Patent Publication Number: US-2023157844-A1

Title: Method and apparatus for minimally invasive insertion of intervertebral implants

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. Application No. 16/865,476, filed May 4, 2020, which is a continuation of U.S. Application No. 16/847,723, filed Apr. 14, 2020, which is a continuation application of U.S. Application No. 16/126,271, filed Sep. 10, 2018, which is a continuation application of U.S. Application No. 15/290,511, filed Oct. 11, 2016, which is a continuation of U.S. Application No. 14/470,820, filed Aug. 27, 2014, which is a continuation of U.S. Application No. 13/933,912, filed Jul. 2, 2013, which is a continuation of U.S. Application No. 13/738,368, filed Jan. 10, 2013, which is a continuation of U.S. Application No. 13/245,130, filed Sep. 26, 2011, which claims a priority benefit to U.S. Provisional Application No. 61/530,031, filed Sep. 1, 2011, to U.S. Provisional Application No. 61/504,120, filed Jul. 1, 2011, to U.S. Provisional Application no. 61/471,030, filed Apr. 1, 2011 and to U.S. Provisional Application No. 61/451,379, filed Mar. 10, 2011. The entire disclosures of U.S. Application No. 13/245,130, filed Sep. 26, 2011, U.S. Provisional Application No. 61/530,031, filed Sep. 1, 2011, U.S. Provisional Application No. 61/504,120, filed Jul. 1, 2011, U.S. Provisional Application No. 61/471,030, filed Apr. 1, 2011 and U.S. Provisional Application No. 61/451,379, filed Mar. 10, 2011 are hereby incorporated by reference in their entireties and should be considered a part of this specification. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present application relates to medic al devices and, more particularly, to a medical device and method for the treating the spine. 
     Description of the Related Art 
     The human spine is a flexible weight bearing column formed from a plurality of bones called vertebrae. There are thirty-three vertebrae, which can be grouped into one of five regions (cervical, thoracic, lumbar, sacral, and coccygeal). Moving down the spine, there are generally seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae, five sacral vertebrae, and four coccygeal vertebrae. The vertebrae of the cervical, thoracic, and lumbar regions of the spine are typically separate throughout the life of an individual. In contrast, the vertebra of the sacral and coccygeal regions in an adult are fused to form two bones, the five sacral vertebrae which form the sacrum and the four coccygeal vertebrae which form the coccyx. 
     In general, each vertebra contains an anterior, solid segment or body and a posterior segment or arch. The arch is generally formed of two pedicles and two laminae, supporting seven processes—four articular, two transverse, and one spinous. There are exceptions to these general characteristics of a vertebra. For example, the first cervical vertebra (atlas vertebra) has neither a body nor spinous process. In addition, the second cervical vertebra (axis vertebra) has an odontoid process, which is a strong, prominent process, shaped like a tooth, rising perpendicularly from the upper surface of the body of the axis vertebra. Further details regarding the construction of the spine may be found in such common references as Gray’s Anatomy, Crown Publishers, Inc., 1977, pp. 33-54, which is herein incorporated by reference. 
     The human vertebrae and associated connective elements are subjected to a variety of diseases and conditions which cause pain and disability. Among these diseases and conditions are spondylosis, spondylolisthesis, vertebral instability, spinal stenosis and degenerated, herniated, or degenerated and herniated intervertebral discs. Additionally, the vertebrae and associated connective elements are subject to injuries, including fractures and torn ligaments and surgical manipulations, including laminectomies. 
     The pain and disability related to the diseases and conditions often result from the displacement of all or part of a vertebra from the remainder of the vertebral column. Over the past two decades, a variety of methods have been developed to restore the displaced vertebra to their normal position and to fix them within the vertebral column. Spinal fusion is one such method. In spinal fusion, one or more of the vertebra of the spine are united together (“fused”) so that motion no longer occurs between them. Thus, spinal fusion is the process by which the damaged disc is replaced and the spacing between the vertebrae is restored, thereby eliminating the instability and removing the pressure on neurological elements that cause pain. 
     Spinal fusion can be accomplished by providing an intervertebral implant between adjacent vertebrae to recreate the natural intervertebral spacing between adjacent vertebrae. Once the implant is inserted into the intervertebral space, osteogenic substances, such as autogenous bone graft or bone allograft, can be strategically implanted adjacent the implant to prompt bone ingrowth in the intervertebral space. The bone ingrowth promotes long-term fixation of the adjacent vertebrae. Various posterior fixation devices (e.g., fixation rods, screws etc.) can also be utilize to provide additional stabilization during the fusion process. 
     Notwithstanding the variety of efforts in the prior art described above, these intervertebral implants and techniques are associated with another disadvantage. In particular, these techniques typically involve an open surgical procedure, which results in higher cost, lengthy in-patient hospital stays and the pain associated with open procedures. In addition, many intervertebral implants are inserted anteriorly while posterior fixation devices are inserted posteriorly. This results in additional movement of the patient. Therefore, there remains a need in the art for an improved apparatus and method for introducing an intervertebral implant. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the implant is advantageously introduced via a minimally invasive procedure, taking a posterolateral approach at least partially through Kambin′ s triangle in a manner that advantageously provides protection to the exiting and traversing nerves. In one arrangement, to facilitate introduction of instruments and/or devices at least partially through Kambin′ s triangle a foraminoplasty is formed. In one embodiment, the foraminoplasty is performed using one or more features provided one or more dilation tubes that can be used to dilate tissue. 
     In accordance with an embodiment, a dilation introducer for orthopedic surgery comprises a first dilator tube having a distal portion and a proximal portion, the outer surface of the first dilator tube having a first outer radius centered around a first longitudinal axis, and a first longitudinal lumen having a first inner radius; a second dilator tube having a distal portion and a proximal portion, the second dilator tube having a second outer radius centered around a second longitudinal axis, a second longitudinal lumen having a second inner radius centered around the first longitudinal axis, the distal portion of the second dilator tube having a generally semi-annular cross-section, the second lumen configured for removably receiving the first dilator tube for slidable movement within the second lumen; wherein the first longitudinal axis is parallel to and laterally offset from the second longitudinal axis. 
     In some embodiments, the dilation introducer can be configured for removably connecting the first and second dilator tubes together in a locked arrangement, whereby in the locked arrangement slidable movement is restricted. In some embodiments, the second dilator tube can be rotatable with respect to the first dilator tube around the first longitudinal axis. In certain embodiments, the generally semi-annular cross-section of the second dilator tube can be configured such that when the first dilator tube is received within the second dilator tube, the outer radial surface of the first dilator tube is partially exposed at the distal end of the first dilator tube. Further, the opening of the generally semi-annular cross-section of the second dilator tube can be oriented opposite the second longitudinal axis with respect to the first longitudinal axis. In some embodiments, the second dilator tube can contain cutting flutes on one side, located opposite the opening of the generally semi-annular cross-section of the second dilator tube. 
     In some embodiments, the dilation introducer can further comprise: a third dilator tube having a distal portion and a proximal portion, the third dilator tube having a third outer radius centered around a third longitudinal axis, a third longitudinal lumen having a third inner radius centered around the second longitudinal axis, the distal portion of the third dilator tube having a semi-annular cross-section, the third lumen configured for removably receiving the second dilator tube for slidable movement within the third lumen; wherein the second longitudinal axis is parallel to and laterally offset from the third longitudinal axis. Further, the dilation introducer can comprise: an access cannula having a distal portion and a proximal portion, the access cannula having a fourth outer radius centered around the third longitudinal axis, a fourth longitudinal lumen having a fourth inner radius centered around the third longitudinal axis, the distal portion of the access cannula having a semi-annular cross-section, the fourth lumen configured for removably receiving the third dilator tube for slidable movement within the fourth lumen. In some embodiments, the access cannula can have a smooth outer surface. 
     In accordance with an embodiment, a method for accessing a patient’s intervertebral disc to be treated in orthopedic surgery is provided, comprising the steps of: passing a first dilator tube along a first longitudinal axis through Kambin′ s triangle until the first dilator tube reaches the intervertebral disc to be treated; passing a second dilator tube along a second longitudinal axis that is parallel to and laterally displaced from the first longitudinal axis, until the distal end of the second dilator contacts the annulus, wherein the second dilator tube has a coarse portion oriented towards the inferior pedicle, and wherein the distal portion of the second dilator tube has a generally semi-annular cross-section, configured such that the second dilator tube does not contact the exiting nerve during insertion. 
     In some embodiments, the method can further comprise: passing a third dilator tube along a third longitudinal axis that is parallel to and laterally displaced from the second longitudinal axis, until the distal end of the third dilator contacts the annulus, wherein the distal portion of the third dilator tube has cutting flutes oriented towards the inferior pedicle, and wherein the distal portion of the third dilator tube has a generally semi-annular cross-section configured such that the third dilator tube does not contact the exiting nerve during insertion. Further, the method can comprise forming a further recess in the inferior pedicle by rotating the second dilator tube back and forth. Alternatively or in addition, the method can further comprise forming a further recess in the inferior pedicle by longitudinally sliding the second dilator tube back and forth. Further still, the method can also comprise: passing an access cannula over the third dilator tube until the distal end of the third dilator contacts the annulus, wherein the distal portion of the access cannula has a generally semi- annular cross-section configured such that the access cannula does not contact the exiting nerve during insertion; rotating the access cannula such that generally semi-annular cross- section opens opposite the exiting nerve; and removing the first, second, and third dilator tubes. In some embodiments, the method can further comprise operating on an intervertebral disc by inserting surgical instruments through the access cannula. 
     In accordance with an embodiment, a method for performing orthopedic surgery is provided that can comprise: introducing a first dilator tube through Kambin′ s triangle; introducing a second dilator tube over the first dilator tube; and removing bone from the inferior pedicle. In some embodiments, the method can further comprise: introducing a third dilator tube over the second dilator tube; and removing additional bone from the inferior pedicle. In some embodiments, the method can further comprise: introducing an access cannula over the third dilator tube; and operating on the spine through the access cannula. 
     In accordance with an embodiment, a dilation introducer for orthopedic surgery is provided that can comprise a first dilator tube having a distal portion and a proximal portion, the outer surface of the first dilator tube having a first outer radius centered around a first longitudinal axis, and a first longitudinal lumen having a first inner radius; and a second dilator tube having a distal portion and a proximal portion, the second dilator tube having a second outer radius centered around a second longitudinal axis, a second longitudinal lumen having a second inner radius centered around the first longitudinal axis, the second dilator tube configured to be slidably advanced over the first dilator tube. In some embodiments, the distal portions first and second dilator tubes both include cutting surfaces on one outer side of the dilator and a generally smooth surface on an opposite outer side of the dilator tube. In some embodiments, the dilation introducer further includes a neuro-monitoring needle. 
     Other features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments in conjunction with the accompanying drawings, which illustrate, by way of example, the operation of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The abovementioned and other features of the inventions disclosed herein are described below with reference to the drawings of the preferred embodiments. The illustrated embodiments are intended to illustrate, but not to limit the inventions. The drawings contain the following figures: 
         FIG.  1    is a lateral elevational view of a portion of a vertebral column. 
         FIG.  2    is a schematic side view of Kambin’s triangle. 
         FIG.  3    is a perspective view of an access cannula in positioned against a vertebral column. 
