Abstract:
A device for dynamic stabilization of bones or bone fragments comprising at least one anchor member for attachment to vertebrae having an opening configured to receive a longitudinal member; and the longitudinal member being viscoelastically deformable and having a predetermined bending resilience.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of pending International Application No. PCT/EP2005/003962, filed Apr. 14, 2005, which claims the benefit of German Patent Application No. 10 2004 048 938.6, filed Oct. 7, 2004, the entire contents of both of which are expressly incorporated herein by reference thereto. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a device for dynamic stabilization of bones or bone fragments, especially vertebrae of the back, having at least one longitudinal member fixable to the vertebrae. 
     BACKGROUND OF THE INVENTION 
     Principal indications for dynamic, especially posteriorly performed, fixation are age- and/or disease-related decay (degeneration) of the integrity of the spine structures, inflammation and/or injuries in the region of the intervertebral disc, of the ligamentous apparatus, of the facet joints and/or of the subchondral bone. 
     Posterior dynamic fixation systems have the function of modifying the pattern of movement in the segment of spine in question that the pain caused by chemical irritation (material of the nucleus in contact with nerve structures) and/or by mechanical irritation (hypermobility) disappears and the metabolism of the structures is preserved or restored. 
     Clinical experience with existing posterior dynamic fixation systems as described, for example, in EP 0 669 109 B1 and in the manual “Fixateur externe” (authors: B. G. Weber and F. Mageri, Springer-Verlag 1985, page 290-336) shows that it is advantageous for a posterior dynamic fixation system to be flexible in respect of bending and rigid in respect of compression (buckling), shear and rotation. A system must accordingly be dimensioned for maximum deformation with regard to flexion and for maximum loading with regard to buckling, shear and rotation. In order to be able to combine these intrinsically contradictory conditions, it has already been proposed to manufacture the longitudinal members from a biocompatible high-performance plastics material. Because of the very low modulus of elasticity of the high-performance plastics materials compared to titanium and steel, the longitudinal members have to be of relatively thick construction compared to the longitudinal members conventionally manufactured from clinically used metal, which although having a positive effect on the resistance to shear and to buckling is detrimental to flexibility. 
     In addition, when using conventional biocompatible high-performance plastics material for longitudinal members, it is problematic that the plastics material in the mechanical fixing “creeps away” at the clamping sites after a relatively short time under the forces occurring therein, with the consequence that re-fixing or even re-implantation becomes necessary. 
     The possibility of being able to bend longitudinal members is of great importance especially in the case of posterior stabilization by means of pedicle screws, because the anatomical conditions are often such that the pedicle screws screwed through the pedicles and into the vertebrae are misaligned. In order that the longitudinal members can nevertheless be connected to the pedicle screws in as stress-free manner as possible, it must be possible for the shape of the longitudinal members to be matched in situ to the position and orientation of the pedicle screws. In the case of polyaxial pedicle screws, the bending adjustment can be limited to one plane, whereas in the case of monoaxial pedicle screws the longitudinal members have to undergo bending adjustment in three dimensions. 
     A further constructional form for a dynamic fixation system is proposed in EP 0 690 701 B 1. This last-mentioned system comprises a connecting rod, the extremities of which are fixable to two neighboring vertebrae and which has a curved central portion so that it is resiliency yielding within certain limits. Otherwise, the connecting rod is not modifiable in respect of how it is shaped. 
     Also, WO 01/45576 A1 proposes a dynamic stabilization system comprising a longitudinal member having two metallic end portions which are fixable in complementary accommodation apertures within the heads of two neighboring pedicle screws. Arranged between the two end portions is an articulation member which is resiliency yielding in the longitudinal direction, preferably made of resiliency yielding material. The two end portions of the longitudinal member are rigid. In addition to that articulation member, the arrangement of a resilient band between two pedicle screws is proposed, which extends parallel to the resilient articulation member. Otherwise, in the case of that arrangement too, the articulation member is, in respect of its longitudinal extension, predetermined during manufacture, that is to say it cannot be modified. 
     Mention should also be made finally of the arrangement according to FR 2 799 949, which is characterized in that the longitudinal member is in the form of a spring element, for example in the form of a leaf spring having a meandering curve shape. 
     Also, the longitudinal member in the case of the arrangement according to WO 98/22033 A1 comprises a spring element which retains its predetermined shape. 
     Also, EP 1 364 622 A1 describes a resilient stabilization system for spines which consists of a resiliently flexible connecting element or longitudinal member which can be passed through the apertures of a plurality of pedicle screws having offset aperture axes and anchored. That connecting element or longitudinal member should preferably be made of a resiliently flexible biocompatible material, preferably plastics material. Aromatic polycarbonate-polyurethane is mentioned as being especially advantageous. This is obtainable as a commercial product, for example under the Trade Mark BIONATE® from Polymer Technology Group, 2810 7th Street, Berkley, Calif. 94710 USA and CHRONOFLEX® C from CardioTech International Inc., 78E Olympia Ave., Woburn, Mass. 01801-2057, USA. The known connecting element or longitudinal member should have sufficient bending resilience about all axes of its cross-section to allow its insertion even into apertures of screw heads that do not lie on one axis but on a line of any desired course or that are naturally offset in various directions because of differing vertebral arrangements. 
     The integration of spring elements into a longitudinal member is also described in GB 2 382 304 A, U.S. Pat. No. 5,480,401, DE 42 39 716 C1, FR 2 827 498 A1, EP 0919 199 A2 or JP 2002/224131. It is common to all these last-mentioned arrangements, however, that they have a relatively complicated mode of construction, that being the case, more specifically, because the mentioned spring elements are integrated as additional components or structural units. In that prior art, the spring elements are not intrinsic to the longitudinal member. 
     The present invention is based on the problem of providing a device for dynamic stabilization of bones or bone fragments, especially vertebrae of the back, having at least one longitudinal member fixable to the vertebrae, which longitudinal member can be matched without complication to the very great variety of stations for implantation without the dynamic being lost and can be firmly fixed lastingly, especially to so-called pedicle screws. 
     SUMMARY OF THE INVENTION 
     The problem is solved in accordance with the invention by the characterizing features of a device for dynamic stabilization of bones or bone fragments comprising: at least one anchor member for attachment to vertebrae having an opening configured to received a longitudinal member; and the longitudinal member being viscoelastically deformable and having a predetermined bending resilience comprising a biocompatible plastics material, whereby the plastics material provides for viscous deformability, and a biocompatible metal, whereby the metal provides for resiliently flexible deformability. 
     The longitudinal member preferably is “viscoelastically” deformable and in each shape state has a predetermined bending resilience. The latter should be imparted especially by a metal portion whereas otherwise the longitudinal member is made principally of plastics material that is tolerable to humans, especially of polycarbonate-urethane or PCU, as is commercially available, for example, under the Trade Mark BIONATE®. The longitudinal member is therefore specifically in the form of a compound construction and consists, on the one hand, of plastics material and, on the other hand, of metal that is tolerable to humans, especially titanium or titanium alloy, the plastics material being primarily responsible for the viscous deformability and the metal being primarily responsible for the bending resilience. 
     As already mentioned, conventional biocompatible plastics materials have the disadvantage that, after being subjected to mechanical pressure for a relatively long period, they yield to that pressure and actually “creep away” under that element of pressure. There is accordingly a risk of the implant becoming loose with obviously disadvantageous consequences. In order to resolve that problem without otherwise losing the afore-mentioned disadvantages, metal is provided, in accordance with the invention, at the clamping sites of the longitudinal member. Clamping is accordingly carried out directly at the metal of the longitudinal member so that the afore-mentioned problem no longer occurs. 
     Preferred, advantageous material properties of the plastics material that is tolerable to humans or biocompatible are: 
     
