Abstract:
There is shown a system and method for reducing the difficulty in percutaneous placement of a spine stabilization brace. A medical implant system has a first bone anchor having a longitudinal axis, a second bone anchor and a brace. The brace couples the first bone anchor to the second bone anchor. A the distal end of the brace may be pivotally coupled to the first bone anchor and also adapted to slide in a generally transverse direction in relation to the longitudinal axis of the first bone anchor.

Description:
TECHNICAL FIELD 
     This invention relates to bony structure stabilization systems and more particularly to systems and methods for percutaneously inserting a pedicle screw stabilization device. 
     BACKGROUND OF THE INVENTION 
     The human spine provides a vast array of functions, many of which are mechanical in nature. The spine is constructed to allow nerves from the brain to pass to various portions of the middle and lower body. These nerves, typically called the spinal cord, are located in a region within the spine called the neuro canal. Various nerve bundles emerge from the spine at different locations along the lateral length of the spine. In a healthy spine, these nerves are protected from damage and/or undue pressure thereon, by the structure of the spine itself. 
     The spine has a complex curvature made up of a plurality (24 in all) of individual vertebrae separated by intervertebral discs. These discs hold the vertebrae together in a flexible manner so as to allow a relative movement between the vertebrae from front to back and from side to side. This movement then allows the body to bend forward and back and to twist from side to side. Throughout this movement, when the spine is operating properly the nerves are maintained clear of the hard structure of the spine and the body remains pain free. 
     Over time, or because of accidents, the intervertebral discs loose height, become cracked, dehydrated, or are simply jarred out of position. The result being that the disc space height is reduced leading to compression of the nerve bundles causing pain and in some cases damage to the nerves. 
     Currently, there are many systems and methods at the disposal of a physician for reducing, or eliminating, the pain by minimizing the stress on the nerve bundles. In some instances, the existing disk is removed and an artificial disk is substituted therefore. In other instances, two or more vertebrae are fused together to prevent relative movement between the fused discs. 
     Often there is required a system and method for maintaining proper space for the nerve bundles that emerge from the spine at a certain location. In some cases a cage or bone graft is placed in the disc space to preserve height and to cause fusion of the vertebral level. As an aid in stabilizing the vertebrae, one or more rods or braces are placed between the fused vertebrae with the purpose of the braces being to support the vertebrae, usually along the posterior of the spine while fusion takes place. These braces are often held in place by anchors which are fitted into the pedicle region of the vertebrae. One type of anchor is a pedicle screw, and such screws come in a variety of lengths, diameters, and thread types. 
     One problem when connecting the braces to the anchors is to position the braces in place as quickly as possible and without doing more damage to the surrounding tissue and muscle of the patient as is absolutely necessary. For that reason, procedures have been developed that allow the physician to secure the anchors in the bony portion of the spine and to then connect the brace between the anchors. Techniques have been developed to allow the surgeon to perform this procedure in a minimally invasive manner, utilizing a percutaneous method. 
     In one such procedure, a first pedicle screw is inserted in a first vertebra to be stabilized. This screw is inserted using a tube, or cannula, extending through the patient&#39;s skin to the pedicle portion of the vertebrae. A second pedicle screw is inserted through a second cannula into the second vertebrae to be stabilized. Under current practice, the physician then must work the brace, or other supporting device, so that each brace end is positioned properly with respect to the preplaced pedicle screws. In order to properly position the brace ends fluoroscope pictures are taken as the brace is worked into position. It is difficult for the physician to know the exact orientation of the brace and even to know for certain when the brace ends have been properly positioned. U.S. Pat. No. 6,530,929 shows one instrument for positioning a stabilization brace between two preplaced anchors. 
     Another problem with both of the approaches discussed above, is that the braces must be made significantly longer than the distance between the pedicle screws to allow for proper attachment of the brace ends to the screws. Placement of the brace is sensitive to anchor alignment since the adjustment establishes the trajectory of the brace. If this trajectory is not established properly, the brace would have to pass through tissue, and, or bone that should not be touched. Also, the brace must enter a separate incision in the back of the patient. In addition to these, the learning curve for manipulation the insertion device of the &#39;929 patent is greater than what should be required. 