         FIG.  4 A  is a plan view of a first and second dilator tubes in a combined position 
         FIG.  4 B  is an enlarged detail view of the distal tip of the first and second dilator tubes shown in  FIG.  4 A . 
         FIG.  5 A  is a plan view of a third dilator tube. 
         FIG.  5 B  is an enlarged detail view of the distal tip of the third dilator tube shown in  FIG.  5 A .. 
         FIG.  6 A  is a side view of the access cannula shown in  FIG.  3   . 
         FIG.  6 B  is an enlarged detail view of the distal tip of the access cannula shown in  FIG.  6 A . 
         FIG.  7 A  is a perspective view of a dilation introducer comprising the first and second dilator tubes of  FIG.  4 A , the third dilator tube of  FIG.  5 A  and the access cannula of  FIG.  6 A . 
         FIG.  7 B  is an enlarged detail view of the distal tip of dilation introducer shown in  FIG.  7 A . 
         FIG.  8 A  is a perspective view of the dilation introducer of  FIG.  7 A  positioned against the spine. 
         FIG.  8 B  is an enlarged detail view of the second dilator tube of  FIG.  7 A  introduced over the first dilator tube of  FIG.  7 A . 
         FIG.  9    is a perspective view of the dilation introducer of  FIG.  7 A , with the third dilator tube introduced over the second dilator tube. 
         FIG.  10    shows the access point before and after the foraminoplasty performed by the dilation introducer of  FIG.  7 A . 
         FIG.  11 A  is a perspective view of the dilation introducer of  FIG.  7 A , with the access cannula introduced over the third dilator tube. 
         FIG.  11 B  is a perspective view of the dilation introducer of  FIG.  7 A , with the access cannula rotated to protect the exiting nerve. 
         FIG.  11 C  is a perspective view of the dilation introducer of  FIG.  7 A , with the first, second, and third dilator tubes removed, while the access cannula remains in place. 
         FIG.  12    is a plan view of an intervertebral implant for delivery through the access cannula. 
         FIG.  13 A  is a plan view of another embodiment of a first dilator tube. 
         FIG.  13 B  is an enlarged detail view of the distal end of the first dilator tube shown in  FIG.  13 A . 
         FIG.  13 C  is an enlarged detail view of the proximal end of the first dilator tube shown in  FIG.  13 A . 
         FIG.  14 A  is a plan view of another embodiment of a second dilator tube. 
         FIG.  14 B  is an enlarged detail view of the distal end of the second dilator tube shown in  FIG.  14 A . 
         FIG.  14 C  is an enlarged detail view of the proximal end of the second dilator tube shown in  FIG.  14 A . 
         FIG.  15 A  is a plan view of another embodiment of a third dilator tube. 
         FIG.  15 B  is an enlarged detail view of the distal end of the third dilator tube shown in  FIG.  15 A . 
         FIGS.  15 C and  15 D  are enlarged detail views of the proximal end of the third dilator tube shown in  FIG.  15 A . 
         FIG.  16 A  is a plan view of another embodiment of an access cannula. 
         FIG.  16 B  is an enlarged detail view of the distal end of the access cannula shown in  FIG.  16 A . 
         FIG.  16 C  is an enlarged detail view of the proximal end of the access cannula shown in  FIG.  16 A . 
         FIG.  17 A  is a plan view of another embodiment of a dilation introducer comprising the first dilator tube of  FIG.  13 A , the second dilator tube of  FIG.  14 A , the third dilator tube of  FIG.  15 A , and the access cannula of  FIG.  16 A . 
         FIG.  17 B  is an enlarged detail view of the distal end of the dilation introducer shown in  FIG.  17 A . 
         FIG.  17 C  is an enlarged detail view of the proximal end of the dilation introducer shown in  FIG.  17 A . 
         FIG.  18 A  is a longitudinal cross-sectional view of the dilation introducer of  FIG.  17 A . 
         FIG.  18 B  is an enlarged detail of the longitudinal cross-sectional view shown in  FIG.  18 A . 
         FIG.  19 A  is a plan view of a dilation introducer equipped with neuro-monitoring leads and a neuro-monitoring needle. 
         FIG.  19 B  is a plan view of the neuro-monitoring needle shown in  FIG.  19 A . 
         FIG.  19 C  is an enlarged detail view of a distal tip of a neuro-monitoring needle of  FIG.  19 A . 
         FIG.  19 D  is an enlarged detail view of the neuro-monitoring leads shown in  FIG.  19 A . 
         FIG.  20 A  is a perspective view of another embodiment of an intervertebral implant in an unexpanded state. 
         FIG.  20 B  is a perspective view of the intervertebral implant shown in  FIG.  20 A  wherein the implant is in an expanded state. 
         FIG.  21    is a bottom view of the intervertebral implant shown in  FIG.  20 A . 
         FIG.  22    is a side view of the intervertebral implant shown in  FIG.  20 B . 
         FIG.  23    is a front cross-sectional view of the intervertebral implant shown in  FIG.  20 B  taken along lines 19-19. 
         FIG.  24 A  is a bottom perspective view of a lower body portion of the intervertebral implant shown in  FIG.  20 A . 
         FIG.  24 B  is a top perspective view of the lower body portion of the intervertebral implant shown in  FIG.  20 A . 
         FIG.  25 A  is a bottom perspective view of an upper body portion of the intervertebral implant shown in  FIG.  20 A . 
         FIG.  25 B  is a top perspective view of the upper body portion of the intervertebral implant shown in  FIG.  20 A . 
         FIG.  26    is a perspective view of an actuator shaft of the intervertebral implant shown in  FIG.  20 A . 
         FIG.  27 A  is a front perspective view of a proximal wedge member of the intervertebral implant shown in  FIG.  20 A . 
         FIG.  27 B  is a rear perspective view of the proximal wedge member of the intervertebral implant shown in  FIG.  20 A . 
         FIG.  28 A  is a front perspective view of a distal wedge member of the intervertebral implant shown in  FIG.  20 A . 
         FIG.  28 B  is a rear perspective view of the distal wedge member of the intervertebral implant shown in  FIG.  20 A . 
         FIG.  29    is a perspective view of a deployment tool according to an embodiment. 
         FIG.  30    is a side cross-sectional view of the deployment tool shown in  FIG.  29    wherein an expandable implant is attached to a distal end thereof 
         FIG.  31    is a perspective view of a rasp tool, according to an embodiment. 
         FIG.  32    illustrates a plan view of an expandable rasp tool, according to an embodiment. 
         FIG.  33 A  is a plan view of a plunger assembly for a graft delivery system, according to an embodiment. 
         FIG.  33 B  is a longitudinal cross-sectional view of the plunger assembly shown in  FIG.  33 A . 
         FIG.  34 A  is a plan view of a funnel assembly for a graft delivery system, according to an embodiment. 
         FIG.  34 B  is a schematic view of the funnel assembly shown in  FIG.  34 A . 
         FIG.  34 C  is an end view of the funnel assembly shown in  FIG.  34 A . 
         FIG.  34 D  is a longitudinal cross-sectional view of the funnel assembly shown in  FIG.  34 A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with certain embodiments disclosed herein, an improved apparatus for inserting an intervertebral implant is provided. For example, in one embodiment, the apparatus may be used to insert surgical instruments and/or one or more intervertebral implants through a minimally invasive procedure to reduce trauma to the patient and thereby enhance recovery and improve overall results. By minimally invasive, Applicant means a procedure performed percutaneously through an access device in contrast to a typically more invasive open surgical procedure. 
     Certain embodiments disclosed herein are discussed in the context of an intervertebral implant and spinal fusion because of the device and methods have applicability and usefulness in such a field. The device can be used for fusion, for example, by inserting an intervertebral implant to properly space adjacent vertebrae in situations where a disc has ruptured or otherwise been damaged. “Adjacent” vertebrae can include those vertebrae originally separated only by a disc or those that are separated by intermediate vertebra and discs. Such embodiments can therefore be used to create proper disc height and spinal curvature as required in order to restore normal anatomical locations and distances. However, it is contemplated that the teachings and embodiments disclosed herein can be beneficially implemented in a variety of other operational settings, for spinal surgery and otherwise. 
     As context for the methods and devices described herein,  FIG.  1    is a lateral view of a vertebral column  10 . As shown in  FIG.  1   , the vertebral column  10  comprises a series of alternative vertebrae  11  and fibrous intervertebral discs  12  that provide axial support and movement to the upper portions of the body. The vertebral column  10  typically comprises thirty-three vertebrae  11 , with seven cervical (C1-C7), twelve thoracic (T1-T12), five lumbar (L1-L5), five fused sacral (S1-S5), and four fused coccygeal vertebrae. 
       FIG.  2    is a schematic view of Kambin’s triangle. This region  20  is the site of posterolateral access for spinal surgery. It can be defined as a right triangle over the intervertebral disc  12  viewed dorsolaterally. The hypotenuse is the exiting nerve  21 , the base is the superior border of the inferior vertebra  22 , and the height is the traversing nerve root  23 . As will be explained below, in one embodiment, the intervertebral disc  12  is accessed through this region by performing a foraminoplasty in which a portion of the inferior vertebra is removed such that surgical instruments or implants can be introduced at this region of the spine. In such a procedure, it is often desired to protect the exiting nerve and the traversing nerve root. Apparatuses and methods for accessing the intervertebral disc through Kambin’s triangle may involve performing endoscopic foraminoplasty while protecting the nerve will be discussed in more detail below. Utilizing foraminoplasty to access the intervertebral disc through Kambin’s triangle can have several advantages (e.g., less or reduced trauma to the patient) as compared to accessing the intervertebral disc posteriorly or anteriorly as is typically done in the art. In particular, surgical procedures involving posterior access often require removal of the facet joint. For example, transforaminal interbody lumbar fusion (TLIF) typically involves removal of one facet joint to create an expanded access path to the intervertebral disc. Removal of the facet joint can be very painful for the patient, and is associated with increased recovery time. In contrast, accessing the intervertebral disc through Kambin’s triangle may advantageously avoid the need to remove the facet joint. As described in more detail below, endoscopic foraminoplasty may provide for expanded access to the intervertebral disc without removal of a facet joint. Sparing the facet joint may reduce patient pain and blood loss associated with the surgical procedure. In addition, sparing the facet joint can advantageously permit the use of certain posterior fixation devices which utilize the facet joint for support (e.g., trans-facet screws, trans-pedicle screws, and/or pedicle screws). In this manner, such posterior fixation devices can be used in combination with interbody devices inserted through the Kambin’s triangle. 
     Dilation Introducer 
       FIGS.  2 - 7 B  illustrate an embodiment of a dilation introducer  100  that can be used to perform percutaneous orthopedic surgery. As will be described in detail below, the dilation introducer in the illustrated embodiments can comprise an access cannula  30 , and a first, second and third dilator tubes  40 ,  45 ,  60 . While the illustrated embodiment includes first, second and third dilator tubes  40 , modified embodiments can include more or less dilator tubes and/or dilator tubes with modified features. It is also anticipated that in some embodiments, the access cannula  30  can be eliminated from the introducer or modified. 
       FIG.  3    illustrates an embodiment of the access cannula  30 , which is shown in a position for performing surgery on an intervertebral disc, for instance transforaminal lumbar interbody fusion. The access cannula  30  in the illustrated embodiment has an inner lumen  31  that allows for surgical instruments and devices to pass through it to access the intervertebral disc  12 . The distal tip of the cannula can be oriented such that surgical instruments have access to the intervertebral disc without contacting with the exiting nerve. The position shown in  FIG.  3    can be achieved by following the method disclosed herein, discussed in more detail below. 
