Abstract:
A surgical retractor is disclosed. The retractor has a body with first and second portions cooperating to displace circularly relative to one another about an axis through a center of the body. A first retractor blade attaches to the first portion of the retractor body, and a second retractor blade attaches to the second portion of the retractor body. The first and second retractor blades define an angle therebetween and the angle is adjusted by the circular displacement of the first and second body portions

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 60/821,541, filed Oct. 6, 2006, and entitled SURGICAL RETRACTOR DEVICE AND METHOD OF USE, which is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The human spine provides a vast array of functions, many of which are mechanical in nature. The spine is constructed to allow nerves from the brain to pass to various portions of the middle and lower body. These nerves, typically called the spinal cord, are located in a region within the spine called the spinal canal. Various nerve bundles emerge from the spine at different locations along the lateral length of the spine. In a healthy spine, these nerves are protected from damage and/or undue pressure thereon by the structure of the spine itself. 
         [0003]    The spine has a complex curvature made up of a plurality of individual vertebrae (twenty-four in all) separated by intervertebral discs. These discs hold the vertebrae together in a flexible manner so as to allow relative movement between the vertebrae from front to back and from side to side. This movement allows the body to bend forward and backward, to twist from side to side, and to rotate about a vertical axis. Throughout this movement, when the spine is operating properly, the nerves are maintained clear of the hard structure of the spine. 
         [0004]    Over time or because of accidents, the intervertebral discs tend to lose height or become cracked, dehydrated, or herniated. The result is that the height of one or more discs may be reduced, which may lead to compression of the nerve bundles. Such compression may cause pain and, in some cases, damage to the nerves. 
         [0005]    Currently, there are many systems and methods at the disposal of a physician for reducing or eliminating the pain by minimizing the stress on the nerve bundles. In some instances, the existing disk is removed and an artificial disk is substituted therefore. In other instances, two or more vertebrae are fused together to prevent relative movement between the fused discs. 
         [0006]    Often there is required a system and method for maintaining or recreating proper space for the nerve bundles that emerge from the spine at a certain location. In some cases, a cage or bone graft is placed in the disc space to preserve or restore height and to aid in fusion of the vertebral level. As an aid in stabilizing the vertebrae, one or more rods or braces are placed between the fused vertebrae with the purpose of supporting the vertebrae, usually along the posterior of the spine, while fusion takes place. These rods are often held in place by anchors that are placed into the pedicle of the vertebrae. 
         [0007]    Minimally invasive surgical procedures have been developed to fuse the vertebrae. Such procedures can reduce pain, post-operative recovery time, and the destruction of healthy tissue. Generally, a pathological site is accessed through portals rather than through a significant incision, which aids in preserving the integrity of the intervening tissues. Minimally invasive surgical procedures are particularly desirable for spinal and neurosurgical applications because of the need for access to locations deep within the body and the possible range of damage to vital intervening tissues. In such procedures, however, it may be necessary to hold the edges of an incision apart to provide a clear operating field within which the surgeon can operate. 
         [0008]    What is needed, therefore, is a tool or retractor adapted to work with minimally invasive procedures that allows the surgeon to have a clear path to the operating field, and a method for using such a tool or retractor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1   a  is a perspective view of one embodiment of a retractor positioned with respect to a layer of tissue. 
           [0010]      FIG. 1   b  is a perspective view illustrating one embodiment of a retractor. 
           [0011]      FIG. 1   c  is a perspective view of the retractor of  FIG. 1   b  with a portion of the retractor removed. 
           [0012]      FIG. 2  is a perspective view of a portion of the retractor of  FIG. 1   b.    
           [0013]      FIG. 3  is a side view of the retractor of  FIG. 1   a  taken along lines  3 - 3 . 
           [0014]      FIG. 4  is a side view of the retractor of  FIG. 1   a  taken along lines  4 - 4 . 
           [0015]      FIG. 5  is a side view of the retractor of  FIG. 4  with the addition of a blade. 
           [0016]      FIG. 6   a  is a side view of the retractor of  FIG. 1   b  taken along lines  4 - 4  with the addition of a blade. 
