Abstract:
The retractor system for use in spinal surgery and other types of surgical procedures that is a simple and efficient solution for minimally invasive access to thoracolumbar spine is disclosed. The fully customizable design allows the surgeon to independently angle the retractor blades and expand the retractor in both cephalad-caudal and medial-lateral directions. With an offering of a range of blade lengths, access can be tailored to the patient&#39;s anatomy. The retractor system provides versatility and control ensuring minimal tissue trauma.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and benefit of U.S. Provisional Patent Application Ser. No. 61/717,202 entitled “Retractor” filed on Oct. 23, 2012 which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     This invention relates to surgical instruments and methods and, more particularly, to surgical retractors for use in spinal surgery and other types of surgical procedures. 
     BACKGROUND 
     Surgical procedures often require the creation of a surgical exposure to clear the field for the surgeon and to provide access to the desired area. The surgical exposure is usually started with an incision of a suitable depth. Surgical instruments known as retractors are then inserted into the incision and used to pull back skin, muscle and other soft tissue to permit access to the region of interest, reach deeper regions of the body, protect adjacent tissues and provide the surgeon with clear visibility of the area of the surgical field. 
     A typical retractor is made up of a retractor body attached to one or more retractor blades. Retractor blades are smooth, thin plates with dull edges that are inserted into the incision to pull back the tissue. Retractor blades come in many different sizes depending on the particular application and physical characteristics of the patient. Retractor blades may be slightly curved or completely flat and may have end prongs of various configurations to make it easier to pull back tissue. The retractor blades can be attached to a wide variety of retractor bodies, such as for hand-held and self-retaining retractors. 
     Hand-held retractors are made up of a simple grip attached to a retractor blade. The retractor blade may be fixed or interchangeable. The retractor blade is inserted into the incision and then the grip is used to pull back the blade to create the surgical exposure. The grip may be attached at an angle to the retractor blade to make it easier to pull back on the blade. Hand-held retractors must be held in place by hand in order to maintain the surgical exposure. 
     Self-retaining retractors have specialized retractor bodies that allow them to maintain a surgical exposure without needing to be held in place by hand. Two common self-retaining retractors are longitudinal retractors and transverse retractors. 
     Longitudinal retractors have a retractor body made up of two seesawing arms with a pair of opposed retractor blades on their respective ends. The retractor body typically has a ratcheting mechanism to lock apart the two opposed retractor blades and hold them in place. This maintains the surgical exposure without the need for the retractor to be held in place by hand. The two arms may be hinged to facilitate access to the retraction site. The retractor blades may be either fixed or interchangeable. 
     Transverse retractors have a retractor body made up of a transverse rack with a fixed arm and a sliding arm. The fixed arm and sliding arm have opposed retractor blades on their respective ends. The sliding arm typically has a turnkey that operates a ratcheting mechanism, which ratchets the sliding arm away from the fixed arm and locks apart the retractor blades. The two arms may be hinged to facilitate access to the retraction site. The retractor blades may be either fixed or interchangeable. 
     The retractors in use today retract the opening created in the body of the patient in a uniform manner. If the surgeon needs a large opening near the spine, for instance, the opening in the body of the patient is typically retracted in a uniform manner. In an “open” spinal surgical procedure, large bands of muscles in the back are stripped free from the spine and retracted off to each side. This allows for excellent visualization of the spine and easy access for the surgeon. The downside of “open” surgery is that there can be considerable back pain from the muscle retraction. Also, the muscles develop some degree of permanent scar formation and damage as a result of the necessary retraction. This creates significant trauma for the patient and increases the patient&#39;s recovery time. What is needed is a surgical retractor customized for spinal surgery that gives a surgeon a suitable area within the body to work on the patient while reducing the required incision size. This reduces trauma to the patient and reduces the patient&#39;s recovery time. 
     SUMMARY 
     According to one aspect of the invention, a surgical retractor is disclosed. The surgical retractor includes a first rail and a second rail connected at an angle and defining a retractor plane. The first rail includes an outer surface and a plurality of teeth recessed with respect to the outer surface such that the plurality of teeth does not extend beyond the outer surface. The second rail includes an outer surface and a plurality of teeth recessed with respect to the outer surface such that the plurality of teeth of the second rail does not extend beyond the outer surface of the second rail. The retractor further includes a first slider configured to slide inwardly and outwardly along the first rail and carry a first blade at an angle to the retractor plane. The first slider includes a first lock configured to arrest movement of the first slider in at least one direction relative to the first rail. The first slider includes a plurality of bearings arranged about the outer surface of the first rail such that the plurality of bearings does not contact the plurality of teeth of the first rail. The second slider is configured to slide inwardly and outwardly along the second rail and carry a second blade at an angle to the retractor plane. The second slider includes a second lock configured to arrest movement of the second slider in at least one direction relative to the second rail. The second slider includes a plurality of bearings housed in the second slider and arranged about the outer surface of second rail such that the plurality of bearings does not contact the plurality of teeth of the second rail. 
     According to another aspect of the invention, a surgical retractor is disclosed. The surgical retractor includes a first rail and a second rail connected at an angle and defining a retractor plane. The first rail includes an outer surface and a plurality of teeth recessed with respect to the outer surface such that the plurality of teeth does not extend beyond the outer surface. The second rail includes an outer surface and a plurality of teeth recessed with respect to the outer surface such that the plurality of teeth of the second rail does not extend beyond the outer surface of the second rail. The retractor further includes a first slider configured to slide inwardly and outwardly along the first rail and carry a first blade at an angle to the retractor plane. The first slider includes a first lock configured to arrest movement of the first slider in at least one direction relative to the first rail. The first slider includes a plurality of bearings arranged about the outer surface of the first rail such that the plurality of bearings does not contact the plurality of teeth of the first rail. The second slider is configured to slide inwardly and outwardly along the second rail and carry a second blade at an angle to the retractor plane. The second slider includes a second lock configured to arrest movement of the second slider in at least one direction relative to the second rail. The second slider includes a plurality of bearings housed in the second slider and arranged about the outer surface of second rail such that the plurality of bearings does not contact the plurality of teeth of the second rail. The retractor further includes a third slider configured to slide inwardly and outwardly along the first rail and carry a third blade at an angle to the retractor plane. The third slider includes a third lock configured to arrest movement of the third slider in at least one direction relative to the first rail. The third slider includes a plurality of bearings arranged about the outer surface of the first rail such that the plurality of bearings does not contact the plurality of teeth of the first rail. The second rail is connected to the third slider. The further including a third rail connected to the second slider. The third rail is in the retractor plane and angled with respect to the first rail. The third rail includes an outer surface and a plurality of teeth recessed with respect to the outer surface such that the plurality of teeth does not extend beyond the outer surface. A fourth slider is configured to slide inwardly and outwardly along the third rail and carry a fourth blade at an angle to the retractor plane. The fourth slider includes a fourth lock configured to arrest movement of the fourth slider in at least one direction relative to the third rail. The fourth slider includes a plurality of bearings arranged about the outer surface of the third rail such that the plurality of bearings does not contact the plurality of teeth of the third rail. 
     According to another aspect of the invention a surgical retractor is discloses. The retractor includes at least two retractor blades that extend from a retractor body that are insertable into a surgical site. At least one of the retractor blades is movable relative to the other in order to expand the surgical site. The retractor body includes at least one rail and at least one slider. The at least one slider carries at least one retractor blade and is configured to move bidirectionally on the rail. The slider has an inner surface defining a passageway that is sized larger than the rail. The passageway is configured to receive the rail in the passageway such that the rail does not contact the inner surface and is configured to contact a plurality of antifriction bearings disposed inside the slider. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of the retractor according to the present invention. 
         FIG. 2  is a top view of the retractor according to the present invention. 
         FIG. 3  is a side elevation view of the retractor according to the present invention. 
         FIG. 4  is an end elevation view of the retractor according to the present invention. 
         FIG. 5  is an end elevation view of the first rail according to the present invention. 
         FIG. 6  is a top view of the first rail according to the present invention. 
         FIG. 7  is an exploded top perspective view of the first rail according to the present invention. 
         FIG. 8  is a top perspective view of a track according to the present invention. 
         FIG. 9  is a top view of a track according to the present invention. 
         FIG. 10  is a sectional view of a track according to the present invention. 
         FIG. 11  is a top perspective view of stop pin according to the present invention. 
         FIG. 12  is top perspective exploded view of the first slider and second rail according to the present invention. 
         FIG. 13A  is a top perspective view of the housing of the first slider according to the present invention. 
         FIG. 13B  is a bottom perspective view of a housing of the first slider according to the present invention. 
         FIG. 13C  is an end elevational view of a housing of the first slider according to the present invention. 
         FIG. 13D  is a cross-sectional view taken along line B-B of  FIG. 13C  of a housing of the first slider according to the present invention. 
         FIG. 14  is a top perspective view of a tow angle post according to the present invention. 
         FIG. 15A  is a top perspective view of the blade mount according to the present invention. 
         FIG. 15B  is a top view of the blade mount according to the present invention. 
         FIG. 16  is a top perspective view of a tow angle return according to the present invention. 
         FIG. 17A  is a top perspective view of a cylindrical bearing according to the present invention. 
         FIG. 17B  is a top perspective view of a pin according to the present invention. 
         FIG. 18A  is a top perspective view of a lock according to the present invention. 
         FIG. 18B  is a cross-sectional view of a lock according to the present invention. 
         FIG. 19  is a top perspective view of the lock spring according to the present invention. 
         FIG. 20  is a side elevation view of the second rail according to the present invention. 
         FIG. 21  is a top view of the second rail according to the present invention. 
         FIG. 22  is a top perspective exploded view of the second rail according to the present invention. 
         FIG. 23  is an exploded view of the third slider according to the present invention. 
         FIG. 24A  is top perspective view of the housing of the third slider according to the present invention. 
         FIG. 24B  is a bottom perspective view of the housing of the third slider according to the present invention. 
         FIG. 24C  is an end elevational view of the housing of the third slider according to the present invention. 
         FIG. 24D  is a cross-sectional view taken along line B-B of  FIG. 24C  of the housing of the third slider according to the present invention. 
         FIG. 25  is top perspective exploded view of the second slider and third rail according to the present invention. 
         FIG. 26A  is a top perspective view of the housing of the second slider according to the present invention. 
         FIG. 26B  is a bottom perspective view of the housing of the second slider according to the present invention. 
         FIG. 26C  is an end elevational view of the housing of the second slider according to the present invention. 
         FIG. 26D  is a cross-sectional view taken along line B-B of  FIG. 26C  of the housing of the second slider according to the present invention. 
         FIG. 27  is a top perspective exploded view of the fourth slider according to the present invention. 
         FIG. 28A  is a top perspective view of the housing of the fourth slider according to the present invention. 
         FIG. 28B  is a bottom perspective view of the housing of the fourth slider according to the present invention. 
         FIG. 28C  is an end elevational view of the housing of the fourth slider according to the present invention. 
         FIG. 28D  is a cross-sectional view taken along line B-B of  FIG. 28C  of the housing of the fourth slider according to the present invention. 
         FIG. 29A  is a top perspective view of the blade according to the present invention. 
         FIG. 29B  is an end elevational view of the blade according to the present invention. 
         FIG. 29C  is a top view of the blade according to the present invention. 
         FIG. 30A  is a top perspective view of the blade instrument according to the present invention. 
         FIG. 30B  is a side elevational view of the blade instrument according to the present invention. 
         FIG. 30C  is an end elevational view of the blade instrument according to the present invention. 
         FIG. 31A  is an end elevational view of the blade instrument connected to the blade according to the present invention. 
