Abstract:
Screw mechanisms that securely connect with and contain an elongated support structure are disclosed. Some of these have locking mechanisms as alternatives to conventional set screws. Some of these use ratcheting systems for securing the elongated support structure. Some of these are multi-axial systems. Some of these are alternatives to conventional systems.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates in general to screw mechanisms for securing a ligament, tether, rod, and other supporting structure to bone. 
       BACKGROUND 
       [0002]    Several techniques, systems, and supporting structures have been developed for correcting and stabilizing the spine. Some systems use supporting structures like a rod, a tether, a ligament, or others disposed longitudinally along a length of the spine or vertebral column. In accordance with such a system, the supporting structure is engaged to various vertebrae along a length of the spinal column by way of a number of fixation elements. A variety of fixation elements are configured to engage specific portions of the vertebra. For instance, one such fixation element is a hook that is configured to engage the laminae of the vertebra. Another very prevalent fixation element is a spinal bone screw which can be threaded into various aspects of the vertebral bone or pelvis. For example, a plurality of spinal bone screws can be threaded into a portion of several vertebral bodies and the sacrum, such as, for example, the pedicles of these vertebrae. The supporting structures can then be affixed to these spinal bone screws to apply corrective and stabilizing forces to the spine. 
         [0003]    Conventional bone screws can be improved to more easily implant or secure the supporting structures, more easily align the supporting structures, or provide other benefits. 
         [0004]    The present disclosure overcomes one or more shortcomings in the art. 
       SUMMARY 
       [0005]    The present disclosure is directed to improved screw mechanisms that securely connect with and contain an elongated support structure. Some of these have locking mechanisms as alternatives to conventional set screws. Some of these use ratcheting systems for securing the elongated support structure. Some of these are multi-axial systems. Some of these are alternatives to conventional systems. 
         [0006]    In one exemplary aspect, a screw mechanism for connection with an elongated supporting structure is disclosed. In exemplary aspect disclosed herein the mechanism includes a threaded anchor portion configured to penetrate bone tissue and includes an outer receiver attached to the threaded anchor portion. The outer receiver is formed with first and second extending legs and has a transverse passage therethrough. The passage has inner sidewalls. The mechanism also includes an inner receiver receivable into the outer receiver and having outer sidewalls. The outer sidewalls of the inner receiver and the inner sidewalls of the outer receiver passage have articulating or deformable connectors formed thereon. These connectors cooperate to permit the inner receiver to articulate relative to the outer receiver. The inner receiver is formed with a first longitudinally extending opening and has a second transverse opening therethrough sized and shaped to receive the stabilizing supporting structure. The inner receiver is deformable from an unlocked condition where the inner receiver is not frictionally engaged with the U-shaped inner surface in a manner that prevents articulation of the inner receiver relative to the outer receiver to a locked condition where the inner receiver is frictionally engaged with the U-shaped inner surface in a manner that prevents articulation of the inner receiver relative to the outer receiver. The mechanism also includes a locking mechanism receivable into the first longitudinally extending opening and configured to apply a driving force that deforms the inner receiver from the unlocked condition to the locked condition. 
         [0007]    In another exemplary aspect, the screw mechanism includes an outer receiver formed with first and second extending legs forming a U-shaped inner surface, the U-shaped surface having a bottom surface and inner sidewalls. An inner receiver is receivable into the outer receiver. The inner receiver has outer sidewalls. The inner receiver is formed with a first longitudinally extending opening having threads on the inner circumference and having a second transverse opening therethrough sized and shaped to receive the elongated supporting structure. The inner receiver has legs deformable from an unlocked condition where the legs are not frictionally engaged with the U-shaped inner surface in a manner that prevents articulation of the inner receiver relative to the outer receiver to a locked condition where the legs are frictionally engaged with the U-shaped inner surface in a manner that prevents articulation of the inner receiver relative to the outer receiver. A locking mechanism is receivable into the first longitudinally extending opening and configured to apply a driving force that deforms the inner receiver from the unlocked condition to the locked condition. 
         [0008]    In another exemplary aspect, the screw mechanism includes an outer receiver formed with first and second extending legs and having a transverse passage therethrough, the passage having inner sidewalls. An inner receiver is receivable into the outer receiver and has outer sidewalls and is configured to articulate relative to the outer receiver. The inner receiver has a first longitudinally extending opening and a second transverse opening. The second transverse opening is sized and shaped to receive the stabilizing supporting structure. The first longitudinal opening is in communication with the second transverse opening. The inner receiver is deformable from an unlocked condition where the inner receiver is not frictionally engaged with the U-shaped inner surface in a manner that prevents articulation of the inner receiver relative to the outer receiver to a locked condition where the inner receiver is frictionally engaged with the U-shaped inner surface in a manner that prevents articulation of the inner receiver relative to the outer receiver. 
