Abstract:
A retractor having an elongate body that provides access to a surgical location within a patient. The elongate body is generally ovoid in cross section and includes a plurality of segments that are connected to one another through a plurality of ratcheting mechanisms. The ratcheting mechanisms permit relative movement of the segments with respect to one another when expander dilators are inserted within the retractor. The segments are surrounded and retained by a resilient elastomeric sleeve. The distal end surfaces of the segments include edges that are configured to mobilize, dissect, split and retract the terminal tissues in the surgical area. The retractor is used in conjunction with a resilient elastomeric pad that is affixed to the patient and firmly engages the outer surface of the elongate body to thereby anchor the retractor to the patient.

Description:
FIELD OF THE INVENTION 
       [0001]    The present system and method relate to devices and methods for performing percutaneous surgeries, and in particular, to a less invasive access portal for use in orthopedic spinal surgery. 
       BACKGROUND OF THE INVENTION 
       [0002]    Open spinal surgical procedures generally require a relatively long incision, extensive muscle stripping, prolonged retraction of tissues, and increase risk of damage to vascular and nerve tissue. This type of procedure usually necessitates many weeks of post-operative recovery due to the use of long hours under general anesthesia, blood transfusions and the unavoidable trauma caused to the body tissues during the procedures. An open surgical procedure will also result in significant permanent scarring leading to fusion disease. 
         [0003]    Surgery performed percutaneously has achieved major improvements over open surgery. The reduction of muscle and tissue dissection significantly reduces post operative recovery pain and recovery time. Percutaneous surgery is particularly beneficial for spinal surgery because the surgical area is deep within the body and in locations surrounded by sensitive and critical body tissues. Tube retractors have been developed to provide minimally invasive access to the surgical area. The ability to dilate muscle tissue, as opposed to strip or detach from the bony anatomy, will reduce the damage and risks normally associated with the open type surgery. 
         [0004]    The typical tube retractor technique starts with the identification of the correct entry point, establishing the trajectory from the skin to the pathology to be addressed and the corresponding skin incision. The initial soft tissue dilator is inserted through the incision and forcefully advanced to the objective site. A series of larger dilators are inserted over the initial dilator thereby sequentially increasing the diameter until the final/operative dilator is inserted. Once the operative dilator is in place it must be fixed in order to resist movement that will result from forces imposed by the patient&#39;s tissue. Currently, the accepted approach to fixation is a point outside of the patient&#39;s anatomy. Typically a rigid arm is attached at one end to the retractor while the opposite end of the arm is attached to a bed rail clamp. Once the retractor is fixed in position, the surgeon begins the operation to address the pathology. Upon completion of the procedure the retractor tube is removed and the skin incision is closed. Because of the reduced morbidity to the patient, the patient&#39;s initial recovery time should be less, blood loss should be less, operating room time should be less, anesthesia time should be less, patient stay in the hospital should be less, return to work time should be less and the overall cost of the procedure should be less 
         [0005]    One of the most difficult aspects of the current technique is that the rigid fixation of the retractor is sometimes subject to unintentional or unavoidable movement of the patient during the course of the surgical procedure. Another consistent problem is the inability of the current designs and methods to adequately retract the muscle tissue at the distal end of the retractor, which for all intents and purposes is the most crucial portion of the retractor. Due to the retractors inability to clear the surgical area the surgeon must resort to cutting, cauterizing and removing the final fibers of muscle. This process of physical tissue removal carries with it increased risk of damage to ancillary tissues and nervous tissues, while at the same time increasing morbidity, blood loss and operative time. These difficulties result in high levels of frustration making the technique less likely to be adopted by the majority of surgeons. The current retractors lack the distraction capability at the distal end of the retractor which is where the strongest forces resisting the retractor are present. In addition the current retractor designs do not accommodate the natural anatomical shape of the patient&#39;s anatomy where the pathology exists. 
       DESCRIPTION OF THE PRIOR ART 
       [0006]    Retractors for use in percutaneous spinal surgery lack the ability to easily efficiently and clearly access the surgical area. Likewise, they do not have a simple, effective and efficient device to anchor the retractor relative to the patient. 
