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. Auxiliary instruments such as the retractor inserter, universal hex driver and blade removal instrument allow quick and controlled access to the surgical site. The retractor system provides versatility and control ensuring minimal tissue trauma.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and is a continuation-in-part of U.S. Provisional Patent Application Ser. No. 60/921,128 entitled “Retractor” filed on Mar. 30, 2007, hereby incorporated by reference in its entirety. This application also claims priority to and is a continuation-in-part of U.S. Provisional Patent Application Ser. No. 60/937,732 entitled “Retractor” filed on Jun. 29, 2007, hereby incorporated by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present invention generally relates to surgical instruments and methods. More particularly, but not exclusively, the present invention relates to surgical retractors for use in spinal surgery and other types of surgical procedures. 
       BACKGROUND 
       [0003]    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. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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. 
         [0010]    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 
       [0011]    According to one aspect of the invention, a surgical retractor is disclosed. The retractor includes a main body and a main body plane. Connected to the right side of the main body is a right track assembly that is configured to be movable inwardly and outwardly with respect to the main body. A left track assembly is connected to the left side of the main body and is configured to be movable inwardly and outwardly with respect to the main body. The retractor further includes a right blade assembly comprising a right upper blade assembly connected to a right lower blade assembly. The right blade assembly is connected to the right track assembly such that right blade assembly moves with the right track assembly. The right upper blade assembly includes a first blade support and a first removable blade connected to the first blade support such that the first blade extends perpendicularly to the main body plane. The right lower blade assembly includes a second blade support and a second removable blade connected to the second blade support such that the second blade extends perpendicularly to the main body plane. The retractor further includes a left blade assembly comprising a left upper blade assembly connected to a left lower blade assembly. The left blade assembly is connected to the left track assembly such that the left blade assembly moves with the left track assembly. The left upper blade assembly includes a third blade support and a third removable blade connected to the third blade support such that the third blade extends perpendicularly to the main body plane. The left lower blade assembly includes a fourth blade support and a fourth removable blade connected to the fourth blade support such that the fourth blade extends perpendicularly to the main body plane. The right upper blade assembly includes a right mounting arm having a longitudinal axis. The right lower blade assembly is movable inwardly and outwardly with respect to the right upper blade along the longitudinal axis of the right mounting arm. The left upper blade assembly includes a left mounting arm having a longitudinal axis. The left lower blade assembly is movable inwardly and outwardly with respect to the left upper blade along the longitudinal axis of the left mounting arm. 
         [0012]    According to another aspect of the present invention, a surgical retractor is disclosed. The retractor includes a main body having a longitudinal axis, a transverse axis and a main body plane. The retractor further includes a right assembly comprising a right upper blade and right lower blade. The right upper and lower blades extend generally perpendicular to the main body plane. The right assembly slides longitudinally with respect to the main body carrying the right upper and right lower blades. The right lower blade slides with respect to the right upper blade along a right mounting arm longitudinal axis. The retractor further includes a left assembly comprising a left upper blade and left lower blade. The left upper and lower blades extend generally perpendicular to the main body plane. The left assembly slides longitudinally with respect to the main body carrying the left upper and left lower blades. The left lower blade slides with respect to the left upper blade along a left mounting arm longitudinal axis. The right mounting arm longitudinal axis is angled with respect to the main body longitudinal axis and the left mounting arm longitudinal axis is angled with respect to the main body longitudinal axis. 
         [0013]    Other advantages will be apparent from the description that follows, including the drawings and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0014]    The invention is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. All figures herein illustrate surgical retractors according to the present invention. 
           [0015]      FIG. 1   a  illustrates a perspective view of the retractor according to the present invention. 
           [0016]      FIG. 1   b  illustrates a top view of the retractor according to the present invention. 
           [0017]      FIG. 1   c  illustrates a bottom view of the retractor according to the present invention. 
           [0018]      FIG. 1   d  illustrates a side view of the retractor according to the present invention. 
           [0019]      FIG. 1   e  illustrates an end view of the retractor according to the present invention. 
           [0020]      FIG. 2   a  illustrates a rear perspective view of the middle assembly connected to the upper right rack and upper left rack assemblies according to the present invention. 
           [0021]      FIG. 2   b  illustrates a front perspective view of the middle assembly connected to the upper right rack and upper left rack assemblies according to the present invention. 
           [0022]      FIG. 2   c  illustrates a side view of the middle assembly connected to the upper right rack and upper left rack assemblies according to the present invention. 
           [0023]      FIG. 2   d  illustrates a cross-sectional view of the middle assembly along line B-B of  FIG. 2   c  according to the present invention. 
           [0024]      FIG. 3   a  illustrates a perspective view of the main body of the middle assembly according to the present invention. 
           [0025]      FIG. 3   b  illustrates a side cross-sectional view of the main body of the middle assembly according to the present invention. 
           [0026]      FIG. 3   c  illustrates a perspective view of the cover of the main body of the middle assembly according to the present invention. 
           [0027]      FIG. 3   d  illustrates a perspective view of a fastener of the main body of the middle assembly according to the present invention. 
           [0028]      FIG. 4   a  illustrates a partial cross-sectional view of the main body assembly and main body sub-assembly according to the present invention. 
           [0029]      FIG. 4   b  illustrates a perspective view of a pinion of the main body sub-assembly according to the present invention. 
           [0030]      FIG. 4   c  illustrates a perspective view of the middle pinion lock of the main body sub-assembly according to the present invention. 
           [0031]      FIG. 4   d  illustrates a perspective view of a spring of the main body sub-assembly according to the present invention. 
           [0032]      FIG. 4   e  illustrates a side view of a spring cap of the main body sub-assembly according to the present invention. 
           [0033]      FIG. 4   f  illustrates a top view of a middle housing release assembly according to the present invention. 
           [0034]      FIG. 4   g  illustrates a rear perspective view of the middle housing release assembly according to the present invention. 
           [0035]      FIG. 4   h  illustrates a rear perspective view of the release body of the middle housing release assembly according to the present invention. 
           [0036]      FIG. 5   a  illustrates a perspective view of an upper right rack assembly according to the present invention. 
           [0037]      FIG. 5   b  illustrates a perspective view of a rack support of an upper right rack assembly according to the present invention. 
           [0038]      FIG. 5   c  illustrates a cross-sectional view of a rack support of an upper right rack assembly according to the present invention. 
           [0039]      FIG. 5   d  illustrates a perspective view of a straight rack of an upper right rack assembly according to the present invention. 
           [0040]      FIG. 5   e  illustrates a perspective view of a tow angle post of an upper right rack assembly according to the present invention. 
           [0041]      FIG. 5   f  illustrates a cross-sectional view of a tow angle post of an upper right rack assembly according to the present invention. 
           [0042]      FIG. 5   g  illustrates a perspective view of a tow angle return of an upper right rack assembly according to the present invention. 
           [0043]      FIG. 5   h  illustrates a perspective view of a pin of an upper right rack assembly according to the present invention. 
