CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the benefit of and/or priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/739,137 filed Dec. 19, 2012, entitled “Dilation Tube System For Neuro Monitoring And Incision Dilation In Spinal Surgery” the entire contents of which is specifically incorporated herein by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to devices used in spinal surgery and, more particularly, to devices for neuro monitoring and incision dilation in spinal surgery. 
     2. Background Information 
     When performing typical spinal surgery it is necessary for the surgeon to contend with and manage various aspects of the procedure. A major aspect of spinal surgery is being able to determine position of a nerve or nerves that are proximate the surgical site. This is necessary to avoid cutting or damaging the nerve or nerves during the surgical procedure. 
     After an incision is made the surgeon locates any spinal nerve or nerves at or proximate the surgical site (i.e. neuro monitoring) before the soft tissue is dilated in order to gain access to the specific surgical area. Currently, the process of neuro monitoring and then dilating the soft tissue to gain access to the specific surgical site involves using a sequence of right-cylinder dilation tubes of increasing diameters. After an initial or first right-cylinder dilation tube is inserted into the incision for neuro monitoring, additional right-cylinder dilation tubes of increasing diameter are positioned over each other until the specific surgical area is reached. 
     The problem with the prior art approach is that current sequence of right-cylinder dilation tubes dilate the incision circumferentially which keeps the center point of the initial right-cylinder dilation tube and the main working channel the same. With the prior art method, the surgeon must continually neuro monitor and potentially adjust the position of the working channel since the prior art right-cylinder dilation tubes grow circumferentially in diameter in all directions—which is both towards and away from the nerve position. 
     It is therefore an object of the present invention to overcome the prior art deficiencies of neuro monitoring and incision dilation for spinal surgery. 
     SUMMARY OF THE INVENTION 
     A system and method for directional and sequential incision dilation with neuro monitoring uses an assembly of separate nesting tubes. Each dilation tube of the dilation tube assembly is configured to provide incision dilation migration in a given direction, distance and angle from an initial dilation tube of the dilation tube assembly that has been inserted in an initial neuro-monitoring area. 
     The dilation tube assembly comprises a plurality of cylindrical, nesting dilation tubes including an initial cylindrical dilation tube that provides a passage for a neuro-monitor. Subsequent cylindrical dilation tubes sequentially increase in size along of increasing diameter each one configured to nest onto a previous cylindrical dilation tube via an off-centered channel, notch or cutout formed in each of the subsequent cylindrical dilation tube. The off-centered cutouts allow the subsequent cylindrical dilation tubes to dilate the soft tissue while at the same time migrate the incision dilation in a particular direction at some angle and/or distance from the initial cylindrical dilation tube insertion point (i.e. the initial neuro-monitoring insertion point). Nesting provides a stable construct. 
     In one form, the initial cylindrical dilation tube is a right-cylinder tube while each subsequent cylindrical dilation tube is an elliptic cylinder tube with a notch or cutout in one wall. The initial dilation tube has a closed passage for a neuro monitoring device. The elliptical configuration provides the directional incision migration. Each notch or cutout is has ends configured and sized to nest onto or fit around a nesting portion of the previous cylindrical dilation tube. Other manners of nesting subsequent cylindrical dilation tubes to provide directional (non-equidistant) incision migration relative to an initial neuro-monitoring insertion point may be used. 
     The present dilation tube assembly is preferably, but not necessarily, used in conjunction with a spinal retractor during the spinal surgery. The spinal retractor includes a posterior blade that is shaped to receive the dilation tube assembly. The posterior blade may or may not be offered without any angulation capabilities for additional rigidity of the construct. The dilation tube assembly permits determination of nerve position then dilating anteriorly (or away from retractor blades) for a known safe placement of the retractor blades. An arm of the retractor that carries the static blade (and which cradles the dilation tube assembly) includes a threaded table attachment bore along with guide holes posterior of the static blade wall for insertion of a neuro-monitoring sounding probe following insertion of retractor/blades if double checking of nerve is desired. 
