Abstract:
A cannula assembly for providing percutaneous access in minimally invasive spinal surgeries, includes an outer cannula, a nerve probe dilator and a multistage dilator system comprising a first dilator, a second dilator, a third dilator and a fourth dilator. The outer cannula and the dilators are slidable relative to each other and are arranged sequentially so that the fourth dilator surrounds the nerve probe dilator, the third dilator slides over a surface of the fourth dilator, the second dilator slides over a surface of the third dilator, the first dilator slides over a surface of the second dilator, and the outer cannula surrounds the first dilator.

Description:
CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS 
     This application claims the benefit of U.S. provisional application Ser. No. 61/490,655 filed May 27, 2011 and entitled “IMPROVED METHODS, TOOLS AND DEVICES FOR PERCUTANEOUS ACCESS IN MINIMALLY INVASIVE SPINAL SURGERIES”, the contents of which are expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to improved methods, tools and devices for providing percutaneous access in minimally invasive spinal surgeries, and more particularly to an access cannula that includes multi-stage dilators and multi-stage cannulae. 
     BACKGROUND OF THE INVENTION 
     It is well known that traditional surgical procedures in locations deep within a patient&#39;s body require a long incision, extensive muscle stripping, prolonged retraction of muscles for visualization, and denervation and devascularization of the adjacent tissue. These procedures result in extensive tissue traumatization and consequently in prolonged recovery time, risk of infections, high hospitalization costs, pain that can be more severe than the pain due to the initial ailment, and in some cases permanent scarring. In minimally invasive surgical procedures, portals are used to access the locations deep in the patient&#39;s body. The use of portals rather than a long incision causes less trauma to the adjacent tissue, reduces the recovery time and pain and may be performed in some case under only local anesthesia. The avoidance of general anesthesia reduces post-operative recovery time and the risk of complications. 
     Minimally invasive surgical procedures are especially desirable for spine surgeries because spine pathologies are located deep within the body without clear muscle planes and there is danger of damaging the adjacent neural and vascular tissues. In treating the majority of spinal pathologies, the spinal muscles are stripped from the bony elements of the spine followed by laminectomy to expose the dura, the nerve roots, and the discs. The incision has to be wide enough and the tissues have to be retracted to maintain a channel from the skin to the floor of the spinal canal that will allow direct visualization. The destruction to the spinal structures is even more extensive during fusion procedures, which require more lateral tissue dissection and exposure to access the transverse processes and pedicles for placement of pedicle screws, rod constructs for stability, and bone graft under direct vision. 
     Multiple attempts have been made to improve the techniques, devices, and instrumentations used for minimal and percutaneous surgery. These include use of percutaneous needle administration of chemonucleolytic agents to enzymatically dissolve the disc and the use of microscopes and loupe magnification to limit the incision size. These two approaches are at the foundation of minimal access surgery, one using an injectable agent and the other using a device to limit the exposure while maximizing the visualization. Unfortunately, the effectiveness and safety of the enzyme, chymopapain used for chemonucleolysis, have been complicated by severe spasms, post-operative pain, and sensitivity reactions including anaphylactic shock. Loupe magnification and microscopes are helpful for improving visualization but are not effective without retractor systems and specialized instruments and devices to make minimal access surgery effective. 
     Substantial progress has been made to develop the necessary devices, instruments, and methods to effectively improve minimal access surgery resulting in improved visualization, less tissue injury, less general anesthesia exposure and improved recovery time and post-operative pain. For example U.S. Pat. Nos. 5,792,044 and 5,902,231 by Foley et al., demonstrate some of the improved methods and instruments for percutaneous surgeries. 
     A problem that occurs frequently in minimally invasive surgical procedures is related to the fact that it is not always known how deep the pathology is located. Accordingly there is a need for a portal with a variable length to accommodate the locations of the various pathologies. Furthermore, in spine fusion procedures intervertebral spacers or connecting elements, such as rods, plates or wires are placed and fixed between two or more locations of the spine. Placement of these spacers or connecting elements requires open surgery, which is currently one of the major limitations of other percutaneous cannula access methodologies. Accordingly there is a need for improved methods, tools and devices that provide percutaneous access in minimally invasive spinal surgeries. 
     SUMMARY OF THE INVENTION 
     The present invention relates to methods and devices for improving percutaneous access in minimally invasive surgeries, and more particularly to methods and devices that provide access channels to locations deep within a patient&#39;s body at various angles and directions and to an access cannula that includes multi-stage dilators and multi-stage cannulae. 
     In general, in one aspect, the invention features a cannula assembly for providing percutaneous access in minimally invasive spinal surgeries, including an outer cannula, a nerve probe dilator and a multistage dilator system comprising a first dilator, a second dilator, a third dilator and a fourth dilator. The outer cannula and the dilators are slidable relative to each other and are arranged sequentially so that the fourth dilator surrounds the nerve probe dilator, the third dilator slides over a surface of the fourth dilator, the second dilator slides over a surface of the third dilator, the first dilator slides over a surface of the second dilator, and the outer cannula surrounds the first dilator. 
