Abstract:
A retractor having interchangeable or replaceable blades facilitates the expansion of a surgical site below an incision in the skin, and establishes a work-through surgical space. The retractor includes a frame connected to two collar arms, a pair of blades connected to the collar arms, a sheath for encompassing the blades and providing a circumscribed working space, and a device for rotating the collar arms, thereby displacing the blades and any tissue surrounding them.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional, of U.S. application Ser. No. 10/943,520, filed on Sep. 17, 2004, the disclosure of which is incorporated herein by reference. This application claims the benefit of the filing date of U.S. Provisional Application No. 60/503,944, filed Sep. 18, 2003, and U.S. Provisional Application No. 60/519,202, filed Nov. 12, 2003, the disclosures of which are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a device used to retract tissue within the body of a patient. More specifically, the present invention relates to a retractor that facilitates enlarging a surgical cavity and providing a work-through channel to the surgical site. 
     Since it is advantageous to perform surgery in ways that minimize tissue trauma, the present minimally invasive approach facilitates a smaller incision, less tissue trauma, and faster patient rehabilitation, as compared to traditional incision and retraction techniques. 
     The various embodiments of the present invention are particularly useful for orthopedic surgery of the spine, but are envisioned to be limitlessly applicable to other surgical techniques and other parts of the body. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides an apparatus for conducting a less invasive surgical procedure by making a relatively small incision in a patient&#39;s skin and forming a larger surgical cavity below the incision. The surgical retractor according to this aspect of the invention includes a mount having a frame connected through two translating pivot points to two collar arms, where the two collar arms are attached together at least one hinge, a pair of blades connected to the collar arms, and an actuator for rotating the two collar arms along the hinge axis, thereby displacing the blades. Preferably, the actuator is located close to the hinge connecting the collar arms, and is not a separate instrument. Also preferably, the actuator is at an angle relative to the frame in order to provide clearance with the patient&#39;s skin when the axis of the retractor is not perpendicular to the skin. Another aspect of the present invention provides that at least a portion of the actuator is part of the frame. 
     One aspect of the actuator includes a screw threadably associated with a housing that is part of the frame. In this aspect, when the screw is turned, or actuated, it moves distally and bears on both collar arms, thus pushing them downwardly and forcing the blades to open. 
     Another preferred aspect of the actuator further includes a ball in communication with the screw and in communication with a hinge pin linking the collar arms together. Optionally, a guide may be attached to the pin, wherein the guide provides a contact surface for the ball. Thus, when the screw is turned, it translates and bears on the ball, which itself moves and bears on the guide, which, because of its connection to the hinge pin, forces the hinge pin and hinge of the two collar arms to move distally, thereby pushing both collar arms downwardly and forcing the blades to open. 
     Yet another preferred aspect of the invention includes a tool, such as a screwdriver or an Allan key, that engages the actuator to move the actuator and thus cause the blades to move, either to separate or to come together. 
     In yet another aspect, the mount is preferably situated above the skin of the patient and has an opening therethrough allowing entry into the surgical cavity. 
     Another aspect of the present invention provides a mount comprising two collar arms attached at two hinge points. The mount includes an opening through its center leading to a channel, whereby a portion of the opening resides on each of the two collar arms. In a preferred embodiment, the opening is of an oval cross-section. However, this opening can be of any diameter, shape, or cross-sectional area. Additionally, the mount can be of any size or shape and the opening in the mount may or may not correspond to the shape of the tube created by the blades that are attached to the collar arms. 
     Another aspect of the present invention further provides blades having a shape and a length. In a preferred embodiment, the blades are curved, whereby together, they form an oval tube when in a non-expanded position. Upon rotation of the collar arms, the blades move outwardly, thereby displacing tissue and enlarging the surgical cavity. The major and minor diameters of the oval tube can be of any size. It should be noted that the blades can be of any shape and may or may not correspond to the shape of the mount. For example, the curvature of the blade may differ from that of the opening. Similarly, the blades can be of any length thereby creating surgical cavities with different depths. Additionally, the blades have tapered ends which facilitate progressive tissue penetration. This allows for improved control during insertion and less damage to the tissue. 