         FIG. 31B  is a cross-sectional view taken along line L-L of  FIG. 31A  of the blade instrument connected to the blade according to the present invention. 
         FIG. 31C  is an end elevational view of the blade instrument connected to the blade according to the present invention. 
         FIG. 31D  is a cross-sectional view taken along line M-M of  FIG. 31C  of the blade instrument connected to the blade according to the present invention. 
         FIG. 32  is a partial sectional view of a blade connected to the blade mount according to the present invention. 
         FIG. 33  is a side view of a slider instrument according to the present invention. 
         FIG. 34A  is a top perspective view of the distraction instrument and retractor according to the present invention. 
         FIG. 34B  is a top perspective view of the distraction instrument and retractor according to the present invention. 
         FIG. 35A  is a top perspective view of the retractor with the first and second sliders distracted according to the present invention. 
         FIG. 35B  is a top view of the retractor with the first and second sliders distracted according to the present invention. 
         FIG. 35C  is an end elevational view of the retractor with the first and second sliders distracted according to the present invention. 
         FIG. 35D  is a side elevational view of the retractor with the first and second sliders distracted according to the present invention. 
         FIG. 36A  is a top perspective view of the retractor with the first, second, third and fourth sliders distracted with respect to each other according to the present invention. 
         FIG. 36B  is a top view of the retractor with the first, second, third and fourth sliders distracted with respect to each other according to the present invention. 
         FIG. 36C  is an end elevational view of the retractor with the first, second, third and fourth sliders distracted with respect to each other according to the present invention. 
         FIG. 36D  is a side elevational view of the retractor with the first, second, third and fourth sliders distracted with respect to each other according to the present invention. 
         FIG. 37A  is a top perspective view of the retractor with the first, second, third and fourth sliders distracted and the blades angled outwardly according to the present invention. 
         FIG. 37B  is a top view of the retractor with the first, second, third and fourth sliders distracted and the blades angled outwardly according to the present invention. 
         FIG. 37C  is an end elevational view of the retractor with the first, second, third and fourth sliders distracted and the blades angled outwardly according to the present invention. 
         FIG. 37D  is a side elevational view of the retractor with the first, second, third and fourth sliders distracted and the blades angled outwardly according to the present invention. 
         FIG. 38A  is a top perspective view of the retractor with the third slider distracted relative to the first slider and the fourth slider distracted relative to the second slider and the blades angled according to the present invention. 
         FIG. 38B  is a top view of the retractor with the third slider distracted relative to the first slider and the fourth slider distracted relative to the second slider and the blades angled according to the present invention. 
         FIG. 38C  is an end elevational view of the retractor with the third slider distracted relative to the first slider and the fourth slider distracted relative to the second slider and the blades angled according to the present invention. 
         FIG. 38D  is a side elevational view of the retractor with the third slider distracted relative to the first slider and the fourth slider distracted relative to the second slider and the blades angled according to the present invention. 
         FIG. 39  is a perspective view of a medial blade according to the present invention. 
         FIG. 40  is a perspective view of a medial blade connected to the retractor according to the present invention. 
         FIG. 41  is a perspective view of three medial blades connected to the retractor according to the present invention. 
         FIG. 42A  is a top perspective view of another variation of the retractor according to the present invention. 
         FIG. 42B  is a top view of another variation of the retractor according to the present invention. 
         FIG. 42C  is an end elevational view of another variation of the retractor according to the present invention. 
         FIG. 42D  is a side elevational view of another variation of the retractor according to the present invention. 
         FIG. 43A  is a top perspective view of the retractor of  FIG. 42  with the sliders extended according to the present invention. 
         FIG. 43B  is a top view of the retractor of  FIG. 42  with the sliders extended according to the present invention. 
         FIG. 43C  is an end elevational view of the retractor of  FIG. 42  with the sliders extended according to the present invention. 
         FIG. 43D  is a side elevational view of the retractor of  FIG. 42  with the sliders extended according to the present invention. 
         FIG. 44  is a top perspective section view of a retractor according to the present. 
     
    
    
     DETAILED DESCRIPTION 
     Before the subject devices, systems and methods are described, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. 
     It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a spinal segment” may include a plurality of such spinal segments and reference to “the screw” includes reference to one or more screws and equivalents thereof known to those skilled in the art, and so forth. 
     All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. 
     The present invention is described in the accompanying figures and text as understood by a person having ordinary skill in the field of surgical retractors. 
     In use, the whole retractor assembly shown in the figures is introduced into the surgical field. Upon introduction, the initial configuration of the retractor is in a closed position such that the retractor blades extend downwardly and all of the distal ends of each blade are in close proximity to one another to allow ease of introduction. Once inserted at the desired location, the retractor forms a small field of visibility. The surgeon then causes the blades to be expanded outwardly by operating the various constructs shown in the figures to customize the degree and directions of retraction. One or more of the blades rotate outwardly and/or translate along multi-axial directions. Once in position, the blades are then locked to achieve a custom retraction according to surgeon preference and patient anatomy. The expanded blades act to spread the muscle and tissue further to provide retraction beyond the ring of view formed when the retractor is first inserted. The retractor of the present invention is customized for the demands of spinal surgery and reduces the “creep” of muscle or other tissue into the surgical field leaving a larger and more secure surgical area to be exposed for surgical access, increased visibility and stability. 
     The entire device may be constructed of surgical steel, or alternatively, various components of the device may be constructed of one or more materials selected from the group consisting of stainless steel, titanium and plastics. 
     With reference to the figures, the retractor will now be described in detail. Various views of a retractor  10  according to the present invention are shown in  FIGS. 1-4 . The retractor  10  includes at least one main or first rail  12 . A first slider  14  and a second slider  16  are connected to the at least one main rail  12 . A second rail  18  is connected to the first slider  14  and a third rail  20  is connected to the second slider  16 . A third slider  22  is connected to the second rail  18  and a fourth slider  24  is connected to the third rail  24 . The main or first rail  12 , the second rail  18  and third rail  20  together with first, second, third and fourth sliders  14 ,  16 ,  22 ,  24  are all coplanar or parallel to the X-Y plane. The three rails  12 ,  18 ,  20  form three coplanar sides of a polygon in the X-Y plane and the sliders  14 ,  16 ,  22 ,  24  each carry at least one blade  26 . Each of the blades  26  extends downwardly from the sliders  14 ,  16 ,  22 ,  24  in a direction substantially perpendicular to the X-Y plane and in a direction substantially parallel to the Z-axis. In the variation shown, the second rail  18  is connected to the first slider  14  such that the second rail  18  is substantially perpendicular to the first rail  12  and the third rail  20  is connected to the second slider  16  such that the third rail  20  is substantially perpendicular to the first rail  12 . Therefore, the polygon formed in the X-Y plane is a three-sided rectangle or three-sided square with the side opposite and parallel to the main or first rail  12  being absent or open. The interior of the retractor polygon defines the retractor zone. 
     Turning now to  FIGS. 5-7 , there is shown a first or main rail  12  according to the present invention. The main rail  12  is an elongate, straight bar that is made of metal such as surgical steel or titanium. The main rail  12  includes a first distal end  28  and a second distal end  30  and has a top surface  32  and a bottom surface  34  interconnected by an inner surface  36  and an outer surface  38  to define a substantially square or rectangular cross-section perpendicular to the longitudinal axis of the main rail  12 . A curved first end surface  40  is formed at the first distal end  28  and a curved second end surface  42  is formed at the second distal end  30 . 
     A handle  44  is optionally included with the first rail  12 . The handle  44  includes a leg  46  that is inserted into a leg opening (not shown) formed in the outer surface  38  of the main rail  12 . A pin  52  is passed through an aperture  54  in the top surface  32 , through a pin aperture  50  formed in the leg  46  and into an aperture  56  formed in the bottom surface  34  and the pin  52  is laser welded to connect the handle  44  to the main rail  12 . 
     The main rail  12  further includes at least one track  58 .  FIGS. 5-7  show a variation having a first track  58   a  and a second track  58   b  connected to the main rail  12 . Although two tracks  58   a ,  58   b  are shown the invention is not so limited and multiple tracks or a single track that is longer is within the scope of the present invention. The first track  58   a  is disposed in a first track-receiving portion  60  and the second track  62  is disposed in a second track-receiving portion  64 . Each of the first and second tracks  58 ,  62  is an elongate bar having a square or rectangular cross-section taken perpendicular to the longitudinal axis or has a cross-section that has the same shape as, although smaller in size than, the cross-section of the first rail  12  within which it is disposed. In the variation shown in  FIGS. 5-7 , the first track  58  is identical to the second track  62  having the same length, shape and configuration that can be seen in greater detail in  FIGS. 8-10 . 
     Turning now to  FIGS. 8-10 , the track  58  includes a flat top surface  66  and a flat bottom surface  68  interconnected by a toothed inner surface  70  and a flat outer surface  72 . Pin apertures  74  extend from the top surface  66  to the bottom surface  68  and are sized and configured for receiving pins  52  for connecting the at least one tracks  58  to a rail. The inner surface  70  of the track  58  is toothed providing a gearing surface or rack for engagement with respective sliders to lock or permit motion of the respective sliders relative to the rail. The inner surface  70  is provided with a plurality of teeth  76 , the detail of which is shown in  FIG. 10 . 
     With particular reference to  FIG. 10 , two adjacent teeth  76  are shown. Each tooth  76  includes a right flank  78  interconnected to a left flank  80  at a top land  82  or point. At least one of the right or left flanks  78 ,  80  is substantially perpendicular to a baseline  84  and at least one of the right or left flanks  78 ,  80  is angled with respect to the baseline  84 . In  FIG. 10 , the left flank  80  is shown angled with respect to the baseline  84  to permit unidirectional movement of a slider, gear tooth or locking tooth in a direction from the left flank  80  toward the right flank  78 . 
     Turning back to  FIGS. 5-7 , the first track-receiving portion  60  is sized and configured to receive the first track  58   a  and the second track-receiving portion  64  is sized and configured to receive the second track  58   b . The first and second track-receiving portions  60 ,  64  are recesses or channels sized and configured to receive their respect tracks  58   a ,  58   b . Pins  52  are passed through apertures  54  in the top surface  32  and bottom surface  34  of the first rail  12  and through pin apertures  74  in the tracks  58 ,  62 . The pins  52  are laser welded to connect the tracks  58 ,  62  to the first rail  12 . As mentioned above, a variation having a single track is within the scope of the invention; wherein the single track is longer and extends across most of the first rail to permit engagement with both sliders  14 ,  16 . 
     Still referencing  FIGS. 5-10 , the two tracks  58   a ,  58   b  provide the first rail  12  with two toothed surfaces  70  such that the teeth  76  are recessed from the inner surface  36  of the first rail  12  as can be seen in  FIG. 6 . The teeth  76  do not protrude or extend beyond the outer surface  36  of the first rail  12 . In one variation, the top land  82  of each tooth  76  is even with the outer surface  36  of the rail  36 . In another variation, the top land  82  is slightly recessed or setback from the outer surface  36  of the top rail  12 . In general, the right or left flanks  78 ,  80  do not protrude beyond the outer surface  36  of the first rail  12 . Thereby, the tracks  58   a ,  58   b  are set within the respective receiving portions  60 ,  64 . In another variation, the first rail  12  does not include first and second tracks  58   a ,  58   b  located within first and second track-receiving portions  60 ,  64 , respectively; instead, the first rail  12  itself is provided with at least one toothed surface as described integrally formed with the rail  12  instead of being formed as insertable tracks separate from the rail. Furthermore, the at least one toothed surface can be located along one or more surfaces of the first rail  12  such as the top surface  32 , bottom surface  34 , inner surface  36  and/or outer surface  38 . 
     The tracks  58   a ,  58   b  are configured to engage a locking tooth of the first and second sliders  14 ,  16  to lock the first and second sliders  14 ,  16  from movement relative to the first rail  12 . Disengagement of a locking tooth from the one of the sliders  14 ,  16  permits the disengaged slider to move relative to the first rail  12 . In another variation, engagement of the locking tooth with a track  58  locks the slider only in one direction along the Y-axis and the slider is free to move in the opposite direction. This unidirectional locking of a slider advantageously facilitates the opening or increasing of the retractor zone without requiring the release of the locking tooth. Preferably, the track and locking tooth are configured such that the locking tooth and track  58  locks movement of the slider in a direction that closes reduces the retraction zone. In other words, the sliders  14 ,  16  are permitted to move outwardly away from the handle  44  along the first rail  12  by the locking tooth ramping over one of the right or left flanks. For example, in the first track  58   a , the right flanks  78  are angled to permit movement of the first slider  14  along the first rail  12  in an outwardly direction with the locking tooth engaged. In the second track  58   b , the left flanks  80  are angled to permit movement of the second slider  16  in an outwardly direction with the locking tooth engaged. 
     Still referencing  FIGS. 5-10 , the first track  58   a  is placed proximally to the first distal end  28  of the first rail  12  such that the left flanks  80  of all of the teeth  76  on the first track  58  are configured to permit unidirectional travel of the first slider  14  in a direction parallel to the X-axis and away from the handle  44  and toward the first distal end  28 . Hence, the left flanks  80  of all of the teeth  76  on the first track  58  are perpendicular to the base  84  or top land  82  and the right flanks  78  are angled to permit the first slider  14  to move outwardly toward the first distal end  28  but prevent or restrict movement of the first slider  14  toward the handle  44  or the second distal end  30  while the locking tooth is engaged. 
     The second track  60  is placed proximally to the second distal end  30  of the first rail  12  such that the left flanks  80  of all of the teeth  76  on the second track  60  are configured to permit unidirectional travel of the second slider  16  in a direction parallel to the X-axis and away from the handle  44  and toward the second distal end  30 . Hence, the right flanks  78  of all of the teeth  76  on the second track  60  are perpendicular to the base  84  or top land  82  when viewed from the top and the left flanks  78  are angled to permit the second slider  16  to move outwardly toward the second distal end  30  but prevent or restrict movement of the second slider  16  toward the handle  44  or the first distal end  28  while the locking tooth of the slider is engaged. 
     Still referencing  FIGS. 1-7  and  FIG. 11 , the first rail  12  includes an aperture  54  near the first distal end  28  extending from the top surface  32  to the bottom surface  34  of the first rail  12  configured to receive a stop pin  86  having an enlarged head  88  as shown in  FIG. 11 . The enlarged head  88  is positioned above the top surface  32  when the stop pin  86  is in place and serves to stop the sliding motion of the first slider  14  preventing it from moving off the first rail  12 . A similar aperture  54  is located near the second distal end  30  extending from the top surface  32  to the bottom surface  34  of the first rail  12  configured to receive a stop pin  86  having an enlarged head  88 . The enlarged head  88  extends above the top surface  32  when the stop pin  86  is in place and serves to stop the sliding motion of the second slider  16  preventing it from falling off the first rail  12 . Of course, the stop pins  86  are placed after the sliders  14 ,  16  are connected to the first rail  12 . The sliders  14 ,  16  are arrested when traveling toward the handle  44  by abutting the handle  44  itself. 
     Turning now to  FIGS. 12-13 , the first slider  14  will now be described. The slider  14  includes a housing  90 , a blade mount  92 , a plurality of antifriction bearings  94  and a lock  96  shown in  FIGS. 18   a - 18   b.    
     The housing  90  of the first slider  14  is made of any suitable material including any metal such as steel, surgical steel or titanium and defines a first rail receiving portion  100  and a second rail receiving portion  102 . The housing is polygonal forming a substantially L-shaped structure having a top surface  104  and a bottom surface  106  interconnected by a plurality of side walls having side surfaces  108  to the outside to define the housing  90 . The first rail receiving portion  100  is formed as a channel or passageway sized and configured to receive the first rail  12  in sliding engagement therein. The passageway of first rail receiving portion  100  includes a first opening formed in a side surface  108  at one end of the housing  90  and extends to a second opening formed in a side surface  108  at a second end of the housing directly opposite from the first opening to define the passageway. The passageway has a cross-sectional area that is slightly larger than the cross-sectional area of the first rail  12  and a cross-sectional shape that is the same as the cross-sectional shape of the first rail  12 . 
     The housing  90  includes a second rail receiving portion  102 . The second rail receiving portion  102  is formed as a channel or passageway that is sized and configured to receive the second rail  18  therein. The passageway of second rail receiving portion  102  includes a first opening formed in a side surface  108  at one end of the housing  90 . A second opening formed in a side surface  108  at a second end opposite the first opening is optional as an alternative variation. The passageway extends from the first opening into the housing  90  and does not necessarily have to extend or open to the second surface  108  opposite the first opening. The passageway has a cross-sectional area that is slightly larger than the cross-sectional area of the second rail  18  and a cross-sectional shape that is the same as the cross-sectional shape defined by the second rail  18 . The first rail receiving portion  100  and the second rail receiving portion  102  are shown to be perpendicular to each other with the first rail receiving portion  100  substantially parallel to the Y-axis and the second rail receiving portion substantially parallel to the X-axis. Although the first and second rail receiving portions  100 ,  102  are shown to be configured at 90 degrees to each other, the invention is not so limited and the first and second rail receiving portions  100 ,  102  can be angled with respect to each other. For example, the angle between the first and second rail-receiving portions  100 ,  102  can be acute at approximately 30 degrees as angled as far apart as approximately 150 degrees. 
     The housing  90  further includes a lock receiving portion  110 . The lock receiving portion  110  is sized and configured to receive a lock  96  therein. The lock receiving portion  110  intersects with the first rail receiving portion  100 , preferably, at approximately 90 degrees. The lock receiving portion  110  includes an opening  112  in a side surface  108  of the housing  90  and defines a channel or passageway extending inwardly from the opening  112  and into the housing  90 . The lock receiving portion  110  traverses or crosses the first rail receiving portion  100 . The lock receiving portion  110  includes a back wall or stop  114  formed at the inside end of the lock receiving portion  110 . In the variation shown in  FIGS. 13   a - 13   d , the lock receiving portion  110  is aligned with the second rail receiving portion  102 , both being perpendicular to the first rail receiving portion  100 . 
     Still referencing  FIGS. 13   a - 13   d , the housing  90  further includes one or more bearing receiving portions  116  along at least two sides of the first rail receiving portion  100  and interconnecting with the first rail receiving portion  100 . The bearing receiving portions  116  are shown to be square or rectangular in shape, although they can have any cross-sectional shape and be curved or rounded. One side of each of the square or rectangular shaped bearing receiving portion  116  is open to the first rail receiving portion  100  such that when an antifriction bearing  94  is inserted in the bearing receiving portion  100 , it provides a point or line contact with the first rail  12 . In the variation shown in  FIGS. 13   a - 13   d , there are a total of eight bearing receiving portions  116  adjacent to the first rail receiving portion  100 . Two bearing receiving portions  116   a ,  116   b  (see  FIG. 13   a ) are located above the first rail receiving portion  100  and generally adjacent to the top surface  32  of the first rail  12  when it is inserted. Two bearing receiving portions  116   c ,  116   d  (see  FIG. 13   b ) are located below the first rail receiving portion  100  and generally adjacent to the bottom surface  34  of the first rail  12  when it is inserted into the housing  90 . Hence, there are four bearing receiving portions  116   a ,  116   b ,  116   c ,  116   d  each having a longitudinal axis that is parallel to the X-axis or otherwise perpendicular to the longitudinal length of the first rail  12  when inserted. The housing  90  further includes pin apertures  118  opening to the side surfaces  108  on either side of the first rail receiving portion  100 . The pin apertures  118  extend inwardly to interconnect with the bearing receiving portions  116  and hold the antifriction bearings  94  in position. The pin apertures  118  have a cross-sectional area that is smaller than the cross-sectional area of the bearing receiving portions  116  taken perpendicular to the longitudinal axes of the bearing receiving portions or Y-axis. 
     Furthermore, two bearing receiving portions  116   e ,  116   f  (see  FIG. 13   d ) are located along one side of first rail receiving portion  100  and generally adjacent to the one side of the first rail  12  when it is inserted into the housing  90 . Two bearing receiving portions  116   g ,  116   h  (see  FIG. 13 ) are located along the opposite or other side of the first rail receiving portion  100  and generally adjacent to the opposite or other side of the first rail  12  when it is inserted into the housing  90 . Hence, there are four bearing receiving portions  116   e ,  116   f ,  116   g ,  116   h  each having a longitudinal axis that is parallel to the Z-axis or otherwise perpendicular to the longitudinal length of the first rail  12  when inserted. The housing  90  further includes pin apertures  118  opening to the top and bottom surfaces  104 ,  106  on either side of the first rail receiving portion  100 . The pin apertures  118  extend inwardly to interconnect with the bearing receiving portions  116  and are configured to receive bearing pins to hold the antifriction bearings  94  in position. The pin apertures  118  have a cross-sectional area that is smaller than the cross-sectional area of the bearing receiving portions  116  taken perpendicular to the longitudinal axes of the bearing receiving portions  116 . 
     The housing  90  further includes a blade mount portion  120 . The blade mount portion  120  is configured to connect to a blade mount  92 . The blade mount portion  120  of the housing  90  is configured as a flange that extends outwardly from the housing  90  and toward the retractor zone. In the variation shown in  FIGS. 13   a - 13   d , the blade mount portion  120  is located in the seat of an L-shaped housing  90  such that the flange extends between and at an angle to the first rail receiving portion  100  and the second rail receiving portion  102 . The blade mount portion  120  includes a threaded aperture  122  configured to receive a threaded tow angle post  124 . 
     The tow angle post  124  is shown in  FIG. 14 . The tow angle post  124  is an elongated fastener having a driving head  126  at the proximal end for engagement with an instrument for driving the post  124  inside the threaded aperture  122 . The tow angle post  124  also includes a middle threaded portion  128  and a distal threaded portion  130 . A middle non-threaded portion  132  is provided on the tow angle post  124  between the middle threaded portion  128  and a distal threaded portion  130 . The distal threaded portion  130  and the non-threaded portion  132  are smaller in diameter relative to the middle threaded portion  128 . The tow angle post  124  is configured to be threadingly inserted into the threaded aperture  122  of the blade mount portion  120  of the housing  90 . With the tow angle post  124  inserted, the non-threaded portion  132  and the distal threaded portion  130  extend to receive a blade mount  92 . 
     A blade mount  92  according to the present invention is shown in  FIG. 15 . The blade mount  92  is configured to connect to the blade mount portion  120  of the housing  90  and, in particular, pivotably attach to underneath the flange. The blade mount  92  includes an aperture  134  for receiving the distal end of the tow angle post  124 . The blade mount  92  includes a blade receiving portion  136  configured to connect to a blade  26  according to the present invention. The blade receiving portion  136  includes an elongated or elliptical aperture  138  having a sidewall  139  that is configured to connect with therein a retractor blade  26  according to the present invention. Two outwardly extending flanges  140  serve to stabilize a blade  26  that is connected to the blade mount  92 . The blade mount  92  includes an aperture  142  configured for receiving a pin  144  (see  FIG. 12 ) there through. A corresponding pin aperture is formed in the housing  90  and configured to receive the pin to connect the blade mount  92  in a pivotable manner to the housing  90 . An additional opening  146  of the slider  14  is formed as a window extending into the blade mount  92  and intersecting with the tow angle post aperture  122  for the attachment of tow angle return. 
     With a tow angle post  124  inserted into the threaded aperture  122  of the housing  90  and its distal non-threaded  132  and threaded portion  130  extending beyond the housing  90 , the blade mount  92  is pivotably connected to the housing  90  by passing a pin  144  through the pin aperture  142  and by passing the aperture  134  of the blade mount  92  onto the distal portion of the tow angle post  124  such that the blade mount  92  is positioned on the non-threaded portion  132 . The blade mount  92  is captured between the housing  90  and a tow angle return  148 . 
     Turning now to  FIG. 16 , a tow angle return  148  will now be described. The tow angle return  148  is a spherically shaped element with a threaded aperture  150  configured to thread onto the distal threaded portion  130  of the tow angle post  124 . When threaded onto the distal end of the tow angle post  124 , the tow angle return  148  serves to capture the blade mount  92  between the tow angle return  148  and the housing  90 . When the tow angle post  124  is threaded into the housing  90 , the tow angle post  124  moves downwardly allowing the blade mount  92  to angulate about the pin  144  in a downward direction. When the tow angle post  124  is threaded up and outwardly from the housing  90 , the tow angle post  124  moves upwardly with the tow angle return  148  contacting the blade mount  92  and pulling or angulating the blade mount  92  upwardly. Removal of the tow angle post  124  is prevented by the tow angle return  148  threaded onto the distal threaded portion  130  of the tow angle post  124 . 
     Turning now to  FIGS. 17   a - 17   b , there is shown an antifriction bearing  94  according to the present invention. The bearing  94  is an elongated cylinder made of appropriate material such as surgical steel or titanium. The elongate cylinder has a circular cross-section and defines an outer surface  152  and an inner surface  154 . The inner surface  154  forms a lumen extending between an open proximal end and an open distal end.  FIG. 17   b  shows a pin  156  sized and configured for insertion into the lumen of the bearing  94 . The length of the pin  156  is longer than the bearing  94  such that the proximal end and distal end of the pin  156  extend beyond the proximal and distal openings of the bearing  94 , respectively. The bearings  94  are sized and configured to fit inside the bearing receiving portions  116  and the pin apertures  118  of the housing  90  to connect the bearing  94  to the housing  90  by welding the pins  156  to the housing  90  capturing the bearings  94  within the bearing receiving portions  116  such that the bearings  94  are free to rotate relative to the housing  90 . Alternatively, a cage or other retainer can be employed to secure the antifriction bearings  94  to the housing  90 . The antifriction bearing  94  is a cylindrical roller having straight sides that provide a line contact with the first rail  12 . The cylindrical rollers are small and may be considered to be needle rollers. Other antifriction elements such as spherical or ball bearings can be used in combination or instead of the cylindrical roller bearings shown in the figures. The roller bearings  94  are disposed in the bearing receiving portions  116  and retained therein by bearing pins  156  welded to the housing  90 . The cylindrical bearings  94  are connected to the housing  90  such that they can rotate about their respective pins  156  relative to the housing  90 . When connected to the housing  90 , the antifriction bearings  94  extend or protrude slightly into first rail receiving portion  100  to contact the first rail  12  disposed therein. 
     Turning now to  FIGS. 18   a - 18   b , there is shown a lock  96  according to the present invention. The lock  96  is sized and configured to be disposed inside the lock receiving portion  110  of the housing  90 . The lock  96  is an elongate shape having a square or rectangular cross section having a first end  158  and a second end  160 . The first end  158  includes an outer surface that extends beyond a side surface  108  of the housing  90  and is configured to be depressible by a finger of a user and as such may include a concave depression  162  for receiving a finger of a user. The lock  96  includes a throughway  164  extending through the lock  96  from one side surface to another side surface and is configured to receive the first rail  12 . The throughway  164  includes an inner surface that includes a locking tooth  166 . The locking tooth  166  extends from the inner surface and into the throughway  164 . The protruding locking tooth  166  includes a locking surface or flank  168  that is substantially perpendicular with respect to the inner surface and an angled or ramped surface or flank  170  that is angled with respect to the inner surface of the lock  96 . The throughway  164  is sized and configured to receive the first rail  12  inside the throughway  164 . Also, the locking tooth  166  is sized and configured to engage with the teeth  76  of the first track  58   a  of the first rail  12  such that the locking flank  168  of the locking tooth  166  engages the perpendicular flanks of the first track  58   a . The angled flank  170  of the locking tooth  166  permits sliding engagement with the angled flanks of the first track  58   a  such that the locking tooth  166  serves as a unidirectional stop. The lock  96  includes a spring  172  depicted in  FIG. 19  that is disposed between the lock  96  and the housing  90 . In particular, the spring  172  is disposed in a spring receiving portion  174  formed at the second end  160  of the lock  96  with the opposite end of the spring  172  abutting the back wall or stop  114  formed at the inside end of the lock receiving portion  110 . The lock receiving portion  110  may also include a spring receiving portion to receive the other end of the spring  172 . The spring  172  is positioned to bias the lock  96  outwardly relative to the housing  90  such that the locking tooth  166  of the lock  96  is engaged with the teeth  76  of the rail  12 . 
     The first slider  14  is assembled with respect to the first rail  12  by inserting the first rail  12  into the first rail receiving portion  100  of the housing  90 . Before the first rail  12  crosses the lock receiving portion  110  of the housing, the lock spring  172  is disposed inside the lock receiving portion  110  followed by the lock  96  which is oriented such that the through-way  164  of the lock  96  is aligned with the first rail receiving portion  110 . The lock  96  may have to be depressed slightly to pass the first rail  12  through the lock throughway  164 . Hence, the lock  96  is captured by the first rail  12  inside the housing  90 . The distal end  28  of the first rail  12  is passed through the housing  90  until the aperture  50  at first distal end  28  extends out from the housing  90 . A stop pin  86  is then inserted into the aperture  50  to prevent the slider  14  from sliding off the first distal end  28 . The first rail  12  is inserted into the first rail receiving portion  110  such that the teeth  76  of the first track  58   a  face inwardly towards the locking tooth  166  of the lock  96  for engagement therewith. The lock  96  is biased by the spring  172  such that the locking tooth  166  engages the teeth  76  of the track  58   a . Since the lock  96  is movable by depressing the first end relative  158  to the housing  90  to thereby release the locking tooth  166  from the teeth  76  of the track  58   a , the track  58   a  can then be moved along the rail  12  in any direction along the Y-axis. In the variation shown, the slider  12  is free to move outwardly toward the first distal end  28  of the first rail  12  with the locking tooth  166  engaged with the teeth  76  on the rail  12  by nature of the ramped locking tooth  166  engaging the angled flacks of the track  58   a . This configuration permits the slider  12  to move outwardly toward the first distal end  28  while the locking tooth  166  is engaged with the track  58   a  but the lock prevents movement of the slider  12  inwardly away from the first distal end  28  as the perpendicular flank  168  of the locking tooth  166  and the perpendicular flank of the track  58   a  would engage each other to arrest movement of the first slider  14  relative to the first rail  12 . This configuration allows the slider  14  to move outwardly to expand the tissue opening or wound area preventing the collapse of the tissue opening allowing users to take surgical action in the retracted zone. To close or move the slider  14  to close or reduce the retraction or tissue opening, the user would depress the first end  158  of the lock  96  to release the locking tooth  166  from engagement with the first track  58   a . The first rail  12  does not contact the housing  90 . Instead, the first rail  12  is configured to contact one or more antifriction bearings  94 . 
     Turning now to  FIGS. 20-22 , there is shown a second rail  18  according to the present invention. The second rail  18  is an elongate, straight bar that is made of metal such as surgical steel or titanium. The second rail  18  includes a proximal end  176  and a distal end  178  and has a top surface  180  and a bottom surface  182  interconnected by an inner surface  184  and an outer surface  186  to define a substantially square or rectangular cross-section perpendicular to the longitudinal axis of the second rail  18 . A curved end surface is formed at the distal end  178 . The proximal end  176  of the second rail  18  is sized and configured to be received inside the second rail receiving portion  102  of the first slider  14 . The second rail  14  is inserted into the second rail receiving portion  102  of the first slider  14  and pins  52  are passed through apertures in the first slider  14  and second rail  18  and welded to connect the second rail  18  to the first slider  14 . Because the second rail receiving portion  102  is perpendicular to the first rail receiving portion  100 , the second rail  18  will be perpendicular to the first rail  12  when connected to the first slider  14 . Movement of the first slider  14  will result in movement of the second rail  18  along with the first slider  14 . 
     The second rail  18  includes at least one track  58 . The track  58  is the same as described above with respect to  FIGS. 8-10 . The track  58  is disposed in a track-receiving portion  188  of the second rail  18 . The track-receiving portion  188  is sized and configured to receive the track  58 . Pins  52  are passed through apertures  190  in the top surface  180  and bottom surface  182  of the second rail  18  and through pin apertures  74  in the track  58 . The pins  52  are laser welded to connect the track  58  to the second rail  18 . Teeth  76  on the track  58  are configured to engage a locking tooth on the third slider  22  such that movement of the third slider  22  with respect to the second rail  18  is prevented or locked. In the variation shown in the figures, the third slider  22  is permitted to travel in one direction and locked in the opposite direction while the locking tooth of the third slider  22  is engaged with the teeth  76  of the track  58 . In such a variation, the flanks are of the locking tooth and track are configured to permit ramped travel over the teeth in one direction and configured to lock against perpendicular flanks in the opposite direction. Preferably the teeth  76  on the track  58  and the locking tooth on the third slider  22  are configured to lock or prevent the third slider  22  from moving toward the first slider  14  while the locking tooth of the third slider  22  is engaged with the teeth  76  on the track  58 . This configuration advantageously permits the retraction zone to be easily opened increased in size by moving the third slider  22  outwardly away from the first slider  14  without requiring release or disengagement of the locking tooth. This configuration also advantageously prevents the third slider  22  from creeping toward the first slider  14  and reducing the size of the retracted opening. 
     Still referencing  FIGS. 20-22 , the track  58  provides the second rail  18  with a toothed surface that is recessed from the inner surface  184  of the second rail  18 . The teeth  76  do not protrude or extend beyond the outer surface of the second rail  18 . In one variation, the top land of each tooth is even with the inner surface  184  of the second rail  18 . In another variation, the top land is slightly recessed or setback from the inner surface  184  of the second rail  18 . In general, the right or left flanks do not protrude beyond the inner surface  184  of the second rail  18 . Thereby, the track  58  is set within the track receiving portion  188 . In another variation, the second rail  18  does not include a track  58  located within track receiving portion  188 ; instead, the second rail  18  itself is provided with at least one toothed surface recessed as described above and integrally formed with the second rail  18  instead of as separate insertable track  58 . Furthermore, the at least one toothed surface can be located along one or more surfaces of the second rail  18  such as the top surface  180 , bottom surface  182 , inner surface  184  and/or outer surface  186 . 
     The track  58  is located proximally to the distal end  178  of the second rail  18  such that the flanks of all of the teeth on the track  58  are configured to permit unidirectional travel of the third slider  22  in a direction parallel to the X-axis and away from the first slider  14  and toward the distal end  178  while the locking tooth of the third slider  22  is engaged. Hence, the left flanks of all of the teeth on the track  58  are perpendicular to the baseline  84  or top land  82  and the right flanks are angled to permit the third slider  22  to move outwardly toward the distal end  178  but prevent or restrict movement of the third slider  22  toward the first slider  14  or the proximal end  176  of the second rail  18 . 
     Still referencing  FIGS. 20-22 , the second rail  18  includes an aperture  190  near the distal end  178  extending from the top surface  180  to the bottom surface  182  of the second rail  18  and configured to receive a stop pin  86  having an enlarged head  88  as shown and described in  FIG. 11 . The enlarged head  88  is not flush but is positioned above the top surface  180  when the stop pin  86  is in place and serves to stop the sliding motion of the third slider  22  preventing it from moving off the second rail  18 . The stop pin  86  is placed after the third slider  22  is connected to the second rail  18 . The third slider  22  is arrested when traveling toward the first slider  14  by abutting the first slider  14  itself. 
     Turning now to  FIGS. 23-24 , the third slider  22  will now be described. The third slider  22  includes a housing  192 , a blade mount  92 , a plurality of antifriction bearings  94  and a lock  96  (see  FIG. 18 ). 
     The housing  192  of the third slider  22  will now be described with reference to  FIGS. 24   a - 24   d . The housing  192  is made of any suitable material including any metal such as steel, surgical steel or titanium and defines a second rail receiving portion  200 . The housing  192  has a top surface  202  and a bottom surface  204  interconnected by a plurality of side walls having side surfaces  206  to the outside to define the housing  192 . The second rail receiving portion  200  is formed as a passageway sized and configured to receive the second rail  18  in sliding engagement with the housing  192 . The second rail receiving portion  200  includes a first opening formed in a side surface  206  at one end of the housing  192  and a second opening formed in a side surface at a second end of the housing  192  directly opposite from the first opening to define a passageway extending therebetween. The passageway has a cross-sectional area that is slightly larger than the cross-sectional area of the second rail and a cross-sectional shape that is the same as the cross-sectional shape of the second rail  18 . 
     The housing  192  of the third slider  22  further includes a lock receiving portion  208 . The lock receiving portion  208  is sized and configured to receive a lock  96  therein. The lock receiving portion  208  intersects with the second rail receiving portion  200 , preferably, at approximately 90 degrees. The lock receiving portion  208  includes an opening in a side surface  206  of the housing  192  and defines a passageway extending inwardly from the opening into the housing  192 . The lock receiving portion  208  traverses or crosses the second rail receiving portion  200 . The lock receiving portion  208  includes a back wall or stop  210  formed at the inside end of the lock receiving portion  208 . 
     Still referencing  FIGS. 21   a - 24   d , the housing  192  of the third slider  22  further includes one or more bearing receiving portions  212  along at least two sides of the second rail receiving portion  200  and interconnecting with the second rail receiving portion  200 . The bearing receiving portions  212  are shown to be square or rectangular in shape, although they can have any cross-sectional shape and be curved or rounded so long as they are configured to receive antifriction bearings  94 . One side of each of the square or rectangular shaped bearing receiving portion  212  is open to the second rail receiving portion  200  such that when an antifriction bearing  94  is inserted in the bearing receiving portion  212  it provides a point or line contact with the second rail  18 . In the variation shown in  FIGS. 24   a - 24   d , there are a total of eight bearing receiving portions adjacent to the second rail receiving portion  200  configured to support the second rail  18 . Two bearing receiving portions  212   a ,  212   b  are located above the second rail receiving portion  200  and generally adjacent to the top  180  of the second rail  18  when it is inserted and two bearing receiving portions  212   c ,  212   d  are located below the second rail receiving portion  200  and generally adjacent to the bottom surface  182  of the second rail  18  when it is inserted. Hence, there are four bearing receiving portions  212   a ,  212   b ,  212   c ,  212   d  each having a longitudinal axis that is parallel to the Y-axis or otherwise perpendicular to the longitudinal length of the second rail  18  when the second rail  18  is inserted inside the housing  192 . The housing  192  further includes pin apertures  214  opening to the side surfaces  206  on either side of the second rail receiving portion  200 . The pin apertures  214  extend inwardly to interconnect with the bearing receiving portions  212  and are configured to hold the antifriction bearings  94  in position. The pin apertures  214  have a cross-sectional area that is smaller than the cross-sectional area of the bearing receiving portions  212  taken perpendicular to the longitudinal axes of the bearing receiving portions or Y-axis. 
     Furthermore, two bearing receiving portions  212   e ,  212   f  are located along one side of second rail receiving portion  200  and generally adjacent to the outer surface  186  of the second rail  18  when it is inserted and two bearing receiving portions  212   g ,  212   h  are located along and generally adjacent to the inner surface  184  of the second rail  18  when it is inserted. Hence, there are four bearing receiving portions  212   e ,  212   f ,  212   g ,  212   h  each having a longitudinal axis that is parallel to the Z-axis or otherwise perpendicular to the longitudinal length of the second rail  18  when the second rail  18  is inserted into the housing  192 . Pin apertures  214  extend inwardly to interconnect with the bearing receiving portions  212  and are configured to hold the antifriction bearings  94  in position. 
     The housing  192  of the third slider  22  further includes a blade mount portion  216 . The blade mount portion  216  is configured to connect to a blade mount  92 . The blade mount portion  216  of the housing  192  is configured as a flange that extends outwardly from the housing  192 . In the variation shown in  FIGS. 24   a - 24   d , the blade mount portion  216  is located inwardly toward the center of the retractor such that the flange extends between and at an angle to the second rail receiving portion  200 . The blade mount portion  216  includes a threaded aperture  218  configured to receive a threaded tow angle post  124  of the same or similar kind described with reference to  FIG. 14 . The tow angle post  124  is configured to be threadingly inserted into the threaded aperture  218  of the blade mount portion  216  of the housing  192 . With the tow angle post  124  inserted, a blade mount  92  of the same kind as described in  FIG. 15  is connected in the same manner. A blade mount  92  is the same as that described with reference to  FIG. 15 . The blade mount  92  is captured between the housing  192  and a tow angle return  148  as described above. The tow angle return  148  is threaded onto the distal end of the tow angle post  124 . 
     Antifriction bearings  94  and bearing pins  156  of the same kind described in reference to  FIGS. 17   a - 17   b  are disposed inside the bearing receiving portions  212  and retained therein by bearing pins  156  welded to the housing  192 . The cylindrical bearings  94  are connected to the housing  192  such that they can rotate about their respective pins  156  relative to the housing  192 . 
     A lock  96  of the same kind as described in reference to  FIGS. 18-19  is disposed inside the lock receiving portion  208  of the third housing  192 . The locking tooth  166  extends from the inner surface and into the through-way  164  of the lock  96 . The protruding locking tooth  166  includes a locking surface that is substantially perpendicular with respect to the inner surface and an angled or ramped surface that is angled with respect to the inner surface of the lock. The through-way is sized and configured to receive the second rail  18  inside the through-way  164 . Also, the locking tooth  166  is sized and configured to engage with the teeth  76  of the track  58  of the second rail  18  such that the locking surface of the locking tooth  166  engages the perpendicular flanks of the track  58 . The angled surface of the locking tooth  166  permits sliding engagement with the angled flanks of the track  76  such that the locking tooth  166  serves as a unidirectional stop. The lock  96  includes a spring  172  that is disposed between the lock  96  and the third housing  192  to bias the locking tooth  166  into the teeth  76  of the track  58  in the second rail  18 . 
     The third slider  192  is assembled with respect to the second rail  18  by inserting the second rail  18  into the second rail receiving portion  200  of the third housing  192 . Before the second rail crosses the lock receiving portion  208  of the housing, the lock spring  172  is disposed inside the lock receiving portion  208  followed by the lock  96  which is oriented such that the through-way  164  of the lock  96  is aligned with the second rail receiving portion  200 . The lock  96  may have to be depressed slightly to pass the second rail  18  through the lock throughway  164 . The lock  96  is captured by the second rail  18  residing inside the third housing  192 . The distal end  178  of the second rail  18  is passed through the third housing  192  until the aperture  190  at first distal end  178  extends out from the third housing  192 . A stop pin  86  is then inserted into the aperture to prevent the third slider  22  from sliding off the second rail  18 . The second rail  18  is inserted into the second rail receiving portion  200  such that the teeth  76  of the track  58  face inwardly towards the locking tooth  166  of the lock  96  for engagement therewith. The lock  96  is biased by the spring  172  such that the locking tooth  166  engages the teeth  76  of the track  58 . Since the lock  96  is movable by depressing the first end  158  relative to the housing  192  to thereby release the locking tooth  166  from the teeth  76  of the track  58 , the third slider  22  can then be moved relative to the second rail  18  in any direction along the X-axis. In the variation shown, the third slider  22  is free to move outwardly toward the distal end  178  of the second rail  18  by nature of the ramped locking tooth  166  engaging the angled flanks of the track  58  as described above. This configuration permits the third slider  22  to move outwardly toward the first distal end  178  but the lock  96  prevents movement of the third slider  22  inwardly away from the first distal end  178  as the perpendicular surface of the locking tooth  166  and the perpendicular flank of the track  58  would engage each other to arrest movement of the third slider  22  relative to the second rail  18 . This configuration allows the third slider  22  to move outwardly to expand the tissue opening or wound area preventing the collapse of the tissue opening allowing users to take surgical action in the retracted zone. To close or move the third slider  22  to close or reduce the retraction or tissue opening, the user would depress the first end  158  of the lock  96  to release the locking tooth  166  from engagement with the recessed track  58 . With the lock  96  depressed to disengage the locking tooth  166 , the second rail  18  does not contact the third slider  22 . Instead, the second rail  18  contacts one or more of the antifriction bearings  94 . 
     Turning now to  FIGS. 25-26 , the second slider  16  will now be described. The second slider  16  is a mirror image of the first slider  14 . The second slider  16  is mounted on the second distal end  30  of the first rail  12  and includes a housing  220 , a blade mount  92 , a plurality of antifriction bearings  94  and a lock  96  (see  FIGS. 18   a - 18   b ). 
     The housing  220  is made of any suitable material including any metal such as steel, surgical steel, or titanium and defines a first rail receiving portion  222  and a third rail receiving portion  224 . The housing is polygonal in shape forming a L-shaped structure having a top surface  226  and a bottom surface  228  interconnected by a plurality of side walls having side surfaces  230  to the outside to define the housing  220 . The first rail receiving portion  222  is formed as a passageway sized and configured to receive the first rail  12  in sliding engagement therein. The passageway of first rail receiving portion  222  includes a first opening formed in a side surface  230  at one end of the housing  220  and extends to a second opening formed in a side surface  230  at a second end of the housing  220  directly opposite from the first opening to define the passageway. The passageway has a cross-sectional area that is slightly larger than the cross-sectional area of the first rail  12  and a cross-sectional shape that is the same as the cross-sectional shape of the first rail  12 . 
     The housing  220  includes a third rail receiving portion  224 . The third rail receiving portion  224  is formed as a passageway that is sized and configured to receive the third rail  20  therein. The passageway of third rail receiving portion  224  includes a first opening formed in a side surface  230  at one end of the housing  220 . A second opening formed in a side surface  230  at a second end opposite the first opening is optional as an alternative variation. The passageway extends from the first opening into the housing  220  and does not necessarily have to extend or open to the second surface opposite the first opening. The passageway has a cross-sectional area that is slightly larger than the cross-sectional area of the third rail  20  and a cross-sectional shape that is the same as the cross-sectional shape defined by the third rail  20 . The first rail receiving portion  222  and the third rail receiving portion  224  are shown to be perpendicular to each other with the first rail receiving portion  222  substantially parallel to the Y-axis and the third rail receiving portion  224  substantially parallel to the X-axis. Although the first and third rail receiving portions  222 ,  224  are shown to be configured at 90 degrees to each other the invention is not so limited and the first and third rail receiving portions  222 ,  224  can be angle with respect to each other. For example, the angle between the first and third rail-receiving portions  222 ,  224  can be acute at approximately 30 degrees as angled as far apart as approximately 150 degrees. 