           [0044]      FIG. 6   a  illustrates a perspective view of an upper left rack assembly according to the present invention. 
           [0045]      FIG. 6   b  illustrates a perspective view of a rack support of an upper left rack assembly according to the present invention. 
           [0046]      FIG. 7  illustrates a top view of a right assembly according to the present invention. 
           [0047]      FIG. 8   a  illustrates a perspective view of an upper right blade support assembly according to the present invention. 
           [0048]      FIG. 8   b  illustrates a perspective view of a mounting arm of an upper right blade support assembly according to the present invention. 
           [0049]      FIG. 8   c  illustrates a cross-sectional view of a mounting arm of an upper right blade support assembly according to the present invention 
           [0050]      FIG. 8   d  illustrates a pinion of a mounting arm sub-assembly according to the present invention. 
           [0051]      FIG. 8   e  illustrates a perspective view of a retaining collar of a mounting arm sub-assembly according to the present invention. 
           [0052]      FIG. 8   f  illustrates a perspective view of a gear lock of a mounting arm sub-assembly according to the present invention. 
           [0053]      FIG. 8   g  illustrates a side view of a pin of a mounting arm sub-assembly according to the present invention. 
           [0054]      FIG. 8   h  illustrates a cross-sectional view of an upper right blade support assembly according to the present invention. 
           [0055]      FIG. 8   i  illustrates a perspective view of a blade support according to the present invention. 
           [0056]      FIG. 8   j  illustrates a partial cross-sectional view of a blade support according to the present invention. 
           [0057]      FIG. 8   k  illustrates a perspective view of a threaded end cap according to the present invention. 
           [0058]      FIG. 9   a  illustrates a perspective view of a lower right blade support assembly according to the present invention. 
           [0059]      FIG. 9   b  illustrates a side view of a ratcheting pin according to the present invention. 
           [0060]      FIG. 9   c  illustrates a perspective view of a lower right blade support according to the present invention. 
           [0061]      FIG. 10  illustrates a top view of a left assembly according to the present invention. 
           [0062]      FIG. 11   a  illustrates a perspective view of an upper left blade support assembly according to the present invention. 
           [0063]      FIG. 11   b  illustrates a perspective view of a mounting arm of an upper left blade support assembly according to the present invention. 
           [0064]      FIG. 11   c  illustrates a cross-sectional view of a mounting arm of an upper left blade support assembly according to the present invention. 
           [0065]      FIG. 11   d  illustrates a perspective view of a gear lock according to the present invention. 
           [0066]      FIG. 11   e  illustrates a cross-sectional view of an upper left blade support assembly according to the present invention. 
           [0067]      FIG. 11   f  illustrates a perspective view of a blade support according to the present invention. 
           [0068]      FIG. 11   g  illustrates a partial cross-sectional view of a blade support according to the present invention. 
           [0069]      FIG. 12   a  illustrates a perspective view of a lower left blade support assembly according to the present invention. 
           [0070]      FIG. 12   b  illustrates a perspective view of a lower left blade support according to the present invention. 
           [0071]      FIG. 13   a  illustrates a perspective view of a blade according to the present invention. 
           [0072]      FIG. 13   b  illustrates a cross-sectional view of a blade according to the present invention. 
           [0073]      FIG. 14  illustrates a retractor in a closed configuration according to the present invention. 
           [0074]      FIG. 15  illustrates a first dilator inserted to a patient&#39;s spine. 
           [0075]      FIG. 16  illustrates a sequentially-dilated incision with access to a patient&#39;s spine. 
           [0076]      FIG. 17   a  illustrates a perspective view of a retractor blade in juxtaposition to a retractor according to the present invention. 
           [0077]      FIG. 17   b  illustrates a partial perspective view of a retractor blade hooked to a blade support according to the present invention. 
           [0078]      FIG. 17   c  illustrates retractor blades of various lengths according to the present invention. 
           [0079]      FIG. 18   a  illustrates a perspective view of a retractor inserter according to the present invention. 
           [0080]      FIG. 18   b  illustrates a side view of a retractor inserter connected to a retractor according to the present invention. 
           [0081]      FIG. 18   c  illustrates a top perspective view of a retractor inserter connected to a retractor according to the present invention. 
           [0082]      FIG. 19   a  illustrates dilators, a retractor and retractor inserter placed in a spinal surgical opening according to the present invention. 
           [0083]      FIG. 19   b  illustrates the retractor placed in a spinal surgical opening according to the present invention. 
           [0084]      FIG. 20   a  illustrates a perspective view of a T-shaped driver connected to the middle pinion of the retractor according to the present invention. 
           [0085]      FIG. 20   b  illustrates a perspective view of the left and right assemblies of the retractor expanded apart according to the present invention 
           [0086]      FIG. 20   c  illustrates a top view of the left and right assemblies of the retractor expanded apart according to the present invention. 
           [0087]      FIG. 21   a  illustrates a perspective view of a T-shaped driver connected to a pinion of an upper left blade support assembly with the lower right and lower left blade supports expanded apart from the upper right and upper left blade supports, respectively, according to the present invention. 
           [0088]      FIG. 21   b  illustrates a top view of a retractor with the lower right and lower left blade supports expanded apart from the upper right and upper left blade supports, respectively, by a distance L according to the present invention. 
           [0089]      FIG. 22   a  illustrates a perspective view of a T-shaped driver connected to a tow angle post of an upper left rack assembly of the retractor with the right and left assemblies angled outwardly according to the present invention. 
           [0090]      FIG. 22   b  illustrates front view of a retractor with the right and left assemblies angled outwardly to a distance T 1  according to the present invention. 
           [0091]      FIG. 22   c  illustrates a front view of a retractor with the right and left assemblies angled outwardly to a distance T 2  according to the present invention. 
           [0092]      FIG. 23  is a table of maximum distal spans for various blade lengths according to the present invention. 
           [0093]      FIG. 24   a  illustrates a perspective view of a blade removal tool according to the present invention. 
           [0094]      FIG. 24   b  illustrates a perspective view of a blade removal tool engaged with a blade in a retractor according to the present invention. 
           [0095]      FIG. 24   c  illustrates a perspective view of a blade removal tool removing a blade from a retractor according to the present invention. 
           [0096]      FIG. 25   a  illustrates a perspective view of a T-shaped driver connected to a tow angle post of an upper left rack assembly of the retractor with the right and left assemblies angled outwardly according to the present invention. 
           [0097]      FIG. 25   b  illustrates a partial perspective view of a retractor illustrating the release body according to the present invention. 
           [0098]      FIG. 25   c  illustrates a partial perspective view of a retractor illustrating the gear lock of the right upper and lower blade supports according to the present invention. 
           [0099]      FIGS. 26   a - 26   c  illustrate various views of the retractor according to the present invention. 
           [0100]      FIGS. 27   a - 27   d  illustrate the middle assembly of the retractor according to the present invention. 