         [0009]    Further aspects, forms, embodiments, objects, features, benefits, and advantages of the present invention shall become apparent from the detailed drawings and descriptions provided herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIGS. 1 and 2  are illustrations of a first embodiment of an exemplary bone screw system for securing an elongated supporting structure in accordance with one or more aspects of the present disclosure. 
           [0011]    FIGS.  3  and  4 A- 4 C are illustrations of a second embodiment of an exemplary bone screw system in accordance with one or more aspects of the present disclosure. 
           [0012]      FIGS. 5A-5C  are illustrations of a third embodiment of an exemplary bone screw in accordance with one or more aspects of the present disclosure. 
           [0013]      FIGS. 6-8 ,  9 A,  9 B, and  10 A- 10 C are illustrations of a fourth embodiment of an exemplary bone screw in accordance with one or more aspects of the present disclosure. 
           [0014]      FIG. 11  is an illustration of an exemplary top clamp usable on a bone screw in accordance with one or more aspects of the present disclosure. 
           [0015]      FIGS. 12 ,  13 A,  13 B, and  14  are illustrations of a fifth embodiment of an exemplary bone screw in accordance with one or more aspects of the present disclosure. 
           [0016]      FIGS. 15 and 16  are illustrations of a sixth embodiment of an exemplary bone screw in accordance with one or more aspects of the present disclosure. 
           [0017]      FIGS. 17A and 17B  are illustrations of a seventh embodiment of an exemplary bone screw in accordance with one or more aspects of the present disclosure. 
           [0018]      FIGS. 18A and 18B  are illustrations of an eighth embodiment of an exemplary bone screw in accordance with one or more aspects of the present disclosure. 
           [0019]      FIGS. 19-21  are illustrations of a ninth embodiment of an exemplary bone screw and an associated assembly tool in accordance with one or more aspects of the present disclosure. 
           [0020]      FIGS. 22A and 22B  are illustrations of a tenth embodiment of an exemplary bone screw in accordance with one or more aspects of the present disclosure. 
           [0021]      FIGS. 23-26  are illustrations of an eleventh embodiment of an exemplary bone screw in accordance with one or more aspects of the present disclosure. 
           [0022]      FIG. 27  is an illustration of a twelfth embodiment of an exemplary bone screw in accordance with one or more aspects of the present disclosure. 
           [0023]      FIGS. 28-30  are illustrations of a thirteenth embodiment of an exemplary bone screw in accordance with one or more aspects of the present disclosure. 
           [0024]      FIG. 31  is an illustration of an alternative shell ring usable with the exemplary bone screw of  FIGS. 28-30 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments, or examples, illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
         [0026]    The embodiments disclosed herein are directed toward systems for more predictably and reliably securing elongated supporting structure, such as ligaments, tethers, and rods, for example, to a bone screw. Furthermore, many of these embodiments simplify the procedure for securing the elongated supporting structure within a bone screw through controlled compression between the screw and the elongated supporting structure. Some of these use a locking mechanism having a preliminary locking condition that loosely secures the elongated supporting structure in place and a final locking condition that more securely holds the elongated supporting structure in place. In addition, some of these embodiments do not require threading of a set screw to secure the elongated supporting structure in place. This reduces the difficulties of ligament reduction and perfect set screw alignment. 
         [0027]    Various embodiments are described as being used with a ligament, a tether, or a rod. However, these embodiments are not limited to being used with the specific type of elongated supporting structures described. It is contemplated that any of the embodiments described herein may be used with any elongated supporting structure, including but not limited to ligaments, rods, tethers, bands, and natural or synthetic devices, known and unknown. In addition, these embodiments are described as being connected to threaded anchor portions. It is contemplated that hooks or other bone connecting mechanisms can be used in place of the threaded anchors. 
         [0028]      FIG. 1  shows an exemplary screw mechanism  100 . The screw mechanism  100  comprises a receiver  102  and a threaded portion  104 . In this exemplary embodiment the receiver  102  comprises a first arm  106  and a second arm  108 . Together these arms receive and secure an elongated supporting structure like a ligament in place. In this embodiment, one or both of the first and second arms  106 ,  108  pivot relative to the other about a swivel mechanism  110 . In some embodiments, the swivel connection is a hinge or pin connection or deformable linkage. The swivel mechanism  110  in this embodiment is a pin extending through a base portion of the first arm  106  and the second arm  108 , thereby pivotably connecting the arms together. Accordingly, the first arm  106  may pivot relative to the second arm  108 . 
         [0029]    In this embodiment, as is apparent in  FIG. 2 , the first arm  106  is movable about the swivel mechanism  110  while the second arm  108  is rigidly fixed relative to the threaded anchor portion  104 . In another exemplary embodiment, the second arm  108  is pivotable relative to the threaded anchor portion  104  and the first arm  106  is fixed relative to the threaded anchor portion  104 . In another embodiment, both the first and second arms  106 ,  108  pivot relative to each other and the threaded anchor portion  104 . 
