Patent Publication Number: US-2005124914-A1

Title: Medical instrument

Description:
TECHNICAL FIELD  
      The invention relates to medical instruments, such as a biopsy needle instrument.  
     BACKGROUND  
      A biopsy needle instrument can be used to obtain a tissue specimen for microscopic examination, e.g., to determine malignancy, while preferably subjecting the patient to the least trauma. In some embodiments, such instruments can have of a long, thin probe, called a stylet, within a close-fitting hollow needle, called a cannula. The stylet has a notch into which tissue can prolapse when the stylet enters the tissue.  
      During use, a firing device first projects the stylet into tissue, followed immediately by the cannula. As the cannula slides over the stylet, the cannula severs tissue that has prolapsed into the notch of the stylet from the surrounding mass, and captures the prolapsed tissue as a specimen within the notch. The instrument can then be withdrawn and the piece of tissue removed from the stylet.  
     SUMMARY  
      The invention relates to medical instruments.  
      In one aspect, the invention features a medical instrument including a housing having a proximal end and a distal end; a stylet having a portion in the housing, the stylet being movable between a first extended position and a first retracted position, the stylet being configured to rotate when moved from the first retracted position to the first extended position; and a cannula coaxially receiving the stylet and having a portion in the housing, the cannula being movable between a second extended position and a second retracted position.  
      Embodiments may include one or more of the following features. The instrument includes a stylet block attached to a proximal end of the stylet and mounted inside the housing. The stylet block includes a first part inside the housing, the first part being moveable between an extended position and a retracted position; and a second part attached to the proximal end of the stylet, the second part being rotatably engaged with the first part and being able to rotate relative to an axis of the stylet. The instrument further includes a stylet spring capable of moving the stylet from the first retracted position to the first extended position; and a cannula spring capable of moving the cannula from the second retracted position to the second extended position. The instrument further includes a first pivoting latch capable of retaining the stylet in a predetermined position when the stylet is in the first retracted position; and a second pivoting latch capable of retaining the cannula in a predetermined position when the cannula is in the second retracted position.  
      The housing can include a semi-cylindrical portion defining a track configured to engage with the second part. The second part can include a projection in contact with a track associated with the housing, the projection and track capable of cooperating to axially rotate the second part and the attached stylet when the stylet is moved between the first extended position and the first retracted position. The track can be molded into the interior side of the housing. The track can be configured to provide unidirectional or multidirectional rotation to the stylet.  
      The stylet can include a notch with a sharpened leading edge. The stylet can include a notch having two openings and/or a ramped surface. The stylet can include an opening opposing the notch.  
      In another aspect, the invention features a method of using a medical instrument. The method includes moving a stylet from a first position to a second position; simultaneously rotating the stylet along an axis of the stylet; and moving a cannula over the stylet.  
      Embodiments may include one or more of the following features. The stylet is oscillated along the axis. The method further includes collecting a sample in a notch of the stylet. Removal of the sample from the notch is achieved by inserting an object through an opening located in the notch. The method further includes removing the sample over an inclined portion of the notch. The stylet is rotated in one direction or multiple directions.  
      Other aspects and features of the invention will be apparent from the description of the preferred embodiments thereof and from the claims. 
    
    
     DESCRIPTION OF DRAWINGS  
       FIGS. 1A and 1B  are schematic drawings of a medical instrument having a stylet and a cannula in their retracted positions and extended positions, respectively.  
       FIG. 2  is a perspective view of a stylet attached to a stylet block.  
       FIGS. 3A and 3B  are perspective views of the stylet and attached stylet block of  FIG. 2  with an associated portion of a housing including a track.  
       FIG. 4  is a schematic view of a track.  
       FIG. 5A  is a side view of a stylet notch;  FIG. 5B  is a cross-sectional view of the stylet notch of  FIG. 5A , taken along line  5 B- 5 B; and  FIG. 5C  is a cross-sectional view of another embodiment of a stylet notch.  
       FIG. 6A  is a side view of a stylet notch; and  FIG. 6B  is a cross-sectional view of the stylet notch of  FIG. 6A , taken along line  6 B- 6 B.  
       FIG. 7  is a side view of a stylet notch.  
       FIG. 8A  is a side view of a stylet notch; and  FIG. 8B  is a cross-sectional view of the notch of  FIG. 8A , taken along line  8 B- 8 B. 
    
    
     DETAILED DESCRIPTION  
      Referring to  FIGS. 1A and 1B , a medical instrument  10  (as shown, a needle biopsy device) includes a housing  12 , a stylet  18 , and a cannula  20  coaxially receiving the stylet. Housing  12  has a proximal end  14  and a distal end  16 . At its distal end  27 , stylet  18  is configured to penetrate tissue and includes a cupped notch  54  configured to cut and to collect a tissue sample. At its distal end  21 , cannula  20  is configured to sever tissue that has prolapsed into notch  54 . Both stylet  18  and cannula  20  have portions in housing  12  and can be moved between retracted positions as shown in  FIG. 1A  and extended positions as shown in  FIG. 1B . During use, stylet  18  and cannula  20  are loaded or cocked to their retracted positions, ready to be triggered. When stylet  18  and cannula  20  are triggered, they rapidly move distally to their extended positions, e.g., to collect a tissue specimen that has prolapsed into notch  54  of the stylet.  