           [0101]      FIGS. 28   a - 28   d  illustrate the upper right rack assembly of the retractor according to the present invention. 
           [0102]      FIG. 29  illustrates the upper left rack assembly of the retractor according to the present invention. 
           [0103]      FIGS. 30   a - 30   c  illustrate the various views of the upper right track assembly connected to the right assembly of the retractor according to the present invention. 
           [0104]      FIG. 30   d  illustrates a first end piece of the retractor according to the present invention. 
           [0105]      FIGS. 31   a - 31   c  illustrate the upper right blade support assembly of the retractor according to the present invention. 
           [0106]      FIG. 32  illustrates the lower right blade support assembly of the retractor according to the present invention. 
           [0107]      FIGS. 33   a - 33   c  illustrate the various views of the upper left track assembly connected to the left assembly of the retractor according to the present invention. 
           [0108]      FIG. 33   d  illustrates a second end piece of the retractor according to the present invention. 
           [0109]      FIGS. 34   a - 34   c  illustrate the upper left blade support assembly of the retractor according to the present invention. 
           [0110]      FIG. 35  illustrates the lower left blade support assembly of the retractor according to the present invention. 
           [0111]      FIGS. 36   a - 36   b  illustrate a blade of the retractor according to the present invention. 
           [0112]      FIG. 36   c  illustrates an illuminator connected to a retractor blade according to the present invention. 
           [0113]      FIGS. 37-43  illustrate translation and angulation of the blades of the retractor according to the present invention. 
           [0114]      FIG. 44   a  illustrates a medial blade of the retractor according to the present invention. 
           [0115]      FIG. 44   b  illustrates two medial blades and one illuminator connected to the retractor according to the present invention. 
           [0116]      FIGS. 44   c - 44   d  illustrate three medial blades and one illuminator connected to the retractor according to the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0117]    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. 
         [0118]    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. 
         [0119]    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. 
         [0120]    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. 
         [0121]    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. 
         [0122]    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. 
         [0123]    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. 
         [0124]    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   a  through  1   e . The retractor  10  includes a middle assembly  12 , an upper right rack assembly  14 , an upper left rack assembly  16 , a right assembly  18 , a left assembly  20  and blades  22 . The upper right and left rack assemblies  14 ,  16  are connected to the middle assembly  12 . Blades  22  are connected to the right and left assemblies  18 ,  20 . The right and left assemblies  18 ,  20  are connected to the upper right and left rack assemblies  14 ,  16 , respectively. 
         [0125]    Turning now to  FIG. 2   a , there is shown the middle assembly  12  connected to the upper right rack assembly  14  and upper left rack assembly  16  of the retractor  10  according to the present invention. The middle assembly  12  includes a main body assembly  24  and a main body sub-assembly  26 . 
         [0126]    Referring now to  FIGS. 3   a ,  3   b ,  3   c , and  3   d , the main body assembly  24  includes a main body  28  (shown in  FIGS. 3   a  and  3   b ) and cover  30  (shown in  FIG. 3   c ) with fastener  32  (shown in  FIG. 3   d ). The main body assembly  24  houses the main body sub-assembly  26  as shown in  FIG. 2   a . The main body includes a main body plane which is coincident with the plane of the paper in which  FIG. 1   b  and  FIG. 1   c  are drawn. In  FIGS. 1   d  and  1   e , the main body plane is perpendicular to the plane of the paper on which these figures are drawn. 
         [0127]    Referring now to  FIGS. 4   a ,  4   b ,  4   c ,  4   d ,  4   e ,  4   f , and  4   g , the components of the main body sub-assembly  26  will now be described. The main body sub-assembly  26  includes a middle pinion  34  (shown in  FIG. 4   b ), a middle pinion lock  36  (shown in  FIG. 4   c ), springs  38  (one shown in  FIG. 4   d ), a spring cap  40  (shown in  FIG. 4   e ), and a middle housing release assembly  42  (shown in  FIGS. 4   f ,  4   g , and  4   h ). The middle housing release assembly  42  includes a release body  44  and pins  46  connected thereto as shown in  FIGS. 4   f  and  4   g.    
         [0128]    Referring back to  FIG. 2   d , the assembly of the main body sub-assembly  26  inside the main body  28  will now be described. The middle pinion  34  is disposed inside the main body  28  and the middle pinion lock  36  is configured to engage the middle pinion  34 . The middle pinion lock  36  is biased by a spring  38  which is held in position by the spring cap  40  inside the main body  28 . The lock  36  permits rotation of the middle pinion  34  in one direction locking it from rotation in an opposite direction. The middle housing release assembly  42  is connected to the main body assembly  24  and configured such that two springs  38  bias the release body  44  outwardly and such one of the pins  46  engage the lock  36  when the release body  44  is depressed to thereby unlock the middle pinion  34  allowing it to rotate in the opposite direction. 
         [0129]    Referring now to  FIGS. 5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  5   f , and  5   h  the upper right rack assembly  14  will now be described. The upper right rack assembly  14  includes a rack support  48  (shown in  FIGS. 5   b  and  5   c ), a straight rack  50  (shown in  FIG. 5   d ), tow angle post  52  (shown in  FIGS. 5   e  and  5   f ), and tow angle return  54  (shown in  FIG. 5   g ). The straight rack  50  is inserted into the rack support  48  and connected by a pin  56  like the one shown in  FIG. 5   h . As shown in  FIG. 5   b , the rack support  48  includes a passageway  58  for receiving a straight rack  50  of the upper left rack assembly  16 . The rack support  48  also includes a second passageway  60  for receiving and connecting to the right assembly  18 . The tow angle post  52  is inserted into a threaded aperture  61  in the rack support  48  and threadingly connected thereto. The tow angle return  54  is inserted into and threadingly connected to the distal end of the tow angle post  52 . As such, the tow angle post  52  and the tow angle return  54  are configured to capture the right assembly  18  therebetween to control the angulation and rotation of the right assembly  18  with respect to the upper right rack assembly  14  as will be described in greater detail below. 
         [0130]    Turning now to  FIGS. 6   a  and  6   b , the upper left rack assembly  16  will now be described. The upper left rack assembly  16  includes a rack support  62  (shown in  FIG. 6   b ), a straight rack  64 , tow angle post  66 , and tow angle return (not shown). The straight rack  64  is inserted into the rack support  62  and connected by a pin (not shown but like the one shown in  FIG. 5   h ). The rack support  62  includes a passageway  72  for receiving the straight rack  50  of the upper right rack assembly  14 . The rack support  62  also includes a second passageway  74  for receiving and connecting to the left assembly  20 . The tow angle post  66  is inserted into a threaded aperture  75  formed in the rack support  62  and threadingly connected thereto. The tow angle return  68  is inserted into and threadingly connected to the distal end of the tow angle post  66  similarly as described above with respect the upper right rack assembly  14 . As such, the tow angle post  66  and the tow angle return  68  are configured to capture the left assembly  20  therebetween to control the angulation and rotation of the left assembly  20  with respect to the upper left rack assembly  16  as will be described in greater detail below. 
