Abstract:
A dynamic spine stabilization element of a spine stabilization assembly includes first and second spinal rod segments that are coupled to one another via a connector. The connector allows movement of a spinal rod segment with respect to the coupling device and/or with respect to another spinal rod segment. This provides limited angulation (e.g. bending) between spinal rod segments allowing for limited movement of the vertebra connected by the present dynamic stabilization element. The connector may allow pivoting motion of the rod segments relative to the coupling device and relative to the other rod segment such as pivoting motion of one rod segment in a first plane and pivoting motion of the other rod segment in a second plane that is perpendicular to the first plane. The connector may also be bendable or flexible. In this form, the connector allows limited flexing, bending or angulation as between the associated spinal rod segments during use. Moreover, ends of the spinal rod segments may be configured to prevent or limit rotation of the spinal rod segments. The configured ends may cooperate with the coupling device to achieve the limitation on rotational movement.

Description:
RELATED APPLICATIONS 
     This patent application claims the benefit of and/or priority to U.S. Provisional Patent Application No. 60/738,380 filed Nov. 18, 2005, entitled “Dynamic Spinal Stabilization Devices and Systems” the entire contents of which is specifically incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention provides devices for the stabilization of the spinal column and, more particularly, to dynamic devices for the stabilization of the spinal column. 
     2. Background Information 
     A significant portion of the population suffers from spinal problems. Such spinal problems may be attributable to disease, trauma and/or other event. In the case of degenerative disc disease, spinal trauma and the like, such conditions are often painful and/or physically deforming. Depending on the situation, the pain and complications caused by these conditions may require that one or more vertebra, facet joints, and/or intervertebral discs be removed from the spinal column. In these procedures, bone fusion is a common treatment used to facilitate the realignment and/or fixation of the remaining spinal elements. 
     Currently, two types of systems or assemblies are utilized for securing and/or stabilizing one or more vertebrae in order to achieve bone fusion. One type of spine stabilizing assembly generally includes two posterior vertebral plates disposed longitudinally on either side of the spinous processes. Each plate is attached between adjacent vertebra using bone anchoring elements, such as bone screws. Together, the plates provide a rigid vertebral fixation. 
     Another type of spine stabilizing assembly generally includes two posterior vertebral rods disposed longitudinally on either side of the vertebrae (e.g. the spinous processes thereof). Like the plates, these rods are attached between adjacent vertebrae using appropriate bone anchoring devices to achieve rigid vertebral fixation. 
     These spine stabilizing assemblies are also used to correct spinal deformities such as scoliosis or the like. For this use, such spine stabilizing assemblies may have spine rods that span two or more vertebrae. 
     A drawback of rigid fixation relates to the loading that occurs on the stabilizing assemblies and especially on the anchoring sites during normal activity. These loads may result in loosening of the assembly from the vertebrae or even breaking of the assembly. Also, fusion subjects the non-fused spine elements to various stresses, particularly the remaining adjacent vertebrae and vertebral discs since these elements must accommodate different degrees of motion. Moreover, spinal fusion limits the range of a patient&#39;s motion. 
     Because of the drawbacks to rigid spine fixation systems, semi-rigid spine fixation systems have been proposed that aim to allow limited intervertebral movement for promoting bone fusion and/or reducing spine stress. These semi-rigid spine fixation systems, however, are far from effective and/or efficient. 
     There is thus a need for an improved semi-rigid spine stabilization device, assembly and/or system. 
     This need and others is accomplished through application of the principles of the subject invention and/or as embodied in one or more various forms and/or structures such as are shown and/or described herein. 
     SUMMARY OF THE INVENTION 
     The present invention provides dynamic spine stabilization elements, systems, assemblies and/or devices particularly, but not necessarily, for posterior spine stabilization. 
     A dynamic spine stabilization element of a spine stabilization system or assembly, includes first and second spinal rods or rod segments that are coupled to one another via a coupling device. The coupling device provides movement or motion of one or more of the spinal rod segments with respect to the coupling device and/or with respect to the other spinal rod segment. The present invention thus provides spinal stabilization elements for spinal stabilization systems that allow for limited angulation (e.g. bending) between spinal rod segments of the spinal stabilization element. This allows for limited movement of the vertebra connected by the present dynamic stabilization element. 