     The housing  220  further includes a lock receiving portion  232 . The lock receiving portion  232  is sized and configured to receive a lock  96  therein. The lock receiving portion  232  intersects with the first rail receiving portion  222 , preferably, at approximately 90 degrees. The lock receiving portion  232  includes an opening in a side surface  230  of the housing  220  and defines a passageway extending inwardly from the opening and into the housing  220 . The lock receiving portion  232  traverses or crosses the first rail receiving portion  222 . The lock receiving portion  222  includes a back wall or stop  234  formed at the inside end of the lock receiving portion  232 . In the variation shown in  FIGS. 26   a - 26   d , the lock receiving portion  232  is aligned with the third rail receiving portion  224 , both being perpendicular to the first rail receiving portion  222 . 
     Still referencing  FIGS. 26   a - 26   d , the housing  220  further includes one or more bearing receiving portions  236  along at least two sides of the first rail receiving portion  222  and interconnecting with the first rail receiving portion  222  such that antifriction bearings inserted into the bearing receiving portion  236  contact the first rail  12 . The bearing receiving portions  236  are shown to be square or rectangular in shape, although they can have any cross-sectional shape and be curved or rounded. One side of each of the square or rectangular shaped bearing receiving portion  236  is open to the first rail receiving portion  222  such that when an antifriction bearing  94  is inserted in the bearing receiving portion  236  it provides a point or line contact with the first rail  12 . In the variation shown in  FIGS. 25-26 , there are a total of eight bearing receiving portions  236  adjacent to the first rail receiving portion  222 . Two bearing receiving portions  236   a ,  236   b  are located above the first rail receiving portion  222  and generally adjacent to the top surface  32  of the first rail  12  when it is inserted. Two bearing receiving portions  236   c ,  236   d  are located below the first rail receiving portion  222  and generally adjacent to the bottom surface  34  of the first rail  12  when it is inserted. Hence, there are four bearing receiving portions  236   a ,  236   b ,  236   c ,  236   d  each having a longitudinal axis that is parallel to the X-axis or otherwise perpendicular to the longitudinal length of the first rail  12  when it is inserted. The housing  220  further includes pin apertures  238  opening to the side surfaces  230  on either side of the first rail receiving portion  222 . The pin apertures  238  extend inwardly to interconnect with the bearing receiving portions  236  and hold the antifriction bearings  94  in position. The pin apertures  238  have a cross-sectional area that is smaller than the cross-sectional area of the bearing receiving portions  236  taken perpendicular to the longitudinal axes of the bearing receiving portions  236 . 
     Furthermore, two bearing receiving portions  236   e ,  236   f  are located along one side of first rail receiving portion  222  and generally adjacent to the outer surface  38  of the first rail  12  when it is inserted and two bearing receiving portions  236   g ,  236   h  are located along the opposite or other side of the first rail receiving portion  222  and generally adjacent to the inner surface  36  of the first rail  12  when it is inserted. Hence, there are four bearing receiving portions  236   e ,  236   f ,  236   g ,  236   h  each having a longitudinal axis that is parallel to the Z-axis or otherwise perpendicular to the longitudinal length of the first rail  12  when it is inserted. The housing  220  further includes pin apertures  238  opening to the top and bottom surfaces  226 ,  228  on either side of the first rail receiving portion  222 . The pin apertures  238  extend inwardly to interconnect with the bearing receiving portions  236  and hold the antifriction bearings  94  in position. The pin apertures  238  have a cross-sectional area that is smaller than the cross-sectional area of the bearing receiving portions  222  taken perpendicular to the longitudinal axes of the bearing receiving portions  222  or Z-axis. 
     The housing  220  further includes a blade mount portion  240 . The blade mount portion  240  is configured to connect to a blade mount  92 . The blade mount portion  240  of the housing  220  is configured as a flange that extends outwardly from the housing  220  and toward the retractor zone. The blade mount portion  240  is located in the seat of an L-shaped housing  220  such that the flange extends between and at an angle to the first rail receiving portion  222  and the third rail receiving portion  224 . The blade mount portion  240  includes a threaded aperture  242  configured to receive a threaded tow angle post  124 . 
     The tow angle post  124  is the same as described with reference to  FIG. 14 . The tow angle post  124  is configured to be threadingly inserted into the threaded aperture  242  of the blade mount portion  240  of the housing  220 . A blade mount  92  shown and described in reference to  FIG. 15  is configured to connect to the blade mount portion  240  of the housing  220  and in particular pivotably attach to underneath the flange as described above. The blade mount  92  is captured between the housing  220  and a tow angle return  148  as described with respect to  FIG. 16 . 
     Antifriction bearings  94  such as the roller bearings  94  as described above with reference to  FIG. 17  are disposed in the bearing receiving portions  236  and retained therein by bearing pins  156  welded to the housing  220 . The cylindrical bearings  94  are connected to the second slider  16  such that they can rotate about their respective pins relative to the housing  220 . When connected to the housing  220  of the second slider  16 , the antifriction bearings  94  extending slightly into first rail receiving portion  222 . 
     A lock  96  as described with reference to  FIG. 18  is disposed inside the lock receiving portion  232  of the housing  220  and configured such that the locking tooth  166  is spring biased to engage the teeth  76  of the third rail  20 . In one variation, the lock  96  is configured to prevent movement of the second slider  16  relative to the first rail  12  unless the lock  96  is depressed against the spring  19  to disengage the locking tooth  166  from the teeth  76  on the first rail  12 . In another variation, the teeth  76  on the first rail  12  are configured or angled with respect to the locking tooth  166  such that unidirectional travel of the second slider  16  is permitted while the without disengaging the lock  96  from being in contact with the first rail  12 . Preferably, unidirectional travel of the second slider  16  in a direction away from the handle  44  is permitted and movement toward the handle is prevented or locked. The angled surface of the locking tooth  166  permits sliding engagement with the angled flanks of the second track  58   b  such that the locking tooth  166  serves as a unidirectional stop. 
     The second slider  16  is assembled with respect to the first rail  12  in the same manner as the first slider  14  is assembled with respect to the first rail  12  with the lock  96  being captured by the first rail  12  inside the housing  220 . A stop pin  86  prevents the second  16  slider from sliding off the second distal end  30  of the first rail  12 . The first rail  12  is inserted into the first rail receiving portion  222  such that the teeth  76  of the second track  58   b  face inwardly towards the locking tooth  166  of the lock  96  for engagement therewith. The lock  96  is biased by the spring  172  disposed between the lock  96  and the housing  220  such that the locking tooth  166  engages the teeth  76  of the second track  58   b . Since the lock  96  is movable by depressing the first end  158  relative to the housing  220  to thereby release the locking tooth  166  from the teeth  76  of the track  58 , the second slider  16  can then be moved along the first rail  12  in any direction along the Y-axis. In the variation shown, the second  16  slider is free to move outwardly toward the second distal end  30  of the first rail  12  with the locking tooth  166  engaged with the teeth  76  on the first rail  12  by nature of the ramped locking tooth arrangement relative to the angled flank arrangement of the second track  58   b . This configuration permits the second slider  16  to move outwardly toward the second distal end  30  but the lock  96  prevents movement of the second slider  16  inwardly away from the second distal end  30  as the perpendicular surface of the locking tooth  166  and the perpendicular flank of the track  58   b  would engage each other to arrest movement of the second slider  16  relative to the first rail  12  with the locking tooth  166  engaged. This configuration allows the second slider  16  to move outwardly to expand the tissue opening or wound area preventing the collapse of the tissue opening allowing users to take surgical action in the retracted zone. To close or move the second slider  16  to close or reduce the retraction or tissue opening, the user would depress the first end  158  of the lock  96  to release the locking tooth  176  from engagement with the second track  58   b . The first rail  12  does not contact the housing  220 . Instead, the first rail  12  contacts one or more antifriction bearings  94  in sliding engagement therewith. 
     The third rail  20  is the same as the second rail  18  shown and described in reference to  FIGS. 20-22 . The proximal end of the third rail  20  is sized and configured to be received inside the third rail receiving portion  224  of the second slider  16 . The third rail  20  is inserted into the third rail receiving portion  224  of the second slider  16  and pins are passed through apertures in the second slider  16  and third rail  20  and welded to connect the third rail  20  to the second slider  16 . Because the third rail receiving portion  224  is perpendicular to the first rail receiving portion  222 , the third rail  20  will be perpendicular to the first rail  12  when connected to the second slider  16 . Movement of the second slider  16  will result in movement of the second rail  20  along with the second slider  16 . 
     The third rail  20  includes at least one track  58 . The track  58  is the same as described above with respect to  FIGS. 8-10  and disposed in a track-receiving portion of the third rail  20 . The track  58  provides the third rail  20  with a toothed surface that is recessed from the inner surface of the third rail  20 . The teeth  76  do not protrude or extend beyond the outer surface of the third rail  20 . Thereby, the track  58  is set within the third rail  20  and located proximally to the distal end of the third rail  20 . The third rail  20  is also provided with a stop pin  86  as described above with respect to  FIG. 11  which serves to stop the sliding motion of the fourth slider  24  from moving off the third rail  20 . The fourth slider  24  is arrested when traveling toward the second slider  16  by abutting the second slider  16  itself. 
     Turning now to  FIGS. 27-28 , the fourth slider  24  will now be described. The fourth slider  24  includes a housing  244 , and a blade mount  92 , a plurality of antifriction bearings  94  and a lock  96  connected to the housing  244 . 
     The housing  244  of the fourth slider  24  will now be described with reference to  FIGS. 28   a - 28   d . The housing  244  is made of any suitable material including any metal such as steel, surgical steel, or titanium. The housing  244  is the same as but a mirror image of the housing  192  of the third slider  22  shown and described with respect to  FIGS. 23-24 . The housing  244  has a top surface  246  and a bottom surface  248  interconnected by a plurality of side walls having side surfaces  250  to the outside to define the housing  244 . The housing  244  includes a third rail receiving portion  252  that is formed as a passageway sized and configured to receive the third rail  20  in sliding engagement with the housing  244 . The third rail receiving portion  252  includes a first opening formed in a side surface  250  at one end of the housing  244  and a second opening formed in a side surface  250  at a second end of the housing  244  directly opposite from the first opening to define a passageway extending therebetween. The passageway has a cross-sectional area that is slightly larger than the cross-sectional area of the third rail  20  and a cross-sectional shape that is the same as the cross-sectional shape of the third rail  20 . 
     The housing  244  of the fourth slider  24  further includes a lock receiving portion  254 . The lock receiving portion  254  is sized and configured to receive a lock  96  therein of the type described in reference to  FIG. 18 . The lock receiving portion  254  intersects with the third rail receiving portion  252 , preferably, at approximately 90 degrees. The lock receiving portion  254  includes an opening in a side surface of the housing  244  and defines a passageway extending inwardly from the opening into the housing  244 . The lock receiving portion  254  traverses or crosses the third rail receiving portion  254 . The lock receiving portion  254  includes a back wall or stop  256  formed at the inside end of the lock receiving portion  254 . 