     Implementations of this aspect of the invention may include one or more of the following features. The outer cannula comprises an elongated tube having first and second opposite sides, third and fourth opposite sides and a rectangular cross section. The first and second opposite sides comprise distal ends terminating in two parallel fork extensions, respectively. The parallel fork extensions are tapered and terminate into inverted trapezoids. The parallel fork extensions are rigid and are dimensioned to fit within an intervertebral space. The distal end of the third side is shorter than the distal end of the fourth side. Each of the first, second, and third dilators comprises a single elongated blade terminating into a tapered distal end and having a proximal end comprising two parallel extensions and a groove formed between the two parallel extensions. Each of the first, second, and third dilators comprises an inner surface having tongue protrusions and each of the second and third and fourth dilators comprises an outer surface having an elongated groove. The tongue protrusions of the first dilator are configured to slide and engage the elongated groove of the second dilator, the tongue protrusions of the second dilator are configured to slide and engage the elongated groove of the third dilator, and the tongue protrusions of the third dilator are configured to slide and engage the elongated groove of the fourth dilator. The fourth dilator comprises a cylindrical inner lumen, rectangular outer surfaces, a cylindrical distal end with a serrated edge and a proximal end having two elongated parallel extensions separated by a distance equal to the diameter of the cylindrical inner lumen. Each of the third and fourth dilators comprises two parallel blades extending from a common proximal end and having separated distal ends terminating in inverted trapezoids. The nerve probe dilator comprises a cylindrical main shaft having a conical shaped distal end and a cylindrical lumen extending the entire length of the cylindrical main shaft and being dimensioned to receive a nerve probe. The nerve probe dilator further comprises a trephine drill surrounding the conical distal end. The cylindrical main shaft comprises a plurality of through openings extending perpendicular to the cylindrical lumen. The assembly may further include a nerve probe impactor comprising an elongated cylindrical body having an elongated slot extending along the length of the cylindrical body. The assembly may further include an impaction handle comprising a rectangular cross section and being dimensioned to slide over the outer cannula. The assembly may further include a multipurpose tool comprising a rectangular body having openings shaped and dimensioned to slide over the nerve probe dilator, the dilators and the outer cannula. The assembly may further include a pedicle reamer tool. The assembly may further include a nerve shield tool. The assembly may further include a cannula holder tool. The cannula holder comprises two pivotally connected spring loaded handles and the two handles comprise proximal ends configured to compress two inner springs, respectively, and distal ends having inner surfaces shaped and dimensioned to match the outer shape and dimensions of the outer cannula. 
     In general, in another aspect, the invention features a cannula assembly for providing percutaneous access in minimally invasive spinal surgeries, including a multistage cannula system, a multistage dilator system and a nerve probe dilator. The multistage cannula system includes a first cannula, a second cannula, a third cannula and a fourth cannula. The multistage dilator system includes a first dilator, a second dilator, a third dilator and a fourth dilator. The cannulae and the dilators are slidable relative to each other and are arranged sequentially so that the fourth dilator surrounds the nerve probe dilator, the fourth cannula surrounds the fourth dilator, the third dilator slides over a surface of the fourth cannula, the third cannula surrounds the third dilator, the second dilator slides over a surface of the third cannula, the second cannula surrounds the second dilator, the first dilator slides over a surface of the second cannula, and the first cannula surrounds the first dilator. 
     In general, in another aspect, the invention features a method for providing percutaneous access in minimally invasive spinal surgeries for inserting a spinal implant, including the following steps. First, providing a cannula assembly comprising an outer cannula, a nerve probe dilator and a multistage dilator system comprising a first dilator, a second dilator, a third dilator and a fourth dilator. The outer cannula and the dilators are slidable relative to each other and are arranged sequentially so that the fourth dilator surrounds the nerve probe dilator, the third dilator slides over a surface of the fourth dilator, the second dilator slides over a surface of the third dilator, the first dilator slides over a surface of the second dilator, and the outer cannula surrounds the first dilator. Next, inserting a nerve probe into the nerve probe dilator and impacting the nerve probe dilator into a first spinal location under the guidance of the nerve probe. Next, sliding the fourth dilator over the nerve probe dilator and impacting the fourth dilator into the first spinal location thereby forming an opening in the first spinal location. Next, measuring the opening&#39;s dimensions and if the spinal implant&#39;s dimensions are smaller than the opening&#39;s dimensions sliding the outer cannula over the fourth dilator and impacting the outer cannula into the first spinal location, and then removing the dilators and inserting the spinal implant into the opening. If the spinal implant&#39;s dimensions are larger that the opening&#39;s dimensions, the method further includes sequentially impacting the third, second and first dilators into the first spinal location until the spinal implant&#39;s dimensions are smaller than the opening&#39;s dimensions. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and description below. Other features, objects, and advantages of the invention will be apparent from the following description of the preferred embodiments, the drawings, and the claims 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the figures, wherein like numerals represent like parts throughout the several views: 