           [0017]      FIG. 6   b  is a side view of the blade of  FIG. 6   a.    
           [0018]      FIG. 7   a  is a side view of the retractor of  FIG. 1   b  taken along lines  4 - 4  with the addition of a blade. 
           [0019]      FIGS. 7   b  and  7   c  are side views of two different embodiments of a blade that may be used with the retractor of  FIG. 7   a.    
           [0020]      FIG. 8   a  is a side view of another embodiment of a retractor with a blade. 
           [0021]      FIG. 8   b  is a side view of the blade of  FIG. 8   a.    
           [0022]      FIGS. 9   a - 9   d  illustrate various embodiments of blades that may be used with the retractor of  FIG. 1   b.    
           [0023]      FIG. 10   a  is a top view of the retractor of  FIG. 1   b  in a first or substantially collapsed position. 
           [0024]      FIG. 10   b  is a top view of a retractor similar to that of  FIG. 10   a  in a second or partially open position. 
           [0025]      FIG. 11  is a perspective view of an embodiment of the retractor of  FIG. 1   b  in a first or substantially collapsed position while being used with a spinal surgery system. 
           [0026]      FIG. 12   a  is a perspective view of the retractor of  FIG. 11  illustrating an exemplary positioning of the retractor with respect to a layer of tissue. 
           [0027]      FIG. 12   b  is a top view of the retractor of  FIG. 12   a  illustrating an exemplary positioning of the retractor with respect to the layer of tissue prior to the insertion of a rod between two extensions. 
           [0028]      FIG. 12   c  is a top view of the retractor of  FIG. 12   a  illustrating an exemplary positioning of the retractor with respect to the layer of tissue after the insertion of a rod between two extensions. 
           [0029]      FIGS. 13-15  are side views illustrating possible orientations of the retractor of  FIG. 12 . 
           [0030]      FIG. 16  is a perspective view of an embodiment of the retractor of  FIG. 11  in a second or substantially open position. 
           [0031]      FIG. 17  is a side view of one embodiment of an instrument that may be used to move a retractor from the substantially collapsed position of  FIG. 11  to the substantially open position of  FIG. 16 . 
           [0032]      FIG. 18  is a cross-sectional view of another embodiment of a retractor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    The present disclosure is directed to systems and methods for retracting tissues in surgical procedures. It is understood that the following disclosure provides many different embodiments or examples. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
         [0034]    Referring to  FIG. 1   a , in one embodiment, a retractor  10  is illustrated in conjunction with an extension  30 , such as may be used in a spinal surgery procedure. As illustrated, the retractor  10  may include a substantially circular body  12  formed by semi-circular body portions  14  and  16  that may move relative to one another, as will be discussed later in greater detail. The body portions  14  and  16  may be coupled to arms  18  and  20 , respectively, that extend outwardly from the circular body  12 . Each arm  18  and  20  may be coupled to a blade  22  and  24 , respectively, which may be used to provide an opening at a surgical site. A locking mechanism  26  may be used to lock the relative positions of the body portions  14  and  16 . 
         [0035]    In the present example, bone anchors  32  and  34  (e.g., pedicle screws) may be fastened to a vertebral body (not shown). The bone anchors  32  and  34  may have polyaxial heads  36  and  38 , respectively, which may be configured to receive a rod  40 . Examples of the extension  30  and its interaction with the bone anchors  32 ,  34 , polyaxial heads  36  and  38 , and rod  40  are illustrated in greater detail in U.S. patent application Ser. No. 10/690,211, filed on Oct. 21, 2003, U.S. patent application Ser. No. 10/990,272, filed on Nov. 16, 2004, and U.S. patent application Ser. No. 10/989,715, filed on Nov. 16, 2004, all of which are hereby incorporated by reference in their entirety. 
         [0036]    In operation, the retractor  10  may be placed in a position “A” above the extension  30 . As illustrated, the arms  18  and  20  may be rotated partially or totally upward. The circular body  12  of the retractor  10  may then be placed over the extension  30  and may slide down the extension to a position “B”. At this point, the arms  18  and  20  may be lowered. It is noted that the locking mechanism  26  may be manipulated to allow movement of the body portions  14  and  16  with respect to one another and to prevent such relative movement. 