         [0007]    U.S. Pat. No. 5,460,170 discloses an adjustable, expandable retractor suitable for use in small surgical incisions or punctures. The device is able to expand the incision or puncture to one or more enlarged cross-sectional areas and designed to protect the edges of the incision or puncture. The surgical retractor comprises a radially expandable tubular body having a control at the proximal end. Pull wires couple the control to the tubular body such that force applied to the control is transmitted to the tubular body as axially compressive force. 
         [0008]    U.S. Pat. No. 3,788,318 discloses an expandable tube, referred to herein as a cannula, is formed by arranging at least one sheet of thin flexible material to form a tube while providing teeth or the like on the interengaging surfaces to permit controlled expansion of the tube by adjusting the surfaces over one another. 
         [0009]    U.S. Pat. No. 6,187,000 discloses a cannula with an expandable portion for enabling an increase in the cross-sectional area of the passage at the distal end. The expandable portion of the tube structure, when expanded, has a conical configuration. 
         [0010]    U.S. Pat. No. 6,652,553 discloses a surgical tool for use in expanding a cannula and includes a first leg having a first end engageable with an inner surface of the cannula. A second leg is connected with the first leg. The second leg has a second end engageable with the inner surface of the cannula. The first and second ends are movable away from each other to apply a radially outwardly directed force to the inner surface of the cannula and cause expansion of the cannula. 
         [0011]    U.S. Pat. No. 7,261,688 discloses a retractor having a working channel formed by a first portion coupled to a second portion. The first and second portions are movable relative to one another from an unexpanded configuration to an expanded configuration to increase the size of the working channel along the length thereof. 
         [0012]    U.S. Pat. Nos. 6,524,320 and 7,144,393 disclose a cannula having an expandable portion for enabling an increase in the cross-sectional area of the passage. The expandable portion of the tubular structure has a slot and a guide member disposed in the slot. The guide member is movable from a first end of the slot toward a second end of the slot to enable the cross-sectional area of the passage to increase. The expandable portion has a stop between the first and second ends of the slot engageable with the guide member to retain the guide member in a position relative to the slot and resist movement of the guide member from the position relative to the slot. In the &#39;393 patent, the expandable portion has a contracted condition in which the cross-sectional area of the distal end of the passage has a first cross-sectional area. The expandable portion has an expanded condition in which the distal end of the passage has a second cross-sectional area greater than the first cross-sectional area. The second cross-sectional area is greater than a cross-sectional area of the proximal end of the passage when the expandable portion is in the expanded condition. A retaining mechanism resists movement of the expandable portion from the expanded condition toward the contracted condition during the surgical procedure. The retaining mechanism is released at the conclusion of the surgical procedure to permit movement of the expandable portion from the expanded condition toward the contracted condition for removal of the structure. The expandable sleeve is provided with a lockable means in the expanded position. 
         [0013]    U.S. Pat. Nos. 7,179,225 &amp; 7,221,451 discloses a retractor has an elongate body and an expandable shroud. The elongate body has an outer surface and an inner surface partially defining a passage. The elongate body also has a first longitudinal edge and a second longitudinal edge. The elongate body is capable of having an enlarged configuration when inserted within the patient. In the enlarged configuration the first longitudinal edge is spaced apart from the second longitudinal edge. The expandable shroud is configured to extend from the first longitudinal edge to the second longitudinal edge when the first and second edges are spaced apart. The shroud partially defines the passage. The cross-sectional area of said passage at a first location is greater than the cross-sectional area of the passage at a second location, wherein the first location is distal to the second location. See FIG. 70 in the &#39;225 patent and FIG. 71 for oval and oblong shape. 
         [0014]    U.S. Pat. No. 7,223,233 discloses methods and devices for illuminating a surgical space in a patient. A retractor provides a portal or working path for access to a working space location in the patient. The retractor transmits and emits light from a light delivery system to illuminate the working channel and surgical space. 
