Abstract:
In one preferred aspect, a method is provided for inserting an instrument set having a tapered configuration into a patient. In another preferred aspect, a method is provided for inserting a cannula having an external threaded portion into bone. In yet another preferred aspect, a method is provided for forming and enlarging an opening in bone.

Description:
RELATED APPLICATION  
       [0001]    This application is a divisional of U.S. application Ser. No. 11/412,341, filed Apr. 27, 2006, which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to a set of instruments having a distal tapered configuration for facilitating insertion of the instruments into a human body. 
         [0004]    2. Description of the Related Art 
         [0005]    Cannulas are used in surgical procedures to access tissue of the human body. To assist in the insertion of the cannula into the tissue, an instrument such as a stylet is inserted into the cannula to function as a guide for the cannula. Typically, the stylet has a diameter less than the diameter of the cannula, creating a stepped transition between the cannula distal end and the stylet. One problem encountered when using a conventional cannula and stylet is that the stepped transition between the cannula and stylet impairs the insertion of the instruments into the surrounding tissue because of the increased resistance encountered upon moving the stepped transition against the surrounding tissue. Therefore, there exists a need for an instrument set having a reduced surface profile in the transition between the distal end of the cannula and the inner instrument when the inner instrument extends from the distal end of the cannula so as to facilitate insertion of the instrument set into a patient and minimize disruption to the tissue of the patient. 
         [0006]    Another problem associated with conventional cannulated instrument sets is that the distal end of a stylet when inserted together with the cannula protrudes a distance from the distal end of the cannula that is insufficient to optimally guide the instrument set into the surgical site of a patient, or optimally penetrate the tissue. Therefore there exists a need for an instrument set that when used with a stylet, will provide the surgeon with increased guidance for inserting the instrument set into the surgical site of the patient while reducing the effort needed for the instrument set to penetrate the tissue. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention in one preferred embodiment includes a method for forming an opening in bone. The method includes providing a cannula having a distal end, a proximal end, a passage therethrough, and a mid-longitudinal axis, the distal end having an outer perimeter converging at an angle toward the mid-longitudinal axis of the cannula. The method further includes providing a stylet having a distal end, a proximal end, and a tapered transition portion proximate the distal end, the tapered transition portion having an angle approximating the converging angle of the outer perimeter of the distal end of the cannula, the stylet being sized and configured to be inserted into the passage of the cannula; placing the stylet into the cannula with at least a portion of the tapered transition portion and the distal end of the stylet extending beyond the distal end of the cannula, the cannula and the stylet forming a smooth transition between the angled portion of the stylet and the converging part of the cannula to facilitate introduction into bone; inserting the distal end of stylet into the bone; advancing into the bone the stylet and cannula together with the tapered transition portion of the stylet contacting the bone prior to the converging part of the cannula to form an opening into the bone, the opening having a reduced transverse dimension proximate the stylet and a larger transverse dimension proximate the cannula; and removing the stylet from the cannula with the cannula remaining in the bone. 
         [0008]    In another preferred embodiment, the present invention includes a method for forming an opening into bone. The method includes providing a cannula having a distal end, a proximal end, a length therebetween, a passage along the length, and an exterior surface, the exterior surface including a thread along at least a portion of the length of the cannula; inserting the cannula through the bone by linear insertion with the bone sliding over the thread with the thread not engaging the bone to a depth in the bone proximate to a final insertion depth; further advancing the cannula into the bone by rotating the cannula to engage the thread of the cannula to the bone until the cannula is at the final depth of insertion, the cannula being in fixed relationship to the bone. 
         [0009]    In a further preferred embodiment, the present invention includes a method for forming an opening in bone. The method includes inserting a stylet into a cannula, the cannula having a distal end, a proximal end, a passage therethrough, and a mid-longitudinal axis, the stylet having a distal end that extends beyond the distal end of the cannula when inserted therein; advancing into the bone the cannula and stylet in fixed relationship to each other along an axis of insertion to a first insertion depth at least in part into the bone to form an opening at a final insertion depth in the bone, the opening having a portion occupied by the stylet with a smaller transverse dimension than a portion of the opening occupied by the cannula; withdrawing the stylet from the cannula with the cannula remaining in the bone; and advancing the cannula further into the opening from the first insertion depth to a second insertion depth along the axis of insertion to enlarge at least a portion of the opening formed by the stylet. 
         [0010]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
         [0011]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a side elevation view of an instrument set having a cannula and stylet in accordance with one embodiment of the present invention. 
           [0013]      FIG. 2  is an enlarged partial side elevation view of a distal end of the instrument set of  FIG. 1  along line  2  of  FIG. 1 . 
