Abstract:
A device, system and method for orthopedic spine surgery using a novel screw-based retractor, disclosed herein, that allows for access to the spine through a minimally or less invasive approach. The retractor device is designed to be coupled to a pedicle screw and then to have opposed arms of the retractor spread apart to open the wound proximally. The retractor is removed by pulling it out of the wound whereby the retractor is deformed to pass over the pedicle screw head. The retractor is intended to be made of a stiff plastic material, sterile packaged and disposable after one use. A system and method for using the retractor and performing a minimally invasive spine surgical procedure are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is a divisional of co-pending U.S. patent application Ser. No. 11/528,223, filed Sep. 26, 2006, which claims priority to U.S. Provisional Application Ser. No. 60/720,670, filed on Sep. 26, 2005, the contents of each of these prior applications are incorporated herein by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to orthopaedic spine surgery and in particular to a minimally invasive retractor and methods for use in a minimally invasive surgical procedure. 
         [0004]    2. Background of the Technology 
         [0005]    There has been considerable development of retractors and retractor systems that are adapted for use in less invasive procedures. Many of the recent developments are based on traditional types of surgical retractors for open procedures, predominantly table-mounted devices of various designs. These devices tend to be cumbersome and are not well adapted for use in small incisions. Standard hand-held surgical retractors are well known in the prior art and can be modified to fit the contours of these small incisions, but they require manual manipulation to maintain a desired placement, thereby occupying one hand of the physician or requiring another person to assist the physician during the procedure. Typical retractors are also positioned into the soft tissue and are levered back to hold the wound open, frequently requiring re-positioning if they dislodge, obstruct the physician&#39;s view, or interfere with access to the surgical site. 
         [0006]    In recent years, minimally invasive surgical approaches have been applied to orthopaedic surgery and more recently to spine surgery, such as instrumented fusions involving one or more vertebral bodies. Unlike minimally invasive procedures such as arthroscopic knee surgery or gallbladder surgery where the affected area is contained within a small region of the body, spinal fusion surgery typically encompasses a considerably larger region of the patient&#39;s body. In addition, arthroscopic surgery and laparoscopic surgery permit the introduction of fluid (i.e. liquid or gas) for distending tissue and creating working space for the surgeon. Surgery on the spine does not involve a capsule or space that can be so distended, instead involving multiple layers of soft tissue, bone, ligaments, and nerves. For these reasons, the idea of performing a minimally invasive procedure on the spine has only recently been approached. 
         [0007]    By way of example, in a typical spine fusion at least two vertebral bodies are rigidly connected using screws implanted into the respective vertebral bodies with a solid metal rod spanning the distance between the screws. This procedure is not generally conducive to a minimally invasive approach. The insertion of pedicle or facet screws is relatively straightforward and can be accomplished through a minimal incision. The difficulty arises upon the introduction of a length of rod into a very small incision with extremely limited access and visibility. A single level fusion may require a 30-40 mm rod to be introduced into a 1 cm incision and a multilevel fusion may require a rod several inches long to fit into a 1 cm incision. For this reason, it is important that the minimal incision be maintained in an open and accessible condition (i.e. as wide as practicable) for introduction of the rod. 
         [0008]    Minimally invasive surgery offers significant advantages over conventional open surgery. First, the skin incision and subsequent scar are significantly smaller. By using more than one small incision rather than one large incision, the need for extensive tissue and muscle retraction may be greatly reduced. This leads to significantly reduced post-operative pain, a shorter hospital stay, and a faster overall recovery. 
         [0009]    Most spine implant procedures are open procedures, and while many manufacturers advertise a minimally invasive method, the procedure is typically not recommended for fusions and focuses on more common and accepted minimally invasive spine procedures such as kyphoplasty, vertebroplasty, and discectomy. 
         [0010]    Medtronic Sofamor Danek&#39;s SEXTANT® is a true minimally invasive device used for screw and rod insertion. Its shortcomings lie with how complicated the system is to use and the requirement for an additional incision for rod introduction. This system also requires that the guidance devices be rigidly fixed to the pedicle screw head in order to maintain instrument alignment and to prevent cross-threading of the setscrew. For these reasons, the surgeon cannot access the surrounding anatomy for complete preparation of the field. Nor does SEXTANT® allow for any variation in the procedure, if need be. 
         [0011]    Depuy Spine&#39;s VIPER™ system is another minimally invasive implant and technique recommended for one or two level spine fusions. This system is less complicated than the SEXTANT® only requiring two incisions for a unilateral, one-level fusion, but it is limited in the same way as the SEXTANT® because it also requires the instrumentation to be rigidly fixed to the pedicle screw. 
         [0012]    Spinal Concept&#39;s PATHFINDER® and NuVasive&#39;s SPHERX® spinal system (as disclosed in U.S. Pat. No. 6,802,844), are marketed as “minimally disruptive” spine fusion implants and procedures. While they have advantages over a general “open” procedure, they do not provide all of the advantages of a truly minimally invasive approach. Their characterization as “minimally open” procedures is a result of the inherent difficulty of introducing a rod in a minimally invasive spinal procedure. In order to introduce a rod long enough to accomplish a single level fusion, these systems describe an incision long enough to accept such a rod, thereby undermining the advantages of a minimally invasive approach. 