         [0015]    U.S. Publication No. 2006/0041270 discloses an expandable sheath is insertable into a patient through an incision. Once inserted and advanced to the target surgical site, the sheath can be expanded to an enlarged diameter. The wall of the sheath is fabricated from a tubular structure comprising filamentous elements that extend axially and at least partially circumferentially along the length of the sheath. The tubular filamentous material is drawn or expanded axially to create the small diameter configuration that is inserted into the patient. A standoff attaches the distal end of the tubular filamentous material to the sheath hub by way of radially movable anchors. Additional filamentous tubular material extends out the proximal end of the hub. A compression mechanism forces the additional filamentous tubular material in the distal direction which causes axial compression and radial or diametric dilation of the working length of the sheath, that part of the sheath that extends beyond the proximal end of the hub. Radial dilation is accomplished with no substantial change in sheath working length. 
         [0016]    U.S. Publication No. 2006/0200023 discloses systems and methods include an anchor engageable to a vertebra and an extender removably mounted to the anchor. The extender includes an insulating member extending at least partially thereabout to electrically insulate the extender and prevent shunting of electrical signals delivered through the extender to the anchor to structures adjacent the extender. Flexible jacket  26  includes a means for monitoring nerves. 
         [0017]    U.S. Publication No. 2008/0234550 discloses a less invasive access port for use in minimally invasive surgery allows for manipulation of the viewing angle into the working site in a transverse plane. According to one exemplary embodiment, the less invasive access port is designed to minimize the need for muscle retraction. Additionally, the less invasive access portal provides sufficient light, irrigation, suction and space for sundrymedical instruments. According to one exemplary embodiment, a less invasive access port device includes a retractor assembly having four retractor blades secured in various positions by pins placed within slots on the retractor blades. A cannula includes integrated interfaces for light, irrigation and suction. A housing forms a collar around a top of the cannula and houses the light, irrigation and suction mechanisms. Instruments and implants may be passed through the cannula and into the working space created by the retractor assembly. Visualization of the working site can be attained under direct vision. 
       SUMMARY OF THE INVENTION 
       [0018]    The present invention is directed to methods and devices for performing percutaneous, minimally invasive spinal surgery. In particular the invention includes a percutaneous tissue retraction device that provides access to the surgical area within the patient. Another aspect of the invention includes a device for anchoring the retractor device directly on the patient without the aid of additional structural elements to affix the retractor to other objects within the operating room such as the operating table. 
         [0019]    The current retractor addresses the current problem making its utilization more reproducible, easier to learn and visualize and increases safety while delivering a more consistent result. 
         [0020]    The anchoring device includes a pad that is affixed to the patient. Should the patient move slightly, intentionally or unintentionally, the retractor maintains the same tissue retraction and the same trajectory. This provides an accurate and stable portal to the patient&#39;s pathology. The pad eliminates the necessity for rigid fixation to a point outside of the field of operation or to an independent immobile point such as a bed rail. The rigid fixation device is metallic and used with conventional metallic split blade retractors that reduce visualization of the approach through the retractor as well as the visualization of the objective site while using operative fluoroscopy. 
         [0021]    The anatomical shape of the distal end of the current retractor produces a significantly improved ability to mobilize, dissect, split and retract the terminal tissues of the psoas muscle at the point on the spine where the entry is to be made. Current distal end designs are parallel to the spine and do not comply with the natural shape of the spine. 
         [0022]    The ovoid shape of the retractor requires less retraction in two different planes while achieving adequate exposure thereby making the procedure easier and more reproducible. 
