Abstract:
A multimode instrument assembly ( 10, 11 ) configurable for performing a dermatotomy in a percutaneous procedure and further configurable for performing cuts in open surgery includes a pointed blade ( 68 ) and a hollow sheath body ( 18, 200 ) disposed to encapsulate the pointed blade ( 68 ) inside a longitudinal instrument cavity ( 32 ) to protect a user. The hollow sheath body ( 18, 200 ) is supported for longitudinal translation with respect to the blade ( 68 ). The hollow sheath ( 18 ) may be positioned and locked at a first position to completely encapsulate the blade ( 68 ) inside the instrument cavity ( 32 ) for safe handling. Otherwise the hollow sheath body ( 18, 200 ) is movable to second and third positions with different lengths of the blade extending out through a front face ( 23 ) of the hollow sheath body ( 18, 200 ). A compression spring biases the hollow sheath body ( 18 ) toward the first safety position. The multimode instrument is primarily intended for making a precise pierce cut with a consistent cut depth and cut length.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multifunctional scalpel usable as a traditional cutting scalpel and usable for dermatotomy or “skin nick” in percutaneous procedures. In particular, the multifunctional scalpel includes elements for engagement to a guide wire, a scalpel blade for safety, positioning the scalpel blade for piercing, and positioning the scalpel blade for conventional cutting. 
     2. Description of the Related Art 
     Percutaneous medical procedures use a needle-puncture of the skin to gain access to an internal location such as a blood vessel, hollow internal cavity, internal organ or other internal location. In many applications, percutaneous medical procedures are preferred over “open” surgery which has more complications. Most percutaneous medical procedures are a variation of the Seldinger technique which involves inserting a hollow needle or trocar into a desired internal location and passing a round-tipped guide wire through the hollow needle until a leading end of the guide wire exits the trocar at the desired internal location. The trocar is then removed by advancing it along the guide wire to its trailing end. While the trocar punctures the skin and installs the guide wire into a blood vessel or other internal cavity, the initial puncture surrounding the guide wire usually needs to be enlarged using a scalpel or other cutting or piercing instrument. After the initial puncture surrounding the guide wire is enlarged, a hollow “sheath” or blunt cannula is passed along the guide wire and inserted through the enlarged puncture wound. The hollow sheath has a larger lumen passing along its axial length and is guided to the desired internal location by the guide wire. Once the sheath is in place, the guide wire is removed and various surgical tools can be installed through the sheath lumen to the desired location. 
     The procedure for enlarging the initial needle puncture surrounding the guide wire is referred to as a dermatotomy or “skin nick”. Ideally, the dermatotomy is substantially coincident with or immediately adjacent to the guide wire entry point. In addition, the depth and size of the dermatotomy may vary for different surgical procedures, different instrument sheath sizes and different body locations. Heretofore the dermatotomy was performed by a surgeon using a conventional scalpel having its cutting blade fully extended and locked in place while held in a free hand and using only visual guidance to position dermatotomy coincident with or immediately adjacent to the guide wire entry point and to make the dermatotomy with a cut depth and length that is suitable for the situation. Even under ideal circumstances, such as with good lighting and a well positioned patient, a dermatotomy performed with a conventional scalpel may not be optimal when it is performed free hand. Moreover, a dermatotomy may need to be performed under non-ideal circumstances, e.g. when performed quickly in an emergency, when preformed in a low light level or when performed with the patient poorly positioned and such procedures are even more difficult to perform optically with a free hand held conventional scalpel. 
     More recently tools have been developed for guided dermatotomy procedures. In particular, US 2004/0181246 by Heppler, discloses a scalpel configured with a pair of wire guides attached to the scalpel and configured to be guided along the guide wire so that the scalpel blade is guided to the location where the dermatotomy needs to be placed, e.g. coincident with or immediately adjacent to the guide wire entry point. As further disclosed in Heppler, the wire guides can be attached to the scalpel handle, to the scalpel blade, to a plate sandwiched between the scalpel handle and the scalpel blade or to a movable safety sheath that fits over the scalpel blade and partially over the scalpel handle. While the improved scalpel taught by Heppler is usable for both freehand cutting and guided dermatotomy procedures, the movable safety sheath disclosed by Heppler appears difficult to use. Moreover, it is unclear from the disclosure how the safety shield is attached to the scalpel or moved from multiple operating positions including a depth stop position. Accordingly there is a need for an improved scalpel usable for guided dermatotomy procedures as well as for free hand cutting that provides a more reliable blade retracting mechanism and blade locking mechanism for locking the blade in a plurality of different positions and a more robust mechanism for setting a blade depth stop position for desired cut depths, such as for consistently performing a dermatotomy with a desired length and cut depth. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems cited in the prior art by providing improved surgical instrument assemblies ( 10 ,  11 ) that support a surgical instrument ( 20 ), such as a scalpel blade, in a fixed position and provide a hollow sheath body ( 18 ) that is longitudinally movable with respect to the surgical instrument  20  to alternately encapsulate the surgical instrument  20  inside a second cavity ( 32 ), in a safety mode, or expose the surgical instrument through a front face ( 23 ), by a desired dimension, when the surgical instrument is being used for surgery. In particular, the sheath body  18 ,  200  is movable to expose different lengths of the surgical instrument  20  for different applications and can be locked in various positions as required. In addition, the surgical instrument assembly is usable to pierce or make an initial cut in a surgical patient. 
