Abstract:
A method for creating a sequence of access channels to provide access for performing surgery on a lumbar spine; through positioning a patient to facilitate surgical access to the lumbar spine; docking a retractor device against a proximal surface of the psoas muscle and maintaining the pre-psoas access channel with the retractor device docked at the proximal surface of the psoas muscle. Making a direct visual inspection of the psoas muscle before splitting the psoas muscle to create and maintain a psoas access channel that extends from the pre-psoas access channel to the spine. Holding open the psoas access channel with a pair of retractor blades. After completing a surgical process on the spine removing the pair of retractor blades from the psoas access channel.

Description:
[0001]    This application is a continuation of co-pending and commonly assigned U.S. patent application Ser. No. 12/798,405 for Surgical Retractor System filed Apr. 3, 2010. The &#39;405 application claims the benefit of two provisional applications, 61/251,281 filed Oct. 14, 2009 and 61/211,835 filed Apr. 3, 2009. All three applications are incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    Surgical retractors are used to provide access to a surgical site and to provide a clear view of the operating field. A retractor has one or more surfaces that contact tissues or organs in order to hold open an incision or to enlarge an anatomical space. The retracted elements may include any of various tissues or organs such as skin, muscle, nerves, blood vessels, or other tissues or organs. In some types of retractors, one or more blades (elongated laminae) serve to retract tissue, with a frame or arm or handles holding the blades at the chosen positions. The positions typically are variable during the positioning process. The blades may have a hook shape, like the letter J. Another type of retractor is a tubular retractor, which is a tube that is open at both ends. In one common embodiment, tubular retractors come in nesting sets. 
         [0003]    Retractors are used for a wide variety of purposes in surgery. However, in some uses, conventional retractors are not entirely satisfactory. Current surgical practice emphasizes access to surgical sites via paths that are not necessarily the most direct, in order to minimize collateral damage in the process of the surgery, or to preferentially incise tissue that heals rapidly. The resulting preferred access paths can be longer or more tortuous than classical access paths, even while producing shorter recovery periods or minimizing damage to tissues. 
         [0004]    In turn, such more complex access paths can be difficult to establish or maintain with a classical retractor. Improved retractor systems, carefully designed and fabricated to allow them to work in concert, are needed to facilitate the performance of these improved methods of surgery. 
       SUMMARY OF THE DISCLOSURE 
       [0005]    Aspects of the teachings contained within this disclosure are addressed in the claims submitted with this application upon filing. Rather than adding redundant restatements of the contents of the claims, these claims should be considered incorporated by reference into this summary. 
         [0006]    This summary is meant to provide an introduction to the concepts that are disclosed within the specification without being an exhaustive list of the many teachings and variations upon those teachings that are provided in the extended discussion within this disclosure. Thus, the contents of this summary should not be used to limit the scope of the claims that follow. 
         [0007]    Inventive concepts are illustrated in a series of examples, some examples showing more than one inventive concept. Individual inventive concepts can be implemented without implementing all details provided in a particular example. It is not necessary to provide examples of every possible combination of the inventive concepts provide below as one of skill in the art will recognize that inventive concepts illustrated in various examples can be combined together in order to address a specific application. 
         [0008]    Other systems, methods, features and advantages of the disclosed teachings will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within the scope of and be protected by the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]    The disclosure can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
           [0010]      FIG. 1  is a longitudinal section view of a surgical retractor system comprising a first retractor and a second retractor. 
           [0011]      FIG. 2  is a perspective view of the second retractor of the surgical retractor system of  FIG. 1 . 
           [0012]      FIG. 3  is a partial section side view of a surgical retractor system similar to that of  FIG. 1 . 
           [0013]      FIG. 3B  is a side view of the second retractor in its deployed form. 
           [0014]      FIGS. 4 ,  5  and  6  are longitudinal section views of a surgical retractor system comprising a first retractor and a second retractor 
           [0015]      FIG. 7  is a transverse section view of the trunk of a human, the view including a vertebra and various soft tissues and organs. 
           [0016]      FIG. 8  is a longitudinal section view of a first retractor after the inserting of the first retractor into a first tissue. 
           [0017]      FIG. 9  is a longitudinal section view of a first retractor and a blunt dissector during the forming of an opening in a second tissue. 
           [0018]      FIG. 10  is a longitudinal section view of a first retractor and a blunt dissector that comprises a spatula after rotation of the spatula to enlarge the opening in the second tissue. 
           [0019]      FIG. 11  is a partial section end view of the first retractor, the spatula, and the opening formed by the spatula in the embodiment of  FIG. 9 . 
           [0020]      FIG. 12  is a partial section end view of the first retractor, the spatula, and the opening after rotation of the spatula in the embodiment of  FIG. 10 . 
           [0021]      FIG. 13  is a longitudinal section view of a first retractor and a second retractor during the advancing of the second retractor through the first working channel and the inserting of the second retractor into the second tissue. 
           [0022]      FIG. 14  is a longitudinal section view of a surgical retractor system comprising a first retractor and a second retractor after the inserting of the second retractor into the second tissue. 
           [0023]      FIG. 15  is a partial section end view of a surgical retractor system comprising a first retractor and a second retractor, the second retractor comprising a jackscrew and a second means for retracting that comprises a plurality of blades. 
           [0024]      FIG. 16  a partial section end view of the surgical retractor system of  FIG. 15  after expanding the second retractor. 
           [0025]      FIG. 17  is a side view of the second retractor of the surgical retractor system of  FIG. 15 , with a driver engaging the jackscrew. 
           [0026]      FIG. 18  is a perspective view of a blade having a curved portion. 
           [0027]      FIG. 19  is a perspective view of a blade having curved portions separated by a cutout. 
           [0028]      FIG. 20  is a partial section end view of a surgical retractor system comprising a first retractor, a second retractor, and an inserter for manipulating the second retractor, the second retractor comprising tabs for engaging the inserter. 
           [0029]      FIG. 21  is a longitudinal section view of the second retractor of the surgical retractor system of  FIG. 20 , with the inserter engaging grooves in tabs on the second retractor. 
           [0030]      FIG. 22  is an end view of a second retractor comprising plural jackscrews. 
           [0031]      FIG. 23  is a longitudinal section view of a surgical retractor system comprising a first retractor and a second retractor, before and after expanding the second retractor. 
           [0032]      FIG. 24  is a partial section end view of a surgical retractor system comprising a first retractor and a second retractor, the second retractor comprising a rack and pinion and a second means for retracting that comprises a plurality of blades. 
           [0033]      FIG. 25  is a partial section end view of the surgical retractor system of  FIG. 24  after expanding the second retractor. 
           [0034]      FIG. 26  is a partial section end view of a surgical retractor system comprising a first retractor and a second retractor, the second retractor comprising a ratchet and a second means for retracting that is U-shaped. 
           [0035]      FIG. 27  is a partial section end view of the surgical retractor system of  FIG. 26  after expanding the second retractor. 
           [0036]      FIG. 28  is a longitudinal section view of a surgical retractor system comprising a first retractor and a second retractor that is removably attachable to the first retractor. 
           [0037]      FIG. 29  is a partial section end view of the surgical retractor system of  FIG. 28 . 
           [0038]      FIG. 30  is a longitudinal section view of the surgical retractor system of  FIG. 28  after the inserting of the second retractor into the second tissue. 
           [0039]      FIG. 31  is a longitudinal section view of a portion of a surgical retractor system similar to that of  FIGS. 28-30 . 
           [0040]      FIG. 32  is a partial section end view of a surgical retractor system comprising a first retractor and a second retractor, the second retractor comprising a second means for retracting that comprises a flexible tube. 
           [0041]      FIG. 33  is a partial section end view of the surgical retractor system of  FIG. 32  after expanding the second retractor by withdrawing the inserter. 
           [0042]      FIG. 34  is a longitudinal section view of the flexible tube and the inserter of the surgical retractor system of  FIG. 32 . 
