Abstract:
The invention relates to a surgical instrument comprising a handling part and a tool part that encompasses at least one movably mounted tool which is actuated via a force-transmitting and/or actuating mechanism. Said force-transmitting and/or actuating mechanism is operated from the handling part and is provided with a fluid-operated drive unit. In order to improve said surgical instrument such that the same can be operated with as much sensitivity as possible, the movably mounted tool can be impinged upon a first acutation force in a first driven position while being impinged upon by at least one second actuation force in a least one second driven position with the aid of the drive unit.

Description:
[0001]    This application is a continuation of U.S. patent application Ser. No. 11/716,523 filed on Mar. 8, 2007, which is a continuation of international application number PCT/EP2005/010501 filed on Sep. 28, 2005, claiming priority from German application number 10 2004 049 247.6 filed on Oct. 1, 2004, each of which is incorporated herein by reference in their entirety and for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a surgical instrument comprising a handling part and a tool part, wherein the tool part comprises at least one movably mounted tool, which is actuable by means of a force-transmitting and/or actuating mechanism that is operable from the handling part, and that the force-transmitting and/or actuating mechanism comprises a fluid-operable drive unit. 
         [0003]    Surgical instruments of the initially described type are known for example in the form of bone punches for the removal of bone, cartilage or similar tissue. The drawback of the known bone punches is that sensitive actuation of the movably mounted tool by means of the fluid-operable drive unit is either possible only to a limited extent or even totally impossible. The reason for this is that the drive unit can either be loaded with a fluid flow of specific pressure or not. This however has the disadvantageous consequence that, in the event of actuation of the actuating mechanism, the instrument is generally transferred abruptly from an inoperative or basic position into a working position or vice versa. This may lead for example to a bone punch removing, not a desired tissue area, but a tissue area lying adjacent thereto. 
         [0004]    Therefore, it would be desirable to provide a surgical instrument of the initially described type which may be operated as sensitively as possible. 
       SUMMARY OF THE INVENTION 
       [0005]    In a surgical instrument of the initially described type, according to the invention it is provided that with the drive unit in a first driving position the movably mounted tool can be subjected to a first actuating force and in at least a second driving position can be subjected to at least a second actuating force. 
         [0006]    The development according to the invention of known surgical instruments has the advantage of allowing a surgeon to control the instrument more sensitively while in use. Particularly when the first actuating force differs from the second actuating force, it is possible for example for the tool in the first drive position to be subjected to a force that, for example in the case of a bone punch, is insufficient to cut through tissue but at most sufficient to move the tool up to the tissue. This allows the surgeon to position the instrument in a desired manner and only then transfer the instrument into the second drive position, in which the tool occupies a working position, in which it is therefore able to cut tissue for example. 
         [0007]    It is advantageous when with the drive unit in a third driving position the movably mounted tool is subjected to a third actuating force. This allows the surgeon to control the instrument even more sensitively as he may exert for example three different actuating forces on the movably mounted tool by means of the force-transmitting and/or actuating mechanism. 
         [0008]    Preferably, the third actuating force corresponds to the sum of the first and second actuating force. This allows the drive unit to be designed for example with two fluid piston units, which may each adopt two drive positions. This leads to a marked simplification of in particular the construction of the drive unit. 
         [0009]    In an advantageous manner, a ratio of the first and second actuating force lies in the range of 4:1 to 9:1. This allows a force of approximately 10 to 20% of the maximum force available from the drive unit to be transmitted to the movable tool in the first drive position. In the case of a bone punch, for example, this force is then insufficient to cut off tissue that is to be removed. 
         [0010]    The construction of the instrument is further simplified when the drive unit comprises a linear drive. This might be disposed parallel to the longitudinal direction but is preferably disposed inclined relative to the longitudinal direction. In this way, it may be disposed inside a handle of the handling part. The instrument may therefore be constructed in a particularly compact, handy manner, for example with a handling part in the form of a pistol grip. 
         [0011]    To make it possible to dispense entirely with an electrical energy supply, it is advantageous if the linear drive comprises at least one fluid cylinder. Fluid cylinders are particularly low-maintenance and generally have a long service life. 
         [0012]    In order to construct the linear drive entirely on the basis of fluid cylinders, it is advantageous if the linear drive comprises two coupled, separately controllable fluid cylinders. This allows the one fluid cylinder to be loaded independently of the other fluid cylinder with a fluid for generating a driving force. Equally, however, both fluid cylinders may also be loaded simultaneously with a fluid, with the result that altogether three active drive positions are selectable. If neither of the two fluid cylinders is loaded with a fluid for generating a driving force, the instrument occupies an inoperative position. This position is subsequently not described as a drive position. 
         [0013]    In order to be able to select three different actuating forces, it is advantageous if the two fluid cylinders have different effective cross sections. If their effective cross sections are identical, then either none, half, or all of the driving force available from the drive unit may be generated. If however the effective cross sections are different, then a first driving force may be less than 50% of the maximum force. The second driving force then corresponds to the difference between the first driving force and the maximum force and is therefore greater than half of the maximum force. 
         [0014]    Drive positions with in particular 10 to 20% of the maximum force, 80 to 90% of the maximum force and the maximum force may be selected when a ratio of the effective cross sections lies in a range of 4:1 to 9:1. 
         [0015]    In an advantageous manner, the at least one fluid cylinder is a pneumatic and/or hydraulic cylinder. A pneumatic cylinder may be operated for example with compressed air, such as is usually available in every operating theatre. 
         [0016]    This has the added advantage that even a not completely sealed system is in principle still operational. Since moreover only air may escape from the system, this does not lead to any compromising of a patient. This might however be the case if hydraulic cylinders were used with a physically non-compatible fluid and a leakage of the drive system were to occur. 