     In one form the first and second spinal rod segments are connected via a coupling device that allows pivoting motion of the rod segments relative to the coupling device and relative to the other rod segment. Particularly, the coupling device allows pivoting motion of one rod segment in a first plane and pivoting motion of the other rod segment in a second plane that is perpendicular to the first plane. 
     In another form, the first and second spinal rod segments are connected via a bendable or flexible coupling device. The coupling device is adapted to allow limited flexing, bending or angulation as between the associated spinal rod segments during use. Particularly, the coupling device allows for 360° angulation. 
     Ends of the spinal rod segments may be configured to prevent or limit rotation of the spinal rod segments. The configured ends may cooperate with the coupling device to achieve the limitation on rotational movement. In another form, the coupling device and/or the configured ends of the spinal rod segments, allow for limited axial movement between rod segments. 
     The spinal rod segments may be straight or curved and may be made in different lengths. Spinal rods of various curvatures may also be provided. A stabilization system may include straight and curved spinal rod segments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the present invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an exploded perspective view of an embodiment of a dynamic spinal stabilization element fashioned in accordance with the present principles; 
         FIG. 2  is a perspective view of the dynamic spinal stabilization element of  FIG. 1  assembled but with a sleeve portion removed; 
         FIG. 3  is a perspective view of an alternative embodiment of the dynamic spinal stabilization element of  FIG. 2  assembled but with a sleeve portion removed; 
         FIG. 4  is a side view of the dynamic spinal stabilization element of  FIG. 1  assembled; 
         FIG. 5  is a sectional view of a portion of the dynamic spinal stabilization element of  FIG. 4  taken along line  5 - 5  thereof; 
         FIG. 6  is a side view of an embodiment of a dynamic spinal stabilization element fashioned in accordance with the present principles; 
         FIG. 7  is a sectional view of a form of the embodiment of the dynamic spinal stabilization element as shown in  FIG. 6 ; 
         FIG. 8  is a sectional view of a portion of the dynamic spinal stabilization element of  FIG. 7  taken along circle  8 - 8  thereof; 
         FIG. 9  is an enlarged, front perspective view of a rod of the dynamic spinal stabilization element of  FIG. 7 ; 
         FIG. 10  is a sectional view of a portion of the dynamic spinal stabilization element in like manner to the sectional view of  FIG. 8  depicting an alternative embodiment of a dynamic connection member of the dynamic spinal stabilization element of  FIG. 7  that allows for axial translation; 
         FIG. 11  is a sectional view of another form of the embodiment of the dynamic spinal stabilization element as shown in  FIG. 6 ; 
         FIG. 12  is an enlarged, front perspective view of a rod of the dynamic spinal stabilization element of  FIG. 11 ; 
         FIG. 13  is a sectional view of a portion of the dynamic spinal stabilization element of  FIG. 11  taken along circle  13 - 13  thereof; 
         FIG. 14  is a sectional view of a further form of the embodiment of the dynamic spinal stabilization element as shown in  FIG. 6 ; 
         FIG. 15  is an enlarged, front perspective view of a rod of the dynamic spinal stabilization element of  FIG. 14 ; 
         FIG. 16  is an enlarged, front perspective view of another rod of the dynamic spinal stabilization element of  FIG. 14 ; 
         FIG. 17  is a sectional view of a portion of the dynamic spinal stabilization element of  FIG. 14  taken along circle  17 - 17  thereof; 
         FIG. 18  is a side view of an embodiment of a dynamic spinal stabilization element fashioned in accordance with the present principles particularly depicting the direction and/or range of flexibility or motion thereof; 
         FIG. 19  is a sectional view another embodiment of a dynamic spinal stabilization element fashioned in accordance with the present principles; 
         FIG. 20  is an enlarged sectional view of a portion of the dynamic spinal stabilization element of  FIG. 19  taken along circle  20 - 20  of  FIG. 19 ; 
         FIG. 21  is an end view of the dynamic spinal stabilization element of  FIG. 19  taken along line  21 - 21  of  FIG. 19 ; 
         FIG. 22  is an enlarged sectional view of a portion of the dynamic spinal stabilization element of  FIG. 19  taken along circle  22 - 22  of  FIG. 19 ; 
         FIG. 23  is a posterior view of a portion of a spinal column having a spinal stabilization system affixed to adjacent vertebrae and utilizing a linear dynamic spinal stabilization element of the present invention; 