         [0013]    The problem of rod introduction warrants further discussion as it is the central problem in minimally invasive spinal fusions. The systems currently on the market address this issue by adding another incision, using a larger incision, or avoiding the issue completely for fusions greater than one level. 
         [0014]    In order to be truly minimally invasive, a spine fusion procedure should have a minimum number of small incisions and not require significant tissue and/or muscle retraction. Furthermore, an improved approach should encompass as many variations and applications as possible thereby allowing the surgeon to adjust the procedure to accommodate the anatomy and surgical needs of the patient as presented. For instance, spinal fusions should not be limited to just one or two levels. 
         [0015]    Therefore, a continuing need exists for an improved device, an improved system, and an improved method for performing minimally invasive spine surgery. 
       SUMMARY 
       [0016]    The present disclosure relates to a device, a system, and a method for a screw-based retractor used in performing minimally invasive spine surgery. The retractor is removably attached to a pedicle bone screw that is used to guide the retractor into place and act as a point of fixation with respect to the patient. Multiple retractors may be used in conjunction with a single screw to allow retraction in multiple directions and multiple retractors may be used with multiple screws, respectively, during a single spine procedure. The retractor may be manufactured for a single use or can be sterilized and reused. Finally, the retractor may also act as a guide that will aid in the insertion of instruments and implants. 
         [0017]    In its nominal position, the retractor will form a generally cylindrical tube with at least one retracting blade. Instrument holes are located perpendicular to the long axis of each retracting blade whereby a standard surgical instrument, such as a Gelpi Retractor, can be used to separate the blades to retract the skin and soft tissue and maintain the field of view. Yet, where the retractor is connected to the pedicle screw the retractor maintains a circular cross-section. Since the retractor is not permanently fixed but is removably attached to the pedicle screw, it is free to have polyaxial rotation allowing the surgeon greater wound access and freedom to operate. Furthermore, polyaxial rotation allows the retractor to expand medial-laterally as well as cephalad-caudally and any combination thereof. This freedom of movement proximally and non-rigid attachment distally decreases the need for retractor re-positioning during a procedure. Proximal stabilization of the retractor is possible when it is used in conjunction with a table-mounted retractor. 
         [0018]    The minimally invasive retractor can be designed to flex proximal or distal to the pedicle screw head. In one embodiment, the retractor has a “living hinge” incorporated into the retractor&#39;s blade design. More than one living hinge can be incorporated to aid in bending along any portion of the blade&#39;s length. 
         [0019]    The cross-section of the blade is a circular ring sector to provide additional stiffness. The geometry will force the blade to bend at the living hinge and still be able to retract the soft tissue pressed against it. 
         [0020]    Minimally invasive retractors having a living hinge or a true hinge located may include at least one window that is aligned with the pedicle screw saddle and allows the insertion of instruments into the surgical site. 
         [0021]    The distal tip of the minimally invasive retractor is bullet shaped to aid in insertion through the soft tissue to where it will seat against the pedicle. The distal tip will also have one or more relief features cut into it to aid in removing the retractor. Upon completion of the procedure, the retractor can be pulled straight out of the wound and the distal tip will expand or separate to pass over the screw and rod assembly. Advantageously, by positioning the distal tip of the retractor around the head of the screw adjacent the bone, the retractor retracts soft tissue from a point below the head of the screw, creating excellent visibility of the screw and surrounding tissue. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Embodiments of the presently disclosed minimally invasive retractor are described herein with reference to the accompanying drawings, wherein: 
           [0023]      FIG. 1  is a perspective view of a minimally invasive retractor according to a first embodiment of the present disclosure; 
           [0024]      FIG. 2  is a bottom view of the minimally invasive retractor of  FIG. 1 ; 
           [0025]      FIG. 3  is a perspective view of a minimally invasive retractor according to a second embodiment of the present disclosure; 
           [0026]      FIG. 4  is a bottom view of the minimally invasive retractor of  FIG. 2 ; 
           [0027]      FIG. 5  is a side view of a minimally invasive retractor and screw assembly including the minimally invasive retractor of  FIG. 1 ; 
           [0028]      FIG. 6  is a perspective view of the minimally invasive retractor and screw assembly of  FIG. 5 ; 
           [0029]      FIG. 7  is an enlarged side view of the detailed area “A” of  FIG. 5 ; 
           [0030]      FIG. 8  is a perspective view of a minimally invasive retractor and screw assembly according to a third embodiment of the present disclosure; 
           [0031]      FIG. 9  is a top view of the minimally invasive retractor and screw assembly of  FIG. 8  showing a rod extending through an expanded passage of the minimally invasive retractor; 
           [0032]      FIG. 10  is a perspective view of a fourth embodiment of the presently disclosed minimally invasive retractor; 
           [0033]      FIG. 11  is a perspective view of a fifth embodiment of the presently disclosed minimally invasive retractor; 
           [0034]      FIG. 12  is a perspective view of a sixth embodiment of the presently disclosed minimally invasive retractor; 
           [0035]      FIG. 13  is a top plan view of bone biopsy needle; 
           [0036]      FIG. 14A  is a perspective view of a scalpel; 
           [0037]      FIG. 14B  is a side view of a dilator and retractor; 