         [0017]    According to a preferred form of construction of the invention, it may be provided that the at least one fluid cylinder is a double-acting fluid cylinder. This allows a piston of the at least one fluid cylinder to be loaded from one side with a fluid for generating a desired driving force. In the opposite direction the piston may equally be loaded with a fluid in order to move the instrument back into a basic position and/or keep it in the basic position. The basic position in an instrument may be selected for example in such a way that the movably mounted tool occupies an open position, i.e. by subjecting it to an actuating force it is transferred from the basic position into a working position, in which it performs a function, for example cuts or holds tissue. 
         [0018]    In order to operate the instrument as a bone punch, it is advantageous when the instrument is designed for the removal of bone, cartilage or similar tissue, having a shank, which extends in a longitudinal direction and carries on its distal end a cutting plate, which is disposed transversely of the longitudinal direction or inclined relative to this longitudinal direction, if the movably mounted tool is a cutting element mounted displaceably on the shank and carrying on its distal end a cutting edge, which is directed towards the cutting plate and movable towards the cutting plate for the cutting of tissue. 
         [0019]    It is particularly advantageous if the tool part is detachably connectable to the handling part. This is particularly easy to achieve when there is disposed on the proximal end of the shank a first coupling element for detachable, positive connection to the force-transmitting and/or actuating mechanism, which has a second coupling element corresponding to the coupling element, and if the first coupling element is a polygon, the outer faces of which are directed radially outwards from a longitudinal axis of the shank. A polygon is particularly easy to manufacture and moreover allows the handling part to be disposed on the tool part in a plurality of discrete rotational positions around the longitudinal axis of the shank. In this case, the number of possible rotational positions usually corresponds to the number of outer faces of the polygon. 
         [0020]    Four, six or eight defined rotational positions are selectable when the polygon is a quadrilateral, a hexagon or an octagon. What is more, the design as a polygon is suitable for ensuring that only tool parts that are approved for the handling part may be connected to the handling part. The coupling element therefore simultaneously forms a kind of coding element for coding a specific type of tool part. 
         [0021]    It is advantageous if the shank at its proximal end is shaped like a sleeve and if the cutting element penetrates the sleeve-like end of the shank. This makes the construction of the shank particularly simple. Furthermore, the sleeve-like end of the shank forms a guide in longitudinal direction for the cutting element. 
         [0022]    In order that the cutting element may be connected easily to the force-transmitting and/or actuating mechanism, it is advantageous if it carries on its proximal end a third coupling element, which is detachably connectable to a drive element of the force-transmitting and/or actuating mechanism, and if the third coupling element is adjoined by stops acting in longitudinal direction of the shank. For example, the drive element may engage between the stops acting in longitudinal direction of the shank or, if the third coupling element is designed in the form of a projection, engage around the lateral stops on the coupling element or even around the coupling element. In this way, a reliable connection and transmission of the driving force from the force-transmitting and/or actuating mechanism to the cutting element may be achieved. 
         [0023]    It is advantageous if, in an inoperative position of the instrument, in which no actuating force is exerted by the force-transmitting and/or actuating mechanism in an actuating direction on the tool, a retaining force may be exerted on the tool by the force-transmitting and/or actuating mechanism in a retaining direction opposite to the actuating direction. Without actuation of the force-transmitting and/or actuating mechanism it is therefore ensured that the instrument always occupies the inoperative position. It is therefore situated always in a defined basic position prior to surgical use. By virtue of the exerted retaining force, moreover, unintentional handling, i.e. holding of the instrument in such a way that the movably mounted tool is oriented parallel to the direction of gravitational force, does not lead to movement of the instrument under the action of gravitational force. 
         [0024]    It is advantageous if the force-transmitting and/or actuating mechanism comprises an actuating member for actuating the drive unit, if the actuating member is movable from a non-actuated basic position, in which the instrument occupies the inoperative position, into an activation position, in which the drive unit occupies the first drive position, and into at least a second activation position, in which the drive unit occupies the second drive position. This allows a surgeon to operate the instrument in a desired manner, namely, to transfer the actuating member from the non-actuated basic position into a first activation position in order to subject the movably mounted tool for example to a low driving force. He may however also actuate the actuating member in such a way that the movably mounted tool is subjected to a maximum force. The actuating member may, but need not necessarily, be of a one-piece construction. It would be conceivable in particular to divide the actuating member, for example in order to control two fluid cylinders separately, for example by means of two independent control valves which a surgeon may, in a similar manner to a trumpet player, actuate independently of one another. 
         [0025]    In order to indicate to the surgeon the position, in which the instrument is situated, it is advantageous if the actuating member is held under spring bias in the basic position. A surgeon therefore always knows, when he picks up the instrument, that it is not actuated. 
         [0026]    A particularly simple construction of the instrument is achieved if the actuating member is mounted pivotably. In particular, a mounting about a pivotal axis parallel to or transversely of the longitudinal direction of the instrument may be provided. 
         [0027]    According to a further, preferred form of construction of the invention, it may be provided that in the first activation position a first resetting force acts upon the actuating member, that in the second activation position a second resetting force acts, and that the second resetting force is greater than the first resetting force. In this way, the surgeon receives tactile feedback about the actuating position or activation position of the actuating member. If, for example, the driving force in the first drive position is lower than the driving force in the second drive position, this is indirectly communicated to the surgeon by the actuating member. Without having to look at a scale, a surgeon may sense the drive position and hence which driving force is being exerted on the movably mounted tool. 
         [0028]    In order to allow a clear distinction between the two activation positions, it is advantageous if the second resetting force is at least twice as great as the first resetting force. 
         [0029]    Resetting forces are particularly easy to generate if, for generating the first and second resetting force, there is provided a resetting unit comprising a first elastic resetting member and a second elastic resetting member. A desired resetting force may therefore be associated with each drive position by selecting a specific elastic resetting member. 
         [0030]    The first and/or the second resetting member is advantageously a spring element. A reliable resetting member may be provided for example in the form of a helical spring. 
         [0031]    It may further be advantageous if the resetting unit is designed to act directly or indirectly upon a control member for controlling the drive unit or upon the actuating member. This further simplifies the construction of the instrument, thereby allowing a particularly compact construction. 