           [0014]      FIG. 3  is a partial cross-sectional side view of the distal end of the cannula of  FIG. 1  with the stylet of  FIG. 1 . 
           [0015]      FIG. 4  is a partial side elevation view of the distal end of the stylet of  FIG. 1 . 
           [0016]      FIG. 5  is a partial side elevation view of the distal end of a stylet in accordance with another preferred embodiment of the present invention. 
           [0017]      FIG. 6  is a partial side elevation view of the stylet of  FIG. 5  rotated approximately 90 degrees. 
           [0018]      FIG. 7  is a partial side elevation view of a distal end of an instrument set having a cannula and stylet in accordance with another preferred embodiment of the present invention. 
           [0019]      FIG. 8  is a partial cross-sectional side view of the distal end of the cannula of  FIG. 7  and stylet of  FIG. 1 . 
           [0020]      FIG. 9  is a partial side elevation view of a distal end of an instrument set having a cannula and stylet in accordance with another preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
         [0022]      FIGS. 1-3  illustrate an instrument set in accordance with one preferred embodiment of the present invention. Preferably, the instrument set includes a cannula and a stylet insertable at least in part into the cannula, the cannula and stylet each having a generally matching tapered profile adapted to facilitate insertion of the instrument set into the tissue of a patient, preferably into the bone of a patient. It will be appreciated by those of ordinary skill in the art that the tapered profile of the instruments set forth below may be adapted for use with other sets having two or more instruments. 
         [0023]    As shown in  FIGS. 1-3 , cannula  100  is adapted to receive at least a portion of a stylet  200  therethrough. Cannula  100  includes a body  102 , and exterior surface  104 , a distal end  106 , and a passage  108  having an interior surface  110 . Cannula  100  also includes a window  112  proximate distal end  106 . Window  112  is preferably sized and configured to permit the passage of a portion an instrument such as a bone displacement instrument therethrough. 
         [0024]    Distal end  106  of cannula  100  includes an outer perimeter  114  having a distal edge  116  and may include a plurality of longitudinal serrations, grooves, or scallops  118 . Serrations  118  cut into bone similar to a serrated knife. Serrations  118  preserve the strength of distal end  106  because they permit the wall of cannula  100  to retain a thickness sufficient to ensure that the distal end remains rigid while at the same time facilitates the insertion of cannula  100  into the surrounding tissue and bone. As shown in  FIGS. 2 and 3 , outer perimeter  114  is preferably tapered relative to the mid-longitudinal axis of cannula  100 . The tapered portion of distal end  106  preferably includes two angled portions  120  and  122 , but may include only one larger angled portion. The first angled portion  120  is preferably at an angle A relative to the mid-longitudinal axis of cannula  100 . A preferred range for angle A is between 0 to 30 degrees relative to the mid-longitudinal axis of cannula  100 . The second angled portion  122  is preferably at an angle B relative to the mid-longitudinal axis of cannula  100 . A preferred range for angle B is between 0 to 30 degrees relative to the mid-longitudinal axis of cannula  100 . Together, angled portions  120 ,  122  form a tapered profile generally in the range of 5 to 45 degrees, more preferably 10 to 45 degrees, and most preferably 15 degrees relative to the mid-longitudinal axis of cannula  100 . It will be appreciated by those of ordinary skill in the art that outer perimeter  114  may have a single, continuous taper to distal edge  116 , or more than two angled portions. It will be further appreciated that outer perimeter  114  may be curved in a plane parallel with the mid-longitudinal axis of the cannula so as to approximate the shape of a spherical or elongated dome. 
         [0025]    As shown in  FIGS. 2-4 , stylet  200  includes a shaft  202  and a distal end  204 . Shaft  202  includes a proximal portion  206 , a transition portion  208 , and a distal portion  210  having a bevel  212  at distal end  204 . Portion  210  preferably has a reduced dimension to facilitate introduction into the tissue in a manner similar to that of a guide wire. As shown in  FIG. 4 , transition  208  is a tapered portion of shaft  202  that converges distally toward the mid-longitudinal axis of stylet  200  to provide a transition from a larger dimension of proximal portion  206  to a smaller dimension of distal portion  210  of shaft  202 . The intersection of transition  208  and proximal portion  206  defines a proximal longitudinal limit  207  of transition  208 . The intersection of transition  208  and distal portion  210  defines a distal longitudinal limit  209  of transition  208 . Preferably, transition  208  is at an angle C relative to the mid-longitudinal axis of stylet  200 . Angle C is preferably in the range of 5 to 45 degrees, more preferably 10 to 45 degrees, and most preferably 14 degrees relative to the mid-longitudinal axis of stylet  200 . 