         [0030]    The screw mechanism  100  includes a locking system  112  for placing the screw mechanism in a preliminary locking condition and in a final locking condition to fixedly secure a ligament within the receiver  102  without the use of a set screw. In this embodiment, the locking system  112  includes a plurality of teeth  114 , which in this embodiment are formed on the first arm  106  and at least one ratcheting engagement tooth  116  formed on the second arm  108 . When a ligament or other longitudinal linkage member is introduced into the receiver  102  the movable first or second arm  106 ,  108 , depending upon the embodiment, will move until the ratcheting engagement tooth  116  engages the teeth  114  of the opposing arm. As the ratcheting engagement tooth  116  ratchets along the teeth  114  the ligament is in a preliminary locking condition within the receiver  102 . Accordingly, it can be manipulated within the receiver such that it may slid axially through the receiver or otherwise be manipulated by the service provider for final placement, but it cannot be removed from the receiver. When the ligament or other type of longitudinal linkage member is properly located, the service provider places the locking system  112  in a final locking condition by further compressing the first and second arms  106  and  108  together such that the ratcheting engagement tooth  116  further engages the additional teeth  114 , decreasing the inner receiver space and compressing upon the ligament or longitudinal linkage member. 
         [0031]    In this embodiment, the teeth  114  are shown on first arm  106  and an engagement tooth  116  is shown on the second arm  108 . Nevertheless, it should be apparent that the teeth  114  may optionally be disposed on the second arm  108  and the engagement tooth  116  may be disposed on the first arm  106 . Also, in the embodiment shown, the second arm  108  extends across the top portion of the screw mechanism  100 . In other embodiments, both the first and second arms  106 ,  108  are shaped so that the locking mechanism is disposed directly above a ligament when the screw mechanism  100  is finally locked on a ligament. Such embodiments accommodate placing the ligament into the receiver from the top, rather than from the side. Other arrangements are also contemplated. 
         [0032]    FIGS.  3  and  4 A- 4 C show another embodiment of a screw mechanism, referenced herein by the numeral  150 . Like the screw mechanism  100  described above, the screw mechanism  150  includes a receiver  152  and a threaded anchor portion  154 . The receiver  152  comprises a first arm  156  and a second arm  158 . Together the first and second arms  156 ,  158  form a ligament receiving opening for receiving the ligament. In this embodiment, a base portion  160  adjacent the threaded anchor portion  154  and the first arm  156  includes a passage or aperture  162  (best seen in  FIG. 3 ) that receives a leg  164  of the second arm  158 . In this embodiment, the leg  164  has a series of teeth  166  formed thereon. The aperture  162  likewise has at least one tooth  168  formed thereon for engaging and ratcheting with the teeth  166  in a manner similar of that discussed above relative to the engagement tooth  116  and the tooth  114  of  FIGS. 1 and 2 . Accordingly, these teeth form a locking system  170  that comprises the teeth  166 , the aperture  162 , and a locking engagement tooth associated with the aperture  162  and the first arm  166 . 
         [0033]    Accordingly, by inserting the leg  164  of the second arm  158  into the aperture  162  until the teeth  166 ,  168  engage, the receiver  152  may be placed in a preliminary locking condition that prevents removal of the ligament from the receiver, but still allows manipulation of the ligament in the receiver. Further advancement of the leg  164  through the aperture  162  ratchets the teeth  166 ,  168  places the receiver  152  in a final locking condition, securing the ligament in place.  FIG. 4B  shows that further advancement may be obtained using an insertion tool  172  that applies lateral loading on the receiver  152  to compress the arms  156 ,  158  into frictional engagement with a ligament  174 .  FIG. 4C  shows the ligament  174  frictionally secured in place. 
         [0034]    All of the screw mechanisms disclosed herein may be formed of any material suitable. In some embodiments, portions of the screw mechanisms are formed of elastic materials suitable for ratcheting and interlocking teeth in the manner described. These materials may include for example, any member of the polyaryletherketone (PAEK) family such as polyetheretherketone (PEEK), carbon-reinforced PEEK, or polyetherketoneketone (PEKK); polysulfone; polyetherimide; polyimide; ultra-high molecular weight polyethylene (UHMWPE); and/or cross-linked UHMWPE. In addition, it may include materials such as cobalt-chromium alloys, titanium alloys, nickel titanium alloys, and/or stainless steel alloys. Shape memory materials having pre-formed memory structures also may be used. Other polymers and metals also are contemplated whether known or unknown at this time. 
         [0035]      FIGS. 5A-5C  show an additional embodiment of a screw mechanism reference herein by the numeral  180 . The screw mechanism  180  includes a receiver  182 , swiveling side blockers  184   a  and  184   b , and a staple  186  (shown in  FIG. 5C ). In this embodiment the swiveling side blockers  184  are formed as semi-cylindrical shells that together cooperate to extend at least partially about the external surface of the ligament.  FIG. 5A  shows the swiveling side blockers  184  in an open condition ready to receive a ligament  188 . 
