Abstract:
A method and associated system of implanting a vertebral anchor such as a pedicle screw assembly includes the steps of implanting a number of pedicle screws into a series of vertebrae; attaching a number of provisional posts to respective pedicle screws, each provisional post including a provisional saddle; bending a rod to conform to a desired alignment of the provisional saddles; removing the provisional posts from the pedicle screw heads; and connecting the bent rod to the pedicle screw heads. Advantageously, the method allows external fitting and sizing of a fixation rod before it is implanted and secured to the vertebral anchors via a minimally invasive manner.

Description:
[0001]     This claims priority to U.S. Provisional Application Ser. No. 60/719,380, filed Sep. 22, 2005 and hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND  
       [0002]     This invention relates to a device and method for vertebral stabilization using pedicle anchors and fixation rods.  
         [0003]     Conventional vertebral stabilization surgery using pedicle screws and fixation rods requires a surgeon to prepare a long incision aligned with the vertebral column of a patient. Pedicle screws are then inserted into a number of vertebrae after which a fixation rod is located with respect to saddles attached to the pedicle screws. The fixation rod is then bent to match the orientation of the pedicle screw heads and/or the desired curvature of the spine. Visualization of the accuracy of the alignment of the rod and the screw heads may be difficult because of visual interference from tissue and blood, for example. Conventional surgical methods require a large midline incision and retraction of skin and muscle to provide the surgeon with sufficient visualization of the pedicle bone structure.  
         [0004]     Improved methods, systems and devices that address these and other shortcomings in the prior art are needed.  
       SUMMARY OF THE INVENTION  
       [0005]     The systems, devices and methods described herein are used to aid in surgery for vertebral stabilization using vertebral anchors and fixation rods. Currently, this type of surgery is often performed using pedicle screws that have top loading saddles to receive rods wherein the rods are bent to match the orientation of the pedicle screw heads and/or the desired curvature of the spine. Rod bending is performed once the screws are placed into vertebrae and, therefore, visualization of the accuracy of the alignment of the rod with the screw heads is difficult. One surgical method according to this invention would follow the same course as traditional surgery except the tissue would not need to be cut between the pedicle screw heads prior to the rods being sized and bent.  
         [0006]     According to embodiments of this invention, provisional pedicle screw posts are attached to pedicle screw heads that would either be cannulated and have an attachment mechanism, or simply have an interlocking fit, to receive the provisional pedicle screw posts with the pedicle screw head saddle. The provisional pedicle screw posts may have links that connect each post to an adjacent post such that the adjacent posts are parallel to each other. The links and posts may be keyed or have other means to maintain the posts in parallel arrangement with each other. Once the posts are linked together, a mock, provisional, or trial saddle is placed on the proximal end of each provisional post. These mock saddles may have an indexed feature to ensure placement in the same trajectory as the pedicle screw saddles. A straight rod may then be placed on the outermost provisional posts. Based on the distance between the center saddle and the rod, the surgeon can determine how much the rod needs to be bent. The rod can then be bent and placed into the provisional saddles to check alignment as well as cut the rod to a proper length.  
         [0007]     Once the modification of the rod is complete, i.e., bending and cutting to length, the tissue can be cut between the pedicle screws and dissected in a minimally invasive manner for placement of the rod followed by closing the incision after rod placement and securing. The rod may come in a series of varying radiuses, i.e., pre-bent, so the surgeon could simply place a pre-bent rod into the provisional saddles and change the rod with a different pre-bent rod as needed. The amount of pre-bending of the rod may be undersized with respect to the saddle trajectory to create more lordosis on the construct when the rod is fixed in place.  
         [0008]     One advantage of the system of this invention is that the pedicle screws could be placed, and the rod modified, sized and bent using this device, after which a minimally invasive interconnecting incision is made to the pedicle screw heads so the rod can be placed and tightened. Alternatively, the modified rod may be inserted into the first incision and fed through all of the pedicle screw head saddles. Either of these insertion methods may potentially reduce the surgical time, as well as reduce necessity of significant tissue dissection and retraction during surgery.  
         [0009]     Another advantage of this system is the increased visualization of the fit of the rod to the pedicle screw head saddles. Very often, this is instrumental in achieving the intended outcome. In traditional surgery, visualization of the actual fit of these components is difficult because of blood and tissue. In addition, elimination of the need to significantly retract tissue is a large benefit that could provide a quicker recovery time.  
         [0010]     Additional features may include an apparatus for determining the trajectory of the connecting rod by use of a modified compass mechanism for extrapolating the correct radius and any obtuse angles that may be encountered with various anatomies. Again, the rods may be checked for correct alignment and length in the mock saddles.  