           [0043]      FIG. 35  is a perspective side view of the flexible tube and the inserter of the surgical retractor system of  FIG. 32 . 
           [0044]      FIG. 36  is a partial section end view of a surgical retractor system comprising a first retractor, a second retractor, and a set of sequential dilators, the second retractor comprising a second means for retracting that comprises a tube. 
           [0045]      FIG. 37  is a partial section end view of the surgical retractor system of  FIG. 36  after removal of the sequential dilators. 
           [0046]      FIG. 38  is a longitudinal section view of the surgical retractor system of  FIG. 36  during the insertion of the tube over a final one of the set of sequential dilators. 
           [0047]      FIG. 39  is a partial section end view of a surgical retractor system similar to that of  FIGS. 36-38  after removal of the sequential dilators, the surgical retractor system including a pin. 
           [0048]      FIG. 40  is a partial section end view of a surgical retractor system comprising a first retractor and a second retractor, the first retractor comprising a first means for retracting that comprises a tube. 
           [0049]      FIG. 41  is a partial section end view of a surgical retractor system comprising a first retractor and a second retractor, the first retractor comprising a first means for retracting that comprises a tube. 
           [0050]      FIG. 42  is a partial section end view of a surgical retractor system comprising a first retractor and a second retractor, the first retractor comprising a first means for retracting that comprises a plurality of blades. 
           [0051]      FIG. 43  depicts embodiments in which first working channel distal region  28  corresponds to less than or equal to various distal-most percentages of the first working channel  25 . 
           [0052]      FIG. 44  is a longitudinal section view of a surgical retractor system comprising a first retractor and a second retractor, in which the first means for retracting has a distal end which is beveled. 
           [0053]      FIG. 45A ,  FIG. 45B ,  FIG. 45C , and  FIG. 45D  show a sequence of cartoons depicting the passage of a retractor through a tube and its deployment at an internal site. 
           [0054]      FIGS. 46A ,  FIG. 46B , and  FIGS. 46C and 47  show a specialized device for configuring a second retractor deployed in or near the distal end of a first retractor. 
       
    
    
     DETAILED DESCRIPTION 
       [0055]    Reference will now be made in detail to several embodiments, examples of which are illustrated in the accompanying drawings. In this description and in the appended claims, the terms a or ‘an’ are used, as is common in patent documents, to include “one” or “more than one”. In this description and in the appended claims, the term ‘or’ is used to refer to a nonexclusive or, unless otherwise indicated. Various retractors are described herein, but the term “retractor” is intended to extend to any devices that embody means for the retraction of tissue, except where specifically limited. “Distal” and “proximal”, unless otherwise qualified, refer to relative distance, with respect to the outside end, of the pathway made to reach the site from the beginning of the procedure, along the route of the path. A “working channel” is a functional route through a tissue or other location in the body, which typically will have its origin at least in part via an externally-applied apparatus, but which may have full, partial or no surrounding external elements when in use. 
         [0056]    The invention describes surgical retractor systems, in which two retractors are designed and constructed, so that they may be deployed cooperatively to reliably achieve results that can only be obtained with difficulty, if at all, with a single retractor, or by use of multiple retractors that are not carefully matched. In preferred embodiments, the retractor systems will combine in ways that allow a second or distal retractor to have a wider opening, at its distal end, than the proximal openings of either retractor. This is important in many situations to provide visibility to the operative site during the procedure. It also, as described below, can provide benefits in terms of stabilizing the retractor in the operating field during the procedure. 
         [0057]    The retractors used in the invention can be selected from any of the types of retractors currently in use, although some combinations are preferred. Generally, the system comprises a first retractor, which is characterized by having an aperture which topologically is open to the outside of the body. The “topological” designation includes both direct access via a portal in the skin or other external body surface (which will likely be the most common mode of use), but also includes access via a natural orifice, including penetration through the wall of a natural orifice, or via a temporary artificial orifice created for other purposes. 
         [0058]    The system of the invention also includes a second retractor. The second retractor is delivered to the site of operation through the first retractor. Such a procedure is outlined in  FIG. 45 , where a second retractor is placed in its compact configuration (panel A) and in this folded state is delivered through a passage in a first retractor, in this case a tubular retractor, as shown in panel B. The second retractor is then opened, as shown in panel C, optionally by passing an opening device ( 63 ) through the first retractor passage. The deployed second retractor is shown in Fig. D. After deployment, the opening device  63  can be removed. The procedure is reversed to remove the second retractor at the end of the procedure. Note that the retractor in panel C has a different blade shape than the equivalent instruments in the other panels. Any of a variety of blade shapes are useful in the invention. The blade shape of panel D is preferred, because it is more readily deployed in a configuration in which the distal tips of the blades are separated by a distance that is greater than the relevant clearance of the first retractor through which it is passed to the operative site. This configuration is preferred because it is more stable in position, once it has been deployed, and because it increases the area which can be visualized and accessed beyond the distal opening of the first retractor. 
         [0059]    The Figures show a variety of deployments and procedures which make the invention more readily apparent to the reader.  FIG. 1  is a longitudinal section view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 , in accordance with an embodiment.  FIG. 2  is a perspective view of the second retractor  31  of a surgical retractor system  10  of  FIG. 1 .  FIG. 3  is a lateral view from outside the body through the channels  21  and  31  to the operative field.  FIG. 3B  is a longitudinal section, similar to  FIG. 1 , of an alternative second (distal) retractor. In each of these embodiments, the system is illustrated as performing steps useful in partially removing or otherwise treating a spinal disc. 
         [0060]    In the embodiment of a surgical retractor system  10  shown in  FIGS. 1-3 , first retractor  21  serves to retract a first tissue  220  and second retractor  31  serves to retract a second tissue  221 . For example, as illustrated, second tissue  221  may comprise muscle and nerves adjacent a vertebra  201  and a spinal disc  210 , the vertebra  201  including a vertebral body  204 . The vertebra  201  and spinal disc  210  are depicted in axial view (the view is taken along the axis of the spine) in  FIG. 1 , and laterally in  FIG. 3 . In the axial view, spinal disc  210  is superimposed upon vertebral body  204 . Much of the vertebra  201  is out of the plane of the section view, and is therefore indicated using dashed lines. In the embodiment of  FIGS. 1-3 , the surgical site that is to be accessed and viewed is the spinal disc  210  and adjacent vertebrae  201  within a spine. 
         [0061]    First retractor  21  comprises a first means for retracting. In the  FIG. 1-3  embodiments, the first means for retracting comprises a tube  22  having proximal end  23  and distal end  24 . The tube  22  defines a first working channel  25  there through. The first working channel  25  extends between the first tube proximal end  23  and the first distal end  24 . The first working channel  25  includes a distal region  28  of the first working channel. In one embodiment, the distal region  28  comprises no more than about 40% of the length of first working channel  25 . 
         [0062]    Second retractor  31  in this embodiment, as shown in  FIGS. 1 ,  2  and  3 , comprises a frame  40  (out of plane in  FIG. 1 ) and a second means for retracting  32 . In the  FIG. 1-3 ,  3 B embodiments, second means for retracting  32  comprises a plurality of blades  41  ( 2 ,  3 ,  3 B). The frame  40  ( FIGS. 2 ,  3 ,  3 B) comprises a means for expanding the second retractor  31 . The plurality of blades  41  are attached to the frame  40 . (Frame  40  is indicated in  FIGS. 2 and 3 ; frame  40  is out of the plane of section in  FIG. 1 ). The plurality of blades  41  includes, as shown in  FIG. 3B , a second means for retracting proximal end  33  and a second means for retracting distal end  34 . The plurality of blades  41  defines a second working channel  35  there through. The second working channel  35  extends between the second means for retracting proximal end  33  and the second means for retracting distal end  34 . The second retractor  31  has a second retractor proximal end  58  and a second retractor distal end  59 . 
