Abstract:
To avoid traditional muscle dissection required in the placement of a screw for a pedicle screw fixation, a retractor is provided having a guide of an appropriate length to provide access from the skin surface to the dorsal aspect of the vertebra over the pedicle. The retractor has a handle to provide appropriate holding leverage and to maintain the guide so as to stabilize the guide against the lateral aspects of the facet with the paraspinous musculature. The retractor has a channel of an appropriate size to accommodate a variety of tools, including a drill bit or a tap. The channel also provides a pathway for a probe or feeler to inspect the placement of the screw.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    Priority is claimed from U.S. Provisional Patent Application No. 60/264,943 filed Jan. 29, 2001 entitled “Retractor And Method For Spinal Pedicle Screw Placement,” which is incorporated by reference in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention is directed to a novel retractor and a method using such retractor for placing spinal pedicle screws.  
         SUMMARY OF THE INVENTION  
         [0003]    Pedicle screw fixation has become an important part of stabilizing the spine to assist in arthrodesis. Traditionally a significant amount of muscle dissection has been required to prepare for screw placement. Recently, various approaches have been developed to minimize unnecessary disturbance of paraspinous structures while still accomplishing satisfactory fixation of the spine and the concomitant grafting necessary to achieve arthrodesis.  
           [0004]    The retractor of the present invention eases intermuscular placement of pedicle screws by providing a minimally invasive approach, and specifically lends itself to image guided applications. The characteristics of the retractor are described below with accompanying figures to illustrate the features.  
           [0005]    The retractor&#39;s guide channel is of an appropriate length to provide access from the skin surface to the dorsal aspect of the vertebra over the pedicle. The handle of the retractor is attached to provide appropriate holding leverage to maintain the position of the retractor and to stabilize its guide portion against the lateral aspect of the facet with the paraspinous musculature.  
           [0006]    An elongated insert may be placed within the guide channel of the retractor. The insert provides a working channel or hollow bore of an appropriate size to accommodate various instruments. For example, the working channel may receive an awl or perforator for the bony cortex, a drill for the pedicle if desired, or a tap for the pedicle and body of the vertebra. The working channel also provides a pathway for a probe or feeler to inspect the placement of the screw. Additionally, the insert may be configured to allow for guided instruments to confirm position of the screw placement. Moreover, attachment of a tracker to the retractor, the insert, or to instruments used through the insert allows coupling of the surgical procedure with an image guided system.  
           [0007]    The retractor is configured such that removal of the insert from the guide channel of the retractor provides a protected working channel for placement of the pedicle screw. The tip of the retractor may be textured and obliquely cut to help maintain position of the retractor against the lateral aspect of the facet. The guide channel is preferably open on one side to allow removal of the retractor after placement of the screw. The channel is of sufficient length to maintain muscle retraction necessary for screw placement.  
           [0008]    The shape of the distal end of the retractor aids easy placement of the retractor with minimal muscle separation, thus helping to displace soft tissues while placing the retractor and minimizing the tendency of the retractor to catch on soft tissue during entry. Preferably, there are projections and a textured distal surface to help maintain position against the bone and to avoid displacement while working through the retractor. The cutout, preferably semicircular or curved, at the distal end is of an appropriate size to allow use of a tap and subsequent placement of a pedicle screw. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a perspective view of one embodiment of the retractor of the present invention, and front and rear views of an embodiment of the insert for the retractor;  
         [0010]    [0010]FIG. 1 a is an enlarged view of the distal end of the retractor;  
         [0011]    [0011]FIG. 2 is a front elevation view of the retractor of FIG. 1, taken along arrow  15 , of one embodiment of the insert for the retractor adapted for use with a surgical tap, and a surgical tap;  
         [0012]    [0012]FIG. 3 is a vertical cross-sectional view of the retractor and an insert mounted within the retractor;  
         [0013]    [0013]FIG. 4 is a horizontal cross-sectional view of the retractor taken along line  4 - 4  of FIG. 3 and an insert mounted within the retractor;  
         [0014]    [0014]FIG. 5 is perspective view of the retractor of the present invention during use in a human spine wherein an insert is placed within the retractor and a tap is inserted through the insert;  
         [0015]    [0015]FIG. 6 is another perspective view of the retractor, with the insert removed and the retractor being used as a guide for emplacement of a pedicle screw;  
         [0016]    [0016]FIG. 7 is a perspective view of a further embodiment of the present invention having a recessed and curved distal tip at its guide portion; and  
         [0017]    [0017]FIG. 8 is a perspective view of the retractor of the present invention fitted with an image tracker on the retractor&#39;s handle, shown in simulated application with the human spine. 