     Another aspect of the present invention further provides blades that are easily detachable from the mount. In a preferred embodiment, the blades are attached to the mount through the use of male and female connectors. These connectors facilitate easily attaching and detaching the blades from the mount. The blades may be attached by compressing them to fit within the opening, and then allowing them to spring back to original shape and engage the respective connectors. Detachment may be similarly achieved by compressing the blades to disassociate the respective connectors, thereby freeing the blades for removal and/or replacement. Other connection configurations are also envisioned. 
     The blades may be constructed of any sturdy material, and preferably from a radiolucent or semi-radiolucent material. In a preferred embodiment, thin, semi-radiolucent aluminum is employed. This allows for improved visualization of the surgical site when viewed on an X-ray with the retractor in place. In another embodiment, a non-autoclavable or non-sterilizable material may also be utilized. 
     The blades, as well as the collar, may also be constructed of a light-conducting material, such as acrylic, for example. Preferably a cable transfers light from a light source to the collar and blades, which then illuminate the working space. 
     It is also contemplated, in a preferred embodiment, that the blades are easily interchangeable. This allows for quick changes in length, depth, or shape of the blades depending upon a particular surgical situation. Thus, among other advantages, the desired length, depth, or shape of blades can be changed without having to utilize an entirely new device. 
     In another preferred embodiment, the blades can be disposable, either in addition to the interchangeable feature, or independent of that feature. In this regard, in a preferred embodiment, the blades may be removable for disposability, or the blades and the collar to which they are connected may be disposable. Preferred methods contemplate the interchangeability, illumination and/or the disposability features in various forms. 
     Another aspect of the present invention further provides a sheath that covers the blades. The sheath expands when the blades are extended outwardly thereby creating an enlarged surgical cavity that is enclosed by the retractor and sheath. The sheath also contracts along with the inward retraction of the blades. In a preferred embodiment, the sheath is constructed of pliable elastic material, such as silicone rubber, thereby allowing for both its expansion and contraction. It is envisioned that the sheath can be made of any material and can be any length, thickness, or shape, as well as transparency or opaqueness. In a preferred embodiment, the sheath fits snuggly over the blades in both the retracted and expanded positions. The sheath material can be such that it facilitates easy assembly onto, and removal from, the blades. The sheath may also be disposable, and a preferred method contemplates such disposability. Additionally, the sheath may cover any portion of the blades up to and including their entire surface area. 
     Another aspect of the present invention provides a bar for use with the retractor. The bar can be easily attached to a rigid, relatively fixed object on a first end and to the retractor on a second end. The bar is used to hold the retractor in position relative to the patient. Multiple bars may also be interconnected, thus forming a support assembly, to allow for discreet positioning of two or more retractors relative to each other. One example of a support assembly is the AF400 SpineTract System manufactured by Omni-Tract Surgical, a division of Minnesota Scientific. However, any type of bar or assembly can be used. 
     Another aspect of the present invention provides an apparatus for dilating an opening created by a small incision in the skin of a patient. The apparatus according to this aspect of the invention includes a guide and a variable number of dilators, whereby the first dilator fit over the guide and subsequent dilators of increasing size are sequentially fit over one another. In a preferred embodiment, the dilators are oval tubes having major and minor inside and outside diameters. Increasingly sized dilators are configured such that each larger dilator can fit over a smaller dilator. In a preferred method, the guide is inserted in an incision in the skin of the patient. Then a first dilator is moved down the guide thereby increasing the size of the surgical cavity. The first dilator has outside major and minor diameters which are slightly smaller than the inside major and minor diameters of the second dilator. The second dilator is then slid over the first dilator, thereby once again increasing the size of the surgical cavity. These steps are repeated until the desired surgical cavity size is achieved with a corresponding sized dilator, at which point the retractor, it its closed form, may be inserted into the surgical cavity over the largest dilator, the dilators removed therefrom, and the retractor expanded to further enlarge the surgical cavity below the incision. 