         [0023]    Likewise, the anatomical shape of the distal end of the dilator when inserted safely and gently, divides/splits the psoas muscle fibers along the longitudinal plane of the spine. The distal end shape of the dilator mobilizes and dissects the muscle fibers more effectively and when subsequently rotated ninety degrees provides a dilator that will safely and gently sweep the terminal fibers in order to enable consistent retraction of the muscle fibers while the retractor is inserted. The final dilator is unique in its ability to create a path for the retractor which complies with the patient&#39;s anatomy in a safe, gentle fashion allowing for efficient mobilization of the muscle fibers and maintaining the muscle retraction when inserting the retractor. Current systems use round dilators with flat bottom surfaces. When the retractor is inserted over the final dilator and the dilator is removed, muscle fibers creep under the end of the retractor and the doctor must then use instruments to sweep the fibers out of the way, under the blades or ablate them 
         [0024]    Accordingly, it is an objective of the instant invention to provide a retractor for performing minimally invasive spinal surgery that provides improved access to the surgical area. 
         [0025]    It is a further objective of the instant invention to provide a retractor device that the surgeon will find more intuitive to use owing to its construction ease of use. 
         [0026]    It is yet another objective of the instant invention to provide a retractor for minimally invasive spinal surgery with an anatomically shaped distal end resulting in a much improved ability to mobilize, dissect, split and retract the terminal tissues of the psoas muscle at the point of the spine where the entry is to be made. 
         [0027]    It is a still further objective of the invention to provide a retractor where the walls of the retractor apply an opening force throughout the length of the retractor and provide a more robust retraction. 
         [0028]    It is a still further objective of the invention to provide a radiolucent retractor for greater visualization during the surgical procedure. 
         [0029]    Other objects and advantages of this invention will become apparent from the following description taken in conjunction with any accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. Any drawings contained herein constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0030]      FIG. 1  is a top view of the retractor showing the retractor segments and the encircling silicone sleeve. 
           [0031]      FIG. 2  is a schematic showing the four segments of the retractor. 
           [0032]      FIG. 3  is enlarged top sectional view of two of the segments and ratcheting mechanism on each of the segments within the circled area of  FIG. 2 . 
           [0033]      FIG. 4  is an enlarged top partial sectional view showing the interengaing teeth of the ratcheting mechanism on each of the segments and the surrounding elastomeric sheath within the circled area of  FIG. 3 . 
           [0034]      FIG. 5  is a front view of the interior surface of one of the semi cylindrical members showing four discrete locations for the teeth which form part of the ratcheting mechanism. 
           [0035]      FIG. 6  is a front view of the interior surface of one of the semi cylindrical showing a continuous set of teeth that run the length of the segment from the proximal to the distal end portions. 
           [0036]      FIG. 7  is a side view of the exterior surface of one of the semi cylindrical segments. 
           [0037]      FIG. 8  is a front view of the exterior surface of one of the semi elliptical segments. 
           [0038]      FIG. 9  is a side view of the exterior surface of one of the semi elliptical segments. 
           [0039]      FIG. 10A  is a side view of a patient with their side in an upward position and patient pad and retractor in place. 
           [0040]      FIG. 10B  is a top view of the patient pad with the initial incision. 
           [0041]      FIG. 11A  is a top view of the tool that is used to rotate the final operative dilator as well as the retractor. 
           [0042]      FIG. 11B  is a side view of the tool that is used to rotate the final operative dilator as well as the retractor. 
           [0043]      FIGS. 12A and 12B  illustrate the initial dilators. 
           [0044]      FIGS. 12C ,  12 D,  12 E and  12 F illustrate various views of the oblong final operative dilator 
           [0045]      FIG. 12G  is an example of a retractor expansion dilator. 
           [0046]      FIG. 13  is a top view of the retractor in position on the patient. 
           [0047]      FIG. 14A  is a top view of the retractor in position within the patient&#39;s body. 
           [0048]      FIG. 14B  is a side view of the retractor positioned within the patient&#39;s body. 
           [0049]      FIG. 15  is a top view of the retractor in position within the patient&#39;s body after being rotated ninety degrees 
           [0050]      FIG. 16A  is a top view of the retractor in position within the patient&#39;s body after being rotated ninety degrees. 
           [0051]      FIG. 16B  is a side view of the retractor positioned within the patient&#39;s body after being rotated ninety degrees. 