     
    
     DETAILED DESCRIPTION  
       [0018]    With reference to FIG. 1, retractor  10  of the present invention is depicted in a perspective view. Retractor  10  preferably comprises two portions, a handle  12  and a guide portion  14 . Handle  12  is attached to the proximal end of guide portion  14 . Handle  12  may be of various configurations to allow access to the surgical site while providing a means of gripping the retractor  10  such that sufficient leverage may be applied to maintain the desired orientation of retractor  10  at the surgical site. In a preferred embodiment, handle  12  is oriented at an angle of between about 90 and about 135 degrees from the guide portion  14 . Handle  12  may include a slot  18  for interconnecting an attachment or a supplemental handle using handle screws  20 . Provision of slot  18  allows for various supplemental handle configurations to be used with retractor  10  to provide different holding leverages, as well as to provide interchangeable geometries that may be desired to overcome spatial constraints imposed by a specific patient&#39;s physical attributes. Alternately, an image tracker may be attached to slot  18  as discussed further below.  
         [0019]    Guide portion  14  is used for access to the interior of the surgical site. Typically, an incision is made in the patient&#39;s skin and muscle. Subsequently, the guide portion  14  is inserted through the exterior portion of the incision to create and maintain access to the interior targeted body part, such as the patient&#39;s spine. As described below, specific features of guide portion  14  provide for improved access to the spine.  
         [0020]    Guide portion  14  is preferably half-cylinder or U-shaped. More particularly, the rear surface  16  of guide portion  14  is preferably convex when viewing retractor  10  from the rear side of retractor  10 . The U-shaped front of guide portion  14  includes a hollow region or guide channel  22 . Guide channel  22  extends from the distal end  23  of guide portion  14  up to and including the upper-most or proximal end of guide portion  14 . In this manner, guide channel  22  may be used to guide surgical tools and implants from the exterior of the surgical site down to the interior-most portion of the surgical site by inserting surgical tools down through the guide channel.  
         [0021]    The distal end  23  of guide portion  14  includes a rounded tip  24 . In addition, the distal end  23  of guide portion  14  is shown as being truncated obliquely along the lower medial face  25  to more closely approximate the lateral aspect of the facet of the paraspinous musculature of the patient, and provide for improved medial positioning of the guide portion  14  for placement of a drill and/or tap into the bony structure of the patient. The rounded tip  24  may further include a cutout or an opening  26  at its end. In a preferred embodiment shown in FIG. 1 a,  opening  26  is semicircular. One or more projections  27  may be provided around the end-most portion of opening  26  to aid in maintaining the position of the retractor  10  during use by stabilizing retractor  10  against the bony surface of the vertebrae. In addition, texturing such as ridges and grooves or machined points may be placed on the medial surface  29  of the lower medial face  25  of guide portion  14  to further stabilize retractor  10  when in use.  
         [0022]    Referring now also to FIGS. 2 and 4, to aid in facilitating use of tools at the distal end of guide portion  14 , an insert  30  may be placed within guide channel  22  to assist the surgeon in guiding and aligning tools along the desired orientation. In a preferred embodiment, insert  30  is generally triangular-shaped and has an aperture or hollow bore  32 . Hollow bore  32  allows various tools to be guided down to the targeted area within the surgical site, such as tap  33 .  
         [0023]    Triangular-shaped insert  30  includes base edges  34 . Base edges  34  of insert  30  cooperate with grooves  36  located within guide channel  22  to stabilize insert  30  within guide channel  22 . Base edges  34  are simply side projections which mate with the grooves  36 . Alternately, in lieu of base edges  34 , insert  30  may include one or more discontinuous side projections (not shown). Similar to the base edges  34  of insert  30 , these side projections could cooperate with a corresponding number of discontinuous grooves (not shown) located within guide channel  22  to aid in stabilizing insert  30  within guide channel  22 .  
         [0024]    Insert  30  includes a distal tip  38 , a longitudinal shaft  40 , a proximal end  42 , and an optional handle  43 . The distal tip  38  of insert  30  may be rounded, defining a perimeter edge  44 . Perimeter edge  44  cooperates with the lower distal portion of groove  36  within guide channel  22  to further stabilize the distal tip  38  of insert  30 , and to further prevent unnecessary entanglement with the patient&#39;s bodily tissues when inserting the insert  30  into the guide channel  22 .  