         [0131]    Turning now to  FIG. 7 , the right assembly  18  will now be described. The right assembly  18  includes an upper right blade support assembly  76  connected to a lower right blade support assembly  78 . 
         [0132]    Turning now to  FIG. 8   a , the upper right blade support assembly  76  will now be described. The upper right blade support assembly  76  includes a mounting arm  80  connected to a mounting arm sub-assembly  82  and blade support  84 . 
         [0133]    Turning now to  FIGS. 8   b  and  8   c , there is shown a mounting arm  80  according to the present invention. The mounting arm  80  includes a mounting arm longitudinal axis, a threaded proximal end  86 , a distal end  88 , a mounting arm sub-assembly receiving portion  90  located near the distal end  88  and a central bore  92  extending between the proximal end  86  and distal end  88 . The mounting arm  80  is configured to be received within passageway  60  of the upper right rack assembly  14 . 
         [0134]    Turning now to  FIGS. 8   d ,  8   e ,  8   f ,  8   g , and  8   h , the mounting arm sub-assembly  82  will now be described. The mounting arm sub-assembly  82  includes a pinion  94  (shown in  FIG. 8   d ), retaining collar  96  (shown in  FIG. 8   e ), gear lock  98  (shown in  FIG. 8   f ), and a pin  100  (shown in  FIG. 8   g ). The pinion  94  is disposed inside the mounting arm  80  and retained therein with the retaining collar  96 . With particular reference back to  FIG. 8   h , the gear lock  98  is connected to the mounting arm  80  via pin  100  and configured for contact with a ratcheting pin (not shown) and in turn with the pinion. A spring  102  is employed to bias the gear lock  98  against a ratcheting pin (not shown) in the central bore  92  to lock the ratcheting pin and pinion  94  in position. The gear lock  98  is configured such that pinion which is interconnected to the ratcheting via teeth is allowed to rotate in one direction locking it from rotation in an opposite direction. The gear lock  98  can be depressed to thereby unlock the pinion  94  allowing it to rotate in the opposite direction. 
         [0135]    Turning now to  FIGS. 8   i  and  8   j , there is shown the blade support  84  according to the present invention. The blade support  84  includes a mounting arm receiving portion  104 , a blade flange  106  configured for attachment to a blade  22 , a tow angle post receiving portion  108  and a tow angle return receiving portion  110 , both the tow angle post receiving portion  108  and the tow angle return receiving portion  110  both comprising a single bore extending through the blade support  84 . 
         [0136]    The mounting arm  80  is inserted into the mounting arm receiving portion  104  and the mounting arm  80  is inserted into the second passageway  60  of the upper right rack assembly  14 . The threaded proximal end  86  is capped with an internally threaded end cap  112  shown in  FIG. 8   k . The mounting arm  80  is oriented and the tow angle post  52  is inserted into the tow angle post receiving portion  108 . The tow angle return  54  is inserted into the tow angle return receiving portion  110  and threaded into the tow angle post  52  capturing the blade support  84  therebetween. 
         [0137]    Turning now to  FIGS. 9   a ,  9   b  and  9   c , there is shown the lower right blade support assembly  78 . The lower right blade support assembly  78  includes a toothed ratcheting pin  114  (shown in  FIG. 9   b ) connected to a lower right blade support  116  (shown in  FIG. 9   c ). 
         [0138]    With particular reference to  FIG. 9   c , the lower right blade support includes a ratcheting pin receiving portion  118  connected to a blade flange  120  configured for attachment to a blade  22 . The ratcheting pin  114  is inserted into the ratcheting pin receiving portion  118 , one end of which includes a stop and the other end being inserted into the central bore  92  of the mounting arm  80  such that the toothed ratcheting pin  114  engages the teeth of the pinion  94  and is permitted to slide with respect to the upper right blade support assembly  76  upon turning of the pinion  94 . 
         [0139]    Turning now to  FIG. 10 , there is shown the left assembly  20 . The left assembly  20  includes an upper left blade support assembly  122  connected to a lower left blade support assembly  124 . 
         [0140]    Turning now to  FIG. 11   a , the upper left blade support assembly  122  will now be described. The upper left blade support assembly  122  includes a mounting arm  126  connected to a mounting arm sub-assembly  128  and blade support  130 . 
         [0141]    Turning now to  FIGS. 11   b  and  11   c , the mounting arm  126  will now be described. The mounting arm  126  includes a mounting arm longitudinal axis, a threaded proximal end  132 , a distal end  134 , a mounting arm sub-assembly receiving portion  136  located near the distal end  134  and a central bore  138  extending between the proximal end  132  and distal end  134 . The mounting arm  126  is configured to be received within second passageway  74  of the upper left rack assembly  16 . 
         [0142]    The mounting arm sub-assembly  128  will now be described. The mounting arm sub-assembly  128  includes a pinion (shown in  FIG. 8   d ), retaining collar (shown in  FIG. 8   e ), gear lock  144  (shown in  FIG. 11   d ), and a pin (shown in  FIG. 8   g ). The pinion is disposed inside the mounting arm  126  and retained therein with the retaining collar. With particular reference to  FIG. 11   e , the gear lock  144  is connected to the mounting arm  126  via a pin  100  and configured for contact with the pinion (not shown in  FIG. 11   e ) via a ratcheting pin (not shown in  FIG. 11   e ). A spring  102  is employed to bias the gear lock  144  against a ratcheting pin (not shown) in the central bore  138  to lock the ratcheting pin and the pinion in position. The gear lock  144  is configured such that the pinion is allowed to rotate in one direction locking it from rotation in an opposite direction. The gear lock  144  can be depressed to thereby unlock the pinion allowing it to rotate in the opposite direction. 
         [0143]    Turning now to  FIGS. 11   f  and  11   g , the blade support  130  will now be described. The blade support  130  includes a mounting arm receiving portion  148 , a blade flange  150  configured for attachment to a blade  22 , a tow angle post receiving portion  152  and a tow angle return receiving portion  154  (shown in  FIG. 11   g ), both the tow angle post receiving portion  152  and the tow angle return receiving portion  154  comprising a bore extending through the blade support  130 . 
         [0144]    Assembly of the upper left blade support assembly  122  will now be described. The mounting arm  126  is inserted into the mounting arm receiving portion  148  and the mounting arm  126  is inserted into the second passageway  74  of the upper left rack assembly  16 . The threaded proximal end  132  is capped with an internally threaded end cap of the like shown in  FIG. 8   k . The mounting arm  126  is oriented and the tow angle post is inserted into the tow angle post receiving portion  152 . The tow angle return is inserted into the tow angle return receiving portion  154  and threaded into the tow angle post capturing the blade support  130  therebetween. 