         FIG. 24  is a side view of the portion of the spinal column of  FIG. 23  depicting use of the linear dynamic spinal stabilization element; 
         FIG. 25  is a posterior view of a portion of a spinal column having a spinal stabilization system affixed to adjacent vertebrae and utilizing a curved dynamic spinal stabilization element of the present invention; and 
         FIG. 26  is a side view of the portion of the spinal column of  FIG. 25  depicting use of the curved dynamic spinal stabilization element. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  depicts an exploded view of an embodiment of a dynamic spinal stabilization element or construct generally designated  100  especially for use in a spinal stabilization system or assembly. The dynamic spinal stabilization element  100  is a rod assembly that is designed to be retained at both ends to bone anchoring elements such as bone screws (see e.g.  FIGS. 23-26 ) of the spinal stabilization assembly. The dynamic spinal stabilization element  100  allows motion or movement relative to first and second rods or rod segments  104  and  106 . Particularly, the dynamic spinal stabilization element  100  allows motion or movement of the rod segments  104 ,  106  in two planes of motion, the two planes of motion being perpendicular to one another. The dynamic spinal stabilization element  100  provides a jointed spinal rod. 
     The dynamic spinal stabilization element  100  has a coupling element  102  that provides jointed coupling or attachment to the rod segments  104 ,  106 . The coupling element  102  is formed of a bio-compatible material of a suitable material strength such as titanium. The coupling element  102  has a generally cylindrical body  110  formed with a first configured end  112  and a second configured end  114 . The first configured end  112  includes a rounded nose  113  and first and second flats  116   a ,  116   b  that are disposed diametrically opposite one another. A bore  118  is formed in the configured end  112  that extends between the flats  116   a ,  116   b  and having an axis that is generally perpendicular to the plane of the flats  116   a ,  116   b . The second configured end  114  includes a rounded nose  115  and first and second flats  122   a ,  122   b  that are disposed diametrically opposite one another. A bore  124  is formed in the configured end  114  that extends between the flats  122   a ,  122   b  and having an axis that is generally perpendicular to the plane of the flats  122   a ,  122   b.    
     The first rod segment  104  is formed of a bio-compatible material of a suitable material strength such as titanium and is characterized by a generally cylindrical body  128  of any appropriate length and/or diameter. The body  128  defines a first end  130  and a second end  132 . The first end  130  is adapted for reception by a retention device of a spinal stabilization assembly, while the second end  132  is adapted for connection with the coupling element  102 . 
     As such, the second end  132  has first and second prongs or flanges  134   a ,  134   b  that define a reception area (slot)  136  therebetween. The edges of the flanges  134   a ,  134   b  are rounded or “squared off.” Each prong  134   a ,  134   b  also includes a bore  135   a ,  135   b , respectively, each having an axis that is generally perpendicular to an axis of the body  128 . The slot  136  is sized to receive the end  114  of the coupling element  102  and, particularly, the flats  122   a ,  122   b  between the prongs  134   a ,  134   b  such that the bore  124  aligns with the bores  135   a ,  135   b . A pivot pin  150   a  extends through the bores  134   a ,  124 ,  135   b  upon assembly. An elongated retaining pin  121  extends into a bore  153   a  of the pivot pin  150   a  and into the body  128 . 
     In this manner, the rod segment  104  may pivot about an axis defined by the pivot pin  150   a  (relative to the coupling element  102 ) or vice versa. This is illustrated in  FIG. 2  by the double-headed arrow about an axis of the rod segment  104  particularly in a plane about the axis thereof. The elongated retaining pin  121  may be of various flexibilities to limit or control the extent of or force required for pivoting movement. 
     The second rod segment  106  is formed of a bio-compatible material of a suitable material strength such as titanium and is characterized by a generally cylindrical body  140  of any appropriate length and/or diameter. The body  140  defines a first end  142  and a second end  144 . The first end  142  is adapted for reception by a retention device of a spinal stabilization assembly, while the second end  144  is adapted for connection with the coupling element  102 . 