     Yet another aspect of the present invention further provides a surgical retractor having a mount and blades as described previously. With the mount in an unexpanded state, the blades form a tube having an opening extending through the mount. This tube has an inside cross-sectional shape larger than that of the largest dilator. This allows for the retractor to be placed over the largest dilator and into the enlarged surgical cavity. In a preferred embodiment, the opening in the mount, the tube formed by the blades of the retractor, and the dilators are all of an oval cross-sectional configuration. However, it is recognized that other shapes and sizes are possible. 
     Another aspect of the present invention provides for a method of creating a larger surgical cavity through a smaller incision in the skin of a patient. A preferred method includes making an incision in the skin of a patient, securing the guide to a portion of the patient, moving a first smaller sized dilator over the guide to expand tissue, adding further increasingly sized dilators over one another and progressively dilating the incision until the desired surgical cavity size is achieved with a correspondingly sized dilator, sliding the retractor over the largest inserted dilator, removing all of the dilators through the retractor, and by using the actuator, rotating the two collar arms of the mount along the hinge axis thereby displacing the blades laterally and moving the patient&#39;s tissue to enlarge a surgical cavity. Alternatively, the guide, and all but the largest dilator, may first be removed from the cavity prior to insertion of the retractor. The amount of rotation of the collar arms of the mount along the hinge axis determines the enlargement of the surgical cavity. 
     Another aspect of the present invention further provides for a method wherein the blades of the retractor are first covered with a sheath before they are introduced into the body of the patient. The sheath, as discussed previously, allows the retractor to form a surgical cavity enclosed by the apparatus. This, in turn, allows for better use of the surgical cavity as surrounding tissue can be prevented from entering the cavity. It is also noted that the sheath may be transparent thus allowing visualization of the expanded cavity outside of the sheath. 
     Another aspect of the present invention further provides for a method wherein, prior to displacing the blades of the retractor, a rod is connected to a rigid, relatively fixed object on the rod&#39;s first end, and to the retractor on the rod&#39;s second end. This step allows for enhanced control of the retractor before and after it is inserted into the body of the patient. 
     Another aspect of the present invention further provides that the retractor be inserted into the body of a patient so that the blades of the retractor displace in the same direction in which the muscles run in the area of the incision. This step facilitates minimizing the amount of damage to the muscle tissue upon the expansion of the blades of the retractor. 
     Yet another aspect of the present invention further provides for a method for creating a surgical cavity in a body wherein, various elements of the present retractor or the entire retractor, are disposable. In a preferred embodiment, additional steps of removing the retractor and disposing of the entire apparatus are performed. In another embodiment, additional steps of removing the retractor and disposing of a portion of it, for example, the blades are performed. In yet another embodiment, additional steps of sterilizing a portion of the retractor and attaching a non-autoclavable, or otherwise non-sterilizable portion, to the sterilized portion are performed. Subsequent to use of the retractor, the non-autoclavable, or otherwise non-sterilizable portion can be disposed. 
     Another aspect of the present invention provides for a kit including the various elements of the present invention. The kit comprises differently sized and shaped mounts, blades, and sheaths. The different elements may be interchanged to conform to the given surgical situation. In another embodiment, a method is contemplated wherein elements of desired shape and size are selected and connected to one another to provide a retractor best suited to create the proper surgical cavity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of the mount portion of the retractor; 
         FIG. 2  is a perspective view of a blade of the retractor; 
         FIG. 3  is a side view of the blade of  FIG. 2 ; 
         FIG. 4  is a view of the inside of the blade of  FIG. 2 ; 
         FIG. 5  is a top view of the blade of  FIG. 2 ; 
         FIG. 6  is a perspective view of the retractor in the closed position; 
         FIG. 7  is a perspective view of the retractor in the open position; 
         FIG. 8  is a perspective view of a sheath; 
         FIG. 9  is a perspective view of the retractor in the open position with a sheath around the displaced blades; 
         FIG. 10  is a perspective view of a dilator assembly; 
         FIG. 11  is a perspective view of a retractor in the closed position with a sheath around the blades, placed over the dilator assembly. 