           [0038]      FIG. 15A  is a side view of a cannulated bone screw tap; 
           [0039]      FIG. 15B  is a front elevational view of the bone screw tap of  FIG. 15 ; 
           [0040]      FIG. 15C  is an enlarged side view of the detailed area “A” of  FIG. 15 ; 
           [0041]      FIG. 16  is a perspective view of a screw inserter having an anti-rotation sleeve; 
           [0042]      FIG. 17  is an exploded side view of the screw inserter of  FIG. 16  shown with a spine screw; 
           [0043]      FIG. 18  is a side view of a screw insertion assembly including the screw inserter of  FIG. 16 , a minimally invasive retractor with a spine screw; 
           [0044]      FIG. 19  is a perspective view of a retraction assembly having a minimally invasive retractor and a Gelpi retractor; 
           [0045]      FIG. 20A  is a perspective view of a cannulated screw showing a rod positioned in a rod receiving passage; 
           [0046]      FIG. 20B  is top view of the screw of  FIG. 20 ; 
           [0047]      FIG. 20C  is a perspective view of the screw of  FIG. 20  illustrating an optional guidewire inserted therethrough; 
           [0048]      FIG. 21  is a perspective view of a retractor extractor instrument according to an embodiment of the present disclosure; 
           [0049]      FIG. 22  is an exploded perspective view of the retractor extractor instrument of  FIG. 18 ; 
           [0050]      FIG. 23  is a perspective view of the retractor extractor instrument of  FIG. 21  coupled to a minimally invasive retractor which is associated with a spine screw; 
           [0051]      FIG. 24  is a front cross-sectional view of a vertebral body with a pair of minimally invasive retractors attached using screws with the blades in their initial position and rods positioned in the passages of the minimally invasive retractors; 
           [0052]      FIG. 25  is a front cross-sectional view of the vertebral body with a pair of minimally invasive retractors attached using screws after retracting tissue with rods positioned in the passages of the minimally invasive retractors; 
           [0053]      FIG. 26  is a front cross-sectional view of a body illustrating insertion of the bone biopsy needle of  FIG. 13  into a vertebral body; 
           [0054]      FIG. 27  is a front cross-sectional view of the body of  FIG. 26  illustrating insertion of a guide wire through the bone biopsy needle; 
           [0055]      FIG. 28  is a front cross-sectional view of the body of  FIG. 27  illustrating tissue separation using the scalpel of  FIG. 14 ; 
           [0056]      FIG. 29  is a front cross-sectional view of the body of  FIG. 27  illustrating insertion of the screw insertion assembly of  FIG. 18 ; and 
           [0057]      FIG. 30  is a front cross-sectional view of the body of  FIG. 29  with the vertebral body shown in a cross-sectional view and illustrating attachment of the screw of the screw insertion assembly to the vertebral body. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0058]    Embodiments of the presently disclosed minimally invasive retraction device will now be described in detail with reference to the drawings wherein like reference numerals identify similar or identical elements. In the drawings and in the description which follows, the term “proximal”, as is traditional, will refer to the end of the minimally invasive retraction device which is closest to the operator while the term “distal” will refer to the end of the device which is furthest from the operator. 
         [0059]    Referring intially to  FIGS. 1 and 2 , a first embodiment of the presently disclosed minimally invasive retractor or retractor is illustrated and generally designated as  10 . Retractor  10  includes an open proximal end  12  and a distal end  14 . In addition, retractor  10  includes a pair of retractor blades  8  having a plurality of instrument holes  6  disposed on each of retractor blades  8 . Instrument holes  6  are configured and dimensioned to cooperate with different surgical instruments as will be discussed in detail hereinafter. A distal region  9  of retractor  10  includes an opening  7  ( FIG. 2 ), at least one slot or window  2 , and a pair of arms  13  extending from distal end  14  to a flexible region or living hinge  4 . Window  2  is sized and configured to receive instruments therethrough. Each retractor blade  8  is attached to living hinge  4  to define a substantially continuous elongate member. A pair of recesses  4   a  are formed between retractor blade  8  and arm  13  to define living hinge  4 . 
         [0060]    Distal end  14  further includes at least one relief region R ( FIG. 2 ) defined by at least one slit  16  extending proximally from opening  7  ( FIG. 2 ). Alternatively, slit  16  may originate at window  2  and extend distally towards opening  7 . It is contemplated that other arrangements of relief structures may be used to define relief region R and these may exist between opening  7  and window  2 . Each slit  16  is a weakened portion of distal end  14 . It may be a score in the material, a perforated region in the material, or another structural arrangement allowing relief region R to be radially displaced away from the centerline of retractor  10  in response to applied forces as will be discussed in detail hereinafter. In addition, distal end  14  has a generally convex outer surface that facilitates insertion of retractor  10  through layers of body tissue. 
         [0061]    Retractor blades  8  and arms  13  are generally arcuate structures that cooperate to define a substantially circular configuration for retractor  10 . Each retractor blade  8  and each arm  13  have an arcuate configuration that is less than about 180° and are radially spaced apart to define a continuous slot  17  along a substantial portion of retractor  10 . In addition, each retractor blade  8  and its corresponding arm  13  define a passage  18  that also extends substantially the entire length of retractor  10 . Passage  18  is expandable, as will be discussed in detail hereinafter, for receiving a rod  3  ( FIG. 9 ) therein. Retractor blades  8  and arms  13  define a substantially circular ring shape, thereby providing sufficient stiffness (i.e. rigidity) such that retractor blades  8  and arms  13  resist bending from the counter forces of the retracted tissues. 