     The present invention will be more apparent upon reading the following detailed description in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  depicts an exemplary embodiment of an assembled dilation tube system fashioned in accordance with the present principles; 
         FIG. 2  is an isometric view of an initial dilation tube of the present dilation tube system; 
         FIG. 3  is an enlarged top view of the initial dilation tube of  FIG. 1 ; 
         FIG. 4  is an isometric view of the initial dilation tube and a secondary dilation tube assembled thereon of the exemplary dilation tube system of  FIG. 1 ; 
         FIG. 5  is an enlarged top view of the assembled initial and secondary dilations tubes of  FIG. 4 ; 
         FIG. 6  is an isometric view of the initial dilation tube, the secondary dilation tube and a tertiary dilation tube assembled thereon of the exemplary dilation tube system of  FIG. 1 ; 
         FIG. 7  is an enlarged top view of the assembled initial, secondary and tertiary dilation tubes of  FIG. 6 ; 
         FIG. 8  is an isometric view of the initial dilation tube, the secondary dilation tube, the tertiary dilation tube and a quaternary dilation tube assembled thereon of the exemplary dilation tube system of  FIG. 1 ; 
         FIG. 9  is an enlarged top view of the initial, secondary, tertiary and quaternary dilations tubes of  FIG. 8 ; 
         FIG. 10  is a side view of the assembled initial, secondary, tertiary and quaternary dilations tubes of the present invention; 
         FIG. 11  is an enlarged partial view of the assembled initial, secondary and tertiary dilation tubes with the quaternary dilation tube having a beveled tip shown being slid over the tertiary dilation tube; 
         FIG. 12  is a top exploded view of the initial, secondary, tertiary and quaternary dilations tubes; 
         FIG. 13  is an isometric view of a spinal retractor holding the dilation tube system of  FIG. 1 ; 
         FIG. 14  is an enlarged top view of a portion of the spinal retractor holding the dilation tube system of  FIG. 13 ; 
         FIG. 15  is an enlarged cross sectioned top view of the present assembled dilation tube system surrounded by blades of the spinal retractor particularly illustrating the directional dilation migration at a given distance or angle from an initial insertion point achieved by the present dilation tube system; and 
         FIG. 16  is a side view of the present assembled dilation tube system with an inserted neuro probe held by the spinal retractor of  FIG. 15  relative to a vertebral section of a patient. 
     
    
    
     Like reference numerals indicate the same or similar parts throughout the several figures. 
     A detailed description of the features, functions and/or configuration of the components depicted in the various figures will now be presented. It should be appreciated that not all of the features of the components of the figures are necessarily described. Some of these non-discussed features as well as discussed features are inherent from the figures. Other non-discussed features may be inherent in component geometry and/or configuration. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1  there is depicted a view of an upper portion of an exemplary embodiment of a directional sequential dilation tube assembly (“dilation tube assembly”), generally designated  10 , fashioned in accordance with the present principles, the dilation tube assembly providing directional and sequential incision dilation migration of a given direction, distance and angle from an initial neuro-monitoring insertion point versus prior art equidistant incision dilation migration from an initial neuro-monitoring insertion point—particularly when used in conjunction with a spinal retractor. 
     The exemplary embodiment of a dilation tube assembly  10  shown in  FIG. 1  and throughout the various figures has four (4) dilation tubes  12 ,  14 ,  16  and  18 . It should be appreciated that the number of dilation tubes may be more or less than four (4) but can be no less than two (2). The dilation tubes are made from a suitable surgical grade material such as stainless steel, titanium, Aluminum or the like and are preferably, but not necessarily, cylindrical tubes. The cylindrical dilation tube  12  is an initial dilation tube while the cylindrical dilation tubes  14 ,  16  and  18  are subsequent sequential dilation tubes. Further dilation tubes (not shown) of the dilation tube assembly would be further subsequent sequential dilation tubes. As seen in  FIG. 1 , the dilation tubes stack upon one another in a nesting fashion such that they are together when assembled. As explained further below, because of their shape the dilation tubes dilate soft tissue of an incision (not shown) while at the same time migrate the incision dilation in a particular direction, distance and angle direction from the initial cylindrical dilation tube insertion point (i.e. the initial neuro-monitoring insertion point as provided by the initial dilation tube) while allowing continuous neuro monitoring via the initial dilation tube from the same location. 
