Abstract:
A medical tubular shaft instrument for gripping and cutting tissue which provides a safe mode of operation. The instrument includes electrodes by which a mechanical contact between a blade and an associated cutting surface can be electrically determined. This determination allows the operating physician to be provided with sufficient information to determine whether the tissue that is to be severed has been successfully severed.

Description:
FIELD OF THE INVENTION 
     The disclosed embodiments relate to a medical instrument, in particular a tubular shaft instrument, for cutting tissue. 
     BACKGROUND 
     In modern medicine, attempts are generally made to minimize damage to intact tissue. Thus, when circumstances permit, minimally invasive surgery is usually the preferred method of operative intervention used. Small incisions and minimal trauma to the tissue lead to less pain after the operation and to rapid recovery and mobilization of the patient. Laparoscopic surgery, during which complex operations are performed in the abdominal cavity, allows similar results. 
     Operations of this type, and the instruments required for them, present a particular challenge to the manufacturers of medical instruments since the majority of the operative steps are performed in very restricted spaces and without direct visual contact. Thus, the medical instruments used for these types of operations must not only be able to operate in the smallest spaces but must also function so reliably that visual monitoring is superfluous and unnecessary. The instruments are preferably constructed such that, even without visual contact, the operating surgeon always has feedback which enables him to draw conclusions about the progress of the operation. 
     This need applies to instruments that are suitable for the separation of tissue. Since scalpels having an open blade are, if anything, unsuitable for minimally invasive surgery (see, e.g., DE 44 44 166 A1), surgeons frequently resort to scissors-type or tong-type instruments having mouth parts. The mouth parts cover the blade during insertion of the instrument as well as hold the tissue to be cut. The blade is then displaced back and forth inside the mouth parts for cutting. 
     In the tong-like instruments, the blade or scalpel is usually covered completely by the associated mouth parts. It is, therefore, all the more difficult to draw conclusions as to whether the gripped tissue has already been completely separated with one or a plurality of cutting movements. This knowledge, however, is crucial for the positive progress of the operation. 
     On the other hand, excessively moving the blade when the tissue is already separated can quickly lead to wear on the instrument. It is necessary to check the instruments for their cutting ability and to replace worn blades. This form of maintenance is not only expensive but is also time-consuming. Often it is not possible to replace individual elements of the instruments, leading to the need to replace the entire instrument. Thus, excess wear should be avoided. 
     The object of the disclosed embodiments is to provide a medical instrument, which allows for reliable separation of tissue while providing long-lasting functionality. 
     SUMMARY 
     Disclosed embodiments include a medical instrument having a first and a second mouth part each with at least one clamping surface for fixing and/or positioning tissue in a fixing plane, a cutting device with a blade, which is disposed opposite one of the mouth parts for cutting tissue and is displaceable over a predetermined cutting path substantially parallel to the fixing plane, a first electrode and a second electrode, which are disposed on the cutting device and/or the clamping surface in such a manner that a mechanical contact between cutting and clamping surface is ascertainable by means of a processing unit connected to the electrodes. 
     The electrodes allow a mechanical contact between a blade and an associated clamping surface in a medical instrument for separating tissue to be ascertained. The mechanical contact may be ascertained electrically or by means of a switch. The processing unit receives the corresponding signals and evaluates them. 
     In a preferred embodiment, the blade may be the first electrode, the clamping surface may be the second electrode and the processing unit may be a device for determining an electrical resistance between the electrodes. The first electrode is thus formed by an electrically conductive blade or an electrically conductive section of the blade. The second electrode is the electrically conductive clamping surface or an electrically conductive section of the clamping surface. The processing unit measures the electrical resistance between the first and the second electrode. Preferably, the processing unit then ascertains that the tissue located immediately under the blade is separated when the resistance is lower that a preset threshold limit. This is necessary as the tissue to be cut has a certain electrical conductivity and consequently a high-ohm contact already exists between the first electrode and the second electrode when the tissue is unseparated. By specifying a threshold value, it is possible to differentiate the contact closure by way of the tissue to be cut from a direct contact closure between the two electrodes. This direct contact closure is an indicator for mechanical contact between blade and clamping surface. 
