Abstract:
Instruments, and methods for performing surgical procedures on the spine, including creating an operative corridor to the spine with a tissue retraction system and registering the tissue retraction system to the patient.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional patent application claiming the benefit of priority from U.S. Provisional Patent Application Ser. No. 61/296,468, filed on Jan. 19, 2010, the entire contents of which is hereby expressly incorporated by reference into this disclosure as if set forth in its entirety herein. 
    
    
     FIELD 
     The present invention relates to implants and methods generally aimed at surgery and, more particularly, to improved systems and methods for performing spine surgery. 
     BACKGROUND 
     Spinal discs serve to cushion and stabilize the spine in addition to distributing stress and damping cyclic loads. The discs may become damaged due to injury or age and symptoms of a damaged disc may include severe pain, numbness or muscle weakness. Fusion is one method of reducing the magnitude of the symptoms of damaged spinal discs. The primary goals of fusion procedures are to provide stability between the vertebrae on either side of the damaged disc and to promote natural fusion of those adjacent vertebrae. 
     In a typical spinal fusion surgery, for example, a tissue retractor is used to create and maintain an operative corridor through a patient&#39;s skin to a target disc space. This retractor is secured to the operating table via an articulating arm. However, this arrangement can have disadvantages in that the retractor is registered to the table, and thus any movement of the patient (however slight) may shift the operative corridor slightly. This can create a delay in the surgical procedure as the surgeon must reestablish the proper operative corridor by repositioning the patient, often requiring additional fluoroscopy usage that wouldn&#39;t otherwise be necessary in order to verify positioning. Furthermore, even if the slight shift of the operative corridor does not require repositioning of the patient, often times there will be tissue creep into the operative corridor due to the split-blade nature of the retractor. Also, slight movement of the operative corridor may cause other anatomical interference with the retractor blades, such as ribs in a thoracic spine example, or the iliac crest in a lumbar spine example. Also, fixation to the spine creates a truly rigid fixation system. The present invention is directed at addressing the shortcomings of the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention accomplishes this goal by providing a tissue retraction system including attachment shims that securely and rigidly attach distal ends of the retractor blades to bone screws implanted in a patient. Thus, the retractor is registered to the patient rather than the operating table. Such a configuration ensures that the operative corridor does not shift relative to the patient at any time. This has the advantage of minimizing tissue creep into the operative corridor, and also removes the potential of anatomical interference since the location of nearby spinal anatomy does not change relative to the operative corridor, once established. Thus, small shifts in patient positioning are not problematic. Also, the present invention allows distraction, compression, and deformity correction. 
     To accomplish this goal, a tissue retraction system is provided including a tissue retractor having a body and a plurality of retractor blades. Attachment shims are also provided to enable secure, rigid attachment of the retractor blades to implanted bone screws. The attachment shims are configured to slideably engage the retractor blades to enable easy introduction into the surgical target site. By way of example only, the attachment shims may have an elongated body with an engagement member at its distal end. In one embodiment, the engagement member includes a ring member having a gap formed therein. The gap allows passage of the one screw therethrough. The gap may be slightly smaller than the portion of the bone screw that traverses the gap, thereby requiring the ring member to slightly flex to allow passage of the bone screw. This enables a “snap-fit” engagement between the shim and the screw. 