       FIGS.  4 A and  4 B  illustrate an embodiment of the first dilator tube  40  and second dilator tube  45  of the dilation introducer  100 . As shown, in the illustrated embodiment, the first dilator tube  40  has a distal portion  41 , an outer radius  42  and a first longitudinal lumen  43 . The illustrated second dilator tube  45  has a distal portion  46 , an outer radius  47  and a second longitudinal lumen  48 . As shown, the first dilator tube can be received within the lumen of the second dilator tube. The outer radius  42  of the first dilator tube can be centered around a first longitudinal axis  44 . The outer radius  47  of the second dilator tube can be centered around a second longitudinal axis  49 . In the illustrated embodiment, the second longitudinal axis  49  is laterally offset from the first longitudinal axis  44 . In the configuration shown, the outer radius of the first dilator tube is nearly equivalent to the inner radius of the second longitudinal lumen such that the first dilator tube can be slidably received within the second dilator tub. The second dilator tube  45  can include a handle  50  for rotating the tube independently of the first dilator tube  40 . In the illustrated embodiment, a collar can be located distal to the handle, with an outer radius larger than the outer radius of the second dilator tube, but smaller than the outer radius of the handle. In a modified embodiment, the first dilator tube  40  can also a separate handle which can be locked together with the handle  50  of the second dilator tube  45 . In one embodiment, the first and second dilator tubes  40 ,  45  can locked longitudinally locked together, such that slidable movement of the first tube with respect to the second is restricted. In one embodiment, the distal portion  46  of the second dilator tube has a flattened edge. This flattened edge advantageously prevents the second dilator tube  45  from penetrating the disc. 
       FIG.  4 B  shows an enlarged detail view of the distal portions of the first and second dilator tubes  40 ,  45  of  FIG.  4 A . The distal portion  46  of the second dilator tube  45  can have a generally semi-annular cross-section, configured such that when the first dilator tube  40  is received within the second dilator tube  45 , the outer radial surface of the first dilator tube  40  is partially exposed at the distal portion  46  of the second dilator tube  45 . The opening of the generally semi-annular cross-section of the second dilator tube can be oriented opposite the second longitudinal axis  49  with respect to the first longitudinal axis  44 . Additionally, the second dilator tube can include cutting flutes or ridges  51  on one side, located opposite the opening of the generally semi-annular cross-section of the second dilator tube  45 . In other embodiments, the cutting flutes may be replaced with a coarse surface (e.g., knurling, sharp edges, abrasive members, etc.) which, when rotated or slid (e.g., back and forth) against bone, will create a recess therein. As noted above, other mechanisms for removing bone can be used, and the cutting flutes are shown here by way of example only. As can be seen in  FIG.  4 B , the inner lumen of the second dilator tube  45  can be off-center. In this configuration, the cutting flutes  51  are further from the axis of rotation than the side opposite the cutting flutes. This is particularly advantageous for performing foraminoplasty while protecting the exiting nerve, as will be discussed in more detail below. 
     Although the illustrated embodiment depicts the first and second dilator tubes as separate elements, in alternative embodiments these two tubes can be coupled formed together as one unified dilator tube with a staggered distal portion. In still other embodiments, the first dilator tube and second dilator tube may be coupled together to form a single component. The tubes may be joined by, for instance, welding, adhesive, mechanical joints, or any other appropriate means. 
     In another alternative embodiment, the first dilator tube may be omitted. Instead, a Jamshidi® needle with a removable handle, or a similar device, may be used to initially define a path to the intervertebral disc. With the handle of the Jamshidi® needle removed, the second dilator tube may be advanced over the Jamshidi® needle, just as with the first dilator tube. In some embodiments, a K-wire or similar device can be inserted through the Jamshidi® needle and/or dilator tubes. 
       FIGS.  5 A and  5 B  illustrate and embodiment of the third dilator tube  60 , which can be configured to be slidably introduced over the second dilator tube  45 . The third dilator tube  60  can include a distal portion  61 , a third outer radius  62  centered around a third longitudinal axis  63 , and a third longitudinal lumen  64  having a third inner radius  65 . The third lumen  64  can be configured to removably receive the second dilator tube (not shown) for slidable movement within the third lumen  64 . In such a configuration, the third longitudinal axis  63  is parallel to and laterally offset from the second longitudinal axis  49 . A handle  66  can allow for rotation of the third dilator tube. In one arrangement, a collar can be located distal to the handle  66 , with an outer radius larger than the outer radius of the third dilator tube  45 , but smaller than the outer radius of the handle. 
     In some embodiments, a button  67  on the handle  66  allows for the operator to toggle between a locked and unlocked configuration. In a locked configuration, the second and third dilator tubes are unable to slide relative to one another. In an embodiment, the locked configuration permits the dilator tubes to rotate independently with respect to one another. In another embodiment, the locked configuration restrains rotational movement as well as slidable movement. The button  67  may comprise a generally rectangular shape with a cut-out large enough for the collar of the second dilator tube  45  to pass therethrough. A spring located underneath the button  67  provides upward pressure on the button. When uncompressed, the cut-out portion of the button presses firmly against the collar of the second dilator tube  45 , which may be received within the handle  66  of the third dilator tube. When uncompressed, the friction of the button  67  against the collar inhibits movement of the third dilator tube  60  with respect to the second dilator tube. In some embodiments, the cut-out portion of the button may form a notch configured to fit within the ridge on the collar of the third dilator tube. Upon compressing the button  67 , the cut-out portion of the button may be moved away from the collar, permitting free movement of the third dilator tube  60  relative to the second dilator tube  45 . 
       FIG.  5 B  shows an enlarged detail view of the distal portion of the third dilator tube of  FIG.  5 A . The distal portion  61  has a generally semi-annular cross-section, and cutting flutes  167  for reaming bone located opposite the opening of the semi-annular cross-section. As with the second dilator tube, in other embodiments the cutting flutes may be replaced or used in combination with a coarse or other cutting or abrading surface which, when rotated or slid against bone, will create a recess therein. As can be seen in  FIG.  5 B , the inner lumen of the third dilator tube  60  may be off-center. In this configuration, the cutting flutes  68  are further from the axis of rotation than the side opposite the cutting flutes. This is particularly beneficial for performing foraminoplasty while protecting the exiting nerve, as will be discussed in more detail below. 
       FIGS.  6 A and  6 B  illustrate an embodiment of the access cannula, which can be configured to be introduced over the third dilator tube (not shown). The access cannula  30  has a distal portion  32 , a fourth outer radius  33  centered around a fourth longitudinal axis  34 , and a fourth longitudinal lumen  31  having a fourth inner radius  35 . The access cannula  30  may be configured to removably receive the third dilator tube (not shown) for slidable movement within the third lumen. A handle allows for rotation of the access cannula  30 . 
     In some embodiments, a button  37  on the handle  36  allows for the operator to toggle between a locked and unlocked configuration. In a locked configuration, third dilator tube and the access cannula are unable to slide relative to one another. In an embodiment, the locked configuration permits the dilator tubes to rotate independently with respect to one another. In another embodiment, the locked configuration restrains rotational movement as well as slidable movement. The button  37  may comprise a generally rectangular shape with a cut-out large enough for the collar of the third dilator tube  60  to pass therethrough. A spring located beneath the button  37  can provide upward pressure on the button. When uncompressed, the cut-out portion of the button can press firmly against the collar of the third dilator tube  45 , which may be received within the handle of the access cannula  30 . When uncompressed, the friction of the button  37  against the collar can inhibit movement of the access cannula  30  with respect to the third dilator tube  60 . Upon compressing the button  37 , the cut-out portion of the button can be moved away from the collar, permitting free movement of the access cannula  30  relative to the third dilator tube  60 . 
       FIG.  6 B  shows an enlarged detail view of the distal portion of the access cannula of  FIG.  6 A . The distal portion  32  can have a generally semi-annular cross-section. In the embodiment shown, the fourth longitudinal lumen may be centered with respect to the outer radius of the access cannula, in contrast to the second and third dilator tubes. In other embodiments, however, the access cannula may also have a longitudinal lumen that may be off-center with respect to the outer radius. In yet another embodiment, the access cannula need not be limited to a cylindrical outer surface. The outer surface could, for instance, have an elliptical, polygonal, or other cross-sectional shape. 
       FIGS.  7 A and  7 B  illustrate one embodiment of the dilation introducer  100  in an assembled configuration. As shown, the access cannula  30  can be positioned over the third dilator tube  60 , which can be positioned over the second dilator tube  45 , which in turn can be positioned over the first dilator tube  40 . The handles  50 ,  151  of the first and second dilator tubes can be locked together to constrain slidable movement, but allow for the second dilator tube  45  to rotate with respect to the first dilator tube  40 . The third dilator tube  60  can be advanced distally until the distal portion  61  of the third dilator tube aligns with the distal portion  46  of the second dilator tube. Further, the access cannula may also be advanced so that the distal portion  32  aligns with the distal portions  46 ,  61  of the second and third dilator tubes. The second and third dilator tubes  45 ,  60  each have cutting flutes  51 ,  68  on their respective distal portions  46 ,  61 . As can be seen, the first, second, and third longitudinal axes  44 ,  49 ,  63  are each laterally offset from one another. 
     In certain embodiments, the first, second and third dilator tubes along with the access cannula can be provided with additional stops that engage the buttons described above. For example, in one embodiment, notches or detents can be provided that engage the button when one tube is advanced distally and reaches a specific location (e.g., end point). In this manner, forward movement of a tube or cannula can be limited once the tube or cannula may be advanced to a desired location. 
       FIG.  7 B  shows an enlarged detail view of the dilation introducer of  FIG.  7 A . The distal portions  46 ,  61 ,  32  of each of the second and third dilator tubes  45 ,  60 , and of the access cannula  30  have generally semi-annular cross-sections. The distal portions  46 ,  61  of the second and third dilator tubes in the illustrated embodiment can have flattened edges, to prevent penetration into the intervertebral disc as each dilator tube is advanced. 
     Method of Use 
       FIGS.  8 A- 12    illustrate one embodiment of a method of performing percutaneous orthopedic surgery using the dilation introducer. With initial reference to  FIG.  8 A , the first dilator tube  40  can be placed through Kambin’s triangle  20  until the distal portion  41  abuts or even penetrates the intervertebral disc  12 . In one arrangement, the second dilator tube  45  can then be advanced over the first dilator tube  40  until the distal portion  46  of the second dilator tube abuts but does not enter the intervertebral disc  12 . 
     As discussed above, although the illustrated embodiment shows the first and second dilator tubes as separate elements, in alternative embodiments these two tubes may be formed together as one unified dilator tube with a staggered distal portion. In still other embodiments, the first dilator tube and second dilator tube may be coupled together to form a single component. In these alternative embodiments, the unified or coupled dilator tube may be advanced until the more distal portion abuts or penetrates the intervertebral disc. 
     In another alternative embodiment, the first dilator tube may be omitted. Instead, a Jamshidi® needle with a removable handle or similar device may be used. In such an embodiment, the Jamshidi® needle may be first introduced to abut or enter the intervertebral disc, after which the handle may be removed. Optionally, a K-wire may be inserted into the Jamshidi® needle after it is in position either abutting or partially penetrating the intervertebral disc. The second dilator tube may then be advanced over the Jamshidi® needle. 
       FIG.  8 B  shows an enlarged detail of the second dilator tube  45  introduced over the first dilator tube  40 . The distal portion  46  of the second dilator tube  45  can have a semi-annular cross-section with an opening that forms a recess with respect to the leading edge of the tube  45 . The second dilator tube  45  can be oriented for advancement over the first dilator tube  40  such that the opening of the semi-annular cross-section faces the exiting nerve  21 . This technique advantageously limits and/or eliminates contact with the exiting nerve. The distal portion  46  of the second dilator tube opposite the opening of the semi-annular cross-section abuts the inferior vertebrae  22 . The cutting flutes (not shown) are positioned against the inferior vertebrae  22 . The second dilator tube  45  may be rotated slightly back and forth, such that the cutting flutes create a recess in the inferior vertebrae  22 , making room for introduction of the third dilator tube. When rotating the second dilator tube, care is taken to minimize any trauma inflicted upon the exiting nerve. Accordingly, in the illustrated embodiment, the tube  45  can be used to remove bone on a side of the tube  45  generally opposite of the nerve  21 . 
     With reference now to  FIG.  9   , the third dilator tube  60  can be introduced over the second dilator tube  45 . In one arrangement, the distal portion  61  of the third dilator tube  60  abuts but does not enter the intervertebral disc. In the illustrated embodiment, a flattened edge of the distal portion can help ensure that the third dilator tube  60  does not penetrate the intervertebral disc or limit such penetration. As with the second dilator tube, the opening of the semi-annular cross-section of the distal portion of the third dilator tube can be positioned to face the exiting nerve (not shown). Contact between the third dilator tube  60  and the nerve can thereby be minimized or eliminated. The cutting flutes  68  of the third dilator tube can be positioned opposite the opening of the semi-annular cross-section, and abut the inferior vertebrae  22 . The third dilator tube  60  may be rotated slightly back and forth, such that the cutting flutes create a further recess in the inferior vertebrae  22 , making room for introduction of the access cannula. Again, care should be taken during the rotation of the third dilator tube to ensure that the exiting nerve is not injured thereby. Accordingly, the third dilator tube can be can be used to remove bone on a side of the tube  60  generally opposite of the nerve  21 . 
       FIG.  10    shows the access area before and after the second and third dilator tubes  45 ,  60  are rotated to create a recess in the inferior vertebrae  22 . The area  70  in the left image demarcated by a dashed line is the portion of bone that can be removed by the second and third dilation tubes  45 ,  60 . This foraminoplasty permits the access cannula to be introduced without disturbing the exiting nerve  21 . The method described is not limited by the precise location of the recess shown in  FIG.  10   . In general, a recess may be formed anywhere along the superior border of the inferior vertebrae  22 , in order to provide improved access for a dilation introducer. 
       FIG.  11 A  shows the access cannula  30  introduced over the third dilator tube  60 . The distal portion  32  of the access cannula  30  abuts but does not enter the intervertebral disc  12 . In one embodiment, the distal portion  32  can be equipped with flattened edges to guard against insertion into the intervertebral disc. As with the second and third dilator tubes  45 ,  60 , the opening of the semi-annular cross-section of the distal portion  32  of the access cannula  30  can be positioned initially to face the exiting nerve (not shown). Contact between the access cannula  30  and the exiting nerve can thereby be minimized during insertion. 
     As can be seen in  FIG.  11 B , the access cannula  30  can then be rotated such that the opening of the semi-annular cross-section faces opposite the exiting nerve (not shown). Since, unlike the second and third dilator tubes  45 ,  60 , the outer surface of the access cannula is smooth, trauma to the exiting nerve may be minimized during this rotation. 
     Referring now to  FIG.  11 C , once the access cannula  30  is in position, which in one embodiment comprising until the distal portion  32  abuts the intervertebral disc  12 , the cannula  30  can be rotated so that the opening of the semi-annular cross-section faces opposite the exiting nerve (not shown), the first, second, and third dilator tubes  40 ,  45 ,  60  may be removed. In one embodiment, rotation of the cannula  30  can gently move the nerve away from the access site while also protecting the nerve as tools and devices may be inserted through the cannula  30 . The access cannula  30  can then provide an open lumen  31  through which surgical tools can be introduced to the site of the intervertebral disc  12 . As noted above, the positioning of the access cannula  30  protects the exiting nerve (not shown) from coming into contact with any of the surgical tools. 
     A example of a surgical tool for use through the access cannula is depicted in  FIG.  12   . The intervertebral implant  80  may be introduced through the access cannula  30 , and released once in position. Although a particular intervertebral implant is shown here, one of skill in the art will readily understand that any number of surgical tools may be introduced through the access cannula. For example, surgical tools to be inserted through the access cannula may include, without limitation, discectomy tools, tissue extractors, bone graft insertion tools, rasps, forceps, drills (e.g,. trephine), rongeurs, curettes, paddle distractors, mechanical distractors, lasers, automated probes, manual probes, and plasma wands. In one embodiment of use, an opening in the disc annulus can be formed and a portion of the disc can be removed using tools advanced through the access cannula  30 . The disc space can be distracted (e.g,. using paddle distractors) before and/or after the implant  80  and/or different or additional interbody devices are inserted through the access cannula  30  and placed between the vertebral bodies to maintain spacing. In some embodiments the disc nucleus or portions thereof is removed while leaving the disc annulus. Bone graft and/or other materials such as, for example, bone morphogenetic proteins (BMPs)can be placed between the vertebrae before, while or after positioning the implant. Fusion can then occur between the vertebrae. In some procedures, fusion can be augmented with other fixation devices such as, for example, pedicle screws and rod constructions, transfacet and transpedicle screws, interbody spacers, rods, plates and cages, which can be used to stabilize a pair of vertebral bodies together. For example, in one arrangement, the fusion is augmented by one or more posterior fixation devices (e.g transfacet and transpedicle screws and/or pedicle screws and rods and/or spinous process spacers). In such a manner, the entire fusion procedure can be done from a posterior position and preferably in a minimally invasive (e.g., percutaneous manner). For example, in one embodiment, the above described procedure is used in combination with the transfacet-pedicular implant system sold by Intervention Spine, Inc. under the trade name PERPOS®, such a system is also described in U.S. Pat. Nos. 7,998,176 and 7,824,429, the entirety of which are hereby incorporated by reference herein. 
       FIG.  13 - 19 D  illustrate another aspect of a dilation introducer  1100  that can be used to perform percutaneous orthopedic surgery. The dilation introducer in this embodiment is similar in some respects to that described above. As will be described in detail below, the proximal portion of the dilation introducer  1100  differs significantly from that of the dilation introducer  100  described above. The dilation introducer  1100  in the illustrated embodiments can comprise an access cannula  130 , and a first, second and third dilator tubes  140 ,  145 ,  160 . While the illustrated embodiment includes first, second and third dilator tubes  140 , modified embodiments can include more or less dilator tubes and/or dilator tubes with modified features. It is also anticipated that in some embodiments, the access cannula  130  can be eliminated from the introducer or modified. 
       FIGS.  13 A to  13 C  illustrate an embodiment of the first dilator tube  140  of the dilation introducer  1100 . As shown, in the illustrated embodiment, the first dilator tube  140  may have distal portion  141 , an outer radius  142  and a first longitudinal lumen  143 . The outer radius  142  can be centered around first longitudinal axis  144 . The distal portion  141  may include a tapered tip  171  of the dilator tube. The proximal portion  172  of the first dilator tube may include a first proximal head  173 , with a threaded portion  174  distal to the gripping portion  175 . In some embodiments, the longitudinal lumen  143  extends through the proximal head  173 , such that a guidewire or K-wire may be introduced through the proximal head  173  and the dilator tube  140 . 
       FIGS.  14 A to  14 C  illustrate an embodiment of the second dilator tube  145 . In the embodiment shown the second dilator tube has a distal portion  146 , and an outer radius  147 . The outer radius may be centered around a second longitudinal axis  149 . The second dilator tube includes a second longitudinal lumen  48  with an inner radius  176 . The outer radius  142  of the first dilator tube may be nearly equivalent to the inner radius  176  of the second dilator tube, such that the first dilator tube  140  can be slidably received within the second longitudinal lumen  148 . The proximal portion  177  of the second dilator tube includes a collar  178 . 
       FIG.  14 B  shows an enlarged detail view of the distal portion of the second dilator tube  145 . The distal portion  146  of the second dilator tube may include a flattened edge  179 . This flattened edge  179  advantageously prevents the second dilator tube  145  from penetrating the intervertebral disc  112 . The tip  180  of distal portion  146  can have a generally semi-annular cross-section, configured such that when the first dilator tube  140  is received within the second dilator tube  145 , the outer radial surface of the first dilator tube  140  is partially exposed at the distal tip  180  of the second dilator tube  145 . The opening of the generally semi-annular cross-section of the second dilator tube can be oriented opposite the second longitudinal axis  149  with respect to the longitudinal axis  127  of the second longitudinal lumen. 
     When the first dilator tube  140  is received within the second dilator tube  145 , the longitudinal axis  127  of the second longitudinal lumen is essentially aligned with the first longitudinal axis  144 . Additionally, the second dilator tube  145  can include cutting flutes or ridges  151  on one side, located opposite the opening of the generally semi-annular cross-section of the second dilator tube  145 . In other embodiments, the cutting flutes  151  may be replaced with a coarse surface (e.g., knurling, sharp edges, abrasive members, etc.) which, when rotated or slid (e.g., back and forth) against bone, will create a recess therein. As noted above, other mechanisms for removing bone can be used, and the cutting flutes are shown here by way of example only. As can be seen in  FIG.  14 B , the inner lumen  148  of the second dilator tube  145  can be off-center. In this configuration, the cutting flutes  151  are further from the axis of rotation than the side opposite the cutting flutes. This is particularly advantageous for performing foraminoplasty while protecting the exiting nerve, as will be discussed in more detail below. 
       FIG.  14 C  shows an enlarged detail view of the proximal portion  177  of the second dilator tube  145 . The collar  178  includes an aperture  181  which may be used in conjunction with the third dilator tube, as described in detail below. In alternative embodiments, the aperture  181  may be instead replaced with a circumferentially oriented groove. 
       FIGS.  15 A to  15 D  illustrate and embodiment of the third dilator tube  160 , which can be configured to be slidably introduced over the second dilator tube  145 . The third dilator tube  160  can include a distal portion  161 , a third outer radius  162  centered around a third longitudinal axis  163 , and a third longitudinal lumen  164  having a third inner radius  165  centered around longitudinal axis  169  that runs parallel to and laterally offset from the third longitudinal axis  163 . The third lumen  164  can be configured to removably receive the second dilator tube  145  for slidable movement within the third lumen  164 . In such a configuration, the second longitudinal axis  149  essentially aligns with the longitudinal axis  169  of the inner lumen  164  of the third dilator tube  160 . The proximal portion  182  includes a handle assembly  183 . 