     As such, the second end  144  has first and second prongs or flanges  146   a ,  146   b  that define a reception area (slot)  148  therebetween. The edges of the flanges  146   a ,  146   b  are rounded or “squared off.” Each prong  146   a ,  146   b  also includes a bore  147   a ,  147   b , respectively, each having an axis that is generally perpendicular to an axis of the body  140 . The slot  148  is sized to receive the end  112  of the coupling element  102  and, particularly, the flats  116   a ,  116   b  between the prongs  146   a ,  146   b  such that the bore  118  aligns with the bores  147   a ,  147   b . A pivot pin  150   b  extends through the bores  147   a ,  118 ,  147   b  upon assembly. An elongated retaining pin  120  extends into a bore  153   b  of the pivot pin  150   b  and into the body  140 . 
     In this manner, the rod segment  106  may pivot about an axis defined by the pivot pin  150   b  (relative to the coupling element  102 ) or vice versa. This is illustrated in  FIG. 2  by the double-headed arrow about an axis of the rod segment  106  particularly in a plane about the axis thereof. The elongated retaining pin  120  may be of various flexibilities to limit or control the extent of or force required for pivoting movement. 
     A sleeve, covering or the like  108  may be provided as part of the dynamic stabilization element  100 . The sleeve  108  is formed by a generally tubular body  158  having a tubular chamber  159 . The diameter of the sleeve  108  is sized to be received over and snugly fit onto the rod segments  104 ,  106  and coupling element  102 .  FIG. 4  depicts the dynamic stabilization element  100  of  FIG. 1  in an assembled form. Again, the double headed arrows illustrate the angulation of the device. The sleeve  108  is formed of a bio-compatible material of a suitable material strength having an appropriate elasticity to allow the pivoting, motion or movement of the assembly joint. In one form, PEEK of a durometer that will allow for angulation (bending or twisting) is used for the sleeve  108 . 
       FIG. 5  depicts a sectional view of the joint defined by the coupling element  102  and the first and second rod segments  104 ,  106 . It can be appreciated that the elongated retaining pins  120 ,  121  flex with pivoting of the respective rod segment  106 ,  104 . The stiffer the retaining pin (less flexible), the greater the resistance to pivoting of the rod segment (more force is required to overcome the modulus of the material and thus provide flexure thereof). Conversely, the less stiff the retaining pin (more flexible), the less the resistance to pivoting of the rod segment (less force is required to overcome the modulus of the material and thus provide flexure thereof). 
       FIG. 3  depicts an alternative embodiment of the dynamic stabilization element  100  of  FIG. 1 . In particular, the dynamic stabilization element  100  of  FIG. 1  utilizes straight rod segments.  FIG. 3  illustrates a dynamic stabilization element  100 ′ that utilizes a curved or bent rod segment  106 ′. The degree of curvature may vary as appropriate as well as the direction of curvature relative to the pivot axis of the coupling element  102 ′ and rod segment  106 ′. While only one ( 106 ′) of the two rod segments  104 ′,  106 ′ of the dynamic stabilization element  100 ′ is curved, it should be appreciated that the other rod segment ( 104 ′) may be curved. The curvature characteristics of each rod segment may be the same or different depending on the application. 
     Referring now to  FIG. 6 , there is depicted another embodiment of a dynamic stabilization element generally designated  170 . The dynamic stabilization element  170  is characterized by first and second spine rods  174 ,  176  and a coupling element  172 . The spine rods  174 ,  176  are adapted to be received by bone attachment assemblies, particularly at ends distal to the coupling element  172 , such that the coupling element  172  is disposed between the bone attachment assemblies. The coupling element  172  is adapted to allow limited bending or angulation as between the rods  174 ,  176 . 
     The dynamic stabilization element  170  is designed to allow angulation in any plane off of (relative to) the axis of the rod (defined as a cone about the axis of the rod). This allows the dynamic rod element  170  to be installed without regard to rotational orientation (which may be necessary for the dynamic stabilization element  100  of  FIG. 1 ). 
