Abstract:
A pedicle screw system includes a pedicle screw and a tulip assembly. A rod is inserted and fixed in the pedicle screw system to surgically connect vertebral bodies. The pedicle screw includes a head portion and a threaded shaft. In one embodiment, the tulip assembly includes a tulip body, a rod-support member, a collar member, a cap, and a fastening member. The tulip body has an upper portion and a lower portion, these portions being displaceable in opposite directions relative to an intermediate web. The tulip body can be intra-operatively coupled to the pedicle screw after the screw has been inserted into the bone. The cap engages with the tulip body to lock the tulip body onto the pedicle screw and thus fix the tulip body at a desired angle relative to the pedicle screw.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 60/622,107 filed Oct. 25, 2004, where this provisional application is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to bone fixation systems and methods of assembly, operation, and/or installation of these systems into cancellous and/or cortical bone.  
         [0004]     2. Description of the Related Art  
         [0005]     Various bone fixation systems for internally fixing, fusing, and/or otherwise supporting portions of a skeletal system for a human or other-type animal are known in the art. Bone fixation systems used along the spinal region of a patient are commonly referred to as a pedicle screw construct or a pedicle screw-coupling device because the pedicle screws are typically inserted and secured into the pedicles. Pedicles are generally understood to refer to the bone that bridges an anterior vertebral body to a lamina. U.S. Pat. No. 5,669,911 provides a detailed and thorough description of a spinal system including a discussion about the various bones and connective tissue associated therewith.  
         [0006]     Pedicle screw constructs typically include a pedicle screw and a rod-coupling mechanism that are pre-operatively assembled. Some examples of pre-operatively assembled pedicle screw constructs are described in U.S. Published Patent Application Nos. 2005/0187548, 2005/0192571, and 2005/0216003. One drawback of pre-operatively assembled pedicle constructs is that the insertion of these constructs through the skin, muscle, and/or other tissue during surgery may cause damage and/or trauma to the tissue because the construct is larger and bulkier than the pedicle screw alone. In addition, the pre-operatively assembled pedicle constructs may be difficult to handle, maneuver, and to ultimately secure to the bone because the surgeon must direct the tool that drives the pedicle screw into the bone down through the rod-coupling mechanism to engage a driving portion of the pedicle screw. Further, the rod-coupling mechanism may be free to rotate relative to the pedicle screw, making it more difficult for the surgeon to guide and engage the tool with the pedicle screw.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The invention is related to systems and methods for achieving internal fixation of vertebral bodies.  
         [0008]     In one aspect, a tulip assembly is coupleable to a pedicle screw having a head portion and a threaded shaft. The head portion is coupled to the threaded shaft. The tulip assembly includes a tulip body having an intermediate web, an upper portion positioned above the intermediate web, and a lower portion positioned below the intermediate web. The upper and lower portions are displaceable in substantially a radial direction relative to the intermediate web. The lower portion is radially expandable by an amount to intra-operatively receive the head portion of the pedicle screw, which may occur after the pedicle screw is secured into bone. A cap is engageable with the upper portion of the tulip body to lock the lower portion of the tulip body onto the head portion of the pedicle screw when the tulip body is at a desired angle relative to the pedicle screw.  
         [0009]     In another aspect, a pedicle screw system includes a pedicle screw and a tulip assembly. The pedicle screw includes a head portion and a threaded shaft, where the head portion is coupled to the threaded shaft. The tulip assembly includes a tulip body and a cap. The tulip body has an intermediate web, an upper portion positioned above the intermediate web, and a lower portion positioned below the intermediate web. The upper and lower portions are displaceable in substantially a radial direction relative to the intermediate web. The lower portion is radially expandable by an amount to intra-operatively receive the head portion of the pedicle screw after the pedicle screw is secured into bone. The cap is engageable with the upper portion of the tulip body to lock the lower portion of the tulip body onto the head portion of the pedicle screw when the tulip body is at a desired angle relative to the pedicle screw and before the rod is locked into the tulip assembly.  
         [0010]     In yet another aspect, a method is provided for installing a pedicle screw system into bone. The pedicle screw system includes a pedicle screw and a tulip assembly. The method begins by inserting the pedicle screw into the bone. Next, but not necessarily in the following sequence, the method includes coupling the tulip assembly to a head portion of the pedicle screw by radially, outwardly displacing a lower portion of a tulip body by an amount sufficient to receive the head portion of the pedicle screw. At least a section of a rod is placed onto a rod-support member that is positioned within the tulip body. The tulip assembly is fixed to the head portion of the pedicle screw by rotationally engaging a cap with the upper portion of the tulip body, the cap configured to cam the upper portion of the tulip body radially outward when rotated, and in turn, cause the lower portion of the tulip body to clamp onto the head portion of the pedicle screw. A fastening member is inserted into the tulip assembly to provide a downward force on at least a portion of the section of the rod to fixedly retain the same in the tulip assembly.  
         [0011]     The foregoing is a summary and thus contains, by necessity, simplifications, generalizations, and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the devices and/or processes described herein, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth herein. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.  
         [0013]      FIG. 1  is an isometric view of a pedicle screw system, according to one illustrated embodiment.  
         [0014]      FIG. 2A  is a top plan view of a pedicle screw.  
         [0015]      FIG. 2B  is a partial cross-sectional elevational view of the pedicle screw of  FIG. 2A  seen along Section  2 B- 2 B.  
         [0016]      FIG. 3  is an exploded isometric view of a tulip assembly, according to one illustrated embodiment.  
         [0017]      FIG. 4A  is a top plan view of a tulip body from the tulip assembly of  FIG. 3 .  
         [0018]      FIG. 4B  is a partial cross-sectional elevational view of the tulip body of  FIG. 4A  seen along Section  4 B- 4 B.  
         [0019]      FIG. 5A  is a top plan view of a collar member from the tulip assembly of  FIG. 3 .  
         [0020]      FIG. 5B  is a cross-sectional view of the collar member of  FIG. 5A  seen along Section  5 B- 5 B.  
         [0021]      FIG. 6A  is a top, plan view of a rod-support member from the tulip assembly of  FIG. 3 .  
         [0022]      FIG. 6B  is a cross-sectional view of the rod-support member of  FIG. 6A  seen along Section  6 B- 6 B.  
         [0023]      FIG. 6C  is a cross-sectional view of the rod-support member of  FIG. 6A  seen along Section  6 C- 6 C.  
         [0024]      FIG. 7A  is a top plan view of a cap assembly from the tulip assembly of  FIG. 3 .  
         [0025]      FIG. 7B  is a cross-sectional view of the cap assembly of  FIG. 7A  seen along Section  7 B- 7 B.  
         [0026]      FIG. 7C  is a partial, cross-sectional elevational view of the cap assembly of  FIG. 7A  seen along Section  7 C- 7 C.  
         [0027]      FIG. 8  shows a flow diagram of a method of assembling a pedicle screw system, according to one illustrated embodiment.  
         [0028]      FIGS. 9A-9E  cooperate with the flow diagram of  FIG. 8  to show various stages of assembly.  
         [0029]      FIG. 10  is a partial, cross-sectional view of the pedicle screw system of  FIG. 1  showing the pedicle screw system in a fully assembled configuration. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]     In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the present tools, assemblies, systems, and methods. However, one skilled in the relevant art will recognize that the assemblies, systems, and methods may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with bone fixation systems and the assembly and/or installation thereof have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments of the present assemblies, systems, and methods.  
         [0031]     Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as “comprises” and “comprising,” are to be construed in an open, inclusive sense, that is, as “including, but not limited to.”Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present assemblies, devices, and systems. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.  
         [0032]     The headings provided herein are for convenience only and do not interpret the scope or meaning of the claimed invention.  
         [0000]     Pedicle Screw System  
         [0033]      FIG. 1  generally shows a pedicle screw system  100  comprising a pedicle screw  102 , a rod  104 , and a coupling assembly  106 , hereinafter referred to as a tulip assembly  106 . During surgery, the tulip assembly  106  is coupled to the pedicle screw  102 . A relative position of the tulip assembly  106  with respect to the pedicle screw  102  may be pre-operatively selected and then intra-operatively achieved. Once the relative position between the pedicle screw  102  and the tulip assembly  106  has been selected, the tulip assembly  106  is fixed or locked relative to the pedicle screw  102  before the rod is fixed or locked into the tulip assembly  106 . It is understand that the relative, angular position of the tulip assembly  106  to the pedicle screw  102  may vary from one pedicle screw system  100  installation to another. In general, the relative position of the tulip assembly  106  to the pedicle screw  102  is selected to achieve a certain amount of spinal correction, which may involve compression, expansion, and/or rotation of at least a portion of a patient&#39;s spine.  