     In particular the surgical instruments ( 10 ,  11 ) are operable in a pierce mode for performing a dermatotomy procedure by placing the front face ( 23 ) of the hollow sheath body ( 18 ,  200 ) against the skin or other surface of a surgical patient and orienting the longitudinal axis of the surgical instrument substantially normal to the skin or other surface of the surgical patient. Next a longitudinal force is applied to the actuator handle in a direction that pushes the handle toward the skin or other surface of a surgical patient. The longitudinal force applied to the handle actuator forces the surgical instrument, in this case a pointed scalpel blade, through the instrument aperture ( 22 ) while simultaneously forcing the hollow sheath body to be translated longitudinally toward the handle actuator. The depth of the pierce cut is controlled by limiting the longitudinal travel distance of the hollow sheath body to a travel distance associated with a desired cut depth of the pointed scalpel. This is accomplished by configuring the hollow sheath body and the handle actuator with an interface suitable for limiting the travel distance of the hollow sheath body. In one example, female engaging elements such as a slot arrangement having a plurality of longitudinal slot is formed on the hollow sheath body and engaged with a male engaging element formed on the handle actuator with one longitudinal slot length equal to the desired hollow sheath body travel distance associated with a desired cut depth of the pierce cut. In addition, the sheath body ( 18 ,  200 ) includes a guide wire receiving groove ( 24 ) formed on an external surface of the sheath body ( 18 ) adjacent to an instrument aperture ( 22 ) formed at the front end of the sheath body. The guide wire receiving groove ( 24 ) receives a guide wire therein and the guide wire is used to guide the surgical instrument ( 20 ), e.g. to guide the scalpel point ( 82 ) to a location defined by the guide wire during a pierce cut. Accordingly, the surgical instruments ( 10 ,  11 ) are usable to perform a guided dermatotomy. 
     The present invention further overcomes problems of the prior art by providing methods for operating a surgical instrument assembly. In particular the methods include positioning a hollow sheath body to a first longitudinal position for encapsulating the surgical instrument inside an instrument cavity and locking the hollow sheath body in the first position when the surgical instrument is not being used for surgery. The method also includes positioning the hollow sheath body to a second longitudinal position for causing the surgical instrument to extend through the instrument aperture with a desired length suitable for performing free hand surgery and locking the hollow sheath body in the second position when the surgical instrument is being used for free hand cutting. 
     Further methods include passing a suture through a notch opening formed through the hollow sheath body adjacent to the surgical instrument and cutting the suture while the surgical instrument is safely encapsulated inside the instrument cavity. 
     A further method include performing a guided dermatotomy procedure by first positioning the hollow sheath body in the first longitudinal position with surgical instrument encapsulated safely inside an instrument cavity but without locking the hollow sheath body in the first position. The instrument is then positioned with the front face of the hollow sheath body on a skin or other surface of a surgical patient while orienting the instrument longitudinal axis substantially normal to the skin surface. A user then applies a longitudinal force to the handle actuator pushing the handle toward the patient skin or other surface. This causes the surgical instrument to pierce the skin of the surgical patient to a desire pierce depth while simultaneously forcing the hollow sheath body toward the handle actuator. The depth of the pierce cut is controlled by limiting the longitudinal travel of the hollow sheath body. It is an object of the present invention to provide a scalpel that can be used for both cutting, in open surgery, and for piercing the skin to a desired depth, e.g. for a performing guided dermatotomy procedure. 
     It is an object of the present invention to provide a scalpel that includes a guide wire receiving groove aligned with a feature of the surgical instrument for receiving a guide wire into the receiving groove and directing the surgical instrument feature to a location defined by the guide wire. 
     It is a further object of the invention to provide a surgical instrument assembly that includes a sheath body ( 18 ,  200 ) that is movable to a LOCK position for enclosing the surgical instrument ( 20 ) inside the sheath body ( 18 ,  200 ) to thereby protect the instrument, to protect the surgical patient, and to protect anyone handling the surgical instrument assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the present invention will best be understood from a detailed description of the invention and a preferred embodiment thereof selected for the purposes of illustration and shown in the accompanying drawings in which: 
         FIG. 1  illustrates a first surgical instrument assembly embodiment shown in an isometric view according to the present invention. 
         FIG. 2  illustrates the first surgical instrument assembly embodiment shown in section view according to the present invention. 
         FIG. 3A  illustrates a first surgical instrument holder embodiment shown in isometric view according to the present invention. 
         FIG. 3B  illustrates a second surgical instrument holder embodiment shown in isometric view according to the present invention. 
         FIG. 4  illustrates a front end of a surgical instrument holder including a pointed scalpel blade attached thereto shown in isometric view according to the present invention. 
         FIG. 5A  illustrates a first arrangement of slotted elements shown in plan view and usable as a female engaging element according to a preferred embodiment of the present invention. 
         FIG. 5B  illustrates the first arrangement of slotted elements usable as a female engaging element shown on a cylindrical wall according to the present invention. 
         FIG. 6A  illustrates a first surgical instrument assembly embodiment shown in section view with a hollow sheath body shown in a LOCK position according to the present invention. 
         FIG. 6B  illustrates the first surgical instrument assembly embodiment shown in section view with a hollow sheath body shown in a PIERCE position according to the present invention. 