         [0037]    As illustrated, after the arms  18  and  20  are lowered while the retractor  10  is in position “B”, a portion of the blades  22  and  24  may be positioned beneath a tissue layer  28 . For example, the tissue layer  28  may be a layer of skin, with the extension  30  positioned within an incision in the tissue layer. As illustrated, an upper portion of the extension  30  may be above the tissue layer  28  and a lower portion below the tissue layer. Accordingly, the retractor  10  may be used to enlarge an opening below the tissue layer  28 . 
         [0038]    It can also be seen in  FIG. 1   a  that the angle of the arms  18  and  20 , and therefore the blades  22  and  24 , may be varied with respect to the body  12 . As will be described in greater detail below, this may allow the angle of the arms  18  and  20 , and blades  22  and  24 , to vary with respect to a longitudinal axis X passing through the body  12 . Such a longitudinal axis is substantially coaxial with the extension  30  inserted through the body  12 . 
         [0039]    The angle between the arms  18  and  20 , and the blades  22  and  24  also varies with the relative adjustment between the two body portions  14  and  16  of the body  12 . The angle between the arms  18  and  20  may be adjustable from substantially no separation, as shown in position “A”, to an acute angle as shown in position “B”. Some embodiments may allow the arms  18  and  20 , and blades  22  and  24  to adjust to a position with an obtuse angle between the arms  18  and  20 . 
         [0040]    Referring to  FIG. 1   b , a perspective view of one embodiment of a retractor  100  is provided. As illustrated, the retractor  100  may include a substantially circular body  102  formed by semi-circular body portions  104  and  106 . In certain embodiments, the body portions  104  and  106  may move relative to one another in a sliding manner. For example, the body portion  106  may include a cavity large enough to receive at least part of the body portion  104  such the body portion  104  slides within and interfits with the body portion  106 . Accordingly, the body portions  104  and  106  may move with respect to one another, and such movement may be restrained to a substantially circular path. In the present embodiment, the body portion  104  may not be removable from the body portion  106  due to a length of the body portion  104  captured within the cavity of the body portion  106  and due to features captured within to prevent disassembly. 
         [0041]    In other embodiments, the general shape of the body  102  may be generally cylindrical with each of the body portions  104  and  106  for a portion of the generally cylindrical shape. In another embodiment, the body  102  may be generally toroidal, donut shaped, or shaped as an annulus. In each of these additional embodiments, the body portion  106  may accommodate the body portion  104  in a sliding interfit relationship, as described. The path of the body portion  104  within the body portion  106  may remain substantially circular. In another embodiment, the body portion  106  may substantially cover the body portion  104 . A window (not shown) on the body portion  106  may be provided allowing circular translation and longitudinal rotation of the arm  102 . 
         [0042]    The body portions  104  and  106  may be coupled to arms  108  and  110 , respectively, that extend outwardly from the circular body  102 . More specifically, a inward end  112  and  116  of each arm  108  and  110 , respectively, may be coupled to their respective body portion  104  and  106 . As will be described later, a distal end  114  and  118  of each arm  108  and  110 , respectively, may be moved as the proximal ends  112  and  116  are rotated. 
         [0043]    As illustrated, in certain embodiments, the arm  108  may include one or more projections  120  and  122  that may extend substantially perpendicularly from a longitudinal axis of the arm. Although not shown in  FIG. 1   b , it is understood that the arm  110  may include similar projections. 
         [0044]    In certain embodiments, the blade  124  may be coupled to the projections  120  and  122  of the arm  108 , and a blade  126  may be coupled to the similar projections (not shown) of the arm  110 . In the present example, one or both of the blades  124  and  126  may be removable, and may be reusable or single use (i.e., molded plastic). For example, the blade  124  may include one or more slots for receiving the projections  120  and  122 . 