     The processing unit may be designed in such a manner that a curve of the resistance is ascertainable along the cutting path. The cutting path defines an observation interval for the processing unit and may, for example, include a back and forth movement of the blade between a distal and a proximal section of the mouth parts. 
     It is possible to detect the movement of the blade manually. Thus a mechanical limit stop during movement of the blade by means of an actuating device can provide information about the distance covered or about the cutting path covered. The processing unit includes a travel sensor and/or electric switch for detecting the displacement of the blade parallel to the clamping surface. The cutting device is designed such that it may be moved back and forth along a longitudinal axis of the medical instrument parallel to the clamping surface. The blade, therefore, should preferably separate the tissue not only at one point but over a cutting area along the previously described longitudinal displacement. To effectively determine whether the tissue is completely separated in this region, it is advantageous to record the blade&#39;s movement over an observation interval or an observation path and to determine whether there is a continuous mechanical contact between blade and clamping surface. The movement of the blade may be ascertained either directly by means of a travel sensor, or it may be ascertained indirectly by means of switches at the end of the cutting range whether the blade has been moved from a first switch to a second switch. Here too, the tissue is only deemed to have been completely separated when there is a mechanical or electrical, in particular a low-ohm, contact between blade and clamping surface within the entire interval or during the entire cutting path, that is to say from a movement of the blade from the first switch to the second switch. 
     The two mouth parts each may include a coagulation electrode for coagulation of the fixed tissue. Consequently, the tissue can be coagulated by means of a high-frequency current prior to mechanical separation by means of the blade. A safe closure of the vessels is ensured prior to mechanical separation. Furthermore, one of the two coagulation electrodes may be linked to the processing unit and thus be used to determine the mechanical contact. For formation of the coagulation electrodes, the mouth parts are either at least partially electrically conductive or they have an electrically conductive coating on the side facing towards the tissue. 
     The at least one mouth part may include a blade guide. The blade guide is used to stabilize the blade during the cutting movement. Furthermore, the blade guide may have the previously described switches or travel sensors in order to determine the blade&#39;s movements. 
     The medical instrument has means for emitting a signal, which is emitted when the resistance drops below a predetermined minimum value over the entire cutting path. This form of display may thus be used not only to determine the resistance and hence the progress at a point or at a position of the blade when separating tissue, but also to determine a complete separation of the tissue over the entire cutting path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosed embodiments will be described in more detail with reference to exemplary embodiments, which will be explained in greater detail with reference to the enclosed drawings. 
         FIG. 1  illustrates a tubular shaft instrument for separating tissue. 
         FIG. 2  illustrates the tool head of the tubular shaft instrument from  FIG. 1 , including a first and a second mouth part, 
         FIG. 3  illustrates the second mouth part of  FIG. 2  in a perspective lateral view. 
         FIG. 4  illustrates the second mouth part of  FIG. 2  in a view from above. 
         FIG. 5  illustrates the second mouth part of  FIG. 2  in a lateral view. 
         FIG. 6  illustrates the first mouth part of  FIG. 2  in a perspective lateral view. 
         FIG. 7  illustrates the first mouth part of  FIG. 2  in a view from above. 
         FIG. 8  illustrates the first mouth part of  FIG. 2  in a lateral view. 
         FIG. 9  is a schematic diagram of two different articulations. 
         FIG. 10  illustrates a cross-section through the tool head of  FIG. 2  with a cutting device. 
         FIG. 11  is a schematic diagram of the cutting device. 
         FIG. 12  is a schematic view of the cutting device in a tubular shaft of a tubular shaft instrument. 