           [0052]      FIGS. 17A and 17B  diagrammatically show the special relationship between the retractor segments, with  FIG. 17B  showing the expanded condition. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0053]    The present invention is directed to methods and devices for performing percutaneoous surgery and in particular spinal surgery. The surgery is performed through a portal or passageway provided by a retractor. The retractor is expandable in situ to thereby increase the size of the surgical area as well as the access thereto. It is particularly constructed to minimize trauma to tissue surrounding the retractor and the surgical area. The retractor can be used with any surgical approach to the spine such as; lateral, postero-lateral and/or antero-lateral, anterior, posterior, posterior mid-line, and in other regions of the body not associated with the spine. 
         [0054]      FIG. 1  is a top view of retractor  1 . As shown retractor  1  is comprised of four discrete segments. As shown, the segments consist of a pair of opposing semi cylindrical members  4 A and  4 B as well as a pair of opposing semi elliptical members  6 A and  6 B. A ratcheting mechanism  8 A and  8 C is located at each of the junctions between opposing semi cylindrical member  4 B and opposing semi elliptical members  6 A and  6 B. Likewise a ratcheting mechanism  8 B and  8 D is located at each of the junctions between semi cylindrical segment  4 A and opposing semi elliptical members  6 A and  6 B. The four segments once assembled and surrounded by a silicone sleeve  10  and form a single working unit that is generally elongated and oval shaped in cross section. The sleeve  10  conforms to the shape of the exterior surfaces of the segments and extends the entire length of the segments from the proximal end, the top portion, to the distal end, bottom portion and exerts a radially directed inward force against segments  4 A,  4 B,  6 A and  6 B. The assembly thereby forms an elongated ovoid shaped retractor wherein the parallel distraction will occur along the length of the retractor based upon the engagement and disengagement of the teeth placed along the longitudinal axis of the retractor. While shown and described as having four segments the retractor could be formed as two segments each including a semi cylindrical segment and a semi elliptical segment. 
         [0055]    The segments  4 A,  4 B,  6 A and  6 B are formed from plastic or any other suitable radio lucent material. Segments  4 A and  4 B each respectively have screw holes  12 A and  12 B designed to receive a bone screw for distal fixation of the retractor to a vertebral body. The segments also contain insulated electrical conductors  16  included in the walls of the segments. The conductors  16  terminate at the proximal and distal surfaces of the segments with exposed electrical contacts to provide an electrical pathway for nerve monitoring Also included within the segments are internal tracks for mounting fiber optical lights  18  to provide illumination of the surgical space located at the distal end of the retractor. Each of the segments  4 A,  4 B,  6 A, and  6 B may contain radio opaque markers  24  to enable visualization throughout the procedure. 
         [0056]      FIG. 2  shows a partially exploded top view if the four segments prior to engagement via the ratcheting mechanisms.  FIG. 3  is an enlarged view of the encircled area of  FIG. 2  As can be seen in  FIG. 3  semi-circular segments have teeth or grooves  20  located on the interior surface adjacent both edges of the semi circular segments  6 A and  6 B. These teeth or grooves  20  are located at four separate points along the length of the segments between the proximal and distal end portions as shown in  FIG. 5 . Alternatively teeth or grooves  20  can run the entire length of the segments from the distal end portion to the proximal end portion as shown in  FIG. 6 . As seen from the front view, the lower distal end surface of segments  6 A and  6 B form a concave edge  26 .  FIG. 7  shows a side view of the external surface of the semi cylindrical segments  6 A and  6 B.  FIG. 8  is a front view of the exterior surface of one of the semi elliptical members  4 A and  4 B. As seen from the front view the lower distal end surface of segments  4 A and  4 B form a convex edge  28 . Concave edges  26  and convex edges  28  form a tip at the distal end of the retractor  1  that is anatomical in shape and particularly configured to significantly improve the ability to mobilize, dissect, split and retract the terminal tissues of the psoas muscle at the point on the spine where the entry is to be made.  FIG. 9  is an exterior surface side view of one of the semi elliptical members  4 A and  4 B. One or both of the segments  4 A and  6 B contain an insulated electrical conductor  16  included in the walls of the segments. A tool  30 , shown in  FIGS. 11A and 11B  is used to facilitate a ninety degree rotation of the retractor as will be explained below. The tool  30  includes a pair of diametrically opposed handles  32  and  34  that are each connected to an annular member  36 . The inner surface  38  of the annular member  36  is configured to operatively cooperate with the external surface of sleeve  10  surrounding the retractor  1  adjacent the top portion thereof. Semi elliptical segments  4 A and  4 B have complimentary teeth or grooves  22 . Teeth or grooves  22  are located on the exterior of semi elliptical segments  4 A and  4 B adjacent each of the edges of semi elliptical segments  4 A and  4 B. Teeth or grooves  22  extend the entire length of the segments form the proximal to distal end portion as shown in  FIG. 9 .  FIG. 4  shows one of the ratcheting mechanisms  8 A- 8 D and the inter engagement of teeth  20  and  22  are well as sleeve  10  which exerts a radially directed inward force on each of the retractor segments. 