         [0045]    It is understood that the term “blade” as used herein does not necessarily imply a cutting edge, and the various edges of a blade may or may not be designed for cutting. For example, the blade  124  may be tapered, with a thicker flat-edged portion near the arm  108  and a narrower round-edged portion at the opposite edge. As will be illustrated later, such a taper may aid in inserting the blade into a surgical site. However, such tapering is not required, and the blade may have any desired shape. Furthermore, the thickness of the blade  124  may vary depending upon the needs of the user. The blade  124  may also have various concavities, convexities, lips, contours and other features promoting efficient retraction within the confines of the prevailing anatomy at a surgical site. 
         [0046]    In the present example, as will be described later in greater detail, the circular body  102  may include a mechanism  128  for locking a position of the body portion  104  relative to that of the body portion  106 . In certain embodiments, locking the body portion  104  relative to the body portion  106  also locks the retractor  100  to an extension, such as the extension  30  of  FIG. 1   a . In other embodiments, the body portion  106  may have vertical grooves or channels (not shown) which slidingly engage with protrusions on the extension to keep the body portion  106  stationary with respect to the extension. In yet other embodiments, protrusions on the inside surface of the body portion  106  may slidingly engage channels or grooves on the exterior surface of the extension. 
         [0047]    Referring to  FIG. 1   c , the circular body  102  is illustrated with a portion of the mechanism  128  removed. In the present example, the mechanism  128  may include an opening  130  in the body portion  104 . In certain embodiments, the opening  130  may extend through the body portion  106  to reveal part of the body portion  104 . A pin  132  may span the opening  130  to secure a lever  134  to the body portion  106 . 
         [0048]    In certain embodiments, the lever  134  may include an enlarged portion  136  that may be shaped to apply pressure to the underlying body portion  106  when in a first position and to release the pressure when in a second position. Such an arrangement may be considered a camming fit with the enlarged portion  136  operating as the cam lobe. The lever  134  may lock the relative positions of the body portions  104  and  106  in a first position (e.g., when down or when proximate to the body portion  104 ) and may allow movement in a second position (e.g., when away from the body portion or when up). In another embodiment, the lever may lock the relative positions of the body portions  104  and  106  when up, but allow movement when down (e.g., proximate the body portion). The pin  132  may extend through a bore  138  in the lever  134  to secure rotation of the lever  134 . 
         [0049]    In other embodiments, different mechanisms for locking the body portions  104  and  106  could be utilized and the camming arrangement shown in  FIG. 1   c  is meant to be illustrative only. In some embodiments, a series of holes defined in the body portions  104  may allow pins to be used to secure the body portions on the proper relative locations once the desired retraction has been achieved. In other embodiments, a racketing mechanism could be utilized where the arms  108  and  110  are retained in the largest angle that they are moved into until released. In further embodiments, the retraction strength needed of the retractor  100  may be slight enough to allow a friction or interference fit between the body portions  104  and  106 . 
         [0050]    Referring to  FIG. 2 , in one embodiment, the body  102  is illustrated without the arms  108  and  110  ( FIG. 1   b ). In the present example, the body portion  104  includes an exterior surface  200  and an interior surface  202 . The exterior and interior surfaces  200  and  202  may be separated by an upper surface  204  and a lower surface  206 . The upper and lower surfaces  204  and  206  may have the same or different widths (e.g., the exterior and interior surfaces  200  and  202  may taper upward toward the upper surface  204  or downward toward the lower surface  206 ). The body portion  104  may also have an interior end  208  that is inserted into the cavity of the body portion  106  and an exterior end  210  that is opposite the end  208 . 
         [0051]    The body portion  106  includes an exterior surface  212  and an interior surface  214 . The exterior and interior surfaces  212  and  214  may be separated by an upper surface  216  and a lower surface  218 . The upper and lower surfaces  216  and  218  may have the same or different widths (e.g., the exterior and interior surfaces  212  and  214  may taper upward toward the upper surface  216  or downward toward the lower surface  218 ). The body portion  106  may also have a cavity end  220  that opens into the cavity of the body portion  106  and an exterior end  222  that is opposite the end  220 . 