         FIG. 13  illustrates an embodiment of a cutting blade. 
         FIG. 14  illustrates another embodiment of a cutting blade. 
         FIG. 15  illustrates another embodiment of a cutting blade. 
         FIG. 16  illustrates a block diagram of an incision monitoring device. 
         FIG. 17  illustrates a perspective view of a tool head in an open position. 
         FIG. 18  illustrates the tool head of  FIG. 17  in a closed position. 
         FIG. 19  illustrates the second mouth part of  FIG. 2  with a tension strip. 
         FIG. 20  is a schematic lateral view of the tubular shaft instrument of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The same reference numerals are used in the following description for identical parts and parts acting in an identical manner. 
       FIG. 1  provides a rough overview of a disclosed embodiment of a tubular shaft instrument  20 . It shows three functional components of the tubular shaft instrument  20 —a handle  110 , a longish tubular shaft  24  and a tool head  30  disposed on the distal end of tube shaft  24 . Tool head  30  provides the tubular shaft instrument&#39;s actual functionality. It is used for cutting and/or coagulating tissue. Handle  110  controls the movement of tool head  30 . In particular, for fixing, coagulating and cutting tissue mouth parts  10 ,  10 ′ (see, e.g.,  FIG. 2 ) may be opened and closed by handle  110 . 
       FIG. 2  shows one disclosed embodiment of a tool head  30  that includes a first mouth part  10  and a second mouth part  10 ′. First mouth part  10  is an oblong body having on its side facing tubular shaft  24  an adapter  25 , which is rigidly joined to the previously described tubular shaft  24 . Second mouth part  10 ′ is attached to first mouth part  10  by way of an articulation  40  and may be brought from an open position for seizing the tissue into a closed position for fixing the tissue. Articulation  40  is designed such that a virtual fulcrum  1  or pivot is located outside first and second mouth parts  10 ,  10 ′. Unlike conventional articulations  40  for such instruments, fulcrum  1  is not, therefore, located in the region where mouth parts  10 ,  10 ′ engage each other or in the tubular shaft  24  close to the longitudinal axis of tube shaft  24 . The illustrated mechanism of articulation  40  acts such that a virtual fulcrum  1  is created above the side of the tubular shaft instrument which faces second mouth part  10 ′. 
     One advantage of such a relocated fulcrum  1  is now described with respect to the schematic diagrams of  FIG. 9 . Illustrated in the top left-hand corner of  FIG. 9  is a conventional articulation  40 , the fulcrum  1  of which is located substantially on the longitudinal axes of mouth parts  10  and  10 ′. In the open position, tip  16 ′ of second mouth part  10 ′ is offset backwards relative to tip  16  of first mouth part  10 . However, as can be seen in the other two diagrams of  FIG. 9  (which illustrate a disclosed embodiment) this is not the case. Instead, in disclosed embodiments, fulcrum  1  is located noticeably above the longitudinal axes of both oblong mouth parts  10 ,  10 ′. With the same opening in respect of the angle formed by first mouth part  10  relative to second mouth part  10 ′, tip  16 ′ of second mouth part  10 ′ is located substantially on or in front of a perpendicular straight line through tip  16  of first mouth part  10 , even in the open state. If second mouth part  10 ′ is opened relative to first mouth part  10 , there is not only a rotary displacement during which the relative alignment of second mouth part  10 ′ changes relative to first mouth part  10  but there is also a longitudinal displacement of second mouth part  10 ′ which is oriented distally, that is to say parallel to the longitudinal axis of first mouth part  10  in the direction of its tip  16 . Conversely, during a closing movement of mouth parts  10 ,  10 ′, there is a longitudinal displacement of second mouth part  10 ′ in the proximal direction. As a result of this, tissue which is located between both mouth parts  10 ,  10 ′, is ultimately drawn into tool head  30 . Furthermore, according to the disclosed embodiments, the lift of second tip  16 , that is to say the distance between first and second tip  16 ,  16 ′, is considerably greater with the same opening angle (see, e.g.,  FIG. 9 , right-hand side as compared to left-hand side). In one disclosed embodiment, the length of mouth parts  10 ,  10 ′ relative to the distance of the longitudinal axis of first mouth part  10  to the fulcrum is in the ratio of approximately 10:1. 