         FIG. 6C  illustrates the first surgical instrument assembly embodiment shown in section view with a hollow sheath body shown in a CUT position according to the present invention. 
         FIG. 7A  illustrates a second surgical instrument assembly embodiment shown in section view with a hollow sheath body shown in a LOCK position according to the present invention. 
         FIG. 7B  illustrates the second surgical instrument assembly embodiment shown in section view with a hollow sheath body shown in a PIERCE position according to the present invention. 
         FIG. 7C  illustrates the second surgical instrument assembly embodiment shown in section view with a hollow sheath body shown in a CUT position according to the present invention. 
         FIG. 8  schematically illustrates markings on outside surfaces of the handle actuator and the hollow sheath body for indicating configurations of the surgical instrument. 
         FIG. 9A  illustrates a second arrangement of slotted elements shown in plan view and usable as a female engaging element according to the present invention. 
         FIG. 9B  illustrates the second arrangement of slotted elements usable as female engaging elements shown on a cylindrical wall according to the present invention. 
         FIG. 10A  illustrates a third arrangement of slotted elements shown in plan view and usable as a female engaging element according to the present invention. 
         FIG. 10B  illustrates the third arrangement of slotted elements usable as female engaging elements shown on a cylindrical wall according to the present invention. 
         FIG. 11A  illustrates a fourth arrangement of slotted elements shown in plan view and usable as a female engaging element according to the present invention. 
         FIG. 11B  illustrates the fourth arrangement of slotted elements usable as female engaging elements shown on a cylindrical wall according to the present invention. 
         FIG. 12  illustrates a front end view of the surgical assembly showing a bridge between the instrument aperture and the guide wire receiving grove, and a guide wire positioned in the groove. 
         FIG. 13A  illustrates a hole for insertion of a guide wire, dilator or catheter, and a pierce cut spaced from the hole by a patient bridge area having a spacing determined by the surgical instrument assembly according to the present invention. 
         FIG. 13B  illustrates an expanded hole of  FIG. 13A  with a dilator partially inserted therein causing the patient bridge area to encroach into the pierce cut opening and still providing a seal against the dilator. 
         FIG. 13C  illustrates the expanded hole of  FIG. 13B  with the dilator  142  fully inserted therein causing the patient bridge area to separate, and the outer skin of the pierce cut providing a seal against the dilator. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1 and 2 ,  FIG. 1  depicts an isometric view of a surgical instrument assembly  10 , according to a first embodiment of the present invention, and  FIG. 2  depicts a section view taken through a longitudinal axis L of the surgical instrument assembly  10 . The surgical instrument assembly  10  generally has a back end  12  formed by a handle actuator  14  and a front end  16 , opposed to the back end  12 , formed by a hollow sheath body  18 . A surgical instrument  20 , such as a scalpel blade, is fixedly attached to an instrument holder  34 A with the instrument holder and scalpel blade  20  supported inside internal hollow cavities of the handle actuator  14  and hollow sheath body  18 . 
     Referring now to  FIGS. 1-4 , the instrument holder  34 A comprises a longitudinal shaft extending along the instrument longitudinal axis L from the front end  16  to the back end  12 . At its front end, the instrument holder  34 A is configured to support the surgical instrument  20  in a desired orientation. At its mid section the instrument holder  34 A includes a longitudinal front shaft portion  62  that guides and supports longitudinal movement of the hollow sheath body  18 . At its back end, the instrument holder  34 A includes a longitudinal back shaft portion  60  that guides and supports rotation of the handle actuator  14  about the longitudinal axis L. 
     Generally, the surgical instrument assembly  10  is configured such that the instrument holder  34 A and surgical instrument  20  remain substantially fixedly disposed along the longitudinal axis L. The surgical instrument assembly  10  is further configured to translate the hollow sheath body  18  longitudinally toward the back end  12  to expose the surgical instrument  20 . The surgical instrument assembly  10  is further configured to rotate the handle actuator  14  about the longitudinal axis L and about the hollow sheath body  18  for locking or unlocking the position of the hollow sheath body  18  at desired positions. As will be detailed below, the hollow sheath body  18  includes a front face  23  and an instrument aperture  22  passing through the front face  23 . As the hollow sheath body  18  is longitudinally translated toward the back end, the surgical instrument  20  is exposed through an instrument aperture  22 . 
     The handle actuator  12  includes a pair of diametrically opposed fins  15  extending radially outward from an outer surface of the actuator handle  12  to improve the gripping of the handle actuator  14  to different operating positions. Of course other gripping aids are usable on the handle actuator  12  without deviating from the present invention. Similarly, the hollow sheath body  18  includes a raised diameter  19  to provide a gripping feature on the hollow sheath body  18  to improve gripping during use as a surgical instrument and while translating the hollow sheath body  18  to different operating positions. 
     In  FIGS. 1 and 2 , the surgical instrument  10  is shown in a safety or LOCK mode wherein the surgical instrument  20  is completely housed inside the hollow sheath body  18  to protect the surgical instrument  20  from damage and to allow safe storage and handling of the surgical instrument  10 . As detailed below, the hollow sheath body  18  may be retracted to exposed the surgical instrument  20  through the aperture  22  and the hollow sheath body  18  may be locked or otherwise held in one or more retracted positions with the surgical instrument  20  exposed for free hand cutting. Alternately, the hollow sheath body  18  may be unlocked in a PIERCE mode wherein the front face  23  is placed against the skin of a surgical patient and the surgical instrument  20  is used to pierce the skin to a desired depth and cut length by pushing the handle actuator  14  longitudinally toward the skin of the surgical patient. 