         [0025]    Referring now to FIGS. 3 and 4, the retractor  10  of the present invention is shown with insert  30  received in the retractor  10 . As described above, the base edges  34  of the triangular-shaped insert  30  mate with corresponding grooves  36  in the guide channel  22  of retractor  10 . The distal tip  38  of insert  30  mates with the distal end  23  and rounded tip  24  of retractor guide portion  14  such that insert  30  does not extend beyond distal end  23 . FIGS.  3  and  4  also depict the hollow bore  32  through which a drill or tap  33  is inserted, thereby guiding the tap  33  to its targeted location.  
         [0026]    With reference to FIG. 5, a tap  33  is shown inserted though the bore  32  of the insert  30 , and the insert is placed in the guide channel  22  of retractor  10 . Tap  33  is used to create an appropriate bore in the bone “B” for receipt of a medical device, such as a pedicle screw “S”. Tap  33  may be sized in diameter to restrict passage of the tap  33  beyond a specified length through insert  30 . Specifically, tap  33  may contain a larger diameter section  50  which prevents passage of the tap  33  beyond the proximal opening  42  of insert  30 .  
         [0027]    With reference now to FIG. 6, once the tapping operation is complete, tap  33  and insert  30  may be removed from guide channel  22 . Guide channel  22  remains in place and is then used to guide a medical device, in this case, a pedicle screw S. The retractor  10  thus provides for proper alignment of the screw S. Further, the opening  26  in the distal end  23  of guide channel  22  is sized and shaped to accommodate the shank of screw S so that screw S may be properly aligned with the bore created by tap  33 . Tool T, such as a medical screwdriver, is then used to finish installation of screw S by screwing screw S into bone B.  
         [0028]    Referring now to FIG. 7, in a further embodiment, a retractor  10 ′ without a rounded tip is illustrated. As shown, the retractor has a recessed and curved distal tip  54 . This embodiment offers the advantage of offering a U-shaped guide channel  22 ; however, a rounded tip is not present to interfere with visibility of the surgical site. The U-shaped guide channel  22  extends from the upper end of guide portion  14  down to the distal end  23  of the guide portion  14 . As with the previous embodiment, distal end  23  of the guide portion  14  may be obliquely cut, with optional projections (not shown) formed at the end-most portion of the distal end  23 . Additional texturing may also be provided along the medial surface of guide portion  14  to assist with stabilizing retractor  10 ′ against the neighboring area of the surgical site.  
         [0029]    Due to the frequently limited amount of exposure of the spine or interior surgical area, the spinal implant procedures lend themselves to use of image guidance for surgery. Examples of such image guidance systems include the BrainLAB System and the Stealth System. As understood by those skilled in the art, these image guidance systems utilize a computer system with a monitor and two cameras that emit infrared signals, thereby determining the patient&#39;s position in the operating room as well as the position of the surgical instruments in relation to the patient&#39;s spine. The image guidance systems use data from standard CT or MRI scans to build a three dimensional image of the patient&#39;s spine. This model is then electronically matched to the patient&#39;s anatomy during surgery, allowing the surgeon, in effect, to see through tissue in order to accurately determine the placement of instruments or devices. During the operation, sensitive structures such as blood vessels and nerves, which the surgeon wants to avoid on the way to the anatomical target, can be visualized. In addition, during the operation the surgeon can follow the movements of his or her instruments on the computer screen in real time.  
         [0030]    Referring now to FIG. 8, retractor  10  is shown in one possible relationship with the human spine. The retractor  10  can be positioned at a desired location in relation to spinal processes and maintained in position with the projections  27  and texturing  28  which assist in anchoring the retractor on the patient. The insert  30  may then be used as a guide for subsequent tapping, or like operations. The retractor  10  with insert  30  provides a working channel for tracked instruments. Attachment of a tracker  60  directly to insert  30 , or alternately to the retractor handle  12  as shown in FIG. 8, allows a surgeon to guide the guide channel  22  of retractor  10 , or hollow bore  32  of insert  30  directly, and thus avoid tracking the instruments themselves, such as a drill or tap  33 .  
         [0031]    All components of the invention described herein are manufactured of a material appropriate for surgical use. For example, the components can be made of stainless steel. However, it is to be understood that other types of materials may also be used, such as titanium or ceramics.  
         [0032]    While various embodiments of the present invention have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention.