Abstract:
A cannula assembly and related methods of use. The cannula assembly includes a cannula and a stylet. The cannula has an outer surface that is non-circular. Rotation of the cannula about its longitudinal axis changes the orientation of the cannula&#39;s larger outer dimension so that the cannula may be used as a distraction tool. Rotation is effected by rotating a stylet handle, which rotates the associated stylet shaft, which in turn rotates the cannula. Related methods include rotating a handle of the stylet, while the shaft of the stylet is disposed in the bore of the cannula, about the first longitudinal axis so as to rotate the cannula about the longitudinal axis to distract vertebral bodies.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to medical devices and procedures for providing access, including percutaneous access, to a desired location in a body. 
         [0002]    Cannulas are frequently employed to provide access to, or to deliver medical implants to, a desired location in a patient. For example, cannulas may be used to provide access to a vertebra, an intervertebral disc, or other area of the spine, to perform a variety of different medical procedures, such as percutaneous delivery of a spinal implant. Typically, such cannulas are round in cross-section, both internally and externally. While some such cannulas have tapered sections, they are not ideal for use as distracting instruments because they require longitudinal displacement toward the spine in order to provide distraction force, which can be problematic. Thus, while cannulas are widely used in spinal surgery, particularly percutaneous spinal surgeries, there remains a need for alternative designs, particularly alternative designs that are better suited for use as distraction instruments. 
       Summary 
       [0003]    The present invention provides a cannula assembly and related method(s) of use, where the cannula has an outer surface that is non-circular. Rotation of the cannula about its longitudinal axis changes the orientation of the cannula&#39;s larger outer dimension so that the cannula may be used as a distraction tool. Rotation is effected by rotating a stylet handle, which rotates the associated stylet shaft, which in turn rotates the cannula. 
         [0004]    In some embodiments, the present invention relates to a method of inserting an implant into a space between adjacent vertebral bodies. The method may comprise inserting a guidewire to a space between adjacent vertebral bodies; thereafter, sliding a cannula assembly over the guidewire so that a distal tip of the cannula assembly extends into the space between the adjacent vertebral bodies. The cannula assembly may comprise a hollow elongate cannula and a stylet. The cannula extends along a first longitudinal axis from a proximal end to a distal end. The cannula has a generally uniform first bore therethrough with a first cross-sectional profile normal to the longitudinal axis that is non-circular. The cannula also has an outer surface having a second non-circular cross-sectional profile with a major dimension along a major axis and a minor dimension along a minor axis. The outer surface may be substantially uniform throughout the cannula&#39;s length. The stylet is sized and configured so that a portion thereof fits in the first bore of the cannula, with the stylet having a handle external to the first bore. The sliding comprises sliding the cannula assembly over the guidewire such that the minor axis of the cannula is generally parallel to the sagittal plane defined by the vertebral bodies and the major axis is generally parallel to the axial plane defined by the vertebral bodies. The method further comprises thereafter, rotating the stylet handle about the first longitudinal axis so as to rotate the cannula about the longitudinal axis to distract the vertebral bodies while the stylet is disposed in the first bore. Thereafter, the stylet is removed. The method continues with thereafter delivering a spinal implant to the space between adjacent vertebral bodies via the cannula while the cannula is oriented such that the major axis of the cannula is generally parallel to the sagittal plane defined by the vertebral bodies and the minor axis is generally parallel to the axial plane defined by the vertebral bodies. The guidewire may be removed prior to or after delivery of the implant. The cannula assembly may remain disposed over the guidewire during the rotating of the handle, which may be an approximately 90° rotation. The second cross-sectional profile associated with the cannula outer surface may comprise opposed flat sections disposed on opposing sides of the major axis and connected via curved sections that extend a generally uniform distance from the first longitudinal axis. 
         [0005]    In some embodiments, the present invention provides a cannula assembly comprising: a hollow elongate cannula extending along a first longitudinal axis from a proximal end to a distal end. The cannula has a generally uniform first bore therethrough with a cross-sectional profile normal to the longitudinal axis that is non-circular. The cannula has an outer surface that is non-circular when viewed normal to the longitudinal axis. The cannula assembly further comprises a stylet extending into the first bore and comprising an elongate shaft and a handle. The elongate shaft of the stylet extends along a shaft axis from a proximal end to a distal end thereof. The handle is mounted to the proximal end of the stylet shaft and extends generally normal to the shaft axis. The stylet shaft has a non-circular cross-section corresponding to the cross-section of the cannula bore and substantially fills the cannula bore in cross-section. The stylet may advantageously have a tapered distal end. The stylet may further comprise a second longitudinal bore extending therethrough; the second longitudinal bore coaxial with the first bore of the cannula. The cannula outer surface has a second cross-sectional profile which may comprise opposed flat sections connected via curved sections that extend a generally uniform distance from the first longitudinal axis. The stylet is advantageously longer than the cannula, although this is not required. 
         [0006]    In various embodiments, the present invention has one or more of the above attributes, alone or in any combination. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows a spinal motion segment as one exemplary location where the present invention has application. 
           [0008]      FIG. 2  shows a cannula assembly according to one embodiment of the present invention. 
           [0009]      FIG. 3  shows a partially exploded view of the cannula assembly of  FIG. 2 . 
           [0010]      FIG. 4  shows a cross section at IV-IV of the cannula of  FIG. 3 . 
           [0011]      FIG. 5  shows a cross section at V-V of the cannula assembly of  FIG. 2  with the guidewire omitted for clarity. 
           [0012]      FIG. 6  shows a guidewire extending to the disc space through the Kambin triangle. 
           [0013]      FIG. 7  shows a cannula assembly being slid over the guidewire of  FIG. 6 . 
           [0014]      FIG. 8  shows the cannula assembly of  FIG. 6  after rotation. 
           [0015]      FIG. 9  shows insertion of a spinal implant into the cannula of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    In one embodiment, the present invention is directed to a cannula assembly  40  and/or method of using a cannula assembly  40  during spinal surgery. In order to provide illustrative context, the following discussion will focus primarily on use of the invention for spinal surgery in the lumbar region of the spine, but it should be understood that the invention may alternatively or additionally be used in other regions of the spine.  FIG. 1  depicts adjacent vertebrae  10 , 14  of the lumbar region of a human spinal column. Each vertebrae  10 , 14  comprises a corresponding vertebral body  11 , 15 , a superior articular process, a transverse process, an inferior articular process, and a spinous process. In addition, between vertebral bodies  11 , 15  is a space  18  normally occupied by an intervertebral disc and bounded by the endplates  12 ,  16  of the vertebral bodies. Due to various conditions, such as a collapsed disc, it may be desired to place an implant in the disc space  18  in order to provide proper structural continuity between the vertebral bodies  11 , 15 . The cannula assembly  40  of the present invention provides a convenient means for delivery of the implant to the desired location. 
         [0017]    The cannula assembly  40  of  FIGS. 2-3  includes a cannula  50  and a stylet  80 . The cannula  50  is a hollow elongated body that extends along a longitudinal axis  51  from a proximal end section  52  to a distal end section  54 . A distal edge  55  lies at the distal most portion of the distal end section  54 . The overall longitudinal length of the cannula  50  is C. A bore  60  extends entirely through the cannula  50  and is advantageously concentric with the exterior surface  70  and substantially uniform throughout its length. The bore  60  is non-circular in cross section. That is, the perimeter  62  of the bore  60  has a profile, normal to axis  51 , that is non-circular. Advantageously, the perimeter profile is partially round, with two flat sections  64  disposed opposite each other and connected by two curved sections  66 . The curved sections  66  advantageously are portions of a circle centered on the bore&#39;s axis  61 , which is collinear with the axis  51  of cannula  50 . Likewise, the outer surface  70  of the cannula  50  is non-circular in cross section, advantageously along its entire length, but at least through the entire distal end section  54 . That is, the profile of the cannula outer surface perimeter  72 , normal to axis  51 , is non-circular. Advantageously, the profile is partially round, with two flat sections  74  disposed opposite each other and connected by two curved sections  76 . Due to the flats  74 , the major axis  77  of the cannula cross section extends through the curved sections  76  and parallel to the flats  74 , while the minor axis  75  of the cannula cross section extends through the flat sections  74  and perpendicular to the major axis  77 . The curved sections  76  advantageously are portions of a circle centered on the bore&#39;s axis  61 . Thus, the cannula  50  advantageously has a generally constant wall thickness T, although such is not required in all embodiments. 
         [0018]    The stylet  80  includes a handle  82  and an elongated shaft  90 . The shaft  90  is designed to slide in the bore  60  of the cannula  50 , and extends along a shaft axis  91  from proximal section  92  to a distal section  94 . The distal section  94  advantageously includes a tip section  95  that tapers in the distal direction. The length of the shaft is S, which is longer than the length C of the cannula  50 . The shaft  90  advantageously includes a shaft bore  98  extending entirely therethrough. The outer surface  100  of the shaft  90  is non-circular and corresponds to the shape of the cannula bore  60 . Thus, the shaft outer surface  100  advantageously has a cross sectional profile with two flat sections  104  on opposing sides and connected by curved sections  106 . The minor axis  107  of the shaft extends through flat sections  104 , while the major axis  109  of the shaft extends through the curved sections  106 . When disposed in the cannula  50 , the shaft  90  advantageously substantially fills the cannula bore  60 , such that the outer surface  100  of the shaft  90  and the inner surface of the cannula bore  60  are for practical purposes in contact along the entire perimeter  62  and along the entire length of the bore  60  with a sliding fit. The handle  82  is mounted to the proximal section  92  of the shaft  90 , and extends generally perpendicular to the shaft axis  91 . The handle  82  may extend in one or advantageously both directions away from the shaft  90 . Any suitable method may be used to join the handle  82  to the shaft  90 , such as by adhesives, including suitable ears on the shaft  90  that are captured by the handle  82 , spline connections, or the like. If desired, a portion of the proximal section  92  of shaft  90  may be enlarged for better mating with handle  82 . Further, if desired, a shoulder may be formed at the edge of such enlargement so that a positive stop is formed to prevent over-insertion of the stylet  80  into the cannula  50 . 
         [0019]    The components of the cannula assembly  40  may be made from any suitable materials known in the art. Just by way of example, the cannula  50  and stylet shaft  90  may be made from stainless steel, while the handle  82  may be made from suitable plastics known in the art. 
         [0020]    As mentioned above, the cannula assembly  40  may be employed to help install a spinal implant  20 . One such spinal implant  20  includes a first vertebra engaging portion  22  moveably coupled to a second vertebra engaging portion  24 . Movement of an actuator  26  causes the implant  20  to move from a collapsed configuration to an expanded configuration, by moving the first and second vertebra engaging portions  24 , 26  away from each other so as to increase the effective height of the implant  20 . For additional information about such type of implants, see U.S. Patent Application Publication Nos. 2009/0198337 and 2006/0206207, and/or U.S. Pat. No. 7,217,293. Of course, other implants  20  may be delivered via the cannula assembly  40 , the particular details of which are unimportant to understanding the present invention. Indeed, while expandable implants  20  are believed advantageous, non-expandable implants  20  may alternatively or additionally be employed. 
         [0021]    The cannula assembly  40  may be used to help position a spinal implant  20  in the disc space  18  between the adjacent vertebrae  10 , 14 . One illustrative method of doing so includes preparing the surgical site in a conventional fashion, and then inserting a guidewire  30  into the disc space  18 , with the outer end of guidewire  30  being outside the patient&#39;s body. A posterior-lateral approach may be used. The guidewire  30  is advantageously routed to the disc space  18  via the Kambin triangle defined by the corresponding traversing and exiting nerves. The cannula assembly  40  is slid over the guidewire  30  by running the guidewire  30  through the bore  98  of the stylet  80  and moving the cannula assembly  40  toward the disc space  18 . The stylet  80  extends distally from the cannula  50 , so the tapered tip  95  of the stylet  80  leads the cannula assembly  40 . The transition from the stylet  80  to the cannula  50  is minimized by the tapered edge  55  of the cannula  50 , which may be similar to that described in U.S. Patent Application Publication No. 2007/0260184. During this sliding on the guidewire  30 , the cannula  50  is oriented so that flats  74  on the cannula outer surface  70  are parallel to the planes endplates  12 , 16  of the vertebral bodies  11 , 15 . Thus, the cannula  50  is inserted into the disc space  18  in its “vertically thinner” orientation. The surgeon then grips the handle  82  and rotates the stylet  80  about the shaft axis  91 . Because the stylet  80  and the cannula bore  60  are non-circular, this causes the cannula  50  to rotate about its axis  51 . Preferably, the rotation is approximately, or exactly, 90° so that the midpoints of the curved sections  76  of the cannula outer surface  70  press against the endplates  12 , 16 . Because the curved sections  76  lie along the major axis  77 , and are therefore farther apart than the flat sections  74 , the vertebral bodies  11 , 15  are distracted apart due to the rotation of the cannula  50 . Thus, the cannula  50  is inserted between the vertebral bodies  11 , 15  oriented so that the minor axis  75  is parallel to the sagittal plane, and rotated so that the major axis  77  is parallel to the sagittal plane, thereby increasing its effective height for separating the vertebral bodies  11 , 15 . 
         [0022]    The stylet  80 , and optionally the guidewire  30 , are then removed, leaving the cannula  50  in place. The implant  20  is then inserted into the proximal end  52  of the cannula  50 , moved along the cannula bore  60 , and pushed out the distal end  54  of the cannula  50  into the disc space  18 . A push rod may be used for this displacement of the implant  20 , and/or a suitable actuation instrument may be used. An actuator instrument may then be used, if appropriate, to further increase the height of the implant  20  by moving its first and second vertebral engaging portions  22 , 24  apart. The cannula  50  is then removed, and the surgical procedure continues as is conventional. If desired, multiple cannula assemblies  40  may be used to install corresponding multiple implants  20  into the same disc space  18 , and/or into multiple disc spaces  18 . 
         [0023]    The discussions above have been in the context of using a guidewire  30  to guide the cannula assembly  40  into place. It should be understood that a “guidewire” may be a flexible or semi-flexible wire (metallic or otherwise), or a more rigid body like a rod. Further, while use of a guidewire  30  is advantageous, such is not strictly required for all embodiments. Further, the guidewire  30  may be removed either prior to or after rotation of the cannula  50 , as is desired. And, the discussion has assumed that the cannula assembly  40  is slid over the guidewire  30  as a unit. However, such is not required in all embodiments, and the stylet  80  and the cannula  50  may be slid over the guidewire  30 , or otherwise positioned prior to rotation, in any sequence or simultaneously. 
         [0024]    The cannula assembly  40  may alternatively be inserted with the major axis  77  of the cannula  50  parallel with the sagittal plane. For such a situation, distraction may be achieved by the tapered tip section  95  of stylet  80 , rather than by rotation of the cannula  50 . 
         [0025]    All U.S. patents and patent application publications mentioned above are hereby incorporated herein by reference in their entirety. 
         [0026]    The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.