     The initial dilation tube  12  is particularly shown in  FIGS. 2 and 3 . The initial dilation tube  12  is defined by a generally right cylinder body  20  having a rounded longitudinal flange, rib, projection or the like  21  and a longitudinal bore  22 . An upper end  27  of the body  20  is generally planar. The longitudinal bore  22  extends the length of the right cylinder body  20  and provides a passage or channel for a neuro probe, device or the like. The initial dilation tube  12  is inserted into the incision such that a neuro monitoring probe, device or the like (or other type of device)  5  extends through the bore  22  (see, e.g.,  FIG. 16 ). The outer surface of the body  20  is preferably smooth, including that of the longitudinal rib  21 . The outside surface of the body  20 , as well as the bodies of the other dilation tubes, may be coated or otherwise made to provide a smooth surface. 
     In  FIG. 3 , an enlarged view of a top of the initial dilation tube  12  is shown to particularly envision its longitudinal and cross-sectional shape and/or configuration. As discerned, the longitudinal flange  21  has a rounded outer surface in like manner and preferably, but not necessarily, concentric with the outer surface of the body  20 . A beveled or angled edge  25  provides a transition between the upper ends of the body  20  and the longitudinal rib  21 . The longitudinal rib  21  extends from the body  20  at a first longitudinal transition  23  on one side of the rib  21  and at a second longitudinal transition  24  on another side of the rib  21 . The first longitudinal transition  23  creates or defines a first shelf or ledge providing a first seat for a first subsequent dilation tube  14 . The second longitudinal transition  24  creates or defines a second shelf or ledge providing a second seat for the first subsequent dilation tube  14 . As seen in  FIG. 11 , the initial dilation tube  12  has a rounded lower end  75 . 
     The dilation tube  12  is the first or initial tube of the dilation tube assembly to be inserted into the incision. The bore  22  of the initial dilation tube  12  permits a monitoring probe  5  or the like to be positioned adjacent a nerve or nerves (neuro-monitoring) once an incision has been made and/or positional stability through which a guide wire, probe, device or the like can be inserted. In this first stage of incision dilation, the initial dilation tube  12  inserted into the incision is preferably, but not necessarily, generally a right-cylinder so as to initially provide a generally equidistant incision dilation area. 
     Referring to  FIGS. 4 and 5  there is depicted a second stage in assembly of the dilation tube structure  10  wherein the first subsequent directional dilation tube  14  is sequentially situated onto the initial dilation tube  12 . The outer shape and configuration of the initial dilation tube  12  allows the nested reception of the first subsequent directional dilation tube  14  via its nesting structures. The first subsequent directional dilation tube  14  is defined by a generally elliptic cylinder body  30  having a generally elliptical outer surface and a rounded longitudinal notch, cutout, channel or the like  31 . An upper end  39  of the body  30  is generally planar. The longitudinal channel  31  extends the length of the elliptic cylinder body  30  and provides a reception site for the initial dilation tube  12  as the first subsequent directional dilation tube  14  is received onto the initial dilation tube  12  during the second stage of incision dilation per the present method. The outer surface of the body  30  is preferably smooth, including the inner surface of the longitudinal channel  31 . An upper portion of the outer surface of the body  30  may include arced notches  38 . 
     Referring to  FIG. 5 , an enlarged view of a top of the first subsequent directional dilation tube  14  is shown to particularly envision its longitudinal and cross-sectional shape and/or configuration. As discerned, the longitudinal channel  31  has a rounded inner surface, shape and size complementary to the outer surface of the body  20  of the initial dilation tube  12  in order to be received on or nest upon the initial dilation tube  12 . The nesting structures include a first longitudinal flange  32  provided at a first edge or end  36  of the channel  31  and a second longitudinal flange  38  provided at a second edge or end  37  of the channel  31 . The shape of the first end  36  is complementary to the shape of the first transition  23  such that the first end  36  of the first subsequent dilation tube  14  seats or nests against the first transition  23  of the initial dilation tube  12 . The shape of the second end  37  is complementary to the shape of the second transition  24  such that the second end  37  of the first subsequent directional dilation tube  14  seats or nests against the second transition  24  of the initial dilation tube  12 . A beveled or angled edge  35  provides a transition between the upper ends of the body  30  and first and second flanges  32 ,  38 . 