         [0052]    The interior surface  214  of the body portion  106  may be semi-circular and, in conjunction with the interior surface  202  of the body portion  104 , may provide a substantially circular or cylindrical opening  224 . Although the opening  224  in the present embodiment may be relatively fixed in size due to the inner surfaces  202  and  222 , it is understood that flexibility in the size of the opening may be provided in other embodiments. Furthermore, the exact shape of the opening  224  may vary in other embodiments as the general shape of the body  102  differs in other embodiments, (e.g., a toroidal body) 
         [0053]    In some embodiments, the exterior end  210  may include a channel  226  and the exterior end  222  may include a channel  228 . The channels  226  and  228  may be sized to receive the arms  108  and  110 , respectively. A pin (see  FIG. 3 ) may span the channel  226  and a pin  230  may span the channel  228 . The pins may couple the arms  108  and  110  to the body portions  104  and  106 , respectively. The channels  226  and  228  may enable the arms  108  and  110  to rotate upward around an axis provided by each pin. The angular positions of the arms with respect to a longitudinal axis proceeding through the body  102  may be maintained by friction between the arms  108  and  110  and the channels  226  and  228 . In other embodiments, the arms  108  and  110  may be held in place by other means or may be free to rotate relatively freely. 
         [0054]    The arc through which each arm  108  and  110  may be rotated may be sufficient to move the arms from a first position to a second position. For example, the first position may be where a longitudinal axis of one or both arms  108  and  110  is substantially aligned with the longitudinal axis extending through the center of the opening  224 . This longitudinal axis extending through the center of the opening  224  may also be the longitudinal axis of the extension  30  ( FIG. 1   a ) when inserted through the body  102 . The second position may be where the longitudinal axis of one or both arms  108  and  110  is separated from the first position by an acute angle, a right angle, or an obtuse angle. It is understood that the arms  108  and  110  may be rotated independently or together. 
         [0055]    Referring to  FIG. 3 , one embodiment of a side view of the retractor  100  of  FIG. 1   b  is illustrated, although  FIG. 3  differs from  FIG. 1   b  in that the arm  108  has been moved into a substantially parallel alignment with the arm  110 . In the present example, each body portion  104  and  106  may be coupled to its respective arm  108  and  110 , respectively, by means of pins  300  and  230 , respectively. As described previously, the body portions  104  and  106  may include the channels  226  and  228 , respectively, and the pins  300  and  230  may span their channel. 
         [0056]    Referring to  FIG. 4 , an embodiment of a side view of the retractor of  FIG. 1   b  is illustrated. As described previously, the arm  110  may include two projections  400  and  402 . The projections  400  and  402  may be fixed, removable, and/or adjustable, and the arm  110  may include a slot or channel  404  configured to receive the projections. For example, the projections  400  and  402  may snap into the channel  404 , or the channel  404  may have an opening at one end into which the projections may be inserted (e.g., in a tongue and groove fitting). In the present embodiment, the projections  400  and  402  may be slidably attached to the arm  110  via the channel  404 . It is understood that the projections  400  and  402  may be fastened to the arm  110  in many different ways, and those described are for purposes of illustration only. 
         [0057]    Referring to  FIG. 5 , the retractor  100  of  FIG. 1   b  is illustrated with the addition of the blade  126  ( FIG. 1   b ). 
         [0058]    Referring to  FIGS. 6   a  and  6   b , in one embodiment, the retractor of  FIG. 1   b  is illustrated with a distance D 1  separating the projections  400  and  402 . The distance D 1  may be selected to provide support for the blade  126  and may coincide with the spacing of slots in the blade. In other embodiments, the slots may be relatively large compared to the width of the projections  400  and  402 . In still other embodiments, the blade  126  may have a single slot into which both projections  400  and  402  are inserted. 
         [0059]    Referring to  FIGS. 7   a - 7   c , in another embodiment, the retractor of  FIG. 1   b  is illustrated with the projections  400  and  402  separated by varying distances smaller than the distance D 1  in  FIG. 6   a . For example, the projections  400  and  402  may be separated by a distance D 2  in order to receive a relatively narrow blade  126  ( FIG. 7   b ), and may be separated by a distance D 3  in order to receive a wider blade  126  ( FIG. 7   c ). Accordingly, the spacing of the projections  400  and  402  may be altered to receive a particular blade. 