         [0011]     In one form thereof, this invention provides a method of implanting a pedicle screw assembly including the steps of implanting a plurality of pedicle screws into a series of vertebrae; attaching a plurality of provisional posts to respective pedicle screws, each provisional post including a provisional saddle; bending a rod to conform to a desired alignment of the provisional saddles; removing the provisional posts from the pedicle screw heads; and connecting the bent rod to the pedicle screw heads. 
     
    
     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 view of a portion of a spinal column including a plurality of vertebrae, and further showing various components of the pedicle fixation rod alignment system of the present invention;  
         [0014]      FIG. 2  is a perspective view of a provisional or pedicle screw head saddle;  
         [0015]      FIG. 3  is a cross-sectional view of a portion of  FIG. 1 , further illustrating the connection between the provisional post, the pedicle screw, and the pedicle screw head saddle; and  
         [0016]      FIG. 4  is a cross-sectional view of a portion of  FIG. 1 , further illustrating a connection between a provisional saddle and a provisional post. 
     
    
       [0017]     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates embodiments of the invention and such exemplification is not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     In general, the system of this invention provides a trial assembly for trialing a pedicle fixation rod exteriorly of a patient during surgery.  
         [0019]     The present method and devices employ similar minimally invasive surgical methods and devices as described in U.S. patent application Ser. No. 11/228,958, entitled APPARATUS AND METHOD FOR MINIMALLY INVASIVE SPINE SURGERY, filed on Sep. 16, 2005, assigned to the assignee of this invention and the disclosure of which is expressly incorporated herein by reference.  
         [0020]     Referring now to  FIG. 1 , a spinal fixation construct according to various embodiments of this invention includes a number of vertebral anchors in the form of pedicle screws  10   a ,  10   b ,  10   c  having pedicle screw heads  11   a ,  11   b ,  11   c , respectively, positioned in vertebrae V 1 , V 2 , and V 3  after a surgeon makes a plurality of small incisions I in the skin of the patient proximate vertebrae V 1 , V 2 , and V 3 . The pedicle screws  10   a ,  10   b ,  10   c  include pedicle screw head saddles  12   a ,  12   b ,  12   c , respectively, shown in  FIGS. 1-2 , each of which typically includes an aperture  13  ( FIG. 2 ) in the bottom thereof through which each pedicle screw  10   a ,  10   b ,  10   c  passes. Provisional, trial, or mock pedicle screw posts  14   a ,  14   b ,  14 C are placed onto the pedicle screw heads  11   a ,  11   b ,  11   c , respectively, via engagement with the pedicle screw head saddles  12   a ,  12   b ,  12   c , respectively. The engagement of the provisional posts  14   a ,  14   b ,  14   c  with respective saddles  12   a ,  12   b ,  12 C may be any attachment mechanism, such as a threading engagement shown in  FIG. 3 , a snap-fit engagement, or an interlocking fit engagement, for example. The provisional posts  14   a ,  14   b ,  14   c  may be cannulated.  
         [0021]     The provisional pedicle screw posts  14   a ,  14   b ,  14   c  extend externally of the patient or percutaneously and are linked together via an alignment arrangement which in one embodiment includes links  16   a ,  16   b , wherein link  16   a  connects provisional post  14   a  to an adjacent provisional post  14   b  such that adjacent posts  14   a  and  14   b  are parallel to each other. Similarly, link  16   b  connects provisional post  14   b  to an adjacent provisional post  14   c  such that adjacent posts  14   b  and  14   c  are parallel to each other. This is accomplished by having the links  16   a ,  16   b  and the provisional posts  14   a ,  14   b ,  14   c  keyed or include any other mechanism to maintain the provisional posts  14   a ,  14   b ,  14   c  parallel to each other. The links  16   a  and  16   b  must be radially lockable with respect to the posts  14   a ,  14   b ,  14   c . The length of each link  16   a ,  16   b  may be adjustable via telescoping joints  17   a  and  17   b  which must also be lockable.  