     The first flange  32  extends from the body  30  at a first longitudinal transition  33  and is generally arc-shaped and preferably, but not necessarily, concentric with the outer surface of the body  30 . The second flange  38  extends from the body  30  at a second longitudinal transition  34  and is generally arc-shaped and preferably, but not necessarily, concentric with the outer surface of the body  30 . The first longitudinal transition  33  creates or defines a first shelf or ledge providing a first seat for a second subsequent directional dilation tube  16 . The second longitudinal transition  34  creates or defines a second shelf or ledge providing a second seat for the second subsequent dilation tube  16 . As seen in  FIG. 11 , the first subsequent directional dilation tube  14  has a rounded lower end  80 . 
     The first subsequent directional dilation tube  14  is configured as an elliptical cylinder with the channel  31  disposed in a side thereof. As such the tube  14  has an elliptic portion  39  that projects outwardly from the channel  31 . Direction of the elliptic portion  39  provides the direction of incision dilation. Rotational orientation of the initial dilation tube  12  determines the angle and direction of incision dilation by the orientation of the first and second transitions  23 ,  24  since the first subsequent directional dilation tube nests onto the initial dilation tube  12 . 
     The first subsequent directional dilation tube  14  is the second dilation tube to be inserted into the incision. The bore  22  of the initial dilation tube  12  still permits monitoring position of the nerve or nerves (neuro-monitoring) while the incision is dilated away from the nerve (e.g. anteriorly) in the desired angle as determined by the rotational orientation of the initial dilation tube  12 . In this second stage of incision dilation, the first subsequent directional dilation tube  14  inserted over the initial dilation tube  12  and into the incision. The elliptical configuration of the body  30  migrates the incision dilation towards the direction of the ellipse. 
     Referring to  FIGS. 6 and 7  there is depicted a third stage in assembly of the dilation tube structure  10  wherein the second subsequent directional dilation tube  16  is situated onto the first subsequent directional dilation tube  14 . The outer shape and configuration of the first subsequent directional dilation tube  14  allows nested reception of the second subsequent directional dilation tube  16 . The second subsequent directional dilation tube  16  is defined by a generally elliptic cylinder body  40  having a rounded outer surface and a rounded longitudinal notch, cutout, channel or the like  41 . An upper end  49  of the body  40  is generally planar. The longitudinal channel  41  extends the length of the elliptic cylinder body  40  and provides a reception site for the first subsequent directional dilation tube  14  as the second subsequent directional dilation tube  16  is received onto the first subsequent directional dilation tube  14  during the third stage of incision dilation per the present method. The outer surface of the body  40  is preferably smooth, including the inner surface of the longitudinal channel  41 . An upper portion of the outer surface of the body  30  may include arced notches  48 . 
     Referring to  FIG. 7 , an enlarged view of a top of the second subsequent directional dilation tube  16  is shown to particularly envision its longitudinal and cross-sectional shape and/or configuration. As discerned, the longitudinal channel  41  has a rounded inner surface, shape and size complementary to the outer surface of the body  30  of the first subsequent directional dilation tube  14  in order to be received on the first subsequent directional dilation tube  14 . Nesting structures include a first longitudinal flange  42  provided at a first edge or end  46  of the channel  41  and a second longitudinal flange  48  provided at a second edge or end  47  of the channel  41 . Others are provided, including the shape of the first end  46  being complementary to the shape of the first transition  33  such that the first end  46  of the second subsequent directional dilation tube  16  seats or nests against the first transition  33  of the first subsequent dilation tube  14 . The shape of the second end  47  is complementary to the shape of the second transition  34  such that the second end  47  of the second subsequent directional dilation tube  16  seats or nests against the second transition  34  of the first subsequent directional dilation tube  14 . A beveled or angled edge  45  provides a transition between the upper ends of the body  40  and first and second flanges  42 ,  48 . 