     While in  FIG. 9  relocated fulcrum  1  is achieved, for the sake of illustration, by way of extensions attached vertically on the proximal ends of mouth parts  10 ,  10 ′, in a preferred embodiment, the formation of fulcrum  1  is purely virtual. This virtual design is achieved by a slotted guide system as is explained below on the basis of  FIGS. 3-8 . Thus, as shown in  FIG. 3 , second mouth part  10 ′ has two curved articulation guide rails  41 ,  41 ′ on its proximal end opposing tip  16 ′. Seen from above ( FIG. 4 ), these articulation guide rails  41 ,  41 ′ run substantially parallel along the longitudinal axis of second mouth part  10 ′ and are spaced apart to form a channel. 
     Seen from the side (see, e.g.,  FIG. 5 ), second mouth part  10 ′ has a spoon-shaped profile. The proximal end of second mouth part  10 ′, in particular articulation guide rails  41 ,  41 ′, thus each have on their upper side a concave section  43 ,  43 ′, which engages with first mouth part  10 . As can be seen in  FIG. 6 , mouth part  10  has two articulation guide pins  42 ,  42 ′, each of which has a convex structural section. During the opening and closing movement of mouth parts  10 ,  10 ′, concave section  43  of first articulation guide rail  41  slides over the adjacent, convex section of first articulation guide pin  42  and concave section  43 ′ of second articulation guide rail  41 ′ slides over the adjacent, convex section of second articulation guide pin  42 ′. The curvature of concave sections  43 ,  43 ′ of both articulation guide rails  41 ,  41 ′ and the corresponding sections of articulation guide pins  42 ,  42 ′ determine the position of virtual fulcrum  1 . With a more pronounced curvature, fulcrum  1  lies closer to tool head  30  than it does with a less pronounced curvature. The effects described with respect of  FIG. 9  thus occur correspondingly more or less pronounced than as described with respect to  FIG. 9 . 
     Compared to articulations that only have a single-point connection, the guide mechanisms or articulation  40  additionally have the advantage of high stability. Due to the convex and concave sections which engage with each other, a large-area contact region is formed and articulation  40  can absorb significantly more force than an articulation having a single-point connection. To further stabilize articulation  40 , first mouth part  10  includes a first articulation guide bearing  46  and a second articulation guide bearing  46 ′. Like articulation guide pins  42 ,  42 ′, articulation guide bearings  46 ,  46 ′ are attached alternately on the inside of the sidewalls of first mouth part  10 . 
     First articulation guide bearing  46  and first guide pin  42  are spaced apart such that they accommodate first articulation guide rail  41  in the space between them. First articulation guide bearing  46  has a concave cross-section, which engages with convex section  44  of first articulation guide rail  41 . On opening and closing the tool head  30 , first articulation guide rail  41 , guided by first guide pin  42  and first articulation guide bearing  46 , rotates about fulcrum  1 . 
     Likewise, second articulation guide rail  41 ′, guided by second guide pin  42 ′ and articulation guide bearing  46 ′, rotates about fulcrum  1 . Second articulation guide rail  41 ′, second articulation guide pin  42 ′, a convex section  44 ′ of second articulation guide rail  41 ′ and second articulation guide bearing  46 ′ are designed for rotation and are disposed symmetrically to first articulation guide rail  41 , first articulation guide pin  42 , convex section  44  of first articulation guide rail  41  and first articulation guide bearing  46 . 