         [0026]    As shown in  FIG. 3 , passage  108  of cannula  100  has a reduced portion proximate distal end  106  of cannula  100  that is sized and configured to have a transverse cross sectional dimension less than the transverse cross sectional dimension of proximal portion  206  of stylet  200 . The reduced portion of passage  108  prevents stylet  200  from extending more than a predetermined distance beyond distal edge  116  of cannula  100  by preventing the larger dimension of proximal portion  206  of shaft  202  to pass therethrough. Preferably, angle C of transition  208  of stylet  200  is at an angle that is between angles A and B of cannula  100 . It will be appreciated by those of ordinary skill in the art that the angles of distal end  106  of cannula  100  and of transition  208  of stylet  200  may be varied without departing from the scope of the present invention. 
         [0027]    When assembled together, the angle of the over-all tapered profiled of outer perimeter  114  and the angle of transition  208  are each preferably within 15 degrees of each other, more preferably within 5 degrees of each other, and most preferably the same or approximately the same angle. Additionally, when fully assembled together, distal edge  116  of cannula  100  is adjacent transition  208  preferably between proximal and distal longitudinal limits  207 ,  209  of transition  208 , both longitudinally and along the radial height of transition  208 . Preferably, distal edge  116  is closer to distal longitudinal limit  209  of transition  208  more than proximal longitudinal limit  207  of transition  208 . It will be appreciated that distal edge  116  may extend before or after the longitudinal limits of transition  208  when the cannula and stylet are assembled to present a smooth transition without departing from the scope of the present invention. 
         [0028]    Referring to  FIGS. 1-3 , in a preferred method for inserting an instrument set such as described above into a human patient, a surgeon grasps the handle of stylet  200  (shown in  FIG. 1 ) and places stylet  200  into cannula  100  with at least a portion of transition  208  and distal end  204  of stylet  200  extending beyond distal end  104  of cannula  100 . If desired, the handles of the instruments may be configured to lock to one another. The surgeon then inserts distal end  204  of stylet  200  into the tissue such as the bone of the patient and continues advancing stylet  200 , along with cannula  100 , into the bone to form an opening into the bone. If desired, cannula  100  may be moved relative to stylet  200  and further advanced into the bone using stylet  200  as a guide wire. Stylet  200  may be withdrawn either partially or completely from cannula  100  with cannula  100  remaining in the bone. Cannula  100  may be further advanced into the bone after the withdrawal of stylet  200  if desired. The instrument set is preferably inserted to a depth sufficient to permit a surgeon to access bone through window  112 . Once stylet  200  is withdrawn, the surgeon may insert other instruments through cannula  100 , such as an instrument to displace bone through window  112 . Cannula  100  may also be used to introduce a material therethrough. Examples of materials include a flowable material such as bone cement; other therapeutic materials such as bone morphogenetic protein, hydroxyapatite, hydroxyapatite tricalcium phosphate, or an anti-microbial substance; or a relatively solid and/or artificial material such as an implant. 
         [0029]    The method is preferably performed in the spine of a human patient. It will be recognized that the instrument set and method of the present invention may be used in other areas of the human body. 
         [0030]    Cannula  100  and stylet  200  are made of a surgical grade material. Examples of suitable materials include, but are not limited to, metal such as stainless steel and titanium, nitinol, carbon composites, and a plastic polymer. It will be appreciated that cannula  100  and stylet  200  may be made of any combination of metal, plastic, carbon composite, nitinol, or other material suitable for the intended purpose. 
         [0031]    In a preferred embodiment of the present invention, cannula  100  has a maximum length along the mid-longitudinal axis of the cannula that is approximately 5.1 inches between the distal end and the handle. The thickness of the wall of the cannula is preferably approximately 0.015 inches. The maximum transverse dimension at distal end  106  of cannula  100  is preferably approximately 0.1 inches. The length of the tapered portion of distal end  106  is preferably generally 0.013 inches between the furthest distal extent of window  112  to distal edge  116 . It will be appreciated that the dimensions set forth above may be varied without departing from the scope of the present invention. 
         [0032]    Stylet  200  preferably has a length along the mid-longitudinal axis of approximately 6.1 inches between the handle and distal end  204 . As shown in  FIGS. 2 and 3 , distal portion  210  of stylet  200  preferably has a length from the tip of distal end  204  to transition  208  that is greater than the length of transition  208 , but less than the length of window  112  of cannula  100 . In a preferred embodiment, distal portion  210  of stylet  200  has a length of approximately 0.5 inches. It will be appreciated that the dimensions set forth above may be varied without departing from the scope of the present invention. 