         [0036]    As will become apparent, the side blockers  184  and the staple  186  form a locking system with a preliminary locking condition and a final locking condition.  FIG. 5B  shows the ligament  188  after being contained by the swiveling side blockers  184   a  and  184   b . As can be seen, as the ligament  188  moves downward between the side blockers  184 , they pivot to enclose and provisionally lock the ligament  188  within the receiver  182 . In some embodiments, the side blockers in this condition cannot be removed from the receiver  182 . Accordingly, in this condition, the screw mechanism  180  is a preliminary locking condition. 
         [0037]    Referring to  FIG. 5C , the staple  186  cooperates with the side blockers  184  of the receiver  102  to place the screw mechanism  180  in a final locking condition. In this embodiment, the staple  186  extends about an exterior of the receiver  182  and applies compression loading upon the receiver  182 . In some embodiments, the receiver sidewalls deform based upon the staple compression to apply loading onto the swiveling side blockers to frictionally lock the blockers relative to the receiver. In other embodiments, the staple  186  presses directly on the ligament and/or blockers to apply a compressive load against the bottom of the U-shape in the receiver  182 . 
         [0038]      FIGS. 6 through 10  show another embodiment of a screw mechanism referenced herein as  200 . The screw mechanism  200  comprises a receiver  202  and a threaded anchor portion  204 . Here, the receiver  202  includes a tulip head forming a bottom clamp  206  and includes top clamp  208 . The bottom clamp  206  includes first and second extending sides  210  that form a transverse opening for receiving the ligament. One of the sides  210  includes a slot  212  formed therein for receiving a portion of the top clamp  208 . 
         [0039]    The top clamp  208  comprises a frame  216 , a ratchet clip  218  and a cap  220 . In this embodiment, the ratchet clip  218  forms a locking system having a preliminary locking configuration and a final locking configuration for securing an elongated supporting structure or ligament. 
         [0040]    The frame  216  includes a curved inner surface  217  for interfacing with and securing the ligament between the top and bottom clamps  208 ,  206 . The ratchet clip  218  comprises two ratchet arms  222  shaped and configured to be received within the slot  212  of the bottom clamp  206 . The ratchet arms  222  have outwardly facing teeth  224  formed thereon for interlocking with corresponding teeth within the slot  212 , described below. 
         [0041]    In one embodiment, at least one of the arms  222  is compliant and elastically deformable. In this embodiment, the arm  222  can be biased toward an engaged position with the teeth in the slot  212 , yet also can elastically deform to disengage the ratchet clip  218  from the teeth in the slot  212 . 
         [0042]      FIG. 7  shows a top view of the bottom clamp  206  with the slot  212 .  FIG. 8  shows a partial cross-section taken through the slot  212  with the ratchet clip  218  of the top clamp  208  in place within the slot  212 . In this cross-section, the engagement teeth  224  of the ratchet clip  218  are shown engaged with corresponding teeth  226  formed in the slot  212  of the bottom clamp  206 . The compliant nature of the arm  222  permits the upper clamp  208  to be received into the slot  212  and such that the teeth  222  engage the teeth  224  in a preliminary locking condition to secure a ligament within the screw mechanism  200 . 
         [0043]    A cap  220  cooperates with the ratchet clip  218  to prevent or reduce the ability of the compliant ratchet arms to elastically deform. Accordingly, the cap  220  and the teeth  224 ,  226  create a locking system with preliminary and final locking conditions. Referring to  FIGS. 9A and 9B , the cap  220  is configured to pivot about an axis to permit the top clamp to be provisionally secured to the bottom clamp  206  and also to lock the top clamp  208  to the bottom clamp  206 . As can be seen in  FIG. 9 , the cap  220  has a noncircular shape. During rotation of the cap, its outer perimeter acts as a cam against one of the locking arms  222  of the ratchet clip  218 . For example, referring to  FIG. 9A , when the cap  220  is aligned primarily in a longitudinal direction as shown, the arm  222  may elastically deflect to permit the ratchet clip  218  to move up or down within the slot  212 , thereby permitting the clamps  206 ,  208  to open and close relative to each other. As can be seen in  FIG. 9B , rotating the cap  220  90° displaces the arm  222  and restricts movement of the arm  222 . Accordingly, the teeth  224  on the arm  222  cannot disengage the teeth  226  in the slot  212  in the bottom clamp  206 . This is a final locking position. 
         [0044]      FIGS. 10A-10C  show a process for securing a ligament  230  within the screw mechanism  200 . Referring first to  FIG. 10A , a ligament  230  may be placed in the tulip shaped bottom clamp  206 . The top clamp  208  may be placed over the ligament  230  so that the ratchet clip  218  enters the slot  212 . The externally facing teeth  224  on the arms  222  engage the internally facing teeth  226  within the slot  212  of the bottom clip  206 . Because the arm  222  is elastically deformable, the teeth  224  can engage and disengage the teeth  226  to permit the top clamp  206  to be moved up or down to place the screw mechanism in a preliminary locked condition about the ligament. 