         FIG. 1A  is a front perspective view of a first embodiment of a multi-component cannula system; 
         FIG. 1B  is an exploded front view of the multi-component cannula system of  FIG. 1A ; 
         FIG. 2A  is a front perspective view of a second embodiment of a multi-component cannula system; 
         FIG. 2B  is an exploded front view of the multi-component cannula system of  FIG. 2A ; 
         FIG. 2C  is an exploded back view of the multi-component cannula system of  FIG. 2A ; 
         FIG. 3A  is an enlarged right side view of the proximal end of the multi-component cannula system of  FIG. 2A ; 
         FIG. 3B  is an enlarged left side view of the proximal end of the multi-component cannula system of  FIG. 2A ; 
         FIG. 4A  is a back perspective view of the multi-component cannula system of  FIG. 2A ; 
         FIG. 4B  is an enlarged view of the distal end of the multi-component cannula system of  FIG. 4A ; 
         FIG. 5A  is a front perspective view of a third embodiment of a multi-component cannula system; 
         FIG. 5B  is an enlarged view of the distal end of the multi-component cannula system of  FIG. 5A ; 
         FIG. 5C  is an enlarged view of the proximal end of the multi-component cannula system of  FIG. 5A ; 
         FIG. 6A  is a perspective view of an 8 mm cannula of the multi-component cannula system of  FIG. 5A ; 
         FIG. 6B  is a front view of the 8 mm cannula of  FIG. 6A ; 
         FIG. 6C  is a front isometric view of the 8 mm cannula of  FIG. 6A ; 
         FIG. 7A  is a perspective view of an 8 mm dilator of the multi-component cannula system of  FIG. 5A ; 
         FIG. 7B  is a front view of the 8 mm dilator of  FIG. 7A ; 
         FIG. 7C  is a front isometric view of the 8 mm dilator of  FIG. 7A ; 
         FIG. 7D  is a top isometric view of the 8 mm dilator of  FIG. 7A ; 
         FIG. 7E  is a bottom isometric view of the 8 mm dilator of  FIG. 7A ; 
         FIG. 8A  is a perspective view of a 10 mm cannula of the multi-component cannula system of  FIG. 5A ; 
         FIG. 8B  is a front view of the 10 mm cannula of  FIG. 8A ; 
         FIG. 8C  is a front isometric view of the 10 mm cannula of  FIG. 8A ; 
         FIG. 9A  is a perspective view of a 10 mm dilator of the multi-component cannula system of  FIG. 5A ; 
         FIG. 9B  is a front view of the 10 mm dilator of  FIG. 9A ; 
         FIG. 9C  is a front isometric view of the 10 mm dilator of  FIG. 9A ; 
         FIG. 10A  is a perspective view of a 12 mm cannula of the multi-component cannula system of  FIG. 5A ; 
         FIG. 10B  is a front view of the 12 mm cannula of  FIG. 10A ; 
         FIG. 10C  is a front isometric view of the 12 mm cannula of  FIG. 10A ; 
         FIG. 11A  is a perspective view of a 12 mm dilator of the multi-component cannula system of  FIG. 5A ; 
         FIG. 11B  is a front view of the 12 mm dilator of  FIG. 11A ; 
         FIG. 11C  is a front isometric view of the 12 mm dilator of  FIG. 11A ; 
         FIG. 12A  is a front isometric view of the nerve probe dilator of  FIG. 5A ; 
         FIG. 12B  is a front isometric view of a trephine drill; 
         FIG. 13A  depicts the step of inserting the nerve probe dilator and the nerve probe in the intervertebral space between two adjacent vertebras; 
         FIG. 13B  depicts the step of inserting the 8 mm cannula over the nerve probe dilator; 
         FIG. 13C  depicts the step of inserting the 8 mm dilator; 
         FIG. 14A  depicts the step of inserting the 10 mm dilator; 
         FIG. 14B  depicts the step of inserting the 12 mm dilator; 
         FIG. 14C  depicts the step of inserting the working cannula; 
         FIG. 15A  depicts the working cannula inserted at an oblique direction in the intervertebral area between a first vertebra and a second vertebra; 
         FIG. 15B  depicts the step of inserting the intervertebral implant through the working cannula of  FIG. 15A ; 
         FIG. 15C  depicts the inserted intervertebral implant in the intervertebral space; 
         FIG. 15D  depicts the step of impacting the inserted dilator; 
         FIG. 15E  depicts the step of removing the inserted dilator; 
         FIG. 16A  is a perspective view of a distraction pin; 
         FIG. 16B  depicts two distraction pin inserted in the pedicles of two adjacent vertebras; 
         FIG. 17A  depicts the step of inserting a distractor over the two distraction pins of  FIG. 16B ; 
         FIG. 17B  depicts the step of inserting an intervertebral spacer through the working cannula in the distracted vertebras of  FIG. 17A ; 
         FIG. 18  is a perspective view of the distractor of  FIG. 17A ; 
         FIG. 19A  is an enlarged perspective view of the distractor legs of the distractor of  FIG. 18 ; 
         FIG. 19B  is an enlarged perspective view of the distractor legs of  FIG. 19A  with one leg pivoted at an angle; 
         FIG. 20A  depicts the step of inserting a solid awl in the intervertebral space between two adjacent vertebras through the iliac crest; 