     As shown in  FIG. 10 , a tension strip  27  is attached on the proximal end of second mouth part  10 ′. More precisely, it is attached approximately centrally on convex sections  44 ,  44 ′ of articulation guide rails  41 ,  41 ′. To achieve this, articulation guide rails  41 ,  41 ′ have a profile for forming an abutting edge  2  ( FIG. 5 ). Preferably, this abutting edge  2  does not run in a straight line parallel to fulcrum  1 , but is instead designed in a semi-circular shape (see, e.g.,  FIG. 19 ). Due to this elongated abutting edge  2 , along which second mouth part  10 ′ and tension strip  27  are welded, the transmission of force into tension strip  27  is homogenized and the tensile and flexural loading capacity of the weld is significantly increased. In alternative embodiments, acute-angled welds or welds with multiple serrations, which provide a comparable result, are conceivable. Tension strip  27  is substantially wider than it is thick parallel to fulcrum  1 . This ensures resilience and bendability of tension strip  27  upon rotation of the second mouth part  10 ′. In the longitudinal direction of the tubular shaft instrument, however, tension strip  27  is relatively stiff such that shear forces may also be generated. 
     By attaching a first end of tension strip  27  to convex sections  44 ,  44 ′ of articulation guide rails  41 ,  41 ′, it is ensured that the tensile force exerted by means of tension strip  27  always acts substantially tangentially to the circular motion of curved articulation guide rails  41 ,  41 ′ about fulcrum  1 . Thus, a uniform transmission of force independent of the opening angle is assured. A second end of tension strip  27  is operatively connected to handle  110  and may be displaced by means of a control device provided thereon. Due to virtual fulcrum  1 , which, as already explained, is located outside and above mouth parts  10 ,  10 ′, the distance between fulcrum  1  and the first end of tension strip  27  is significantly greater than the distance achieved with normal articulations. Thus, the embodiment of the described tubular shaft instrument has a significantly higher leverage by means of which second mouth part  10 ′ may be moved over tension strip  27 . 
     Each of mouth parts  10 ,  10 ′ has a clamping surface  12 ,  12 ′ for fixing the tissue. First mouth part  10  thus has, on a distal section, a first clamping surface  12  which faces upwards. First clamping surface  12  is formed to be substantially concave transverse to the longitudinal axis of first mouth part  10 . In the closed state of tool head  30 , convex second clamping surface  12 ′ of second mouth part  10 ′ lies substantially parallel to this first clamping surface  12 . 
     In one disclosed embodiment, these clamping surfaces  12 ,  12 ′ are not only suitable for securely fixing the tissue to be cut later, they also form the electrodes for a coagulation process. To achieve this, sections of clamping surfaces  12 ,  12 ′ are electrically conductive and connected via printed conductors to a high-frequency current source, which is also controllable by way of handle  110 . Thus the gripped tissue may be cauterized to such an extent prior to the cutting procedure that separation is possible without bleeding. Preferably, sections at least of mouth parts  10 ,  10 ′ are manufactured from ceramic material by injection molding. Thus the guide elements, in particular articulation guide rails  41 ,  41 ′ and articulation guide pins  42 ,  42 ′ of articulation  40 , are easy to form. Forming articulation  40  of ceramic material creates an electrical insulation between mouth parts  10 ,  10 ′, in particular between their electrodes for coagulation. 
     In one disclosed embodiment, the actual mechanical cutting process takes place after coagulation. To achieve this, a cutting device  50  is moved parallel to a fixing plane x-y (see, e.g.,  FIG. 11 ), which is defined by clamping surfaces  12 ,  12 ′. This cutting device  50  includes a blade  51  for separating the tissue in addition to a guide wire  52  by means of which a displacement of blade  51  in the longitudinal direction of the tubular shaft instrument (x-axis) is possible. 