         [0060]    Referring to  FIGS. 8   a  and  8   b , in yet another embodiment, the arm  110  may be configured to receive a blade  126  ( FIG. 8   b ) without the use of projections. The arm  110  may have the same channel  404  previously described (e.g., configured for a snap or tongue in groove fitting) or may be configured differently. Accordingly, the blade  126  may couple to the arm  110  in a manner similar to the projections. 
         [0061]    Referring to  FIGS. 9   a - 9   d , various embodiments of a blade  126  are illustrated. It is understood that many different variations are possible and the blade  126  is not limited to the illustrated examples. Furthermore, in other embodiments, multiple blades may be used with a single arm. For example, a separate blade may be attached to each projection of an arm. 
         [0062]    Referring to  FIG. 10   a , a top view of one embodiment of the retractor  100  of  FIG. 1   b  is illustrated in a first or substantially closed position. In this position, a substantial part of the body portion  104  is exposed and the arms  108  and  110  are relatively close together. This position is reflective of substantially zero angle between the arms  108  and  110 . Stated another way the arms  108  and  110  are parallel. It is understood that the body portion  104  may be extended until the exterior end  210  contacts the exterior end  222  of the body portion  106 , which may indicate that the retractor  100  is fully closed. In this position the blades  124  and  126  are touching or are relatively close together and will therefore have substantially zero angle, or a very acute angle, between them. In the present example, the locking mechanism  128  is in the closed position, thereby preventing movement of the body portion  104  relative to the body portion  106 . 
         [0063]    Referring to  FIG. 10   b , a top view of one embodiment of the retractor  100  of  FIG. 1   b  is illustrated in a second or substantially open position. In this position, a substantial portion of the body portion  104  is contained within the cavity of the body portion  106  and the arms  108  and  110  are relatively far apart or at a wide angle with respect to one another. It is understood that the body portion  104  may be retracted into the cavity until, for example, the arm  108  contacts the cavity end  220  of the body portion  106 , which may indicate that the retractor  100  is fully open or encounters enough tissue resistance so as to halt opening. It can be seen that the body portions  104  and  106  will form only a portion of a circle, cylinder, or toroid (depending upon the particular embodiment) when the retractor  100  is open. 
         [0064]    In the present example, the locking mechanism  128  is in the open position, thereby allowing movement of the body portion  104  relative to the body portion  106 . The present embodiment also provides attachment points  140  which may be used for attaching an instrument ( FIG. 17 ) to aid in opening the retractor  100 . 
         [0065]    Referring to  FIG. 11 , in one embodiment, the retractor  100  of  FIG. 1   b  is illustrated in conjunction with an extension  1100 , such as may be used in a spinal surgery procedure. In the present example, bone anchors  1102  and  1104  (e.g., pedicle screws) may be fastened to a vertebral body (not shown). The bone anchors  1102  and  1104  may have polyaxial heads  1106  and  1108 , respectively, which may be configured to receive a rod  1110 . Examples of the extension  1100  and its interaction with the bone anchors  1102 ,  1104 , polyaxial heads  1106  and  1108 , and rod  1110  are illustrated in previously incorporated U.S. patent application Ser. Nos. 10/690,211; 10/990,272; and 10/989,715. 
         [0066]    In operation, the retractor  100  may be placed in a position “A” above the extension  1100 . As illustrated, the arms  108  and  110  may be rotated partially or totally upward, or angle toward the axis X. The circular body  102  of the retractor  100  may then be placed over the extension  1100  and may slide down the extension to a position “B”. At this point, the arms  108  and  110  may be lowered. In this position, the arms  108  and  110  may be substantially orthogonal to the axis X. It is noted that the locking mechanism  128  is down, indicating that the body portions  104  and  106  are locked with respect to one another. Accordingly, the opening  224  ( FIG. 2 ) may be sized to slide over the extension  1100  regardless of the state of the retractor  100  (e.g., open or closed). However, in the present example, the opening  224  may only slide over the extension  1100  when the locking mechanism  128  is open. 