         FIG. 20B  depicts the step of inserting a tissue protector over the solid awl of  FIG. 20A ; 
         FIG. 20C  depicts the step of impacting the tissue protector of  FIG. 20B ; 
         FIG. 21A  depicts the step of removing the tissue protector of  FIG. 20B ; 
         FIG. 21B  depicts the step of inserting the nerve probe dilator; 
         FIG. 21C  depicts the step of inserting the nerve probe; 
         FIG. 22A  depicts the step of inserting the trephine drill; 
         FIG. 22B  depicts the opening in the iliac crest that was drilled with the trephine drill of  FIG. 22A ; 
         FIG. 22C  depicts the step of inserting the 8 mm dilator; 
         FIG. 23A  depicts the step of inserting the 10 mm dilator; 
         FIG. 23B  depicts the step of inserting the 12 mm dilator; 
         FIG. 23C  depicts the step of inserting the working cannula; 
         FIG. 24A  depicts the step of removing all dilators; 
         FIG. 24B  depicts the step of inserting the intervertebral implant; 
         FIG. 24C  depicts the inserted intervertebral implant; 
         FIG. 25A  depicts the nerve probe impactor inserted over the nerve probe dilator; 
         FIG. 25B  depicts a detailed view of the nerve probe impactor inserted over the nerve probe dilator; 
         FIG. 25C  depicts a perspective view of the nerve probe impactor; 
         FIG. 25D  depicts a top view of the nerve probe impactor; 
         FIG. 26A  depicts a perspective view of another embodiment of the 8 mm dilator; 
         FIG. 26B  is a bottom view of the 8 mm dilator of  FIG. 26A ; 
         FIG. 26C  is a top view of the 8 mm dilator of  FIG. 26A ; 
         FIG. 27A  depicts a front perspective view of another embodiment of the 14 mm cannula; 
         FIG. 27B  is a side perspective view of the 14 mm cannula of  FIG. 27A ; 
         FIG. 27C  is a back view of the 14 mm cannula of  FIG. 27A ; 
         FIG. 28A  depicts a cannula impactor inserted over a cannula; 
         FIG. 28B  depicts the cannula impactor of  FIG. 28A  prior to being inserted over a cannula: 
         FIG. 28C  depicts a perspective view of the cannula impactor of  FIG. 28A ; 
         FIG. 29A  depicts a front perspective view of another embodiment of the assembled 8 mm and 10 mm dilators; 
         FIG. 29B  depicts a back perspective view of the embodiment of the assembled 8 mm and 10 mm dilators of  FIG. 29A ; 
         FIG. 29C  depicts a side view of the embodiment of the assembled 8 mm and 10 mm dilators of  FIG. 29A ; 
         FIG. 30A  depicts a back perspective view of another embodiment of the exploded multi-component system; 
         FIG. 30B  depicts a front perspective view of the embodiment of the exploded multi-component system of  FIG. 30A . 
         FIG. 31  depicts a multipurpose tool; 
         FIG. 32A  depicts the multipurpose tool of  FIG. 31  inserted over a nerve probe dilator; 
         FIG. 32B  depicts the multipurpose tool of  FIG. 31  inserted over a cannula; 
         FIG. 33A  depicts a front view of a pedicle reamer tool; 
         FIG. 33B  depicts a side view of the pedicle reamer tool of  FIG. 33A ; 
         FIG. 34  depicts a nerve shield tool; 
         FIG. 35A  depicts a cannula holder tool; 
         FIG. 35B  is a top view of the cannula holder tool of  FIG. 35A ; 
         FIG. 35C  depicts the cannula holder tool of  FIG. 35A  holding a cannula; 
         FIG. 36A  depicts a tissue shim dilator near a cannula; 
         FIG. 36B  depicts the tissue shim dilator of  FIG. 36A  inserted into the cannula; 
         FIG. 36C  depicts a front perspective view of the tissue shim dilator of FIG.  36 A;and 
         FIG. 36D  depicts a side view of the tissue shim dilator of  FIG. 36A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to improved methods, tools and devices for providing percutaneous access in minimally invasive spinal surgeries, and more particularly to cannula system that includes multi-stage dilators and multi-stage cannulae. 
     Referring to  FIG. 1A , and  FIG. 1B , access cannula system  300  includes a 14 mm working cannula  390  surrounding sequentially a 14 mm dilator  380 , a 12 mm cannula  350 , a 12 mm dilator  360 , a 10 mm cannula  330 , a 10 mm dilator  340 , an 8 mm cannula  310 , an 8 mm dilator  320  and a nerve probe dilator  370 . Working cannula  390  includes an elongate tube  390  having a rectangular cross section and four side surfaces  390   a ,  390   b  (shown in  FIG. 3B ),  390   c  (shown in  FIG. 4A ), and  390   d . Side surfaces  390   a  and  390   b  are opposite and parallel to each other and their distal ends terminate in parallel fork extensions  392   a ,  392   b , respectively, that are tapered. Fork extensions  392   a ,  392   b  are rigid, are used for distraction purposes, and are dimensioned to fit in the intervertebral space. Fork extensions  392   a ,  392   b  include openings  394   a ,  394   b  (shown in  FIG. 1B ), respectively. The proximal ends of side surfaces  390   a ,  390   b  also include openings  398   a ,  398   b  (shown in  FIG. 3B ), respectively. Openings  394   a ,  394   b  and  398   a ,  398   b  function as fiduciary marks during fluoroscopy and are used for alignment purposes. Proximal end openings  398   a ,  398   b  are also used for gripping purposes. The 12 mm cannula  350 , 10 mm cannula  330  and 8 mm cannula  310  are shaped similar to cannula  390  and are dimensioned to surround the corresponding 12 mm dilator  360 , 10 mm dilator  340 , and 8 mm dilator  320 , respectively, and to be surrounded by the 14 mm cannula  390 , 12 mm cannula  350 , and 10 mm cannula  330 , respectively, and by the 14 mm dilator  380 , 12 mm dilator  360 , and 10 mm dilator  340 , respectively. 