       
         
               
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 tensile strength at 50% elongation 
                 about 650-5500 
                 psi 
               
               
                   
                 tensile strength at 100% elongation 
                 about 900-6000 
                 psi 
               
               
                   
                 ultimate tensile strength 
                 about 6500-11000 
                 psi 
               
             
          
           
               
                   
                 ultimate limit of elongation 
                 about 250%-600% 
               
             
          
           
               
                   
                 modulus of elasticity 
                 about 4000-270000 
                 psi 
               
               
                   
                 bending stress on 5% deflection 
                 about 150-11000 
                 psi. 
               
               
                   
                   
               
             
          
         
       
     
     It is also advantageous for the plastics material to have a temperature expansion coefficient (×10 6 ) of 90/° C. to 150/° C. 
     Alternatively, besides polycarbonate-urethane (PCU), the plastics portion can also consist of polyurethane, silicone-urethane copolymer or like material or a mixture thereof. The preferred criteria is that the parameters mentioned above are present or that the material has similar properties to PCU. 
     The dimensions and the proportions of plastics material and metal are preferably so selected that the longitudinal member, when held at one extremity, can be resiliently deflected, within a predetermined shape state, about an angle of 5° to 12°, especially about 7° to 9°, over a length which corresponds to the spacing between two neighboring vertebrae or about 2-5 cm. To be resiliently deflected means that, after deflection, the longitudinal member or the corresponding portion of the longitudinal member restores itself 100% automatically after deflection. 
     It should be mentioned at this point that the device preferably is also suitable for anterior implantation when it is necessary for the point of rotation of the spine segment in question to be moved anteriorly. 
     As a result of the compound construction it is also possible to reduce the dimensions of the longitudinal member consisting primarily of high-performance plastics material to a minimum, that is to say for it to be made substantially smaller than a longitudinal member were it to be made exclusively from biocompatible high-performance plastics material. 
     In addition, the metal portion on the one hand should be so dimensioned that its critical bending angle is greater than or equal to the maximum bending angle of the stabilized vertebra that is present in association with the dynamic fixation system and on the other hand should be so constructed that the longitudinal member remains dimensionally stable after the in situ bending adjustment. 
     DE 93 08 770 U1 describes a plastics rod having a metal core. That plastics rod serves as a test rod or template in order to be able to match the shape of the longitudinal members to the position and orientation of the pedicle screws in optimum manner. For that purpose it must be possible for the shape of the test rod to be adjusted by hand in situ in the patient. The test rod accordingly consists of a soft plastics material (for example, silicone) and a metal rod that can readily be plastically deformed (for example, pure aluminum). When the test rod has the same external diameter as the longitudinal member, the test rod exactly reproduces the shape required for it to be possible to insert the longitudinal member in the pedicle screws in a stress-free manner. The present invention differs from the teaching according to DE 93 08 770 U1 on account of the above-defined condition that:
     a) the at least one longitudinal member is plastically deformable, by application of a pre-specified bending force, from a first shape state “A” to a second, alternative shape state “B”, the bending force required being substantially greater than the peak forces occurring in vivo, and   b) the at least one longitudinal member is, within the particular stable shape states, resiliently flexible, that being the case, more specifically, within the limits set by the mechanical interplay between the fixation system and the segment of spine, which limits define a so-called “resilient flexing range”.   

