Abstract:
A spinal fixation access system includes a vertebral anchor with selectively attached extension members to extend percutaneously from the spine. The surgical procedure associated with this invention involves making small, discrete incisions for the placement of select vertebral anchors. The extension members retract soft tissue, muscle and the like to thereby provide visibility and access to the head of the anchor. Through the extension members, instrumentation such as a spine rod, set screw and other required hardware may be delivered to the anchors. Once a spine rod or other components are secured to the pedicle screws, the extension members are disengaged from the anchors and removed from the patient.

Description:
BACKGROUND 
       [0001]    This invention relates generally to spinal fixation devices and more specifically relates to a system and associated method for minimally invasive installation of vertebral anchors and connecting elements of spinal fixation constructs. 
         [0002]    The human spinal column is a highly complex system of bones and connected tissues that provide support for the body and protects the delicate spinal cord and nerves. The spinal column includes a series of vertebrae stacked one atop the other. Each vertebral body includes a relatively strong cortical bone portion forming the outside surface of the body and a relatively weak cancellous bone portion forming the center of the body. An inter-vertebral disc is situated between each vertebral body that provides for cushioning and dampening of compressive forces applied to the spinal column. The vertebral canal containing delicate spinal cords and nerves is located just posterior to the vertebral bodies. 
         [0003]    A variety of types of spinal column disorders may be caused by abnormalities, disease, trauma or the like and result in debilitating pain as well as diminished nerve function in many cases. One known technique to address many such spinal conditions is commonly referred to as spinal fixation. Surgical implants are used for fusing together and/or mechanically immobilizing adjacent vertebrae of the spine. Spinal fixation may also be used to improve the position of the adjacent vertebrae relative to one another so as to alter the overall alignment of the spine. Such techniques have been used effectively to treat many spinal conditions and to relieve pain suffered by the patient. 
         [0004]    One particular spinal fixation technique includes immobilizing the spine by using orthopedic spine rods which run generally parallel to the spine. This is accomplished by exposing the spine posterially and fastening hooks or bone screws to the pedicles of the appropriate vertebrae. The vertebral anchors or screws are generally placed two per vertebrae, one at each pedicle on either side of the spinal column and serve as anchor points for the spine rods. The aligning influence of the rods forces the spine to conform to a more desirable shape. In many cases, the spine rods are bent to achieve the desired curvature of the spinal column. 
         [0005]    Installation of such spinal fixation constructs conventionally requires a surgeon to prepare a long incision aligned with the spinal column of a patient. The pedicle screws, hooks or other vertebral anchors are then attached to a number of vertebrae after which the spine rod is located with respect to saddles or U-shaped channels attached to the vertebral anchors. The spine rod is then bent to match the relative position of the anchor heads. Visualization of the accuracy of the alignment of the spine rod and the anchor heads may be difficult because of visual interference from tissue and blood in the surgical field. Conventional surgical methods require a large midline incision and retraction of skin, muscle and other tissue to provide the surgeon with sufficient visualization of the pedicle bone structure. 
         [0006]    The accuracy of the placement and configuration of the spine fixation elements are very important. In combination with the relatively long incision required for the installation of the fixation construct, extended surgical procedures and related difficulties or complications are generally recognized as major contributing influences for extended patient recovery and less than optimal spinal fixation results. 
       SUMMARY OF THE INVENTION 
       [0007]    This invention addresses these and other shortcomings in the prior art. The devices and methods associated with this invention are used to aid in the surgery for vertebral stabilization using pedicle hooks, screws, anchors and fixation components. 
         [0008]    According to various embodiments of this invention, vertebral anchors such as pedicle screws are inserted into the target vertebrae of a patient&#39;s spinal column. The pedicle screw may be cannulated for proper positioning and installation. In one aspect, this invention provides an access system which involves a pedicle screw with an extension member adapted to be coupled to the anchor and extend percutaneously from the spine. The surgical procedure associated with this invention involves making small, discrete incisions for the placement of select pedicle screws. The extension members on the pedicle screws retract soft tissue, muscle and the like to thereby provide the surgeon visibility and access to the head of the pedicle screw. Through the extension member, instrumentation such as a spine rod, set screw and other required hardware may be delivered to the pedicle screws. 