     Referring to  FIG. 2A ,  FIG. 2B  and  FIG. 2C , in a second embodiment, access cannula system  300  includes a 14 mm working cannula  390  surrounding sequentially a 14 mm dilator  380 , a 12 mm dilator  360 , a 10 mm dilator  340 , an 8 mm dilator  320  and a nerve probe dilator  370 . In the embodiment of  FIG. 1A  and  FIG. 2A , each dilator  380 ,  360 ,  340 , includes a single elongated blade  382 ,  362 ,  342 , respectively. Blades  382 ,  362 ,  342  have a tapered distal end and terminate into points  384 ,  364 ,  344 , shown in  FIG. 1B . The proximal ends  385 ,  365 ,  345  of blades  382 ,  362 ,  342  include two parallel extensions  385   a - 385   b ,  365   a - 365   b , and  345   a - 345   b , respectively, shown in  FIG. 3A  and  FIG. 3B . Extensions  385   a ,  385   b  are spaced apart and a groove is formed between them. The groove is dimensioned so that the blade  382  can slide over the 12 mm dilator  360  and the end  385  can be stacked over the proximal end  365  of the 12 mm dilator  360 , as shown in  FIG. 3A  and  FIG. 3B . Similarly, extensions  365   a ,  365   b  are spaced apart and a groove is formed between them. The groove is dimensioned so that the blade  362  can slide over the 10 mm dilator  340  and the end  365  can be stacked over the end  345  of the 10 mm dilator  340 , as shown in  FIG. 3A  and  FIG. 3B . Similarly, extensions  345   a ,  345   b  are spaced apart and a groove is formed between them. The groove is dimensioned so that the blade  342  can slide over the 8 mm dilator  320  and the end  345  can be stacked over the 8 mm dilator  320 , as shown in  FIG. 3A  and  FIG. 3B . Extensions  385   a ,  385   b  include openings  387   a ,  387   b , respectively, which are used for engaging a tool used to insert or remove the dilator  380 . Similarly, extensions  365   a ,  365   b  include openings  367   a ,  367   b , respectively, which are used for engaging a tool used to insert or remove the dilator  360 . Similarly, extensions  345   a ,  345   b  include openings  347   a ,  347   b , respectively, which are used for engaging a tool used to insert or remove the dilator  340 . Referring to  FIG. 2C , the bottom surfaces of blades  380 ,  360  and  340  include elongated tongue protrusions  388 ,  368  and  348 , respectively. Referring to  FIG. 2B , the top surfaces of blades  360 ,  340  and of dilator  320  include dovetail slots  366 ,  346  and  326 , respectively. Tongue protrusions  388 ,  368  and  348  are dimensioned to engage and slide within the dovetail slots  366 ,  346  and  326 , respectively, as the blades slide over each other and are stacked inside the working cannula  390 . 
     Referring to  FIG. 5A ,  FIG. 5B , and  FIG. 5C , in another embodiment, access cannula system  100  includes a 14 mm working cannula  190  surrounding sequentially a 12 mm dilator  160 , a 10 mm dilator  140 , an 8 mm dilator  120  and a nerve probe dilator  170 . Working cannula  190  includes an elongate tube  190  having a rectangular cross section and four side surfaces  190   a ,  190   b ,  190   c , and  190   d . Side surfaces  190   a  and  190   b  are opposite and parallel to each other and their distal ends terminate in parallel fork extensions  192   a ,  192   b , respectively. Fork extensions  192   a ,  192   b  are tapered and terminate into inverted trapezoids  196   a ,  196   b , respectively. Fork extensions  192   a ,  192   b  are rigid, are used for distraction purposes, and are dimensioned to fit in the intervertebral space. Fork extensions  192   a ,  192   b  include openings  194   a ,  194   b , respectively. Openings  194   a ,  194   b  function as fiduciary marks during fluoroscopy and are used for alignment purposes during fluoroscopy. The proximal ends of side surfaces  190   a ,  190   b  also include openings  198   a ,  198   b , respectively. Openings  198   a ,  198   b  function as fiduciary marks during fluoroscopy and are used for alignment purposes and for gripping purposes. Side surfaces  190   c  and  190   d  are opposite and parallel to each other. In other embodiments, side surface  190   d  includes a cutout  430  at the distal end and has a shorter length than the opposite surface  190   c , as shown in  FIG. 27A-FIG .  27 C. Cutout  430  allows the cannula to surround the inferior pedicle and to protect the nerve root that is on the opposite side of the cutout. 