         [0067]    With additional reference to  FIG. 12   a , the retractor  100  of  FIG. 1   b  is illustrated with a tissue layer  1200 . For example, the tissue layer  1200  may be a layer of skin, with the extension  1100  positioned within an incision in the tissue layer. It is understood, however, that the blades  124  and  126  of the retractor  100  may be suitable for retraction of other tissue such as muscle and/or fat. As illustrated, the upper portion of the extension  1100  may be above the tissue layer  1200  and the lower portion below the tissue layer. Pressure, indicated by arrows  1202 , may be applied by the tissue layer  1200  against the blades  124  and  126 . The locking mechanism  128  may be used after opening the retractor  100  (e.g., moving the arm  108  relative to the arm  110 ) to counteract pressure  1202  from the tissue layer  1200  to keep the retractor open. Here is can be seen that the angle between the blades has been increased to allow access into the wound cavity. 
         [0068]    Referring to  FIG. 12   b , a top view of one embodiment of the retractor  100  of  FIG. 12   a  is illustrated. In the present example, a second extension  1204  is positioned over the bone anchor  1102  and polyaxial head  1106  ( FIG. 12   a ). As illustrated, the arms  108  and  110  of the retractor  100  may be moved apart to provide an opening between the extensions  1100  and  1204 . 
         [0069]    Referring to  FIG. 12   c , the top view of  FIG. 12   b  is illustrated with the rod  1110  in place between the polyaxial heads  1106  and  1108  ( FIG. 12   a ). In the present example, to secure the rod  1110 , a locking device  1206  may be inserted into the polyaxial head  1108  and a locking device  1208  may be inserted into the polyaxial head  1106 . As such locking devices are described in the previously incorporated U.S. patent application Ser. Nos. 10/690,211; 10/990,272; and 10/989,715, they will not be described in detail herein. 
         [0070]    With reference to  FIGS. 12   b - c , it can be seen how the angle between the blades  108  and  110  corresponds to varying degrees of retraction. The relationship of the blades  108  and  110  when in the original, closed position can be seen in dotted line. In order to assist in opening the retractor, attachment points  140  are provided. In some embodiments, an instrument ( FIG. 17 ) may be used to apply outward force to the blades to provide the appropriate angle therebetween for effective retraction. As described, the retractor  100  can then be locked into the open position. The attachment points  140  may be knobs or stems on the arms  108  and  110  or blades  124  and  126 . 
         [0071]    Referring to  FIGS. 13-15 , various embodiments of the retractor  100  of  FIG. 11  illustrate possible orientations of the retractor based on the orientation of the extension  1100 . For example, in  FIG. 13 , the extension  1100  may have an angled orientation (indicated by solid lines) wherein the arms  108  and  110  form an obtuse angle with the upper portion of the extension as compared to a vertical orientation (indicated by dashed lines). In  FIG. 14 , the extension  1100  may have an angled orientation (indicated by solid lines) wherein the arms  108  and  110  form an acute angle with the upper portion of the extension as compared to a vertical orientation (indicated by dashed lines).  FIG. 15  illustrates a vertical orientation wherein the arms  108  and  110  form a substantially ninety degree angle with the upper portion of the extension when the arms are lowered from a first position “ 1 ” to a second position “ 2 ”. It is noted that the arms  108  and  110  may remain substantially parallel to the tissue layer  1200  throughout the different orientations illustrated in  FIGS. 13-15 . In addition, the arms  108  and  110  may remain together or they may be placed separately. 
         [0072]    Referring to  FIG. 16 , the retractor  100  of  FIG. 11  is illustrated in position “B” with the locking mechanism  128  having been opened to allow movement of the body portion  104  relative to the body portion  106 . In this opened configuration, the arms and blades may be adjusted between closed, acute, and obtuse angles. 