         [0062]    Opening  7  is located at distal end  14  of retractor  10  and is sized for receiving the shank of a threaded screw  40  ( FIG. 20 ) therethrough, but inhibiting passage of a head  42  of screw  40  so as to support screw  40  at distal end  14  of retractor  10 . The interior surface of distal end  14  has a generally concave spherical geometry that is adapted to mate with head  42  of pedicle screw  40  that is best seen in  FIG. 11 . 
         [0063]    Retractor  10  is formed from a suitable biocompatible material having the desired physical properties. That is, retractor  10  is formed of a biocompatible, sterilizable material in a suitable configuration and thickness so as to be sufficiently rigid to be held on the screw when desired during insertion and a surgical procedure and to provide retraction of tissue, and yet is sufficiently bendable to be spread apart to provide retraction and to be forcibly removed from the screw as necessary and appropriate. It is contemplated that retractor  10  may be formed from polymers such as polypropylene, polyethylene, or polycarbonate. Additionally, retractor  10  may be formed from silicone, polyetheretherketone (“PEEK”), or another suitable material. Retractor blade  8  is bendable away from the centerline of retractor  10  in response to applied forces, wherein retractor blade  8  bends at living hinge  4 . Bending retractor blade  8  away from the centerline (i.e. radially outwards) creates a larger opening through retractor  10  and also acts to retract the surrounding tissue at the selected surgical site. Installation and use of retractor  10  in surgical procedures will be discussed in detail hereinafter. 
         [0064]    Referring now to  FIGS. 3 and 4 , a second embodiment of the present disclosure is illustrated as retractor  30  having an open proximal end  32  and a distal end  34 . Retractor  30  includes a pair of retractor blades  36 . Similar to retractor  10 , distal end  34  has an interior surface with a generally concave spherical geometry that is adapted to mate with the head of a pedicle screw and has a generally convex outer surface that facilitates insertion of retractor  30  through layers of body tissue. Additionally, retractor  30  includes an opening  7  ( FIG. 4 ) that is substantially identical to opening  7  of retractor  10 . 
         [0065]    As in the previous embodiment, blades  36  have an arcuate configuration that is less than about 180° and are radially spaced apart to define a continuous slot  37  along a substantial portion of retractor  30 . Additionally, retractor blades  36  define a passage  35  through retractor  30 . In this embodiment, retractor blades  36  are also flexible, but bend radially outwards from a centerline of retractor  30  near relief regions R ( FIG. 4 ). As in the previous embodiment, relief regions R are defined by slits  16  (shown as a pair of slits in  FIG. 4 ) as previously discussed in connection with retractor  10 . In this embodiment, retraction of tissue with retractor blades  36  utilizes manual manipulation of retractor blades  36  by the physician rather than using a surgical instrument in cooperation with instrument holes  6  of retractor  10  ( FIG. 1 ). Removal of retractor  30  from the surgical site is accomplished by pulling retractor  30  proximally (i.e. away from the pedicle screw) and spreading or breaking distal end  34  along slits  16  such that relief regions R and retractor blades  36  separate from each other. As such, the physician can readily remove the two parts from the surgical site. Similar to passage  18  ( FIG. 1 ), passage  36  is selectively expandable and contractible for receiving rod  3  therein. 
         [0066]    In  FIGS. 5-7 , retractor  10  is illustrated in an assembled condition with a pedicle screw  40 . Pedicle screw  40  extends through opening  7  ( FIG. 7 ) such that threads of pedicle screw  40  extend beyond distal end  14  ( FIG. 7 ) for insertion into a target site in a bone (e.g. a vertebral body). As shown in the figures, when pedicle screw  40  is inserted in retractor  10 , the head of pedicle screw  42  ( FIG. 20 ) mates with the interior geometry of distal end  14 . As shown, rod receiving passage  44  of pedicle screw  40  ( FIG. 20 ) aligns with opening  17  between retractor blades  8  facilitating the insertion of rod  3  ( FIG. 20 ) into screw head  42 . In addition, pedicle screw  40  is pivotable about the longitudinal axis of retractor  10  allowing retractor  10  to be attached in a first angular orientation with respect to the vertebral body, but pivotable about pedicle screw  40  increasing the amount of tissue that may be retracted using retractor  10 . 
         [0067]    Another embodiment of the presently disclosed retractor is illustrated in  FIGS. 8 and 9  and shown generally as retractor  50 . Retractor  50  is similar to retractor  10 , but includes a plurality of living hinges  4  along with their corresponding recesses  4   a . Retractor  50  is about 6 inches long and is readily adjusted to a desired length by removing excess material using scissors or a knife. In addition, retractor  50  has an inner diameter that is approximately 16 mm and retractor blades are approximately 1 mm thick. Each living hinge  4  is about 1-2 mm in height and each blade section  8   a  is about 5 mm. Instrument holes  6  are on 1 cm centerlines. Slot  17  is typically at least 5.5 mm, but will vary according to the size of the rod that will be inserted into the patient. In particular, each retractor blade  8 ′ includes a plurality of blade sections  8   a . Each blade section  8   a  is connected to an adjacent blade section  8   a  by a living hinge  4 . Thus, the plurality of blade sections  8   a  and living hinges  4  define retractor blade  8 ′. As in the previous embodiment ( FIG. 1 ), each blade section  8 ′ is substantially parallel to arm  13  to define slot  17  between retractor blades  8 ′. 