         [0034]      FIGS. 2A and 2B  show the pedicle screw  102  having an elongated, threaded portion  108  and a head portion  110 . Pedicle screws  102  are generally known in the art, but the head portions  110  may vary depending on what type of tulip assemblies  106  will be coupled to the pedicle screws  102 . The head portion  110  of the pedicle screw  102  includes a driving feature  112 , which is used for the initial insertion of the pedicle screw  102  into a pedicle, which is a part of a vertebra that connects the lamina with a vertebral body. In addition, the driving feature  112  may be used to adjust the pedicle screw  102  even after the tulip assembly  106  is coupled to the pedicle screw  102 . In the illustrated embodiment, the head portion  110  of the pedicle screw  102  includes a dual diameter head comprising a greater diameter  116  and a lesser diameter  118 .  
         [0035]     In one embodiment, the pedicle screw  102  is cannulated, wherein a channel  114  extends through the entire length of the pedicle screw  102 . The channel  114  allows the pedicle screw  102  to be maneuvered over and receive a Kirschner wire, commonly referred to as a K-wire. The K-wire is typically pre-positioned using imaging techniques, for example, fluoroscopy imaging.  
         [0036]      FIG. 3  shows the tulip assembly  106  comprising a coupling body  120  (hereinafter referred to as a tulip body  120 ), a collar member  122 , a rod-support member  124 , a cap  126 , and a setscrew  127 . The tulip assembly  106  and cap  126  may be assembled pre-operatively or, alternatively, may be assembled intra-operatively.  
         [0037]      FIGS. 4A and 4B  show the tulip body  120  having a lower portion  128  and an upper portion  130 . The lower portion  128  includes a web  132 , a spherical bore  134 , a counterbored region  136 , a radial flange  138 , and first outer perimeter  140 . The web  132  is positioned just above the spherical bore  134  and may operate as a fulcrum such that when the upper portion  130  is radially, outwardly displaced, or vice-versa, the lower portion  128  below the web  132  is simultaneously radially, inwardly displaced, or vice-versa, and the size and position of the web  132  remains relatively neutral to the applied displacement. Thus, the web  132  acts as a fulcrum by permitting the upper portions  130  to respond to radially inward or outward displacement of the lower portion  130  and vice-versa.  
         [0038]     For example and as will be further described in the assembly methods below, the tulip body  120  is placed over the head portion  110  of the pedicle screw  102  by radially compressing (e.g., squeezing) the upper portion  130  of the tulip body  120  so that the spherical bore  134  opens by an amount sufficient to receive the head portion  110  of the pedicle screw  102 . In one embodiment, the tulip body  120  is placed over the head portion  110  of the pedicle screw  102  intra-operatively (i.e., during surgery). Likewise, the lower portion  128 , in particular a region  142  beneath the web  132 , is compressible during pre-operative assembly of the tulip assembly  106 . During pre-operative assembly, the region  142  is squeezed to cause the upper portion  130  to splay apart (i.e., open wider and/or expand) to allow the rod-support member  124  to be inserted into an opening  144  of the tulip body  120 . In addition, squeezing the region  142  permits the collar member  122  to be moved over the radial flange  138  and encircle at least part of the lower portion  128  of the tulip body  120 . It is understood that squeezing the region  142  may be achieved by applying an inward radial force on at least a portion of the first outer perimeter  140  that corresponds to the region  142 . Additionally or alternatively, squeezing the region  142  may be achieved by applying an outward radial force to an inner surface  146  of the upper portion  130  of the tulip body  120  or by installing the cap  126  as will be described in more detail below.  
         [0039]     The upper portion  130  includes a second outer perimeter  148  and a cap-mating groove  150 . The second outer perimeter  148  is larger than the first outer perimeter  140  of the lower portion  128 . The cap-mating groove  150  includes a lip  152 . The cap-mating groove  150  is sized to receive the cap  126 , wherein the lip  152  is arranged to retain the cap  126  as will be described in more detail below.  
         [0040]      FIGS. 5A and 5B  show the collar member  122  having an outer perimeter  154 , an inner perimeter  156 , an upper surface  157   a , a lower surface  157   b , and a cutout  158 . The outer perimeter  154  is sized to be approximately the same as the second outer perimeter  148  of the upper portion  130  of the tulip body  120 . In one embodiment, the collar member  122  is pre-operatively assembled with the tulip body  120 . In particular, the inner perimeter  156  is sized to fit over and be slidable on the first outer perimeter  140  of the lower portion  128  of the tulip body  120 , for example during pre-operative assembly. The upper surface  157   a  is configured to engage the shoulder  159  ( FIG. 4B ) of the tulip body  120  and the lower surface  157   b  is configured to engage the top portion of the radial flange  138  of the tulip body  120  during assembly therewith. The cutout  158  is wide enough and deep enough to receive at least a portion of the rod  104 . Although the cutout  158  in the illustrated embodiment is relatively square or rectangular in shape, the cutout may take the form of a semi-circular arc, have more pronounced, radiused corners, or even have a parabolic shape, for example.  