     Prior to the cutting process, blade  51  is drawn back towards tubular shaft  24  far enough that premature injury of the tissue is not possible. Preferably, the blade in first mouth part  10  is at the level of articulation guide pins  42 ,  42 ′. From this starting position, blade  51  is brought onto fixing plane x-y by way of a ramp  55  integrated in second mouth part  10 ′ (see, e.g.,  FIG. 4 ). This ramp  55  is located between the two articulation guide rails  41 ,  41 ′. Second mouth part  10 ′ provides a blade guide  53  for the displacement of blade  51  or the cutting device  50 . This blade guide  53  is an oblong opening extending along the longitudinal axis of second mouth part  10 ′. In order to hold blade  51  perpendicular to fixing plane x-y, second mouth part  10 ′ has side parts  60 ,  60 ′ in a central region. The side parts  60 ,  60 ′ are disposed parallel to each other such that they form a channel extending lengthways. Blade  51  or the cutter is guided in this channel. 
     After closing mouth parts  10 ,  10 ′, blade  51  thus glides out of its starting position over ramp  55  into the previously described channel and may there be pulled or pushed distally and proximally over the tissue. Blade  51  is preloaded relative to fixing plane x-y in order to ensure that this displacement separates the tissue step-by-step. A preloading device exerts a force perpendicular to fixing plane x-y, which presses blade  51  against the plane. This force is built up via the resilience of guide wire  52  and its curvature. As can be seen from  FIG. 12 , guide wire  52  is curved perpendicular to fixing plane x-y in the plane preloaded by blade  51 . A crimp  56  is located in a front section of guide wire  52 . Crimp  56  is integrated in guide wire  52  in such a manner that in the fully extended state of cutting device  50 , that is to say when blade  51  is at the distal end of mouth parts  10 ,  10 ′, the crimp in tubular shaft  24  is likewise at the distal end of the shaft. Crimp  56  is used to transfer at least part of the force exerted by the curvature of guide wire  52  perpendicular to fixing plane x-y to tubular shaft  24  and has corresponding contact points. The curvature of guide wire  52  is provided such that if the proximal end of the guide wire runs parallel to tubular shaft  24 , the distal end of unattached guide wire  52  is curved downwards and blade  51  lies at least partially below fixing level x-y. Guide wire  52  is operatively connected to handle  110  in such a manner that blade  51  can be moved back and forth in tool head  30  by means thereof. 
     Various other embodiments are conceivable with respect to the design of blade  51 . These will be described in the following on the basis of  FIGS. 13 ,  14  and  15 . One idea of the disclosed embodiment is that blade  51  has at least one section which runs substantially parallel to fixing plane x-y and thus parallel to the fixed tissue. Consequently, during the cutting procedure, blade  51  glides over the tissue until it is completely separated. Unlike in conventional cutting procedures, it can thus be ensured that even when blade  51  is blunt the tissue will be separated and will not be crushed due to the mechanical pressure. The section of the cutting blade formed parallel to fixing plane x-y likewise has the advantage that blade  51  rests on the tissue not only at a single point but usually over a longer region. Therefore, the wearing of blade  51  at only certain points is prevented. 
       FIG. 13  shows a semicircular blade  51 , having a convex curvature. Blade  51  is disposed on the underside of guide wire  52 . It has a blade curvature  54  distally and proximally to the tubular shaft instrument. 
       FIG. 14  shows a blade  51 , comprising two semicircles each disposed one behind the other. 
       FIG. 15  shows a blade  51 , having a blade curvature  54  distally, and a section perpendicular to guide wire  52  proximally. 
     Preferably, blade  51  includes microteeth. 
     In another disclosed embodiment (see, e.g.,  FIG. 10 ), guide wire  52  is a rail. The rail may be designed in such a manner that is has the same functionality as guide wire  52 . Preloading relative to fixing plane x-y may be achieved by means of the rail&#39;s intrinsic resilience or by means of a separate device (e.g., a spring). 
     The cutting device  50  of the disclosed embodiments has been described so far as being used in conjunction with the advantageous articulation shape. Both disclosed embodiments, however, may also be executed separately from one another. 