         [0063]    Second retractor  31 , as shown in  FIG. 2  or  3 B, is dimensioned to be insertable through the first working channel  25 . Second retractor  31  is positionable vicinally to the distal end  24  of the first retractor, with the second retractor distal end  59  positioned distal to the first working channel  25 , and with the second retractor proximal end  58  positioned distal to the first working channel  25  or within the first working channel distal region  28 . 
         [0064]      FIG. 3  is a partial section end view of a surgical retractor system  10  similar to that of  FIG. 1 . In the embodiment of  FIG. 3 , first means for retracting  22  is a tube  42  with a cross-sectional shape that is a rounded rectangle, and a second retractor  31  has a plurality of blades  41  serving as a means for retracting. Two vertebrae  201  and a spinal disc  210  are depicted in lateral view. Each vertebra  201  includes a vertebral body  204 . In the embodiment of  FIG. 3 , the second tissue  221  that is retracted by the second retractor  31  includes the psoas major muscle  225  and various nerves  224 . The psoas major muscle  225  is an elongate muscle that runs laterally to the lumbar region of the spine, roughly parallel to the spine axis. In  FIG. 3  and other figures herein, the psoas major muscle  225  is depicted as transparent, revealing the outlines of the vertebra  201  and spinal disc  210 . In the embodiments of  FIGS. 1-3 , second retractor  31  is inserted into an opening  230 , having a lenticular-shaped outline, in the psoas major muscle  225 . Those of skill in the art will recognize that the term iliopsoas is sometimes used as a term for a combination of the psoas major muscle and the relatively shallow layer of the iliacus. 
         [0065]    Nerves  224  (depicted as dashed lines) originate at spinal nerve roots  226 . Each spinal nerve root  226  emerges from the spine through an intervertebral foramen  219 , which is a passage between the posterior portions of adjacent vertebrae  201 . Nerves  224  pass through, under, or over the psoas major muscle  225 ; the exact route of the nerves  224  varies with the spine level and the individual patient. 
         [0066]    As described in connection with  FIGS. 1-2 , second retractor  31  is disposed adjacent the distal end  24  of the first means for retracting  21 . In some embodiments, the second retractor distal end  59  is positioned distal to the first working channel  25  (see  FIG. 2 ) and the second retractor proximal end  58  is also positioned distal to the first working channel  25 , so that the entire second working channel  35 , defined by second means for retracting  32 , is distal to the first working channel  25 . Embodiments of this type are described in connection with  FIGS. 4 and 5 . In other embodiments, such as that of  FIG. 1 , the second retractor distal end  59  is positioned distal to the first working channel  25  and the second retractor proximal end  58  is positioned within the first working channel distal region  28 . In these embodiments, the second working channel  35 , defined by second means for retracting  32 , is disposed partially within first working channel distal region  28  and partially distal to first working channel  25 . 
         [0067]    The distal region  28  of the first channel usually corresponds to the distal-most 40 percent or less of the first working channel  25 , as described in connection with  FIGS. 1-2 .  FIG. 3B  depicts an embodiment in which first working channel distal region  28  corresponds to the distal-most 40 percent of the first working channel  25 . In this embodiment, first working channel proximal region  29  corresponds to the remaining 60 percent of first working channel  25 . Second retractor proximal end  58  is positioned within the first working channel distal region  28 . Thus, second working channel  35  does not extend into first working channel proximal region  29 . 
         [0068]    In other embodiments, first working channel distal region  28  may correspond to other distal-most percentages of the first working channel  25 , but preferably the distal-most percentage is less than or equal to 40 percent. In the  FIG. 1  embodiment, for example, first working channel distal region  28  corresponds to approximately the distal-most three (3) percent of first working channel  25 . In the  FIG. 3B  embodiment, for example, first working channel distal region  28  corresponds to approximately the distal-most 20 percent of first working channel  25 . A scale within  FIG. 3B  indicates several distal-most percentages of first working channel  25 . The percentages are indicated as fractions. 
         [0069]    In  FIGS. 1-3B , the positioning of second retractor  31  adjacent to first means for retracting distal end  24  results from the advancing of second retractor  31  through first working channel  25 , as described in connection with  FIGS. 1-3B . Second retractor  31  and second working channel  35  temporarily pass through first working channel proximal region  29  ( FIG. 3B ) while en route to the final position adjacent distal end  24 . 
         [0070]    First means for retracting  22  may comprise any structure that is capable of defining a first working channel  25 . For example, first means for retracting  22  may comprise tube  42  ( FIG. 3 ) or a plurality of blades  41  ( FIG. 3B ). In the embodiment of  FIG. 3 , first means for retracting  22  comprises a tube  42  having a cross-sectional shape that is a rounded rectangle.  FIGS. 40-42  below depict other embodiments of first means for retracting  22 . 
         [0071]    Second means for retracting  32  may comprise any structure that is capable of defining a second working channel  35 . Second means for retracting  32  may comprise, for example, a plurality of blades  41  or a sleeve  57  or a tube  42 . In the embodiment of  FIG. 3 , second means for retracting  32  comprises a plurality of blades  41 .  FIGS. 15-39  as described below depict various embodiments of second means for retracting  32   
         [0072]    A tool  60  that is received within first working channel  25  and within second working channel  35 , for example as illustrated in  FIG. 1 , may be any type of tool that may be used to probe, manipulate, or view the surgical site of interest. For example, tool  60  may be a cutting instrument or grasping instrument, or a means for irrigating or suctioning the surgical site, or a type of inserter for installing an implant or prosthesis, or a driver for transmitting pounding force or rotational force, or an endoscope. The tool  60  may comprise a plurality of tools  60  that are received simultaneously or sequentially within first working channel  25  and second working channel  35 . 
         [0073]    First retractor  21  is sufficiently large to receive the tool  60  through the first working channel  25  and for advancing second retractor  31  through the first working channel  25 . In some embodiments, first retractor  21  may be relatively large in order to improve visibility or to facilitate the use of tools  60  or to facilitate the advancing of a prosthetic implant through first working channel  25 . In one example, as illustrated in  FIG. 3 , a rectangular or oval tube  42  for use in a lateral approach to the spine may have a 12 centimeter length, 42 millimeter width, and 35 millimeter depth. In other embodiments, the depth and width may be greater than or equal to 10, 15, 20, or 25 millimeters or more. In an embodiment with a relatively long first retractor  21 , as in the  FIG. 1-3  embodiment, transverse dimensions greater than or equal to 20 or 25 millimeters may be advantageous. First retractor  21  may be tapered along its length. 
         [0074]    Second retractor  31  is sufficiently large to allow receiving the tool  60  through the second working channel  35  and, in some embodiments, to allow receiving a prosthetic implant through second working channel  35 . In one example, second retractor  31  may have a 32 mm width and an 18 mm depth, suitable for receiving a prosthetic implant that is relatively wide, and also suitable for being received within an oval or rectangular first retractor  21 . 
         [0075]    In some embodiments, a prosthetic implant may be installed at a surgical site that is accessed using a surgical retractor system  10  as described herein. The prosthetic implant may be any type of implant for installation at any anatomical location. For example, the prosthetic implant may be an intervertebral spacer  66  as depicted in  FIG. 14 . In such embodiments, the first working channel  25  is capable of receiving the prosthetic implant (e.g. an intervertebral spacer  66 ) and the second working channel  35  is capable of receiving the prosthetic implant. The prosthetic implant (e.g. an intervertebral spacer  66 ) is advanced through the first working channel  25  and through the second working channel  35  and installed at the surgical site of interest. In one example, an intervertebral spacer  66  for use in a lateral approach may have a 35 millimeter length, a 20 millimeter width, and a height of 15 millimeters. 
         [0076]    The prosthetic implant may have fixed dimensions, or it may be expandable after arrival at the surgical site, or the prosthetic implant may be a modular implant comprising plural modules that are advanced sequentially and then joined together at the surgical site. U.S. Pat. No. 7,267,690 issued to Felt describes some examples of modular implants for use in a surgical site that is a spinal disc  210 . 