         [0068]    When retractor blades  8 ′ are urged radially outward from their initial or rest position towards their retracted position, the size of passage  18  increases. This increase in the size and area of passage  18  improves access to the surgical target site (i.e. near where the retractor is inserted into tissue), thereby increasing visibility of the target site, access for instruments, and access for surgical implants. As shown in  FIG. 9 , rod  3  is positioned in passage  18  after the surrounding tissue has been retracted using retractor  50 . These advantages will be discussed in detail hereinafter. Additionally, the plurality of living hinges  4  greatly increases the adaptability of retractor  50  in comparision to retractor  10 . While retractor blades  8  of retractor  10  ( FIG. 1 ) generally bend at its single living hinge  4 , the additional living hinges  4  present along retractor blades  8 ′ of retractor  50  permit bending with increased flexibility at a number of positions along the length of each retractor blade  8 ′. Thus, retractor blades  8 ′ will bend at the living hinge  4  that corresponds to the plane defined by the surface of the patient&#39;s body tissue. By using this construction, retractor  50  is usable in patient&#39;s having different tissue thicknesses between the vertebral body and the surface of their skin. In addition, since each retractor blade  8 ′ has a plurality of living hinges  4  and blade sections  8   a , it is not required for each retractor blade  8 ′ to bend at the same point along the length of retractor  50 , thereby accommodating variances in the depth that retractor  50  is inserted. For example, one retractor blade  8 ′ may bend at its fourth living hinge  4 , while the other retractor blade  8 ′ may bend at its sixth living hinge  4 , thereby accommodating variances in tissue thickness and orientation of retractor  50 . 
         [0069]    In  FIG. 10 , a further embodiment of the presently disclosed retractor is illustrated and generally referenced as retractor  60 . Retractor  60  is similar to retractor  10  ( FIG. 1 ) with the differences discussed in detail hereinafter. As in the previous embodiment, retractor  60  includes a distal end  14   a  with a distal region  9   a . Distal region  9   a  includes arms  13   a  that extend circumferentially and do not form a portion of slot  17  as in the previous embodiment. A living hinge  4 ′ is defined between window  2  and slot  17 . In addition, distal region  9   a  includes slits  16   a  that are full cuts through the material of distal region  9   a  defining a plurality of relief regions R′. In this embodiment, relief regions R′ are more flexible such that retractor  60  may be separated from a pedicle screw (not shown) and subsequently affixed to the pedicle screw. This configuration permits a surgeon to remove and subcutaneously relocate retractor  60  to gain access to the vertebral disc space. As in the previous embodiments, positioning window  2  distally of slot  17  allows retractor  60  to expand in a medial-lateral orientation such that rod  3  ( FIG. 8 ) may be inserted through passage  18  into the target site. 
         [0070]      FIG. 11  illustrates an alternate embodiment of the presently disclosed retractor that is generally referenced as  70 . Retractor  70  is substantially similar to the embodiment previously identified as retractor  60  ( FIG. 10 ). However, in this embodiment distal region  9   b  only includes one arm  13   a , thereby increasing the lateral opening near distal end  14   b  and defining window  2   a  that is larger than previously disclosed window  2  ( FIG. 10 ). This embodiment provides increased access to the target site, thereby allowing larger implants or instruments to be positioned in the target site. 
         [0071]    Another embodiment of the presently disclosed retractor is illustrated in  FIG. 12  and referenced as retractor  80 . Retractor  80  includes the same or substantially similar components as described hereinabove with respect to retractor  10  ( FIG. 1 ). In this embodiment, retractor  80  includes only one retractor blade  8 . This configuration allows greater variability in creating the retracted space as well as increasing access to the target site for using larger instruments or inserting larger devices than possible with retractor  10  ( FIG. 1 ). 
         [0072]    It is contemplated that any of the previously disclosed retractors may be formed of a bendable resilient material such that when external spreading forces (i.e. from a Gelpi retractor or the physician&#39;s hands) are removed, the retractor blades will return towards their initial position (e.g., substantially parallel to the centerline). It is also contemplated that any of the previously disclosed retractors may be formed of a bendable non-resilient material such that when the external spreading forces are removed, the retractor blades resist returning to their initial position and remain in the retracted position. 
         [0073]    Other components of the presently disclosed system will now be discussed with reference to  FIGS. 13-23 . In  FIG. 13 , a bone biopsy needle (e.g. a Jamshidi needle)  100  is illustrated. Needle  100  includes a handle  102  disposed at a proximal end of needle  100 , an elongate tubular member  104  extending distally from handle  102 , and a stylet  106 . Stylet  106  has a sharpened distal tip  108  that is adapted for penetrating tissue, including bone. In addition, tubular member  104  has a lumen extending from its proximal end to its distal end for receiving stylet  106  therethrough. Stylet  106  is releasably attached to handle  102  such that it may removed once the target site has been pierced by distal tip  108 . After stylet  106  is removed, a guidewire  1  ( FIG. 27 ) may be inserted through tubular member  104  and secured or attached at the target site using known techniques. 