         [0009]    In another aspect of this invention, a deformation arrangement is used to couple the extension member to the anchor head. In one embodiment, the deformation arrangement is a flange on one end of the extension member and one or more slits in the flange allow the flange to expand when being installed and removed from the anchor head. 
         [0010]    Once the extension member is secured on the anchor, a restrictor is coupled to the flange to inhibit expansion of the deformation arrangement and maintain secure placement of the extension member on the anchor while the spinal fixation construct is being installed or serviced. The extension members for each pedicle screw extend beyond the surface of the skin (i.e., percutaneously) thereby retracting soft tissue and muscle enabling the surgeon to install the spinal fixation construct with smaller discrete incisions as opposed to an extended incision. As such, a more minimally invasive surgical procedure can be accomplished with this invention thereby allowing for visualization of the installation components during the surgery and promoting patient recovery post-surgery. 
         [0011]    As a result of these and other aspects of this invention, increased efficiency and accuracy is provided for installation of a spinal fixation construct in a minimally invasive atmosphere thereby promoting patient recovery and optimum spinal surgery results. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a side elevational and partial cross-sectional view of a spinal fixation construct being surgically implanted in selected vertebrae of a patient&#39;s spine according to one embodiment of this invention; 
           [0014]      FIG. 2  is a perspective view of a vertebral anchor extension member utilized in the spinal fixation construct shown in  FIG. 1 ; 
           [0015]      FIG. 3  is a front elevation al view of the extension member of  FIG. 2 ; 
           [0016]      FIG. 4  is a side elevational view of the extension member of  FIG. 2 ; 
           [0017]      FIG. 5  is a side elevational view of the extension member of  FIG. 2  being coupled to a vertebral anchor in the form of a pedicle screw; 
           [0018]      FIG. 6  is a view similar to  FIG. 5  with a restrictor being installed on the extension member; 
           [0019]      FIG. 7  is a view of the assembled vertebral anchor and extension member according to the first embodiment of this invention; 
           [0020]      FIG. 8  is a partial cross-sectional view of the assembled vertebral anchor and extension member of  FIG. 7  with a spine rod and set screw being inserted through the extension member; 
           [0021]      FIG. 9  is a perspective view of a second embodiment of a vertebral anchor extension member utilized in a spinal fixation construct according to this invention; 
           [0022]      FIG. 10  is a front elevational view of the extension member of  FIG. 9 ; 
           [0023]      FIG. 11  is a side elevational view of the extension member of  FIG. 9 ; 
           [0024]      FIG. 12  is a perspective view of a restrictor according to one embodiment for use with the extension member of  FIG. 9 ; 
           [0025]      FIG. 13  is a perspective view of a pair of restrictors as shown in  FIG. 12  assembled with the extension member of  FIG. 9 ; 
           [0026]      FIG. 14  is a cross-sectional view taken along line  14 - 14  of  FIG. 13 ; 
           [0027]      FIG. 15  is a front elevational view of the embodiment of  FIG. 13  with the extension member assembled with a restrictor; 
           [0028]      FIG. 16  is a side elevational view of the assembly of  FIG. 15 ; 
           [0029]      FIG. 17  is a side elevational view in partial cross-section of the extension member of  FIG. 15  being coupled to a vertebral anchor in the form of a pedicle screw; 
           [0030]      FIG. 18  is a view similar to  FIG. 17  with the extension member mounted on the pedicle screw; 
           [0031]      FIG. 19  is a cross-sectional view taken along line  19 - 19  of  FIG. 18  of a restrictor being installed on the extension member; 
           [0032]      FIG. 20  is a view of the assembled vertebral anchor and extension member of  FIG. 19 ; and 
           [0033]      FIG. 21  is a partial cross-sectional view of the vertebral anchor and extension member of  FIG. 20  with a spine rod and set screw being inserted through the extension member. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    Referring to the Figs., various embodiments of a minimally invasive spinal fixation construct  10  and associated installation method are shown. In  FIG. 1 , the spinal fixation construct  10  includes a number of vertebral anchors  12  which in one embodiment are each pedicle screw assemblies, each of which is inserted into selected vertebrae  14  of a patient. The pedicle screw assemblies  12  are joined together in the spinal fixation construct by a connecting element  16  which in one embodiment is a spine rod. The connecting element  16  may be something other than a rigid rod according to alternative embodiments of this invention. According to various aspects of this invention, the individual pedicle screw assemblies  12  may be inserted into the patient through discrete and often individual incisions  18  in the patient&#39;s skin  20 . In certain instances, a single incision  18  may be available to provide installation of multiple pedicle screw assemblies  12  in adjacent vertebrae  14 . The small, discrete incisions  18  provide the opportunity for insertion of a cannulated pedicle screw via a K-wire (not shown) inserted through the incision  18  to the precise location on the vertebrae  14  for proper installation of the pedicle screw  12 . While cannulated and other pedicle screw assemblies are shown and described herein, one of ordinary skill in the art will appreciate that other types of vertebral anchors and vertebrae engaging mechanisms can be utilized such as hooks for anchoring the connecting element  16  to the patient&#39;s spinal column. 