       FIG.  15 B  shows an enlarged detail view of the distal portion of the third dilator tube of  FIG.  15 A . The distal portion  161  of the third dilator tube may include a flattened edge  185 . This flattened edge  185  advantageously prevents the third dilator tube  160  from penetrating the intervertebral disc  112 . The tip  184  of the distal portion  161  has a generally semi-annular cross-section, and cutting flutes  167  for reaming bone located opposite the opening of the semi-annular cross-section. As with the second dilator tube, in other embodiments the cutting flutes may be replaced or used in combination with a coarse or other cutting or abrading surface which, when rotated or slid against bone, will create a recess therein. As can be seen in  FIG.  15 B , the longitudinal lumen  164  of the third dilator tube  160  may be off-center. In this configuration, the cutting flutes  167  are further from the axis of rotation than the side opposite the cutting flutes. This is particularly beneficial for performing foraminoplasty while protecting the exiting nerve, as will be discussed in more detail below. 
       FIGS.  15 C and  15 D  show enlarged detail views of the proximal portion  182  of the third dilator tube  160 . The proximal portion  182  includes a handle assembly  183 . A first latching button  186  may be configured for constraining the movement of the third dilator tube relative to the second dilator tube, as described in more detail below. In various embodiments, the latching button  186  may constrain slidable movement, rotational movement, or both. A second latching button  187  may be located distal the first latching button  186 , and may be configured to constrain the movement of the access cannula relative to the third dilator tube, as described in more detail below. The distal end of the handle assembly  183  includes an overhanging lip  191  into which the proximal grip  136  of the access cannula can be removably received. When the proximal grip  136  of the access cannula is received within the overhanging lip  191 , the locking pin  1103  slides within the locking pinhole  1104  on the proximal grip  136  of the access cannula, thereby restricting rotational movement of the access cannula relative to the third dilator tube. In various embodiments, the locking pinhole may be omitted, permitting rotation of the access cannula  130  relative to the third dilator tube  60 . 
       FIGS.  16 A to  16 C  illustrate an embodiment of the access cannula  130 , which can be configured to be introduced over the third dilator tube  145 . The access cannula  130  has a distal portion  132 , a fourth longitudinal axis  134 , and a fourth longitudinal lumen  131  having a fourth inner radius  135 . The access cannula  130  may be configured to removably receive the third dilator tube (not shown) for slidable movement within the third lumen. A handle  136  allows for rotation of the access cannula  130 . 
       FIG.  16 B  shows an enlarged detail view of the distal portion of the access cannula of  FIG.  16 A . The distal portion  132  can have a generally semi-annular cross-section. In the embodiment shown, the fourth longitudinal lumen may be centered with respect to the outer radius of the access cannula, in contrast to the second and third dilator tubes. In other embodiments, however, the access cannula may also have a longitudinal lumen that is off-center with respect to the outer radius. In yet another embodiment, the access cannula need not be limited to a cylindrical outer surface. The outer surface could, for instance, have an elliptical, polygonal, or other cross-sectional shape. 
       FIG.  16 C  shows an enlarged detail view of the proximal portion  193  of the access cannula of  FIG.  16 A . The proximal grip  136  may provide additional leverage while advancing the access cannula over the third dilator tube. The proximal grip  136  includes a larger diameter portion  198  and a smaller diameter portion  199 . The smaller diameter portion  199  includes a circumferential channel  1107  for use in interlocking with the third dilator tube, as discussed in detail below. A locking pinhole  1104  can receive the locking pin  1103  on the third dilator tube, thereby restraining rotational movement of the access cannula  160  relative to the third dilator tube  145 . 
       FIGS.  17 A to  17 C  illustrate one embodiment of the dilation introducer  1100  in an assembled configuration. As shown, the access cannula  130  can be positioned over the third dilator tube  160 , which can be positioned over the second dilator tube  145 , which in turn can be positioned over the first dilator tube  140 . The handle assembly  183  of the third dilator tube may be in a locked configuration with the proximal grip  136  of the access cannula can be locked together to constrain slidable movement, but allow for the access cannula  130  to rotate with respect to the third dilator tube  160 . Additionally, the second dilator tube  145  may be locked together with the third dilator tube to constrain slidable movement, while still allowing the second dilator tube  145  to rotate with respect to the third dilator tube. Alternatively, the second dilator tube may be in a locked configuration preventing both slidable and rotational movement with respect to the third dilator tube  145 . The third dilator tube  60  can be advanced distally until the distal portion  161  of the third dilator tube aligns with the distal portion  46  of the second dilator tube. Further, the access cannula  130  may also be advanced so that the distal portion  32  aligns with the distal portions  146 ,  161  of the second and third dilator tubes. The second and third dilator tubes  145 ,  160  each have cutting flutes  151 ,  167  on their respective distal portions  146 ,  161 . As can be seen, the first, second, and third longitudinal axes  144 ,  149 ,  163  are each laterally offset from one another. 
     In certain embodiments, the first, second and third dilator tubes  140 ,  145 ,  160  along with the access cannula  130  can be provided with additional stops that engage the proximal grip  136  of the access cannula and the handle assembly  183  of the third dilator tube described above. For example, in one embodiment, notches or detents can be provided that engage the proximal grip  136  or handle assembly  183  when one tube is advanced distally and reaches a specific location (e.g., end point). In this manner, forward movement of a tube or cannula can be limited once the tube or cannula is advanced to a desired location 
       FIG.  17 B  shows an enlarged detail view of the distal portion of the dilation introducer of  FIG.  17 A . The distal portions  146 ,  161 ,  132  of each of the second and third dilator tubes  145 ,  160 , and of the access cannula  130  may have generally semi annular cross-sections. The distal portions  146 ,  161  of the second and third dilator tubes  145 ,  160  in the illustrated embodiment can have flattened edges  179 ,  185  to prevent penetration into the intervertebral disc as each dilator tube is advanced. 
       FIG.  17 C  shows an enlarged detail view of the proximal portion of the dilation introducer of  FIG.  17 A . The proximal grip  136  of the access cannula  130  is shown in a locked configuration with the handle assembly  183  of the third dilator tube  160 . The smaller diameter portion (not shown) may be received within the overhanging lip  191  on the distal end of the handle assembly  183 . Latching buttons  186 ,  187  constrain movement of the third dilator tube relative to the second dilator tube, and of the access cannula relative to the third dilator tube, respectively. The gripping portion  175  of proximal head  173  of the first dilator tube  140  is visible at the proximal end of the dilation introducer. As shown, the first dilator tube may be fastened to the handle assembly  183  by means of the threaded portion  174  (not shown) on the proximal head  173  and the threaded receiving portion  190  (not shown) of the handle assembly  183 . As shown, this fastening constrains both rotational and slidable movement of the first dilator tube relative to the third dilator tube. In various embodiments, the first dilator tube may be affixed to the handle assembly  183  by other means that allow for free rotational movement, free slidable movement, or both. 
     Referring to  FIGS.  18 A and  18 B , a dilation introducer  1100  is shown in a locked assembled configuration. The dilation introducer  1100  includes a first dilator tube  140 , a second dilator tube  145 , a third dilator tube  160 , and an access cannula  130 . The first dilator tube has a distal portion  141  with a tapered tip  171 , and a proximal portion  172  having a proximal head  173 . In various embodiments, the first dilator tube  140  may be cannulated, for example to allow passage of a guide wire down the longitudinal axis  143  of the first dilator tube  140 , or the first dilator tube may be without a lumen and uncannulated. The second dilator tube  145  has a distal tip  180  with a flattened edge  179 , a proximal portion  177  with a collar  178 , and a longitudinal lumen  148 . The first dilator tube  140  may be removably received within the second dilator tube  145 . 
     The third dilator tube  160  has a distal tip  184  with a flattened edge  185 , a proximal portion  182  with a handle assembly  183 , and a longitudinal lumen  164 . The second dilator tube  145  may be removably received in the longitudinal lumen  164  of the third dilator tube  160  for slidable movement within the third dilator tube  160 . The threaded portion  174  of the proximal head  173  of the first dilator tube engages with the interior threaded receiving portion  190  of the handle assembly  183  of the third dilator tube  160 . With the proximal head of the first dilator tube affixed to the handle assembly  183 , the first and third dilator tubes  140 ,  160  may be locked together for length and rotation. The second and third dilator tubes may be connected together in a locked configuration with a first latching button  186  disposed on the handle assembly  183  of the third dilator tube  160  and extending through a first aperture  1105  in the handle assembly  183  of the third dilator tube  160 , so that the first latching button  186  may be moveable between a radially inward locking position (arrow  1101 ) and a radially outward unlocking position (arrow  1102 ). 
     The distal end  196  of the first latching button may be removably received in aperture  181  of the second dilator tube  145  so as to engage and lock the second and third dilators together in the locking position. Alternatively, the latching button may be received in a circumferentially oriented groove of the second dilator tube, which may or may not extend completely around the second dilator tube. The first latching button  186  may be pulled radially outwardly to release the second dilator tube  145 , to allow the third dilator tube  160  to slide with respect to the second dilator tube  145 . 
     The access cannula  130  has a distal portion  161 , a proximal portion  193 , a proximal grip  136 , and longitudinal lumen  164 . The third dilator tube  145  may be removably received within the access cannula  130  for slidable movement within the longitudinal lumen  131  of the access cannula  130 . The third dilator tube  145  and the access cannula  130  also have a locked configuration in which the access cannula  130  may be not permitted to slidably telescope over the third dilator tube  145 . 
     The proximal portion  193  of the access cannula  130  includes a proximal grip  136  with a larger diameter portion  198  and a smaller diameter portion  199 . The smaller diameter portion  199  may be sized to fit under an overhanging lip  191  of the third dilator tube, when the longitudinal axes of the third dilator tube and access cannula may be aligned. There may be a circumferentially oriented channel  1107  in the exterior of the smaller diameter portion  919  for receiving a distal end  197  of a second latching button  187 . The circumferentially oriented channel  1107  does not need to extend completely around the exterior of the smaller diameter portion  199 . 
     The third dilator tube  145  and the access cannula  130  may be connected together in a locked configuration with the second latching button  187  disposed on the overhanging lip  191  of the handle assembly  183  of the third dilator tube  145 . The second latching button extends through an aperture  1106  in the overhanging lip  191  of the handle assembly  183  and may be movable between a radially inward locking position (arrow  194 ) and a radially outward unlocking position (arrow  195 ). The distal end  197  of the second latching button  187  may be removably received in the channel  107  located in the smaller diameter portion  199  of the access cannula  130 , in the locking position, to lock the third dilator tube  45  and the access cannula  130  in the locked assembled configuration. The second latching button  187  may be pulled radially outward to release the access cannula  130  to slide to the unlocked configuration. Furthermore, the second and third dilator tubes  140 ,  145  may be removed together as a unit from the access cannula  130 . In other words, the first dilator tube  140  and second dilator tube  145  can be kept locked together and can be removed from the access cannula  130  by unlocking the second latching button  187  alone. An advantage of this embodiment is that the latching buttons  186 ,  187  may be both removable from the surgical field with the release of the third dilator tube from the access cannula  130 . 
     The access cannula being free of protuberances, such as the latching buttons, is less likely to catch surgical sponges and sutures, for example, on the dilation introducer. 
     Dilation Introducer With Neuro-Monitoring 
       FIGS.  19 A to  19 D  show another aspect of a dilation introducer, in which the first dilator tube may be replaced with a neuro-monitoring needle  1108 . The neuro-monitoring needle  1108  includes a wire  1109  which may be enclosed by a needle cannula  1110 , with the wire  1109  exposed at the distal tip  1111 . The needle cannula  1110  may be surrounded by dielectric coating  1112  along its length for insulation. A knob  1115  may be located on the proximal portion  1116  of the neuro-monitoring needle  1108 . A first neuro-monitoring lead  1113  may be attached to the proximal portion  177  of the second dilator tube  145 . A second neuro-monitoring lead  1114  may be attached to the proximal portion  183  of the third dilator tube  160 . 