     The longitudinal member is accordingly so dimensioned that the biocompatible high-performance plastics material can be lastingly plastically deformed using appropriate forces whilst, in the deformed state, it should have sufficient bending resilience. That bending resilience is imparted to the plastics material by the metal, which additionally has the advantage and purpose of defining “creep-proof” pressure sites or clamping sites for the longitudinal member. 
     It should also be mentioned at this point that the longitudinal member should be so constructed that it is as rigid as possible with regard to compression and shear forces occurring in vivo and so constructed that the construct consisting of longitudinal member and anchoring means is substantially resistant to torsion. In that condition the longitudinal member contributes to the alleviation of pain and to the healing process. 
     The longitudinal member can be in the form of a flat band or strip or, preferably, can have a rotationally symmetrical, circular, polygon-like or elliptical cross-section, the cross-section remaining constant over the entire length in the longitudinal direction of the longitudinal member, varying in accordance with a mathematically describable rule and/or changing in abrupt manner. To that extent, as many degrees of freedom as possible should be provided. 
     In addition, it should be ensured that the longitudinal member is so dimensioned that, in the mentioned “resilient flexing range”, the surface stress is preferably below the dynamic breaking stress. This also applies to the individual components of the longitudinal member. 
     In addition, the aim is to make available a dynamic stabilization system that is based on following fundamental considerations: 
     The purpose in the present case is to develop a dynamic pedicle screw system, suitable for posterior insertion, which does not fuse pathologically changed spine segments but rather supports the particular structures in their function in a controlled manner. 
     As already mentioned above, principal indications for a dynamic system are diseases, inflammation and/or injuries in the region of the intervertebral disc, of the ligamentous apparatus, of the facet joints and/or of the subchondral bone. In those situations it is important to modify the loading pattern in the particular area so that the pathological condition at least does not deteriorate. Healing would be ideal but, at least in the case of degenerative diseases, that may not be possible. 
     The aim of the dynamic system is, however, not only to freeze the pathological condition or possibly to bring about healing but to form, together with the spinal structures concerned, a unit, consisting of the dynamic system and the spinal structures, which promotes the proper taking in of nutrients by the bone structures and the surrounding tissues. 
     As soon as a pedicle screw system is inserted from a posterior direction, the point of rotation of the movement segment concerned may be automatically displaced from, and potentially outside of the intervertebral disc in a posterior direction, should it still be flexible. Posterior displacement of the point of rotation into the region of the posterior facet joints can have the following effects, depending on the pathology: 
     1. Source of Pain: “Posterior Facet Joints”: 
     Depending on the position of the posteriorly displaced center of rotation relative to the posterior facet joints and on the axial compressibility of the system, movement in the joints is more or less dramatically reduced. By that means, the preconditions are created for a degeneratively changed joint to be able to recover as a result of missing hyaline joint cartilage being replaced at least in theory by fibrous cartilage (Salter&#39;s passive motion principle). A precondition of recovery is, however, that the system can be implanted in a stress-free manner. 
     2. Source of Pain: “Posterior Annulus” of the Intervertebral Disc; Lordosis and Intervertebral Disc Height Preserved: 
     Tears can occur in the posterior annulus of the intervertebral disc as a result of traumatic developments or degenerative changes. These tears often start from the nucleus and penetrate ever farther towards the outer, innervated edge of the annulus. Magnetic resonance imaging (MRI) allows identification of pockets of liquid in the region of the afore-mentioned tears. These so-called “hot spots” can be an indication of an inflammatory process in the region of the posterior annulus. Inflammation can occur, inter alia, in that region where granulation tissue growing in from the outside and/or nerve endings also meet nuclear material pushing through from the inside through tears in the annulus (physiological pain). The continuous subsequent flow of nuclear material permanently contributes to that inflammation process. 
     Theoretically, however, inflammation is not absolutely necessary in order to produce pain; rather, the mechanical pressure of a pocket of liquid on afferent nerve endings can alone cause pain. Suitable stabilization can halt the inflammation process and even trigger healing. 
     This Gives Rise to the Following Considerations: 
     As a result of the posterior displacement of the point of rotation of the spine segment, its range of movement in flexion and extension is dramatically reduced and the axial force acting on the intervertebral disc is uniformly distributed over the whole of the intervertebral disc. As a result, with “global” flexion/extension of the patient, the nuclear material is no longer squeezed to and fro, that is to say less nuclear material, which stimulates the inflammation process, is pressed through tears in the posterior annulus and against the inflammation site. As a result, the preconditions are created for healing of the inflammation and for the start of a repair process. 
     3. Problem: “Primary Disc Hernia”: 
     In a disc hernia a connection exists between the nucleus and the surroundings of the annulus. As a result, nuclear material can subsequently flow continuously through tears in the annulus. In a nucleotomy, the discharged material and also material from the nucleus are removed, the latter to avoid a secondary disc hernia. As a result, the lesion of the posterior annulus is made larger operatively. 
     In this case too, posterior displacement of the point of rotation of the spine segment reduces subsequent flow of nuclear material. The disc hernia can no longer grow, and discharged material, if it has not already been removed operatively, is encapsulated and is reabsorbed by the body. A repair process may take place at the posterior annulus. 
     Accordingly, in the case of a primary disc hernia a dynamic system has the advantage, at least theoretically, that operative intervention can be minimized (it is not necessary to open the epidural space and cause additional damage to the annulus). As a result, optimum conditions can be created for healing and restoration of the function of the intervertebral disc. 
     4. Source of Pain: “Posterior Annulus of the Intervertebral Disc” (Collapse of Intervertebral Disc): 
     Pain in the posterior annulus can be caused by delamination of the annulus. Delamination of the posterior annulus occurs when the nucleus is dehydrated and the intervertebral disc has accordingly collapsed. As a result of the posterior displacement of the point of rotation to the region behind the posterior facet joints, the pressure in the region of the posterior annulus is reduced, which prevents further delamination of the posterior annulus. As a result the preconditions are created for healing/scarring of the annulus, provided of course that the annulus has an appropriate healing potential. 
     5. Source of Pain: “Upper Plate/Subchondral Bone”: 
     Using MRI it is possible to detect changes in the liquid metabolism in the subchondral bone of the vertebra. In particular, it is also possible to ascertain a sclerotic change in the bony upper plate, which indicates restriction or stoppage of the nutritional supply to the intervertebral disc. A sclerotic change in the upper plate is not readily reversible. The degenerative “downfall” of the intervertebral disc is pre-programmed. 
     Another possibility is an increased liquid content, for which there are two explanations:
     a) inflammation in the subchondral region leading to inflammatory pain;   b) backing-up as a result of “blockage” of the connecting channels in the cartilaginous upper plate of the vertebra (caused by sclerotic changes etc.).   