         [0074]    Referring now to  FIG. 14 , a cannulated scalpel  120  is illustrated. Scalpel  120  includes a housing  125  having a blade  126  disposed therein. Blade  126  has a sharpened distal end  124  for separating tissue. In addition, distal end  124  includes an opening  124   a  that cooperates with an opening  128  located at proximal end  122  and defines a channel through scalpel  120  for slidably receiving guidewire  1  ( FIG. 14A ) therethrough. 
         [0075]      FIG. 14A  shows a dilator  300  configured and dimensioned to be received through a retractor  10  with distal atraumatic blunt tip  302  protruding through opening  7  in retractor  10 . Dilator  300  includes a longitudinal passage therethrough having a distal opening  304  for receiving guidewire  1  therethrough. Alternatively, it is contemplated that rather than a retractor, dilator  300  may be used together with a cannula (not shown). Although less desirable, a series of dilators and cannulas can be used. 
         [0076]    In  FIGS. 15-15B , a cannulated bone tap  140  is shown. Bone tap  140  includes an elongated body  142  having a proximal end  146  and a distal end  144 . Distal end  144  includes a helical thread  145  for forming threads in a hole that is formed in a bony structure (i.e. a vertebral body). Proximal end  146  includes a tool engagement region  147  that is adapted for cooperating with a driving or rotating tool  178  ( FIG. 29 ) and forming the threads in the bony structure. Driving and rotating tools are well known in the art. In addition, proximal end  146  and distal end  144  cooperate to define a channel  148  extending through bone tap  140  such that bone tap  140  may be slid along guidewire  1 . Bone tap  140  is available in a number of different sizes in a range of about 5.5 mm to about 7.5 mm. Alternatively, other bone taps may be used that match the size of the screw threads of the screw that will be implanted into bone. 
         [0077]    A screw inserter  160  is illustrated in  FIGS. 16 and 17 . Screw inserter  160  includes an anti-rotation sleeve  150  and a housing  170 . Housing  170  includes a body  172  having a pair of handles  174  extending therefrom. Handles  174  facilitate positioning and/or rotating screw inserter  160 . A tubular member  176  extends distally from body  172  and includes a plurality of holes  175 . A shaft  166  ( FIG. 17 ) is disposed through a lumen of tubular member  176  and is rotatable therein. A tool engaging surface  163  is disposed at a proximal end  162  of shaft  166 . At a distal end  164  of shaft  166 , a screw engaging structure  165  is disposed that is adapted and configured to releasably engage a head  42  of pedicle screw  40 . In particular, screw inserter includes a cross-member  164  and threads  173 . During assembly of screw inserter  160  and pedicle screw  40  ( FIG. 20 ), screw engaging structure  165  is inserted into head  42  such that cross-member  163  occupies rod receiving recess  44  and threads  173  engage threaded portion  45  of pedicle screw  40 . This arrangement releasably secures pedicle screw  40  to screw inserter  160 . When assembled with pedicle screw  40 , rotation of shaft  166  also causes rotation of pedicle screw  40  without causing rotation of housing  170 . Anti-rotation sleeve  150  is located along an outer surface of tubular member  176  and includes protruding pins or buttons  152 . 
         [0078]    As best seen in  FIG. 18 , buttons  152  are configured and adapted to releasably engage instrument holes  6  of retractor  10 . Although retractor  10  is illustrated in cooperation with screw inserter  160 , screw inserter  160  is configured and adapted to cooperate with retractor  50 ,  60 , and  70 . Buttons  152  of screw inserter  160  engage instrument holes  6  such that no rotational forces are transferred to the selected retractor while rotating and inserting pedicle screw  40  into a selected vertebral body. This arrangement permits insertion of pedicle screw  40  while minimizing displacement of the selected retractor from its desired location (i.e. target site). 
         [0079]    A common spreader, or Gelpi retractor  180  is shown in  FIG. 19  in cooperation with retractor  10 . Gelpi retractor  180  includes a pair of curvate arms  185  that are pivotably connected at pivot point  186 . A pair of finger rings  184  are located at a proximal end of Gelpi retractor  180  that permit the physician to selectively move arms  185  towards and away from each other. A finger  182  is located at a distal end of each arm  185  and is configured to releasably engage an instrument hole  6  in retractor  10 . As shown, finger rings  184  are laterally offset from arms  185 . Thus, pivotable movement of arms  185  urge retractor blades  8  towards and away from each other in response to movement of finger rings  184 . Moving finger rings  184  towards each other pivots arms  185  away from each other and urge retractor blades  8  away from each other, thereby enlarging passage  18 . Consequently, movement of finger rings  184  away from each other has the opposite effect. Gelpi retractor  180  is also configured and adapted to cooperate with retractor  50 ,  60 , and  70 . 
         [0080]      FIGS. 20-20B  illustrate a cannulated minimally invasive pedicle screw  40 . Pedicle screw  40  includes a helical thread  43  that is sized and configured for insertion into a threaded hole created by bone tap  140 . A head  42  includes a tool engaging portion that is adapted to cooperate with screw inserter  160  as previously discussed. A rod receiving passage  44  is formed in head  42 . In addition, head  42  includes a threaded portion  45  that is adapted to removably attach to the screw inserter  160  and receive a setscrew (not shown). The setscrew compresses against rod  3  in passage  44  and frictionally engages rod  3  to hold it in a desired position. Setscrews are well known in the art. A throughbore  47  extends between a proximal end and a distal end of pedicle screw  40  for receiving guidewire  1  therethrough ( FIG. 20B ). 