     The wire  1109  may comprise a conductive material, such as silver, copper, gold, aluminum, platinum, stainless steel, etc. A constant current may be applied to the wire  1109 . the needle cannula  1110  may be insulated by dielectric coating  1112 . Although the coating shown here is dielectric, any sufficiently insulative coating may be used. Alternatively, an insulative sleeve may encase the wire. This arrangement protects the conductive wire  1109  at all points except the most distal tip  1111 . As the exposed tip of the wire  1109  is advanced through the tissue, it continues to be supplied with current. When the tip  1111  approaches a nerve, the nerve may be stimulated. The degree of stimulation to the nerve is related to the distance between the distal tip  1111  and the nerve. Stimulation of the nerve may be measured by, e.g., visually observing the patient’s leg for movement, or by measuring muscle activity through electromyography (EMG) or various other known techniques. 
     Utilizing this configuration may provide the operator with added guidance as to the positioning of the first dilator tube to the surgical access point and through Kambin’s triangle. With each movement, the operator may be alerted when the tip of the first dilator tube approaches or comes into contact with a nerve. The operator may use this technique alone or in conjunction with other positioning assistance techniques such as fluoroscopy and tactile feedback. The amount of current applied to the wire  1109  may be varied depending on the preferred sensitivity. Naturally, the greater the current supplied, the greater nerve stimulation will result at a given distance from the nerve. In various embodiments the current applied to the conductive wire  1109  may not be constant, but rather periodic or irregular. Alternatively, pulses of current may be provided only on demand from the operator. 
     Although not shown here, a similar configuration may be applied to the second and third dilator tubes, and to the access cannula. Each may include a conductive wire embedded within the tube, or it may be separately attached. In either configuration, a distal tip of conductive wire may be exposed and the wire may be provided with current. As the dilator tube or access cannula is advanced through the tissue and towards the access site, nerve stimulation may be monitored as described above. The current supplied to each of the first, second, and third dilator tubes and to the access cannula may be controlled independently, so that when nerve stimulation is observed, the operator may supply current separately to each wire to determine which wire or wires are nearest to the nerve. Alternatively, current may be supplied only to one wire at any given point in the procedure. For example, the current may be supplied to the wire associated with the dilator tube or access cannula that is being moved at that point in the operation. 
     Although the method as described above utilizes an embodiment of the dilation introducer as shown in  FIGS.  3 - 7 B , it will be understood that the procedure may be adapted for use with various other embodiments of the dilation introducer. For instance, the dilation introducer with alternative handle assembly, as shown in  FIGS.  13 A- 18 C , may be used with appropriate modifications to the method described above. For instance, as the proximal head  173  of the first dilator tube  140  may be screwed into the handle assembly  183  of the third dilator tube  160 , the first dilator tube  140  must be unscrewed and removed prior to advancing the third dilator tube over the second dilator tube. Additionally, the latching buttons  186 ,  187  of the handle assembly  183  may be used to control the locking and unlocking of the dilator tubes relative to one another. 
     Alternatively, the dilation introducer equipped with neuro-monitoring, as shown in  FIGS.  19 A-D , may be substituted. The method performed may be then similar to that described above, except that in addition the method involves monitoring nerve stimulation to assist with placement and guidance of the dilator tubes and access cannula. As described above, the current supplied to the conductive wires may be varied and controlled in order to determine the optimal location for the dilation introducer and/or access cannula. 
     Implant 
     With respect to the implant  80  described above, the implant  80  can comprise any of a variety of types of interbody devices configured to be placed between vertebral bodies. The implant  80  can be formed from a metal (e.g., titanium) or a non-metal material such as plastics, PEEK™, polymers, and rubbers. Further, the implant components can be made of combinations of non metal materials (e.g., PEEK™, polymers) and metals. The implant  80  can be configured with a fixed or substantially fixed height, length and width as shown, for example, in the embodiment of  FIG.  12   . In other embodiments, the implant can be configured to be expandable along one or more directions. For example, in certain embodiments the height of the implant can be expanded once the device advanced through the access cannula and positioned between vertebral bodies (e.g., within the disc space within the annulus). 
     Additional detail of one embodiment of such an expandable implant can be found in  FIG.  20 A- 30   . As shown, in  FIGS.  20 A-B , in the illustrated embodiments, the implant  200  can be configured such that proximal and distal wedge members  206 ,  208  are interlinked with upper and lower body portions  202 ,  204 . The upper and lower body portions  202 ,  204  can include slots (slot  220  is shown in  FIG.  20 A , and slots  220 ,  222  are shown in  FIG.  20 B ; the configuration of such an embodiment of the upper and lower body portions  202 ,  204  is also shown in  FIGS.  20 A- 21 B , discussed below). In such an embodiment, the proximal and distal wedge members  206 ,  208  can include at least one guide member (an upper guide member  230  of the proximal wedge member  206  is shown in  FIG.  20 A  and an upper guide member  232  of the distal wedge member  208  is shown in  FIG.  22   ) that at least partially extends into a respective slot of the upper and lower body portions. The arrangement of the slots and the guide members can enhance the structural stability and alignment of the implant  200 . 
     In addition, it is contemplated that some embodiments of the implant  200  can be configured such that the upper and lower body portions  202 ,  204  each include side portions (shown as upper side portion  240  of the upper body portion  202  and lower side portion  242  of the lower body portion  204 ) that project therefrom and facilitate the alignment, interconnection, and stability of the components of the implant  200 .  FIG.  20 B  is a perspective view of the implant  200  wherein the implant  200  is in the expanded state. The upper and lower side portions  240 ,  242  can be configured to have complementary structures that enable the upper and lower body portions  202 ,  204  to move in a vertical direction. Further, the complementary structures can ensure that the proximal ends of the upper and lower body portions  202 ,  204  generally maintain spacing equal to that of the distal ends of the upper and lower body portions  202 ,  204 . The complementary structures are discussed further below with regard to  FIG.  21 - 25 B . 
     Furthermore, as described further below, the complementary structures can also include motion limiting portions that prevent expansion of the implant beyond a certain height. This feature can also tend to ensure that the implant is stable and does not disassemble during use. 
     In some embodiments, the actuator shaft  210  can facilitate expansion of the implant  200  through rotation, longitudinal contract of the pin, or other mechanisms. The actuator shaft  210  can include threads that threadably engage at least one of the proximal and distal wedge members  206 ,  208 . The actuator shaft  210  can also facilitate expansion through longitudinal contraction of the actuator shaft as proximal and distal collars disposed on inner and outer sleeves move closer to each other to in turn move the proximal and distal wedge members closer together. It is contemplated that in other embodiments, at least a portion of the actuator shaft can be axially fixed relative to one of the proximal and distal wedge members  206 ,  208  with the actuator shaft being operative to move the other one of the proximal and distal wedge members  206 ,  208  via rotational movement or longitudinal contraction of the pin. 
     Further, in embodiments wherein the actuator shaft  210  is threaded, it is contemplated that the actuator shaft  210  can be configured to bring the proximal and distal wedge members closer together at different rates. In such embodiments, the implant  200  could be expanded to a V-configuration or wedged shape. For example, the actuator shaft  210  can comprise a variable pitch thread that causes longitudinal advancement of the distal and proximal wedge members at different rates. The advancement of one of the wedge members at a faster rate than the other could cause one end of the implant to expand more rapidly and therefore have a different height that the other end. Such a configuration can be advantageous depending on the intervertebral geometry and circumstantial needs. 
     In other embodiments, the implant  200  can be configured to include anti-torque structures  250 . The anti-torque structures  250  can interact with at least a portion of a deployment tool during deployment of the implant to ensure that the implant maintains its desired orientation (see  FIGS.  29 - 30    and related discussion). For example, when the implant  200  is being deployed and a rotational force is exerted on the actuator shaft  210 , the anti-torque structures  250  can be engaged by a non-rotating structure of the deployment tool to maintain the rotational orientation of the implant  200  while the actuator shaft  210  is rotated. The anti-torque structures  250  can comprise one or more inwardly extending holes or indentations on the proximal wedge member  206 , which are shown as a pair of holes in  FIGS.  20 A-B . However, the anti-torque structures  250  can also comprise one or more outwardly extending structures. 
     According to yet other embodiments, the implant  200  can be configured to include one or more apertures  252  to facilitate osseointegration of the implant  200  within the intervertebral space. As mentioned above, the implant  200  may contain one or more bioactive substances, such as antibiotics, chemotherapeutic substances, angiogenic growth factors, substances for accelerating the healing of the wound, growth hormones, antithrombogenic agents, bone growth accelerators or agents, and the like. Indeed, various biologics can be used with the implant  200  and can be inserted into the disc space or inserted along with the implant  200 . The apertures  252  can facilitate circulation and bone growth throughout the intervertebral space and through the implant  200 . In such implementations, the apertures  252  can thereby allow bone growth through the implant  200  and integration of the implant  200  with the surrounding materials. 
       FIG.  21    is a bottom view of the implant  200  shown in  FIG.  20 A . As shown therein, the implant  200  can comprise one or more protrusions  260  on a bottom surface  262  of the lower body portion  204 . Although not shown in this Figure, the upper body portion  204  can also define atop surface having one or more protrusions thereon. The protrusions  260  can allow the implant  200  to engage the adjacent vertebrae when the implant  200  is expanded to ensure that the implant  200  maintains a desired position in the intervertebral space. 
     The protrusions  260  can be configured in various patterns. As shown, the protrusions  260  can be formed from grooves extending widthwise along the bottom surface  262  of the implant  200  (also shown extending from a top surface  264  of the upper body portion  202  of the implant  200 ). The protrusions  260  can become increasingly narrow and pointed toward their apex. However, it is contemplated that the protrusions  260  can be one or more raised points, cross-wise ridges, or the like. 
       FIG.  21    also illustrates a bottom view of the profile of an embodiment of the upper side portion  240  and the profile of the lower side portion  242 . As mentioned above, the upper and lower side portions  240 ,  242  can each include complementary structures to facilitate the alignment, interconnection, and stability of the components of the implant  200 .  FIG.  17    also shows that in some embodiments, having a pair of each of upper and lower side portions  240 ,  242  can ensure that the upper and lower body portions  202 ,  204  do not translate relative to each other, thus further ensuring the stability of the implant  200 . 
     As illustrated in  FIG.  21   , the upper side portion  240  can comprise a groove  266  and the lower side portion can comprise a rib  268  configured to generally mate with the groove  266 . The groove  266  and rib  268  can ensure that the axial position of the upper body portion  202  is maintained generally constant relative to the lower body portion  204 . Further, in this embodiment, the grooves  266  and rib  268  can also ensure that the proximal ends of the upper and lower body portions  202 ,  204  generally maintain spacing equal to that of the distal ends of the upper and lower body portions  202 ,  204 . This configuration is also illustratively shown in  FIG.  18   . 