     Still referencing  FIGS. 27-28 , the housing  244  of the fourth slider  24  further includes one or more bearing receiving portions  258  along at least two sides of the third rail receiving portion  252  and interconnecting with the third rail receiving portion  252 . The bearing receiving portions  258  are shown to be square or rectangular in shape, although they can have any cross-sectional shape and be curved or rounded. One side of each of the square or rectangular shaped bearing receiving portion  258  is open to the third rail receiving portion  252  such that when an antifriction bearing  94  is inserted in the bearing receiving portion  258  it provides a point or line contact with the third rail  20 . In the variation shown in  FIGS. 28   a - 28   d , there are a total of eight bearing receiving portions  258  adjacent to the third rail receiving portion  252 . Two bearing receiving portions  258   a ,  258   b  are located above the third rail receiving portion  252  and generally adjacent to the top surface of the third rail  20  when it is inserted. Two bearing receiving portions  258   c ,  258   d  are located below the third rail receiving portion  252  and generally adjacent to the bottom of the third rail  20  when it is inserted. Hence, there are four bearing receiving portions  258   a ,  258   b ,  258   c ,  258   d  each having a longitudinal axis that is parallel to the Y-axis or otherwise perpendicular to the longitudinal length of the third rail  20  when it is inserted. The housing  244  further includes pin apertures  260  opening to the side surfaces  250  on either side of the third rail receiving portion  252 . The pin apertures  260  extend inwardly to interconnect with the bearing receiving portions  258  and are configured to hold the antifriction bearings  94  in position. The pin apertures  260  have a cross-sectional area that is smaller than the cross-sectional area of the bearing receiving portions  258  taken perpendicular to the longitudinal axes of the bearing receiving portions  258 . 
     Furthermore, two bearing receiving portions  258   e ,  258   f  are located along one side of third rail receiving portion  252  and generally adjacent to the outer surface of the third rail  20  when it is inserted. Two additional bearing receiving portions  258   g ,  258   h  are located along the opposite or other side of the third rail receiving portion  252  and generally adjacent to the inner surface of the third rail  20  when it is inserted. Hence, there are four bearing receiving portions  258   e ,  258   f ,  258   g ,  258   h  each having a longitudinal axis that is parallel to the Z-axis or otherwise perpendicular to the longitudinal length of the third rail  20  when inserted. The housing  244  further includes pin apertures  260  opening to the top and bottom surfaces  246 ,  248  on either side of the third rail receiving portion  252 . The pin apertures  260  extend inwardly to interconnect with the bearing receiving portions  258  and are configured to hold the antifriction bearings  94  in position. 
     The housing  244  of the fourth slider  24  further includes a blade mount portion  262 . The blade mount portion  262  is configured to connect to a blade mount  92 . The blade mount portion  262  of the housing  244  is configured as a flange that extends outwardly from the housing  244 . In the variation shown in  FIGS. 28   a - 28   d , the blade mount portion  162  is located inwardly toward the center of the retractor  10  such that the flange extends between and at an angle to the third rail receiving portion  252 . The blade mount portion  262  includes a threaded aperture  264  configured to receive a threaded tow angle post  124  of the same or similar kind described with reference to  FIG. 14 . The tow angle post  124  is configured to be threadingly inserted into the threaded aperture  264  of the blade mount portion  262  of the housing  244  to attach a blade mount  92  of the type described with reference to  FIG. 15  to the housing  244  capturing the blade mount  92  with a tow angle return  148  shown and described with reference to  FIG. 16 . 
     Antifriction bearings  94  and bearing pins  156  of the kind described in reference to  FIGS. 17   a - 17   b  are disposed inside the bearing receiving portions  258  and retained therein by bearing pins  156  welded to the housing  244 . The cylindrical roller bearings  94  are connected to the housing  244  such that they can rotate about their respective pins  156  relative to the housing  244 . 
     A lock  96  of the same kind described in reference to  FIG. 18  is disposed inside the lock receiving portion  254  of the housing  244 . The throughway  164  of the lock  96  is sized and configured to receive the third rail  20  inside the throughway  164 . Also, the locking tooth  166  is sized and configured to engage with the teeth  76  of the track  58  of the third rail  20 . The angled surface of the locking tooth  166  permits sliding engagement with the angled flanks of the track  58  such that the locking tooth serves as a unidirectional stop while the lock  96  is engaged with the track  58 . The lock  96  includes a spring  172  that is disposed between the lock  96  and the housing  244 . In particular, the spring  172  is disposed in a spring receiving portion  174  formed at the second end  160  of the lock  96  with the opposite end of the spring abutting the back wall or stop  256  formed at the inside end of the lock receiving portion  254 . The lock receiving portion  254  may also include a spring receiving portion to receive the other end of the spring  172 . The spring is positioned to bias the lock  96  outwardly relative to the housing  244  to engage the locking tooth  166  to the track  58  of the third rail  20 . 
     The fourth slider  24  is assembled with respect to the third rail  20  by inserting the third rail  20  into the third rail receiving portion  252  of the housing  244 . Before the third rail  20  crosses the lock receiving portion  254  of the housing  244 , the lock spring  172  is disposed inside the lock receiving portion  254  followed by the lock  96  which is oriented such that the through-way  164  of the lock  96  is aligned with the third rail receiving portion  252 . The lock  96  is captured by the third rail  20  residing inside the housing  244 . The distal end of the third rail  20  is passed through the housing  244  until the aperture at distal end extends out from the housing  244  and a stop pin  86  is then inserted into the aperture to prevent the fourth slider  24  from sliding off the third rail  20 . The third rail  20  is inserted into the third rail receiving portion  252  such that the teeth  76  of the track  58  face inwardly towards the locking tooth  166  of the lock  96  for engagement therewith. The lock  96  is biased by the spring  172  such that the locking tooth  166  engages the teeth  76  of the track  58  of the third rail  20 . Since the lock  20  is movable by depressing the first end relative to the housing  244  to thereby release the locking tooth  166  from the teeth  76  of the track  58 , the fourth slider then can be moved relative to the third rail in any direction along the X-axis. In the variation shown, the fourth slider  24  is configured to move outwardly toward the distal end  178  of the third rail  20  while the locking tooth  166  is engaged by nature of the ramped locking tooth surface engaging the angled flanks of the track  58 . This configuration permits the fourth slider  24  to move outwardly toward the distal end  178  while the lock is engaged but the lock  96  is configured to prevent movement of the fourth slider  24  inwardly toward the second slider  16 . This configuration allows the fourth slider  24  to move outwardly to expand the tissue opening or wound area preventing the collapse of the tissue opening allowing users to take surgical action in the retracted zone. To close or move the fourth slider  24  to close or reduce the retraction or tissue opening, the user would depress the lock  96  to release the locking tooth  166  from engagement with the track  58  of the third rail  20 . With the lock  96  depressed to disengage the locking tooth  166 , the third rail  20  does not contact the fourth slider  24 . Instead, the third rail  20  contacts one or more antifriction bearings  94  disposed inside the housing  244 . 
     Turning now to  FIG. 29 , there is shown a retractor blade  266  according to the present invention. The retractor blade  266  is configured to removably attach to the blade mount  92  of each slider. The blades  266  are interchangeable with other blades  266  of different lengths and/or widths. Each blade  266  is an elongated piece of metal or plastic having a length and a width and a generally concave inner surface  268  and a convex outer surface  270 . The concave inner surface  268  is configured to face the open retractor zone. The blade  266  includes a cantilevered flange  272  integrally formed down the middle of the blade  266 . The proximal end  274  of the flange  272  is free to flex inwardly and outwardly with respect to the rest of the blade  266  whereas the distal end  276  of the flange  272  is integrally connected to the blade  266 . The proximal end  274  of the flange  272  includes a first ledge  278  that extends out from the outer surface  270  of the blade  266 . The proximal end  280  of the blade  266  includes a second ledge  282  extending from the outer surface  270  of the blade  266 . A gap  284  is defined proximal to the proximal end  274  of the flange  272  and configured to receive a hook  300  of a blade instrument  288 . The proximal end  280  of the blade  266  includes two guides  286  that extend from the outer surface  270  and are configured to receive the two outwardly extending flanges  140  on the blade mount  92  of a slider. 
     The blade  266  is connected to the blade mount  92  by first aligning the two guides  286  with the two flanges  140  of the blade mount  92 . The first ledge  272  will contact the top of the sidewall  139  of the blade mount aperture  138 . Further distal movement of the blade  266  will result in the first ledge  278  deflecting inwardly towards the inner surface  268  of the blade  266 . The lower surface of the first ledge  278  is ramped to permit ease of deflection of the first ledge  278 . After the sidewall of the blade mount aperture passes the first ledge  278 , the first ledge  278  will snap back to its normal undeflected state and into residence underneath the sidewall  139  which will be also captured underneath the second ledge  282  retaining the blade  266  to the blade mount  92 . The first ledge  282  is capable of deflection to capture and release the blade  266 . 
     Turning now to  FIGS. 30   a - 30   b , there is shown a blade instrument  288 . The blade instrument  288  is configured for inserting and removing a blade  266 . The blade instrument  288  includes an inner elongated rod  290  having handle  292  attached to the proximal end and a pronged distal end  294 . The pronged distal end  294  includes a first prong  296  adjacent to and spaced apart from a second prong  298 . The first prong  296  includes a hook  300  at the distal end and the second prong  298  includes two outwardly protruding knobs  302 . The blade instrument  288  further includes an outer shaft  304  having a lumen that is sized and configured to receive the elongated rod  290  inside the lumen of the shaft  304 . The shaft  304  is connected such that it is movable along the longitudinal axis relative to the elongated rod  290 . 
     Turning now to  FIGS. 31   a - 31   b , the blade  266  is connected to the blade instrument  288  by capturing the hook  300  of the first prong  296  into the gap  284  of the blade  266 . Both prongs  296 ,  298  are flexible and the second prong  298  is oriented towards the outer surface  270  of the blade  266  and the first prong  296  is oriented towards the inner surface  268  of the blade  266  with the hook  300  of the first prong  296  disposed inside the gap  284  to retain the blade  266  connected to the blade instrument  288 . The outer shaft  304  is moved distally over the pronged distal end  294  to cover at least in part the pronged distal end  294  and prevent the prongs  296 ,  298  from splaying apart and disconnecting from the blade  266 . When connected to the blade instrument  288 , the blade  266  can be carried with or without the outer shaft  304  covering the pronged distal end  294 . The pronged distal end  294  is uncovered by moving the outer shaft  304  proximally as shown in  FIG. 31   a  such that the blade  266  is free to be released from the blade instrument  288  and connected to the blade mount  92  of the retractor  10 . The second prong  298  is positioned inside the aperture  138  of the blade mount  92  and together with the blade  266 , moved distally to snap the first ledge  278  underneath the blade mount  92  beneath the sidewall  139  and position the second ledge  282  above the blade mount sidewall  139  as shown in  FIG. 32 . 
     To remove the blade  266  from the retractor  10 , the blade instrument  288  is positioned by inserting the second prong  298  into the blade receiving aperture of the blade mount until the knobs  302  contact the proximal end  280  of the blade  266 . Insertion of the blade instrument  288  will result in the first ledge  278  being deflected toward the inner surface  268  of the blade  266  and out from underneath the blade mount sidewall  139  freeing it for removal in the proximal direction. The first prong  296  is positioned such that the hook  300  is inside the gap  284  of the blade  266 . To assist the deflection of the first ledge  278 , the outer shaft  304  is movable from a first position in which the prongs  296 ,  298  are not inside the lumen of the outer shaft  304  to a second position in which the outer shaft  304  covers at least a portion of the prongs  296 ,  298  such that the prongs are not outwardly deflectable and maintained in a closed positioned for capturing and removal of the blade  266  as shown in  FIG. 31   b.    