     Another, more recent, approach has been to insert the cannulas over the respective pedicle areas of the vertebrae to be stabilized and then measure the distance between the cannulas. This measurement is then used to select, or cut, a rod, adding a bit to the dimension to ensure that the rod can be rigidly affixed to each anchor. In addition, each rod must be bent a certain amount (or a pre-bent rod utilized) to reflect the curvature of the spine. Once the proper rod dimension and shape is obtained each end of the rod is positioned in a separate one of the cannulas and the rod is worked downward toward the anchors passing through a separation of muscle and tissue from the skin line to the pedicle site. This placement of the rod is facilitated by a long handheld gripper which must then be manipulated to position the rod ends over the respective anchors so as to be captured by set screws in the tops of the respective anchors. Proper positioning of the rod ends is difficult, and requires repeated use of fluoroscopy to insure that the rod is fully seated and in a correct position. 
     BRIEF SUMMARY OF THE INVENTION 
     In one embodiment, there is shown a system and method for reducing the difficulty in percutaneous placement of a spine stabilization brace by coupling the brace to a pedicle screw in a single assembly. The brace-screw assembly is delivered along with an anchor extension through a cannula for anchoring in the vertebrae pedicle. The anchor extension, which becomes a cannula for working on the brace from the exterior of the patient, is constructed with partial slot openings along two sides. Once the screw portion of the brace-screw assembly is locked in place with respect to the first vertebrae, the proximal end of the brace is below the skin line. The brace is then repositioned so that the proximal end leaves the cannula through one slot and is captured by a corresponding slot positioned in a second cannula coupled to a second anchor. Once captured, the proximal end of the brace is guided by the second cannula to a receptacle positioned in the second vertebrae. In one embodiment, the distal end of the brace is designed to adjust about the head of the first anchor and is further designed to allow for polyaxial as well as lateral movement, thereby adjusting for relative distances and angles between vertebrae. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the Claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended Claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sketch of the human spine showing a pair of cannulas positioned with respect to two vertebrae; 
         FIGS. 2A-2F  show a cut-away view showing different stages of the installation of the stabilization device; 
         FIG. 3A  shows a side view of two vertebrae; 
         FIG. 3B  shows a top view of a single vertebrae; 
         FIG. 4  shows an embodiment of a slated cannula; 
         FIG. 5A  shows a brace-anchor assembly within a cannula; 
         FIG. 5B  is a cross-section view taken through line  5 B- 5 B of  FIG. 5A ; 
         FIG. 5C  is a cross-section view taken through line  5 C- 5 C of  FIG. 5A ; 
         FIG. 6A  shows the receiving cannula attached to a receiving anchor; 
         FIG. 6B  is a cross-section view taken through line  6 B- 6 B of  FIG. 6A ; 
         FIG. 6C  is a cross-section view taken through line  6 C- 6 C of  FIG. 6A ; 
         FIG. 7A  shows the brace-anchor assembly of  FIG. 5A  with the brace in a brace-down (rotated) position; 
         FIG. 7B  is a cross-section view taken through line  7 B- 7 B of  FIG. 7A ; 
         FIG. 7C  is a cross-section view taken through line  7 C- 7 C of  FIG. 7A ; 
         FIG. 8A  shows the receiving cannula of  FIG. 6A  having captured a brace from an adjacent cannula; 
         FIG. 8B  is a cross-section view taken through line  8 B- 8 B of  FIG. 8A ; 
         FIG. 8C  is a cross-section view taken through line  8 C- 8 C of  FIG. 8A ; 
         FIG. 9  shows an embodiment of a hinged brace; 
         FIG. 10  shows an embodiment of a pair of anchors each firmly attached to a brace; 
         FIG. 11  illustrates one embodiment of a screw driver applying force to a brace; and 
         FIGS. 12A and 12B  illustrate one embodiment of a tool for positioning the brace. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to  FIG. 1 , there is shown a sketch of human spine  10  showing a pair of tubes, or cannulas  41  and  42  extending through skin  101  into vertebrae L5 and L4. Cannula  41  is positioned over the pedicle of vertebrae L5 (as will be discussed), and cannula  42  is positioned over the pedicle of vertebrae L4. This procedure is being illustrated with respect to vertebrae L4 and L5 but could be performed with respect to any vertebrae or with respect to any bony portions of the body (human or animal) where a brace is to be placed between two points. The distance D is variable as desired. The sketch of  FIG. 1 , as are the sketches shown in other figures, are not to scale and are shown for illustration purposes with angles selected for clarity of explanation and not necessarily selected to be anatomically correct. 