         [0145]    Turning now to  FIGS. 12   a  and  12   b , there is shown the lower left blade support assembly  124 . The lower left blade support assembly  124  includes a toothed ratcheting pin  156  of the like shown in  FIG. 9   b  connected to a lower left blade support  158  (shown in  FIG. 12   b ). 
         [0146]    With particular reference to  FIG. 12   b , the lower left blade support  158  includes a ratcheting pin receiving portion  160  connected to a blade flange  162  configured for attachment to a blade  22 . The ratcheting pin  156  is inserted into the ratcheting pin receiving portion  160 , one end of ratcheting pin  156  including a stop and the other end being inserted into the central bore  138  of the mounting arm  126  such that the toothed ratcheting pin  156  engages the teeth of the pinion and is permitted to slide with respect to the upper left blade support assembly  122 . 
         [0147]    As seen in the figures, the left assembly  20  is a mirror image of the right assembly  18 . 
         [0148]    Turning now to  FIGS. 13   a  and  13   b , there is shown a retractor blade  22  that is configured to be removably attached to the blade supports  84 ,  116 ,  130 ,  158  making the blades  22  interchangeable with other blades of different length(s). The blade  22  includes a hook or tang  164  for connecting with the blade supports. The hook  164  is capable of deflection to capture and release a retractor blade  22 . 
         [0149]    The use of the retractor will now be discussed. With reference to  FIG. 14 , 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 W of the closed retractor base. The closed retractor base dimension W is shown in  FIG. 14  to be approximately 2.0 to 5.0 centimeters in one variation and in another variation approximately 2.6 centimeters. 
         [0150]    Referring now to  FIG. 15 , a first dilator  200  is inserted into the incision and advanced through the fascia and muscle tissue. Placement of the first dilator  200  is confirmed with fluoroscopy and by palpating the bony anatomy  201 . Additional dilators two-through-four  202  are placed sequentially by passing the next largest dilator over the previously inserted dilator as shown in  FIG. 16 . 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  204  on the last dilator as shown in  FIG. 16 . The tissue depth read from the etch markings  204  directly corresponds to the suggested retractor blade length for use with the retractor  10 . The selected blades are inserted into the four blade supports  84 ,  116 ,  130 ,  158  as shown in  FIG. 17   a . When a blade  22  is fully seated within a blade support there is an audible and tactile “click”. Also, when the blade  22  is fully engaged with the blade supports, the hook  164  of the retractor blade  22  is clipped over the blade support as shown in  FIG. 17   b . Various retractor blades  22  of different lengths are shown in  FIG. 17   c  ranging from approximately 30 mm to 120 mm. Each length being coded to a different retractor blade color for ease of selection and installation into the retractor  10 . 
         [0151]    Turning now to  FIG. 18   a , to facilitate placement, a retractor inserter  206  having a knob  208  is provided. The knob  208  is oriented into an unlocked position and the retractor inserter  206  is placed over the retractor  10  aligning the holes on the retractor with the holes on the inserter as shown in  FIGS. 18   b  and  18   c . To secure the inserter onto the retractor, the knob is turned clockwise until a mechanical stop is reached and the etch markings on the inserter indicate the locked position. 
         [0152]    Turning now to  FIGS. 19   a  and  19   b , retractor placement is shown. With the dilators  200 ,  202  in place in the patient and the retractor  10  connected to the inserter  206 , the handles  210  of the retractor inserter  206  are used to toggle the retractor  10  through the tissue opening the dilators  200 ,  202  into position over the bony anatomy with the fanned support base  212  positioned next to the midline. After placement of the retractor  10  is confirmed with fluoroscopy, the dilators  200 ,  202  are removed and the retractor inserter  206  is disengaged by turning the knob  208  counterclockwise to the unlocked position and pulling it upwardly to remove the retractor inserter  206 . The retractor  10  is secured to a rigid arm (not shown) at the fanned support base  212  which accommodates both flat and pin style clamps. 
         [0153]    Turning now to  FIGS. 20   a ,  20   b  and  20   c , translation of the retractor  10  will now be discussed. A T-shaped handle hex driver  214  is inserted into the hex socket of the middle pinion  34  as shown in  FIG. 20   a . When the pinion  34  is rotated, the retractor  10  expands from the configuration shown in  FIG. 20   a  into the configuration shown in  FIG. 20   b . The maximum cephalad-caudal span is shown by the distance C in  FIG. 20   c . C is any dimension in the range of 5.0 and 20 centimeters. In one variation, C is approximately 8 centimeters. Although dimension C is called a cephalad-caudal span, the invention is not so limited as the retractor can be oriented in a number of other orientations with respect to patient anatomy and the dimension is not limited thereby. Distance C is the distance of maximum expansion attainable between the right and left assemblies  18 ,  20 . 
         [0154]    Turning now to  FIGS. 21   a  and  21   b,  for medial-lateral translation, or upper-to-lower translation, the hex driver  214  is inserted into one or more of the two hex sockets of pinions  94 ,  140  as shown in  FIG. 21   a.  Each click with turning of the hex driver expands the lower right and left blade support assemblies  78 ,  122  outwardly in the medial-lateral direction by approximately 1.0 mm and up to a maximum span L in the range of between approximately 2.0 centimeters and approximately 10.0 centimeters and in one variation approximately 4.5 centimeters as shown in  FIG. 21   b . The hex driver  214  can be switched back and forth between hex sockets of pinions  34 ,  94  and  140  expanding a few millimeters each time until the optimal working channel is achieved according to surgeon preference. Of course, although dimension L is referred to as the medial-lateral translation distance, the invention is not limited to the orientation of the instrument with respect to the patient anatomy. The distance L is the distance between the upper and lower units of the right and left assemblies  18 ,  20 . 
         [0155]    Turning now to  FIGS. 22   a ,  22   b  and  22   c , angulation of the retractor blades  22  is shown. To angle the retractor blades  22 , the hex driver  214  is inserted into the one or more of the two hex sockets of the tow angle posts  52 ,  66 . Turning the right tow angle post  52  angles the blades of the right assembly  18  and turning the left tow angle post  66  angles the blades of the left assembly  20 . The blades  22  angle up to a maximum of approximately 30 degrees in one variation. Maximum anglation 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  22  of a first length are employed, the maximum distal span is distance T 1  which for a 30 millimeter long blade is approximately 11 centimeters as shown in  FIG. 22   b . If blades of a second length are employed, the maximum distal span is distance T 2  which for a 90 millimeter long blade is approximately 17 centimeters as shown in  FIG. 22   c . A table of approximate maximum distal spans corresponding to certain blade lengths is shown in  FIG. 23 . 
         [0156]    Turning now to  FIGS. 24   a ,  24   b  and  24   c , blade removal will now be described. If a smaller or larger blade length is required after the retractor has been placed inside the patient, a blade removal tool  216  is employed. The blade  22  to be removed is first identified and then the blade removal tool  216  is held in one hand and aligned such that the proximal leg  218  of the tool  216  is in line with the corresponding slot  220  on top of the blade  22  as shown in  FIG. 24   b . The blade removal tool  216  is pushed down into the slot  220  and then the handles of the blade removal tool  216  are squeezed together to release the blade  22 . When the handles are squeezed, the proximal leg  218  of the tool contacts the blade  22  while the distal leg  222  of the tool depresses the hook  164  on the blade  22  deflecting it to release the blade from the retractor  10  as the tool is pulled up as shown in  FIG. 24   c.    