         FIG. 12  is a perspective view of another embodiment of a mount portion of the retractor. 
         FIG. 13  is a perspective cut-away view of half of a retractor in the closed position with the mount of  FIG. 12 ; 
         FIG. 14  is a perspective cut-away view of half of a retractor in the open position with the mount of  FIG. 12 ; and 
         FIG. 15  is a perspective view of a surgery set-up including a frame assembly supporting two retractors. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts one embodiment of the mount  10  with a first collar arm  11  and a second collar arm  12  rotatable around hinge axis  13 . Collar arms  11  and  12  are rotatably connected to each other at forward hinge point  14  and rearward hinge point  15 , and connected to frame  19  at first hinge  49  and second hinge  50 . Specifically, first collar arm  11  is connected to frame  19  at first hinge  49  by a first hinge pin  52  that extends through a first slot  56  in frame  19 . Similarly, second collar arm  12  is connected to frame  19  at second hinge  50  by a second hinge pin  54  that extends through a second slot  57  in frame  19 . Hinge points  14  and  15 , as well as hinges  49  and  50 , allow for the rotational movement of collar arms  11  and  12 . Additionally, slots  56  and  58  on frame  19  accommodate hinges  49  and  50 , respectively, and allow for the horizontal translation of hinges  49  and  50  with respect to frame  19 . Actuator  17  is oriented on frame  19  such that its rotational actuation causes it to translate distally (identified as DT in  FIG. 7 ). Thus, as actuator  17  translates distally, it acts upon collar arms  11  and  12  causing the rotation of collar arms  11  and  12  around hinge axis  13 , and causing hinge axis  13 , itself, to translate distally. Rotation around hinge axis  13  is facilitated and accompanied by rotation of collar arms  11  and  12  around hinges  49  and  50 , respectively, as well as translation of hinges  49  and  50  toward the center of frame  19  along slots  56  and  58 , respectfully. All this motion, in turn, causes the expansion of the apparatus. Other actuating mechanisms for expanding and contracting the retractor  1  are also envisioned. 
     Mount channel  18  is oval in shape and located centrally between first and second collar arms  11  and  12 . Mount channel  18  facilitates movement of instruments and other materials into and out of the surgical cavity created by the present invention. Mount channel  18  further comprises mount connection points  20 ,  21 ,  22 , and  23  that allow for the connection between collar arms  11  and  12  and blades  24  and  25  (FIGS.  2 , 3 , and  4 ). 
       FIGS. 2-5  show views of first blade  24 , which is a mirror image of second blade  25  (shown in  FIG. 6 , for example). First blade  24  has a proximal end  26 , a distal end  36 , an inner portion  68  and a peripheral portion  70 . Blade  24  also has blade connection points  27  and  28 , hole  72 , rearward slit  64  and forward slit  66 . Additionally, as seen in  FIGS. 3 and 4 , the distal end  36  of blade  24  is tapered toward its periphery  70  to facilitate easier insertion through tissue. 
     As shown in assembled form in  FIGS. 13 and 14 , for example, proximal end  26  of blade  24  is connected at blade connection points  27  and  28 , as well as at hole  72 , to corresponding connection points  22  and  23 , as well as pin  76 , on first collar arm  11 . Blade  24  gets connected to collar arm  11  by compressing proximal end  26 , therefore moving blade connection points  27  and  28  toward each other, so as to prepare for assembly with connection points  22  and  23  on collar arm  11 . Slits  64  and  66  facilitate this compression. It is recognized that compression of points  27  and  28  may be achieved by other configurations, and/or in other ways as well. 
     Once proximal end  26  is released from compression, blade  24  regains its original shape and firmly attaches to collar arm  11  through connections  27  to  22 ,  28  to  23 , and  72  to  76 . The male/female relationship of these connections, as well as the friction fit, allows the blade  24  to remain attached to the first collar arm  11  upon release of the compressive force that had been applied to the proximal end of blade  24 . 