         [0081]    A retractor extractor instrument  200  is illustrated in  FIGS. 21-23 . Retractor extractor  200  includes handle portion  190 , arms  210  and  220 , and extractor bar  230 . Handle portion  190  includes a handle grip  192  having openings  193 ,  194  disposed at one end thereof. Pin  196  extends through opening  194  and pivotably couples handle portion  190  to arms  210 ,  220  by extending through holes  212 ,  222  of arms  210 ,  220 . A pin  195  extends through opening  193  and pivotably couples handle portion  190  to pivot bar  198  through hole  198   a . At an opposing end of pivot bar  198 , hole  1986  receives a pin  197 . Pin  197  extends between arms  210 ,  220  and is slidably captured therebetween. In particular, pin  197  slides proximally and distally within a recess  224  of arm  220 . Arm  210  has an identical recess that is not shown. Additionally, pin  197  extends through an opening  236  of extractor bar  230 . Retractor bar has a slot  230  that extends parallel to its longitudinal axis and slidably receives posts  202  therethrough. Posts  202  are attached to blade portions  216 ,  226  through openings  218 ,  228 . Additionally, posts  202  are adapted to releasably engage instrument holes  6  of the previously disclosed retractors ( FIG. 23 ). At a distal end of extractor bar  230 , a blunt end  234  is located for bluntly engaging head  42  of pedicle screw  40  or a rod disposed therein. 
         [0082]    Pivoting handle grip  192  towards arms  210 ,  220  simulataneously moves extractor bar  230  distally (i.e. towards the screw) such that pins  202  on arms  210 ,  220  and distal blunt end  234  move apart relative to each other. This simultaneous relative movement between extractor bar  230  and pins  202  causes the retractor to separate from the pedicle screw at the relief regions without applying any appreciable downward forces on the implant or the patient. 
         [0083]    Use of the presently disclosed system will now be described with reference to  FIGS. 24-30 . In a first method, retractor  10  is assembled with pedicle screw  40  as shown in  FIG. 24 . The assembled apparatus is inserted into an incision through the patient&#39;s skin S and muscle/fat tissue T such that pedicle screw  40  is subsequently threaded into a vertebral body V. Once the desired number of retractors  10  are affixed to vertebral body V, retractor blades  8  are spread apart to retract skin S and tissue T to create a retracted area at the target site. Alternatively, retractor  50  may be assembled with pedicle screw  40  to retract tissue as shown in  FIG. 25 . In either method, rod  3  is inserted in passage  18  when passage  18  is in an expanded state (i.e. tissue has been retracted). Additionally, rod  3  is repositioned through passage  18  and subcutaneously such that is may be secured to fastening regions of pedicle screws in adjacent vertebral bodies. 
         [0084]    Turning now to  FIGS. 26-30 , an alternate technique is illustrated. Biopsy needle  100  is inserted through skin S of the patient until its distal end contacts the selected point on vertebral body V. Biopsy needle  100  may be inserted in a known manner, such as percutaneously under fluoroscopic imaging, or under optical or magnetic image guidance (such as the STEALTH® system available from Medtronic Sofamor Danek). A small puncture in the vertebral body V is made using sharpened distal tip  108  ( FIG. 13 ). After pin  106  is removed from biopsy needle  100 , guidewire  1  is inserted through biopsy needle  100  and affixed to vertebral body V. Guidewire  1  now is in position to direct further instruments and devices to the selected location on vertebral body V. Alternately, guidewire  1  may be insterted into vertebral body V without first using biopsy needle  100 . The size of the working area may be increased at the physician&#39;s discretion. In instances where it is desired to increase the working area, the physician may use scalpel  120  along guidewire  1  ( FIG. 28 ) to dissect additional tissue. In order to permit inspection of the position of guidewire  1  prior to insertion of a spine screw, a dilator  300  and optional retractor  10  may be inserted over the guidewire by inserting guidewire  1  through dilator opening  304  ( FIG. 14A ) with the dilator inserted through retractor  10 . Once the dilator tip with retractor is inserted to the target site, the dilator may be removed and placement of the guidewire may be inspected through the retractor. If the surgeon is satisfied with the placement of guidewire  1 , then the procedure may continue through the retractor or the retractor may be removed and another inserted with a screw. If, on the other hand, the surgeon desires to change the guidewire location, another guidewire may be placed through the retractor, such as by inserting bone biopsy needle  100  through the retractor to a different placement in the bone and inserting a new guidewire at the new location. The former guidewire may then be removed. If desired, the physician may pre-drill a threaded bore in vertebral body V using bone tap  140  inserted along guidewire  1  to prepare the bore. 
         [0085]    Once the target site is ready to accept a pedicle screw and retractor, an assembly including pedicle screw  40 , retractor  10 , and screw inserter  160  is slid along guidewire  1  to reach the target site. Using optional driving handle  178  ( FIG. 29 ), the physician rotates screw inserter  160  to drive pedicle screw  40  into vertebral body V ( FIG. 30 ). After pedicle screw  40  is secured in vertebral body V, screw inserter  160  is removed and retractor  10  remains in place secured by the screw which has been inserted into bone. This technique is also adapted for use with retractor  50 . The finished result of the attached retractors is the same as shown in  FIGS. 24 and 25 . 