         [0057]    The present system is a patient based retractor that does not require fixation to an articulating arm. The patient based retractor includes a pad  40  that eliminates the necessity for a rigid fixation to a point outside of the field of operation or to an independent immobile point such as a bed rail. The pad  40  is applied to the sterilized area on the patient&#39;s body  41 . The physical properties of the material including its size, thickness and composition cause significant friction, or adhesion, between the pad and the sterile site on the patient&#39;s skin. By way of example,  FIGS. 10A and 10B  illustrate the pad  40  in a deployed position. This can be reinforced with the application of tape and or IOBAN® if necessary. By way of example the pad can be formed from a polyurethane material. While the pad  40  and retractor  1  have been shown for use during minimally invasive spinal surgery it should be understood that the anchoring pad  40  could be used in combination with retractor  1  or a retractor of any configuration and for other types of surgery as well, such as laparoscopic gal bladder surgery or appendectomy. 
         [0058]    The tube retractor technique starts with identifying the correct entry point, and correct trajectory from the skin to the pathology to be addressed. A top view of the incision  42  is shown in  FIG. 10B . The initial soft tissue canulated dilator  50  of circular cross section, as shown in  FIG. 12A , is inserted through the incision and forcefully advanced to the objective site. A series of larger diameter dilators as shown in  FIG. 12B ,  51  and  52 , are inserted over the initial dilator sequentially increasing in diameter until the final operative diameter is inserted. The final operative dilator  54  is oblong in cross section as is shown in  FIG. 12C through 12F .  FIG. 12C  is a front perspective view of the ovoid shaped final dilator.  FIG. 12D  is a side view of the bottom or distal end surface  56  of the final dilator that is convex in shape on both side wall portions.  FIG. 12E  is a perspective bottom view of the bottom or distal end surfaces of the final dilator that shows the front and back wall surfaces having bottom edges  58  that are concave in shape. The two convex surfaces at the lower edge of the side wall portions and the concave edges on the front and back walls form a distal or end surface that is anatomical in shape and particularly configured to significantly improved the ability to mobilize, dissect, split and retract the terminal tissues of the psoas muscle at the point on the spine where the entry is to be made. Once in its proper position the oblong operative dilator  54  is rotated ninety degrees and then counter rotated back to its original position using the tool  30 .  FIG. 13  is a top view of the retractor in position on the patient.  FIG. 14A  is a top view of the retractor  1  in position within the patient&#39;s body and  FIG. 14B  is a side view of the retractor within the patient&#39;s body  41 . As shown in  FIGS. 14A and 14B  the spinal disc  60  is located between vertebral bodies  62  and  64 . As shown, each vertebral body includes a spinous process bone  66  and a pair of pedicle bones  68 . Either segment  6 A or  6 B can be seen in this view. Once in this position, the retractor  1  is then rotated ninety degrees using tool  30  to the position shown in  FIGS. 15 .  FIG. 15  is a top view of the retractor  1  in position on the patient after being rotated. The shape of the distal end of the retractor segments provides a significant improvement in the ability to mobilize, dissect, split and retract the terminal tissues of the psoas muscle at the point on the spine where entry is to be made. Current designs are parallel to the spine and do not comply with the natural shape of the spine. Thereby allowing the terminal psoas muscle fibers to creep under the retractor and completely undermine the process and in many cased reduces the overall success and intention of the minimally invasive technique. The ninety degree rotation of the retractor  1  enables the distal portions of the psoas muscle to be mobilized and retracted via the retractor. This action reduces muscle creep thereby reducing the necessity for the surgeon to cut, cauterize and remove muscle fibers to access to the pathology. 