     The first-mentioned inflammation can be overcome by suitable measures provided that the tissue in question is not permanently damaged. 
     In the latter case, the elevated pressure in the subchondral bone caused by the backing-up can, at least theoretically, result in mechanical irritation of the afferent nerve endings (mechanical pain). Measures bringing about a reduction in pressure in the subchondral region can at least reduce the mechanical pain if not cause it to disappear completely. However, the cause of the problem can be removed only with difficulty, even in the latter case. 
     Posterior displacement of the point of rotation to the region behind the posterior facet joints results in reduction of the load not only on the intervertebral disc but also on the subchondral bone located underneath. Accordingly, a suitable dynamic fixation creates the preconditions for the alleviation of pain and, in the case of inflammation in the region of the subchondral bone, even for healing. 
     6. Source of Pain: “Nerve Roots”: 
     Mechanical pressure on the nerve roots results in numbness and muscle weakness radiating out into the lower extremities, but not in pain. Pain (ischialgia, etc.) occurs only when inflammation-triggering nuclear material emerges through tears in the posterior annulus and presses on the nerve roots. 
     In this case too, posterior displacement of the point of rotation of the spine segment reduces the subsequent flow of the nuclear material stimulating the inflammation process. As a result, the preconditions are created for healing of the inflammation and for the start of a certain repair process in the posterior annulus. It is even feasible to remove a disc hernia if there is no continuing flow of new nuclear material. 
     7. Problem: “Spinal Fracture”: 
     In the case of a spinal fracture, it is usually the cranial vertebra of the segment concerned and the associated intervertebral disc that are affected. With the aid of good blood flow, bone healing of the vertebra no longer constitutes a problem with the fixation techniques described herein. Unlike the vertebra, healing of the intervertebral disc is, because of the lack of blood flow, subject to other rules and takes substantially longer. Changing from a rigid posterior fixation to a flexible posterior fixation after about 6 months brings about a reduction in the load on the intervertebral disc and allows certain flexibility of movement. Depending on the magnitude of the decrease in load and the remaining scope for movement, the preconditions are created for healing of the intervertebral disc provided that the supply to the intervertebral disc from the subchondral region of the adjacent vertebrae is not impeded (for example, as a result of callus formation in the region of the subchondral bone). 
     The posterior displacement of the point of rotation of the particular spine segment brought about in the case of a posteriorly implanted dynamic system brings about a reduction in the load on the injured intervertebral disc as already described hereinbefore and, in addition, allows axial deformation, which is important for the nutritional supply to the intervertebral disc. 
     In light of the above considerations, it is therefore also an aim, but not a requirement of the present invention, as a result of posterior displacement of the point of rotation of an affected spine segment, to immobilize the posterior annulus of the intervertebral disc concerned, with the consequence that posterior outflow of nuclear material is correspondingly reduced, whilst at the same time axial deformation, which is important for the nutritional supply to the intervertebral disc, should be possible, more specifically in such a manner that the intervertebral disc and the associated upper plates are subjected to pressure in a substantially homogeneous manner. Accordingly, it is also an objective of the present invention to make available a sufficiently dynamic stabilization system by means of which the point of rotation of the affected spine segment is displaced in a posterior direction in a predetermined manner. 
     Accordingly, the system should also preferably be distinguished firstly by an extremely elegant construction and operation technique and the advantages of a dynamic system, on the one hand, and by the possibility of optimum determination of the posterior point of rotation of a predetermined spine segment, on the other hand. 
     That problem preferably is solved by longitudinal member connecting means which preferably connects at least two longitudinal member portions. 
     From a medical point of view, it is preferable for the bone anchorage means, for example pedicle screws, that the connection between the bone anchorage means and the longitudinal member is polyaxial to guarantee stress-free implantation of the longitudinal member. After the implantation of the longitudinal member, said polyaxial connections can be lockable. 
     With respect to a viscoelastic longitudinal member, the load acting on the longitudinal member should be limited without compromising the strength of the locked polyaxial connection. This can be accomplished by having a load bearing means parallel to the longitudinal member which transfers a part of the load produced by the locking means directly to the clamping means locking the polyaxiality. For example, the load bearing means can be a fork engulfing the longitudinal member with a remaining distance “x” between the load bearing means and the clamping means. When the locking means is tightened, the resulting compression is initially taken up only by the viscoelastic longitudinal member causing a flattening of the longitudinal member. As soon as the deformation of the longitudinal member is equal to the distance “x”, the additional compression will be directly transferred through the load bearing means to the clamping means locking the polyaxiality. The distance “x” depends on the mechanical characteristics of the viscoelastic longitudinal member. 
     A preferable embodiment of a polyaxial connection between the bone anchorage means and the viscoelastic longitudinal member is provided by a connecting element which can be clicked in situ onto the bone anchorage means with the polyaxiality preferably between the connector and the bone anchorage means. If a patient requires a revision surgery or conversion to fusion by replacing the viscoelastic longitudinal member by a metallic longitudinal member, the connector has only to be replaced by leaving the bone anchorage means in place. 
     Another preferred embodiment of a device is characterized in that the longitudinal member consists of a plastics rod, around which a metal wire, preferably a flat metal band, is helically wound. Preferably, the metal band is embedded in the plastics material. In a specific embodiment, the metal band is embedded in the plastics material in such a manner that it forms, together with the plastics material, a continuously smooth surface. The metal band can have interruptions, for example rows of holes, which are filled with plastics material. 
     Clamping of the longitudinal member constructed in such a manner is always carried out at locations reinforced, or covered, by the metal band. The longitudinal member is preferably in the form of a solid-construction plastics rod. However, it is also feasible for the longitudinal member to be in the form of a hollow rod or tube. 
     The metal band winding acts like an outer helical spring, giving the longitudinal member the requisite resilience in the particular deformed state, more particularly a resilience which exceeds that which is intrinsic to the plastics rod. 
     When the diameter of the longitudinal member is about 6.0 to 8.0 mm, the width of the metal band is about 4.0 to 6.0 mm. The afore-mentioned interruptions may then have a diameter of about 2.0 to 3.0 mm. 
     If the longitudinal member is in the form of a hollow rod or tube, the wall thickness is about 1.5 to 2.0 mm, preferably about 1.5 mm. 
     In a specific embodiment, the winding of the metal band around the plastics rod is tightly spaced so that the axial spacing between neighboring turns of metal band is only about 1.5 to 3.0 mm. The winding of the metal band is carried out at an angle of about 15° to 30° relative to the plane extending perpendicular to the longitudinal axis of the longitudinal member, or cross-sectional plane. The metal band may consist of titanium or titanium alloy and has a thickness of about 0.2 to 0.4 mm, of course that being dependent, in the final analysis, on the overall dimensions of the longitudinal member. 
     The end-face extremities of the longitudinal member are preferably metal caps or metal discs. Those end-face metal caps or metal discs can also be connected to one another by means of a wire passing centrally through the longitudinal member, more specifically in such a manner that the end-face metal caps or metal discs can be tensioned with respect to one another in an axial direction. For that purpose, the central metal wire extends through the metal caps or metal discs, more specifically in such a manner that it projects outwards at the end faces as projecting portions, each of those projecting portions having a screw thread so that tensioning nuts can be screwed onto the central metal wire from the outside. 
     In an alternative embodiment, the longitudinal member is also a plastics rod in which a metal armoring has been embedded. That metal armoring can be constructed in numerous different ways. 
