Abstract:
This invention relates to a surgical access instrument having a distal tip which facilitates introduction of the instrument into and through hard or dense tissue, but which facilitates removal of some or all of the instrument through the application of minimal withdrawal forces.

Description:
RELATED APPLICATION  
       [0001]    This application claims the benefit of U. S. provisional patent application Serial No. 60/283,990 filed Apr. 16, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention generally relates to hand-held tools and instruments and to procedures that deploy these instruments through tissue to access interior regions of the body.  
         BACKGROUND OF THE INVENTION  
         [0003]    There are many different types and styles of hand-held surgical instruments that physicians use to gain access into interior body regions. These instruments are intended to penetrate tissue by the application of pushing forces, twisting forces, or both in combination.  
           [0004]    Often, a single surgical procedure will require the physician to employ different surgical instruments, each possessing a different size, shape and function. The procedure will typically require the physician to deploy these instruments in both soft and hard tissue to meet the diagnostic or therapeutic objectives of the procedure. The physician will often need an enhanced mechanical advantage to advance an instrument through tissue, particularly through dense or hard tissue such as bone. Often, surgical hammers or mallets are often utilized to advance these instruments through such hard or dense tissues.  
           [0005]    Where surgery is conducted is the proximity of vital areas of the body, such as near the brain, other nerves, major veins or arteries, it is often preferred to make an initial approach using a very small diameter needle, such as a spinal needle. A stylet or guide wire may then be positioned to establish a safe access path to the surgical site, along which any number of larger surgical tools can be advanced. Such larger tools are typically cannulated so that the stylet or guide wire passes through a lumen in at least a portion of the larger surgical tools, desirably guiding the tool to the surgical site.  
           [0006]    Once access has been achieved and/or the surgical procedure has been completed, the surgical instruments are generally removed from the patient. Where the surgical tools were difficult to insert through dense or hard tissue, however, they will often be difficult to remove from this tissue as well. Various surgical instruments have been created to facilitate removal of “stuck” tools, some similar to claw-hammers or crowbars, which desirably give a physician a mechanical advantage, thereby increasing the physician&#39;s ability to withdraw the tool. Similarly, reverse-impacting devices or “slap-hammers” have been developed which use the momentum developed by a moving mass to increase the physician&#39;s ability to pull on surgical tools with increasing force. While these devices magnify the practitioner&#39;s strength, allowing surgical tools to be removed from such harder tissues, they do not address the underlying problem of reducing the tendency for such tissues to retain such instruments in the first place.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a surgical access instrument having a distal tip which facilitates introduction of the instrument into and through dense tissue, but which facilitates removal of some or all of the instrument through the application of minimal withdrawal forces.  
           [0008]    One aspect of the invention provides a tool comprising a first functional instrument and a second functional instrument. The first and second functional instruments engage to form a composite tool. The composite tool has a distal tip particularly suited for advancement and retraction from dense or hard tissue such as bone. In one embodiment, the distal tip is cannulated to allow the tool to be advanced along a stylet or guide wire into a targeted tissue region. In another embodiment, the distal tip is solid to allow the tool to cut through tissue.  
           [0009]    In a general embodiment of the present invention, the distal tip of the composite tool comprises a plurality of facet faces, which desirably present a non-continuous and/or non-uniform surface to the dense tissue through which the tool passes. During introduction of the tool, directly or along a stylet or guide wire, these faces facilitate separation of soft and hard tissue planes, desirably minimizing trauma to such tissues. In addition, as the instrument is withdrawn from the hard or dense tissue, the tendency for the distal tip to “stick” in the dense or hard tissue is minimized, thereby reducing the amount of force required to remove the tool from such tissues. By presenting a non-continuous surface to the dense tissue, the tip significantly reduces the amount of frictional and/or retention forces experienced by the tool, and significantly reduces the size and/or effect of the “locking zone” on the distal tip of the tool. The present invention further minimizes the surface area against which retention forces may act.  
           [0010]    Other objects, advantages and embodiments of the invention are set forth in part in the description that follows, and in part, will be obvious from this description, or may be learned from the practice of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective view of one embodiment of a composite tool constructed in accordance with the teachings of the present invention, separated into its component parts;  
         [0012]    [0012]FIG. 2 is a perspective view of the composite tool of FIG. 1;  
         [0013]    [0013]FIG. 3 is a front perspective view of the composite tool of FIG. 1;  
         [0014]    [0014]FIG. 4 is a side view of one embodiment of a trocar constructed in accordance with the teachings of the present invention;  
         [0015]    [0015]FIG. 5 is an end view of the trocar of FIG. 4, taken along line  5 - 5 ;  
         [0016]    [0016]FIG. 6 is a cross-sectional view of the trocar of FIGS. 4 and 5, taken along line  6 - 6 ;  
         [0017]    [0017]FIG. 7 is a cross-sectional view of the trocar of FIGS. 4 and 5, taken along line  7 - 7 .  
         [0018]    [0018]FIG. 8 is a side view of one embodiment of a trocar constructed in accordance with the teachings of the present invention.  