         [0041]      FIGS. 6A, 6B , and  6 C show the rod-support member  124  having a rod-support surface  160 , an outer surface  162 , an upper surface  164 , and an opening  166 . The rod-support surface  160  is contoured to receive the rod  104 . In one embodiment, a diameter of the rod-support surface  160  is contoured to achieve a tight fit with the rod  104 , where the tight fit increases the contact stress and/or friction between the rod-support surface  160  and the rod  104 .  
         [0042]     The outer surface  162  is sized to fit through the opening  144  of the tulip body  120  and be placed in the counterbored region  136  of the tulip body  120  when the rod-support member  124  is pre-operatively assembled with the tulip body  120 . The upper surface  164  engages a portion of the counterbored region  136  to retain the rod-support member  124  in the counterbored region  136  of the tulip body  120 . The opening  166  of the rod-support member  124  permits access to the driving feature  112  of the pedicle screw  102 . Accordingly, the opening  166  permits the adjustment of the pedicle screw  102  after the tulip assembly  106  has been coupled to the pedicle screw  102 .  
         [0043]      FIGS. 7A, 7B , and  7 C show the cap  126  having cam extensions  168 , grooves  170 , and internal threads  172 . The cam extensions  168  include protuberances  176  and lead radii  178 . The protuberances  176  operate as an interlocking feature such that when the cap  126  is coupled to the tulip body  120 , the protuberances  176  of the cap  126  interlock with the detents  152  of the tulip body  120  (see  FIG. 10 ). In addition, this interlocking feature permits the protuberances  176  to radially restrain the upper portion  130  of the tulip body  120 , which may reduce or eliminate post-operative, outward, radial expansion (i.e., splaying) of the upper portion  130  of the tulip body.  
         [0044]     In one embodiment, an effective cam length  180  of the cap  126  is slightly larger than an internal, diametrical distance  182  ( FIG. 4B ) of the cap-mating groove  150  of the upper portion  130  of the tulip body  120 . Thus, a maximum length  180  from one cam extension outer surface  169   a  to another cam extension outer surface  169   b  is greater than the internal, diametrical distance  182  between the cap-mating grooves  150  of the tulip body  120 . When the cap  126  is installed in this type of embodiment, the effective cam length  180  cams open the opening  144  in the upper portion  130  of the tulip body  120  by at least a small amount. This camming action is projected to the lower portion  128  of the tulip body  120  and operates to cause the spherical bore  134  to clamp and/or lock onto the head portion  110  of the pedicle screw  102 . This locking of the tulip body  120  onto the pedicle screw  102  occurs before the rod  104  is fixed to the tulip assembly  106  with the setscrew  127 .  
         [0000]     Operation/Assembly  
         [0045]      FIG. 8  is a flowchart showing a method  200  of assembling a pedicle screw system  100 , according to one illustrated embodiment. In combination and cooperation with method  200 , reference may be made to  FIGS. 9A-9E  to further describe and/or explain aspects of the assembly method  200 .  
         [0046]     The assembly method  200  begins at step  202  where the collar member  122  and the rod-support member  124  are pre-operatively assembled with the tulip body  120  as described above. It is understood that this pre-operative assembly may take place generally within the hospital or surgical center, possibly even in or near the operating room, or alternatively may take place at a manufacturer before the respective parts are shipped.  
         [0047]     As shown in  FIG. 9A , the pedicle screw  102  is insertably secured in the bone  302  with the head portion  110  of the pedicle extending above the bone surface  304  in step  204 . The upper portion  130  of the tulip body  120  is compressed and/or squeezed to allow the head portion  110  of the pedicle screw  102  to be received in the spherical bore  134  ( FIG. 4B ) in the lower portion  128  of the tulip body  120  in step  206 . The upper portion  130  of the tulip body  120  is released in step  208 , which allows the tulip body  120  to re-assume its natural or unloaded position. In addition, the greater diameter  116  ( FIG. 2B ) of the head portion  110  of the pedicle screw is contiguous with the spherical bore  134  of the tulip body  120  while the lesser diameter  118  ( FIG. 2B ) contacts the rod-support member  124 .  
         [0048]     As shown in  FIG. 9B , the collar member  122 , which is already on the tulip body  120 , is slid down the tulip body  120  in step  210 . Sliding the collar member  122  down the tulip body  120  keeps the region  142  ( FIG. 4B ) of the tulip body  120  from re-opening and/or spreading apart and thus retains the head portion  110  of the pedicle screw  102  within the spherical bore  134  ( FIG. 4B ) of the tulip body  120 . In this configuration, the tulip assembly  106  is secured to the head portion  110  of the pedicle screw  102 , but remains free to rotate relative to the pedicle screw  102 .  