         [0157]    Turning now to  FIGS. 25   a ,  25   b  and  25   c , 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 by turning the one or more of the two hex sockets of the tow angle posts  52 ,  66  with the hex driver  214  as shown in  FIG. 25   a . To retract the extended right and left assemblies  18 ,  20 , the release body  44  is depressed as shown in  FIG. 25   b  effecting cephalad-caudal release. To retract the extended lower right blade support  84 , the gear lock  98  is depressed as shown in  FIG. 25   c  effecting medial-lateral release of the right side. With reference back to  FIG. 25   a , to retract the extended lower left blade support  158 , the gear lock  144  is depressed effecting medial lateral release of the left side. 
         [0158]    Turning now to  FIGS. 26   a  and  26   b , there is shown another variation of the retractor according to the present invention. Like reference numbers will be used to describe like parts with respect to this variation of the retractor. The retractor  10  includes a middle assembly  12 , an upper right rack assembly  14 , an upper left rack assembly  16 , a right assembly  18 , a left assembly  20  and blades  22 . The upper right and left rack assemblies  14 ,  16  are connected to the middle assembly  12 . Blades  22  are connected to the right and left assemblies  18 ,  20 . The right and left assemblies  18 ,  20  are connected to the upper right and left rack assemblies  14 ,  16 , respectively. 
         [0159]    Referring now to  FIGS. 27   a ,  27   b ,  27   c , and  27   d , the middle assembly  12  includes a main body assembly  24  and a main body sub-assembly  26 . The main body assembly  24  includes a main body  28  (shown in  FIGS. 27   a  and  27   b ) and cover  30  (shown in  FIG. 27   c ) with fastener. The main body assembly  24  houses the main body sub-assembly  26  as shown in  FIG. 27   d . The main body includes a main body plane which is coincident with the plane of the paper in which  FIG. 26   b  is drawn. 
         [0160]    Referring particular reference now to  FIG. 27   a , the components of the main body sub-assembly  26  will now be described. The main body sub-assembly  26  includes a middle pinion  34  (of a type shown in  FIG. 4   b ), a middle pinion lock  36  (of a type shown in  FIG. 4   c ), springs  38  (one shown in  FIG. 4   d ), a spring cap  40  (of a type shown in  FIG. 4   e ), and a middle housing release assembly  42  (shown in  FIGS. 4   f ,  4   g , and  4   h ). The middle housing release assembly  42  includes a release body  44  and pins  46  connected thereto as also shown in  FIGS. 4   f  and  4   g . The main body sub-assembly  26  is substantially the same as that described above with respect to  FIGS. 4   a - 4   h . Also, the assembly of the main body sub-assembly  26  inside the main body  28  is substantially the same as described above with respect to  FIGS. 4   a - 4   h  and will now be described. The middle pinion  34  is disposed inside the main body  28  and the middle pinion lock  36  is configured to engage the middle pinion  34 . The middle pinion lock  36  is biased by a spring  38  which is held in position by the spring cap  40  inside the main body  28 . The lock  36  permits rotation of the middle pinion  34  in one direction locking it from rotation in an opposite direction. The middle housing release assembly  42  is connected to the main body assembly  24  and configured such that two springs  38  bias the release body  44  outwardly and such one of the pins  46  engage the lock  36  when the release body  44  is depressed to thereby unlock the middle pinion  34  allowing it to rotate in the opposite direction. The cover  30  and fasteners are used to contain the main body sub-assembly  26  inside the main body assembly  24 . 
         [0161]    Referring now to  FIGS. 28   a ,  28   b ,  28   c  and  28   d , the upper right rack assembly  14  will now be described. The upper right rack assembly  14  includes a rack support  48 , a straight rack  50 , a first tow angle post  52   a , a second tow angle post  52   b  (wherein the first and second tow angle post are the same and shown in  FIG. 28   b ) and tow angle return  54  connected to each of the tow angle posts  52   a ,  52   b . A tow angle return  54  is shown in  FIG. 28   c . The straight rack  50  is inserted into the rack support  48  and connected by a pin (not shown). As shown in  FIG. 28   a , the rack support  48  includes a passageway  58  for receiving a straight rack  50  of the upper left rack assembly  16 . The rack support  48  also includes a second passageway  60  for receiving and connecting to the right assembly  18 . The first and second tow angle posts are inserted into respective threaded apertures in the rack support  48  and threadingly connected thereto. The tow angle post  52  includes a hex socket  59  and a first threaded portion  53  and a second threaded portion  55  as shown in  FIG. 28   b . The first threaded portion  53  connects with the rack support  48  and the second threaded portion  55  connects with the threaded portion  57  ( FIGS. 28   c  and  28   d ) on the tow angle return  54 . The tow angle return  54  includes an access portal  63  (shown in  FIG. 28   d ) for delivery and assembly of the tow angle return, holding it in place as it is threaded to the tow angle post, and injecting weld material or adhesive to connect the tow angle post to the tow angle return. The tow angle return  54  is threaded onto to the distal end of the tow angle post  52  at the second threaded portion  55 . As such, the first tow angle post  52   a  and the tow angle return  54  are configured to capture a first portion of the right assembly  18  therebetween to control the angulation and rotation of said first portion of the right assembly  18  with respect to the upper right rack assembly  14 . The second tow angle post  52   b  and tow angle return  54  are connected and configured to capture a second portion of the right assembly  18  as will be described in greater detail below. 
         [0162]    Turning now to  FIG. 29 , the upper left rack assembly  16  will now be described. The upper left rack assembly  16  includes a rack support  62 , a straight rack  64 , a first tow angle post  66   a , a second tow angle post  66   b , and a tow angle return of the type shown in  FIGS. 28   b  and  28   c  connected to each of the tow angle posts  66   a ,  66   b . The straight rack  64  is inserted into the rack support  62  and connected by a pin (not shown). The rack support  62  includes a passageway  72  for receiving the straight rack  50  of the upper right rack assembly  14 . The rack support  62  also includes a second passageway  74  for receiving and connecting to the left assembly  20 . The first and second tow angle posts are inserted into respective threaded apertures in the rack support  62  and threadingly connected thereto. The tow angle returns are inserted into and threadingly connected to the distal ends of the tow angle posts  66   a  and  66   b  similarly as described above with respect the upper right rack assembly  14 . As such, the first tow angle post  66   a  and the tow angle return are configured to capture a first portion of the left assembly  20  therebetween to control the angulation and rotation of said first portion of the left assembly  20  with respect to the upper left rack assembly  16 . The second tow angle post  66   b  and the tow angle return are configured to capture a second portion of the left assembly  20  therebetween to control the angulation and rotation of said second portion of the left assembly  20  as will be described in greater detail below. 