         [0086]    Retractor blades  8  are spread apart to retract tissue in the working area. As previously discussed, retractor blades  8  may be spread apart using Gelpi retractor  180  ( FIG. 19 ) or by the physician manually grasping retractor blades  8  to urge them apart. After the desired retraction is achieved, rod  3  is inserted through passage  18  of retractor  10 ,  50  and is guided through window  2 . 
         [0087]    It has been found that a rod of sufficient length for a multiple level implant construct may be inserted subcutaneously so that the rod is aligned with and inserted into a plurality of screw heads. This technique may be particularly useful in so-called 360 degree procedures where an interbody implant is inserted using an anterior approach and a screw-rod construct is inserted using a posterior approach. Alternatively, the surgeon may selectively make an incision between adjacent retractors. The latter approach permits a rod to be inserted through the incision to adjacent screws. Once rod  3  is positioned between pairs of pedicle screws  40  and, in particularly through the respective rod receiving passages  44 , rod  3  is secured in place using setscrews as previously discussed. 
         [0088]    Once the screw-rod construct is complete, retractors  10 ,  50  are removed from the patient using retractor extractor  200 . Retractor extractor  200  is positioned atop pedicle screw  40  such that distal end  234  of extractor bar  230  ( FIG. 23 ) rests flush against the set screw installed in head  42  of pedicle screw  40  or rests upon the rod installed in an alternate pedicle screw. The physician repositions retractor blades  8  towards arm blades  216 ,  226  ( FIG. 22 ) of retractor extractor  200  such that posts  202  engage instrument holes  6 . Once retractor extractor  200  is installed, the physician pivots handle grip  192  towards arms  210 ,  220 . This pivotable movement drives extractor bar  230  distally against head  42  while simultaneously pulling retractor blades  8  proximally such that relief regions R ( FIG. 1 ) separate from each other along slits  16 . As such, retractor  10 ,  50  is separated from pedicle screw  40  without imparting significant downward or rotational forces against the patient&#39;s body. Retractor  10 ,  50  may now be removed from the patient and this process may be repeated for each installed retractor. 
         [0089]    In an alternate procedure, the physician first prepares the surgical site including positioning a guidewire as discussed hereinabove, optionally using scalpel  120  to prepare an incision, and inserting one of the previously disclosed retractors without a pedicle screw. Once the selected retractor is positioned in a desired location, the physician retracts the surrounding tissue as discussed hereinabove. Subsequently, the physician attaches pedicle screw  40  to the vertebral body V using screw inserter  160 . In this method, the selected retractor is already in position prior to attaching pedicle screw  40  to vertebral body V. In particular, the physician assembles pedicle screw  40  and screw inserter  160 . Once assembled, the screw insertion assembly is inserted into passage  18  of the retractor and pedicle screw  40  is rotated such that it bores into vertebral body V and head  42  seats on the interior surface of the distal region of the retractor and thus attaches the retractor to vertebral body V. Optionally, the physician may use cannulated bone tap  140  to prepare the bore. 
         [0090]    In the disclosed embodiments, each retractor is utilized, but not limited to, a method whereby an initial incision is made in the skin of approximately 10-15 mm in length. Surgeon preference will dictate the need for one or more stages of dilators to aid in expanding the wound before introducing one or more retractors in combination with pedicle screws. Normal surgical techniques may be used to close the incision(s). 
         [0091]    In the disclosed embodiments, the retractor may be manufactured from medical grade plastic or metal, thermoplastics, composites of plastic and metal, or biocompatible materials. A plastic part is made from, but not limited to, polypropylene and polyethylene. Plastic parts may be transparent or opaque and may have radio opaque markers for visibility during various imaging techniques. A metallic part utilizes such materials as, but not limited to, aluminum, stainless steel, and titanium. In addition, the parts may have a reflective or non-reflective coating to aid in increasing visibility in the wound and may have an artificial lighting feature. 
         [0092]    The disclosed retractors, as with any surgical instrument and implant, must have the ability to be sterilized using known materials and techniques. Parts may be sterile packed by the manufacturer or sterilized on site by the user. Sterile packed parts may be individually packed or packed in any desirable quantity. For example, a sterile package may contain one or a plurality of retractors in a sterile enclosure. Alternatively, such a sterile surgical kit may also include one or a plurality of bone biopsy needles ( FIG. 13 ), guide wires ( FIG. 20B ), sterile cannulated scalpels ( FIG. 14 ), or dilators ( FIG. 14A ). 
         [0093]    It will be understood that various modifications may be made to the embodiments of the presently disclosed retraction system. Therefore, the above description should not be construed as limiting, but merely as exemplifications of embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the present disclosure. 
         [0094]    For example, while the foregoing description has focused on spine surgery, it is contemplated that the retractors and methods described herein may find use in other orthopedic surgery applications, such as trauma surgery. Thus, where it is desired to insert a screw or pin into bone in a minimally invasive manner, or otherwise to access a surgical target site over a guidewire, the dilator, scalpel and retractors (or some of them) of the present disclosure may be used, with or without a bone screw.