     The first flange  42  extends from the body  40  at a first longitudinal transition  43  and is generally arc-shaped and preferably, but not necessarily, concentric with the outer surface of the body  40 . The second flange  48  extends from the body  40  at a second longitudinal transition  44  and is generally arc-shaped and preferably, but not necessarily, concentric with the outer surface of the body  40 . The first longitudinal transition  43  creates or defines a first shelf or ledge providing a first seat for a third subsequent dilation tube  18 . The second longitudinal transition  44  creates or defines a second shelf or ledge providing a second seat for the third subsequent directional dilation tube  18 . As seen in  FIG. 11 , the second subsequent directional dilation tube  16  has a beveled lower end  70 . 
     The second subsequent directional dilation tube  16  is configured as an elliptical cylinder with the channel  41  disposed in a side thereof. As such the tube  16  has an elliptic portion  49  that projects outwardly from the channel  41 . Direction of the elliptic portion  49  provides the direction of incision dilation which coincides with the direction of the elliptic portion  39  of the first subsequent directional dilation tube  14 . 
     The second subsequent directional dilation tube  16  is the third dilation tube to be inserted into the incision. The bore  22  of the initial dilation tube  12  still permits monitoring position of the nerve or nerves (neuro-monitoring) while the incision is further dilated away from the nerve (e.g. anteriorly) in the desired angle as determined by the rotational orientation of the initial dilation tube  12 . In this third stage of incision dilation, the second subsequent directional dilation tube  16  inserted over the first subsequent directional dilation tube  14  and into the incision. The elliptical configuration of the body  40  further migrates the incision dilation towards the direction of the ellipse. The nesting structures provide a stable construct. Moreover, the nesting structures allow one dilation tube to be precisely assembled onto the previous dilation tube from the vertical position, essentially vertically sliding one dilation tube onto the other dilation tube. 
     Referring to  FIGS. 8 and 9  there is depicted a fourth, and with this embodiment of dilation tube assembly, a final stage in assembly of the dilation tube structure  10  wherein the third subsequent directional dilation tube  18  is situated onto the second subsequent directional dilation tube  16 . The outer shape and configuration of the second subsequent directional dilation tube  16  allows nested reception of the third subsequent directional dilation tube  18  in like manner to the previous dilation tubes. The third subsequent directional dilation tube  18  is defined by a generally elliptic cylinder body  50  having a rounded outer surface and a rounded longitudinal notch, cutout, channel or the like  51 . An upper end  59  of the body  50  is generally planar. The longitudinal channel  51  extends the length of the elliptic cylinder body  50  and provides a reception site for the second subsequent directional dilation tube  16  as the third subsequent directional dilation tube  18  is received onto the second subsequent directional dilation tube  16  during the fourth stage of incision dilation per the present method. The outer surface of the body  50  is preferably smooth, including the inner surface of the longitudinal channel  51 . An upper portion of the outer surface of the body  50  may include arced notches  58 . 
     Referring to  FIG. 9 , an enlarged view of a top of the third subsequent dilation tube  18  is shown to particularly envision its longitudinal and cross-sectional shape and/or configuration. As discerned, the longitudinal channel  51  has a rounded inner surface, shape and size complementary to the outer surface of the body  40  of the second subsequent dilation tube  16  in order to be received on the second subsequent dilation tube  16 . A first edge  53  is provided at a first end of the channel  51 , while a second edge  54  is provided at a second end of the channel  51 . Again, the tube has nesting structures. The shape of the first end  53  is complementary to the shape of the first transition  43  such that the first end  53  of the third subsequent directional dilation tube  18  seats or nests against the first transition  43  of the second subsequent directional dilation tube  16 . The shape of the second end  54  is complementary to the shape of the second transition  44  such that the second end  54  of the third subsequent directional dilation tube  18  seats or nests against the second transition  4  of the second subsequent directional dilation tube  16 . A beveled or angled edge  55  provides a transition between the upper ends of the body  50  and first and second ends  53 ,  54 . As seen in  FIG. 11 , the third subsequent directional dilation tube  18  has a beveled lower end  60 . 