         [0032]    According to a preferred form of construction of the invention, a control member may be provided for controlling the drive unit and that the actuating member acts directly or indirectly upon the control member. Such a development is advantageous particularly when an actuating circuit and a working circuit are not operated with the same form of energy. For example, one circuit may be operated electrically, another by means of a pressure-loaded operating means, for example a fluid. This entails a conversion of control signals, for example electrical or mechanical, into specific fluid flows or electrical signals for the drive unit. 
         [0033]    The construction of the instrument becomes particularly simple if the control member comprises at least one control valve. The control valve may be actuable for example electrically, electronically or mechanically. This makes it possible to provide a mechanical, electrical or electronic actuating member. 
         [0034]    In order to be able to realize three different drive positions, it is advantageous if the at least one control valve has at least three different switching positions. This makes it possible for example to realize an inoperative position of the instrument as well as a first and a second drive position, in which a first and a second actuating force may be exerted on the movably mounted tool. 
         [0035]    It is advantageous if the control valve comprises a valve plunger, when on the valve body a least one port connectable to a fluid source and two ports for each double-acting fluid cylinder are provided, when in a first position of the valve plunger at least one of the fluid cylinders can be loaded with fluid in a retaining direction, when in a second position of the valve plunger at least one of the fluid cylinders can be loaded at both sides with different fluid flows, and when in a third position of the valve plunger at least one of the fluid cylinders can be loaded with a fluid counter to the retaining direction. By virtue of the loading at both sides of at least one of the fluid cylinders in the second position of the valve plunger a particularly gentle transfer from the first into the second and then also into the third position of the valve plunger may be realized. In particular, it is possible with such a control valve to subject one or more of the double-acting cylinders to a retaining force, in a second position to load one of the fluid cylinders with a fluid flow counter to the retaining direction in order to generate a first, low actuating force, and finally in the third valve position to load some or all of the fluid cylinders with a fluid in order to generate a maximum driving force. 
         [0036]    In order as far as possible to generate three different driving forces with the drive unit, it is advantageous if in the second position of the valve plunger a fluid flow is distributed unevenly to the two ports of at least one fluid cylinder. By this means, the at least one fluid cylinder is moved in a defined manner by a specific force difference in a predetermined direction and so either a retaining force or a driving force is generated. 
         [0037]    It is advantageous if the valve plunger is provided with a plurality of annular grooves and in a valve body in different switching positions defines different annular chambers, the ratios of cross section of which in dependence upon a fluid pressure are mutually adapted in such a manner that in the second switching position only a fraction of a maximum actuating force may be generated by the at least one fluid cylinder. In principle, it would be conceivable with one control valve to operate only a single fluid cylinder, wherein in different switching positions of the control valve a double-acting fluid cylinder is loaded with different pressure differences at both sides of its piston in order thereby to generate different driving forces. The valve plunger of the described design is easy to manufacture. Furthermore, this allows easy selection of desired driving force ratios. 
         [0038]    In an advantageous manner, at least two control valves are provided, each having at least two switching positions. In this way, a total of four switching positions, including an inoperative position, may be defined. Two control valves have the advantage that either none, one of the two or both simultaneously may be pressed. A surgeon can therefore also immediately know, in which drive position the instrument is situated. 
         [0039]    In an advantageous manner, the at least two control valves are manually separately actuable. A surgeon can therefore tell directly by touch or feel, in which working position the instrument is situated. 
         [0040]    It is advantageous if on the tool part at least one coding unit is provided for coding the nature and/or type of the tool part and when on the handling part a decoding unit is provided for decoding the nature and/or type of the tool part. By means of a coding of the tool part, the handling part may for example be set so as to limit a maximum force that may be generated by the drive unit. Particularly when sensitive tool parts are used, this may prevent damage to the tool part. The coding moreover makes only approved tool parts being connectable to the instrument. 
         [0041]    According to a preferred form of construction of the invention, it may be provided that the at least one coding unit comprises no or at least one projection protruding from the tool part or at least one recess disposed in the tool part, that the decoding unit comprises an operating-mode switching member that corresponds to the at least one projection or the at least one recess, that the operating-mode switching member has at least a first and a second operating-mode position, and that the operating-mode switching member in accordance with the coding of the tool part occupies one of the at least two operating-mode positions. For example, by means of the operating-mode switching member a fluid flow or an energy supply of the drive unit elsewhere may be limited to prevent damage to the tool part. 
         [0042]    It is therefore advantageous if the at least two operating-mode positions are associated with maximum actuating forces of the drive unit. For example, in a first operating-mode position a maximum driving force of the drive unit may be generated, in a second operating-mode position on the other hand only a reduced driving force, for example only a driving force corresponding to approximately 80 to 90% of the maximum force, may be generated. 
         [0043]    It is advantageous if the operating-mode switching member is coupled to the control member and if the operating-mode switching member in at least one operating-mode position directly or indirectly deactivates at least one switching position of the control member. For example, the operating-mode switching member may be constructed in such a way that it mechanically or by means of control technology prevents the control member being moved into a switching position, in which with the drive unit a maximum force for actuating the movable tool may be generated. 
         [0044]    A detailed explanation of the invention is provided by the following description of a preferred form of construction in connection with the drawings. The drawings show: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]      FIG. 1 : a longitudinal sectional view through a bone punch in a non-actuated position; 
           [0046]      FIG. 2 : an enlarged view of the handling part of the instrument in  FIG. 1 ; 
           [0047]      FIG. 3 : an enlarged detail of a switching valve illustrated in  FIG. 2 ; 
           [0048]      FIG. 4 : a view similar to  FIG. 2  of the instrument in a first working position; 
           [0049]      FIG. 5 : a view similar to  FIG. 3 , but in the first working position; 
           [0050]      FIG. 6 : a view similar to  FIG. 2  in a second working position; and 
           [0051]      FIG. 7 : a view similar to  FIG. 3 , but in the second working position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0052]      FIGS. 1 to 7  show a surgical instrument according to the invention in the form of a bone punch, which is provided as a whole with the reference character  10 . The bone punch  10  comprises two basic sub-assemblies, namely a handling part  12  and a punching tool provided with the reference character  14 . 