     Since first blade  24  is a mirror image of second blade  25 , it is understood that the above description equally applies to the connection of second blade  25  to second collar arm  12 . It is further recognized that many other connection configurations from the ones described above are possible. Such configurations may permit for interchangeability of blades  24  and  25 , or just the removability of the blades for sterilization or disposability. Interchangeability allows a surgeon to readily change blades  24  and  25  depending upon, for example, the desired surgical cavity depth and/or cross-sectional area. Thus a surgeon may be provided with a kit of variably sized and shaped blades from which desired blades may be selected for a particular surgery or technique. Additionally, disposability of the blades allows for easier post-use handling techniques. 
       FIG. 5  shows a top view of first blade  24  where the blade&#39;s curvature is readily apparent. When placed together, blades  24  and  25  form a tube that is open at both the proximal and distal ends, with an oval channel therebetween. As shown in  FIG. 6 , this is the case when actuator  17  has not been translated distally and collar arms  11  and  12  have, therefore, not been rotated around hinge axis  13 . 
     Actuator  17  comprises a screw  60  that is threadably assembled in housing  62 , which is part of frame  19 . As best seen in  FIG. 7 , in opening the retractor  1 , upon distal translation DT of screw  60  through housing  62 , collar arms  11  and  12  rotate around hinge axis  13  as hinge axis  13  is moved distally. In conjunction with this motion, first collar arm  11  rotates in direction r 1  around first hinge  49  as hinge  49  translates in direction t 1  in slot  56  ( FIG. 1 ), and second collar arm  12  rotates in direction r 2  around second hinge  50  as hinge  50  translates in direction t 2  in slot  58  ( FIG. 1 ). In this manner, blades  24  and  25  are displaced in respective retraction directions R 1  and R 2 , and retractor  1  is opened. The displacement of blades  24  and  25  spreads apart tissue within the original incision and creates a larger surgical cavity, allowing for a larger working space for a surgeon. Additionally, as shown in  FIGS. 3 and 6 , for example, the distal ends  36  of blades  24  and  25  are tapered so as to allow easier insertion into the body of a patient. 
     It is recognized that the screw  60  may be engaged by a tool, such as screwdriver or an Allan key, to cause it to turn. Additionally, it is envisioned that multiple variations of the type of tool, interface with the screw, as well as screw types, or even the absence of a screw, are possible to accomplish moving the blades of the retractor towards and away from each other. 
     The material used in the construction of blades  24  and  25  is generally of a rigid type to support the spreading of the body tissue, such as aluminum, for example. In a preferred embodiment, the material is radiolucent or semi-radiolucent thereby allowing for the improved visualization of the anatomy when viewed on an X-ray with the retractor  1  in place. In other embodiments, the material may be non-autoclavable or otherwise non-sterilizable, and disposable. This further allows for the interchangeability of blades  24  and  25 , to suit a particular surgical cavity. 
       FIG. 8  shows an embodiment of a sheath  29  of the present invention. Sheath  29  is preferably made of a pliable, elastic, and translucent material, such as silicone rubber, and fits snugly around blades  24  and  25 . Preferably, sheath  29  is assembled over blades  24  and  25  when the retractor  1  is in the unexpanded condition, such as in  FIG. 6 . Upon distal translation DT of screw  60  of actuator  17 , and displacement R 1  and R 2  of blades  24  and  25 , sheath  29  stretches and forms an enclosure around blades  24  and  25 , as shown in  FIG. 9 . This enclosure allows for a more manageable surgical cavity by preventing tissue from entering the cavity. Sheath  29  may also be made of a completely clear material, so that when in the expanded condition, a surgeon may see tissue and objects through sheath  29  when it is in the surgical cavity. 
     Preferably, to prevent sheath  29  from riding up on blades  24  and  25  during the opening of the retractor  1 , the sheath  29  is sized slightly shorter than the length of the longest vertical peripheral dimension of blades  24  and  25 , as seen in  FIG. 3 . In this configuration, when retractor  1  is opened, the distal end of sheath  29  stretches over and hooks onto the distal central edges of the blades  24  and  25 , thus preventing the sheath&#39;s movement up the blades. 