         [0163]    Turning now to  FIGS. 30   a ,  30   b ,  30   c  and  30   d , the upper right track assembly  14  is shown connected to the right assembly  18 . The right assembly  18  will now be described. The right assembly  18  includes an upper right blade support assembly  76  connected to a lower right blade support assembly  78 . 
         [0164]    Turning now to  FIGS. 31   a,    31   b , and  31   c  the upper right blade support assembly  76  will now be described. The upper right blade support assembly  76  includes a mounting arm  80  ( FIGS. 31   a  and  31   b ) connected to a mounting arm sub-assembly  82  ( FIGS. 31   a  and  31   b ) and blade support  84  ( FIG. 31   c ). 
         [0165]    Turning now to  FIGS. 31   a  and  31   b,  there is shown a mounting arm  80  according to the present invention. The mounting arm  80  includes a longitudinal axis, a proximal end  86 , a distal end  88 , a mounting arm sub-assembly receiving portion  90  located near the distal end  88  and a central bore  92  extending between the proximal end  86  and distal end  88 . The mounting arm  80  is configured to be received within passageway  60  of the upper right rack assembly  14  and connected thereto. 
         [0166]    Still referencing  FIGS. 31   a  and  31   b , the mounting arm sub-assembly  82  will now be described. The mounting arm sub-assembly  82  includes a pinion  94  (of the type shown in  FIG. 8   d ), retaining collar  96  (shown in  FIG. 8   e ), gear lock  98  (also shown in  FIG. 8   f ), and a pin  100  (shown in  FIG. 8   g ). The pinion  94  is disposed inside the mounting arm  80  and retained therein with the retaining collar  96 . The gear lock  98  is connected to the mounting arm  80  via pin  100  and configured for contact with a ratcheting pin (not shown) and in turn with the pinion  94 . A spring  102  is employed to bias the gear lock  98  against a ratcheting pin (not shown) in the central bore  92  to lock the ratcheting pin and pinion  94  in position. The gear lock  98  is configured such that pinion which is interconnected to the ratcheting pin via teeth is allowed to rotate in one direction locking it from rotation in an opposite direction in a manner such that incremental extension of the ratcheting pin is locked in place with turning of the pinion  94 . The gear lock  98  can be depressed to thereby unlock the pinion  94  allowing it to rotate in the opposite direction thereby permitting retraction of the ratcheting pin. 
         [0167]    Turning now to  FIG. 31   c,  there is shown the blade support  84  according to the present invention. The blade support  84  includes a mounting arm receiving portion  104 , a blade flange  106  configured for attachment to a blade  22 , a tow angle post receiving portion  108  and a tow angle return receiving portion  110 , both the tow angle post receiving portion  108  and the tow angle return receiving portion  110  are interconnected. 
         [0168]    The mounting arm  80  is inserted into the mounting arm receiving portion  104  and the mounting arm  80  is inserted into the second passageway  60  of the upper right rack assembly  14 . The threaded proximal end  86  is capped with an internally threaded end cap  112  like the one shown in  FIG. 8   k . The mounting arm  80  is oriented and the first tow angle post  52   a  is inserted into the first tow angle post receiving portion  108 . The tow angle return  54  is inserted into the tow angle return receiving portion  110  and threaded onto the first tow angle post  52   a  and connected thereto with adhesive or welding material injected through the tow angle return access portal  63  capturing the blade support  84  therebetween as shown in  FIG. 30   b.    
         [0169]    Turning now to  FIG. 32 , there is shown the lower right blade support assembly  78 . The lower right blade support assembly  78  includes a toothed ratcheting pin  114  connected to a lower right blade support  116 . The lower right blade support includes a ratcheting pin receiving portion  118  connected to a blade flange  120  configured for attachment to a blade  22 . The ratcheting pin  114  is inserted into the ratcheting pin receiving portion  118 , one end of which includes a stop and the other end being inserted into the central bore  92  of the mounting arm  80  such that the toothed ratcheting pin  114  engages the teeth of the pinion  94  and is permitted to slide with respect to the upper right blade support assembly  76  upon turning of the pinion  94 . A second tow angle post  52   b  is inserted into a second tow angle post receiving portion  232  of a first end piece  224  and threaded to the second tow angle post return inserted through a tow angle post receiving portion  234  of the first end piece  224  (shown in  FIG. 30   d ) and connected thereto with adhesive or welding material injected through the tow angle return access portal  63  capturing the first end piece  224  therebetween as shown in  FIGS. 26   c  and  30   c.    
         [0170]    Turning now to  FIGS. 33   a ,  33   b  and  33   c , the upper left track assembly  16  is shown connected to the left assembly  20 . The left assembly  20  will now be described. The left assembly  20  includes an upper left blade support assembly  122  connected to a lower left blade support assembly  124 . 
         [0171]    Turning now to  FIGS. 34   a ,  34   b , and  34   c , the upper left blade support assembly  122  will now be described. The upper left blade support assembly  122  includes a mounting arm  126  ( FIGS. 34   a  and  34   b ) connected to a mounting arm sub-assembly  128  ( FIGS. 34   a  and  34   b ) and blade support  130  ( FIG. 34   c ). 
         [0172]    Turning now to  FIGS. 34   a  and  34   c , the mounting arm  126  will now be described. The mounting arm  126  includes a longitudinal axis, a proximal end  132 , a distal end  134 , a mounting arm sub-assembly receiving portion  136  located near the distal end  134  and a central bore  138  extending between the proximal end  132  and distal end  134 . The mounting arm  126  is configured to be received within second passageway  74  of the upper left rack assembly  16  and connected thereto. 
         [0173]    Still referencing  FIGS. 34   a  and  34   b , the mounting arm sub-assembly  128  will now be described. The mounting arm sub-assembly  128  includes a pinion  94  (shown in  FIG. 8   d ), retaining collar  96  (shown in  FIG. 8   e ), gear lock  144  (shown in  FIG. 11   d ), and a pin  100  (shown in  FIG. 8   g ). The pinion  94  is disposed inside the mounting arm  126  and retained therein with the retaining collar  96 . The gear lock  144  is connected to the mounting arm  126  via a pin  100  and configured for contact with the pinion  94  via a ratcheting pin (not shown). A spring  102  is employed to bias the gear lock  144  against a ratcheting pin (not shown) in the central bore  138  to lock the ratcheting pin and the pinion in position. The gear lock  144  is configured such that the pinion is allowed to rotate in one direction locking it from rotation in an opposite direction in a manner such that incremental extension of the ratcheting pin is locked in place with turning of the pinion. The gear lock  144  can be depressed to thereby unlock the pinion allowing it to rotate in the opposite direction thereby permitting retraction of the ratcheting pin. 