     In a preferred embodiment, there is provided a device for dynamic stabilization of bones or bone fragments comprising: at least one anchor member for attachment to vertebrae having an opening configured to receive a longitudinal member; and the longitudinal member being viscoelastically deformable and having a predetermined bending resilience comprising a biocompatible plastics material, whereby the plastics material provides for viscous deformability, and a biocompatible metal, whereby the metal provides for resiliently flexible deformability. 
     There is also provided a device for dynamic stabilization of bones or bone fragments comprising: at least one anchor member for attachment to vertebrae having an opening configured to receive a longitudinal member; and the longitudinal member being viscoelastically deformable and having a predetermined bending resilience comprising a plastic rod comprising biocompatible plastics material in which metal armoring comprising biocompatible metal is embedded. 
     There is also provided a device for dynamic stabilization of bones or bone fragments comprising: at least one anchor member for attachment to vertebrae having an opening configured to receive a longitudinal member; the longitudinal member being viscoelastically deformable and having a predetermined bending resilience comprising a biocompatible plastics material, whereby the plastics material provides for viscous deformability, and a biocompatible metal, whereby the metal provides for resiliently flexible deformability; and metal armoring comprising at least three metal rods extending parallel to the longitudinal member. 
     There is also provided a device for dynamic stabilization of bones or bone fragments comprising: at least one anchor member for attachment to vertebrae having an opening configured to receive a longitudinal member; and the longitudinal member being viscoelastically deformable and having a predetermined bending resilience comprising a biocompatible plastics material, whereby the plastics material provides for viscous deformability, a biocompatible metal, whereby the metal provides for resiliently flexible deformability; and at least a portion of the metal forms a continuous spiral. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Corresponding examples embodying a stabilization system will be explained hereinbelow in greater detail with reference to the accompanying exemplary and illustrative drawings. The drawings are merely exemplary to illustrate the structure of devices and features that may be used singularly or in combination with other features and structures. The invention should not be considered limited to the embodiments shown. 
         FIG. 1  is a view from the posterior direction of a spine segment comprising four vertebrae, with posterior stabilization of that segment; 
         FIG. 2  is a side view along line  2 - 2  according to  FIG. 1  of the arrangement according to  FIG. 1 ; 
         FIG. 3  is a diagrammatic side view of a first embodiment of a longitudinal member; 
         FIG. 4  is a diagrammatic side view of a second embodiment of a longitudinal member; 
         FIG. 5  is a diagrammatic side view of a third embodiment of a longitudinal member; 
         FIG. 6  is a perspective view of an end-face end portion of a metal armoring of the longitudinal member according to  FIG. 5 ; 
         FIG. 7  is a longitudinal section through part of a fourth embodiment of a longitudinal member; 
         FIG. 8  is a diagrammatic cross-section through the embodiment according to  FIG. 7 ; 
         FIG. 9  is a diagrammatic longitudinal section through a fifth embodiment of a longitudinal member; 
         FIG. 10  is a model view for the stabilization system of  FIG. 3 , which also applies in corresponding manner to the other embodiments; 
         FIG. 11  is a diagrammatic side view of a fifth embodiment of a longitudinal member contained within diagrammatic cross section of anchoring members; 
         FIG. 12  is a diagrammatic side view of a sixth embodiment of a longitudinal member contained within a diagrammatic cross section of anchoring members; 
         FIG. 13  is a diagrammatic side view of a seventh embodiment of a longitudinal member contained within diagrammatic cross section of anchoring members; 
         FIG. 14  is a diagrammatic side view of an eighth embodiment of a longitudinal member, similar to the longitudinal member of  FIG. 13 , but configured for a two level stabilization, the longitudinal member contained within three anchoring members; 
         FIG. 15  is a diagrammatic side view of a ninth embodiment of a longitudinal member having an enlarged spiral portion, and contained within a diagrammatic cross-section of two anchoring members; 
         FIG. 16  is a diagrammatic side view of a tenth embodiment of a longitudinal member having an enlarged spiral portion, similar to the longitudinal member of  FIG. 14  but configured for a two level stabilization, the longitudinal member contained within a diagrammatic cross-section of three anchor members; 
         FIG. 17  is a diagrammatic side view of an eleventh embodiment of a longitudinal member contained within diagrammatic cross section of anchoring members; 
         FIG. 18  is a diagrammatic side view of a twelfth embodiment of a longitudinal member contained within diagrammatic cross section of anchoring members; 
         FIG. 19A  is a diagrammatic side view of a thirteenth embodiment of a longitudinal member contained within diagrammatic cross section of anchoring members; 
         FIG. 19B  is a diagrammatic side view of the embodiment of  FIG. 19A  of a longitudinal member contained within diagrammatic cross section of anchoring members; 
         FIG. 19C  is a diagrammatic side view of the embodiment of  FIG. 19A  of a longitudinal member contained within diagrammatic cross section of anchoring members; 
         FIG. 20A  is a diagrammatic side view of a fourteenth embodiment of a longitudinal member contained within diagrammatic cross section of anchoring members, configured for a two level stabilization, the longitudinal member contained within a diagrammatic cross-section of three anchor members; 
         FIG. 20B  is a diagrammatic side view of the embodiment of  FIG. 20A  of a longitudinal member contained within diagrammatic cross section of anchoring members, configured for a two level stabilization, the longitudinal member contained within a diagrammatic cross-section of three anchor members; 
         FIG. 20C  is a diagrammatic side view of the embodiment of  FIG. 20A  of a longitudinal member contained within diagrammatic cross section of anchoring members, configured for a two level stabilization, the longitudinal member contained within a diagrammatic cross-section of three anchor members; and 
         FIG. 21  is a graphic representation of a waisted cross-section. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  show part of a spine, reference letter “V” denoting the individual vertebra. Reference letter “S” denotes the spine. While the stabilization system is shown and described with reference to its use for spiral applications, it is understood and contemplated that the stabilization system may have applications in other areas of the body and in animals. 
     The individual vertebra “V” have been stabilized posteriorly; more specifically, for that purpose pedicle screws have been screwed into four vertebrae “V” from the posterior direction. The heads of the screws  10  each have accommodation apertures or accommodation slots or openings for accommodating a rod-shaped longitudinal member  11 . The longitudinal member  11  is, as can be seen especially from the further figures, of generally round rod-shaped construction and is fixed by clamping in the heads of the pedicle screws  10 . In that manner, a spine segment having four vertebrae “V” can be stabilized. The longitudinal member or members  11  are so designed that they are plastically deformable, by application of a predetermined bending force, from a first stable shape state to a second, alternative stable shape state in accordance with  FIGS. 1 and 2 . However, within that implantation state, the longitudinal members  11  should be resiliently or elastically flexible, more specifically within predetermined limits as described above. As a result, dynamic stabilization of a predetermined spine segment is achieved preferably with all the advantages mentioned hereinbefore. The aforementioned bending resilience of the longitudinal member(s)  11  is indicated in  FIG. 2  by a double-headed arrow  14  and is so dimensioned that, in situ, when the longitudinal member  11  is held at one extremity, it can be resiliently deflected, within a dimensionally stable state, about an angle of about 8° (double-headed arrow  14 ). Accordingly, flexion in the sagittal plane is provided. 
     It should be mentioned again at this point that the described device can comprise longitudinal member connecting means, by means of which at least two longitudinal member portions can be connected to one another. The longitudinal member connecting means can have, for example, two longitudinal member accommodation apertures or accommodation slots or openings located opposite one another, into each of which one longitudinal member end portion can be inserted and, by means of a clamping screw or the like, fixed. The longitudinal member connecting means may be a pedicle screw, such as, for example, a monoaxial or polyaxial pedicle screw, or hook, or other device and mechanism for attaching the longitudinal member to one or more vertebrae. 
     The longitudinal member connecting means can be either of rigid or, preferably, of resiliently flexible construction. They preferably allow segment-wise implantation of longitudinal members and highly individual stabilization of a portion of spine. 