     Referring to  FIG. 6A-FIG .  6 C, the 8 mm cannula  110  is shaped similar to cannula  190  and is dimensioned to surround the corresponding 8 mm dilator  120 . Referring to  FIG. 8A-FIG .  8 C, the 10 mm cannula  130  is shaped similar to cannula  190  and is dimensioned to surround the corresponding 10 mm dilator  140 . Referring to  FIG. 10A-FIG .  10 C, the 12 mm cannula  150  is shaped similar to cannula  190  and is dimensioned to surround the corresponding 12 mm dilator  160 . 
     Referring to  FIG. 7A-FIG .  7 C, the 8 mm dilator  120  includes a cylindrical inner lumen  128  surrounded by rectangular outer surfaces  120   a ,  120   b ,  120   c  and  120   d . Outer surfaces  120   a    120   b  include grooves (dovetail slots)  126   a ,  126   b , respectively, used to engage tongue protrusions  148   a ,  148   b , respectively, of the 10 mm dilator  140 , as will be described below. Dilator  120  has a cylindrical distal end  122 , with a serrated edge  125 . Dilator  120  also has a proximal end  124  that includes two elongated extensions  124   a ,  124   b . Extensions  124   a ,  124   b  are parallel to each other and are separated by a distance corresponding to the diameter of the inner lumen. Dilator  120  also includes a second elongated through opening  127  used for accommodating a nerve probe, as shown in  FIG. 7D  and  FIG. 7E . A nerve probe is used for detecting nerves in the vicinity of the dilator distal end  122  during the insertion of the dilator. 
     Referring to  FIG. 9A-FIG .  9 C, the 10 mm dilator  140  includes two parallel blades  142   a ,  142   b  that extend along the cannula axis  99  from a common proximal end  145  and have separated distal ends  141   a ,  141   b , respectively. Distal ends  141   a ,  141   b  are tapered and terminate into inverted trapezoids  143   a ,  143   b , respectively. The outer surfaces of blades  142   a ,  142   b  include grooves  146   a ,  146   b , respectively. The inner surfaces of blades  142   a ,  142   b  include elongated tongue protrusions  148   a ,  148   b , respectively. Tongue protrusions  148   a ,  148   b  are dimensioned to engage the corresponding outer surface grooves  126   a ,  126   b  of the 8 mm dilator  120 . Proximal end  145  includes two tapered extensions  144   a ,  144   b  that are spaced apart from each other and parallel to each other. Extensions  144   a ,  144   b  extend along the cannula main axis  99  and are perpendicular to the blades  142   a ,  142   b , respectively. Extensions  144   a ,  144   b  include openings  147   a ,  147   b , respectively, used for engaging an insertion or removal tool. 
     Referring to  FIG. 11A-FIG .  11 C, the 12 mm dilator  160  includes two parallel blades  162   a ,  162   b  that extend along the cannula axis  99  from a common proximal end  165  and have separated distal ends  161   a ,  161   b , respectively. Distal ends  161   a ,  161   b  are tapered and terminate into inverted trapezoids  163   a ,  163   b , respectively. The outer surfaces of blades  162   a ,  162   b  include grooves  166   a ,  166   b , respectively. The inner surfaces of blades  162   a ,  162   b  include elongated tongue protrusions  168   a ,  168   b , respectively. Tongue protrusions  168   a ,  168   b  are dimensioned to engage the corresponding outer surface grooves  146   a ,  146   b  of the 10 mm dilator  140 . Proximal end  165  includes two tapered extensions  164   a ,  164   b  that are spaced apart from each other and parallel to each other. Extensions  164   a ,  164   b  extend along the cannula main axis  99  and are perpendicular to the blades  162   a ,  162   b , respectively. Extensions  164   a ,  164   b  include opening  167   a ,  167   b , respectively, used for engaging an insertion or removal tool. 
     Referring to  FIG. 12A , nerve probe dilator  170  includes a cylindrical main shaft  174  extending along axis  171  and having a distal end  173 , proximal end  176  and a lumen  172 . Lumen  172  is dimensioned to receive nerve probe  175 , shown in  FIG. 13A . Distal end  173  has a conical shape and is used for tissue dilation purposes. Proximal end  176  has threads or circular protrusions  176   a  used for engaging a handle  179 , shown in  FIG. 13A . Referring to  FIG. 12B , in another embodiment, nerve probe dilator  180  includes a trephine drill  182  surrounding the conical distal end  186 . Trephine drill  182  includes teeth  184  used for drilling through bone, or cartilage. 
     Referring to  FIG. 13A , in operation, first a safe insertion trajectory is determined using active radiographic and optical imaging and the nerve probe  175  is inserted in the intervertebral space  80  between two adjacent vertebras  90   a ,  90   b . Once a safe distance from any adjacent nerves has been determined, nerve probe dilator  170  is threaded over the nerve probe  175  and is impacted in the intervertebral space  80  with the nerve probe impactor  410 , shown in  FIG. 25A  and  FIG. 25B . Nerve probe impactor  410  has an elongated cylindrical body having a slot  412  extending the entire length of the elongated body, as shown in  FIG. 25C  and  FIG. 25D . Slot  412  is dimensioned to slide over and accommodate the nerve probe  175 . 