         [0073]    With additional reference to  FIG. 17 , a device  1700  illustrates one embodiment of an instrument that may be used to force apart the arms  108  and  110  and their respective blades  124  and  126 . In the present example, the device  1700  includes opposing arms  1702  and  1704  that are joined by a pin  1706 . User gripping surfaces  1708  and  1710  may be provided for the opposing arms  1702  and  1704 , respectively. Ends  1712  and  1714  of the opposing arms  1702  and  1704 , respectively, may be configured to engage the attachment points  140 , the body portions  104  and  106 , the arms  108  and  110 , and/or blades  124  and  126 . 
         [0074]    Referring again to  FIG. 16 , using an instrument such as the device  1700  of  FIG. 17 , the arms  108  and  110  of the retractor  100  may be moved from a substantially closed position ( FIGS. 11 and 12 ) to the illustrated substantially open position. When open, the blades  124  and  126  may create a void within the tissue to allow access to a surgical site. It is understood that the arms  108  and  110  may be stopped at any position between fully closed and fully open, and the positions illustrated herein are not limiting. Once the arms  108  and  110  are in the desired position, the locking mechanism  128  may be closed (not shown) to prevent further movement of the body portions  104  and  106 . This may prevent the arms  108  and  110  from being forced together by the pressure asserted by the surrounding tissue and may lock the retractor  100  onto the extension  1100 . 
         [0075]    Referring to  FIG. 18 , in another embodiment, a retractor  1800  may include a different mechanism for opening and closing than that discussed above. In the present example, the retractor  1800  may include a substantially circular body  1802  formed by semi-circular body portions  1804  and  1806 . The body portions  1804  and  1806  may move relative to one another. For example, the body portion  1806  may include a cavity large enough to receive at least part of the body portion  1804 . Accordingly, the body portions  1804  and  1806  may move with respect to one another, and such movement may be restrained to a substantially circular path. In the present embodiment, the body portion  1804  may not be removable from the body portion  1806  due to a length of the body portion  1804  captured within the cavity of the body portion  1806 . The body portions  1804  and  1806  may be coupled to arms  1808  and  1810 , respectively, which extend outwardly from the circular body  1802 . 
         [0076]    In the present embodiment, a driver  1812  may be coupled to a shaft  1814 . The shaft  1814  may include threads  1816  and may be contained within a sleeve or housing  1818 . The outer surface of the body portion  1804  may include a series of depressions  1820  that engage the threads  1816 . The body portion  1806  may or may not contain a means for engaging the threads  1816 . 
         [0077]    In operation, as the driver  1812  is rotated, the shaft  1814  and the associated threads  1816  are also rotated. The threads  1816  engage the depressions  1820  in the body portion  1804  and cause the body portion to rotate. The direction of rotation may depend on the direction of rotation of the driver. Accordingly, using the mechanism illustrated, the arms  1808  and  1810  may be moved together or apart using the driver  1812 . It can be seen that the shaft  1814  and threads  1816  may operate as a worm gear to move the body portion  1814  relative to the body portion  1806 . 
         [0078]    In such an embodiment as shown in  FIG. 18 , an instrument such as the device  1700  of  FIG. 17  may not be needed. Furthermore, in embodiments where there is sufficient friction within the retractor  1800 , a locking means such as the locking mechanism  128  of  FIG. 1   b  may not be needed. 
         [0079]    It is understood that a variety of materials may be used to form the various components of the retractors described herein. For example, various metals, alloys, plastics, and other materials may be used to create a retractor, and various portions of the retractor may be formed from different materials. In another example, a material such as cloth or mesh may be coupled to the distal ends  114  and  118  of the arms  108  and  110 , respectively, and the material may form a third side when the arms are separated. In operation, the material may be folded between the blades  124  and  126  when the blades are initially inserted into the surgical site, and the material may then be pulled tight to couple the distal ends  114  and  118  as the blades are separated. 
         [0080]    The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. For example, various elements of the embodiments described above may be combined with elements of other embodiments, and characteristics of one embodiment may be incorporated into another embodiment. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the invention is intended to encompass within its scope such processes, machines, manufacture, compositions of matter, means, methods, or steps, and it is intended that the scope of the invention not be limited by this detailed description. 
         [0081]    Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.