     Several alternative configurations of the attachment shim are possible without departing from the scope of the present invention. According to one embodiment, the ring member may include a 270° arc between the base of the shim and the gap. According to another embodiment, the ring member may include a generally C-shaped clamp mechanism. According to another embodiment, the ring member may be offset from the retractor blade via an extension. According to yet another embodiment, the, engagement member may comprise a locking bar with a set screw. Cannulated screws may be utilized—placed over K-wires inserted into the bone on either side of the disc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein: 
         FIG. 1  is a perspective view of an example of a tissue retraction assembly capable of being used with the present invention, shown in an initial “closed” position; 
         FIGS. 2-3  are perspective and top plan views, respectively, of the tissue retraction assembly of  FIG. 1 , shown in a secondary “open” position; 
         FIGS. 4-5  are perspective views of an example of an attachment shim for use with the tissue retraction assembly of  FIG. 1 , according to one embodiment of the present invention; 
         FIG. 6  is a perspective view of the attachment shim of  FIG. 4  engaged with an example of a bone screw; 
         FIG. 7  is a perspective view of an example of an attachment shim according to an alternative embodiment of the present invention; 
         FIG. 8  is a perspective view of an example of an attachment shim according to an another embodiment of the present invention; 
         FIG. 9  is a perspective view of an example of an attachment shim according to an another embodiment of the present invention; 
         FIG. 10  is a plan view of a step in engaging the attachment shim of  FIG. 4  with a retractor blade forming part of the tissue retraction assembly of  FIG. 1 ; 
         FIG. 11  is a top plan view of the tissue retraction assembly of  FIG. 1  in an “open” position allowing access to a pair of implanted pedicle screws according to one embodiment of the present invention; and 
         FIG. 12  is a top plan view of the tissue retraction assembly of  FIG. 11  including attachment shims engaged with the bone screws according to one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The tissue retraction system disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
       FIGS. 1-3  illustrate an example of a tissue retraction assembly  10  configured for use with the attachment shim of the present invention. By way of example only, the tissue retraction assembly  10  is similar to one disclosed in U.S. Provisional Patent Application No. 61/105,791, filed Oct. 15, 2008 and entitled “Systems and Methods for Performing Spinal Fusion Surgery,” the contents of which are incorporated herein by reference with no claim of inventorship. The tissue retraction assembly  10  is configured to establish an operative corridor through a patient&#39;s skin to a surgical target site. By way of example only, the surgical target site may be an intervertebral disc located between adjacent vertebral bodies of a human spine. Although described for use in this fashion, the tissue retraction system described herein may be used with any part of the body without departing from the scope of the present invention. Prior to using the retractor, an initial distraction assembly (not shown) may be used to establish an initial distraction corridor. For example, this initial distraction assembly may include a K-wire and sequential dilator kit of the kind commonly used in the art. The tissue retraction assembly  10  is configured to slideably engage the tissue distraction assembly in initial “closed” configuration (as shown in  FIG. 1 ), and thereafter be moved to a second “open” position (as shown in  FIGS. 2-3 ) to establish and maintain the operative corridor (or working channel). According to one broad aspect of the present invention, the tissue retraction assembly  10  includes a retractor body  12  and a plurality of retractor blades  14 ,  16 ,  18 . Retractor blades  14 ,  16 ,  18  may be provided in any size and shape suitable to establish and maintain an operative corridor to the surgical target site. For example, the retractor assembly  10  is shown in a “closed” position in  FIG. 1 , wherein the initial “closed” position has a generally circular cross-section. However, a plurality of retractor blades may be provided having an initial “closed” position having a generally oblong cross-section without departing from the scope of the present invention. 
     In the example shown, the retractor body portion  12  includes a housing member  20 , a rack member  22 , and a medial retraction member  24 . Broadly, the housing member  20  provides a scaffold to hold the various components together. The rack member  22  is dimensioned to provide a mechanism to expand the retractor blades  16 ,  18  in a first (e.g. caudal-cranial) direction. The medial retraction member  24  provides a mechanism to expand the retractor blade  14  in a second (e.g. medial) direction. 
       FIGS. 4-5  illustrate an example of an attachment shim  30  according to one embodiment of the present invention. Attachment shim  30  is dimensioned to provide temporary but secure and rigid attachment of the retractor blades  16 ,  18  to a bone screw inserted into the surgical target site. Attachment shim  30  includes an elongated body  32  and an engagement member  34  positioned distally on the shim  30 . By way of example, the engagement member  34  of the attachment shim  30  of this embodiment is in the form of a broken ring having an opening or gap  36  positioned therein. The gap  36  is dimensioned to allow the passage of at least a portion of a bone screw therethrough. By way of example only, the gap  36  may be large enough to allow passage of a shank portion of a bone screw, such that the engagement member may be side loaded onto the shank below the head of the bone screw (which may or may not be mated with a rod receiving tulip portion—not shown). The gap  36  may be provided with a dimension slightly smaller than a passable portion of a bone screw, such that the ring  35  is required to flex or deform slightly to allow passage of the portion of the bone screw, then snap back into place once the bone screw has passed through the gap. Such a dimension of the gap  36  creates a “snap-fit” relationship between the attachment shim  30  and the bone screw. 
     The attachment shim  30  further includes attachment features  38  that enable the shim to be slideably advanced along the retractor blades  16 ,  18 . Attachment features  38  are wing-like extensions that engage the tracks  40  on the retractor blade  16 ,  18  ( FIG. 10 ). Optionally, attachment shim  30  may further include a control element  42  comprising a deflectable portion that interacts with a plurality of recesses  44  provided on the retractor blades  16 ,  18  ( FIG. 10 ). This feature is provided to allow the shim to be controllably advanced to the surgical target site. 