     Next, the 8 mm dilator  120  is attached to a handle  197  and is slid over the nerve probe dilator  170 , as shown in  FIG. 13B . The area within the 8 mm dilator range is probed with the nerve probe to determine a safe distance from any adjacent nerves and then the 8 mm dilator is impacted in the intervertebral space  80 , as shown in  FIG. 13C . If the height of the intervertebral implant  200  is smaller than the opening achieved with the 8 mm dilator  120 , an 8 mm cannula  110  is inserted over the 8 mm dilator, the 8 mm dilator is removed and the implant  200  is inserted in the intervertebral opening. If the height of the intervertebral implant  200  is larger than the opening achieved with the 8 mm dilator  120 , the 10 mm dilator  140  is impacted over the 8 mm dilator in the intervertebral space  80  with the impactor  185 , as shown in  FIG. 14A ,  FIG. 15D  and  FIG. 15E . Impactor  185  has a tip  187  that is inserted in openings  147   a ,  147   b  of the 10 mm dilator, as shown in  FIG. 15D . Again, the height of the intervertebral implant  200  is checked against the achieved opening, and if it is smaller than the opening, a 10 mm cannula  130  is inserted over the 10 mm dilator, the 8 mm dilator and the 10 mm dilator are removed and the implant  200  is inserted in the intervertebral opening. If the height of the intervertebral implant  200  is still larger than the opening achieved with the 10 mm dilator  140 , the 12 mm dilator  160  is impacted over the 10 mm dilator in the intervertebral space  80 , as shown in  FIG. 14B . The process repeats until an opening that accommodates the intervertebral implant  200  is achieved. At that point, a working cannula  190  is impacted into the intervertebral space  80  with impactor handle  440 , as shown in  FIG. 28A-FIG .  28 B and  FIG. 15A , and all dilators are removed with tool  185 , as shown in  FIG. 15F . Impactor handle  440  has a hollow body with a rectangular cross section and is dimensioned to slide over the proximal end of cannula  190 , as shown in  FIG. 28B . Next, intervertebral implant  200  is inserted through the working cannula  190  and is placed in the intervertebral opening, as shown in  FIG. 15B  and  FIG. 15C . All of the above mentioned operational steps are guided through fluoroscopic and optical imaging. 
     In some operations, the adjacent vertebras  90   a ,  90   b  need to be distracted prior to the placement of the intervertebral implant  200  in the intervertebral space  80 . Referring to  FIG. 16A  and  FIG. 16B , two distractor pins  210   a ,  210   b  are inserted in first locations of the adjacent vertebras  90   a ,  90   b , respectively. Distractor pin  210  includes an elongated shaft  212  that has a threaded distal end  216 . The threaded distal end  216  is inserted in the desired vertebral location. Next, a distractor  220  is used to spread the inserted distractor pins  210   a ,  210   b  apart. Referring to  FIG. 17A , distractor  220  includes a fixed carrier leg  222  and a movable carrier leg  224 . Movable carrier leg  224  moves along track  221  that extends from the proximal end  222   e  of the fixed carrier leg  222 . Fixed carrier leg  222  includes components  222   a ,  222   b , and  222   c  that are hingably connected to each other. Movable carrier leg  224  includes components  224   a ,  224   b , and  224   c  that are hingably connected to each other. Tubular pin components  225   a  and  225   b  extend from and are pivotally connected to the distal ends of components  222   c  and  224   c , respectively. Tubular pin components  225   a ,  225   b  are dimensioned to slide over the distractor pin shafts  212  and they can pivot up to  360  degrees around axis  229  independent from each other, as shown in  FIG. 19A . and  FIG. 19B . In operation, tubular pin components  225   a ,  225   b  are placed over distractor shafts  212   a ,  212   b  and then the movable carrier leg is translated along track  221  and set at the desired distraction length. Next, an opening is impacted in the intervertebral disk space  80  with the above mentioned cannula system and then the intervertebral implant  200  is inserted in the opening, as shown in  FIG. 17B . 