     According to a further aspect of the present invention, the hollow sheath body  18  includes a wire receiving groove  24  formed on an external surface thereof. The wire receiving groove  24  is provided to engage with a guide wire such as a wire that may be exiting from a blood vessel or internal cavity of a surgical patient such as during the initial steps of a percutaneous medical procedure. Generally, the guide wire receiving groove  24  is formed on an external surface of the hollow sheath body  18  at the front end  12  front end adjacent to the instrument aperture  22  and the wire receiving groove  24  is aligned with an axis of the surgical instrument  20 , such as a cutting blade point, or the like, for guiding the axis of the surgical instrument  20  to a desired location such as toward the initial needle puncture that was used to insert the guide wire into the surgical patient. 
     According to a further aspect of the present invention, the hollow sheath body  18  includes a notch  17  passing through an outside wall of the hollow sheath body  18  near the front end  16 . In particular, the notch  17  is positioned to provide access to a cutting blade of the surgical instrument  20  at times when the surgical instrument  20  is completely encapsulated by the hollow sheath body  18  such as when the hollow sheath body is in the lock position. Accordingly, the cutting blade of the surgical instrument  20  can be used to cut a suture, or the like, without exposing the blade. To cut a suture or the like, the surgical instrument assembly  10  is positioned to receive the suture through a top opening of the notch  17  and tension between the suture and the blade is used to cut the suture at a desired position without exposing the surgical instrument  20 . This is a very important safety feature in an operating room environment. The notch  17  has a top opening sized and shaped large enough to allow a suture material to enter the notch  17  and be cut by the blade, but the top opening is formed to prevent the blade from cutting anything that will not fit through the top opening. Accordingly the notch  17  is formed with a top opening dimension of approximately 3 mm or less and preferably about 1 mm. 
     Referring to  FIGS. 1 and 2  the handle actuator  14  comprises an annular body disposed along the longitudinal axis L and encloses a first internal longitudinal cavity  26  extending along the longitudinal axis L and sized to receive a back portion of the hollow sheath body  18  therein. The first internal longitudinal cavity  26  is closed at its back end by an end wall  28  and forms a first aperture  30  at the first longitudinal cavity front end. 
     The hollow sheath body  18  comprises an annular body disposed along the longitudinal axis L and encloses a second internal longitudinal cavity  32 , extending along the longitudinal axis L and sized to receive the surgical instrument holder  34 A, shown in  FIG. 3A , or an alternate embodiment of the surgical instrument holder  34 B, shown in  FIG. 3B , therein. The second longitudinal cavity  32  forms a second aperture  36  at the second longitudinal cavity back end and the second longitudinal cavity  32  is shaped at the front end as may be required to enclose the surgical instrument  20  and to provide a suitable instrument aperture  22  that allows the surgical instrument  20  to pass through a front wall  23 . 
     Turning now to  FIGS. 2 ,  3 A,  3 B,  4 , and the section views of  FIGS. 6A-7C , two different embodiments of surgical instrument holders  34 A and  34 B are shown in isometric view in  FIGS. 3A and 3B  respectively. The instrument holder  34 A installs in the surgical instrument assembly  10 , as shown in the section views of FIGS.  2  and  5 A- 6 C. The instrument holder  34 B installs in a second embodiment of a surgical instrument assembly  11 , shown in the section the views of  FIGS. 7A-7C . 
     Referring to both  FIGS. 3A and 3B  the instrument holders  34 A and  34 B include a pointed scalpel blade  68  attached to front ends thereof. The holders  34 A and  34 B each comprise a solid substantially uniform diameter elongated front shaft portion  62  disposed along the surgical instrument longitudinal axis L and extending between an instrument holding portion  70  and an increased diameter back shaft portion  60 . The back shaft portion  60  has a larger diameter than the front shaft portion  62  and includes features on the back end thereof for interfacing with the handle actuator  14 . In particular, the back shaft portion  60  includes a back end formed with an annular groove  66  having a decreased groove diameter axially centered with respect to the longitudinal axis L for interfacing with the handle actuator  14 . In addition, a shoulder is formed at the intersection of the back shaft portion  60  and the front shaft portion  62  and the shoulder provides an annular land surface  64 . As depicted in  FIG. 3A , the first instrument holder  34 A has a long front shaft  62  with the annular land surface  64  positioned adjacent to the annular groove  66  near the back end of the instrument holder  34 A. As depicted in  FIG. 3B , the second instrument holder  34 B has a shorter front shaft  62  with the annular land surface  64  approximately positioned at the mid point of the holder  34 B. 
     Referring now to  FIG. 4 , the instrument holders  34 A and  34 B each include an instrument holding portion  70 , which may be formed integral with the front shaft portion  62 , or which may comprise a separate element fixed or removable from the front shaft portion  62 . Generally, the instrument holding portion  70  provides features usable to attach a surgical instrument, e.g. the scalpel  68 , to the instrument holder  34 A or  34 B and for orienting the scalpel  68  in a desired orientation and or location with respect to the longitudinal axis L. 