       FIG. 6  illustrates the attachment shim  30  in engagement with an example of a bone screw  44 . The attachment member  32  fits over the head of the bone screw  44  to allow for secure interaction between the attachment member  32  and bone screw  44 . This interaction between the attachment member  34  and bone screw  44  is important because it provides a temporary but secure attachment for the retractor blades to help keep the operative corridor secure during the surgical procedure, enabling the retractor to be secured to the patient (via the screws) rather than the hospital bed (via an articulating arm). Thus, if the patient were to be moved slightly in any direction, the retractor would move with the patient, and the operative corridor would not change at all since the retractor is secured at the screws. 
     As shown by way of example in  FIGS. 4-6 , the gap  36  is positioned on one side of the ring  35  near the base of the shim  30 . However, other configurations are possible. For example,  FIG. 7  illustrates an example of an attachment shim  50  according to an alternative embodiment of the present invention. Attachment shim  50  is like attachment shim  30  except for the orientation of the ring portion  55 . Attachment shim  50  includes an elongated body  52  and an engagement member  54  positioned distally on the shim  50 . By way of example, the engagement member  54  of the attachment shim  50  of this embodiment is in the form of a broken ring  55  having an opening or gap  56  positioned therein. In the embodiment of  FIG. 7 , the gap  56  is positioned within the ring  55  opposite the base of the shim  50 , in a generally C-shaped configuration. The attachment shim  50  further includes attachment features  58  that enable the shim to be slideably advanced along the retractor blades  16 ,  18 . Attachment features  58  are wing-like extensions that engage the tracks  40  on the retractor blade  16 ,  18  ( FIG. 10 ). Optionally, attachment shim  50  may further include a control element  59  comprising a deflectable portion that interacts with a plurality of recesses  44  provided on the retractor blades  16 ,  18  ( FIG. 10 ). 
       FIG. 8  illustrates an example of an attachment shim  60  according to another alternative embodiment of the present invention. Attachment shim  60  is like attachment shims  30  except for the orientation of the ring portion  65 . Attachment shim  60  includes an elongated body  62  and an engagement member  64  positioned distally on the shim  60 . By way of example, the engagement member  64  of the attachment shim  60  of this embodiment is in the form of a broken ring  65  having an opening or gap  66  positioned therein. In the embodiment of  FIG. 8 , the ring  65  is oriented in an approximate 270° arc that is separated from the base of the shim  60  by an extension  67 . The attachment shim  60  further includes attachment features  68  that enable the shim to be slideably advanced along the retractor blades  16 ,  18 . Attachment features  68  are wing-like extensions that engage the tracks  40  on the retractor blade  16 ,  18  ( FIG. 10 ). Optionally, attachment shim  60  may further include a control element  69  comprising a deflectable portion that interacts with a plurality of recesses  44  provided on the retractor blades  16 ,  18  ( FIG. 10 ). 
       FIG. 9  illustrates an example of an attachment shim  70  according to yet another alternative embodiment of the present invention. Attachment shim  70  is like attachment shim  50  except for the orientation of the ring portion  75 . Attachment shim  70  includes an elongated body  72  and an engagement member  74  positioned distally on the shim  70 . By way of example, the engagement member  74  of the attachment shim  70  of this embodiment is in the form of a broken ring  75  having an opening or gap  76  positioned therein. In the embodiment of  FIG. 9 , the gap  76  is positioned within the ring  75  opposite the base of the shim  70 , in a generally C-shaped configuration that is separated from the base of the shim  70  by an extension  77 . The attachment shim  70  further includes attachment features  78  that enable the shim to be slideably advanced along the retractor blades  16 ,  18 . Attachment features  78  are wing-like extensions that engage the tracks  40  on the retractor blade  16 ,  18  ( FIG. 10 ). Optionally, attachment shim  70  may further include a control element  79  comprising a deflectable portion that interacts with a plurality of recesses  44  provided on the retractor blades  16 ,  18  ( FIG. 10 ). 
     According to another embodiment, the engagement member may comprise a locking bar with set screw (not shown). This configuration can be advantageous in situations where the implanted bone screw includes a tulip portion. The locking bar is received within the tulip, and a set screw is employed to lock the locking bar within the tulip. 