         [0033]    Referring now to  FIGS. 5 and 6 , a stylet in accordance with another preferred embodiment of the present invention is shown and referred to by the reference number  300 . Stylet  300  is similar to stylet  200  except that distal end  304  includes a plurality of facets  312 ,  314 . It will be appreciated by those of ordinary skill in the art that the number and configuration of the facets may be varied without departing from the scope of the present invention. For example, as shown in  FIG. 6 , stylet  300  preferably includes a plurality of facets  312 ,  314  at an angle to each other. A third facet (not shown) extends on another side to form a tri-faceted configuration at distal end  304  of style  300 . 
         [0034]    Referring now to  FIGS. 7 and 8 , a cannula in accordance with another preferred embodiment of the present invention is shown and generally referred to by the reference number  400 . As shown in  FIG. 8 , a cannula  400  is similar to cannula  100  except that distal edge  416  of cannula  400  forms a sharp edge. Additionally, outer perimeter  414  has an angled portion at an angle D which is preferably in the range of 10 to 45 degrees relative to the mid-longitudinal axis of cannula  400 . Angle D has a steeper angle as compared to angle B shown in  FIG. 3 . The configuration shown in  FIG. 8  permits a smoother transition  426  between distal edge  416  of cannula  400  and transition  208  of stylet  200 . The nearly seamless transition  426  further facilitates insertion of the instrument set into the surrounding tissues of the patient at least in part due to the reduction of the surface profile of the leading end of the cannula. 
         [0035]    Referring now to  FIG. 9 , a cannula in accordance with another preferred embodiment of the present invention is shown and generally referred to by the reference number  500 . Cannula  500  is similar to cannula  100  except that body  502  includes a thread  528  proximate the distal end. Thread  528  is configured such that once the instrument set is partially inserted into the patient to a depth where thread  528  contacts bone, the surgeon may rotate cannula  500  about the mid-longitudinal axis and threadably secure cannula  500  to one or more bones of the patient. Thread  528  has a low profile thread height to allow cannula  500  to slide into tissue without significant engagement of the thread with the surrounding tissue. The furthest extent of thread  528  as measured along the mid-longitudinal axis of cannula  500  is preferably less than the maximum longitudinal extent of the tapered distal end portion of cannula  500 . It will be appreciated that thread  528  may be configured and placed along the length of cannula  500  in a manner sufficient for the intended purpose of cannula  500 . For example, as shown in  FIG. 5 , thread  528  is preferably configured to engage a pedicle of a vertebra of a human spine. 
         [0036]    A preferred method for using the instrument set shown in  FIG. 9  includes inserting by linear insertion the instrument set at least partially into the patient through a portion of bone and tissue; inserting the set to a depth until thread  528  contacts a portion of bone, such as a pedicle of a human spine; rotating cannula  500  about its mid-longitudinal axis to engage thread  528  within a portion of bone; and withdrawing stylet  200  from cannula  500 . Once the procedure has been completed through cannula  500 , cannula  500  is then rotated in the opposite direction of insertion to disengage cannula  500  from the bone of the patient. 
         [0037]    The tapered configuration of the instrument set of the present invention is applicable to a wide variety of instruments. For example and without limitation, cannula  100  could be a sheath, sleeve, retractor, or any other tubular or cannulated member. Instrument  200  could be a stylet, obdurator, trocar, bone tamp, forceps, or any other instrument insertable in a tube having a portion adapted to extend beyond the distal end of the tube. 
         [0038]    Advantages of the present invention include, for example, the ability of the user to more precisely place the instrument set within the patient. The tapered configuration of the present invention has the advantage of minimizing disruption of surrounding tissues and bone as the instrument set is being inserted into the patient. The tapered configuration of the cannula advantageously functions as a depth stop to the stylet to keep the distal end of the stylet from extending too far beyond the distal end of the cannula. An advantage of the longitudinal serrations at the distal end of the cannula is that the serrations facilitate insertion similar to a serrated knife to permit a more precise placement of the instrument set within the patient. An advantage of the thread shown in  FIG. 9  is that the surgeon is able to attach the cannula to the patient to provide a more stable base for subsequent use of instruments through the cannula. 
         [0039]    It will be appreciated by those of ordinary skill in the art that the present invention described above may take alternative forms without departing from the scope of the present invention. For example, distal portion  210  of shaft  202  of stylet  200  may be tapered along its length and may, if desired, have an angle substantially matching or precisely matching that of transition  208  to create an elongated taper. It will be appreciated that cannula  100  and stylet  200  need not have a circular cross section, but may have any other type of cross section suitable for the intended purpose. For example, the cross section of either instrument may be that of an elongated oval or other non-circular shape such as a square, or a shaft with a keel to prevent the inner instrument from rotating within the cannula. 
         [0040]    Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.