         [0077]    In some embodiments, the first retractor  21  may be expanded during or after its insertion into the first tissue  220 . The first working channel diameter  27  means the diameter after the expanding is complete and the first working channel  25  is ready to receive the tool  60  and is ready for advancing of the second retractor  31 . Similarly, the second working channel diameter  37  means the diameter after any expanding of second retractor  31  is complete. 
         [0078]      FIG. 4  shows a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 . In the embodiment of  FIG. 4 , the second working channel&#39;s proximal end  58  is positioned distal to the first working channel  25 . In the embodiments of  FIGS. 1 and 4 , first retractor  21  is docked at a proximal surface of the second tissue  221 . 
         [0079]      FIG. 5  shows a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 . In the embodiment of  FIG. 5 , the second working channel proximal end  58  is positioned distal to the first working channel  25 . In the  FIG. 5  embodiment, first retractor  21  is not docked at a proximal surface of the second tissue  221 ; there is a gap between first means for retracting distal end  24  and the second tissue  221 . 
         [0080]      FIG. 6  shows a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 . In the  FIG. 6  embodiment, the second working channel  35  is at an angle with respect to the first working channel  35 . Hence, the proximal end  58  of the second channel  35  is positioned partially distal to the first working channel  25  and partially within the first working channel distal region  28 . Nevertheless, first working channel distal end axis  26  is sufficiently aligned with second working channel proximal end axis  36  to permit the receiving of a tool  60  simultaneously in the first working channel  25  and in the second working channel  35 . 
         [0081]    The range of overlap of the second retractor with respect to the first retractor is variable, as is shown in  FIGS. 4 ,  5 , and  6 . It is preferred in many situations that there be at least some overlap between the retractors, for example in the range of about 5% to 40% overlap, in order to provide a functional pivot point. A pivot point, in this context, is an arrangement of retractors which allows relative pivoting between the first and second retractor (in terms of alignment of their axes, for example), so that the general direction of the path to the ultimate target need not lie along a single axis. Preferably, the pivot point is deep in the tissue, for example for allowing optimal visualization of the target site. However, an actual physical overlap of the first and second retractors, as shown in  FIGS. 4 and 6 , is not required. The same effect can be produced in the arrangement of  FIG. 5 , wherein there is no physical overlap of the retractors, but an alignment is preserved during pivoting by the proximity of surrounding tissues. 
         [0082]    In an alternative embodiment, shown in  FIG. 36-38 , the surgical retractor system  10  may comprise a set of sequential dilators  55 , shown here as  55  A-C, with the first means for retracting  22  being sized for insertion over a final one of the set of sequential dilators  55 . Similarly, surgical retractor system  10  may comprise a set of sequential dilators  55 , with the second means for retracting  42  being sized for insertion over a final one of the set of sequential dilators  55 . A set of sequential dilators  55  may be used with any type of first means for retracting  22  or second means for retracting  32 , such as a plurality of blades  41  or a tube  42 . The embodiment of  FIGS. 36-38  depicts an example of a surgical retractor system  10  that comprises a set of sequential dilators  55 . In the  FIG. 36-38  embodiment, a first one  55 A of the set of sequential dilators  55  may comprises a spatula. In other embodiments, a first one  55 A of a set of sequential dilators  55  may be any type of blunt dissector, such as a cylindrical rod. 
         [0083]    Surgical retractor system  10  embodiments may be used in various anatomical locations. Similarly, method embodiments described herein may be used in various anatomical locations. Thus, the first tissue  220  and the second tissue  221  that are to be retracted may be any type of tissues in any anatomical location. While many of the system embodiments and method embodiments described herein are described in connection with spine surgery, surgical retractor system  10  and various methods described herein may be used for retracting any combination of a first tissue  220  and a second tissue  221 . For example, first tissue  220  and second tissue  221  may be tissues within the brain, head, neck, thorax, pelvis, or abdomen. 
         [0084]    Passage may be through tissue or through space. Any organ with a cavity that can be passed through to access tissues to be retracted may be treated by the devices and methods of the invention. As an example, the pleural cavity could be first tissue  220  and a great vessel could be a great vessel. First tissue  220  and second tissue  221  may be regions within a single organ or tissue. For example, first tissue  220  and second tissue  221  may be a first region and a second region within a single muscle, the first region being relatively free of sensitive elements such as nerves, the second region including one or more sensitive elements such as nerves. 
         [0085]    The general attributes of surgical retractor system  10  that are described in connection with the embodiments of  FIGS. 1-6  apply also to other embodiments. The description of those general attributes is not repeated for each embodiment described herein. 
         [0086]      FIG. 7  is a transverse section view of the trunk of a human, the view including a vertebra  201  and a spinal disc  210  within the spine and also various soft tissues and organs. The spinal disc  210  and the vertebra  201 , which includes vertebral body  204 , are depicted in axial view, as in  FIG. 1 . In this axial view, spinal disc  210  is superimposed upon vertebral body  204 . Spine surgery may employ any of various approaches to the spine such as an anterior or posterior or lateral approach. In  FIG. 7 , anterior is to the left of vertebra  201 , posterior is to the right of vertebra  201 , and lateral is above or below the vertebra  201 , each in the plane of the paper. 
         [0087]    For a lateral approach to the spine at the level depicted in  FIG. 7 , the first tissue  220  that is to be retracted includes skin  222 , muscles  223 , and a portion of the intestines  228 , as shown in  FIG. 8 . Retraction of first tissue  220  enlarges the retroperitoneal space  227 . For a lateral approach, the second tissue  221  that is to be retracted includes the psoas major muscle  225  as well as various nerves  224 . Nerves  224  are depicted in  FIG. 3 , as structures outlined by dashes. In  FIG. 3 , the nerves depicted have been avoided or retracted from the path of the channel  21 . Within the psoas major muscle  225 , the elongate muscle fibers  229 , shown here in cross section, run roughly parallel to the spine axis. In the transverse section view of  FIG. 7 , a portion of the muscle fibers  229  are depicted as small circles (cross-sectioned muscle fibers  229 ) within the psoas major muscle  225 . 
         [0088]    For spine surgery, a patient may be positioned in a particular way in order to facilitate the surgery. For a lateral approach to the spine, the patient is typically positioned so that the psoas major muscle  225  is stretched and thinned compared to the cross-sectional profile depicted in  FIG. 7 .  FIG. 1  and  FIGS. 8-14  depict the psoas major muscle  225  in a stretched and thinned configuration. 
         [0089]    In  FIGS. 8-14 , a first method for accessing a surgical site is described. Broadly, the method comprising a series of steps, the method comprising: 
         [0090]    (a) inserting a first retractor  21  into a first tissue  220  to retract the first tissue  220 , the first retractor  21  including a first retractor distal end  24  and a first working channel  25 , the first working channel  25  including a first working channel distal region  28  (see  FIG. 14 ); 
         [0091]    (b) advancing a second retractor  31  ( FIG. 13-14 ) through the first working channel  25 , the second retractor  31  including a second retractor distal end  34 ; 
         [0092]    (c) inserting the second retractor  31  into a second tissue  221  to retract the second tissue  221  while positioning the second retractor  31  adjacent the first retractor distal end  24 , wherein the positioning of the second retractor  31  includes positioning the second retractor proximal portion  38  to be external to the first working channel  25  or to be within the first working channel distal region  28 , wherein the first retractor  21  remains proximal to the second tissue  221  during the inserting of the second retractor  31 . 
         [0093]      FIGS. 8-14  depict such a series of steps performed during the particular example of the creation of an access route from the skin to the interior of a vertebral disk. This method may be performed using a surgical retractor system such as the surgical retractor system embodiments described herein. The surgical retractor system  10  may comprise, in addition to a first retractor  21  and a second retractor  31 , other elements such as a blunt dissector  61  and an inserter  63  for manipulating the second retractor  31 . In the embodiment of  FIGS. 8-14 , the surgical site that is to be accessed is a spinal disc  210  and adjacent vertebra  201  within a spine, and the approach to the spine is a lateral approach. Fluoroscopy may be used during the performance of the method, with the patient positioned on a radiolucent surgical table. 