     From  FIGS. 1 and 2  it can otherwise also be seen that stabilization of a portion of spine by means of the device is carried out that flexibility is present only in respect of flexion and extension. As a result, pressure on the upper plate and intervertebral disc is considerably reduced without losing axial deformation of the intervertebral disc, which is important for the nutritional supply thereof. The described longitudinal member also is preferably constructed that it can be lastingly deformed using a predetermined force which exceeds anatomical or in vivo peak forces. That deformation is carried out outside of the implantation; it should preferably be possible without special ancillary apparatus. Deformation is accordingly carried out “on site” by the operating surgeon. 
     Both in the longitudinal direction of the longitudinal member and also in the direction transverse thereto, the longitudinal member should be stable, that is to say unyielding, with respect to anatomically shear forces usually present in vivo. In addition, it is very often desirable for the longitudinal member to be torsion-resistant in order to ensure that extension of the vertebral segment concerned generally occurs substantially only about a posteriorly displaced point of rotation approximately horizontal. As already mentioned hereinbefore, the longitudinal member can be in the form of a flat band or strip. In the embodiments described, longitudinal members in the shape of round rods are implanted. 
     With respect to the bending resilience, it should also be mentioned that the angular range mentioned hereinbefore is based on a length of the longitudinal member  11  which corresponds to the spacing between two neighboring vertebrae, that is to say a spacing of about 2 cm to about 6 cm, especially about 4 cm to about 5 cm. 
     Reference numeral  15  denotes the entire stabilization system shown in  FIGS. 1 and 2 . 
     In the case of the embodiment according to  FIG. 3 , the longitudinal member  11  consists of a plastics rod  12 , around which a flat metal band  13  is helically wound. The metal band  13  is embedded in the plastics material of the rod  12 , more specifically in such a manner that, together with the plastics material, it forms a continuously smooth surface. The metal band moreover has interruptions  16  in the shape of circles or elongate holes, which are likewise filled with plastics material so that a substantially smooth surface of the rod-shaped longitudinal member  11  is produced. With respect to preferred dimensions for a longitudinal member of such a kind, reference is made to the statements hereinbefore. 
     The end-face extremities of the longitudinal member  11  can be, and preferably are, limited by metal caps or metal discs. In the embodiment according to  FIG. 3 , the end-face limitation is defined by metal caps  17  out from which the helical sheathing of the plastics-comprising rod  12  is then developed. 
     The plastics rod  12  can also be tube- or tubule-shaped, that is to say hollow. The end faces are closed off by metallic discs or plugs. In the final analysis, the embodiment of the plastics rod is dependent on the application area and also on the requisite dimensional stability and flexibility of the longitudinal member. 
     Reference numeral  18  denotes the clamping sites of the longitudinal member  11  in  FIG. 3 . Accordingly, the longitudinal member  11  is clamped in the region of the metallic sheathing. As a result it is possible to avoid the plastics material retreating or “creeping away” under the pressure of a clamping screw after a relatively long period of use. Because the winding of the metal band  13  on the plastics rod  12  is very tightly spaced, the longitudinal member  11  according to  FIG. 3  can be clamped at practically any location. 
     The embodiments of  FIGS. 4-9  are all characterized in that the longitudinal member consists of a plastics rod  12  in which metal armoring is embedded. The latter can be, for example, in the form of a round or flat profile having a meandering curve shape, the meandering curves preferably extending to the peripheral surface of the longitudinal member  11 , which otherwise consists of plastics material. In the case of the embodiment according to  FIG. 4 , the metal armoring is formed by a flat profile  19 , which is defined by one or more “V”-shaped or “W”-shaped elements  20  alternately rotated 180° and connected together. Each of the “V”-shaped or “W”-shaped elements  20  extends to the peripheral surface of the longitudinal member  11 , which otherwise consists of plastics material, with those parts of the armoring which reach the surface, in conformity with the peripheral surface of the longitudinal member  11 , each being rounded in accordance with the cross-sectional periphery of the longitudinal member. 
     The central members  21  of the “V”-shaped or “W”-shaped elements  20  are widened both in the longitudinal direction and in the transverse direction to form support surfaces  22 , which are rounded off in the direction transverse to the longitudinal axis of the longitudinal member  11  and integrated flush into the peripheral surface  24  of the longitudinal member  11 . The outer surfaces  23  of the connecting members  24  of the “V”-shaped or “W”-shaped elements  20  are likewise rounded off in each case in the direction transverse to the longitudinal axis of the longitudinal member  11  so that they can be integrated flush into the peripheral surface of the longitudinal member  11 . The longitudinal member  11  according to  FIG. 4  is clamped or fixed at the metal surfaces of the central member  21  and connecting member  24 , which are flush with the peripheral surface of the longitudinal member  11 . In that regard,  FIG. 4  shows, in diagrammatic manner, on the one hand, the so-called “best case” and, on the other hand, the “worst case”. The “best case” situation is indicated in  FIG. 4  by the clamps  25 . The “worst case” situation corresponds to the relative position of the clamps  25 ′ in  FIG. 4 . 
     Otherwise, the flat profile  19  is constructed with a waisted cross-section as depicted in  FIG. 21 . The metal portion may be formed similar to an “I” beam as shown, or similar to a “C”-shape (not shown) if  FIG. 21  is bisected. The plastic material may be on one or both sides of the middle columnar support of the “I” beam or “C”-shaped element. 
     In the plane of the sheet of the drawing, the metal armoring  19  according to  FIG. 4  is relatively flexible, or resilient in flexion. In the plane perpendicular to the sheet of the drawing, the flat profile  19  is relatively rigid. Accordingly, therefore, there is a preferred plane of deformation, which has to be taken into account on implantation. 
     In the case of the embodiment according to  FIGS. 5 and 6 , the metal armoring comprises three metal rods  26 , which extend parallel to the longitudinal direction of the longitudinal member  11  and at the same angular spacing from one another (see  FIG. 6 ) and which are fixed at the end faces through star-shaped discs  27 , especially being shrunk into corresponding through-holes. In  FIG. 6 , reference numeral  28  denotes those through-holes. 
     Held between the three metal rods  26  are a plurality of disc-shaped supporting elements  29 , each of which extends to the peripheral surface of the longitudinal member  11 , which otherwise consists of plastics material. The supporting elements  29  are spaced apart from one another in the axial direction, and, in particular, preferably spaced apart equally from one another. The intermediate space is filled by plastics material. The longitudinal member  11  is a round rod of biocompatible high-performance plastics material, for example PCU, having armoring in accordance with  FIGS. 5 and 6 . The disc-shaped supporting elements  29  have, at their edges, three recesses  30 , through which the metal rods  26  extend. The three recesses  30  are each arranged uniformly around the periphery of the supporting discs  29 . 
     The metal rods  26 , embedded in the plastics material, each extend close to the peripheral surface of the longitudinal member  11 . In this case too, the metal rods serve to ensure the bending resilience in a predetermined stable shape state of the longitudinal member  11 . For better anchorage between the plastics material and metal it is also feasible for the surface of the metal rods  26  to be roughened. 
     The embodiment according to  FIGS. 7 and 8  is characterized in that the metal armoring comprises at least one central metal rod  31 , which extends parallel to the longitudinal direction of the longitudinal member  11  and on which metal sleeves  32  are mounted. The metal sleeves may comprise a hub having longitudinal elements  34  extending therefrom. Longitudinal recesses  33  separate the longitudinal elements  34 . The metal sleeves  32  have at their end faces respectively facing one another longitudinal recesses  33 , in this case three, arranged uniformly around the periphery, into which recesses  33 , longitudinal elements  34  formed there between of a directly neighboring metal sleeve  32  can be inserted so that neighboring metal sleeves  32  can, if required, be pushed into one another, offset at an angle to one another, on the at least one metal rod  31 , as shown in  FIG. 7 . The angular offset between neighboring metal sleeves can be seen more clearly from  FIG. 8 . 