         [0035]    As shown generally in FIGS.  1  and  5 - 8 , a vertebral anchor  12  according to one embodiment of this invention includes a pedicle screw  12  having a threaded shaft  20  and a distal tip  22  for insertion and stable positioning into the pedicle area of the patient&#39;s vertebrae  14 . The pedicle screw  12  shown herein is a polyaxial pedicle screw in which a polyaxial body  24  mounted opposite from the distal tip  22  of the screw  12  to a screw head  26  provides for a variety of orientations of the polyaxial body  24  relative to longitudinal axis of the screw  12  as is common with many pedicle screw systems. The polyaxial body  24  coupled to the pedicle screw head  26  includes a saddle or U-shaped channel  28  ( FIGS. 19-20 ) formed between a pair of spaced arms  30  extending upwardly. The polyaxial body  24  is adapted to receive the spine rod  16  in the saddle or U-shaped channel  28  and the spine rod  16  is securely retained by the polyaxial body  24  via a fastener such as a set screw  32  ( FIG. 8 ) threadably received therein as is common with many known pedicle screw systems. 
         [0036]    One aspect of various embodiments of this invention includes an extension member  34  projecting upwardly from the vertebral anchor head  24  as shown in FIGS.  1  and  5 - 8 . Due to the relative position and configuration of the extension members  34  on the vertebral anchors  12  according to embodiments of this invention, slots  36  are provided and in communication with the U-shaped channel or saddle  28  of the anchor head  24 . Advantageously, the extension members  34  project through the incision  18  such that a distal end  38  of the members  34  is located percutaneously above the patient&#39;s skin when the anchor  12  is inserted into the vertebrae  14  as shown in  FIG. 1 . 
         [0037]    One embodiment of an extension member  34  according to this invention is shown particularly in  FIGS. 1-8 . The extension member  34  is elongate and adapted to extend percutaneously from the body when the anchor  12  is secured to the patient&#39;s vertebrae  14 . The elongate extension member  34  in this embodiment is an elongate tubular sleeve having a generally arcuate sidewall  40  with a generally circular cross-sectional configuration. The extension member  34  has a first more proximal end  42  adapted to be coupled to the anchor head  24  and the second or distal end  38  adapted to be positioned percutaneously for access to the anchor head  24  through a lumen  44  formed by the arcuate sidewall  40  of the extension member  34 . The first end  42  of the extension member  34  includes a flange  46  having an enlarged diameter relative to the sidewall  40  of the extension member  34 . As shown most clearly in  FIGS. 2-4 , the flange  46  has an upper and a lower portion  46   a ,  46   b  with a shoulder  48  formed in between them. A beveled rim  50  forms a transition from the flange  46  to the sidewall  40  of the extension member  34 . As shown in  FIGS. 2 and 3 , the extension member  34  includes a full-length slot  36   a  and a proximal slot  36   b  positioned diametrically opposite from the full-length slot  36   a . Both of the slots  36   a ,  36   b  are in communication with the proximal end  42  of the extension member  34  proximate the flange  46 . 
         [0038]    Referring particularly to  FIGS. 5 and 6 , a socket  52  is formed on the interior of the flange  46  and is sized and configured to meet with the anchor head  24  when the extension member  34  is mounted to the anchor  12 . In this embodiment of the invention, the socket  52  has a generally upwardly tapered configuration with a throat or entry region  54  being more narrow than the upper portion of the socket  52 . This contour corresponds to the contour of the anchor head  24  thereby providing a snug and secure mating relationship as shown generally in  FIG. 6 . 