         [0045]    In some embodiments, the top clamp  206  is connected within the slot  212  prior to introducing the ligament  230 . In these embodiments, the receiver  204  is a side-loading receiver. After placing the ligament  230  between the clamps, the top clamp is pressed downwardly to secure the ligament in the preliminary locked condition. 
         [0046]    Once the ligament is properly positioned relative to the spine, the cap  220  may be rotated 90° by a locking tool to drive or splay the ratchet arms  222  apart such that the teeth  224  engage the teeth  226 , placing the mechanism in a final locking condition, as shown in  FIG. 10C . 
         [0047]      FIG. 11  illustrates an alternative embodiment of a top clamp, referenced herein as  240 . The top clamp  240  includes a frame  241  that cooperates with the cap  220 . Here however, the frame  241  has a top portion  242  and a bottom portion  244 . The bottom portion  244  includes two legs  245  with teeth  246  extending therefrom. Here, the teeth  246  face inwardly. Accordingly, the top clamp  240  may be used to engage with a bottom clamp having outwardly facing teeth that interlock with the teeth  246 . Rotating the cap  220  against the frame  241  elastically expands the frame and separates the inwardly facing teeth. 
         [0048]      FIG. 12  discloses another exemplary embodiment of a screwing mechanism referenced herein by the numeral  250 . This includes a receiver  252  and a threaded anchor portion  254 . The receiver  252  includes a top clamp  256  and a tulip shaped bottom clamp  258  similar in some respects to the bottom clamp  206  described above. Like the top clamp  208  described above, the top clamp  256  includes arms  260  that are elastically deformable between a preliminary locked condition and a final locking condition. In this embodiment, teeth  262  on the arms  260  face inwardly. The cap  220  manipulates the arms  260  as described above between the preliminary locked and the final locked conditions. 
         [0049]    In this embodiment the lower clamp  258  is formed with the slot  264  through which the arms  260  of the upper clamp  256  may be introduced. A protrusion  266  having externally facing teeth  268  is disposed within the slot  264 . The teeth  268  are shaped and configured to interlock with the teeth  262  of the upper clamp  256 . In this embodiment, in order to provide simple assembly, the bottom clamp  258  includes a casing cover  270 . The casing cover  270  cooperates with and forms a part of the bottom clamp  258  to form the slot  264 . It also reduces a chance of lateral movement of the arms  260  relative to the lower clamp  258 . 
         [0050]      FIGS. 13A and 13B  show the screw mechanism  250  in a locked condition and in an unlocked condition. Referring first to  FIG. 13A , the top clamp  256  may be placed so that the arms  260  extend on either side of the protrusion  266 . The teeth  262  interlock with the teeth  268  as shown in  FIG. 13A . Because the tooth  262  and teeth  268  are sawtooth shaped, the upper clamp  256  may be advanced downwardly to apply compression loading against an elongated support structure that may be contained between the clamps. In so doing the arms  260  elastically deformed to accommodate the locking and interlocking teeth. Accordingly, when the top and bottom clamps are spaced apart and loosely holding a ligament in place, the clamps may be considered to be in a preliminary locked position. However, when the ligament is properly located as desired, the top clamp  256  may be forced downwardly to lock the ligament in place. In order to unlock the top and bottom clamps  256 ,  258 , the cap  220  may be turned to forcibly displace one or both of the arms  260  as shown in  FIG. 13B . In so doing, the teeth  262  disengage from the teeth  268 . With the teeth disengaged, the upper clamp  256  may be moved upwardly or downwardly relative to the lower clamp. 
         [0051]      FIG. 14  shows an exemplary application tool  280  for implanting and operating the screw mechanism  250 . In this case the implantation tool  280  comprises a pressure generator  280 , that may be turned to drive the upper clamp downwardly relative to the lower clamp so that the ratcheting teeth on the top and bottom clamps engage. The screw mechanisms  200  and  250 , as well as other embodiments disclosed herein, may be assembled intra-operatively. 
         [0052]      FIG. 15  shows an additional embodiment of a screw mechanism referenced herein by the numeral  300 . The screw mechanism includes a receiver  302  and a threaded anchor portion  304 . As with the other embodiments disclosed herein, the receiver  302  is tulip-shaped, having two legs forming a transverse opening through which the ligament  305  extends. In this embodiment, extenders  306  extend from opposing lateral sides of the receiver  302 . These displace and secure tissue from overlapping the receiver  102  thereby providing access to the receiver  102  for the ligament  305 , as shown in  FIG. 15 . 