     Upon the reverse translation of screw  60  and the return of blades  24  and  25  to their original state, sheath  29  returns to its original form as well. Depending on the pliability of the material used to construct sheath  29 , the sheath may aid in bringing blades  24  and  25  back to their original, unexpanded condition. In any event, the tissue surrounding the blades  24  and  25  aids in compressing the blades back to their unexpanded condition. It should be noted that various materials with the above desirable properties for the sheath  29  may improve the cost-effectiveness of the sheath&#39;s  29  disposability. Additionally, the sheath  29  may be of any shape or size and may cover any area of the retractor  1 , thereby creating any portion of covered and non-covered areas of blades  24  and  25 . 
       FIG. 10  shows dilator assembly  30 . This assembly is utilized prior to the introduction of retractor  1  into the body of the patient. Dilator assembly  30  includes guide  31  and increasingly sized dilators  32 ,  33 ,  34 , and  35 . Each of these dilators is a tube with an outside cross-section and an inside cross-section. The inside cross-section of each dilator is slightly larger than the outside cross-section of the next smallest dilator, while the outside cross-section of each dilator is slightly smaller than the inside cross-section of the next largest dilator. This allows for successive dilators to be placed over one another. Initially, guide  31  is inserted through an incision and secured within the body of a patient. Dilator  32  is then slid over guide  31  into the incision, thereby spreading the incision, and creating a surgical cavity having an area corresponding to the size of the dilator&#39;s outside cross-section. This step is repeated with successive dilators  33 ,  34 , and  35  until the desired surgical cavity is achieved. It should be noted that any quantity of variously-sized dilators may be used to achieve this surgical cavity. Additionally, the dilators may be of any size or shape as long as they interact with one another as described above and allow the surgical cavity to be created and enlarged. 
     With reference to  FIG. 11 , subsequent to inserting all the desired dilators into the incision, retractor  1  is inserted over the largest dilator  35  in the cavity. This is done while blades  24  and  25  are together, whereby they form a passage extending distally from mount channel  18 . This passage is large enough to accommodate the largest dilator  35  within it. Additionally, the tapered distal ends  36  of blades  24  and  25  facilitate easier insertion through the tissue. 
     Once retractor  1  is in place over the largest dilator  35 , the guide  31  and all dilators  32 - 35  are removed from the surgical cavity. This leaves an opening corresponding to the passage extending from the proximal ends  26  to the distal ends  36  of the blades  24  and  25 . Blades  24  and  25  of retractor  1  may then be expanded, thus enlarging the surgical cavity. It is also contemplated that retractor  1  may be inserted into the body in an orientation allowing blades  24  and  25  to displace in the same direction in which the muscles run in the area of the surgical site. Orienting retractor  1  in this fashion helps minimize muscle tissue damage and contributes to a faster recovery time from surgery for the patient. However, retractor  1  may be oriented in any fashion necessary to create a larger surgical cavity, in any area of the body. The introduction of retractor  1  into the body of a patient allows for the preservation of a small portal at the skin&#39;s surface. 
       FIGS. 12-14  show another preferred embodiment of a retractor  2  of the present invention. This retractor  2  features a different frame  80  and actuator arrangement  90  from frame  19  and actuator  17  of retractor  1 . Here, actuator  90  comprises a screw  96  threadably engaged in an actuator housing  94 , and a ball  100  within the housing  94 . The ball  100  rides on a bearing element  106  that resides on hinge pin  102 . Hinge pin  102  couples the first and second collar arms  11  and  12  together at rearward hinge point  15 , while hinge pin  104  couples collar arms  11  and  12  together at forward hinge point  14 . Both hinge pins,  102  and  104 , are on the same hinge axis  13 . It is understood, however, that other variations are also possible. 
     The housing  94  is part of frame  80 , but is oriented at an angle that is other than parallel to hinge axis  13 . Additionally, the exterior  92  of housing  94  is shaped to serve the same function as retractor connection segment  16  of retractor  1 , which is to facilitate coupling the retractor to a support structure that aids in maintaining the position of the retractor in place relative to the patient. The proximal interior of housing  92  contains a stop ring  98  which serves as a restriction to retraction of screw  96  beyond the proximal end of housing  94 , to prevent screw  96  from being inadvertently removed from housing  94  during the closing of retractor  2 . 