         [0039]    One aspect of the extension member  34  according to this embodiment of the invention is one or more slits  56  in the flange  46  which allow the flange  46  to temporarily expand or deform while the extension member  34  is being coupled to or uncoupled from the anchor  12 . As shown most clearly in  FIGS. 2-4 , the flange  46  includes a number of minor slits  56   a  which have a main portion  58  angled relative to the longitudinal axis of the extension member  34  and terminate in the lower portion  46   b  of the flange with a hook  60 . One or more major slits  56   b  are also provided in the flange  46  and the major slits include a main portion  58  similar to the configuration of the minor slits. The major slits each also include an adjoining hook portion  60 . The minor slits  56   a  terminate with the hook portion  60  whereas the major slits  56   b  include an angled portion  62  projecting from the hook portion  60 . The angled portion  62  transitions the major slit  56   b  through the shoulder  48  of the flange  46 . The major slit  56   b  terminates in a keyhole-shaped configuration  64  which is aligned generally with the longitudinal axis of the extension member  34  ( FIG. 4 ). In alternative embodiments, any number and/or configuration of sized or shaped slits can be used to provide for the desired deflection characteristics. 
         [0040]    The major and minor slits  56   ab ,  56   a  allow the flange  46  of the extension member  34  to temporarily expand as the throat  54  of the extension member  34  passes over the outwardly tapered distal portion  66  of the anchor head  24 . Continued downward movement of the extension member  34  as shown in  FIG. 5  allows the larger diameter portion  66  of the anchor head  24  to enter into the larger diameter portion of the socket  52  in the flange  46  and the reduced neck region  68  of the anchor head  24  seats within the reduced diameter throat  54  of the flange  46 . The slits  56  allow the flange  46  to expand outwardly as shown in  FIG. 5  until the anchor head  24  is seated within the socket  52  as shown in  FIG. 6 . At that time, the slits  56  allow the flange  46  on the extension member  34  to relax into a mating configuration with the anchor head  24 . 
         [0041]    While the portion  66  of the anchor head  24  and the socket  52  are shown and described as having tapered, mating configuration, other configurations and designs are envisioned within the scope of this invention to provide a retained fit between the extension member  34  and the anchor head  24 . 
         [0042]    Another aspect of this embodiment of the invention is a restrictor  70  which when selectively coupled to the extension member  34  inhibits deformation of the flange  46 . In one embodiment, the restrictor  70  is an elongate collar which telescopically fits downwardly around the sidewall  40  of the extension member  34 . As shown in  FIG. 6 , the collar or restrictor  70  includes an internal cavity  72  sized and configured to mate with the upper portion of the flange  46   a  and the lowermost edge  74  of the collar seats upon the shoulder  48  of the flange  46  as shown in  FIG. 7 . With the collar  70  mated onto the extension member  34 , expansion of the flange  46  is restricted thereby adding to the secure mating relationship of the extension member  34  on the anchor  12 . The collar  70  inhibits the flange  46  from expanding and restricts the slits  56  from expanding. The upper end of the collar  70  may extend percutaneously through the incision  18  as shown in  FIG. 1 . The collars  70  may include slots  76  corresponding to the orientation, size and configuration of the slots  36  in the extension members  34 . When the collars  70  are telescopically mated with the extension members  34 , the slots  36 ,  76  in the respective components are aligned. 
         [0043]    Referring to  FIGS. 9-21 , a second embodiment of this invention is shown. This embodiment of the invention also includes an extension member  34  adapted to be coupled to the head  24  of the anchor  12  to provide access for the surgeon during installation of the spinal fixation construct  10 . The extension member  34  of this embodiment also utilizes a restrictor  70  to inhibit expansion or deformation of the flange  46  on the extension member  34  coupled to the anchor head  12 . 
         [0044]    As shown in  FIGS. 9-11 , the extension member  34  includes the full-length slot  36   a  and two partial-length slots  36   b ,  36   c  each extending from opposite ends of the extension member  34  ( FIG. 10 ). Moreover, the flange  46  according to this embodiment of the extension member includes the lower portion  46   b  and shoulder  48 . However, the upper portion of the flange  46   a  does not extend around the entire circumference of the sidewall  40  and is formed in two diametrically opposite sections  46   a ,  46   a  which extend upwardly from the shoulder  48 . A major slit  56   b  extends through each of the upper flange portions  46   a  as shown in  FIGS. 9 and 11 . Moreover, notches  78  are provided in the flange  46  to separate the flange  46  into downwardly projecting lugs  80  formed between the notches  78 . The major slit  46   b  originates in one of the notches  78  and projects through the upper portion of the flange  46   b  and into the sidewall  40  of the extension member  34  as shown in  FIGS. 9 and 11 . The peripheral rim  50  of the upper portion of the flange  46   b  is undercut as shown most clearly in  FIG. 10 . The undercut rim  50  of the upper flange portion  46   b  extends around the entire perimeter of that component. 
