Abstract:
In a surgical obturator with a tubular housing, with a blade carrier displaceable in the tubular housing in the longitudinal direction between an advanced cutting position and a retracted protected position, a blade with a cutting edge being held on the blade carrier, the cutting edge being guided in a correspondingly extending guide of the tubular housing, with a protective cap engaging over the blade and being displaceable in the tubular housing in the longitudinal direction between an advanced rest position in which the blade is completely covered in its protected position and a retracted work position, the protective cap having a slit through which the cutting edge of the blade passes and, in the work position of the protective cap, projects over the latter, and with a retracting device arranged in the tubular housing and displacing the blade from the cutting position to the protected position, the retracting device being activatable by displacement of the protective cap from the work position to the rest position, in order to reduce the size of the retracting device, it is proposed that the retracting device comprise a switching element which fixes the blade in the cutting position and, upon activation, releases the blade for displacement to the rest position, the switching element being mounted in the tubular housing so as to be freely rotatable about the longitudinal axis of the tubular housing and immovable in the longitudinal direction, and the switching element being rotatable, upon displacement of the blade carrier and/or the protective cap in the longitudinal direction of the tubular housing, by means of a cam guide which is operative between the switching element, on the one hand, and the blade carrier and/or the protective cap, on the other hand.

Description:
[0001]    This application is a continuation of internal application number PCT/EP2007/009299 filed on Oct. 26, 2007.  
         [0002]    The present disclosure relates to the subject matter disclosed in international application number PCT/EP2007/009299 of Oct. 26, 2007 and German application number 10 2006 059 012.0 of Dec. 14, 2006, which are incorporated herein by reference in their entirety and for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The invention relates to a surgical obturator for piercing a body wall with a tubular housing, with a blade carrier displaceable in the tubular housing in the longitudinal direction between an advanced cutting position and a retracted protected position, a blade with a cutting edge being held on the blade carrier, the cutting edge being guided in a correspondingly extending guide of the tubular housing, with a protective cap engaging over the blade and being displaceable in the tubular housing in the longitudinal direction between an advanced rest position in which the blade is completely covered in its protected position and a retracted work position, the protective cap having a slit through which the cutting edge of the blade passes and, in the work position of the protective cap, projects over the latter, and with a retracting device arranged in the tubular housing and displacing the blade from the cutting position to the protected position, the retracting device being activatable by displacement of the protective cap from the work position to the rest position. 
         [0004]    Such a surgical obturator is described in German utility model 20 2006 008 405 U1. Herein the retracting device is arranged in the grip area of the obturator where quite a lot of space is available for complex mechanics of the retracting device. 
         [0005]    Such retracting devices are also known from other known surgical obturators. These ensure that the blade or a trocar tip is automatically retracted when the body wall is fully pierced. In all cases, the constructions of the retracting devices are complicated. These retracting devices have a lot of parts and a large space requirement and, therefore, in all cases, they must be arranged in an area remote from the blade or the trocar tip, in some cases, in the grip of the obturator (EP 0 499 457 B1; EP 0 705 077 B1; EP 0 600 921 B1) or in an unwieldy special construction (U.S. Pat. No. 5,462,532 A). 
         [0006]    The object of the invention is to so construct a generic surgical obturator that the retracting device is of less complicated construction and has a lower space requirement than known retracting devices. 
       SUMMARY OF THE INVENTION 
       [0007]    This object is accomplished in a surgical obturator of the kind described at the outset, in accordance with the invention, in that the retracting device comprises a switching element which fixes the blade in the cutting position and, upon activation, releases the blade for displacement to the rest position, the switching element being mounted in the tubular housing so as to be freely rotatable about the longitudinal axis of the tubular housing and immovable in the longitudinal direction, and the switching element being rotatable for switchover, upon displacement of the blade carrier and/or the protective cap in the longitudinal direction of the tubular housing, by means of a cam guide which is operative between the switching element, on the one hand, and the blade carrier and/or the protective cap, on the other hand. 