         [0053]    The punching tool  14  comprises an elongate shank  18 , which extends in a longitudinal direction  16  and carries on its distal end a cutting plate  20 , which is inclined at an angle of approximately 45° relative to the longitudinal direction  16 . A proximal end of the shank forms a coupling piece  22  in the form of an elongate cuboid, which is quadrilateral in cross section and has chamfered longitudinal edges. The coupling piece  22  is provided with a through-bore  24  that defines the longitudinal axis  16 . There is further formed on the coupling piece  22  at a slight distance from the proximal end of the shank  18  a groove-like indentation  26  extending in peripheral direction, wherein a base of the indentation forms a quadrilateral  28 . The quadrilateral  28  serves as a first coupling element for twist-proof connection of the punching tool  14  to the handling part  12 . The coupling element (quadrilateral  28 ) simultaneously forms a kind of coding element for coding a specific type of tool part. A side wall  30  of the indentation  26  adjoining the quadrilateral  28  on the proximal side forms a stop acting in a distal direction. A side wall  32  adjoining the indentation  26  on the distal side forms a stop acting in a proximal direction. 
         [0054]    On the distal side of the indentation  26  there are formed on the coupling piece  22  four identical securing bores  34 , which extend in radial direction relative to the longitudinal axis  16  as far as the through-bore  24  through the coupling piece  22 . The cuboidal coupling piece  22  moreover reduces in diameter at the distal side and at its end has a substantially circular-sleeve-like shape. 
         [0055]    The punching tool  14  comprises a punch  36 , which on its distal end carries a cutting edge  38 , which is inclined relative to the longitudinal axis  16  by the same angle as the cutting plate  20 . The punch  36  rests substantially along its entire length flat against a shank surface  40  of the shank  18 . At the proximal end the punch  36  penetrates the through-bore  24  of the coupling piece  22 . In this region the punch  36 , which at the distal end is otherwise substantially cuboidal in cross section, is cylindrical in shape. Adjoining the cylindrical portion of the punch  36  at the proximal end is a quadrilateral, plate-shaped flange  42 , which at the distal end delimits a coupling square  44  and forms a stop acting in proximal direction. Adjoining the coupling square  44  and forming an end of the punch  36  is a square end plate  46 , which forms a stop acting in distal direction. The flange  42  moreover forms a stop, which acts in distal direction and strikes against the proximal end of the coupling piece  22  when the cutting edge  38  occupies its most distal position, i.e. rests against the cutting plate  20 . 
         [0056]    For stabilizing a movement of the punch  36  relative to the shank  18 , in addition to the guide formed by the coupling piece  22  there is disposed on the distal end of the shank a guide groove  48 , which widens in cross section away from the shank surface  40 . Guided in the guide groove  48  is a guide projection  50 , which protrudes from the punch  36  and extends parallel to the longitudinal axis  16  in proximal direction from the distal end of the punch  36 . The guide projection  50  and the guide groove  48  are constructed in a substantially corresponding manner, for example they may have a dovetail shape. 
         [0057]    Starting from the cutting edge  38  the punch  36  is provided with a blind-hole-like recess, which extends parallel to the longitudinal axis  16  and serves as a tissue reservoir  52  for tissue removed by the bone punch  10 . Tissue  54  that has been punched out by the cutting edge is pushed into the tissue reservoir  52  through a distal opening  56  thereof and, upon further punching-out of tissue  54 , is advanced in proximal direction, i.e. in the direction of the arrow A in  FIG. 1 . In the embodiment illustrated in the drawings, for emptying the tissue reservoir  52  there is provided in the punch  36  a discharge opening  58 , which is formed by a bore of the punch  36  that extends obliquely relative to the longitudinal axis and establishes a fluid connection between the tissue reservoir  52  and an area surrounding the punching tool  14 . Tissue  54  that has been punched out and stored in the tissue reservoir  52  may be discharged out through the discharge opening  58 . In an alternative, non-illustrated form of construction of the invention, there may be provided in the punch  36  an ejector in the form of a rod, which is displaceable parallel to the longitudinal axis  16  and by means of which, starting from the proximal end of the tissue reservoir  52 , tissue stored therein may be expelled in distal direction out through the opening  56 . 
         [0058]    The handling part  12  of the bone punch  10  is designed substantially in the form of a housing similar to a pistol grip. It comprises an elongate cuboidal upper housing part  60 , which extends parallel to the longitudinal axis  16  and has an opening  66  facing in distal direction and forms a substantially elongate, cuboidal receiving chamber  64  for the coupling piece  22  of the shank  18 . Transversely thereof and with a slight inclination in proximal direction a handle  62  projects from the upper housing part  60 . 
         [0059]    The upper housing part  60  comprises a sliding cover  70 , which is guided parallel to the longitudinal axis  16  by means of two guides in the form of rib-like projections on either side in longitudinal grooves in side walls  72  of the upper housing part  60  that extend parallel to the longitudinal axis  16 . The sliding cover  70  in its most distal position completely covers the receiving chamber  64  and in its most proximal position predominantly clears the receiving chamber  64 , thereby forming an insertion opening, through which the coupling piece  22  may be inserted into the receiving chamber  64  in a direction transversely of the longitudinal axis  16 . 
         [0060]    On inner sides of the side walls  72  two coupling projections  74 , which face one another and form a second coupling element, are positioned opposite one another. They are designed substantially in the form of flat cuboids, the dimensions of which are so selected that the two coupling projections  74  may engage between the side walls  30  and  32  into the indentation  26  and rest substantially against the quadrilateral  28 . By this means, the punching tool  14  is fixed axially on the handling part  12 . 