         [0053]    In this embodiment, the locking system comprises a staple  308  that may be received over the receiver  302  to secure the ligament in place and create a closed eyelet. In this embodiment, the staple  308  may be formed of an elastically deformable material and/or the receiver  302  may be formed of an elastically deformable material such that the staple  308  may be snap fitted onto the receiver  302 . The embodiment shown includes a single tooth  310  on the staple  308  that may be received into a channel  312  formed about the receiver  302 . Although only one tooth  310  and one receiver channel  312  are shown, it would be apparent that additional teeth and receiver channels may also be used in order to provide a preliminary locking condition that would still permit the ligament  305  to be moved relative to the receiver  302  and a final locking condition that securely locks the ligament  305  to the screw mechanism  100 . In such an embodiment, to place the screw mechanism in the final locking condition, the staple would be further advanced over the receiver in a ratcheting manner.  FIG. 16  shows one example where the receiver  302  and the staple  308  cooperate to secure the ligament  305  in place. Once the ligament is secured in the receiver  302 , the extenders  306  may be removed from the screw mechanism. 
         [0054]      FIGS. 17A and 17B  show an additional embodiment of a screw mechanism  350  for locking a ligament  355  in place. The screw mechanism  350  includes a receiver  352  and extenders  354  extending from lateral sides of the receiver  352 . Accordingly, as explained above, the extenders  354  may be used to displace and hold back soft tissue so that a medical service provider has direct access to the receiver  352  for placement of a ligament  355 . However, once the ligament is placed, a locking system is used to secure a ligament  355  within the receiver  352 . In this case, the locking system comprises a crimpable sleeve  356  that slips over the exterior surfaces of the extenders  354  in the manner shown in  FIG. 17A . These extenders may then be used to lock the ligament in place. Alternate blocking mechanisms can be envisioned such as revisable blockers, screw-based blocking mechanisms and revisable or removable crimps. For example, polymer and metal crimps may be able to be snapped into place and also may be forcibly removable to offer a revisable connection. 
         [0055]    Referring now to  FIG. 17B , the crimpable sleeve  356  may be slid along the extenders  354  until it is adjacent to the receiver  352 . In this state, the device is in a preliminary locking condition because the ligament  350  is provisionally locked within the screw mechanism  350 . Once the ligament is located as desired, the crimpable sleeve  356  may be further advanced over the extenders to securely hold the ligament  355  within the receiver. In the embodiment shown, the receiver  352  is formed of a deformable or compliant material that may be deformed by the extenders and crimpable sleeve  356 . Accordingly, the receiver  352  may be wrapped around the ligament in the final locking condition. Once the crimpable sleeve is in place, the sleeve  356  may be crimped or otherwise secured onto the extenders  354  in order to lock it in place. The excess material of the extenders  354  may be snipped off or otherwise removed. Although disclosed as extenders, the elements  354  may be tethers, ligaments, cables, threads, among other materials. 
         [0056]    In other embodiments, the extenders are the deformable portion acting against the ligament to secure it in place, instead of the receiver itself. In such embodiments the receiver walls may be shorter than is shown in  FIGS. 17A  and B such that the extenders directly contact at least a portion of the ligament when in the final locking condition. 
         [0057]      FIGS. 18A and 18B  show another embodiment of a screw mechanism referenced herein by the numeral  400 . Like the other embodiments described herein, the screw mechanism  400  includes a tulip-shaped receiver  402  for receiving ligament. In this embodiment, a locking system includes a staple  404  comprising a set screw  406 . The staple  404  is receivable onto the receiver  402 . In this embodiment, the staple  404  may be slid laterally such that grooves  408  formed in the exterior surface of the receiver  402  receive protrusions  410  formed in the inner surface of the staple  404  such that the staple  404  interlocks with the receiver  402 . 
         [0058]    The staple  404  includes an aperture  412  that receives the set screw  406 . When the staple  404  is connected to the receiver  402 , the ligament  405  is preliminarily locked within the screw mechanism  400  in that it can be further manipulated relative to the receiver  402 . Tightening the set screw  406  against the ligament may finally lock the ligament relative to the screw mechanism  100 . Although the embodiment shown in  FIGS. 18A and 18B  show a locking staple transversely connected to the receiver  402 , in other embodiments, the staple connects to the receiver by advancing the staple over the receiver longitudinally as is shown in  FIG. 5C . Although shown with a flat bottom, the set screw may have any bottom surface, including a central protrusion, knurling, or other configuration. 
         [0059]      FIGS. 19-21  disclose an additional screw mechanism  450  that may be used to preliminarily lock and finally lock a ligament in place. This embodiment comprises a tulip head receiver  454  and a staple  456 . The staple  456  is sized and shaped to extend about the exterior surface of the receiver  454 . The external surface of the tulip head  454  includes at least one lip or edge  455  for snap-fitting or ratcheting the staple  456  onto the receiver  454 . In this embodiment, the staple  456  is formed as a band with ears  458  that interface with an insertion tool  460  shown in  FIG. 20 . The tool  460  holds the staple  456  and connects the staple  456  to the receiver  454 . 