     In the particular example where the surgical instrument is a conventional scalpel blade  68  formed with a pointed tip  82 , the instrument holding end  70  is formed with a flat surface  72  for receiving a shank  80  of the scalpel blade  68 , thereon. The flat surface  72  also includes a pair of attaching posts  74  and  76  attached thereto and extending substantially perpendicular from the flat surface  72  to engage with a slotted opening  78 . The slotted opening  78  is sized to mate with the attaching posts  74  and  76  and the attaching posts  74  and  76  are positioned and oriented to align an axis of the scalpel blade  68  with the instrument longitudinal axis L. Specifically, the scalpel  68  is oriented coplanar with the longitudinal axis L and the blade point  82  is offset from the longitudinal axis L by a desired offset distance C. In addition, the fit of the slotted opening  78  with the attaching posts  74  and  76  may be an interference or snap fit to mechanically clamp the blade shank  80  in position. Alternately, other clamping or attaching elements may be employed. 
     According to a preferred embodiment of the present invention, the surgical instrument assemblies  10  and  11  are configured with the scalpel blade  68 . However, other scalpel blade types including a rounded scalpel blade, a micro-blade scalpel are usable without deviating from the present invention. Moreover other surgical instruments such as other cutting tools, solid or hollow needles, probes directors, tweezers or forceps, dilators, expanders or retractors are usable without deviating from the present invention. Moreover other medical devices such as electronic or optical instruments, drug delivery devices or the like, that may need to be guided along a guide wire to a wire puncture may be usable in combination with the features and elements of the present invention described herein. 
     Referring to  FIGS. 2 ,  3 A and  6 A- 6 C the surgical instrument holder  34 A and the attached surgical instrument  20  installs into the hollow sheath body  18  second longitudinal cavity  32  through the second aperture  36 . In the example of  FIGS. 6A-6C , the second longitudinal cavity  32  has a substantially uniform diameter  42  over its full length for receiving the instrument holder front shaft diameter  62  therein. Alternately, a front portion of the second longitudinal cavity  32  may be shaped as required to receive larger surgical instruments  20  therein. An annular land surface  45  is formed by the back end of the sheath body  18  and is used as a bearing surface for a compression spring  53 . The compression spring  53  is a cylindrical spring element open along its longitudinal axis and the spring  53  installs over the instrument holder front end diameter  62  and is captured between the annular land surface  45 , formed on the back end of the sheath body  18 , and the annular land surface  64  formed on the instrument holder  34 A adjacent to the annular groove  46 . The compression spring  53  delivers a longitudinal separating force between the instrument holder  34 A, which is longitudinally fixed in place, and the sheath body  18 , which is longitudinally movable and the spring  53  tends to bias the longitudinal position of the sheath body  18  toward the instrument front end  16 . 
     Referring to FIGS.  3 B and  7 A- 7 C, the second embodiment of the surgical instrument assembly  11  includes a second embodiment of a hollow sheath body  200  formed with an internal cavity  202  formed therein. In this embodiment, the surgical instrument holder  34 B and surgical instrument  20  install into the longitudinal cavity  202  through the aperture  204 . The internal cavity  202  has a substantially uniform front diameter  206 , sized to receive the instrument holder front diameter  62  therein, and the second longitudinal cavity  202  has a larger back diameter  208  sized to receive instrument holder back shaft portion  60  therein. A shoulder separating the front diameter  206  and back diameter  208  forms an annular land surface  210  which is used as a bearing surface for a compression spring  52 . The compression spring  52  is a cylindrical spring element open along its longitudinal axis and the spring  52  installs over the instrument holder front diameter  62  and is captured between the annular land surface  210  and the annular land surface  64  formed on the instrument holder  34 B. The compression spring  52  delivers a longitudinal separating force between the instrument holder  34 B, which is longitudinally fixed in place, and the sheath body  200  which is longitudinally movable, and the spring  52  tends to bias the sheath body  200  toward the instrument front end  16 . 
     In each of the example instrument assemblies  10  and  11 , internal surfaces of the sheath body  18  and  200 , and external surfaces of the instrument holder  34 A,  34 B as well as internal surfaces of the actuator handle  14  and external surfaces of the hollow sheath body  18  and  200  are fit together with a clearance fit that allows longitudinal translation of the sheath body  18 ,  200  with respect to the instrument holders  34 A or  34 B and the actuator handle  18  as well as rotation of the actuator handle  18  about the longitudinal axis L and about hollow sheath body  18  and the clearance fits are made sufficiently small that the surgical instrument  20 , instrument holder  34 A,  34 B sheath body  18 ,  200  and actuator handle  14  are maintained in substantial alignment with the instrument longitudinal axis L. Specifically, the diametrical clearance between mating elements may range from about 0.25-1.25 mm. 