     The third subsequent directional dilation tube  18  is configured as an elliptical cylinder with the channel  51  disposed in a side thereof. As such the tube  18  has an elliptic portion  59  that projects outwardly from the channel  51 . Direction of the elliptic portion  59  provides the direction of incision dilation which coincides with the direction of the elliptic portion  49  of the second subsequent directional dilation tube  16 . 
     The third subsequent directional dilation tube  18  is the fourth (and here, final) dilation tube to be inserted into the incision. The bore  22  of the initial dilation tube  12  still permits monitoring position of the nerve or nerves (neuro-monitoring) while the incision is further dilated away from the nerve (e.g. anteriorly) in the desired angle as determined by the rotational orientation of the initial dilation tube  12 . In this fourth stage of incision dilation, the third subsequent directional dilation tube  18  inserted over the second subsequent directional dilation tube  16  and into the incision. The elliptical configuration of the body  50  further migrates the incision dilation towards the direction of the ellipse.  FIG. 10  depicts a side view of all of the dilation tubes assembled (i.e. the present dilation tube assembly  10 ). 
     It should be appreciated that more subsequent dilation tubes having like configurations may be position between the initial dilation tube and the final dilation tube. 
       FIG. 12  shows the four directional dilation tubes in an exploded view to illustrate how the various dilation tubes are received on one another and nest together. 
       FIGS. 13 and 14  show the spinal retractor  100  holding the present directional dilation tube assembly  10 . The retractor  100  has a body  101  that is configured to be mounted relative to a spine patient via a threaded bore (or attachment location)  120  of the static arm  107  of the body  101 . The body  101  has a first adjustable arm  102  that holds an articulating portion  105 , and a second adjustable arm  103  that holds an articulating portion  106 . The articulating portion  105  is configured to receive a blade  108 , while the articulating portion  107  is configured to receive a blade  109 . The arm  104  may or may not be static regarding articulation and holds the configured blade  110 . The arm  104  may also have guide holes  121   a ,  121   b , and  121   c  posterior of the wall of the static blade  110  for insertion of a neuro-monitoring sounding probe following insertion of the retractor blades if double checking of nerve position is desired. The arm  104  may hold the blade  110  static such that the blade  110  has no angulation capabilities for additional rigidity of the construct. 
     A more complete description of a spinal retractor such as can be used in place of retractor  100 , with the exception of a static posterior blade  110 , is found in U.S. patent application Ser. No. 13/720,800 filed Dec. 19, 2012, the specification of which is specifically incorporated herein by reference. 
       FIG. 15  is an illustration depicting the directional dilation tube assembly  10  surrounded by the blades  108 ,  109  and  110  of the retractor  100  particularly showing the configuration of the static blade  110  for receiving the stacked configuration of dilation tubes  12 ,  14 ,  16 ,  18 . As easily discerned, the bore  22  of the initial dilation tube  12  permits monitoring position of a nerve or nerves while migrating the incision dilation towards the elliptic portions of the tubes. 
       FIG. 16  shows the directional dilation tube assembly  10  held by the retractor  100  relative to a human vertebral section, particularly a vertebra V, spinal column SC, and vertebral disc D. The directional dilation tube assembly  10  has been fully assembled and a neuro monitoring probe, device or the like  5  extends through the bore  22  of the initial dilation tube  12  from an upper end of the body  20  to a lower end of the body  20 .  FIG. 16  provides an exemplary manner of using the present directional dilation tube assembly  10 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.
A directional sequential dilation system includes a dilation tube assembly having a plurality of cylindrical, nesting directional dilation tubes including an initial cylindrical dilation tube that provides a passage for neuro-monitoring. Subsequent cylindrical directional dilation tubes sequentially increase in size including the increase in diameter. Each tube is configured to nest onto a previous cylindrical directional dilation tube via an off-centered structure formed in each of the subsequent cylindrical directional dilation tubes. The off-centered cutouts allow the subsequent cylindrical dilation tubes to dilate the soft tissue while at the same time sequentially migrate the incision dilation in a particular direction and distance from the initial cylindrical dilation tube insertion point (i.e. The initial neuro-monitoring insertion point). The directional sequential dilation system is particularly useful in spinal surgery.