       FIG. 10  illustrates the step of coupling the attachment shim member  30  to the retractor blade  16 . The shim  30  is coupled to the blade  16  by engaging the attachment features  38  of the shim  30  to the tracks  40  on the blade  16 . The shim  30  is then advanced along the length of the blade  16  until it is at the distal end of the blade. The interaction between the control element  42  of the shim  30  and the recess  44  of the blade  16  prevent the shim  30  from migrating along the blade  16  during surgery. At this point, the shim  30  is ready to be engaged to the bone screw  44 , as described above. The shim  30  is removable from the blade  16  with the use of an appropriate removal tool (not shown) configured to disengage the control element  42  from the recess and slideably remove the shim  30  from the blade  16 . 
     To use the retractor  10  according to the method of the present invention, creation of the operative corridor may follow methodology of initial distraction and retraction commonly known in the art. For example, the first step is the placement of one or more K-wires through small incisions in the skin to the target surgical site. To assist with this, the surgeon may use navigated guidance system. At this point, an initial dilator is advanced over the K-wires toward the surgical target site. Next, a secondary dilator is advanced over the initial dilator to enlarge the distraction corridor. This secondary dilation step may be repeated with sequentially larger dilators until a desired size of the distraction corridor is reached. 
     Once the distraction corridor is sized to the desire of the surgeon, retractor blades  14 ,  16 ,  18  (attached to the retractor  10 ) are advanced over the tissue distraction assembly. Once the blades have been inserted, the retractor may be (though not necessarily) secured in position relative to the hospital bed using an articulating arm. The tissue distraction assembly may be removed because the retractor blades are now maintaining the operative corridor. The operative corridor may now be expanded in the first direction (e.g. caudal and cephalad) by causing the retractor blades  16 ,  18  to move. At this point, the operative corridor may be retracted in the second direction (e.g. medially) if desired. Once the desired operative corridor is established, bone screws are driven into the bone. In the example provided herein, a pair of bone screws are inserted—a cranial screw and a caudal screw (“cranial” and “caudal” being used to describe the relative positioning within the surgical target site). Preferably, the caudal-most retractor blade  16  will be positioned caudally of the caudal bone screw  44 , and the cranial-most retractor blade  18  will be positioned cranially of the cranial bone screw  44 , thereby ensuring that the surgeon&#39;s entire operative field is included within the established operative corridor (as shown in  FIG. 11 ). 
     As illustrated by  FIG. 12 , once the bone screws have been implanted successfully, attachment shims  30  may be employed to securely attach the caudal and cranial retractor blades to the respective bone screws. At this point, the retractor  10  is disconnected from the articulating arm, and the articulating arm may be removed from the surgical field. The retractor  10  is now securely attached to the bone screws implanted in the patient, and the operative corridor is established with respect to the patient. If the patient were to move in any way (e.g. slight bumping or rotating of the body), the established operative corridor would not change. The surgeon may now work on the disc space to perform the desired surgical technique. Rod receiving tulips may thereafter be connected to the bone screws (if not previously engaged) and a fixation rod fixed in position prior to removing the fixation shims (if desired) since the shims  30  are disengaged sideways from the bone screw  44  beneath the tulip. 
     Furthermore, if a fixation plate is desired, the plate may be attached to the bone screws (which may be provided in the form of bolts) without first removing the attachment shims  30 . This is possible because the gap  36  enables the shim  30  to be disengaged from the bone screw  44  from underneath the plate. 
     An additional advantage of securing the retractor blades to the bone screws is that the retractor may be used to distract the disc space if desired. This may be done before or after the retractor has been detached from the articulating arm without departing from the scope of the present invention. 
     According to one embodiment, the retraction system of the present invention may be used in scoliosis treatment. For example, bone screws may be inserted in a desired spinal location (e.g. T10-L2 vertebral levels) according to the above described procedure. Preferably, the retractor  10  is inserted at the apex of a scoliosis curve. The retractor blades may then be secured to the bone screws and used to compress the area. Fixation rods (not shown) may then be advanced along the operative corridor and secured into position. The fulcrum of the retractor may thereafter aid in the reduction process. 
     Although described with respect to specific examples of the different embodiments, any features of the systems and methods disclosed herein by way of example only may be applied to any of the embodiments without departing from the scope of the present invention. Furthermore, procedures described for example only involving specific structure (e.g. vertebral bone) may be applied to another structure (e.g. femur) without departing from the scope of the present invention. Further, while this invention has been described in terms of a best mode for achieving this invention&#39;s objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the invention.