     Referring to  FIG. 7 , there is depicted a cross-sectional view of a form of the dynamic stabilization element  170  of  FIG. 6 , generally designated  170 ′. The dynamic stabilization element  170 ′ has a first rod or rod segment  174 ′ and a second rod or rod segment  176 ′. The first rod  174 ′ is characterized by a generally cylindrical rod body  178  formed of a suitable bio-compatible material of sufficient strength. The rod body  178  terminates at one end in a head  179 . The second rod  176 ′ is characterized by a generally cylindrical rod body  180  formed of a suitable bio-compatible material of sufficient strength. The rod body terminates at one end in a head  181 . The heads  179 ,  181  of respective rods  174 ′,  176 ′ are received in coupling device  172 ′. 
     In  FIG. 8 , an enlargement of the coupling device  172 ′ is shown.  FIG. 9  is an enlargement of the end of the rod segment  176 ′ since the end of the rod segment  174 ′ is identical. The end of the rod segment  176 ′ terminates in a head  181  defined in size by an annular groove  184 . The head defines an end surface  183 . Referring back to  FIG. 8 , the coupling device  172 ′ is adapted to retain the ends  179 ,  181  of the respective rods  174 ′,  176 ′. The coupling device  172 ′ is formed by a membrane, sheath or the like  173 . The membrane  173  is preferably, but not necessarily, formed of PEEK with a durometer that will allow for limited angulation (bending) or flexing relative to the rods. 
     The membrane  173  is formed by a middle portion  192  and first and second end portions  196 ,  200 . The first end portion  196  has an annular ridge  197  on an inside surface thereof that is configured to receive the groove  182  of the head  179  of the rod body  178 . The second end portion  200  has an annular ridge  201  on an inside surface thereof that is configured to receive the groove  184  of the head  181  of the rod body  180 . An elastomeric spacer  190  is disposed between the end surfaces of the heads  179 ,  181  within the membrane  173 . The coupling member  172 ′ provides bending between the rods, but prevents axial movement of either rod. 
     Referring to  FIG. 10 , there is depicted a cross-sectional view of a portion of a form of the dynamic stabilization element  170 ′ of  FIG. 7 , generally designated  170 ″. The dynamic stabilization element  170 ″ is identical to the dynamic stabilization element  170 ′ with the exception of the rod segments. Particularly, a rod segment body  178 ′ has a head  179 ′ that is defined by an annular groove  182 ″. The annular groove  182 ′ is axially longer than the annular groove  182  of the rod body  178 . This allows the rod body  178 ′ to limitedly axially move relative to the membrane  173 . The rod segment body  180 ′ has a head  181 ′ that is defined by an annular groove  184 ′. The annular groove  184 ′ is axially longer than the annular groove  184  of the rod body  180 . This allows rod body  180 ′ to limitedly axially move relative to the membrane  173 . The elastomeric spacer  190  provides limited compression for axial movement of the rods. 
     Referring to  FIG. 11 , there is depicted a cross-sectional view of another form of the dynamic stabilization element  170  of  FIG. 6 , generally designated  170 ′″. The dynamic stabilization element  170 ′″ has a first rod or rod segment  174 ″ and a second rod or rod segment  176 ″. The first rod  174 ″ is formed of a suitable bio-compatible material of sufficient strength and terminates at one end in a head  226 . The second rod  176 ′ is formed of a suitable bio-compatible material of sufficient strength and terminates at one end in a head  212 . The heads  212 ,  226  are received in the coupling device  172 ″. 
       FIG. 12  is an enlargement of the rod segment  176 ″ particularly of the head  212  thereof. The rod segments and thus the ends of the rod segments  174 ″ and  176 ″ are identical. The end of the rod segment  176 ″ terminates in a head  212 , the diameter of which may be larger than the diameter of the rod body. The head end  214  is defined by an end surface  214  and diametrically opposed, axially extending arcuate ridges, walls, or the like  218 ,  219  formed on an axial periphery of the end. The ridges  218 ,  219  form like open spaces between the ends thereof that are adapted to receive ridges  218 ,  219  of the rod segment  174 ″. This provides a restricted rotation feature as between the rod segments  174 ″,  176 ″. Also, as the rods subside, or collapse upon each other, the rod segment join acting as one solid member, and no longer provide angulation or rotation. This is provided in various embodiments herein. 
     In  FIG. 13 , an enlargement of the coupling device  172 ″ is shown. The coupling device  172 ″ is adapted to retain the ends  212 ,  226  of the respective rods  176 ″,  174 ″. The coupling device  172 ″ is formed by a one-piece membrane, sheath or the like  224 . The membrane  224  is preferably, but not necessarily, formed of PEEK with a durometer that will allow for limited angulation (bending) or flexing relative to the rods. The membrane  224  is, in one form, over-molded on to the rod ends. 