         [0061]    As may be seen particularly well in  FIG. 1 , on the distal side of the coupling projections  74  the upper housing part  60  is provided at its underside with a downwardly open, cup-shaped indentation  68 , which in the direction of the receiving chamber  64  is connected by a bore  76 . The indentation  68  in the direction remote from the receiving chamber  64  is provided from the outside with a disc  78 , which forms a radially inwardly projecting flange. The indentation  68  is used to receive a securing knob  80 , which comprises a cylindrical bolt  82  that penetrates the bore  76  and carries a head  84 , wherein in the transition region between the head  84  and the bolt  82  a radially outwardly projecting annular flange  86  is formed. Adjacent to the bore  76  there is supported in the indentation a helical spring  88 , which surrounds the bolt  82  and is supported by its other end against the underside of the head  84 . As a result, the annular flange  86  in a basic or inoperative position, such as is illustrated in  FIGS. 1 and 3 , is pressed against the disc  78 . The securing knob  80  may be moved counter to the action of the helical spring  88  in the direction of the receiving chamber  64 , as is indicated in  FIG. 4  by the arrow E. The securing knob  80  is moreover disposed in such a way that, when the coupling piece  22  is inserted into the receiving chamber  64 , in the basic position, in which the helical spring  88  presses the annular flange  86  against the disc  78 , the securing knob  80  substantially positively fills the securing bore  34 . In the inserted state of the coupling piece  22 , however, the securing knob  80  may only be moved in the direction of the receiving chamber  64  when an annular groove  90 , which in peripheral direction surrounds the cylindrical part of the punching tool  14  that penetrates the through-bore  24 , overlaps with the security bores  34  in radial direction. As is shown in  FIG. 1 , this is the case when the punching tool  14  is in its most proximal position relative to the shank  18 , i.e. when there is the maximum distance between the cutting edge  38  and the cutting plate  20 . If the securing knob  80  is then pressed, then, as illustrated in  FIG. 4 , a front end of the bolt  82  engages into the annular groove  90 , thereby preventing a movement of the punching tool  14  parallel to the longitudinal axis  16 . 
         [0062]    A pneumatic drive device provided as a whole with the reference character  92  is disposed substantially in and/or on the handle  62 . The drive device  92  comprises an actuating lever  94 , which is disposed at a side of the handle  62  facing in distal direction, directly underneath the upper housing part  60 , and mounted pivotably about a swivel axis running transversely to the longitudinal axis  16 , a switching valve  96  that is actuable by means of the actuating lever  94 , and a drive unit that comprises a first pneumatic cylinder  98  and a second pneumatic cylinder  100 . 
         [0063]    The two pneumatic cylinders  98  and  100  are each of a double-acting design, wherein the first pneumatic cylinder  98  comprises a cylindrical piston chamber  102 , in which a piston  106  sealed by means of two sealing rings  104  is displaceable parallel to the axis of symmetry of the piston chamber  102 . The piston chamber  102 , in an identical manner to the handle  62 , is slightly inclined relative to the longitudinal axis  16 . Projecting from the piston  106  and directed towards the receiving chamber  64  is a piston rod  108 , which is guided in a piston bore  110  that connects the piston chamber  102  to the receiving chamber  64 . A piston chamber  112  directly adjoins the piston chamber  102 , namely with a slightly larger inside diameter. In this, a displaceably mounted piston  114  is sealed by means of two sealing rings  116  and connected by a piston rod  118  directly to the piston  106 . The two pneumatic cylinders  98  and  100  therefore form an, as a whole, rotationally symmetrical piston/cylinder unit. The piston chambers  102  and  112  are separated by a sealing disc  120  that is penetrated by the piston rod  118 . Each of the two pneumatic cylinders  98  and  100  is provided with two ports X and Y, through which the pistons  106  and  114  can be acted upon by compressed air. The ports X are in this case disposed in each case at an end of the respective piston chamber  102  or  112  remote from the receiving chamber  64 , so that the pistons  106  and  114  upon loading with compressed air through the ports X are moved in the direction of the arrow B in  FIG. 1 . The ports Y are disposed in each case at the other end of the two piston chambers  102  and  112 , so that the pistons  106  and  114  when acted upon by compressed air through the ports Y are moved in an opposite direction to the arrow B. 
         [0064]    Adjoining the piston rod  108  and directed towards the receiving chamber  64  is a cuboidal extension  122 , which carries a drive pin  124  that projects on both sides transversely of the longitudinal axis  16  and of the longitudinal axis of the piston rod  108 . Extending parallel to the drive pin  124  and disposed in the transition region of the upper housing part  60  to the handle  62  is a bearing shaft  126 , which is used to mount an L-shaped angle lever  128 . A first lever arm  130  of the angle lever  128  is directed substantially towards the receiving chamber  64 , a second lever arm  132  is oriented in proximal direction substantially parallel to the receiving chamber  64 . 
         [0065]    Free ends of the two lever arms  130  and  132  are slotted in each case in the direction of the bearing shaft  126  parallel to a plane of symmetry of the bone punch  10 , so that the free ends are each of a U-shaped design. The angle lever  128  is disposed in such a way that the slotted free end of the first lever arm  130 , which is designed in the form of two disc-shaped drivers  134 , engages on both sides around the coupling square  44  between the flange  42  and the end plate  46  but does not project laterally beyond the flange  42  and the end plate  46 . The first lever arm  130  is moreover tapered in such a manner relative to the drivers  134  that only these may come into contact with the flange  42  and the end plate  46 . The slotted end of the second lever arm  132  is provided with in each case one elongate-hole-like slot  136  and surrounds the extension  122 , wherein the drive pin  124  engages into the slots  136  and is guided therein. 