     Referring to  FIGS. 1 ,  2 , and  6 A- 7 C the back end of the surgical instrument holders  34 A and  34 B and the back end of the sheath body  18  or  200  install into the handle actuator first longitudinal cavity  26  by passing through the actuator handle front end aperture  30 . The actuator handle  14  includes an annular lip  46  formed substantially opposed to the end wall  28 . The annular lip  46  reduces the diameter of the first longitudinal cavity  26  and is axially centered with respect to longitudinal axis L. The annular lip  46  is provided to engage with the instrument holder annular groove  66  by pressing or otherwise placing the back end of the instrument holder back shaft  60  into engagement with the annular lip  46 . Alternately the handle actuator  14  may be configured with two longitudinal half sections that engaged with the annular groove  66  at assembly and that may be bonded or otherwise fastened together at assemble. The engagement of the annular lip  46  with the annular groove  66  prevents longitudinal movement of the instrument holder  34 A or  34 B and the handle actuator  14 . The annular lip  46  and annular groove  66  are each sized to fit together with a clearance fit. The clearance fit is made sufficiently large that the actuator handle  14  can be rotated about the longitudinal axis L with respect to the instrument holder  34 A or  34 B. Meanwhile, the clearance fit between the annular lip  46  and annular groove  66  is small enough to maintain the instrument holder back shaft  66  in substantial alignment with the instrument longitudinal axis L. For example, the diametrical and axial clearances between the annular lip  46  and annular groove  66  may range from about 0.25-1.25 mm. Alternately, a snap ring or other suitable fastener may be used instead of the annular lip  46  and installed through an annular groove formed through the handle actuator  14 . 
     Referring now to  FIGS. 2 , and  5 A- 6 C, the handle actuator  14  includes a fixed pin  48  or other male engaging element protruding substantially axially inward from an inner wall of the first longitudinal cavity  26 . The pin  48  may be integrally formed with the handle actuator  14 , such as molded in place, or the pin  48  may comprise a set screw, or the like, threaded through a wall of the first longitudinal cavity  26 . The sheath body  18 ,  200  includes a female engaging element  50 , such as an arrangement of slotted elements described below for receiving the male engaging element  48  therein. Specifically, the female engaging element  50  passes fully or partially through an outer wall of the sheath body  18  and is sized to movably receive the fixed pin  48  therein with a minimum of clearance between the pin and female engaging element  50 . The longitudinal position of the pin  48  is fixed with respect to the actuator handle end wall  28  such that rotation of the actuator handle  14  rotates the pin  48  in a circular path around the longitudinal axis L at a fixed longitudinal position. By engaging with the slot  50 , the rotation of the actuator handle  18  and therefore the pin  48  about the longitudinal axis L may be used engage the pin  48  with various features of the female engaging element  50 , such as detents and longitudinal slot sections, in order to select a desired longitudinal position of the sheath body  18 ,  200 . Accordingly, the female engaging element  50  may be formed with various longitudinal slots, and with detents which when engaged with the pin  48  allow longitudinal translation of the hollow sheath body  18 ,  200  and may hold the sheath body in desired longitudinal positions. In addition, the pin  48  may be supported on a flexure extending between the pin  48  and the handle actuator  14  for allowing the pin  48  to flex axially away from the longitudinal axis L during assembly of the instrument. Alternately, the entire actuator handle  14  may be constructed as a flexure with flexible elements formed integral with the actuator handle to flexibly expand its inside diameter during assembly to allow the pin  48  to pass over the hollow sheath body  18 ,  200  before engaging with the female engaging element  50 . 
     According to the invention, the surgical instrument assembly  10  and  11  are assembled by installing the spring  52  or  53  onto the instrument holder front shaft  62 , installing the surgical instrument  20  onto the instrument holding portion  70  and then installing the surgical instrument holder  34 A,  34 B into the sheath body second longitudinal cavity  32 ,  202  through the sheath body second aperture  36 ,  204 . The back end of the surgical instrument holder  34 A,  34 B and the back end of the sheath body  18 ,  200  are then installed into the actuator handle first longitudinal cavity  26  through the handle actuator first aperture  30  and pushed longitudinally from the front end  16  to engage the instrument holder annular groove  66  with the handle actuator annular lip  46 . The handle actuator  14  is then rotated about the longitudinal axis L until the male engaging element or fixed pin  48  is engaged with the female engaging elements or arrangement of slotted elements  50 . 
     Referring now to  FIGS. 5A and 5B , a preferred embodiment of a female engaging slot arrangement  90  is shown in plan view in  FIG. 5A  and shown in  FIG. 5B  disposed on a hollow cylindrical element  92 . The element  92  corresponds with a cylindrical mid section of the hollow sheath body  18  or  200 . The female engaging slot arrangement  90  may comprise slotted openings passing completely through the thickness of an outer annular wall of the cylindrical element  92  or the slotted openings may have a slot depth that is less than the wall thickness of the cylindrical element  92  but deep enough to engage with the male engaging element  48 . The surgical instrument longitudinal axis L is shown coincident with the longitudinal axis of the hollow cylindrical element  92  and the cylindrical element front end and back end correspond with the surgical instrument front end  16  and back end  12  as described above. 
     According to a preferred embodiment of the present invention, the male engaging pin  48  engages with the female engaging slot arrangement  90  while the hollow sheath body  18 ,  200  is continuously biased toward the front end  16  by the compression springs  52 ,  53 . In the LOCK position, the hollow sheath body  18 ,  200  is at its front most position where it encapsulates the surgical instrument  20 . In the Lock position, the male engaging pin  48  is engaged with a back detent slot  94 . To unlock the surgical instrument assembly, a user grasps the hollow sheath body gripping region  19  and the handle actuator  14  and pulls the sheath body  18 ,  200  toward the instrument back end  18  until the pin  48  is engaged with the cross slot section  96 . Thereafter the handle actuator  14  can be rotated clockwise, as viewed from the back end  18 , to engage with a cut slot  98 . Alternately, the handle actuator  14  may be rotated counter-clockwise to engage with a pierce slot  100 . 