     The membrane  224  defines an interior chamber  225  that receives the heads  212 ,  226 . The rods  174 ″,  176 ″ are rotationally oriented relative to one another so as to interlock respective ridges  218 ,  219 . The ridges  218 ,  219  also limit angulation. 
     Referring to  FIG. 14 , there is depicted a cross-sectional view of a further form of the dynamic stabilization element  170  of  FIG. 6 , generally designated  170 ″″. The dynamic stabilization element  170 ″″ has a first rod or rod segment  174 ′″, a second rod or rod segment  176 ′″ and a coupling device  172 ′″. The first rod  174 ′″ is formed of a suitable bio-compatible material of sufficient strength and terminates at one end in a head  242 . The second rod  176 ′″ is formed of a suitable bio-compatible material of sufficient strength and terminates at end  258  in a configured boss  260 . The head  242  and configured boss  260  are received in the coupling device  172 ′″. 
       FIG. 15  is an enlargement of the rod segment  176 ′″ particularly showing the head  242  thereof on the end of the rod body  240 . The head  242  has a diameter that is larger than the diameter of the rod body  240 . The head  242  defines an annular, peripheral rim  244  that defines an interior, cavity or recess  246 . The recess  246  has a first surface  248  that is semi-circular in shape, and a second surface  250  that is semi-circular in shape. The second surface  250  is at a depth from the rim  244  that is greater than the depth of the first surface  248  so as to define a perpendicular ledge  252  therebetween. 
       FIG. 16  is an enlargement of the rod segment  174 ′″ particularly showing the end  258  of the rod body  256  and particularly the configured boss  260  thereof. The end  258  has a diameter that is the same as the diameter of the rod body  256 . The boss  260  defines a semi-circular first surface  262 , and a second semicircular surface  264 . The first surface  262  is raised relative to the second surface  264  so as to define a perpendicular ledge  266  therebetween. 
     The rod ends are thus complementary providing an anti-rotation feature as between the rod segments  174 ″,  176 ″ when received in the coupling device. Particularly, the end  258  of the rod  174 ′″ is received into head  242  of the rod  176 ′″ such that the first surface  262  of the end  258  abuts or aligns with the second surface  250  of the head  242 , while the second surface  264  of the end  258  abuts or aligns with the first surface  248  of the head  242 . The ledges  252  and  266  also abut. 
     In  FIG. 17 , an enlargement of the coupling device  172 ′″ is shown. The coupling device  172 ′″ is adapted to retain the ends  242  and  258  of the respective rods  176 ′″,  174 ′″. The coupling device  172 ′″ is formed by a one-piece membrane, sheath or the like  270 . The membrane  270  is preferably, but not necessarily, formed of PEEK with a durometer that will allow for limited angulation (bending) or flexing relative to the rods. The membrane  270  is, in one form, over-molded on to the rod ends. 
     The membrane  224  defines a first interior chamber  272  that is sized to overlay the end  258  and a second interior chamber  274  that is sized to overlay and retain the head  242 . The rod  174 ′″ is rotationally oriented relative to the rod  176 ′″ so as to interlock. The rod  174 ′″ is also limitedly axially movable relative to the coupling device  172 ′″ and thus the rod  176 ′″. 
       FIG. 18  depicts a general dynamic stabilization device  170   a  with rod segments  174   a  and  176   a  joined by coupling element  172   a  representing the various forms of the dynamic stabilization device  170 . The double-headed arrows illustrate the manner of flex, bending or angulation, as well as axial movement where permitted, achieved by the dynamic stabilization device. 
       FIGS. 19-22  depict another embodiment of a dynamic spinal stabilization element or construct generally designated  400  especially for use in a spinal stabilization system or assembly. The dynamic spinal stabilization element  400  is a rod assembly that is designed to be retained at both ends to bone anchoring elements (see e.g.  FIGS. 23-26 ) of a spine stabilization assembly. The dynamic spinal stabilization element  400  allows controlled motion, movement and/or bending relative to first and second rods or rod segments  402  and  404 . The dynamic spinal stabilization element  400  provides a jointed spinal rod having controllable degrees of freedom or bending (compression-distraction). 