     Referring again to  FIG.  21   , the implant  200  is illustrated in the unexpanded state with each of the respective slots  222  of the lower body portion  204  and lower guide members  270 ,  272  of the respective ones of the proximal and distal wedge members  206 ,  208 . In some embodiments, as shown in  FIGS.  20 - 21 A and  23 - 25 B , the slots and guide members can be configured to incorporate a generally dovetail shape. Thus, once a given guide member is slid into engagement with a slot, the guide member can only slide longitudinally within the slot and not vertically from the slot. This arrangement can ensure that the proximal and distal wedge members  206 ,  208  are securely engaged with the upper and lower body portions  202 ,  204 . 
     Furthermore, in  FIG.  22   , a side view of the embodiment of the implant  200  in the expanded state illustrates the angular relationship of the proximal and distal wedge members  206 ,  208  and the upper and lower body portions  202 ,  204 . As mentioned above, the dovetail shape of the slots and guide members ensures that for each given slot and guide member, a given wedge member is generally interlocked with the give slot to only provide one degree of freedom of movement of the guide member, and thus the wedge member, in the longitudinal direction of the given slot. 
     Accordingly, in such an embodiment, the wedge members  206 ,  208  may not be separable from the implant when the implant  200  is in the unexpanded state (as shown in  FIG.  20   ) due to the geometric constraints of the angular orientation of the slots and guide members with the actuator shaft inhibiting longitudinal relative movement of the wedge members  206 ,  208  relative to the upper and lower body portions  202 ,  204 . Such a configuration ensures that the implant  200  is stable and structurally sound when in the unexpanded state or during expansion thereof, thus facilitating insertion and deployment of the implant  200 . 
     Such an embodiment of the implant  200  can therefore be assembled by placing or engaging the wedge members  206 ,  208  with the actuator shaft  210 , moving the wedge members  206 ,  208  axially together, and inserting the upper guide members  230 ,  232  into the slots  220  of the upper body portion  202  and the lower guide members  270 ,  272  into the slots  222  of the lower body portion  204 . The wedge members  206 ,  208  can then be moved apart, which movement can cause the guide members and slots to engage and bring the upper and lower body portions toward each other. The implant  200  can then be prepared for insertion and deployment by reducing the implant  200  to the unexpanded state. 
     During assembly of the implant  200 , the upper and lower body portions  202 ,  204  can be configured to snap together to limit expansion of the implant  200 . For example, the upper and lower side portions  240 ,  242  can comprise upper and lower motion-limiting structures  280 ,  282 , as shown in the cross-sectional view of  FIG.  23   . After the wedge members  206 ,  208  are engaged with the upper and lower body portions  202 ,  204  and axially separated to bring the upper and lower body portions  202 ,  204  together, the upper motion-limiting structure  280  can engage the lower motion-limiting structure  282 . This engagement can occur due to deflection of at least one of the upper and lower side portions  240 ,  242 . However, the motion-limiting structures  280 ,  282  preferably comprise interlocking lips or shoulders to engage one another when the implant  200  has reached maximum expansion. Accordingly, after the wedge members  206 ,  208  are assembled with the upper and lower body portions  202 ,  204 , these components can be securely interconnected to thereby form a stable implant  200 . 
     Referring again to  FIG.  22   , the implant  200  can define generally convex top and bottom surfaces  264 ,  262 . In modified embodiments, the shape can be modified 
       FIGS.  24 A-B  illustrate perspective views of the lower body portion  204  of the implant  200 , according to an embodiment. These Figures provide additional clarity as to the configuration of the slots  222 , the lower side portions  242 , and the lower motion-limiting members  282  of the lower body portion  204 . Similarly,  FIGS.  25 A-B  illustrate perspective views of the upper body portion  202  of the implant  200 , according to an embodiment. These Figures provide additional clarity as to the configuration of the slots  220 , the upper side portions  240 , and the upper motion-limiting members  280  of the upper body portion  202 . Additionally, the upper and lower body portions  202 ,  204  can also define a central receptacle  290  wherein the actuator shaft can be received. Further, as mentioned above, the upper and lower body portions  202 ,  204  can define one or more apertures  252  to facilitate osseointegration. 
       FIG.  26    is a perspective view of an actuator shaft  210  of the implant  200  shown in  FIG.  20   . In this embodiment, the actuator shaft  210  can be a single, continuous component having threads  294  disposed thereon for engaging the proximal and distal wedge members  206 ,  208 . The threads can be configured to be left hand threads at a distal end of the actuator shaft  210  and right hand threads at a proximal other end of the actuator shaft for engaging the respective ones of the distal and proximal wedge members  208 ,  206 . Accordingly, upon rotation of the actuator shaft  210 , the wedge members  206 ,  208  can be caused to move toward or away from each other to facilitate expansion or contraction of the implant  200 . Further, as noted above, although this embodiment is described and illustrated as having the actuator shaft  210  with threads  294 . 
     In accordance with an embodiment, the actuator shaft  210  can also comprise a tool engagement section  296  and a proximal engagement section  298 . The tool engagement section  296  can be configured as a to be engaged by a tool, as described further below. The tool engagement section  296  can be shaped as a polygon, such as a hex shape. As shown, the tool engagement section  296  is star shaped and includes six points, which configuration tends to facilitate the transfer of torque to the actuator shaft  210  from the tool. Other shapes and configurations can also be used. 
     Furthermore, the proximal engagement section  298  of the actuator shaft  210  can comprise a threaded aperture. The threaded aperture can be used to engage a portion of the tool for temporarily connecting the tool to the implant  200 . It is also contemplated that the proximal engagement section  298  can also engage with the tool via a snap or press fit. 
       FIGS.  27 A-B  illustrate perspective views of the proximal wedge member  206  of the implant  200 . As described above, the proximal wedge member can include one or more anti-torque structures  250 . Further, the guide members  230 ,  270  are also illustrated. The proximal wedge member  206  can comprise a central aperture  300  wherethrough an actuator shaft can be received. When actuator shaft  210  is used in an embodiment, the central aperture  300  can be threaded to correspond to the threads  294  of the actuator shaft  210 . In other embodiments, the actuator shaft can engage other portions of the wedge member  206  for causing expansion or contraction thereof 
       FIGS.  28 A-B  illustrate perspective views of the distal wedge member  208  of the implant  200 . As similarly discussed above with respect to the proximal wedge member  206 , the guide members  232 ,  272  and a central aperture  302  of the proximal wedge member  206  are illustrated. The central aperture  302  can be configured to receive an actuator shaft therethrough. When actuator shaft  210  is used in an embodiment, the central aperture  302  can be threaded to correspond to the threads  294  of the actuator shaft  210 . In other embodiments, the actuator shaft can engage other portions of the wedge member  208  for causing expansion or contraction thereof 
     Referring now to  FIG.  29   , there is illustrated a perspective view of a deployment tool  400  according to another embodiment. The tool  400  can comprise a handle section  402  and a distal engagement section  404 . The handle portion  402  can be configured to be held by a user and can comprise various features to facilitate implantation and deployment of the implant. 
     According to an embodiment, the handle section  402  can comprise a fixed portion  410 , and one or more rotatable portions, such as the rotatable deployment portion  412  and the rotatable tethering portion  414 . In such an embodiment, the tethering portion  414  can be used to attach the implant to the tool  400  prior to insertion and deployment. The deployment portion  412  can be used to actuate the implant and rotate the actuator shaft thereof for expanding the implant. Then, after the implant is expanded and properly placed, the tethering portion  414  can again be used to untether or decouple the implant from the tool  400 . 
     Further, the distal engagement section  404  can comprise a fixed portion  420 , an anti-torque component  422 , a tethering rod (element  424  shown in  FIG.  30   ), and a shaft actuator rod (element  426  shown in  FIG.  26   ) to facilitate engagement with and actuation of the implant  200 . The anti-torque component  422  can be coupled to the fixed portion  420 . As described above with reference to  FIGS.  20 A-B , in an embodiment, the implant  200  can comprise one or more anti-torque structures  250 . The anti-torque component  422  can comprise one or more protrusions that engage the anti-torque structures  250  to prevent movement of the implant  200  when a rotational force is applied to the actuator shaft  210  via the tool  400 . As illustrated, the anti-torque component  422  can comprise a pair of pins that extend from a distal end of the tool  400 . However, it is contemplated that the implant  200  and tool  400  can be variously configured such that the anti-torque structures  250  and the anti-torque component  422  interconnect to prevent a torque being transferred to the implant  200 . The generation of the rotational force will be explained in greater detail below with reference to  FIG.  30   , which is a side-cross sectional view of the tool  400  illustrating the interrelationship of the components of the handle section  402  and the distal engagement section  404 . 
     For example, as illustrated in  FIG.  30   , the fixed portion  410  of the handle section  402  can be interconnected with the fixed portion  420  of the distal engagement section  404 . The distal engagement section  404  can be configured with the deployment portion  412  being coupled with the shaft actuator rod  426  and the tethering portion  414  being coupled with the tethering rod  424 . Although these portions can be coupled to each other respectively, they can move independently of each other and independently of the fixed portions. Thus, while holding the fixed portion  410  of the handle section  402 , the deployment portion  412  and the tethering portion  414  can be moved to selectively expand or contract the implant or to attach the implant to the tool, respectively. In the illustrated embodiment, these portions  412 ,  414  can be rotated to cause rotation of an actuator shaft  210  of an implant  200  engaged with the tool  400 . 
     As shown in  FIG.  30   , the tether rod  424  can comprise a distal engagement member  430  being configured to engage a proximal end of the actuator shaft  210  of the implant  200  for rotating the actuator shaft  210  to thereby expand the implant from an unexpanded state to an expanded state. The tether rod  424  can be configured with the distal engagement member  430  being a threaded distal section of the rod  424  that can be threadably coupled to an interior threaded portion of the actuator shaft  210 . 
     In some embodiments, the tool  400  can be prepared for a single-use and can be packaged with an implant preloaded onto the tool  400 . This arrangement can facilitate the use of the implant and also provide a sterile implant and tool for an operation. Thus, the tool  400  can be disposable after use in deploying the implant. 
     Referring again to  FIG.  29   , an embodiment of the tool  400  can also comprise an expansion indicator gauge  440  and a reset button  450 . The expansion indicator gauge  440  can be configured to provide a visual indication corresponding to the expansion of the implant  200 . For example, the gauge  440  can illustrate an exact height of the implant  200  as it is expanded or the amount of expansion. As shown in  FIG.  30   , the tool  400  can comprise a centrally disposed slider element  452  that can be in threaded engagement with a thread component  454  coupled to the deployment portion  412 . 
     In an embodiment, the slider element  452  and an internal cavity  456  of the tool can be configured such that the slider element  452  is provided only translational movement in the longitudinal direction of the tool  400 . Accordingly, as the deployment portion  412  is rotated, the thread component  454  is also rotated. In such an embodiment, as the thread component  454  rotates and is in engagement with the slider component  452 , the slider element  452  can be incrementally moved from an initial position within the cavity  456  in response to the rotation of the deployment portion  412 . An indicator  458  can thus be longitudinally moved and viewed to allow the gauge  440  to visually indicate the expansion and/or height of the implant  200 . In such an embodiment, the gauge  440  can comprises a transparent window through which the indicator  458  on the slider element  452  can be seen. In the illustrated embodiment, the indicator  458  can be a marking on an exterior surface of the slider element  452 . 
     In embodiments where the tool  400  can be reused, the reset button  450  can be utilized to zero out the gauge  440  to a pre-expansion setting. In such an embodiment, the slider element  452  can be spring-loaded, as shown with the spring  460  in  FIG.  30   . The reset button  450  can disengage the slider element  452  and the thread component  454  to allow the slider element  452  to be forced back to the initial position. 