     Referring to  FIG. 20A-24C , in another embodiment, a trans-iliac access is used for the placement of the intervertebral implant. First, a K-wire is inserted in the desired location and then with the guidance of anterior-posterior (AP) and lateral fluoroscopic imaging a lateral incision is made in the L5/S1 intervertebral joint  80  through the iliac crest  70  with a solid awl  270 , shown in  FIG. 20A . Next, a tissue protector  280  is slid over the solid awl  270  and is impacted into the iliac crest with inserter tool  230 , shown in  FIG. 20B . Next, the solid awl  270  is removed (shown in  FIG. 20C ), and a drill  285  is inserted into the tissue protector  280  and is used to drill an opening through the iliac crest  70 , shown in  FIG. 21A . Next, the nerve probe dilator  170  is inserted through the drilled opening and is advanced to the L5/S1 intervertebral joint  80 , under fluoroscopic imaging and nerve monitoring with the nerve probe  175 , shown in  FIG. 21B . Next, the nerve probe dilator  170  is impacted into the L5/S1 intervertebral joint  80 , shown in  FIG. 21C . Next, the 18.4 mm trephine drill  180  is used to drill an access opening  72  through the iliac crest  70 , shown in  FIG. 22A  and  FIG. 22B . Next, the 8 mm, 10 mm and 12 mm stage dilators  120 ,  140  and  160 , respectively, are used to created the desired space in the L5/S1 intervertebral joint  80  for the placement of the intervertebral implant  200 , as shown in  FIG. 22C-FIG .  23 C, and described above. Next, a working cannula  190  is inserted over the largest dilation cannula and the working cannula is advanced to the desired L5/S1 intervertebral disc height, as shown in  FIG. 24A . Next, all dilators are removed, and discectomy is performed using paddle shavers to rough up the endplates of the two adjacent vertebras,  90   a ,  90   b . Finally, implant  200  is inserted with inserter  195  through cannula  190  and placed in the desired L5/S1 intervertebral space  80 , as shown in  FIG. 24B , and then the cannula  190  is removed, as shown in  FIG. 24C . 
     Access cannula system  100 ,  300  is made of metals, alloys, titanium, stainless steel, plastic or other inert materials. Typical dimensions include a length in the range of 100 mm to 250 mm, and cannula width or diameter in the range of 8 mm to 16 mm. In some embodiments, the 8 mm dilator  120  includes through-openings  420  extending perpendicular to the cylindrical inner lumen, as shown in  FIG. 26A-FIG .  26 C and in  FIG. 29A-FIG .  29 C and  FIG. 30A-FIG .  30 B. Through-openings  420  are used in connection with a multipurpose tool  450 , as shown in  FIG. 32B . Multipurpose tool  450  includes a plate-shaped body  451  having openings  454 ,  452 , a side slot  453  and a rod  456  extending from a side surface, as shown in  FIG. 31 . Multipurpose tool  450  may be used as an impactor for the nerve probe dilator  170  as shown in  FIG. 32A . In this configuration the nerve probe  175  is threaded through opening  452  and a force is applied onto the plate-shaped body  451  in order to impact the nerve probe  170  into a spinal location. Multipurpose tool  450  may also be used as an impactor for the 8 mm dilator  120 , as shown in  FIG. 32B . In this configuration, the 8 mm dilator is inserted into opening  454  and a crossbar  458  is inserted through one of the through-openings  420  in the 8 mm dilator above the plate-shaped body  451  in order to prevent the 8 mm dilator from sliding through the opening  454 . The plate-shaped body  451  is oriented perpendicular to the main axis of the 8 mm dilator and a force is applied onto the plate-shaped body  451  in order to impact the dilator into a spinal location. 
     Other tools used in connection with the cannula system  100  include a pedicle reamer tool  460 , shown in  FIG. 33A  and  FIG. 33B , a nerve shield tool  470 , shown in  FIG. 34 , a cannula holder  480 , shown in  FIG. 35A-FIG .  35 B, and a tissue shim dilator  490 , shown in  FIG. 36A-FIG .  36 D. The pedicle reamer tool  460  includes a cylindrical shaft  462 , a reamer  464  at the distal end of the shaft  462  and a handle  466  at the proximal end of the shaft  462 . The nerve shield  470  includes an elongated semi-cylindrical body  472  and a handle  474  that is oriented at an angle relative to the elongated semi-cylindrical body  472 . The elongated semi-cylindrical body  472  is placed in front of the nerve that is intended to shield. The cannula holder tool  480  includes two spring loaded handles  482   a ,  482   b  that are pivotally connected at pivot point  485 . The two handles  482   a ,  482   b  have proximal ends that are configured to compress two inner springs  484   a ,  484   b , in order to open and close the distal ends  486   a ,  486   b , respectively. The distal ends  486   a ,  486   b  have inner surfaces shaped and dimensioned to match the outer shape and dimensions of the outer cannula. The tissue shim dilator  490  is used for pushing tissue out of the cannula  190  and it includes an elongated blade  491  having an L-shaped plate  492  attached to its proximal end. The L-shaped plate  492  includes two legs  492   a ,  492   b  that are perpendicular to each other and a rectangular through-opening  492  formed in leg  492   a . The L-shaped plate  492  is attached to the elongated blade  491  so that leg  492   a  is vertical to the elongated plate  491  and leg  492   b  is parallel to the elongated plate  491  and it forms a gap  493  with the elongated plate  491 . The tissue shim dilator is shaped and dimensioned to fit within the outer cannula  190 , as shown in  FIG. 36A , and  FIG. 36B . Gap  493  is dimensioned so that leg  492   b  slides over the outer surface of the outer cannula  190 , while blade  491  slides into the central opening of the outer cannula  190 . Leg  492   a  acts a stop for the tissue shim dilator  490  and allows the end  490   a  of the blade  491  to reach the top of the cutout  430  of the outer cannula  190 , as shown in  FIG. 36B . 
     Several embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.