         [0060]      FIG. 21  shows the receiver head  454  with a ligament  462  contained therein. As can be seen, the staple  456  is secured about the circumference of the receiver below the lip or edge  455 . In this manner the ligament  462  is secured in a final locking condition in the screw mechanism  450 . In this embodiment, one or both of the staples  456  and the receiver  454  may be formed of a relatively elastic material that permits the staple  456  to be slid over the lip  455 . Some embodiments include more than one edge or lip  455 . In these embodiments, the staple  456  may be advanced over the first lip or edge while still leaving the ligament  462  relatively loose within the screw mechanism  450  for additional manipulation. To place the staple in a final locking condition, the staple may be further advanced over the additional tapered lock mechanisms until the staple compresses and secures the ligament within the receiver. 
         [0061]      FIGS. 22A and 22B  show another screw mechanism referenced herein by the numeral  550 . Like the screw mechanisms described above, the screw mechanism  550  includes a tulip shaped receiver  552 . A locking system for securing a ligament within the receiver  552  includes a staple  554  receivable over the receiver  552 . In this embodiment, the receiver  552  includes legs  556  having a lower overall height than those in prior embodiments. For example, legs  556  extends from a base surface of a transverse opening formed by the tulip head a distance less than screw mechanisms described above. The staple  554 , however, compensates for the short receiver by having legs  558  extending a length greater than the staples described above. Accordingly, although the overall height of the receiver  552  and staple  554  may be unchanged from prior embodiment, in this embodiment, the receiver legs  556  are shorter while the staple legs  558  are longer. 
         [0062]    Together, the receiver legs  556  and the staple legs  558  form the transverse opening. In this embodiment, at last half of the circumference of the opening formed by the legs  556  and  558  is formed by the staple  558 . In some embodiments, the staple forms between 50% and 80% of the circumference of the transverse opening formed by the staple legs and receiver legs. In some embodiments, the height of the legs  556  is less than the diameter of an associated ligament or rod. In some embodiments, the height of the legs  556  is less than one half of the diameter of an associated ligament or rod. 
         [0063]    Accordingly, when a ligament  562  is placed within the receiver  552 , the ligament  562  extends above the top of the tulip legs  556 , or alternatively may fit neatly within the tulip leg  556  and the staple  554  provides the locking mechanism. In this embodiment, a connecting mechanism connects the receiver  552  and the staple  554 . It includes a protrusion  560  receivable within a recess  562 . As shown, the protrusion  560  is formed on the staple  554  and the recess  562  is formed on the receiver  552 . In this embodiment, the staple  554  may be snapped into position via an introducer. This holds the ligament within the tulip of the receiver  552  that allows longitudinal sliding for tensioning under reductive maneuvers. In some embodiments, the staple includes an aperture that receives a set screw for securing the ligament similar to that shown in  FIGS. 18A and 18B . 
         [0064]      FIGS. 23-27  show a screw mechanism having a univariable head assembly that permits rotation of the ligament or a solid longitudinal member relative to the screw within at least a single plane. In this embodiment, the screw mechanism, referred to herein by the reference  700 , includes a receiver  702 , a threaded anchor portion  704 , and an inner receiver referred to herein as an inner block  706  that provides variation in rod angle relative to the threaded anchor portion  704  and the receiver  702 . In this embodiment, the inner block  706  is sized and configured to be disposed within the receiver  702 . 
         [0065]    The receiver  702 , as in other embodiments disclosed herein, comprises two legs  708  forming a tulip-shaped head. Instead of directly interfacing with the ligament or rod, however, the receiver  702  receives the inner receiver as the inner block  706 . In this embodiment, the receiver legs  708  each include a receiving depression  710  formed therein that receives corresponding portions of the inner block  706 . 
         [0066]    The inner block  706  includes a body  712  having legs  714  extending therefrom. The legs have articulating connectors  716  outwardly projecting therefrom that are receivable into the receiving depressions  710  of the receiver  702 . In this embodiment, the articulating connectors  716  are cylindrical protrusions that fit within the receiving depressions  710  and are configured to articulate about an axis formed by the cylindrical shape. In this manner, the inner block  706  pivots about the articulating connectors  716  relative to the receiver  702 . As shown in  FIG. 23 , when the inner block  706  is received within the receiver  702 , the legs  714  are spaced from a bottom portion of the receiver  702 . This is a preliminary locking condition, however, as the final locking condition will be discussed further below. The inner legs  714  are separated by a gap  718 . The legs  714  and the body  712  together comprise a transverse opening sized and shaped to receive the rod  701 . The body  712  includes a longitudinal opening for receiving a set screw  720 . The longitudinal opening is in communication with the transverse opening. 