         [0174]    Turning now to  FIG. 31   c,  there is shown the blade support  130  according to the present invention. The blade support  130  includes a mounting arm receiving portion  148 , a blade flange  150  configured for attachment to a blade  22 , a tow angle post receiving portion  152  and a tow angle return receiving portion  154 , both the tow angle post receiving portion  152  and the tow angle return receiving portion  154  comprising interconnected bores through the blade support  130 . 
         [0175]    The mounting arm  126  is inserted into the mounting arm receiving portion  148  and the mounting arm  126  is inserted into the second passageway  74  of the upper left rack assembly  16 . The threaded proximal end  132  is capped with an internally threaded end cap of the like shown in  FIG. 8   k . The mounting arm  126  is oriented and a third tow angle post  52   c  is inserted into the tow angle post receiving portion  152 . The tow angle return is inserted into the tow angle return receiving portion  154  and threaded into the tow angle post capturing the blade support  130  therebetween as shown in  FIG. 33   b.    
         [0176]    Turning now to  FIG. 35 , there is shown the lower left blade support assembly  124 . The lower left blade support assembly  124  includes a toothed ratcheting pin  156  connected to a lower left blade support  158 . The lower left blade support  158  includes a ratcheting pin receiving portion  160  connected to a blade flange  162  configured for attachment to a blade  22 . The ratcheting pin  156  is inserted into the ratcheting pin receiving portion  160 , one end of ratcheting pin  156  including a stop and the other end being inserted into the central bore  138  of the mounting arm  126  such that the toothed ratcheting pin  156  engages the teeth of the pinion and is permitted to slide with respect to the upper left blade support assembly  122  upon turning of the pinion  94 . A fourth tow angle post  52   d  is inserted into a fourth tow angle post receiving portion  226  of a second end piece  230  and threaded to a third to a tow angle post return inserted through a tow angle post return receiving portion  228  (shown in  FIG. 33   d ) and connected thereto with adhesive or welding material injected through the tow angle return access portal capturing the end piece  230  therebetween as shown in  FIGS. 26   c  and  33   c.    
         [0177]    As seen in the figures, the left assembly  20  is a mirror image of the right assembly  18 . 
         [0178]    Turning now to  FIGS. 36   a  and  36   b , there is shown an other variation of a retractor blade  22  that is configured to be removably attached to the blade supports  84 ,  116 ,  130 ,  158  making the blades  22  interchangeable with other blades of different length(s). The blade  22  includes a hook or tang  164  for connecting with the blade supports. The hook  164  is capable of deflection to capture and release a retractor blade  22 . The blade further includes a channel  236  for receiving the blade supports. The blade channels  236  are configured to support an illuminator  240  as shown in  FIG. 36   c . As seen in the figures, the retractor blades are connected to the blade supports such that the blades extend perpendicularly with respect to the general plane in which right and left assemblies  18 ,  20  lie. The blades comprise elongate bodies having an inner face and an outer face and a longitudinal axis expending from a proximal end to a distal end. The inner face is generally concave such that the inner faces of four blades placed together form a circular inner perimeter. 
         [0179]    The use of the retractor is substantially the same as described above with reference to  FIGS. 14-19 . 
         [0180]    Turning now to  FIG. 37 , translation of the retractor  10  will now be discussed. With blades  22  attached and the retractor  10  positioned inside the operative site, a T-shaped handle hex driver  214  is inserted into the hex socket of the middle pinion  34  as shown in  FIG. 37 . When the pinion  34  is rotated, the retractor  10  expands into the configuration shown in  FIG. 20  along the direction shown by the arrows A. As the T-shaped hex driver  214  is incrementally turned, the expanded position is locked in position. Reversal of the expansion is accomplished by depressing the release body  44  which unlocks the position for retraction. 
         [0181]    Turning now to  FIG. 38 , the hex driver  214  is shown inserted into the hex socket of the pinion  94  in the upper left blade support  122  and rotated to drive the ratcheting pin  156  to extend outwardly the lower left blade support  158  as shown by the arrows B. In one variation, reversal of the extension of the lower left blade support  158  is accomplished by rotating the hex driver  214  in the opposite direction. In an alternative variation, the gear lock  144  is employed as a quick release of the extension of the lower left blade support  158  into a relatively retracted position. 
         [0182]    Turning now to  FIG. 39 , the hex driver  214  is shown inserted into the hex socket of the pinion  94  in the upper right blade support  76  and rotated to drive the ratcheting pin  114  to extend outwardly the lower right blade support  116  as shown by the arrows C. In one variation, reversal of the extension of the lower right blade support  116  is accomplished by rotating the hex driver  214  in the opposite direction. In an alternative variation, the gear lock  98  is depressed to quickly release the lock and permit quick retraction of the lower right blade support  116 . 
         [0183]    Turning now to  FIG. 40 , the hex driver  214  is shown inserted into the hex socket of tow angle post  52   c  and rotated to pivot the upper left blade support  130  with respect to the mounting arm  126  of the upper left blade support assembly  122  as shown by the arrows D. Reversal of the pivoting is accomplished by rotating the hex driver within the tow angle post  52   c  in the opposite direction to an angle desired by the surgeon. 
         [0184]    Turning now to  FIG. 41 , the hex driver  214  is shown inserted into the hex socket of tow angle post  52   a  and rotated to pivot the upper right blade support  84  with respect to the mounting arm  80  of the upper right blade support assembly  76  as shown by the arrows E. Reversal of the pivoting is accomplished by rotating the hex driver within the tow angle post  52   a  in the opposite direction to an angle desired by the surgeon. 
         [0185]    Turning now to  FIG. 42 , the hex driver  214  is shown inserted into the hex socket of tow angle post  52   d  and rotated to pivot the lower left blade support  130  with respect to the upper left rack assembly  16  as shown by the arrows F. Reversal of the pivoting is accomplished by rotating the hex driver within the tow angle post  52   d  in the opposite direction to a desired angle. 
         [0186]    Turning now to  FIG. 43 , the hex driver  214  is shown inserted into the hex socket of tow angle post  52   b  and rotated to pivot the lower right blade support  116 . with respect to the upper right rack assembly  14  as shown by arrows G. Reversal of the pivoting is accomplished by rotating the hex driver within the tow angle post  52   b  in the opposite direction to a desired angle. 
         [0187]    Turning now to  FIGS. 44   a ,  44   b ,  44   c  and  44   d , there is shown a medial blade  250  configured for placement between blade supports  84 ,  116 ,  130 ,  158  for additional tissue retraction capability. The medial blade  250  includes a channel  252  for hooking onto one of the ratcheting pins and movable into a desired position along the ratcheting pin as shown in  FIG. 44   b . Another variation of the medial blade  250  is shown in  FIGS. 44   c  and  44   d  where the medial blade is shown hooked on one of the straight racks  50 ,  64 . One variation of the medial blade  250  shown in  FIG. 44   d  includes an angled portion  254  configured to angle the blade into the working space for tissue retraction. 
         [0188]    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.