     The procedure to insert the brace between vertebrae L5 and L4 is as follows: The surgeon identifies the desired vertebral levels and pedicle positions via standard techniques. Once the target vertebrae are identified, a small incision  102  is made through skin  101  and a tracking needle (or other device) is inserted to pinpoint exactly where each anchor is to be placed. A fluoroscope, or other x-ray technique, is used to properly position the tracking needle. Once the proper position is located, guide wire (K wire)  22  ( FIG. 2A ) is positioned with its distal end against the pedicle, in this case pedicle  37 - 1  of vertebrae L5. A guide wire  23  may be similarly positioned with its distal end against pedicle  37 - 1  of vertebrae L4, as shown in  FIG. 2A . The surgeon then slides a series of continuing larger sized dilators  12 ,  12   a ,  12   b ,  12   c  down wire  22 , and slides a series of continuing larger sized dilators  13 ,  13   a ,  13   b ,  13   c  down wire  23  as shown in  FIG. 2B . 
     Approximately four or five dilators are used until a diameter suitable for passing the pedicle screw and its extensions is achieved. A tap is sent down over the K wire to tap a hole into the pedicle in preparation for receiving the anchor, which in this case is a pedicle screw. This tap will usually be a size slightly smaller than the pedicle screw thread size selected for that patient and that level. 
     After the hole is tapped and the K wire and the inner dilators, such as dilators  13 ,  13   a ,  13   b , are removed, the surgeon is ready to introduce the anchor into the vertebrae. As shown in  FIG. 2C , prior to inserting the anchor, brace  90  is attached to screw  51  to form a brace-screw assembly. This assembly is then positioned at the distal end of cannula  41  and a screwdriver or wrench ( 1101  shown in  FIG. 11 ) is inserted into cannula  41  and attached to the proximal end  91  of brace  90 . The entire assembly is then inserted into dilator  13 C. The screwdriver engages with proximal end  91  of brace  90  so as to allow the surgeon to screw pedicle screw  51  into the pre-tapped hole in vertebrae L5. Pressure on the screwdriver forces the screw to be in-line with the brace, which, in turn, is in-line with the screwdriver. The screwdriver can be removeably attached to end  91  of brace  90  by engaging, for example, flat  94  (shown in  FIG. 11 ) and/or hole  95  (shown in  FIG. 9 ). 
     This same procedure would be repeated for each additional level, in this case level L4, except that screw  61  has assembly  62  affixed thereto. Assembly  62  is adapted to receive proximal end  91  of brace  90  as will be more fully described herein. 
     For a single level the above procedure is typically performed first on one side of both vertebral levels and then on the other side. When finished, four pedicle screws are inserted, holding two braces positioned laterally with respect to the center of the spine. 
     Once both screws are in place in vertebrae L5 and L4, dilators  12 C and  13 C are removed and, the surgeon slides a blunt dissection tool into incision  102  ( FIG. 1 ) and gently parts the muscle bundle below the skin between vertebrae L4 and L5. Alternatively, the blunt dissection tool could go down the second cannula and, starting at the bottom of the second cannula  41 , work open the muscle bundle between the cannula working upward as far as is necessary. Using this procedure, the muscles (and other tissue), only need be separated to a point where the brace  90  must pass. Thus, the separation need not go to the skin level. This reduces trauma even further. 