         [0019]    [0019]FIG. 9 is an end view of the trocar of FIG. 8. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]    The present invention overcomes the problems and disadvantages associated with current strategies and designs in insertion devices for use in accessing hard and/or dense tissues. In particular, the present invention describes insertion devices which may be used in treating various locations within human and/or animal bodies, such as the methods and instruments described in U.S. Pat. Nos. 4,969,888, 5,108,404, 5,827,289, 5,972,015, 6,048,346 and 6,066,154, each of which are incorporated herein by reference.  
         [0021]    [0021]FIG. 1 shows a composite instrument  10  for penetrating tissue. The composite instrument  10  includes a first functional instrument  20  and a second functional instrument  40 , and a composite handle  12  comprising a first handle  22  and a second handle  42 . The composite handle  12  aids a physician in manipulating the composite instrument  10 , but a physician can also desirably use the first handle  22  to independently manipulate the first instrument  20  or the second handle  42  to independently manipulate the second instrument  40  during use.  
         [0022]    The number and type of instruments  20  and  40  can vary. FIG. 1 shows two representative instruments  20  and  40 , each having a different size and function. In one embodiment, the first functional instrument  20  is a trocar instrument, and the second functional instrument  40  is a cannula instrument. The first instrument  20  functions as a trocar instrument to penetrate tissue. A trocar has a proximal end  32  and a distal end  34 . The distal end  34  is tapered to present a penetrating surface  35 . In use, the penetrating surface  35  is intended to penetrate soft tissue and/or hard, dense tissue in response to pushing and/or twisting forces applied by the physician at the first handle  22 , or the composite handle  12 .  
         [0023]    The first handle  22  is coupled to the trocar  30  at the proximal end of the trocar  32 . If desired, the proximal end of the trocar  30  could be formed in a T-shape (not shown), with the first handle  22  being molded around the T-shaped end. This arrangement would significantly increase the mechanical strength of the bond between the handle  22  and the trocar  30 , and allows significant longitudinal and torsional forces to be transmitted from the handle  22  to the trocar  30  without bond failure. Alternatively, with or without a T-shaped end, the proximal end  32  of the trocar  30  can be scored (not shown) to increase the mechanical strength of the bond between the trocar  30  and the handle  22 , or various bonding adhesives could be used, with varying results.  
         [0024]    In an alternate embodiment, the trocar  30  includes an interior lumen (not shown), which passes through the handle  22  and the body of the trocar  30 . The interior lumen accommodates the passage of a stylet and/or conventional spinal needle assembly, to guide the deployment of the first instrument  20 , by itself or nested with the second instrument  40 , through soft tissue to a targeted hard and/or dense tissue such as bone.  
         [0025]    The second instrument  40  functions as a cannula instrument or guide sheath, and includes a cannula  50 . The cannula  50  of the second instrument  40  is desirably somewhat larger in diameter than and not as long as the trocar  30  of the first instrument  20 . The second instrument  40  includes an interior lumen  44  that extends through the instrument from its distal end  54  to its proximal end  52 . The interior lumen  44  is sized to accept the trocar  30 . The size of the lumen  44  desirably allows each instrument to slide and/or rotate relative to the other when the handles are not engaged.  
         [0026]    The distal end  54  of the second instrument  40  presents an end surface  60 . In use, the end surface  60  of the second instrument  40  desirably presents a low-profile surface, which can penetrate soft tissue surrounding the first instrument  20  in response to pushing and/or twisting forces applied at the composite handle  12  or the second handle  42 .  
         [0027]    The proximal end  52  is coupled with the second handle  42 . If desired, the proximal end  52  of the cannula can be flared and/or notched (not shown), with the second handle  42  molded around the proximal end  52 . The flared and/or notched proximal end can increase the mechanical strength of the bond between the cannula  50  and the second handle  42 , allowing significant longitudinal and torsional forces to be transmitted between the second handle  42  and the cannula  50  without bond failure. As with the trocar  30 , however, alternative bonding methods such as scoring of the cannula  50  and/or the use of various adhesives could be employed, with varying results.  
         [0028]    The first handle  22  and the second handle  42  are designed to comfortably accommodate a hand, to desirably interlock to form a composite handle  12  that resists relative movement between the first and second instruments during introduction into and/or removal from hard or dense tissue. The first handle  22  desirably includes a receiving channel  26  with a latch mechanism  36  that engages a corresponding latch notch  56  on the second handle  42 . In one embodiment, the latch mechanism includes a latch finger  63  situated to engage the latch notch of the second handle  42 . The latch finger is carried on a hinge  62  in the first handle  22 . The hinge  62  is desirably made from resilient plastic material and possesses plastic memory, forming a flexible hinge.  
         [0029]    The latch finger  60  is cantilevered on the hinge  62  for pivoting movement within the first handle  22 . The plastic memory of the hinge  262  normally biases the finger  60  toward a normal position, in which the finger will rest within the notch  56 , providing that the two parts are in alignment. The latch finger  60  can be displaced out of its normal alignment in response to an applied force from the practitioner desiring to separate the two instruments.  