     If engaged with the cut slot  98 , the user pulls the sheath body  18 ,  200  further toward the instrument back end  18 , and then further rotates the handle actuator  14  clockwise to engage the pin  48  with a cut detent slot  102 . Once engaged in the cut detent slot  102 , the spring bias force pushes the hollow sheath body forward against the male engaging pin  48  thereby locking the hollow sheath body  18 ,  200  in a CUT position. The cut position is shown in  FIGS. 6C and 7C  which show the surgical instrument  20  extending out from the instrument aperture by a distance E. 
     If rotated to the pierce slot  100 , the bias force pushes the hollow sheath body forward to engage the male engaging pin  48  with a pierce detent  104  and hold it in place therein. The pierce detent  104  is co-aligned with the pierce slot  100 . The pierce detent  104  is configured to position the sheath body substantially in its forward most position which encapsulates the surgical instrument  20 . To use the surgical instrument in the PIERCE mod, the user places the instrument front face  23  against the skin of a surgical patient with the instrument longitudinal axis L substantially normal to the skin surface. The user uses the wire receiving groove  24  with a guide wire  21  exiting from the surgical patient to position the front wall or face  23  for making a piece cut adjacent to the where the guide wire  21  exits a blood vessel or internal cavity of the surgical patient. The user then pushes the handle actuator  14  substantially longitudinally thereby driving the instrument holder and surgical instrument toward the skin of the surgical patient where the surgical instrument  20  pierces the skin proximate to the guide wire. In response to the user pushing the handle actuator  14  substantially longitudinally, the hollow sheath body  18  remains stationary while the male engaging pin  48  moves along the length of the pierce slot  100 . Accordingly, the depth of the piercing cut is controlled by the length of the pierce slot  100  which stops the travel of the handle actuator and surgical instrument holder when the male engaging pin  48  impacts the front end of the piercing slot  100 . 
     After completing a piercing cut, the bias force of the compression spring  52 ,  53  acts to separate the handle actuator  14  and sheath body  18 ,  200  thereby retracting the surgical instrument  20  from the surgical patient until the male engaging pin  48  is once again in the pierce detent  104  and the handle actuator, surgical instrument holder  34 A or  34 B and the surgical instrument  20  have moved to a position where the surgical instrument is again encapsulated inside the hollow sheath body  18 ,  200 . In the PIERCE mod, the surgical instrument  20  moves to extend out from the front face  23  by a distance D shown in  FIGS. 6B and 7B . The distance D is controlled by the length and position of the pierce slot  100 . 
     Referring now to  FIG. 8 , example markings or other indicia usable on outside surfaces of the surgical instrument  10 ,  11  are shown schematically. An single arrow head  120  is shown on an outside surface near a front edge of the handle actuator  14  centered on the longitudinal axis L. The arrow head  120  points toward a lock symbol  122  shown on an external surface of the hollow sheath body  18 ,  200  and adjacent to an edge of the handle actuator  14 . The arrow  120  and lock symbol  122  are positioned such that with the arrow head  120  pointing toward the lock symbol  122 , the handle actuator  14  and hollow sheath body  18 ,  200  are positioned in the LOCK position. 
     Two additional symbols are shown on the outside surface of the hollow sheath body to the left and right of the lock symbol  122 . The symbol  124  is a pierce symbol and the symbol  126  is a cut symbol. When the handle actuator  14  is rotated to align the male engaging pin  48  with the pierce  100  or pierce engaging slot  104  the arrow head  120  points toward the pierce symbol  124 . When the handle actuator  14  is rotated to align the male actuator pin  48  with the cut slot  98  or the cut detent  102 , the arrow head  120  points toward the cut symbol  126 . Any of the symbols  120 - 126  may be marked or decaled onto outside surface of the handle actuator or the hollow sheath body or the symbols  120 - 126  may be formed as surface features such as raised or recessed surfaces. 
     Referring now to  FIGS. 9A-11B , three different configurations of female engaging slot arrangements  300 ,  310 ,  322  are shown in a plan view in  FIGS. 9A ,  10 A and  11 A. The female slot arrangements  300 ,  310  and  322  are also shown disposed on a hollow cylindrical element  93  in  FIGS. 9B ,  10 B and  11 B. These alternative slot embodiments are shown to illustrate additional methods and configurations for longitudinally translating the hollow sheath body  18 ,  200  to alternately expose the surgical element  20  through the instrument aperture  22  or to encapsulate the surgical element  20  inside the hollow sheath body  18 ,  200  according to further aspects of the present invention. 
     In the longitudinal slot arrangement  300 , shown in  FIGS. 9A and 9B  the slot arrangement  300  includes a longitudinal slot  302  and three detents  304 ,  306  and  308 . A lock detent  302  corresponds to the LOCK position such that when the male engaging pin  48  is engaged with the lock detent  302  the hollow sheath body  18 ,  200  is positioned to encapsulate the surgical instrument  20  and held in place. A cut detent  308  corresponds the CUT position such that when the male engaging pin  48  is engaged with the cut detent  308  the hollow sheath body  18 ,  200  is positioned to expose the surgical instrument  20  by the distance E from the front face  23  as shown in  FIGS. 6C and 7C  and held in place. In addition, an intermediate detent  306  is provided such that when the male engaging pin  48  is engaged with the intermediate detent  306  the hollow sheath body  18 ,  200  is positioned to expose the surgical instrument  20  by less than the distance E from the front face  23 , such as a distance D shown in  FIGS. 6B and 7B  and held in place. 