         [0066]    The second lever arm  132  is approximately twice as long as the first lever arm  130 . The angle lever  128  therefore forms, on the one hand, a force deflection unit for deflecting a driving force, which may be generated in the direction of the arrow B in  FIG. 1  by the pneumatic cylinder  98  and  100 , in a drive direction extending parallel to the longitudinal axis  16  and symbolized by the arrow C in  FIG. 1 . At the same time, the angle lever  128  also forms a mechanical advantage unit, by means of which the driving force generated by the piston/cylinder unit is doubled owing to the length ratio of the lever arms  130  and  132 . 
         [0067]    The pneumatic cylinders  98  and  100  are controlled by means of the switching valve  96 , which is disposed in the region of an end  63  of the handle  62  facing away from the receiving chamber  64 , in an elongate cylindrical hollow chamber  137  extending parallel to the second pneumatic cylinder  100 , and comprises a plunger  138 , which is actuable by the actuating element  94  and displaceable parallel to the pistons  106  and  114 . The switching valve  96  as a whole is of a rotationally symmetrical design, wherein the plunger  138  comprises an elongate cylindrical plunger body  139  that penetrates the switching valve  96 . An end of the plunger  138  facing towards the actuating lever  94  forms a plunger tip  162 , which is reduced in one stage in diameter and penetrates a bore  166 , which penetrates the hollow chamber  137  at an inner end face  164 , and rests directly against an actuating surface  95  of the actuating lever  94  that faces the end  63 . The bore  166  has a diameter smaller than an outside diameter of the plunger body  139 , so that the end face  164  forming an inner annular surface forms a stop for the plunger body  139 . 
         [0068]    An end of the plunger body  139  remote from the actuating element  94  is provided with a blind hole  140  that is open in the direction of the end  63 , so that this end of the plunger body  139  is designed like a sleeve. A helical spring  142  is supported against a blind hole base  141  of the blind hole  140  that faces the end  63 . 
         [0069]    A sleeve-like valve insert  168  is inserted into the hollow chamber  137 , filling the entire length thereof, and is penetrated by the plunger body  139  along the axis of symmetry thereof. Adjacent to its end facing the end  63 , the valve insert  168  is provided with a short externally threaded portion  170 , which is designed to correspond with a short internally threaded portion  172  adjacent to an end of the hollow chamber  137  facing the end  63 . The valve insert  168  is screwed by means of the externally threaded portion  170  into the hollow chamber  137  and is therefore axially fixed. 
         [0070]    An inside diameter of the valve insert  168  roughly corresponds to a maximum outside diameter of the plunger body  139 . The inside diameter of the valve insert  168  is moreover widened in one stage roughly along the length of the externally threaded portion  170 , thereby forming a valve chamber  148 , the diameter of which is slightly larger than a maximum outside diameter of the plunger body  139 . The valve chamber  148  is closed in the direction of the end  63  by a cover  174 , the inner side of which forms a base  151  facing towards the actuating lever  94 . 
         [0071]    The base  151  is interrupted centrally by an inlet opening  150  in the form of a bore. The one-stage widening in the interior of the valve insert  168  forms an annular wall  147  facing towards and extending parallel to the base  151 . This annular wall  147  forms a stop for a disc  144 , the outside diameter of which corresponds to the inside diameter of the valve chamber  148  and which has a circular through-hole, the diameter of which is slightly smaller than a maximum outside diameter of the plunger body  139 . The previously mentioned helical spring  142  is supported by its other end against the base  151  and surrounds the inlet opening  150  of the valve chamber. The maximum outside diameter of the helical spring  142  is so selected that the spring penetrates the through-hole of the disc  144  without play. The helical spring  142  presses the plunger  138  in the direction of the actuating lever  94 , so that the switching valve  96  in the non-actuated state rests with its plunger tip  162  against the actuating surface  95  of the actuating lever  94 . A further helical spring  146  is supported by one end against the disc  144  and by the other end against the base  151  and surrounds the helical spring  142 . The helical spring  146  has a spring constant that is many times greater than that of the helical spring  142 . 
         [0072]    The plunger  138  may be moved from a non-actuated position, such as is shown in  FIGS. 1 to 3 , counter to the action of the helical spring  142  towards the disc  144  until the sleeve-like end of the plunger body  139  strikes against the disc  144 . The switching valve  96  then occupies a first switching position, such as is shown in  FIGS. 4 and 5 . If the actuating lever  94  is pivoted further, the sleeve-like end of the plunger body  139  drives the disc  144  then also counter to the action of the helical spring  146 . This second switching position is shown in  FIGS. 6 and 7 . Thus, upon actuation of the actuating lever  94  an operator may infer a switching position of the switching valve  96  from the resetting forces generated by the helical springs  142  and  146  and exerted on the plunger  138 . As the spring constant of the helical spring  146  is many times greater than that of the helical spring  142 , an operator receives tactile feedback that a transfer from the first switching position to the second switching position has occurred. 
         [0073]    Starting from its end resting against the end face  164 , the valve insert  168  is provided with altogether eleven identical annular grooves  176  to  186 , wherein there is inserted into each of the even-numbered annular grooves  176 ,  178 ,  180 ,  182 ,  184 ,  186  a sealing ring  188  that forms a sealing lip for the plunger body  139 . 
         [0074]    The plunger body  139  is provided with an annular groove system, which is described with reference to  FIG. 3 . In the basic position of the switching valve  96  illustrated in  FIG. 3 , the sealing ring  188  inserted into the annular groove  176  seals off the plunger body  139  in the direction of the bore  166 . At the level of the annular groove  177  an outside diameter of the plunger body  139  is reduced in one stage and forms an annular groove  190 . Opposite the sealing ring  188  inserted in the annular groove  178 , the outside diameter of the plunger body  139  is reduced once more in one stage and forms an annular groove  191 . The outside diameter of the plunger body  139  then increases again in one stage and forms an annular groove  192  that lies opposite the annular groove  179 . The sealing ring  188  inserted into the annular groove  180  again rests sealingly against the maximum outside diameter of the plunger body  139 . This is in turn adjoined by an annular groove  193  of the plunger body  139  that is reduced in its outside diameter in one stage but has a larger outside diameter than the identical annular grooves  190  and  192 . Lying opposite the sealing ring  188  inserted into the annular groove  182  is a further annular groove  194 , the outside diameter of which roughly corresponds to that of the annular grooves  190  and  192 . This is in turn adjoined by an annular groove  195 , which corresponds to the annular groove  193  and is formed opposite the annular groove  184 . 