         [0067]      FIG. 24  shows a top view of the screw mechanism  700 . As can be seen, the set screw  720  is received within the inner block  706 . It advances through an aperture formed in the top of the inner block  706  to directly engage and press against the rod  701 .  FIG. 25  is one example showing the articulation that may occur about the articulating connectors  716  within the receiving depressions  710 . Accordingly, the screw mechanism  700  in  FIGS. 23 through 26  permits rod angulations within a single plane. When the rod  701  extends through the transverse opening within the inner block  706 , the rod  701  is preliminarily locked to the screw mechanism  700 . It may still be advanced further through the opening or otherwise manipulated. 
         [0068]      FIG. 26  shows the screw mechanism  700  in a final locking condition As can be seen, the set screw  720  is advanced until it contacts the rod  701 . Further driving the set screw  720  displaces the rod  701  in the longitudinal direction of the screw mechanism  700 . As the rod displaces, the rod acts against the legs  714  of the inner block  706  forcing them to splay apart into contact with the inner surface of the receiver  702 . As the set screw  720  is further advanced, the legs  714  frictionally lock against the receiver  702  in a final locking condition, where the inner block  706  is immovable relative to the receiver  702 . In this manner, the screw mechanism  700  has a provisional locking condition and a final locking condition for securing the rod  701  at a desired angled condition relative to the threaded anchor portion  704 . 
         [0069]      FIG. 27  shows another embodiment of a screw mechanism referenced herein as  750 . The screw mechanism  750  is similar in most respects to the screw mechanism  700  just described and includes both a receiver  752  and an inner body  754 . In this embodiment, however, the articulating connectors  716  and the receiving depression  710  formed within the receiver  752  are displaced from a lower portion of the receiver body to a higher area. Accordingly, a pivot axis of the inner block  754  relative to the receiver  754  does not intersect the longitudinal axis of the rod  701 . Instead, in the embodiment shown, the pivot axis is spaced from or offset from the longitudinal axis of the rod  701 . Accordingly, pivoting the inner block  754  relative to the receiver  752  results in a displacement more suitable for certain applications. 
         [0070]      FIGS. 28 to 31  disclose a variable closed head connector screw mechanism referenced herein by the numeral  800 . The screw mechanism  800  includes a receiver  802  and a threaded anchor portion  804 . In this embodiment, the receiver  802  is a closed head receiver having openings to a transverse passage for receiving a rod  805 . The receiver  802  includes a concave inner surface portion  806  forming a chamber that permits articulation of inner shells, or an inner receiver. In this embodiment, the receiver  802  forms an outer frame for an upper inner shell  808  and a bottom inner shell  810 . These shells cooperate to form a ring around the rod  805  within the closed head receiver  802 . In this embodiment, the rod  805  is spaced from the inner surface  806  of the receiver by the inner shells  808 ,  810 . As best seen in  FIG. 29 , the shape of the concave surface  806  within the receiver  802  constrains movement and pivoting of the shells  808  and  810 . In the embodiment shown, the range of articulation may be within the range of about 45°. 
         [0071]    As shown in  FIG. 29 , the inner shells  808 ,  810  have interlocking portions  814  that aid in maintaining the shells connected together. Here, the interlocking portion  814  comprises a receiving U-shaped portion on the bottom inner shell  810  and a protruding tongue-shaped portion on the upper inner shell  808 . The interlocking portions  814  are arranged to mechanically secure the inner shells together within the closed head receiver  802 . 
         [0072]    When a rod extends through the shells  808 ,  810 , it can be manipulated with the shells  808 ,  810  within the receiver  802  until movement is locked using a locking system. Accordingly, the device has a preliminary locking condition. The rod can be held in a final locking condition by driving a set screw  820  through a passage  822  in the receiver  802 . The set screw  820  contacts and bears against the inner shells  808 ,  810  to drive them together about the rod  805 . This secures the rod in place relative to the shells and secures the shells  808 ,  810  into frictional engagement with the inner surface  806  of the closed head receiver  802 . Accordingly, the set screw locks the screw mechanism  800  and the rod relative to the receiver  802 . In some embodiments, even when the set screw is tightened, shell rotation is limited not only by the frictional engagement, but also by the shape of the concave surfaces  806 . Accordingly, even when tightened about a rod, the shells may be sized to provide only a given range of articulation, which could be, for example, within a range of about 45 degrees. Other ranges also are contemplated, including 30 degrees, 60 degrees, and others. 
         [0073]      FIG. 31  shows another set of inner shells  850 ,  852 . Like those described above, these form a ring that can receive a rod. Here, instead of forming a rounded tongue and groove, the interlocking portions of the shells  850 ,  852  have a triangular-shape. As described above, one of the inner shells  850 ,  852  is received within the other inner shell to limit the movement of the inner shells relative to each other. 
         [0074]    Applicants note that the use of directional terms herein, such as upper, lower, lateral, and others are merely exemplary, and may encompass other directions, such as the device being on its side, unless so indicated. Although several selected embodiments have been illustrated and described in detail, it will be understood that they are exemplary, and that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the following claims.