     The first rod segment  402  is formed of a bio-compatible material of a suitable material strength such as titanium and is characterized by a generally tubular body  403  of any appropriate length and/or diameter. The second rod segment  404  is formed of a bio-compatible material of a suitable material strength such as titanium and is characterized by a generally tubular body  405  of any appropriate length and/or diameter. 
     The dynamic spinal stabilization element  400  has a coupling element  408  that provides jointed coupling or attachment of the rod segments  402  and  404 . The coupling element  408  is formed of a bio-compatible material of a suitable low durometer such as PEEK or a carbon fiber reinforced PEEK. The coupling element  408  may also be metal such as titanium. The coupling element  408  is formed of a plurality of rings here shown as a center ring  408  having curved faces that form a frusto-conical cross section, first right and left adjacent rings  432  and  434  each having concentric curved faces, second right and left adjacent rings  436  and  438  each having concentric curved faces, and third right and left adjacent rings  440  and  442  each having concentric curved faces. More or less adjacent rings may be provided. 
     The dynamic spinal stabilization element  400  also includes a spring rod  406  made from a hardened titanium (e.g. 6AL4VELI) for providing a spring temper and having a rod body  410  that extends through the rod segments  402  and  404 . The spring rod  406  has a head  412  that is sized to abut the end of the rod segment  402  and an externally threaded tip  414 . An internally threaded nut  420  is provided on the threaded tip  414 . The nut  420  includes a stop  422  that abuts an end  415  of the tip  414 . Adjustment of the nut  420  changes the amount of dynamization of the element  400 . Particularly, as the nut is tightened, the head  412  presses against the end of the rod segment  402  to provide compression. The more compression the less degrees of freedom of dynamization. As the nut is loosened, there is less compression and more degrees of freedom of angulation. Moreover, as the nut is loosened, the spring rod will carry the load and the adjacent rings (coupling element  408 ) act as stops for angulation. The adjacent rings may also aid in preventing stress risers on the spring rod. 
     The dynamic spinal stabilization element  400  can come in lordosed and straight versions. Sizes can vary but exemplary sizes are 5.5 mm and 6.35 mm. There can also be one (1) through three (3) levels available with static and dynamic combinations. Rings or spacers of the connector can be added of an elastomeric compound that provides for movement (dynamization) as described. 
       FIGS. 23 and 24  depict a portion of a spinal column  300  (lower lumbar) to which is attached a dynamic stabilization assembly  310  utilizing a present dynamic stabilization element  316  representing any one of the present dynamic rod structures. Particularly, a first bone anchoring device  312  of the dynamic stabilization assembly  310  is attached to a first vertebra  304 , while a second bone anchoring device  314  of the dynamic stabilization assembly  310  is attached to a second, adjacent vertebra  302 . A first straight rod segment  322  is retained by the first bone anchoring device  312  while a second straight rod segment  320  is retained by the second bone anchoring device  314 . The two straight rod segments  320 ,  322  are joined by a dynamic coupling element  318 . 
       FIGS. 25 and 26  depicted the lower portion of the spinal column  300  to which is attached another dynamic stabilization assembly  410  utilizing a present dynamic stabilization element  416  representing any one of the present dynamic rod structures. Particularly, the first bone anchoring device  412  of the dynamic stabilization assembly  410  is attached to a first vertebra  304 , while a second bone anchoring device  414  of the dynamic stabilization assembly  410  is attached to a second, adjacent vertebra  302 . A first curved rod segment  422  is retained by the first bone anchoring device  412  while a second curved rod segment  420  is retained by the second bone anchoring device  414 . The two curved rod segments  420 ,  422  are joined by a dynamic coupling element  418 . 
     It should be appreciated that the rod segments can be embodied in a multi-level format. Dynamic stabilization assemblies according to the present invention may also include more than one connector. One or more of the present dynamic stabilization assemblies allow for in-situ adjustability. Such in-situ adjustment can limit flexion, extension, rotation and translation (subsidence). 
     It should also be appreciated that the above description is only exemplary of the principles of the subject invention. Therefore, other embodiments are contemplated and within the present scope. 
     It should moreover be appreciated that the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, of adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.