         [0075]    The sealing ring  188  inserted into the annular groove  184  once more completely seals off the plunger body  139 . 
         [0076]    The odd-numbered annular grooves  177 ,  179 ,  181 ,  183  and  185  are provided with air inlet openings X, Y and P, which are diagrammatically represented by dashes in the drawings and are connected to the two pneumatic cylinders  98  and  100  as well as to a non-illustrated compressed air source in the following manner. The annular groove  181  is provided with an inlet opening denoted by P, which is connected to the non-illustrated compressed air source. The inlet opening X provided at the annular groove  179  is connected to the two inlet openings of the pneumatic cylinders  98  and  100 , which are denoted there likewise by X. Furthermore, the annular groove  183  is provided with an inlet opening denoted by Y, which is likewise connected to the inlet openings denoted by Y of the pneumatic cylinders  98  and  100 . There are moreover connected to the annular grooves  177  and  185  inlet openings that are both denoted by R. These form ventilation openings, through which compressed air may escape from the system. 
         [0077]    The three possible switching positions of the switching valve  96  are described in detail below. As has already been described, in the non-actuated position of the actuating lever  94  illustrated in  FIGS. 1 to 3 , a so-called inoperative or basic position, the inlet openings X and R of the hollow chamber  137  that are connected to the annular grooves  177  and  179  are fluidically connected. As a result, the two pneumatic cylinders  89  and  100  are ventilated through their inlet openings X. The inlet openings P and Y connected to the annular grooves  181  and  183  are likewise fluidically connected by the annular chambers defined by means of the annular grooves  193 ,  194  and  195 . Thus, the compressed air source is connected via the switching valve  96  to the inlet openings Y of the pneumatic cylinders  98  and  100  in such a way that the two pneumatic cylinders  98  and  100  are moved jointly into their end position counter to the direction indicated by the arrow B. The instrument therefore occupies a retaining position, which corresponds to the inoperative or basic position. There is a maximum distance between the cutting edge  38  and the cutting plate  20 . 
         [0078]    When the actuating lever  94  is pivoted towards the handle  62 , the plunger  138  is moved in the direction of the disc  144 . The switching valve  96  then occupies the first switching position illustrated in  FIGS. 4 and 5 . As a result of the differently selected outside diameters of the annular grooves  190  to  195 , on the one hand the annular grooves  181 ,  179  and  177  are connected to one another so that compressed air may flow through the inlet P of the switching valve  96  and through the inlet X at the annular groove  179  to the inlets X of the two pneumatic cylinders  98  and  100 , these however being connected via the connection by means of the annular grooves  190 ,  191  and  192  also to the ventilation opening R of the annular groove  177 . On the other hand, the inlet P at the annular groove  181  is fluidically connected by the annular grooves  193 ,  194  and  195  to the inlet Y at the annular groove  183  and to the inlet R at the annular groove  185 . Compressed air may therefore flow through the inlets Y into the pneumatic cylinders  98  and  100 . As a result of the specially selected outside diameters of the annular grooves  190 ,  191 ,  192  as well as  193 ,  194  and  195 , the fluid flows into the inlets X and Y, with which the two pneumatic cylinders  98  and  100  are loaded, are distributed in such a way that a resulting driving force acting in the direction of the arrow B corresponds to approximately 20% of a maximum propulsion force that may be generated by the two pneumatic cylinders  98  and  100 . This force, as is illustrated in the area D outlined by dashes in  FIG. 4 , is not sufficient to cut through tissue  54  that is to be removed but is sufficient to move the cutting edge  38  into abutment with the tissue  54 . 
         [0079]    If however the actuating lever  94  is moved further in the direction of the handle  62  as far as the stop, the plunger  138  is transferred into the second switching position, which is illustrated in  FIGS. 6 and 7 . The sealing rings  188  inserted in the annular grooves  178  as well as  182  and  186  completely seal off the plunger body  139 , thereby establishing, on the one hand, a fluid connection between the inlet opening X connected to the annular groove  179  and the inlet opening P connected to the annular groove  181  and, on the other hand, a fluid connection between the inlet opening Y connected to the annular groove  183  and the inlet opening R connected to the annular groove  185 . In this switching position both pneumatic cylinders  98  and  100  are loaded through their inlet openings X with compressed air from the compressed air source. A loading with compressed air in the opposite direction is not possible because the inlet openings Y are connected to the ventilation opening R, which is connected to the annular groove  185 , and are therefore ventilated. Both pneumatic cylinders  98  and  100  are therefore driven in the direction of the arrow B in  FIG. 1 , thereby allowing a maximum driving force to be generated and transmitted to the punch  36 . 
         [0080]    In order further to improve tactile feedback for an operator of the bone punch, the inlet opening X connected to the annular groove  179  may be connected also to the inlet opening  150  of the valve chamber  148 . If in the second switching position, such as is illustrated in  FIGS. 6 and 7 , both of the pneumatic cylinders  98  and  100  are loaded with compressed air of maximum pressure, then this pressure acts also in the same direction as the helical springs  142  and  146 , with the result that a surgeon has to apply an increased actuating force in order to maintain the second switching position of the actuating lever  94 . 
         [0081]    There now follows a detailed description of the mode of operation of a slightly modified form of construction of the drive device  92  of the instrument. 
         [0082]    In a non-actuated position of the actuating lever  94 , the first pneumatic cylinder  98  is loaded with compressed air through its inlet Y in such a manner that the piston  106  is moved against the sealing disc  120 . The bone punch then occupies its open position, i.e. the driver  134  holds the end plate  46  of the punch  36  in its most proximal position. There is a maximum distance between the cutting edge  38  and the cutting plate  20 . 
