two handle portions 21,22, which are connected via a joint 23 with each other. One jaw 24 is provided longitudinally with a recess 25 into which the stiffener 7 and / or the elastic body can be 5.6 was added. The other jaw 26 has a cutting edge 27 which is transverse to the recess 25 movable substantially. The length of the jaws as well as the arrangement of the cutting edge in the distal direction is preferably chosen so that on the one hand a section within the intervertebral region is possible, on the other hand even the necessary Abtrennkräfte can be safely applied. The cutting blade itself can be designed as a replaceable blade. Of course, according to the invention can also find use pliers, are their grip parts at an angle to the longitudinal axis.

p0032After the elastic body has been shortened to the desired length, the separating device is retracted together with the stiffening 7th The implant takes account of its shape-retaining properties of the spiral shape. The implant also retains under load at its spiral shape without a special fixing the free end would be necessary.

p0033The previously described method for introducing a helical implant into a cavity, advantageously comes to teaching, practice, and demonstration purposes for use.