     Between the end-face longitudinal recesses  33  of the metal sleeves  32 , spaced away from the free extremity, the longitudinal elements  34  are connected to one another by a central, preferably star-like, connecting element  35 , the connecting element  35  having a central longitudinal hole  36  for accommodation of the central rod  31 , on which the metal sleeve or sleeves  32  can be mounted. The metal sleeves  32  accordingly form, in the region of end faces inserted into one another, a kind of articulated connection  37 , which allows bending of the longitudinal member  11  within predetermined limits. 
     The external diameter of the metal sleeves  32  otherwise corresponds to the external diameter of the plastics portion of the longitudinal member  11 . The sleeves  32  are embedded in the plastics material. Preferably, however, the external diameter of the metal sleeves  32  corresponds to the external diameter of the plastics-comprising longitudinal member  11  so that the external peripheral surfaces of the metal sleeves  32  and longitudinal elements  34  are an integral part of the peripheral surface of the longitudinal member  11 . The longitudinal member  11  according to  FIGS. 7 and 8  can be lastingly fixed, that is to say firmly clamped, in the region of those metal sleeves, preferably directly next to an articulated connection. 
       FIG. 9  shows a fifth embodiment of a longitudinal member, wherein the metal armoring comprises three metal rods  31  extending parallel to the longitudinal direction of the longitudinal member  11 , one of the extremities of two of the metal rods  31  being fixed, especially welded, to one of the two end-face end caps  38 , more specifically the right-hand end cap  38  in  FIG. 9 , whilst the other, in that case free, extremity of each is embedded in the plastics material  39 . The third rod  31 , namely the middle rod in  FIG. 9 , is fixed to the other end cap  38 , namely the left-hand end cap  38  in  FIG. 9 . The right-hand, free extremity of that third metal rod is, in contrast, accommodated, floating, in the plastics material  39 . The free extremities of the metal rods  31  each have a thickened portion  40 , the thickened portions of the upper and lower metal rods  31  in  FIG. 9  being formed to make a connection of the free extremities of those two metal rods. The thickened portion  40  promotes embedding in the plastics material and the clamping action of the latter on resilient deformation of the longitudinal member  11 . In this context it is to be noted that the longitudinal member according to the invention is constructed according to the so-called Kelvin-Voigt model. The longitudinal members  11  shown constitute a modified Kelvin-Voigt model, in particular having a serially appended resilient element (spring element). 
     Otherwise it can be seen from  FIG. 9  that the respective free extremities of the metal rods  38  are embedded in the plastics material  39  within sleeve-like portions  41  of the end-face end caps  38  of the longitudinal member  11 . 
     It should also be mentioned that the end-face end caps  38  in  FIG. 9 , or  27  in  FIG. 6 , of the longitudinal member  11  can be tensioned with respect to one another in the axial direction. 
     In the embodiments shown, the metal rods described herein (e.g.,  26  in  FIGS. 5 and 6 ;  31  in  FIG. 7 ; and  38  in  FIG. 9 ) each have a constant diameter over their length. However, it is feasible for the diameter to vary over the length, for example decreasing or increasing continuously or in stepwise manner towards the middle of the longitudinal member  11  or vice-versa. 
     Otherwise it should also be mentioned in respect of  FIG. 9  that between the two end caps of the metal rods  31  there are held supporting elements  29  corresponding to those described in connection with  FIGS. 5 and 6 . Clamping of the longitudinal member  11  can take place at those supporting elements  29 , and also in the region of the end caps  38 , without there being a risk of that clamping becoming loose after a relatively long period of use. The supporting elements  29  also have the function of metal wire spacer elements, that is to say they keep the metal wires at a constant spacing from one another over their length. That spacing is maintained even after plastic deformation of the longitudinal member  11 . As a result, a defined “flexing” of the longitudinal member is also obtained after deformation thereof. 
     In addition to its viscous deformation property, the biocompatible high-performance plastics material used herein also preferably has the property of having a shock-absorbing action. 
     It should also be mentioned that it is desirable for the plastics material to prevent the formation of openings in the longitudinal member into which tissue could grow. The longitudinal member  11  is, in the case of all the embodiments described, is preferably a round rod having a smooth surface. The plastics material used is preferably transparent so that the metal armoring is visible. As a result it can also be seen at which sites the longitudinal member  11  can be tightly clamped. 
       FIG. 10  shows the fundamental difference between the system according to the invention (the right-hand illustration in  FIG. 10 ) and the prior art (the left-hand and middle illustrations in  FIG. 10 ) using the so-called Kelvin-Voigt model. In the case of the prior art according to the left-hand illustration in  FIG. 10 , the longitudinal member or connecting rod consists of, for example, titanium or a titanium alloy. Such a rod comprises both a flexing or spring component and also a clamping component, with both components being in parallel connection with respect to one another. When, instead of titanium or the like, plastics material, for example PCU, is used, a further flexing component is added in series to the two afore-mentioned components (middle illustration in  FIG. 10 ). In accordance with the invention, yet another flexing component is introduced, in parallel, to the last-mentioned model (right-hand illustration in  FIG. 10 ). 
     This last-mentioned model very clearly represents the “recoiling” effect that is desirable for the composite. The spring in each of the two Kelvin-Voigt models according to the left-hand and middle illustrations of  FIG. 10  in parallel connection to the clamper does, of course, also result in a certain “recoiling” effect. According to mechanical tests with PCU material, that effect is relatively slow. Recovery of the PCU material takes several hours. By means of the metal component in parallel connection to the PCU material, for example the metal spiral according to  FIG. 3 , the “recoiling” effect of the PCU material can be accelerated to a greater or lesser degree depending on the material selected and on the geometry of the metal component. 
     In the embodiment according to  FIGS. 11 and 12 , the longitudinal member  11  consists of a continuous spiral of biocompatible metal such that the resulting structure is tube- or tubule-shaped, having a hollow cavity  50  in the center. The wire forming the spiral may be round or preferably flat ribbon wire. Because the longitudinal member is fairly homogenous along its length (e.g., a continuous spiral structure), the position of the pedicle screws  10  can be located anywhere along the length of the spiral longitudinal member. The longitudinal member preferably has the same diameter throughout the structure which promotes percutaneous application of the longitudinal member. 
     The hollow spiral longitudinal member can be filled with biocompatible plastics material, for example PCU. The plastics material can fill the gaps of the spiral wire as well as the hollow core of the spiral. The spiral wire may be flush with the plastics material at the perimeter of the longitudinal member, or may only fill the hollow cavity  50 , or may only partially fill the gaps between the spiral wire. The spiral wire filled with biocompatible plastics material provides resistance to collapse in the area of the pedicle screw and an overall resistance to buckling. The plastics material filling the gaps of the spiral provides a larger stiffness in compression. Only the core portion of the plastics material contributes to the resistance in the tension since the metal spirals are separated by the plastics material in between the gaps of the spiral. 
     The longitudinal member can also consist of cross holes  42 , which can be used for anchorage of the biocompatible plastics material, as depicted in  FIG. 11 . The cross holes may provide relative movement between the metal spiral and the biocompatible plastics material filling. The spiral longitudinal member can be locked in the pedicle screws  10  using a clamping mechanism as described above. 
     In the embodiment according to  FIGS. 13 and 14 , the longitudinal member  11  consists of alternating non-spiral portion  44  and spiral portion  43 . The spiral portion  43  is structured as described above for the embodiments of  FIGS. 11 and 12 . The non-spiral portion  44  of the longitudinal member can be structured as described for prior embodiments above. Because the longitudinal member is non-homogenous along its length (e.g., alternating non-spiral and spiral portions), the position of the pedicle screws  10  along the length of the longitudinal member has preferred locations. The pedicle screws  10  preferably are positioned outside of the spiral portion  43  and can be compatible with any pedicle screw system, thus no special clamping mechanism may be required. 