         [0083]    If the actuating lever  94  is moved counter to the helical spring  142  without the plunger  138  striking against the disc  144 , only the piston  106  is moved in the direction of the arrow B in  FIG. 1  by means of pressure loading through the inlet X between the piston  106  and the rotatable disc  120 . A ratio of the effective cross sections of the first pneumatic cylinder  98  and the second pneumatic cylinder  100  is approximately 1:4, so that initially only a driving force amounting to approximately 20% of a maximum possible driving force is generated and transmitted via the angle lever  128  to the punch  36 . The thus reduced force acting upon the punch  36  is typically insufficient to cut through tissue  54 , for example bone parts, that are to be removed. The force, as is illustrated in the area D outlined by dashes in  FIG. 4 , is only sufficient to bring the cutting edge  38  up to the tissue. In this first actuating position of the actuating lever, an operator of the bone punch  10  may therefore lay the cutting plate  20  in a desired manner against the tissue  54  to be removed, without the tissue  54  actually being cut through at this stage. 
         [0084]    Once the cutting position has been determined, the actuating lever  94  may be fully depressed. The plunger  138  is then moved also counter to the helical spring  146 , the operator sensing this because of the increased actuating force that has to be applied in order to pivot the actuating lever  94 . The switching valve  96  then occupies a switching position, in which both the first pneumatic cylinder  98  and the second pneumatic cylinder  100  are loaded with compressed air through their inlets X, namely in such a way that both pistons  106  and  114  are moved in the direction of the arrow B. A maximum force of the drive device  92  is therefore transmitted via the angle lever  128  to the punch  36  and is capable of cutting through tissue  54  in a desired manner. In this position, inlets Y of the pneumatic cylinders  98  and  100  that are not loaded with compressed air are ventilated in each case. 
         [0085]    When load is removed from the actuating lever  94 , the helical springs  142  and  146  press the plunger  138  back into its basic position, the punch  36  is then loaded once more by pressure loading of the pneumatic cylinder  98  in an opposite direction to the arrow B, with the result that the punch  36  is transferred from its cutting position illustrated in  FIGS. 6 and 7 , via its intermediate position illustrated in  FIGS. 4 and 5 , back into its basic position illustrated in  FIG. 1 , i.e. its most proximal position. 
         [0086]    So much for the mode of operation of the slightly modified form of construction of the drive device  92 . 
         [0087]    To rule out inadvertent actuation of the drive device  92  as a result of an operator pressing the actuating lever  94 , in the proximal region of the upper housing part  60  a safety valve  154  is disposed. The safety valve  154  comprises a valve plunger  156 , which is mounted so as to be displaceable transversely of the longitudinal axis  16  and is spring-biased against an inner side of the cover  70 . When, as is illustrated in  FIG. 1 , the cover  70  is closed, the valve plunger  156  occupies a position, in which it establishes a fluid connection between the compressed-air supply line  152  and the inlet opening  150  of the switching valve  96 . However, when the cover  70  is opened, the end of the valve plunger  156  projecting from the safety valve  154  slides along a stop slope  158  on the inner side of the cover  70 , with the result that the spring-biased valve plunger  156  is moved further out of a body of the safety valve  154 . The safety valve  154  therefore changes its switching position and then interrupts a connection between the compressed-air supply line  152  and the inlet opening  150  of the switching valve  96 , with the result that an actuation of the actuating lever  94  remains ineffective because the drive device  92  is therefore cut off from the compressed air source. It is only when the sliding cover  70  is completely closed again that the valve plunger  156  is pressed far enough into the body of the safety valve  154  for the safety valve  154  to return to the switching position, in which the compressed-air supply line  152  is fluidically connected to the inlet opening  150  of the switching valve  96 . 
         [0088]    Should the bone punch  10  require cleaning while in use, for example because tissue  54  has become jammed between the cutting edge  38  and the cutting plate  20 , there is no need for a surgeon to let go of the bone punch  10 . A person assisting the surgeon may clean a gap between the cutting edge  38  and the cutting plate  20  without running any risk of being injured, even if the operator actuates the actuating lever  94 . In a non-actuated position of the actuating lever  94 , the annular groove  90  and the securing bores  34  overlap. This is illustrated in  FIG. 1 . The person assisting the surgeon may therefore press the securing knob  80  counter to the action of the helical spring  88  so that the bolt  82  engages into the annular groove  90 , in the manner illustrated in  FIG. 4 . A movement of the punch  36  in distal direction is therefore prevented, even in the event of the surgeon pressing the actuating lever  94 . Once the tissue part  54  to be removed has been cut off and removed, the person assisting the surgeon may let go of the securing knob  80  and the surgeon may proceed with the operation. The described cleaning operation is particularly easy to carry out because the securing knob  80  is disposed far enough away from the actuating lever  94 , in particular on the distal side thereof, for the securing knob  80  to be always freely accessible to the person assisting the surgeon. 
         [0089]    By virtue of the special development of the coupling piece  22 , in particular by virtue of providing the quadrilateral  28 , it is possible to connect the punching tool  14  in four different positions to the handling part  12 . In  FIGS. 1 to 5  the punching tool  14  is connected to the handling part  12  in such a way that a gap between the cutting plate  20  and the cutting edge  38  is facing upwards. The two parts of the bone punch  10  may however also be connected to one another in such a way that the gap is facing downwards or towards one of the two sides of the bone punch  10 . To alter a position of the punching tool  14  relative to the handling part  12 , the sliding cover  70  merely has to be displaced in proximal direction until the receiving chamber  63  may be opened and the punching tool  14  removed. The punching tool  14  may then be rotated through 90°, 180° or 270° and inserted back into the receiving chamber  64 . Displacing the cover  70  in distal direction closes the receiving chamber  64  and moreover secures the coupling piece  22  and hence the punching tool  14  on the handling part  12 .