         [0094]    In one embodiment, for inserting of a first retractor  21  into a first tissue  220  (step a), an incision is made in the skin  222  and the muscles  223  of the abdominal wall are split. The first retractor  21  is inserted through the incision and through the split muscles  223 , passing into the retroperitoneal space  227  and staying posterior to the intestine  228 . The first retractor  21  is then re-oriented so that it is directed towards the vertebral body  204  and the overlying psoas major muscle  225 . 
         [0095]      FIG. 8  is a longitudinal section view of a first retractor  21  after the inserting of the first retractor  21  into a first tissue  220  to retract the first tissue  220 , in accordance with an embodiment. The first retractor  21  includes a first retractor distal end  24  and a first working channel  25 . The first working channel  25  includes a first working channel distal region  28  (also see  FIGS. 1 ,  14 ). The first retractor distal end  24  is the same as the first means for retracting distal end  24  described in connection with other Figures herein. 
         [0096]    The embodiment of  FIG. 8  includes a step of docking the first retractor  21  at a proximal surface  231  of the second tissue  221  prior to performing other steps such as advancing a second retractor  31  through the first working channel  25 . The docked first retractor  21  is seated firmly against the proximal surface  231  of the second tissue  221 , which in this embodiment is the psoas major muscle  225 . In other embodiments, such as the embodiment of  FIG. 5 , the first retractor  21  may not be docked at the second tissue  221 . 
         [0097]    In some embodiments, the method of accessing a surgical site may comprise a step of forming an opening  230  in a second tissue  221 , as shown in  FIGS. 8-14  (see  FIGS. 11-12 ).  FIG. 9  is a longitudinal section view of a first retractor  21  and a blunt dissector  61  during the forming of an opening  230  in a second tissue  221 , in accordance with an embodiment. 
         [0098]    For example, tissue  221  may be a psoas muscle. As a first step, blunt dissector  61  is pushed into tissue  225  until it contacts disc  210 .  FIG. 10  shows a longitudinal section view of a first retractor  21  and a blunt dissector  61  that comprises a spatula  62 , after rotation of the spatula  62  to enlarge the opening  230  in the second tissue  221 . 
         [0099]    This is also shown in  FIG. 11 , which is a partial section end view of the first retractor  21 , the spatula  62 , and the opening  230  formed by the spatula  62  in the embodiment of  FIG. 9 .  FIG. 12  is a partial section end view of the first retractor  21 , the spatula  62 , and the opening  230  after rotation of the spatula  62  in the embodiment of  FIG. 10 . 
         [0100]    In the embodiment of  FIGS. 9-13 , a blunt dissector  61  is used for forming an opening  230  in the second tissue  221  prior to inserting the second retractor  31  into the second tissue  221 , as in step (c) of the method. For the embodiment of  FIGS. 9-13 , inserting the second retractor  31  into the second tissue  221  comprises inserting the second retractor  31  into the opening  230 . In another embodiment, an opening  230  may be formed in second tissue  221  using a cutting instrument such as a scalpel or a laser, rather than using a blunt dissector  61 . 
         [0101]    Blunt dissector  61  may be any type of blunt dissector such as a cylindrical rod or a spatula  62 . In the embodiment of  FIGS. 9-12 , blunt dissector  61  comprises a spatula  62 , such as a tool known as a Cobb elevator. A spatula  62  may be inserted into a muscle such as the psoas major muscle  225  with the blade of the spatula  62  parallel to the natural planes within the muscle in order to gently divide the muscle with minimal tearing. After the initial forming of the opening  230 , as depicted in  FIGS. 9 and 11 , the spatula  62  may be rotated to enlarge the opening  230 , as depicted in  FIGS. 10 and 12 . 
         [0102]    When the second tissue  221  includes nerves  224 , an opening  230  may be initiated and enlarged with careful attention to the nerves  224 . Nerves  224  may be damaged if they are stretched, pinched, or severed. Nerves  224  that are beneath the surface of the second tissue  221  may be identified by tactile feedback through the blunt dissector  61  and also by viewing the second tissue  221  during the forming of the opening  230 . Nerves  224  are depicted in  FIG. 3  and in  FIGS. 11-12 . 
         [0103]    The embodiment of  FIGS. 9-13  typically also includes a light source  65 , shown in  FIG. 9 . In the embodiment of  FIGS. 9-13 , first retractor  21  includes a collar or frame  40  attached to the first retractor&#39;s proximal end  23 . The collar or frame  40  may be attached to an arm  64  which is secured to the surgical table to stabilize first retractor  21 . A light source  65  may be mounted on the arm  64  or on the collar or frame  40 . The light source  65  may shine down into first working channel  25  from above, as depicted in  FIGS. 9-13 . In another embodiment, light source  65  may extend further within first working channel  25  or second working channel  35  so that light is emitted nearer to the second tissue  221  or nearer to the surgical site. 
         [0104]    In some embodiments, the method of accessing a surgical site may comprise a step of viewing the second tissue  221  through the first working channel  25  prior to or during the forming of an opening  230  in the second tissue  221 . Viewing of the second tissue  221  or the surgical site through the first working channel  25  may include the use of a loupe or surgical microscope or other optical tools, with the assistance of light emitted from light source  65 . The ability to view internal surfaces with good illumination and minimal obstruction by devices is an important improvement provided by this invention. For example, one can visualize the tissue at the end of at least said first channel through said first passageway, in the embodiment of  FIG. 13 . 
         [0105]      FIG. 13  is a longitudinal section view of an embodiment showing a first retractor  21  and a second retractor  31  during the advancing of the second retractor  31  through the first working channel  25  and the inserting of the second retractor  31  into the second tissue.  FIG. 14  is a longitudinal section view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31  after the inserting of the second retractor  31  into the second tissue  221 . An inserter  63  ( FIG. 13 ) may be used to manipulate the second retractor  31  during the advancing and the inserting of the second retractor  31 . 
         [0106]    As depicted in  FIGS. 13 and 14 , a method comprises inserting the second retractor  31  into a second tissue  221  to retract the second tissue  221  while positioning the second retractor  31  adjacent the first retractor distal end  24 . In  FIG. 14 , the positioning of the second retractor  31  includes positioning the second retractor proximal portion  33  to be external to the first working channel  25  or to be within the first working channel distal region  28 . In this embodiment, the first retractor  21  remains proximal to the second tissue  221  during the inserting of the second retractor  31 . The positioning of second retractor  31  is described in more detail in connection with  FIGS. 4-6 . First retractor  21  usually does not intrude into second tissue  221 , but instead remains proximal to second tissue  221 . Preferably the first working channel distal region  28 , which may overlap the second retractor  35 , corresponds to no more than about the distal-most 30 percent of the first working channel. 
         [0107]    In the embodiment of  FIG. 14 , a tool  60  is received within first working channel  25  and second working channel  35 . In the  FIG. 14  embodiment, the tool  60  is an inserter for an intervertebral spacer  66  (a prosthetic implant) that is being installed within the spinal disc  210 . In the embodiment of  FIG. 1 , the depicted tool  60  is a curette. A curette and other tools  60  may be used to prepare a spinal disc  210  for installation of an intervertebral spacer  66 . Various tools  60  may be used with surgical retractor system  10 , each tool being received within first working channel  25  and second working channel  35 . In the example of spine surgery, tools  60  may be used, for example, to treat a vertebra  201  or a spinal disc  210 , or to install a prosthetic implant within or adjacent a spine. 
         [0108]    In some embodiments, the method of accessing a surgical site may comprise a step of advancing a prosthetic implant through the first working channel  25  and through the second working channel  35 .  FIG. 14  depicts an embodiment in which a prosthetic implant, such as an intervertebral spacer  66 , has been advanced through the first working channel  25  and through the second working channel  35  using an inserter tool  60 . The prosthetic implant is positioned within spinal disc  210 . 