     Once an opening in the muscles has been developed between cannulas  41  and  42 , brace  90  is then positioned, by pivoting, as shown in  FIG. 2D , by sliding a tool (for example, tool  1200 ,  FIG. 12A ) down cannula  41  to engage proximal end  91  of brace  90 . The tool could have a force fit with end  91  or as shown in  FIG. 12A , can have handle  1201  and trigger control  1204  for controlling removable attachment with brace  90 . One or more wires  1205 ,  1206  and  1207  extending inside tool portions  1202 ,  1203 , can be controlled by triggers  1204  and  1208  so that spring loaded grips (not shown) controlled by wire  1202  can mate with hole  95  (shown in  FIG. 9 ). Trigger  1208  can control wire  1205  to releasably grip end  91  of brace  90 . Once portion  1203  is mated with end  91  of brace  90  the surgeon can pull the tool slightly outward to disengage brace end  92  from screw  51 . The surgeon can then operate wires  1206  and  1207 , via trigger  1204 , or otherwise, which wires pull on one side of tool portion  1203  to bend tool portion  1203 , as shown in  FIG. 12B . This bending forces brace end  91  out of cannula  41  (through opening  402  thereof) and through the prepared muscle opening and into opening  402  of cannula  42 . Once within cannula  42 , tool end  1203 , under control of the surgeon, manipulates brace end  91  down cannula  42  and into a mating relationship with screw  61 . Once this mating relationship is achieved, (as will be discussed) tool end  1203  is released from brace end  91 , under control of wire  1205  and tool  1200  is removed from both cannulas. Wires  1206  and  1207  are used on opposite sides of tool  1200  under control of trigger  1208  to control bending and unbending of tool portion  1203 . Note that only temporary locking mechanism and/or tool bending mechanism, including pneumatic and hydraulic can be used, if desired. 
     Slots  402  of the respective cannulas are positioned fully under the skin line  101  of the patient. Brace  90  can have any shape desired. It can be flat, oval or rod shaped and the cross-section need not be constant in shape or diameter. 
     The surgeon receives positive feedback (a sensory event), either by feel (for example, a snap action) or by sound (for example, a click), or both when brace  90  is properly mated with assembly  62 . If desired, one or both of assembly  52  or  62  mounted to the respective pedicle screws  51  and  61  can be angularity adjusted (as will be discussed) to accommodate the patient&#39;s body structure. The polyaxial nature of assemblies  52  and  62  with respect to the anchors allows for such adjustments which are necessary for a variety of reasons, one of which is that the angulation between adjacent vertebral pedicles varies. 
     As shown in  FIG. 2E , after all angular and lateral adjustments are made, set scres  220 , or other locking devices, are introduced down cannulas  41  and  42  to lock each end of brace  90  to its respective pedicle screw. 
     As shown in  FIG. 2F , once the proximal end of brace  90  is snapped in place to screw  61  and set screws  220  are tightened, cannulas  41  and  42  can be removed and the incision closed. As discussed, this procedure would then be repeated on the opposite side of spinous process  33 . 
       FIG. 3A  is a lateral view of two vertebrae segments and L5 and L4. Nerve roots  32  are shown coming out from spinal cord  301 . The nerve roots become compressed when vertebrae L4 collapses down upon vertebrae L5 when disc  31  becomes reduced in size due to injury, a dehydration or otherwise. Spinous processes  33  form a portion of the posterior of the vertebral bodies. 
       FIG. 3B  is a top view of vertebrae L4 and is similar to other lumbar levels. A Vertebra L4 includes vertebral body  36 , spinous process  33 , neuro canal  34 , and transverse processes  35 . The pedicle region, such as pedicle  37 , is the bony area bridged roughly between outer wall  38  and neuro frame  34 . Areas  37 - 1  and  37 - 2  are the target areas for the pedicle screws, as discussed above. 
       FIG. 4  shows cannulas  41  and  42  which could be identical, if desired. Cannula  41  includes opening  401  to allow for lateral adjustment of the distal end of brace  90 . On cannula  42 , opening  402  can be adjusted downward from that of cannula  41  (because of the arc of brace  90 ) so as to more precisely capture and retain proximal end  91  of brace  90 . Also, as will be seen, the opening  402  on cannula  42  can be adopted to receive the shape of end  91  of brace  90 , and lower opening  401  eliminated, if desired. 
       FIG. 5A  shows pedicle screw  51 , and brace rod adjustment assembly  52 . Assembly  52  acts as a hinge for brace  90  positioned within cannula  41 . Screw portion  51  is extended out from the base of the connection in an in-line orientation with brace  90 . By the application of torque to proximal end  91  of brace  90  by a screwdriver (or wrench), as discussed above, and or as shown in  FIG. 11 , screw  51  can be turned so that it can be screwed into the bone as desired. Note that assembly  52  has two openings  520  and  521  which, as will be seen, allow brace  90  to pivot. 