         [0022]     Once the provisional posts  14   a ,  14   b ,  14   c  are linked together, provisional, trial, or mock saddles  18   a ,  18   b ,  18   c  ( FIGS. 1-2 ) are placed on proximal ends  15   a ,  15   b ,  15   c  of each respective provisional post  14   a ,  14   b ,  14   c . The connection of the provisional saddles  18   a ,  18   b ,  18   c  with respective the provisional posts  14   a ,  14   b ,  14   c  may be via any suitable connecting arrangement, such as a connecting screw  19   b  shown in  FIG. 4 , a thread-type engagement, or a snap-fit engagement. Alternatively, the provisional saddles  18   a ,  18   b ,  18   c  may be integrally formed with the provisional posts  14   a ,  14   b ,  14 C and made of stainless steel. The provisional saddles  18   a ,  18   b ,  18   c  may have an indexed feature to place them in the same trajectory as the pedicle screw head saddles  12   a ,  12   b ,  12   c . Additionally, the provisional saddles  18   a ,  18   b ,  18   c  have identical geometries as respective pedicle screw head saddles  12   a ,  12   b ,  12   c . Next, a rod  20  can be placed in each of the provisional saddles  18   a ,  18   b  and  18   c  or only on the provisional saddles  18   a ,  18   c  of the outermost provisional posts, i.e., provisional posts  14   a  and  14   c . Based on the distance between the provisional saddle  18   b  on the provisional post  14   b  and the rod  20 , the surgeon determines how much the rod  20  needs to be bent. The rod  20  can then be bent and placed into the provisional saddles  18   a ,  18   b , and  18   c  to check alignment as well as to be cut for proper length.  
         [0023]     Advantageously, the system and method of this invention facilitates replication of the exact relative geometry and positioning of the pedicle screw head saddles  12   a ,  12   b ,  12   c  attached to the respective vertebrae by using the provisional pedicle screw posts  14   a ,  14   b ,  14   c , the provisional saddles  18   a ,  18   b ,  18   c , and the links  16   a ,  16   b . The external replication of the internal geometry and positioning of the saddles  12   a ,  12   b , and  12   c  allows a surgeon to use minimally invasive surgical techniques to implant the rod  20 , thereby reducing the necessity for significant tissue dissection and retraction.  
         [0024]     Once the sizing of the rod  20  is complete, the tissue can be cut between the pedicle screws  10   a ,  10   b ,  10   c  in a minimally invasive manner with minimal or no tissue retraction so that the rod  20  can be placed and tightened onto each pedicle screw  10   a ,  10   b ,  10   c  via appropriate set screws (not shown) followed by closing of the incision. The rod  20  may come in a series of varying radiuses, i.e., pre-bent, so that the surgeon could simply place the pre-bent rods into the provisional saddles  18   a ,  18   b ,  18   c  and change size as needed. This could also be used to undersize the radius of the rod  20  versus the saddle trajectory to create more lordosis on the construct when the rod  20  is placed and tightened.  
         [0025]     One advantage of this method, system and device is that the pedicle screws  10   a ,  10   b ,  10   c  may be placed into the vertebrae V 1 , V 2 , and V 3 , and the rod  20  is sized and bent using this device, after which a minimally invasive interconnecting incision is made to the pedicle screw heads  11   a ,  11   b ,  11   c  so that the rod  20  can be placed and tightened. This could potentially reduce the surgical time, as well as reduce the necessity of significant tissue dissection and retraction during surgery. Alternatively, after the rod  20  is bent to the correct size, the rod  20  may be inserted through the first incision, i.e., the incision I made for insertion of pedicle screw boa, and fed through the pedicle screw head saddles  12   a ,  12   b ,  12 C without requiring any additional incision of tissue, thereby advantageously reducing the amount of trauma inflicted on a patient during surgery.  
         [0026]     Another advantage of this system is the increased visualization of the fit of the rod  20  to the pedicle saddles  12   a ,  12   b ,  12 C which is instrumental in achieving the intended outcome. In traditional surgery, it is typically difficult to see the actual fit of these components because of blood and tissue. In addition, the elimination of the need to significantly retract tissue is a large benefit that could provide a quicker recovery time.  
         [0027]     In an alternative embodiment, the system could include an apparatus (not shown) for determining the trajectory of the connecting rod  20  by use of a modified compass mechanism that could be connected to the provisional pedicle screw posts  14   a ,  14   b ,  14   c  and extrapolate the correct radius as well as obtuse angles that may be encountered with various anatomies. Then, these values could be used to properly bend the rod  20 . Again, the rod  20  could be checked in the provisional saddles  18   a ,  18   b ,  18   c  prior to making the interconnecting incision.  
         [0028]     Although the invention is described throughout as being applied to three vertebrae, i.e., a two-level system, the invention may be used with any number of vertebrae that need to be fixed together by a fixation system. Additionally, this invention may also be used in transverse fixation systems. Additionally, the pedicle screws are shown and described herein, but other types of vertebral anchors could be utilized such as hooks and other vertebral anchor mechanisms.  
         [0029]     While this invention has been described as having a preferred design, the invention can be further modified within the spirit and scope of this disclosure. This invention therefore covers any variations, uses, or adaptations using its general principles. Further, this invention is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.