      In particular, during use, stylet  18  is configured to rotate about its longitudinal axis  58  when moved from its retracted position to its extended position. The rotational motion of stylet  18  can enhance its cutting action, thereby enhancing the performance of instrument  10 . Referring to  FIGS. 2, 3A  and  3 B, at its proximal end  24 , stylet  18  is attached to a stylet block  22 . Stylet block  22  includes a first, outer part  26  and a second, inner part  28  (as shown, a generally tubular structure). Inner part  28  is connected to stylet  18  and can rotate within outer part  26 , about the longitudinal axis  58  of the stylet. More specifically, inner part  28  includes a projection or an arm  36  extending radially outward from the inner part and engaging with a track  38 . As shown in  FIGS. 3A and 3B , track  38  is an elongated channel defined in a curved, semi-cylindrical member  30  connected to housing  12 . Track  38  extends helically in a direction (A) parallel to axis  58  so that as stylet block  22  is propelled distally along direction A during use, projection  36  travels along the track and rotates inner part  28  and stylet  18  (arrow B). Track  38  can be extend such that projection  36  travels from greater than zero degree to about 175 degrees relative to a starting position. The degree of travel of projection  36  can be greater than or equal to about 0°, 30°, 60°, 90°, 120°, or 150°; and/or less than or equal to about 175°, 150°, 120°, 90°, 60°, or 30°, relative to the starting position.  
      In other embodiments, track  38  is configured to rotate stylet  18  in more than one direction. Referring to  FIG. 4 , track  38  extends along member  30  in a first direction X and then changes to a second direction Y, as shown, transverse to direction X. As a result, as projection  36  travels along track  38 , stylet  18  rotates in a first direction and then in a second direction, e.g., clockwise and then counter-clockwise, thereby imparting an oscillating and rotating motion to the stylet. Track  38  can change direction multiple times to impart more oscillations. In some embodiments, track  38  is defined by the interior surface of housing  12 , e.g., by injection molding.  
      Referring again to  FIGS. 1A and 1B , cannula  20  is a hollow sheath that slidably receives stylet  18 . From distal end  21 , cannula  20  extends into housing  12  where the cannula is attached to a longitudinally movable (arrow C) cannula block  25 .  
      Still referring to  FIGS. 1A and 1B , instrument  10  further includes components that retain stylet  18  and cannula  20  in their retracted positions, and components that propel the stylet and the cannula to their extended positions. To hold cannula  20  and stylet  18 , instrument  10  includes, respectively, a cannula latch  48  mounted pivotally to housing  12  at point  49  and a stylet latch  46  mounted pivotally to the housing at point  47  ( FIG. 1A ). Stylet latch  46  extends to the exterior of housing  12  to form a trigger  50  capable of firing instrument  10  during use, as described below. Both latches  48  and  46  are capable of pivoting about their respective attachment points to release the stylet or the cannula from engagement. To propel cannula  20  and stylet  18 , instrument  10  includes, respectively, a cannula spring  44  located proximal of cannula block  25 , and a stylet spring  42  located proximal to stylet block  22 .  
      Other features and embodiments of needle biopsy devices are described in commonly-assigned U.S. Ser. No. 10/300,249, filed Nov. 20, 2002; and U.S. Ser. No. 10/300,512, filed Nov. 20, 2002, both hereby incorporated by reference. Examples of suitable stylet  18  and cannula  20  configurations are exemplified by the ASAP™ Automated Biopsy System having a Delta Cut® needle or a Channel Cut® needle (available from Boston Scientific Corp., Natick, Mass.), and described in Chu, U.S. Pat. No. 5,989,196, hereby incorporated by reference.  
      In operation, cannula  20  and stylet  18  are loaded (e.g., moved proximally and retained in their retracted positions) and subsequently fired (e.g., released and propelled distally). More specifically, cannula  20  and cannula block  25  are first moved proximally until the cannula block engages with and is held by cannula latch  48  ( FIG. 1A ). Cannula spring  44  is compressed between cannula block  25  and cannula latch  48 . Next, stylet  18  and stylet block  22  are moved proximally until the stylet block engages with and is held by stylet latch  46 . Stylet block  22  compresses stylet spring  42 . Instrument  10  is loaded and ready to be fired.  
      To fire instrument  10 , distal end  27  of stylet  18  is placed adjacent to a target area, and trigger  50  is actuated. Sliding trigger  50  proximally pivots stylet latch  46  about point  47  and disengages the stylet latch from stylet block  22 . Upon disengagement, stylet block  22  and stylet  18  are propelled distally by the spring force of stylet spring  42 , which allows the stylet to penetrate the targeted area, e.g., tissue. As stylet  18  translates distally, projection  36  of stylet block  22  travels along track  38  (e.g., distally and spirally), thereby imparting rotational motion to the stylet  18 . Stylet block  22  then strikes cannula latch  48 , which causes the cannula latch to pivot about point  49  and to disengage from stylet block  25 . Upon disengagement, cannula block  25  and cannula  20  are propelled distally by the spring force of spring  44 , which allows the cannula to slide over stylet  18  and to sever a specimen that has prolapsed into notch  54  of stylet  18 .  