         [0045]    The restrictor  70  according to this embodiment of the invention is shown particularly in  FIGS. 12 and 13 . The restrictor  70  is provided in two distinct members, one identical with the other. The restrictor  70  has a generally L-shaped configuration with an upper tab  82  projecting generally perpendicular from the major body portion  84  of the restrictor  70 . The restrictor  70  has a lower enlarged yoke portion  86  at an opposite end from the tab  82 . The yoke portion  86  includes a U-shaped recess  88  providing a bifurcated configuration to the yoke  86 . The U-shaped recess  88  is bounded by a sloped edge go which is sized and configured to mate with the tapered rim  50  of the upper portion of the flange  46   a  to form a dove tail or rabbet joint as shown in  FIGS. 13-16 . A pair of the restrictors  70  on diametrically opposite sides of the extension member  34  and are each aligned with the one of the upper flanges  46   a ,  46   a  and inserted downwardly as shown in  FIG. 19  until the U-shaped recess  88  of each restrictor  70  is seated on the associated upper flange portion  46   a  of the extension member  34 . The configurations of the rim of the upper flange  46   b  and the U-shaped recess edge go provide positive locking engagement in the form of a rabbet or miter joint ( FIG. 14 ) to thereby inhibit expansion of the extension member  34  after it is seated upon the anchor head  24  as shown in  FIG. 20 . In alternative embodiments, the restrictors  70  may be modular relative to extension member  34  or integrated as a single functioning assembly or unit and may utilize a variety of mating geometries, not just a dovetail or rabbet joint. 
         [0046]    Similar to other previous described embodiments of this invention, once the extension member  34  and restrictors  70  are seated on the anchor head  24 , the connecting member  16  in the form of a spine rod may be inserted through the lumen  44  formed in the extension member  34  toward the anchor head  24  for installation onto the vertebral anchors  12  on the spinal fixation construct  10 . The set screw  32  may subsequently be inserted through the lumen  44  for mating with the anchor  12  as shown in  FIG. 21 . 
         [0047]    One advantage provided by this invention is shown generally in  FIG. 1 . With the pedicle screws  12  inserted into the appropriate vertebrae  14 , the extension members  34  project from the screw assemblies  12  percutaneously. The enhanced visualization and access afforded by the percutaneous positioning of the extension members  34  in the general orientation of the associated anchors  12  is a significant advantage for the accurate and precise positioning of the spinal fixation components. Referring to  FIGS. 8 and 21 , the spine rod  16  may be inserted through the slots and into the saddles  28  of the anchors  12 . This may be accomplished with incisions  18  which are adjacent to the pedicle screw assemblies  12  as shown in  FIG. 1 . The access slots provided in the extension member  34  and the restrictors  70  provide communication between the various adjacent pedicle screw assemblies  12  so that the spine rod  16  may be inserted into the saddles  28  of the anchor heads  24  in a minimally invasive and less disruptive procedure than previously realized. 
         [0048]    Once the set screws  32  are installed in the anchor heads  24 , the restrictors  70  and then the extension members  34  can be removed from the anchors  12  and out of the patient through the incisions  18 . The slits  56  allow for expansion of the flange  46  once the restrictor  70  is removed to permit the anchor head  24  removal from the socket  52 . 
         [0049]    As a result, a more minimally invasive spinal fixation construct installation procedure is provided by the pedicle screw assemblies, collars and associated devices of this invention without the need for extended incision and associated difficulties. Moreover, increased visualization and minimally invasive disruption are realized with this invention. 
         [0050]    From the above disclosure of the general principles of this invention and the preceding detailed description of at least one embodiment, those skilled in the art will readily comprehend the various modifications to which this invention is susceptible. Therefore, we desire to be limited only by the scope of the following claims and equivalents thereof.