     In the slot arrangement  310 , shown in  FIG. 10A  a longitudinal slot  312  includes a lock detent  314  at its back end and a cut detent  316  at it front end. The longitudinal slot  312  is used to move the hollow sheath body  18 ,  200  between the LOCK position, shown in  FIGS. 6A and 7A , and the CUT position, shown in  FIGS. 6C and 7C . A cross slot section  318  allows the male engaging pin  48  to engage with a pierce slot  320  when the handle actuator  14  is rotated. With the male engagement pin  48  engaged with a back end of the pierce slot  320  the hollow sheath body  18  is position to encapsulate the surgical instrument  20  and the hollow sheath body is movable to allow the surgical instrument assembly to operate in the PIERCE mod as described above. 
     In the slot arrangement  322 , shown in  FIGS. 11A and 11B , includes a spiral slot  321 , a lock detent  324 , a cut detent  326  and a middle detent  328 . With the male engaging pin  48  engaged with the lock detent  324  the surgical instrument  20  is encapsulated by the hollow sheath body  18 , which is held in place. With the male engaging pin  48  engaged with the cut detent  326 , the surgical instrument extends out from the sheath body by a distance E as shown in  FIGS. 6C and 7C , and the sheath body is held in place. With the male engaging pin  48  engaged with the middle detent  328  the surgical instrument extends out from the sheath body by less than the distance E, such as a distance D shown in  FIGS. 6B and 7B , and the sheath body is held in place. 
     Referring to  FIG. 12  and  FIG. 13A ,  FIG. 13A  illustrates a hole or puncture  132  in a patient  130  for insertion of the guide wire  21 , a dilator or a catheter, and a pierce cut  136  is spaced from the hole  132  by the bridge  13 . The surgical instrument assembly  10  is positioned normal or perpendicular to the surface of the surgical patient adjacent to the existing guide wire  21  extending from the hole or puncture  132  on the surgical patient  130  so that the front face  23  rests on the surface of the surgical patient. The groove  24  receives the guide wire  21  and the pierce mode of the surgical instrument assembly  10  is activated, resulting in a cut  136  approximately 0.5 mm from the edge of the puncture or hole  132  from where the guide wire  21  is exiting. The resulting space between the inner edge of the cut  136  facing the hole  132  and the edge of the hole  132  is referred to as the patient bridge area  134  which plays an important role in preventing infections in the patient  130 . As noted above the bridge width area  134  resulting from the piercing mode of the present instrument assembly  10  is approximately 0.5 mm in the present embodiment, but this may be varied depending on experiences with patients. 
     Referring to  FIG. 12 , the front end  16  of the surgical instrument assembly  10  is shown comprising the front wall or face  23 , the instrument aperture  22 , a groove  24  for receiving a guide wire, a guide wire  21 , and a bridge  13  which is the distance between the right edge of the instrument aperture  22  and the tip of the groove  24  facing the aperture  22 . The groove  24  may be V-shaped as shown in  FIG. 12  or it may be other known shapes such as U-shaped. In the present embodiment the width of the bridge  13  is approximately 0.5 mm. However, one skilled in the art will recognize that the width of the bridge  13  may be varied depending on experiences with patients for reducing bleeding or infection. As previously discussed, the groove  24  receives a guide wire  21  that may be exiting from a blood vessel or internal cavity of a surgical patient. 
     Referring to  FIG. 13B ,  FIG. 13B  illustrates the hole of  FIG. 13A  expanded with a dilator  142  partially inserted therein causing the patient bridge area  134  to expand due to its elasticity into the area of the pierce cut  136 . The surface of the patient bridge area  134  against the dilator acts as a sling and continues to provide a seal to prevent fluids from escaping from the hole  132 . 
     Referring to  FIG. 13C ,  FIG. 13C  illustrates the hole  132  of  FIG. 13B  with the dilator  142  inserted when a dermatotomy is too close to the hole  132  therein causing the patient bridge area  134  to widen and separate into portions  134   a  and  134   b . Eventually, parts  134   a  and  134   b  disappear and are absorbed into a larger open area  136 ,  140  where bleeding or infection can occur. A pierce cut made contiguous to the guide wire, or too close to the guide wire, is a common outcome of using a standard scalpel and ordinary skill of the art. The surgical instrument assembly  10  ensures that the patient bridge area  134  is adequate in size to remain intact when the dilator is inserted. The use of the surgical instrument assembly  10  to produce the accurate pierce cut  136  produces the approximate 0.5 mm bridge between the hole  132  and the pierce cut  136  which cooperates in providing a seal around the dilator or catheter without leaving any open area where bleeding or infection could occur.  FIG. 13B  represents the desired outcome using the surgical instrument  10 .  FIG. 13C  represents an undesirable, yet common outcome using a standard scalpel and ordinary skill of the art. 
     It will also be recognized by those skilled in the art that, while the invention has been described above in terms of preferred embodiments, it is not limited thereto. Various features and aspects of the above described invention may be used individually or jointly. Further, although the invention has been described in the context of its implementation in a particular environment, and for particular applications, e.g. as a surgical instrument assembly, those skilled in the art will recognize that its usefulness is not limited thereto and that the present invention can be beneficially utilized in any number of environments and implementations where it is desirable to enclose an instrument inside a sheath and to guide the instrument to a desired location during use. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the invention as disclosed herein.