     Screw  51  is connected to assembly  52  as will be described herein. This combination is attached to the distal end of cannula (extension)  41  by, for example, constructing flexible fingers at the distal end of cannula  41  and constructing on the inside of these fingers protrusions in the form, for example, of small pyramids. These pyramids then fit into a tight mating relationship with mating structures constructed on the parity of assembly  52 . When it is desired to release cannula  41  from assembly  52 , upward pressure and perhaps a tap is applied to the ring at the proximal end of cannula  41 . That upward force causes the fingers to fly outward. Thereby releasing the above-described mated structures. This same arrangement is used to assemble and release cannula  42  from assembly  62  ( FIG. 6A ) 
       FIG. 5B  is a cross-section taken through line  5 B- 5 B of  FIG. 5A  and shows screw  51  attached to brace  90  via assembly  52 . Brace  90  is shown curved to approximate the spinal curvature. The length of brace  90  is selected to show the distance between the respective anchors. For the L5-L4 level this distance is approximately 35 mm to 45 mm. 
       FIG. 5C  shows screw  51  having neck  53  and head  54 . Screw  51  also has recess area  55  designed for mating with end  92  of brace  90 . This mating call be a slot or other flat configuration or any means of connecting two structures together so that force (in this embodiment the force is torque) can be delivered from one to another. Brace  90  will, when desired, lift upward so as to unmate end  92  from flat  55  so that brace  90  can then pivot with respect to assembly  52 . Bearings  501  positioned in slots  93  of brace  90  facilitate such pivoting. Slots  93  serve to limit the in-line and lateral distance brace  90  can move. Bearings  501  also serve as a pivot point for brace  90  and to prevent brace  90  from turning. 
     Assembly  52  allows brace  90  to move from the in-line position to a rotated position while also accommodating the lateral motion of brace  90 . This lateral motion accommodates different lateral distances between anchors. Assembly  52  can be constructed in different ways and from different materials as desired, for example, as shown in U.S. Pat. No. 5,672,176 hereby incorporated by reference herein. When brace  90  is repositioned to approximately a 90° angle and a set screw (not shown) is in place within threads  506 , pressure is applied downward on the side of brace  90 . This action, in turn, applies pressure on clamp  502 , forcing wedge  503  against head  54  of screw  51 . This then locks the polyaxial mechanism in place and prevents brace  90  from further movement with respect to screw  51 . This clamping action also maintains the relative angular position between brace  90  and screw  51 . Spring band  505  snaps between a groove in clamp  502  and a groove in shell  504  holding assembly  52  together. Note that assembly  52  can be separate from screw  51  as shown or can be constructed integral thereto. Also note that the polyaxial motion described is not necessary and can be eliminated, if desired. 
       FIG. 6A  shows cannula  42  having slot  403 , with opening  402  positioned to receive end  91  of brace  90 . Once end  91  is captured within slot  402 , end  91  passes down inside cannula  42  crrying brace  90  down slot  403  toward assembly  62 . Slot  620  in assembly  62  allows brace  90  to enter assembly  62 . 
       FIG. 6B  is a cross-section taken along lines  6 B- 6 B of  FIG. 6A , and shows assembly  62  with receptacle  66 . Receptacle  66  is designed, in one embodiment, to snap together with end of brace  90 . This snap-action provides positive feed back to the surgeon, either by feel or audibly, or both. This tactile (or audible) feed back is caused, for example by end  91  passing into receptacle  66 . In one embodiment, a force fit could be achieved between end  91  and receptacle by making the inner circumference of the outer rim of receptacle  66  smaller than the diameter of end  91 . Mating can be facilitated by cutting small grooves or slots in receptacle  66  to allow receptacle  66  to expand around end  91  for a locking fit. This expansion occurs as end  91  enters into receptacle  66 . As the mating occurs, end  92  of brace  90  ( FIG. 7A ) is free to move laterally with respect to anchor  51  since brace  90  is held in place (as discussed above) by bearings  501  riding in slots  93  ( FIG. 7C ). 
       FIG. 6C  shows an expanded view of assembly  62  mounted to head  64  of screw  61 . Receptacle  65  accepts a wrench or screw driver from the surgeon for inserting screw  61  into the bone and is accessible through the base of receptacle  66 . Clamp  602  acts on wedge  603  to apply force on head  64  of screw  61 . Until tightened fully by a set screw positioned within threads  505 , assembly  62  is free to rotate polyaxially around head  64  of anchor  61 . This polyaxial movement can, if desired, be eliminated. 