     Further, collar arms  11  and  12  also have cutouts  82  and  84 , respectfully, which aid in attaching and removing blades  24  and  25  to collar arms  11  and  12 , by providing additional manipulation space for the proximal ends  26  of blades  24  and  25 . 
       FIGS. 13 and 14  show a cut-away view of half of retractor  2 , where actuator  90 , frame  80 , first collar arm  11 , and first blade  24  are visible.  FIG. 13  shows retractor  2  in the closed position, while  FIG. 14  shows retractor  2  in the open position. 
     Beginning with the closed arrangement of retractor  2  in  FIG. 13 , to expand the blades  24  and  25  of the retractor  2 , screw  96  is advanced distally in housing  94 . As screw  96  is advanced, it pushes on ball  100 , which, in turn, pushes on bearing element  106 . Bearing element  106  is coupled to hinge pin  102  which is part of rearward hinge point  15 . Hinge pin  102  rotatably joins collar arms  11  and  12 , and hinge point  15  is capable of moving distally. Thus, as screw  96  is advanced, ball  100  pushes downwardly on bearing element  106 . Bearing element  106  then moves downwardly together with hinge pin  102 , which causes hinge point  15  to move distally and, therefore, blades  24  and  25  to expand from the closed configuration in  FIG. 13  to the open configuration in  FIG. 14 . The amount of distal movement of hinge point  15  is the same as the vertical component of the movement of ball  100  from its position in  FIG. 13  to its position in  FIG. 14 . Thus, in opening the retractor  2 , ball  100  moves from an elevated rearward position on bearing element  106 , as shown in  FIG. 13 , to a lowered forward position on bearing element  106 , as shown in  FIG. 14 . 
     Preferably, ball  100  is made of a ceramic material, and has a low-friction surface. The ceramic material is used for the resulting strength of the ball  100 , while the low-friction surface is to diminish the undesirable friction forces associated with the functioning of actuator  90 , which otherwise increase the effort required to open the retractor  2 . Bearing element  106  and screw  96  may be made of any suitable material, and have any suitable surface finish, to compliment and improve the functionality and compatibility of the retractor  2 , given the above parameters. For example, the tip of screw  96  that contacts ball  100 , may have a low-friction surface to further diminish the frictional forces involved in advancing ball  100  along bearing element  106 . 
       FIG. 15  shows a typical configuration where one or more retractors are used in conjunction with a support assembly  47 . The support assembly  47  comprises a first bar  37  connected to a first retractor  43  through a first holder  38 . Optionally, there is a second bar  44  connected to a second retractor  45  through a second holder  46 . The first and second bars are joined together at coupling  48 . The support assembly  47  is ultimately attached to a rigid structure that facilitates maintaining the retractors  43  and  45  in relative position with respect to the patient. 
     An example of a support assembly of this type is the AF400 SpineTract System manufactured by Omni-Tract Surgical, a division of Minnesota Scientific. However, different support assemblies can be used, including but not limited to single support assemblies, where only one retractor is utilized. 
     It is further contemplated that the retractor of the present invention may be utilized on any part of the patient where a small incision but large subcutaneous operating area is desirable. 
     It is also contemplated that objects including but not limited to surgical instruments, surgical implants, and connection devices can be introduced into the body of a patient through the retractor of the present invention. The methods of use, as described above, may be performed with one or more retractors, with or without support assemblies, and in sequences different from those described. Additionally, the steps utilizing dilators may or may not be performed. Alternatively, various quantities, sizes, or shapes of dilators may be utilized. Finally, the present invention may be a kit encompassing the various elements disclosed above. This kit may include, but is not limited to, differently sized and shaped mounts  10 , blades  24  and  25 , and sheaths  29 . Any or all of these different elements may be interchanged to suit the desired surgical cavity. Depending upon the conditions, a surgeon may select different mounts  10 , blades  24  and  25 , and sheaths  29  for assembly and use. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.