         [0109]    In some embodiments, the method of accessing a surgical site may comprise a step of viewing the second tissue  221  through the first working channel  25  prior to advancing the second retractor  31  through the first working channel  25 . In some embodiments, the method of accessing a surgical site may comprise a step of viewing the second tissue  221  through the first working channel  25  during the inserting of the second retractor  31  into the second tissue  221 . 
         [0110]    In some embodiments, second means for retracting  32  may be expandable, as described in connection with  FIGS. 15-35 . In some embodiments, the method of accessing a surgical site may comprise a step of expanding the second retractor  31  after inserting the second retractor  31  into the second tissue  221 . The second retractor  31  may be expanded using various means such as means described in connection with  FIGS. 15-35 . In the embodiment of  FIG. 13 , the second retractor  31  is narrower than the opening  230  in the second tissue  221  during the inserting of the second retractor  31  into the second tissue  221 . The second retractor  31  may be expanded after the inserting so that it fills the opening  230 . In other embodiments, such as that of  FIG. 30 , the second retractor  31  may be inserted snugly into a second tissue  221  with subsequent expansion of the second retractor  31 , the expansion causing further retraction of the second tissue  221 . 
         [0111]    In another embodiment which differs from the  FIG. 9-13  embodiment, no opening  230  is formed in second tissue  221  prior to inserting the second retractor  31  into the second tissue  221 . In such an embodiment, second retractor  31  may comprise a pair of closely apposed blades  41  which serve as a second means for retracting  32 . The closely apposed blades  41  may also serve as a means for dissecting or cutting the second tissue  221 , so that the inserting of second retractor  31  into second tissue  221  occurs simultaneously with the forming of an opening  230 . After the inserting of the second retractor  31  into second tissue  221 , the blades  41  may be spread apart, with expanding of the second retractor  31 , to create a second working channel  35  between the blades  41 . 
         [0112]      FIG. 15  is a partial section end view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 , the second retractor  31  comprising a jackscrew  50  and a second means for retracting that comprises a plurality of blades  41 , in accordance with an embodiment. 
         [0113]      FIG. 16  is a partial section end view of the surgical retractor system  10  of  FIG. 15  after expanding the second retractor  31 . The plurality of blades  41  have moved apart, thereby enlarging the first working channel  35 . 
         [0114]      FIG. 17  is a side view of the second retractor  31  of the surgical retractor system  10  of  FIG. 15 , with a driver  67  engaging the jackscrew  50 . Rotation of the driver  67  may be used to adjust the distance between the plurality of blades  41  for expanding or contracting second retractor  31 . 
         [0115]    In the  FIG. 16  embodiment, first retractor  21  comprises a track  47  and a pin  54  that is slidably received within track  47 . The track  47  and the pin  54  are elongate elements that extend for part or all of the distance between first retractor proximal end  23  and first retractor distal end  24 . Pin  54  may be inserted into vertebra  201  (see  FIG. 14 ) in order to stabilize first retractor  21 . Another example of a track  47  is depicted in the  FIG. 28-30  embodiment. 
         [0116]      FIG. 18  is a perspective view of a blade  41  having a curved portion  43 , in accordance with an embodiment. A curved portion  43  at the tip of a blade  41  (for example, at  34  in  FIG. 17 ) may help to retract tissue, and a curved portion  43  may be used in any embodiment of a first retractor  21  and in any embodiment of a second retractor  31 .  FIG. 19  is a perspective view of a blade  41  having a curved portions  43  separated by a cutout  44 , in accordance with an embodiment. A cutout  44  may be useful when a first retractor  21  or a second retractor  31  contacts an object whose surface is curved or irregular. For example, a first retractor  31  may be seated against a surgical site that includes a vertebral body  204 . The vertebral body  204  generally is somewhat curved and the surface may be irregular because of osteophytes. 
         [0117]      FIGS. 20 and 21  depict views of a surgical retractor system  10  comprising a first retractor  21 , a second retractor  31 , and an inserter  63  for manipulating the second retractor  31 , the second retractor  31  comprising tabs  45  for engaging the inserter  63 . A distal portion of an inserter  63  is depicted in  FIG. 21 , and another inserter  63  is depicted in  FIG. 13 . Inserter  63  may be used for manipulating the second retractor  31  in various ways, including advancing, inserting, repositioning, and removing of the second retractor  31 .  FIG. 21  is a longitudinal section view of the second retractor  31  of the surgical retractor system  10  of  FIG. 20 , with the inserter  63  engaging grooves  46  in tabs  45  on the second retractor  31 . 
         [0118]    Inserter  63  in the  FIG. 20-21  embodiment includes a pair of members, the distal end of each member engaging one of the tabs  45  of second retractor  31 . The spacing of the members may be adjusted narrower or wider in order to engage the grooves  46  and also to disengage from the grooves  46 . For example, the members may be linked by a resilient linkage, so that the inserter  63  is similar to a forceps, or the inserter  63  may be a scissoring type of instrument with a pair of handles that control the spacing of the members. In other embodiments, inserter  63  may engage second retractor  31  through other means such as a threaded connection or a jaw that grips a portion of the second retractor  31 . 
         [0119]      FIG. 22  is an end view of a second retractor  31  comprising plural jackscrews  50 . As described in connection with the embodiment of  FIGS. 15-17 , a jackscrew  50  may be used for expanding or contracting second retractor  31 . It may be advantageous in some situations to have more than one jackscrew or other mechanism to exert force upon the blades  41 . For a second retractor  31  that includes plural jackscrews  50  or other means for expanding or contracting, it may be useful to drive the plural jackscrews synchronously using, for example, a geared mechanism. 
         [0120]      FIG. 23  is a longitudinal section view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 , after expanding the second retractor  31 , in accordance with an embodiment. In the  FIG. 23  embodiment, the second retractor  31  is expanded to have a transverse dimension that is greater than or equal to the transverse dimension of the first retractor  21 . The dashed outlines indicate the position of the second tissue  221  prior to retraction by the second retractor  31 . The second retractor  31  may be contracted, reversing the expansion, for removal through first retractor  21 . 
         [0121]    For a surgical retractor system  10  as shown in  FIG. 23 , second retractor  31  may be inserted into a second tissue  221  after the advancing of the second retractor  31  through the first working channel  25 . The second retractor  31  has a second retractor transverse dimension that is sized to permit the advancing of the second retractor  31  through the first working channel  25 . 
         [0122]    The second retractor  31  may have an expanded transverse dimension that is different from the initial transverse dimension during the advancing through the first working channel  25 . 
         [0123]      FIG. 24  is a partial section end view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 , the second retractor  31  comprising a rack and pinion  51  and a second means for retracting that comprises a plurality of blades  41 , in accordance with an embodiment. The rack and pinion  51  is attached to one end of each blade  41  at the upper edge of the blade  41 , so that the rack and pinion  51  is held above the second tissue  221  by the blades  41 . A driver, such as the driver  67  depicted in  FIG. 17 , may be used to rotate the pinion in the rack and pinion  51  to adjust the distance between the plurality of blades  41  for expanding or contracting second retractor  31 .  FIG. 25  is a partial section end view of the surgical retractor system  10  of  FIG. 24  after expanding the second retractor  31 . 
         [0124]      FIG. 26  is a partial section end view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 , the second retractor  31  comprising a ratchet  52  and a second means for retracting  57  that is U-shaped, in accordance with an embodiment. The ratchet  52  includes an arc that is attached to one end of the U-shaped second means for retracting  57  and a pin that engages the arc, the pin being attached to a second end of the U-shaped means for retracting  57 . The ratchet  52  is attached at the upper edge of the U-shaped means for retracting  57 , so that the ratchet  52  is held above the second tissue  221  by the U-shaped means for retracting  57 .  FIG. 27  is a partial section end view of the surgical retractor system  10  of  FIG. 26  after expanding the second retractor  31 . The second working channel diameter  37  is indicated. 