     In the embodiments of  FIGS. 11-20 , the spiral preferably has a pitch of about 4 mm to about 6 mm, more preferably about 5 mm. The length of the longitudinal member is preferably about 47 mm to about 53 mm, more preferably about 50 mm for single level applications. The length may be changed depending upon many factors, including the size of the patient and the number of discs or vertebrae effected. The width of the spiral wire is preferably about 1 mm to about 3 mm, more preferably about 2 mm. The gaps or spacing  46  between the spiral wire is preferably about 1 mm to about 3 mm, more preferably about 2 mm. Preferably at least two revolutions of the spiral are mechanically active. The diameter of cross holes  42  is preferably about 1 mm to about 3 mm, more preferably about 2 mm. The spiral portion of the embodiment of  FIG. 15  is preferably about 10 mm in length to about 14 mm in length, more preferably about 12 mm in length. The dimensions described above are merely exemplary to illustrate the structure of devices and features that may be used singularly or in combination with other features and structures. One of ordinary skill would recognize that the embodiments should not be considered limited to these specific dimensions, but may be changed for different applications and conditions. 
     The longitudinal member can also consist of cross holes  42  at the end of the spiral portion, which can be used for anchorage of the biocompatible plastics material, as depicted in  FIGS. 13 and 14 . The cross holes may provide relative movement between the metal spiral and the biocompatible plastics material filling. 
     The hollow spiral portion of the longitudinal member can be filled with biocompatible plastics material via a hollow end  45  of the non-spiral portion  44 . By adding biocompatible plastics material to the hollow end  45  of the non-spiral portion  44 , the spiral portion  43  and the hollow end of the longitudinal member preferably are filled with biocompatible plastics material, resulting in a longitudinal member whose hollow cavities preferably are completely filled with biocompatible plastics material. The longitudinal member of the embodiments of  FIGS. 13 and 14  is also characterized in that the diameter is identical throughout the structure which promotes percutaneous application of the longitudinal member. 
     As depicted in  FIG. 14 , the embodiment described above can be constructed to have one or more spiral portions  43  along the length of the longitudinal member  11 . One or more spiral portions  43  may be provided along the length of the longitudinal member configured so that they are located between adjacent vertebrae, when implanted, and in addition to or alternatively one or more spiral portions may be provided along the length so that multiple level stabilizations can be performed, for example a two level stabilization as illustrated in  FIG. 14 . 
     As described above for the embodiments depicted in  FIGS. 13 and 14 , in the embodiment according to  FIGS. 15 and 16 , the longitudinal member  11  consists of alternating non-spiral portion  44  and spiral portion  43 . In this embodiment the spiral portion  43  is larger in diameter than the non-spiral portion  44 . This construction provides for greater flexibility and dynamic movement of the device. Since the longitudinal member consists of two diameters, percutaneous application of the longitudinal member may be difficult, and transitions (not shown) such as tapered regions may be provided. Preferably the spiral portion is sealed against body fluids and the like. 
     As depicted in  FIG. 16 , the embodiment described above can be constructed to have one or more spiral portions  43  along the length of the longitudinal member  11 . One or more spiral portions  43  may be provided along the length of the longitudinal member configured so that they are located between adjacent vertebrae, when implanted, and in addition to or alternatively one or more spiral portions may be provided along the length so that multiple level stabilizations can be performed, for example a two level stabilization as illustrated in  FIG. 16 . 
     In the embodiment according to  FIG. 17 , the longitudinal member  11  consists of non-spiral portion  44  and spiral portion  43 , wherein the non-spiral portion  44  is located at one end of the spiral portion  43 . The spiral portion  43  is structured as described above for the embodiments of  FIGS. 11 and 12 . The non-spiral portion  44  of the longitudinal member can be structured as described for prior embodiments above. The end  51  of the spiral portion  43  which is most distal to the non-spiral portion  44  can be inflexible and may consist of an overhang  52  from the pedicle screw  10  that may be at least 5 mm in length. 
     At least one pedicle screw can be located anywhere along the non-spiral portion  44 . The remaining pedicle screws  10  can be positioned anywhere along the length of the spiral portion  43 . The longitudinal member  11  preferably has the same diameter throughout the structure which promotes percutaneous application of the longitudinal member. The longitudinal member  11  can be locked in the pedicle screws  10  using a clamping mechanism as described above. 
     As depicted in  FIG. 18 , the embodiment described above can be constructed to have one or more non-spiral portions  44  and one or more spiral portions  43  along the length of longitudinal member  11  such that multiple level stabilizations can be performed, for example a three level stabilization as illustrated in  FIG. 18 . This structure can provide both inflexible or fusion stabilization through the use of the non-spiral portions, as well as more flexible or dynamic stabilization through the use of the spiral portions. The spiral portion  43  is structured as described above for the embodiments of  FIGS. 11 and 12 . The spiral portion  43  can be constructed as in  FIGS. 15 and 16 . The non-spiral portion  44  of the longitudinal member can be structured as described for prior embodiments above. 
     In the embodiment according to  FIGS. 19A ,  19 B and  19 C, the longitudinal member can be structured as described above for the embodiment of  FIG. 13  wherein the longitudinal member  11  consists of alternating non-spiral portion  44  and spiral portion  43 . A locking cap  55  or a solid rod extension  56  may be inserted into one end of the non-spiral portion  44 , as depicted in  FIGS. 19A and 19B  or into both ends as depicted in  FIG. 19C . 
     As depicted in  FIG. 20A , the embodiment described above can be constructed to have one or more spiral portions  43  along the length of the longitudinal member  11 . One or more spiral portions  43  may be provided along the length of the longitudinal member configured so that, when implanted, they are located between adjacent vertebrae and in addition to or alternatively one or more spiral portions may be provided along the length so that multiple level stabilizations can be performed, for example a two level stabilization as illustrated in  FIG. 20A . A locking cap  55  or a solid rod extension (not shown) may be inserted into one end of the non-spiral portion  44  (not shown), or into both ends as depicted in  FIG. 20A . 
     In the embodiment according to  FIGS. 20B and 20C , the longitudinal member is structured similar to the longitudinal member as described above for the embodiment of  FIG. 20A . The longitudinal member  11  may consist of two or more units consisting of alternating spiral portions  43  and non-spiral portions  44 . The longitudinal member units may be connected to each other via a connecting plug  58 . The connecting plug  58  when the longitudinal member is implanted may be located at the pedicle screw  10 . A locking cap  55  or a solid rod extension (not depicted) may be inserted into one end of the non-spiral portion  44 , as depicted in  FIG. 20C  or into both ends as depicted in  FIG. 20B . 
     The present invention has been described in connection with the preferred embodiments. These embodiments, however, are merely for example and the invention is not restricted thereto. It will be understood by those skilled in the art that other variations and modifications can easily be made within the scope of the invention as defined by the appended claims, thus it is only intended that the present invention be limited by the following claims. 
     LIST OF REFERENCE SYMBOLS 
     
         
         V Vertebra 
         S Spine 
           10  pedicle screw 
           11  longitudinal member 
           12  plastics rod 
           13  metal collar 
           14  double-headed arrow 
           15  stabilization system 
           16  Interruption 
           17  metal cap 
           18  circular surface 
           19  Flat profile 
           20  w-shaped elements 
           21  central member 
           22  support surface 
           23  outer surface 
           24  connecting member 
           25  clamp 
           25 ′ clamp 
           26  metal rod 
           27  metal disc 
           28  through-hole 
           29  supporting or spacer element 
           30  recess 
           31  metal rod 
           32  metal sleeve 
           33  longitudinal recess 
           34  longitudinal element 
           35  connecting element 
           36  longitudinal hole 
           37  articulated connection 
           38  End cap 
           39  plastics material 
           40  thickened portion 
           41  sleeve-like portion 
           42  cross holes 
           43  spiral portion 
           44  non-spiral portion 
           45  hollow end 
           46  gap or spacing 
           50  hollow cavity 
           51  end of spiral portion 
           52  overhang 
           55  locking cap 
           56  solid rod extension 
           58  connecting plug