     Additional details and embodiments of an expandable implant can be found in U.S. Pat. Application No 2008/0140207, filed Dec. 7, 2007 as U.S. Pat. Application No. 11/952,900, the entirety of which is hereby incorporated by reference herein. Bone Rasp 
     Another example of a surgical tool for use through the access cannula is a bone rasp. One embodiment of such an bone rasp can be found in  FIG.  31   . As shown in this figure, a rasp tool  800  can be configured to be inserted through the access cannula  30  into the intervertebral disc space. The rasping tool  800  can then be used to abrade or file the inferior surface of the superior vertebrae and/or the superior surface of the inferior vertebrae. The rasping tool  800  may comprise an elongated body  810  and a scraping component  812 . A handle  816  may be proximally attached to the elongated body  810 . As shown, the rasping tool  800  includes an open sleeve  808  within which the elongate body  810  is slidably received. This configuration may permit the elongated body  810  and scraping component  812  to slide relative to the open sleeve  808 . 
     The entire assembly, including the elongate body  810 , open sleeve  808 , and scraping component  812  are dimensioned such that the rasping tool  800  can slide longitudinally within the access cannula  30 . In use, the rasp tool  800  may be inserted through the access cannula until it reaches the intervertebral disc space. Using the handle  716 , a physician may slide the elongate body  810  and scraping component  812  backward and forward, while the open sleeve  808  remains stationary relative to the access cannula  30 . In other embodiments, the open sleeve  808  is omitted, and the elongate body  810  is inserted directly into the access cannula  30 , and is dimensioned to slidably move within it. In certain embodiments, the elongate body  808  may freely rotate within the open sleeve  808 , or within the access cannula  30 , in order to permit the physician to rasp a surface at any desired angle. In other embodiments, the orientation of the elongate body  808  may be fixed, such that rasping is only permitted along a predetermined angle relative to the access cannula. 
     In certain embodiments, the rasping tool may be expandable. As shown in  FIG.  32   , a rasp tool  800  can be configured to define an unexpanded configuration shown in  FIG.  32   . When the tool  800  is initially inserted into the working sleeve, the tool  800  can be positioned in the unexpanded configuration. After the tool  800  is advanced into the intervertebral disc, the tool  800  can be expanded to the expanded configuration. 
     In the embodiment illustrated in  FIG.  32   , the tool  800  can comprise an elongated body  810  and one or more scraping components  812 ,  814 .  FIG.  32    illustrates a longitudinal view of the tool  800 . As illustrated, the scraping components  812 ,  814  can each comprise an outer surface that is configured to scrape or create friction against the disc. For example, the outer surfaces can be generally arcuate and provide an abrasive force when in contact with the interior portion of the disc. In particular, it is contemplated that once the tool  800  is expanded, the scraping components  812 ,  814  can rasp or scrape against the vertebral end plates of the disc from within an interior cavity formed in the disc. In this manner, the tool  800  can prepare the surfaces of the interior of the disc by removing any additional gelatinous nucleus material, as well as smoothing out the general contours of the interior surfaces of the disc. The rasping may thereby prepare the vertebral endplates for fit with the implant as well as to promote bony fusion between the vertebrae and the implant. Due to the preparation of the interior surfaces of the disc, the placement and deployment of the implant will tend to be more effective. 
     It is contemplated that the tool  800  can comprise an expansion mechanism that allows the scraping components  812 ,  814  to move from the unexpanded to the expanded configuration. For example, the tool  800  can be configured such that the scraping components  812 ,  814  expand from an outer dimension or height of approximately 9 mm to approximately 13 mm. In this regard, the expansion mechanism can be configured similarly to the expansion mechanisms of the implants disclosed herein, the disclosure for which is incorporated here and will not be repeated. 
     Further, it is contemplated that the scraping components  812 ,  814  can comprise one or more surface structures, such as spikes, blades, apertures, etc. that allow the scraping components  812 ,  814  to not only provide an abrasive force, but that also allowed the scraping components  812 ,  814  to remove material from the disc. In this regard, as in any of the implementations of the method, a cleaning tool can be used to remove loosened, scraped, or dislodged disc material. Accordingly, in various embodiments of the methods disclosed herein, and embodiment of the tool  800  can be used to prepare the implant site (the interior cavity of the disc) to optimize the engagement of the implant with the surfaces of the interior of the disc (the vertebral end plates). 
     After the implant site has been prepared, the implant can be advanced through the second working sleeve into the disc cavity. Once positioned, the implant can be expanded to its expanded configuration. For example, the implant can be expanded from approximately 9 mm to approximately 12.5 mm. The surgeon can adjust the height and position of the implant as required. Additionally, other materials or implants can then be installed prior to the removal of the second working sleeve and closure of the implant site. 
     Graft Delivery Device 
     With reference now to  FIGS.  33 A to  34 D , a bone graft delivery device is disclosed which may be inserted through the access cannula for use in the intervertebral space. For example, the bone graft material can be inserted into the intervertebral disc space in order to promote rapid fixation between the adjacent vertebrae. The bone graft material may be inserted before insertion of an intervertebral implant. Alternatively, the bone graft material may be inserted following insertion of the intervertebral implant. In some implementations, bone graft material is delivered both prior to and following insertion of the intervertebral implant. Bone graft material may be autologous, allograft, xenograft, or synthetic. In addition to bone graft material, other materials may be introduced to the treatment site, as desired. For example, bone morphogenetic proteins may be introduced with a carrier medium, such as a collagen, through use of the disclosed delivery device. 
       FIGS.  33 A and  33 B  show a plunger assembly  900 . The plunger assembly  900  includes an elongate shaft  902 . In some embodiments, the shaft  902  is substantially rigid. The plunger assembly  900  includes a distal tip  906 , which is connected to the elongate shaft  902  by a flexible member  904 . A plunger knob  908  is positioned at the proximal end of the plunger assembly  900 . 
       FIGS.  34 A-D  show a funnel assembly  910 . The funnel assembly  910  includes a bent shaft  912 . The bent shaft  912  may be substantially straight along the majority of its length, with a bend positioned nearer the distal portion of the bent shaft  912 . In other embodiments, a plurality of bends may be included in the bent shaft  912 . The particular orientation of the bend may be adjusted to provide for improved access to the intervertebral disc space when the funnel assembly is inserted through the access cannula. A receptacle  914  is located at the proximal end of the funnel assembly  910 . 
     The bent shaft  912  includes a central lumen  916  which runs from the opening of the receptacle at the proximal end to the distal opening of the funnel assembly  910 . The plunger assembly  900  is configured to be slidably received within the funnel assembly  910 . Accordingly, the dimensions of the distal tip  906 , flexible member  904  and the elongate shaft  902  are such that they may slide into the opening at the receptacle  914  of the funnel assembly  910 . As the plunger assembly  900  is advanced through the lumen  916  of the funnel assembly  910 , the distal tip  906  may reach the bent portion of the bent shaft  912 . Due to the pliable nature of flexible member  904 , the distal tip  906  may be advanced along lumen  916  through the curve in bent shaft  912 . The plunger knob  908  may be configured to be mated with the receptacle  914 , such that when the plunger assembly  900  is fully advanced into the funnel assembly  910 , the plunger knob  908  contacts the receptacle  914 . As shown, the receptacle  914  has a hollow conical shape, with the plunger knob  908  having a corresponding conical surface. The shapes of both the receptacle  914  and plunger knob  908  may be varied, and need not be limited to conical shapes, nor even to corresponding shapes. Slot  918  is an opening on the outer surface of bent shaft  912 , and may be positioned near the distal end of the funnel assembly  910 . The slot  918  may provide for an additional aperture through which bone graft material may flow during injection to the treatment site, as described in more detail below. 
     In use, bone graft material is introduced into the lumen  916  of the funnel assembly  910 . The bone graft material may either be introduced through the receptacle  914  at the proximal end, or it may be back-filled by inserting the bone graft material through the opening in the distal end of the funnel assembly  910 . Upon insertion of the plunger assembly  900  into the funnel assembly  910 , the distal tip  906  pushes the bone graft material along the length of the bent shaft  912  and eventually out of the funnel assembly  910 . 
     It should also be noted that bone chips and/or autograft must be made into pieces small enough to flow through the funnel assembly  910 . Otherwise, the funnel assembly  910  may become congested and the bone graft may not flow into the target site as desired. 
     Once the bone graft material is loaded into the funnel assembly, the bone graft material can be deployed at the target site. The funnel assembly can be inserted into the access cannula until the distal tip of the funnel assembly is positioned adjacent to the target site. The location of the distal tip of the funnel instrument can be modified to any desired location for deploying the graft material at the target site. Due to the bend in the funnel assembly  910 , the device may be rotated within the access cannula in order to achieve different angles of approach. The bend may therefore provide for improved access to different regions of the intervertebral disc space. Then, inserting the plunger assembly  900  through the funnel assembly  910 , a desired amount of graft material can be injected at the target site. In certain embodiments, the funnel assembly  910  and plunger assembly  900  can each be placed over a k-wire. The plunger assembly  900  can then be advanced into the funnel assembly  910  to deploy the graft into the disc. 
     As the bone graft material flows through the lumen  916  of funnel assembly  910 , it passes slot  918  near the distal end of the bent tube  912 . In some embodiments, the opening of slot  918  is smaller than the opening of lumen  916 , such that, absent backpressure, bone graft material preferentially exits the funnel assembly  910  through the distal opening of lumen  916 . As the target site is filled with bone graft material, however, it may become increasingly difficult to advance the plunger assembly  900  and introduce new bone graft material through the lumen  916 . In the event that such resistance is present, some of the bone graft material may be forced through slot  918 , thereby providing an alternate distribution route for the bone graft material. In certain embodiments, a plurality of slots  918  may be provided around the circumference of bent shaft  912 . The position of slot  918  may be varied depending on the desired distribution of bone graft material at the treatment site. As discussed above, the funnel assembly  910  may be rotated within the access cannula, allowing for bone graft material exiting the slot  918  to be deposited in various locations at the treatment site. 
     Although the embodiments shown herein depict a dilation introducer with three dilator tubes and one access cannula, other variations are possible. For instance, as noted above, a dilation introducer may include only two dilator tubes and an access cannula. In another embodiment, a dilation introducer may include four or more dilator tubes and an access cannula. In a modified arrangement, the access cannula would be replaced by a dilator tube, wherein the dilator tube with cutting flutes would remain in place, with the inner dilator tubes removed to provide access for surgical tools. The skilled artisan will readily ascertain that many variations of this sort are possible without departing from the scope of the present invention. 
     The specific dimensions of any of the embodiment disclosed herein can be readily varied depending upon the intended application, as will be apparent to those of skill in the art in view of the disclosure herein. Moreover, although the present inventions have been described in terms of certain preferred embodiments, other embodiments of the inventions including variations in the number of parts, dimensions, configuration and materials will be apparent to those of skill in the art in view of the disclosure herein. In addition, all features discussed in connection with any one embodiment herein can be readily adapted for use in other embodiments herein to form various combinations and sub-combinations. The use of different terms or reference numerals for similar features in different embodiments does not imply differences other than those which may be expressly set forth. Accordingly, the present inventions are intended to be described solely by reference to the appended claims, and not limited to the preferred embodiments disclosed herein.