     Thus,  FIGS. 17 and 18 , for example, show cutting device  50  in a tool head  30 , whereby second mouth part  10 ′ is not in operative connection with first mouth part  10  by way of a slotted guide system. Here fulcrum  1  lies substantially on the longitudinal axis of mouth parts  10 ,  10 ′ 
     In another disclosed embodiment, the tubular shaft instrument includes a cut monitoring device. This device determines when the tissue between the two clamping surfaces  12 ,  12 ′ is completely separated. In a disclosed embodiment, when the tissue is completely separated blade  51  rests on first clamping surface  12 . Since clamping surface  12  includes an electrode for coagulation, at least a portion of the clamping surface  12  is electrically conductive. According to a disclosed embodiment, at least one section of blade  51 , which mechanically contacts separating surface  12  when the tissue is separated, is likewise formed of an electrically conductive material. The electrical contact between blade  51  and clamping surface  12  is determined by a cut monitoring device. The gripped tissue is deemed to be completely separated when a continuous electrical contact exists between blade  51  and clamping surface  12  during a complete cutting movement by tip  16 ′ of second mouth part  10 ′ up to ramp  55 . As can be seen from  FIG. 16 , the cut monitoring device includes a processing unit  100 , a display device  101 , a switch  103  and a travel sensor  102  for determining and displaying the progress of the cutting procedure. Travel sensor  102  determines the position or displacement of blade  51  and consequently helps to define an observation period that preferably covers a complete blade movement. Switch  103  is formed, in the simplest case, by electrically conductive blade  51  and first clamping surface  12 . Since the tissue to be cut has a certain electrical conductivity, electric switch  103  is only deemed to be closed when a low-ohm connection exists between clamping surface  12  and blade  51 . A corresponding device is connected upstream of processing unit  100 . If processing unit  100  ascertains that there is a continuous low-ohm contact between blade  51  and clamping surface  12  during a complete observation period, it indicates to the user (by means of display device  101 ) that the gripped tissue has been completely separated. Since the displacement of blade  51  over clamping surface  12  without tissue sandwiched between damages the device, the indication of complete separation allows the cutting to stop, thus protecting cutting device  50 . 
     Alternatively, it may also be constantly indicated to the user whether there is a direct mechanical contact between blade  51  and clamping surface  12 . As the user performs the movement of blade  51  manually, he can draw conclusions independently as to whether the tissue is adequately separated. 
     In another disclosed embodiment, travel sensor  102  includes two electrical contact regions on the distal and proximal ends of blade guide  53 , which are designed in such a manner that it is possible to determine contact between blade  51  and the distal contact region as well as between blade  51  and the proximal contact region. Processing unit  100  can thus determine the start and end of the observation interval. 
       FIG. 20  shows a schematic detail view of handle  110  of  FIG. 1 . Handle  110  includes a handle body  117  having a first handle lever  122  integrally formed on the underside thereof. Handle lever  122  has an opening for receiving a plurality of fingers, preferably the middle, ring and little finger. A second handle lever  122 ′ is rotatably joined to handle body  117  close to first handle lever  122 . Mouth parts  10 ,  10 ′ of tool head  30  may be opened and closed by means of a proximal and distal displacement of second handle lever  122 ′ relative to first handle lever  122 . Handle levers  122 ,  122 ′ form a hand trigger  120  and can thus be grasped in the user&#39;s hand such that the entire tubular shaft instrument can be guided with one hand. To achieve this, the hand encloses sections of handle lever  122 ,  122 ′. An extension  125  (which engages in a toothed rack  124 ) is located on the end of second handle lever  122 ′ facing away from handle body  117 . This toothed rack  124  is attached at a right angle to the longitudinal axis of first handle lever  122  on its end facing away from handle body  117 . The teeth of toothed rack  124  are designed in such a manner that second handle lever  122 ′ can be moved step by step towards handle lever  122  and the correspondingly set position remains without a continued exertion of a force. In order to release this fastening of handle levers  122 ,  122 ′ to each other, toothed rack  124  is pressed away from extension  125  such that they are no longer engaged. 