         [0125]      FIG. 28  is a longitudinal section view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31  that is removably attachable to the first retractor  21 , in accordance with an embodiment. In  FIG. 28 , second retractor  31  is depicted at two positions which correspond to two time points: second retractor  31 A is depicted before the attaching to first retractor  21 , and second retractor  31 B is depicted during the advancing of the second retractor  31 B. 
         [0126]    In the  FIG. 28  embodiment, first retractor  21  comprises one or more tracks  47 , preferably plural tracks  47 . In the  FIG. 28  embodiment, a second means for retracting comprises a plurality of blades  41 . As indicated for second retractor  31 A, second retractor  31  may comprise a frame or collar  40  that links the blades  41 . Each blade  41  is attached to the first retractor  21  through a pivot  49  and a means for attaching which comprises a connector  48 . The means for attaching (connector  48 ) is slidable along track or tracks  47 . During the advancing of the second retractor  31  through the first working channel  25 , the blades  41  are tilted inwards at second retractor distal end  34 , to facilitate insertion of the second retractor  31  into the second tissue  221 . In another embodiment, blades  41  may have a fixed upright orientation, rather than being tilted initially. 
         [0127]      FIG. 29  is a partial section end view of the surgical retractor system  10  of  FIG. 28  after the inserting of the second retractor  31  into the second tissue  221 . The blades  41  have been rotated so that they are no longer tilted.  FIG. 30  is a longitudinal section view of the surgical retractor system  10  of  FIG. 28  after the inserting of the second retractor  31  into the second tissue  221 , in accordance with an embodiment. The blades  41  have been rotated so that they are no longer tilted. A means for locking  53  secures the blades  41  in the upright (not tilted) orientation. In an embodiment, the blades  41  can be further tilted to expand the distal opening (see  FIG. 45D , for example). In the  FIG. 30  embodiment, means for locking  53  is a wedge that may be inserted from above. For example, means for locking  53  may be a wedge that slides within track  47  and that is attached to a shaft that extends upward for manipulation of the means for locking  53 . 
         [0128]      FIG. 31  is a longitudinal section view of a portion of a surgical retractor system  10  similar to that of  FIGS. 28-30 , in accordance with an embodiment.  FIG. 31  includes two views A and B, which correspond to different states of the means for locking  53 . In view A, the blades  41  are tilted and means for locking  53  is in the unlocked (collapsed) state. In view B, the blades  41  are rotated so that they are no longer tilted, and means for locking  53  is in the locked state. In the  FIG. 31  embodiment, the means for locking  53  is a rotatable arm attached to a shaft that extends upward for manipulation of the means for locking  53 . The shaft within means for locking  53  may be secured at a specific vertical position relative to first retractor  21  using, for example, a pin or a threaded nut. 
         [0129]    In other embodiments, second retractor  31  may be removably attachable to first retractor  21  using other means for attaching. The means for attaching may include, for example, a pin on the second retractor  31  that engages a dimple or hole on the inner surface of first means for retracting  22 . The means for attaching may include, for example, an elongate hanger for suspending the second retractor  31  within first working channel  25 , the hanger extending between the second retractor  31  and a proximal location on first retractor  21 . 
         [0130]      FIG. 32  is a partial section end view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 , the second retractor  31  comprising a second means for retracting that comprises a flexible tube  42 , in accordance with an embodiment. In other embodiments, tube  42  may not be flexible.  FIG. 32  depicts second retractor  31  (flexible tube  42 ) during the insertion of second retractor  31  into the second tissue  221 . Flexible tube  42  is held by the prongs  68  of a forked inserter  63  (see  FIGS. 34-35 ).  FIG. 33  is a partial section end view of the surgical retractor system  10  of  FIG. 32  after expanding the second retractor  31  by withdrawing the inserter  63 .  FIG. 34  is a longitudinal section view of the flexible tube  42  and the inserter  63  of the surgical retractor system  10  of  FIG. 32 . The prongs  68  of the inserter  63  grip the flexible tube  42  and compress it. 
         [0131]      FIG. 35  is a perspective side view of the flexible tube  42  and the inserter  63  of the surgical retractor system  10  of  FIG. 32 . Inserter  63  includes a second pair of members  69  that are capable of moving relative to the long dimension of inserter  63 . To release flexible tube  42  from inserter  63  after flexible tube  42  is inserted into second tissue  221 , prongs  68  are pulled upward while members  69  push down on the second means for retracting proximal end  33  (i.e., the top of the flexible tube  42 ). The  FIG. 33  embodiment includes pins  54  that are inserted into each vertebra  201 . The pins  54  pass just inside of flexible tube  42  and may serve to stabilize second retractor  31  (flexible tube  42 ). Pins  54  may be slidably received within tracks  47  in first retractor  21 , as described in connection with  FIG. 16 . 
         [0132]      FIG. 36  is a partial section end view of a surgical retractor system  10  comprising a first retractor  21 , a second retractor  31 , and a set of sequential dilators  55 , the second retractor  31  comprising a second means for retracting that comprises a tube  42 , in accordance with an embodiment. In the embodiment of  FIG. 36 , the set of sequential dilators  55  comprises three sequential dilators  55 A,  55 B, and  55 C. In the  FIG. 36  embodiment, a first one  55 A of the set of sequential dilators comprises a spatula. Tube  42  is sized for insertion over a final one  55 C of the set of sequential dilators  55 .  FIG. 37  is a partial section end view of the surgical retractor system  10  of  FIG. 36  after removal of the sequential dilators  55 . 
         [0133]      FIG. 38  is a longitudinal section view of the surgical retractor system  10  of  FIG. 36  during the insertion of the tube  42  over a final one  55 C of the set of sequential dilators  55 . The view of  FIG. 38  is taken in a plane A-A′ of  FIG. 36 . Tube  42  is advanced by an inserter  63 . 
         [0134]      FIG. 39  is a partial section end view of a surgical retractor system  10  similar to that of  FIGS. 36-38  after removal of the sequential dilators  55 , the surgical retractor system  10  including a pin  54 , in accordance with an embodiment. The pins  54  may serve to stabilize second retractor  31  (tube  42 ). Pins  54  may be slidably received within tracks  47  in first retractor  21 , as described in connection with  FIG. 16 . 
         [0135]      FIG. 40  is a partial section end view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 , the first retractor  21  comprising a first means for retracting that comprises a tube  42 , in accordance with an embodiment. In the embodiment of  FIG. 40 , the tube  42  has a cross-sectional shape that is a rounded square.  FIG. 41  is a partial section end view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 , the first retractor  21  comprising a first means for retracting  22  that comprises a tube  42 , in accordance with an embodiment. In the embodiment of  FIG. 40 , the tube  42  has a cross-sectional shape that is a circle. 
         [0136]      FIG. 42  is a partial section end view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 , the first retractor  21  comprising a first means for retracting that comprises a plurality of blades  41 A, in accordance with an embodiment. In the embodiment of  FIG. 42 , the plurality of blades  41 A comprises three blades  41 A. The first working channel diameter  27  is indicated. In some embodiments, first means for retracting  21  may be expandable. In the embodiment of  FIG. 42 , for example, first means for retracting  21  comprises a plurality of blades  41 A which are depicted after expanding of first retractor  21  by moving apart blades  41 A. In some embodiments, the method of accessing a surgical site may comprise a step of expanding the first retractor  21  after inserting the first retractor  21  into the first tissue  220 . 