      Instrument  10  can then be withdrawn from the targeted area. The specimen can be removed from notch  54  by first retracting cannula  20  and cannula block  25  proximally. The specimen can be placed on a slide or in a preservative solution. If desired, stylet  18  can be retracted to load instrument  10  and to collect another specimen.  
      In other embodiments, other configurations or designs of notch  54  can be used. For example, referring to  FIGS. 5A and 5B , a notch  51  is defined in part by a leading edge  70  and a trailing edge  57 . Leading edge  70 , which is used to cut tissue, can be relieved to sharpen the edge and to enhance cutting. The relief can be an off-center cut using, for example, a ball end mill to produce a small undercut or chamfer that forms a facet to serve as a cutting edge. The cutting edge can have a thickness of about 0.002 inch or less. In some cases, notch  51  can be formed by broaching the notch from a stylet. Broaching allows minimal material to be removed per cut, thereby reducing (e.g., minimizing) induced stresses and material deformation. The cupped portion of the notch can be formed by milling with a ball end milling apparatus that has a diameter larger than the stylet to form a sharpened edge (e.g., edge  70 ). The edge can be polished to remove any burrs and further enhance sharpness. In other embodiments, referring to  FIG. 5C , the cupped portion  63  of a notch extends to less than the diameter or width (as shown, half) of the notch. The remaining cross-sectional portion of the notch can enhance the strength of the stylet.  
      Alternatively or in addition, a substantial portion of material of stylet  18  can be removed in the vicinity of a notch to enhance (e.g., increase) the size of a specimen that can be collected. Referring to  FIGS. 6A and 6B , a notch  53  is defined by distal edge  56 , a proximal edge  58 , and a sidewall  60 . Sidewall  60  can be lowered to increase to volume of notch  53 . In some embodiments, the top of sidewall  60  is formed anywhere from about 15% of the outer diameter of stylet  18  below the center line (D) to about 15% of the outer diameter of the stylet above the center line (D). For example, the top of sidewall  60  can be about 10% or 5% of the stylet O.D. below or above the center line (D).  
      In some cases, stylet  18  can be reinforced to enhance its strength. Referring to  FIG. 7 , stylet  18  can include solid plugs  55  located proximally and/or distally to notch  54 . Plugs  55  can be made of, for example, stainless steel rods welded or soldered to a tubular stylet, to enhance the rigidity of stylet  18 , such as in embodiments in which the sidewalls are lowered. Plugs  55  also provide other methods of making stylet  18 . For example, a notch can be formed in a hollow tube, which is subsequently reinforced with plugs  55  to form stylet  18 . By starting with a hollow tube, vis-a-vis a solid tube, less material need to be removed to form the notch, thereby reducing waste, manufacturing time, and cost.  
      A stylet notch can also include features that enhance removal of a specimen. Referring to  FIGS. 8A and 8B , a notch  59  includes a ramped surface  61  and a bottom slot  62  (i.e., notch  59  has a second opening other than the opening that defines the notch). A specimen in notch  59  can be removed by sliding the specimen up ramped surface  61 . Alternatively or in addition, an object, such as a probe, can be inserted through slot  62  to dislodge the specimen from notch  59 . In some embodiments, the ramped surface is inclined (β) about 5 to about 80 degrees relative to longitudinal axis  72 . Ramped surface  61  can be formed at the distal and/or proximal end of a notch. Slot  62  can extend the entire length of a notch or only a portion thereof. Slot  62  can be of any shape, e.g., rectangular, oval, polygonal, etc. In some cases, ramped surface  61  defines the proximal portion of notch  59 , i.e., the notch does not include proximal edge  58 . A ramped surface and/or an opening can be combined with any of the embodiments of notches described above.  
      In some embodiments, housing  12  can be made of different materials, e.g., to enhance the grip or “feel” of instrument  10 . For example, housing  12  can be formed of materials with different hardness, e.g., a core of relatively hard material and an outer layer of relatively soft material. The outer layer can be a foamy material, such as a urethane, to enhance the grip and/or to absorb vibrations from the firing of instrument  10 . Housing  12  can be formed with two or more different materials.  
      The components of instrument  10  (e.g., housing  12 , latches  46  and  48 , stylet block  22 , or cannula block  25 ) described above can be formed by conventional injection molding techniques, e.g., of polycarbonate and/or ABS. Stylet  18 , cannula  20 , and springs can be formed of stainless steel.  
      Terms such as “side” or “bottom” are used to describe embodiments as shown in the orientation of the figures and not intended to be limiting.  
      Other embodiments are within the claims.