     Handle  110  has a finger trigger  130 , which is likewise rotatably attached to handle body  117 . Cutting device  50 , in particular blade  51 , may be displaced distally by operating finger trigger  130 . A spring element (not illustrated) inside handle body  117  returns finger trigger  130  to its starting position after operation, as a result of which cutting device  50  is displaced proximally. Finger trigger  130  is disposed distally in front of first handle lever  122  in such a manner that finger trigger  130  can be operated with the first finger on grasping handle levers  122 ,  122 ′. 
     Handle  110  has a momentary contact switch  116  on the proximal side of handle body  117 , which controls the coagulation current. In an alternative embodiment, it is possible to provide a control device having a plurality of actuating elements by means of which a plurality of coagulation modes may be selected and performed, instead of momentary contact switch  116 . It is likewise conceivable to provide display device  101  on handle body  117 . 
     In one disclosed embodiment, tubular shaft  24  and handle  110  are designed in such a manner that tubular shaft  24  may be detachably inserted into handle  110 . To achieve this, a receiving opening  112 , which can be closed by means of a cover, is located on the side of handle  110 . 
     Thus, prior to the operation, a sterile disposable tubular shaft  24  having appropriate tool head  30  and cutting device  50  is inserted into reusable handle  110  and locked therein. Reuse of tubular shaft  24  and the associated devices is not envisaged. Handle body  117  has a first coupling element  114 , a second coupling element  114 ′ and a third coupling element  114 ″ for mechanical connection of tool head  30 , cutting device  51  and tubular shaft  24 . A ring provided on the proximal end of tubular shaft  24  engages with third coupling element  114 ″ in such a manner that the tubular shaft is rigidly connected to handle body  117 . A first inner tube adapter  22  engages, by means of a ring likewise disposed on the proximal end, with first coupling element  114 , which is in operative connection with second handle lever  122 ′. The displacement of second handle lever  122 ′ is transferred to first coupling element  114  by means of a mechanism disposed inside handle body  117  and transfers this displacement in turn to first inner tube adapter  22 . This is directly or indirectly joined mechanically to second mouth part  10 ′ by way of tension strip  27 . A longitudinal displacement of first inner tube adapter  22  relative to tubular shaft  24  thus brings about opening and closing of mouth parts  10 ,  10 ′. 
     A second inner tube adapter  22 ′ is disposed movably relative to first inner tube adapter  22  inside the first inner tube. This inner tube adapter  22 ′ is operatively connected to guide wire  52  and displaces blade  51 . Inserting tubular shaft  24  into handle body  117  engages a proximal ring on the end of second inner tube adapter  22 ′ with second coupling element  114 ′ and transfers the displacement or the force exerted by means of finger trigger  130  to cutting device  50 . 
     In order to make it easier to insert disposable tubular shaft  24 , a removable fastening is provided thereon, which holds inner tube adapter  22 ,  22 ′ in a predetermined position relative to tubular shaft  24 . The tubular shaft  24  is designed in such a manner that the rings are easily insertable into coupling elements  114 ,  114 ′,  114 ″ 
     Coupling elements  114 ,  114 ′,  114 ″ are designed such that tubular shaft  24  may be rotated relative to handle  110 . Thus the alignment of tool head  30  can be adjusted freely relative to handle  110 . During rotation, the rings of inner tube adapters  22 ,  22 ′ and of tubular shaft  24  rotate in coupling elements  114 ,  114 ′,  114 ″ and thus form an articulation. 
     It should be pointed out here that all the above described parts and in particular the details illustrated in the drawings are essential for the disclosed embodiments alone and in combination. Adaptations thereof are the common practice of persons skilled in the art.