         [0049]     As shown in  FIGS. 9C and 9D , the collar member  122  is rotated by an amount sufficient to align the cutout  158  in the collar member  122  with the rod-support surface  160  of the rod-support member  124  in step  212 . As the collar member  122  is rotated, the upper and lower surfaces  157   a ,  157   b  of the collar member  122  become vertically constrained by the shoulder  159  and the radial flange  138  of the tulip body  120 , respectively.  
         [0050]     As shown in  FIG. 9D , the rod  104  is placed in the tulip assembly  106  in step  214 . The rod  104  is seated on the rod-support surface  160  of the rod-support member  124 . At least a portion of the rod  104  extends through and out of one of the cutouts  158  in the collar member  122 . The cap  126  is oriented and placed in the upper portion  130  of the tulip body  120  in step  216 .  
         [0051]     As shown in  FIG. 9E , the cap  126  is rotated by an amount to allow the cam extensions  168  of the cap  126  to engage the grooves  150  in the upper portion  130  of the tulip body  120  in step  218 . As the cam extensions  168  of the cap  126  engage the grooves  150 , the upper portion  130  of the tulip body  120  is forced to expand radially outward because the maximum outer diameter  180  ( FIG. 7A ) of the cam extensions  168  is larger than the inner diameter  182  ( FIG. 4B ) of the grooves  150 . The radial, outward expansion of the upper portion  130  of the tulip body  120  causes the lower portion  128 , in particular the spherical bore  134 , to clamp onto the head portion  110  of the pedicle screw  102 . The amount of clamping force is sufficient to substantially prevent any relative movement between the tulip assembly  106  and the pedicle screw  102 . Thus, the rotation of the cap  126  into the grooves  150  of the tulip body  120  locks the tulip assembly  106  onto the pedicle screw  102 .  
         [0052]     As best seen in  FIG. 10 , the setscrew  127  is threaded into the cap  126  in step  220 , which completes the assembly of the pedicle screw system  100 . The setscrew  127  applies pressure to the rod  104 , which clamps the rod  104  between the rod-support member  124  and the setscrew  127 . The rod-support member  124  is in contact with the lesser diameter  118  of the head portion  110  of the pedicle screw  102 .  
         [0000]     Advantages  
         [0053]     One possible advantage of the pedicle screw system  100  is that the dual diameter head portion  110  of the pedicle screw  102  allows the rod-support member  124  to sit low in the tulip assembly  106 , which reduces the overall height of the tulip assembly  106  or, alternatively stated, reduces how much the tulip assembly  106  extends above the head portion  110  of the pedicle screw. This reduced height may mitigate soft tissue irritation, especially post-operatively.  
         [0054]     Yet another possible advantage is that the dual diameter head portion  110  permits the various components of the tulip assembly  106  to remain concentric, which may permit easier movement (e.g., less frictional binding and/or resistance) between the tulip assembly  106  and the head portion  110  of the pedicle screw  102 .  
         [0055]     Yet another possible advantage is that the cap  126  may be easily rotated in the tulip body  120  to cause the radial, outward expansion of the upper portion  130  of the tulip body  120 . The radial, outward expansion provisionally locks the tulip body  106  to the pedicle screw  102  by causing the lower portion  128 , in particular the spherical bore  134 , to clamp onto the head portion  110  of the pedicle screw  102 . Thus, the angular position of the tulip body  106  relative to the pedicle screw  102  may be quickly locked, then unlocked, and then re-locked at a different angular orientation by merely rotating the cap  126 . This flexibility allows the surgeon to repetitively and intra-operatively adjust, if necessary, the angular orientation of the tulip assembly  106  relative to the pedicle screw  102  without causing extra stress to the pedicle screw  102  and/or the bone  302 .  
         [0056]     Yet another possible advantage is that the protuberances  176  of the cap  126  radially restrain the upper portion  130  of the tulip body  120 , thus reducing or possibly eliminating any post-operative splaying and/or undesired flexing of the upper portion  130  of the tulip body  120 . Accordingly, the post-operative life of the pedicle screw system  100  may be longer when compared to other, conventional pedicle screw constructs, which in turn may reduce or eliminate any follow-up, repair, and/or maintenance-type spinal operation, for example to fix or replace a broken pedicle screw construct.  
         [0057]     All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, including but not limited to U.S. Provisional Patent Application No. 60/622,107 filed Oct. 25, 2004, are incorporated herein by reference, in their entirety.  
         [0058]     From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.