       FIG. 7A  shows the brace/screw assembly with brace  90  repositioned approximately 90° with respect to screw  51 . Screw  51  would be embedded in a bony structure (or other hard structure), not shown in  FIG. 7A . In a particular application, the exact rotation will depend upon many factors, including the angle between anchors and the angle the respective anchors make with respect to the bone in which they are imbedded. 
       FIG. 7B  slows a cross-section taken along line  7 B- 7 B of  FIG. 7A . As shown, brace  90  is rotated approximately 90° with respect to assembly  52 . End  92  of brace  90  has been disengaged from mating structure  55  on head  54  of screw  51 . In  FIG. 7B , set screw  220  is shown about to press down on brace  90  to compress brace  90  to screw head  54 , as previously discussed. 
       FIG. 7C  is a cross-section taken through line  7 C- 7 C of  FIG. 7A  and again shows brace  90  rotated 90° with respect to screw  51 . Lateral movement of brace  90  (in and out of the page in  FIG. 7C  and left and right in  FIG. 7B ) is facilitated by berings  501  riding in grooves  93  of brace  90  and acting both as a fulcrum and as lateral limitation. All such movement is inhibited when set screw  220  presses down on brace  90 . Wing  511  on clamp  503  prevents clamp  503  from upward movement. 
       FIG. 8A  shows the receptacle/screw assembly with brace  90  positioned in its capture mode with respect to assembly  62 . Assembly  62  is, in turn, mounted on head  64  of screw  61 . Screw  61  would be embedded in a second bony structure (on other hard structure) not shown in  FIG. 8A . 
       FIG. 8B  shows a cross-section taken along line  8 B- 8 B of  FIG. 8A . End  91  of brace  90  is captured by receptacle  66 . Set screw  220  is shown applying downward pressure on brace  90  in order to lock brace  90  to screw head  64  as previously discussed. The inner geometry of receptacle  66  is keyed to match the proximal end of brace  90 . 
       FIG. 8C  shows a cross-section taken along line  8 C- 8 C of FIG  8 A. End  91  of brace is shown mated with receptacle  66  and locked tight by set screw  220 . Once set screw  220  presses down on brace  90 , hinge assembly  62  clamps against head  64  of screw  61  to prevent further movement of brace  90  with respect to screw  61 . Area  610  is created in assembly  62  such that receptacle  66  can expand as brace end  91  passes into the receptacle. Wing  611  on wedge  603  prevents wedge  603  from moving upward. 
       FIG. 9  shows one embodiment of brace  90  with distal end  92  and proximal end  91 . Slot  93  is longer than actually necessary to allow for lateral movement of brace  90  during the seating process so as to allow for different distances between anchors. As discussed, distal end  92  can have any shape required for mating with head  54  of screw  51  for the purpose of force transfer. Also note that proximal end  91  has a ball (or partial ball) shape for capture by slot  402  of cannula  42 . End  91  can have any shape, provided such shape is adapted for capture by cannula  42 . 
       FIG. 10  shows a single level brace system  1000  having brace  90  with its distal end  92  clamped tightly with respect to screw  51  (a first anchor) and its proximal end  91  clamped tightly with respect to screw  61  (a second anchor). Each of these anchors is firmly supported in a respective bony structure (not shown in  FIG. 10 ) of a patient. Note that brace  90  is slightly curved to, at least partially, adjust for the spine curvature. Also note that the respective anchors are not necessarily parallel to each other but each has assumed an angle necessary for proper placement in the pedicle (or other bony area) of the respective vertebra. While the brace has been shown with respect to the L4 and L5 vertebrae, the system, method, and device discussed herein are not so limited and can be used between any bony or other hard portions that must be supported, including single level or multilevel. 
     For bracing two or more levels, one option is to skip one or more vertebral levels onto the anchor, another option is to use a “pass-through” anchor assembly on the skipped vertebral level(s). The pass-through assembly can be adapted for locking to the brace on the portion of the brace passing through the middle assemblies. Another option would be to have a dual headed anchor on the center vertebra which accepts braces, one brace from each of the other surrounding levels. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended Claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended Claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.