         [0030]    Once the composite tool is located within a desired position in the hard or dense tissue, the first instrument  20  can be removed from the second instrument  40 , such that the interior lumen  44  of the second instrument  40  provides an access passageway into and/or through the hard or dense tissue. Desirably, the practitioner will depress the latch finger  60 , which disengages the first handle from the second handle, and then the practitioner can withdraw the trocar  30  from the interior lumen  44 .  
         [0031]    Prior to such removal, the distal tip of the trocar  30  typically extends out of the distal tip of the cannula  50 , and is generally in contact with the dense or hard tissue. This tissue, which contacts the trocar  30 , will generally resist withdrawal of the trocar  30  into the interior lumen  44 . This resistance is created by various factors, one of which can be frictional forces induced by the tissue on the shaft/distal tip of the trocar. The surfaces of a smooth, rounded distal tip (such as shown in FIGS. 1 through 3) will often be held in a “self-locking” region of the hard or dense tissue, at which point the force required to withdraw the tip tends towards a maximum value. To withdraw the trocar  30  from this region of tissue, the practitioner will often have to exert considerable force, sometimes on the order of fifty or one-hundred (50 or 100) or more pounds of force. Moreover, because rotation of the cannula  50  is often undesirable at this point, and the first and second handles typically inhibit independent rotation during initial withdrawal of the trocar  30 , rotation of the trocar  30  is generally precluded, possibly rendering the required pullout forces to even greater amounts.  
         [0032]    The present invention significantly reduces the pullout forces necessary to remove a trocar from hard and/or dense tissue. FIG. 4 depicts one embodiment of a trocar  200  which incorporates a distal tip  210  constructed in accordance with the teachings of the present invention. Because many of the features of this trocar are similar to those previously described, like reference numerals will be used to denote similar components.  
         [0033]    The trocar  200  includes a shaft  205  and a distal tip  210 . A lumen  207  desirably extends through the central axis of the trocar  200 . The distal tip  210  incorporates a plurality of angled facets  225  which desirably provide a smooth transition from the distal tip  210  of the trocar  200  to the distal tip of the cannula  50  and, during advancement of the composite tool through soft and/or hard tissues, facilitate separation of tissue planes to minimize tissue trauma and permit advancement of the cannula through tissues. The facets  225  comprise rounded sections  230  and flat sections  235 , which in the disclosed embodiment are distributed symmetrically about the distal tip  210 . Of course, if desired these sections  230  and  235  could be distributed in various alternate arrangements, including non-symmetrically about the distal tip  210  of the instrument. In at least one alternate embodiment, a small section of the shaft  205  may also extend from the distal tip of the cannula.  
         [0034]    In this embodiment, as the trocar  200  is withdrawn from the cannula  50 , the hard or dense tissue will typically oppose removal of the instrument. Generally, forces opposing removal can comprise the frictional forces between the tissue and shaft  205  as well as frictional forces between the tissue and distal tip  210 . As the trocar  200  is first withdrawn, the distal tip  210  of the shaft  205  may be located within a “self locking” region of the tissue, in which the forces attempting to retain the tip tend towards a maximum value. This “self locking” region is generally dependent, at least in part, upon the geometry of the distal tip. By incorporating multiple facet faces, however, the non-uniform profile of the distal tip  210  desirably alters the size and/or effect of the “self locking” region, desirably reducing the magnitude of the force opposing withdrawal of the instrument. Moreover, in another embodiment, the trocar  200  is desirably sized such that, when mated with the cannula  50 , only the distal tip  210  of the trocar  200  extends from the distal tip  60  of the cannula  50 . Accordingly, during withdrawal of the trocar  200  from the cannula  50 , only the distal tip  210  of the trocar  200  encounters resistance from the hard or dense tissue, further reducing overall withdrawal forces. The cannula  50  may also be faceted to ease withdrawal of the tool.  
         [0035]    Alternatively, as shown in FIGS. 8 and 9, the trocar  200  includes a shaft  205  and a distal tip  210 . A lumen  207  desirably extends through the central axis of the trocar  200 . The distal tip  210  incorporates a single facet  240  which encircles the trocar  200 . The facet  240  is flat, and the sections  245  and  250  are rounded. The single facet face  240  desirably disrupts the size and/or effect of the “self locking” region, desirably reducing the magnitude of the force opposing withdrawal of the instrument.  
         [0036]    The instruments described herein may be comprised of a generally rigid material common in medical device applications, including, but not limited to, plastics, metals, ceramics or composite materials. In one embodiment, the instruments are comprised of stainless steel. While the disclosed devices and methods are more specifically described in the context of the treatment of human vertebrae, other human or animal bone types can be treated in the same or equivalent fashion. By way of example, and not by limitation, the present systems and methods could be used in any bone having bone marrow therein, including the radius, the humerus, the vertebrae, the femur, the tibia or the calcaneous.  
         [0037]    Other embodiments and uses of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. All documents referenced herein are specifically and entirely incorporated by reference. The specification and examples should be considered exemplary only, with the true scope and spirit of the invention being indicated by the following claims. As will be easily understood by those of ordinary skill in the art, variations and modifications of each of the disclosed embodiments, including combinations thereof, can be easily made within the scope of this invention as defined by the following claims.