         [0137]    In  FIG. 43 , several distal-most percentages are indicated as fractions. For example, the fraction 0.8 indicates 80 percent, and the fraction 0.1 indicates 10 percent. For example, first working channel distal region  28  may correspond to less than or equal to the distal-most 80, 70, 60, 50, 40, 30, 20, 10, or 5 percent of the first working channel  25 . In the second retractor  31  embodiment depicted in  FIG. 43 , second means for retracting proximal portion  38  is relatively long compared to first working channel  25 , so that first working channel distal region  28  corresponds to less than or equal to the distal-most 80 percent (indicated as fraction 0.8) of first working channel  25 . In other embodiments, first working channel distal region  28  may correspond to less than or equal to a smaller percentage (fraction) of first working channel  25 , as indicated by the fractions depicted in  FIG. 43 . 
         [0138]      FIG. 44  is a longitudinal section view of a surgical retractor system  10  comprising a first retractor  21  and a second retractor  31 , in which the first retractor distal end  24  is beveled, in accordance with an embodiment. The beveled first retractor distal end  24  facilitates an oblique surgical approach to a surgical site that is partially obstructed by another element. In the  FIG. 44  embodiment, second tissue  221  is a muscle lateral to a spine. The surgical site in the spine, in this example, includes a spinal disc  210  that is between a vertebral body  204  (e.g. lumbar vertebra L5) and a second body, e.g. sacrum  236 , which is part of the pelvis. 
         [0139]    A lateral approach to this particular spinal disc  210 , using an orientation that is perpendicular to the spine axis, is obstructed by the ilium  238  of the pelvis. To circumvent the ilium  238 , first retractor  21  is oriented obliquely to the spine axis, passing above the iliac crest  238  and aiming obliquely downward to dock upon the second tissue (muscles)  221 . The beveled first means for retracting distal end  24  facilitates docking of first retractor  21  upon second tissue  221  and facilitates the inserting of second retractor  31  into second tissue  221 . First retractor  21  may be attached to an arm (not shown) which is secured to the surgical table to stabilize first retractor  21 , as described in connection with the embodiment of  FIGS. 9-13 . 
         [0140]    This site is a common site needing treatment, but this lower trauma approach is not accessible with conventional systems. 
         [0141]      FIG. 45  shows the process of deployment of a retractor pair of the invention. Panel A shows a retractor in its non-expanded form, with its two blades touching at their tips. In Panel B, the retractor of Panel A, as a second retractor, is passed (using conveying means, not shown) through a first, tubular retractor, in this case in the preferred form (straight sides, round shoulders), which may be flexible enough to be round (approximately circular) during delivery. In Panel C, a device is applied to the second retractor, opening up the blades. In Panel D, the deployed retractor is shown. This process is reversed to remove the retractors after the completion of the procedure. A preferred feature is seen in Panel D of  FIG. 45 , in which the opened-up retractor has a separation in the blades which progresses from widest at the distal points, and narrowing in the blade separation at the proximal end. This orientation is reversed (Panel B) or evened out (not illustrated) as the retractor is inserted and removed. 
         [0142]    Moreover, the ability to perform this reversal makes the use of a blade-type retractor as the second retractor to be a preferred alternative, compared to the use of a tubular retractor. This is because the limiting diameter of a tube is more difficult to expand when it is the second, more distal retractor. Moreover, the bladed reactor of  FIG. 45  offers a built-in retention capacity when it is expanded while at or near the most distal site of its deployment, because to the extent that it displaces any tissue (for example by having the tips slide along a bone as the retractor is expanded), the tissue will tend to press on the retractor blades, forcing them against the bone or other structure, and in doing so, tending to prevent the displacement of the retractor towards the proximal end of the site until the procedure is completed, and the retractor is retracted. 
         [0143]    There is a preference towards use of a tube, preferably of the “square with rounded corners” type, as the first retractor. This is because expansion over sequentially introduced nesting dilating tubes can be fast and minimally traumatic. However, especially if the proximal span of the first retractor can be short, a blade type retractor can be effective as the first retractor in the practice of the invention. 
         [0144]    In any of these embodiments, various procedures can be used to enhance tissue separation at any or all of the creation of a passage for said first retractor, or said for second retractor, or for purposes of the procedure at tissue distal of said second retractor. 
         [0145]    Retractor Insertion and Deployment 
         [0146]    Adjustable retractors are normally applied directly to a surgical site accessible from outside the body, and can be adjusted to an expanded state, and later collapsed with the mechanism of retraction, such as screw or ratchet, located outside the body. At greater depths within the body, this requires a powerful mechanism with bulky and rigid blades. In the retractor systems of the invention, conventional adjustable retractors used as second retractors can be applied with the mechanism of retraction at depths of ten centimeters or more in the body 
         [0147]    A first type of custom retractor adjuster was developed from a section of a hexagonal wrench bonded to the tip of a flexible shaft. However, torque control with strictly manual methods can be difficult, and it is difficult to precisely control the orientation of the retractor while it is being expanded. 
         [0148]    An improved retractor inserter has been created, which allows control of placement and retrieval, along with controllable application of torque to the retractor to localize it in situ.  FIG. 46  shows an example of the assembled retractor inserter, and  FIG. 47  shows the device in exploded view. 
         [0149]    The inserter  400  (also shown as  63  in  FIG. 45 ) has a handle  401 , and a movable control  403 . The control  403 , together with a squeezable member  402  (see next figure), allows the hook  407  of distal end  404  of the external fixed shaft  406  to be closed, working against spring  405  by pulling a rod (not seen) to contact the hook  407 , by moving distally within fixed shaft  406 . The distal end  404  can be seen gripping a retractor in  FIG. 45C . 
         [0150]      FIG. 47  shows an exploded view of the retractor inserter  400 . In addition to the parts named above, the pusher rod assembly  414 , riding within shaft  406 , and the driver rod assembly  415  riding within pusher rod  414  are shown. The driver rod carries a tip  416  which mates with the adjustment mechanism of the retractor (not shown). Torque is applied to the proximal end  420  of driver rod  415  by torque knob  413 . 
         [0151]    In use, a retractor for use in the invention is grasped by placing it in the hook  407 . It is held there by pressing squeezable member  402 . The retractor is then inserted to the site of use, typically through a previously-deployed first retractor, to the site where it is to be used to retract tissue. Once the tips of the blades of the retractor have been placed at a desired location, typically distally of a distal end of a first retractor, then the torque knob  413  is rotated to drive the blades of the retractor to the open state. After the procedure is complete, the retractor is removed by reversing this procedure. Both the retractor and the retractor inserter are at least potentially re-usable, after cleaning and sterilization. 
         [0152]    Optional features of the retractor inserter include one-way ratcheting action of the torque knob  413 , so that it can expand the retractor with rapid short, partial turns; together with a reversing control or a ratcheting release to allow the retractor to be removed from the site. A second, preferred feature is to place force-limiting features in the torque knob, or in a functionally equivalent position, to limit the force which can be applied to the expansion of the retractor. A simple method is to spring-load the driver rod assembly  415  of  FIG. 47 , for example with a spring  419  riding against push rod  414  shown in  FIG. 47 , so that the maximum rotational torque that can be applied to a retractor is limited (rising with the degree of compression of the spring). Such an instrument is normally calibrated before use. Other adjustable torque control or other force limiting mechanisms are known and may be applicable to this device. 
         [0153]    The detailed design of a retractor inserter is presented as an example of a highly useful accessory in the system of the invention. The examples show a relatively close alignment of the second retractor relative to the first retractor, but the invention also encompasses greater degrees of divergence. A retractor inserter of the invention can be any retractor inserter which can place a second retractor in a location within the body, wherein said location is characterized in having one or more of orientation, angulation and depth, all relative to a first retractor, that are different from the orientation, angulation and depth of the first retractor. 
         [0154]    Additional embodiments of the retractor inserter can be envisaged by the person of ordinary skill, and the use of retractor inserters in surgery, and especially in the surgical procedures of the present invention, is an object of the present invention. 
         [0155]    Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of skill in the art to which the disclosed invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods, devices, and materials are as described. Although we have described in detail various embodiments, those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be by the following claims. Other embodiments and modifications will be apparent to those of skill in the art in light of this text and accompanying drawings. The following claims are intended to include all such embodiments, modifications and equivalents.