     The use of the retractor  10  will now be discussed. The entry point for the retractor  10  into the patient is determined with anterior, posterior and lateral fluoroscopy. An incision is made in the patient that is slightly larger than the width dimension of the closed retractor base. The closed retractor base dimension is approximately 2.0 to 5.0 centimeters in one variation and in another variation approximately 2.6 centimeters, which is the distance between the distal ends of the blades in the closed non-angled orientation. A first dilator is inserted into the incision and advanced through the fascia and muscle tissue. Placement of a dilator is confirmed with fluoroscopy and by palpating the bony anatomy. Additional dilators are placed sequentially by passing the next largest dilator over the previously inserted dilator. If resistance is met, a scalpel is used to further incise the skin and fascia. Retractor blade length is selected by measuring the tissue depth from the etch markings provided on the last dilator. The tissue depth read from the etch markings directly corresponds to the suggested retractor blade length for use with the retractor  10 . The selected blades are inserted onto the blade mounts. When a blade  166  is fully seated within a blade mount there is an audible and tactile “click”. Various retractor blades  266  of different lengths are interchangeable with the retraction and range from approximately 30 mm to 120 mm in length. Each length being coded to a different retractor blade color for ease of selection and installation into the retractor  10 . With the blades  266  attached to the retractor  10 , the retractor  10  is inserted into a patient wound for distracting tissue of the surgical site. 
     Turning now to  FIG. 33 , a slider instrument  306  according to the present invention will now be described. The slider instrument  306  is used for distracting the retractor  10  to increase the retractor zone for obtaining surgical access to the target tissue site. The slider instrument  306  includes a handle  308  at the proximal end and a pair of movable prongs  310  at the distal end. The prongs  310  are sized and configured for insertion into distraction apertures  312  formed in the top surface each of the sliders  14 ,  16 ,  22 ,  24 . 
       FIG. 34   a  illustrates the slider instrument  306  positioned above a retractor  10  such that prongs  310  are above and aligned with distraction apertures  312  in the first and second sliders  14 ,  16  with the handle  308  in a first position. The prongs  310  are inserted into the distraction apertures  312  as shown in  FIG. 34   b  and the handle  308  squeezed to spread apart the prongs  310  and sliders  14 ,  16  from the orientation shown in  FIG. 34  to the orientation shown in  FIG. 35  for a medial-lateral distraction. The medial-lateral translation distance is approximately 1.0 mm and up to a maximum span in the range of between approximately 2.0 centimeters and approximately 10.0 centimeters in one variation. The slider instrument  306  is removed and positionable inside distraction apertures  312  in the first and third sliders  14 ,  22  to move them apart from each other and also into the second and fourth sliders  16 ,  24  to move them apart from each other from the orientation shown in  FIG. 35  to the orientation shown in  FIG. 36  for a cephalad-caudal expansion of the retractor. Of course, although distraction is referred to in the medial-lateral and cephalad-caudal direction with respect to the patient, the invention is not limited to the orientation of the instrument with respect to the patient anatomy.  FIG. 36  illustrates a fully distracted retractor  10  with all of the sliders  14 ,  16 ,  22 ,  24  spread apart from each as much as possible with the blades  266  in substantially vertical orientation. A hex socket instrument (not shown) can be used to turn the tow angle posts of each of the sliders  14 ,  16 ,  22 ,  24 , respectively, to angulate the blades  266  outwardly from the orientation shown in  FIG. 36  to the orientation shown in  FIGS. 37   a - 37   d  or to any position therebetween. The blades  266  angle up to a maximum of approximately 30 degrees in one variation. Maximum angulation of the blades  266  with respect to the Z-axis is between approximately 5 and 80 degrees. The size of the opening at the distal end of the blades depends upon blade length. If blades of a first length are employed, the maximum distal span for a 30-millimeter long blade is approximately 11 centimeters as shown. If blades of a second length are employed, the maximum distal span for a 90-millimeter long blade is approximately 17 centimeters for example. 
     The retractor  10  is shown in  FIGS. 38   a - 38   d  with the third slider  22  distracted relative to the first slider  14  and the fourth slider  24  distracted relative to the second slider  16  and the blades  266  angled from a vertical orientation relative to the Z-axis. Any combination or degree of slider distraction and degree of angulation makes the retractor  10  suitable for customized distraction of the operative space. 
     Turning now to  FIG. 39 , there is shown a medial blade  314  configured for placement on at least one of the rails  12 ,  18 ,  20  between the sliders  14 ,  16 ,  22 ,  24  for additional tissue retraction capability. The medial blade  314  includes a channel  316  for hooking onto one of the rails  12 ,  18 ,  20  and movable into a desired position along the rails  12 ,  18 ,  20 . A locking knob  318  is provided for tightening the channel  316  onto the rail for connecting therewith. The distal end of the medial blade  314  is shown to include teeth  320 .  FIG. 40  illustrates a single medial blade  314  hooked on the first rail  12 .  FIG. 41  illustrates a medial blade  314  connected to the first rail in addition to a second and third medial blades  314  connected to the second and third rails  18 ,  20 . The medial blades  314  can be connected to the rails for retaining tissue between the blades  266  from creeping into the retractor zone and may be angled for tissue retraction. 
     Removal of the retractor  10  will now be described. To remove the retractor  10  from the patient, any of the blades that are angled are reset to zero degrees with respect to the Z-axis by using a hex socket instrument to turn the one or more of the tow angle posts  124 . To close the retractor  10  to thereby minimize or reduce the size of the retractor zone, any one of the locks  96  on the any of the sliders  14 ,  16 ,  22 ,  24  are depressed to disengage the locking tooth  166  from the track  58 . With the locking tooth  166  disengaged, the sliders will easily slide in any direction along the rail and into a closed orientation relative to the other sliders to close the retractor  10  for its subsequent removal. For example, the lock  96  of the first slider  14  is depressed to move the first slider  14  toward the second slider  16  along rail  12 . Similarly, the lock  96  of the third slider  22  is depressed to free it for movement along the second rail  18  and in a direction toward the first slider  14  to reduce the retractor size. Also, the lock  96  of the fourth slider  24  is depressed to slide it toward the second slider  16 . The fully closed orientation of the sliders  14 ,  16 ,  22 ,  24  on the retractor  10  resembles the device depicted in  FIG. 1 . From this orientation, the retractor  10  is easily removed from the surgical site. 
     Turning now to  FIGS. 42   a - 42   b , there is shown another variation of a retractor  400  according to the present invention. The retractor  400  includes a rail housing  401  connected to a first rail  402  and second rail  404 . A first slider  406  is movably connected to the first rail  402  and a second slider  408  is connected to the second rail  404 . 
     The rail housing  401  includes a first rail receiving portion and a second rail receiving portion. The first and second rail receiving portions are configured to receive and connect the first and second rails  402 ,  404 . In the variation shown, the first and second rail receiving portions are angled such that connected first and second rails  402 ,  404  are angled with respect to each other and parallel to the X-Y plane. The angle between the first and second rails  402 ,  404  is shown to be greater than 90 degrees. The rail housing  401  includes a blade mount  92  of the same kind as described above with reference to  FIG. 15  and connected in the same pivotable manner and provided with removable and interchangeable blades  266 . 
     The first slider  406  includes a first rail receiving portion sized and configured to receive the first rail  40  in sliding engagement. The first slider  406  also includes bearing receiving portions configured to receive antifriction bearings  94  such that two bearings  94  are resident above and configured for contact with the top surface of the first rail  402  and two bearings  94  are resident below and configured for contact with the bottom surface of the first rail  402 . Also, two bearings  94  are resident on one side and two bearings  94  are resident on the other side of the first rail  402  in the same manner as described above with the first, second, third, and fourth sliders  14 ,  16 ,  22 ,  24 . The first slider  406  is also provided with a lock having a locking tooth configured for engagement with at least one recessed track  58  of the first rail  402 . The first slider  406  is substantially U-shaped and the second slider  408  is also U-shaped and configured to be a mirror image of the first slider  406 . Hence, the second slider  408  includes a second rail receiving portion configured to receive the second rail  404  therewith and with the same configuration of bearings  94  surrounding the second rail  404  including a lock and locking tooth as described above. Of course, the second rail  404  includes at least one recessed track  58  for engagement with the locking tooth. The first and second sliders  406 ,  408  each include a pivotably connected blade mount  92  of the like described above. The retractor  400  includes only three blades  266  such that each are configured to form a third of the circumference of the retractor zone defined by the closed orientation of the retractor  400 . The U-shaped sliders  406 ,  408  are connect to their respective rails  402 ,  404  and extend away and return toward the rail housing  401  to provide blade mounts  92  for a close circular configuration of the blades  266 . A slider instrument  306  is inserted into distraction apertures  312  to move the first slider  406  relative to the rail housing  401  and a second time to move the second slider  408  relative to the rail housing  401  to space apart the first and second sliders  406 ,  408  along the first and second rails  402 ,  404 , respectively, from the orientation shown in  FIGS. 42   a - 42   b  to the orientation shown in  FIGS. 43   a - 43   b . The retractor zone clearly visible in  FIG. 43   b  is elongated in shape. 
     Turning now to  FIG. 44 , there is shown a top perspective view of a section of the retractor  10  illustrating the configuration of the antifriction bearings  94  in a slider relative to a rail.  FIG. 44  shows two antifriction bearings  94   a ,  94   b  along the top surface of a rail. These two bearings  94   a ,  94   b  are located as far apart as possible inside the slider  410  to provide as much lateral stability and support to the rail as possible given the restraints provided by the lock  96 . Two bearings  94   c ,  94   d  are positioned facing the bottom surface of the rail and are located directly beneath or aligned with the top two bearings  94   a ,  94   b . In order to provide maximum stability, two vertical bearings  94   e ,  94   f  positioned alongside the rail are configured to be as close as possible to the horizontal bearings  94   a ,  94   c  and two vertical bearings  95   g ,  94   h  are positioned alongside the rail to be as close as possible to the horizontal bearings  94   b ,  94   d . Each cylinder bearing of the plurality of bearings in the slider  410  have the same diameter and define a longitudinal axis about which each cylinder bearing is rotatable. The plurality of cylinder bearings in the slider  410  are arranged such that at least one cylinder bearing of the pair of cylinder bearings  94   a ,  94   b  that are adjacent to a first side of the rail are spaced from at least one cylinder bearing of the pair of cylinder bearings  94   f ,  94   h  that are adjacent to a second side of the first rail by a distance of not less than approximately one diameter as measured between their axes with the first side of the rail being adjacent to and intersecting with the second side of the rail. For example, the axis of bearing  94   a  is approximately one diameter away from the axis of bearings  94   f and  94   e . Since bearing  94   a  is directly inline with bearing  94   c , bearing  94   c  is spaced apart from bearings  94   e  and  94   f  by a distance of approximately one diameter as measured from their axes. 
     The retractor  10  defines a retractor body that lies in a retractor plane with the retractor blades depending from the retractor plane. The blades are initially perpendicular to the retractor plane to provide the smallest size for insertion into a small incision. The blades can then be angled with respect to the plane to increase the tissue retraction. Generally, when a blade is moved relative to the rail or angled relative to the slider, it is moved against tissue and as such encounters opposing forces that torque the slider relative to the rail on which it is mounted. Because tissue, in particular, muscle can be very tough and offer much resistance to retraction forces exerted by the retractor, the torque on the slider relative to the rail can be very great. In prior art retractors, this torque resulted in sticktion or otherwise extreme pressure between the blade carrier and the rail and metal to metal contact of a typical rack and pinion construction. This invention successfully alleviates this undersirable trait of the prior art devices. 
     The preceding merely illustrates the principles of the invention. It will be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. The scope of the present invention, therefore, is not intended to be limited to the exemplary embodiments shown and described herein. Rather, the scope and spirit of present invention is embodied by the appended claims. 
     Although this application discloses certain embodiments and examples, it will be understood by those skilled in the art that the present inventions extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Further, the various features of these inventions can be used alone, or in combination with other features of these inventions other than as expressly described above. Thus, it is intended that the scope of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above.