         [0059]    Once the retractor  1  is rotated into final position the final and initial dilators are withdrawn from the patient. At this point, a series of retractor expansion dilators, shown in  FIG. 12C , are available for expansion of the retractor  1 . These expansion dilators are canulated and assist in centering the retractor with the initial k-wire that is already in place. The expansion dilators are 14, 16, 18 and 20 mm in diameter. As progressively larger expansion dilators are inserted within the retractor  1 , segments  4 A,  4 B,  6 A and  6 B move relative to one another by virtue of ratcheting mechanisms  8 A,  8 B,  8 C and  8 D. By way of example, it is contemplated that the distance between segments  4 A and  4 B at their mid points can be increased from 14 mm to 18 mm and the distance between segments  6 A and  6 B at their mid points can be increased from 18 mm to 22 mm, as shown diagrammatically in  FIGS. 17A and 17B . At this point the expansion dilators are removed and the operation can proceed. The retractor is anchored at the near portion by frictional engagement with pad  40 . In addition the retractor  1  may be anchored at the distal end portion using bone screws that are inserted through holes  12 A and  12 B of the retractor and threaded into the vertebral body. The pad  40  eliminates the need for a rigid fixation to a point outside the surgical field or to an independent fixed point such as a bed rail. The elimination of these metallic supports that are typically associated with minimally invasive tube or split blade retractors increases the visualization of the approach through the retractor and visualization of the surgical site while using operative fluoroscopy. 
         [0060]    The retractor system of the present invention was developed to provide minimally invasive access to a patient&#39;s pathology. The ability to dilate muscle tissue, as opposed to the process where the muscle tissue to stripped or detached from the skeletal structure will usually reduce the morbidity associated with the standard invasive technique. The procedure to utilizing the retractor system of the present invention starts with the identification of the correct entry point, the proper trajectory from the skin to the pathology to be addressed as well as the point of incision. After the initial incision has been made through the patient based anchoring pad and into the skin the initial soft tissue dilator is inserted through the incision and forcefully advanced to the objective site. The initial dilator is 6 mm in diameter and round in cross section. Thereafter, a series of progressively larger dilators are inserted over the initial dilator; increasing in diameter until the final operative dilator is inserted. The final operative dilator is oblong in cross section. Once the final operative oblong dilator is in place it is then rotated ninety degrees by tool  30  and then counter rotated ninety degrees back to its initial position. The retractor  1  is then placed over the final operative dilator and forcefully advanced to the objective site. Once in position the retractor is then rotated ninety degrees by using a tool  30 . Thereafter the initial and final dilators are removed. Following removal of the dilators used for initial delivery, a series of expansion dilators, are inserted into the center of the retractor  1  to expand the open area or portal within the retractor. These expansion dilators are circular in cross section and range in diameter from 14 mm to 20 mm. As the expansion dilators are inserted the ratcheting mechanisms  8 A,  8 B,  8 C, and  8 D allow relative movement between the adjacent retractor segments by virtue of the disengagement and reengagement of the teeth  20  and  22 . The expansion dilator creates a force directed radially outwards thereby causing a shift in the alignment of teeth  20  and  22 . Simultaneously resilient sleeve  10  exerts a radially inward directed force maintaining the teeth  20  and  22  in their newly established position. 
         [0061]    All patents and publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains. All patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. 
         [0062]    It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and any drawings/figures included herein. 
         [0063]    One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.