         [0008]    The movements of the protective cap and the blade carrier, which essentially take place in the longitudinal direction of the tubular housing, are thus used to rotate a switching element by means of cam guides about the longitudinal axis of the tubular housing. This rotational movement of the switching element is used to fix the blade carrier in the cutting position and release it again once the protective cap, after penetration of the body wall, is displaced from the work position to the rest position. The conversion of the displacement of the blade carrier and the protective cap to a rotational movement of the switching element enables a compact construction with only a few individual parts to be achieved and, therefore, this retracting mechanism can be accommodated in the tubular housing itself, preferably in the immediate area of the blade carrier. This does not require the outer dimensions of the tubular housing to be increased or special accommodation areas to be provided for the retracting device. 
         [0009]    In accordance with a preferred embodiment, the protective cap is acted upon by a spring which displaces the protective cap from the work position to the rest position. The displacement of the protective cap to the work position thus takes place against the force of this spring. This spring is also responsible for the protective cap, following complete penetration of the body wall, no longer being held back by the body wall, but being displaced by the opening created by the obturator into the rest position. 
         [0010]    Furthermore, it may be provided that the blade carrier is acted upon by a spring which displaces the blade carrier from the cutting position to the protected position. This spring is responsible for the blade carrier, following completion of the cutting operation and by virtue of the displacement of the protective cap from the work position to the rest position, which activates the retracting device, being retracted from the cutting position to the protected position. 
         [0011]    Provision is made in accordance with a particularly preferred embodiment for the protective cap and the blade carrier to be acted upon by a common spring which pushes these apart, the common spring displacing, on the one hand, the protective cap from the work position to the rest position and, on the other hand, the blade carrier from the cutting position to the protected position. In this construction, this spring is accorded a double function. 
         [0012]    Here it is particularly advantageous for the spring to be a helical spring which is arranged in the interior of the blade carrier and is supported on a projection of the protective cap that extends through the wall of the blade carrier into the interior thereof. In this way, a very compact arrangement of protective cap, blade carrier and spring is obtained. 
         [0013]    The cutting edge of the blade may be straight-lined. However, in accordance with a preferred embodiment, provision is made for the cutting edge of the blade to be of helical configuration, so that the blade carrier, upon displacement in the longitudinal direction relative to the tubular housing, and the protective cap upon longitudinal displacement relative to the blade carrier, are rotated relative to each other about the longitudinal axis of the blade carrier. This rotation takes place by virtue of the guidance of the cutting edge in the tubular housing and by virtue of the guidance of the protective cap imparted to it by the cutting edge passing through the slit in the protective cap. A helical guidance of the cutting edge has the advantage that when piercing the body wall, the surgeon can perform this in a particularly sensitive manner with a combined advancing and rotational movement. This construction also has the advantage that the component of the rotational movement imparted to the blade carrier and the protective cap can also contribute to the rotation of the switching element. 
         [0014]    The blade carrier may advantageously comprise a sleeve-shaped shaft which is arranged concentrically with the tubular housing. 
         [0015]    It is expedient for the blade carrier to be connected to a push rod which extends through the tubular housing as far as a push device at the end of the tubular housing remote from the blade. By means of this push rod which, for example, may be provided with a pushbutton, the blade carrier can be displaced forwards in the longitudinal direction in the tubular housing, so that the blade carrier can thereby move from the retracted protected position to the advanced cutting position. 
         [0016]    Provision is made in accordance with a particularly preferred embodiment for the switching element to be a sleeve which concentrically surrounds the blade carrier. This concentric arrangement allows accommodation of the parts in an extremely small space and also enables optimal functioning of the cam guide operative between blade carrier and switching element. 
         [0017]    It may then be provided that the cam guide operative between the switching element and the blade carrier is formed by cam tracks and cams adapted to abut thereon, the cams and the cam tracks being arranged on the outer side of the blade carrier and on the inner wall of the sleeve-shaped switching element, respectively. 
         [0018]    In particular, it is advantageous for a plurality of similar cam tracks and cams to be arranged along the circumference of the blade carrier and the sleeve-shaped switching element such that in successive work cycles the cams respectively abut on an adjacent cam track. Thus, in one work cycle the switching element is switched further through a certain angular amount, and after such a work cycle the cams then abut on the following, identically constructed cam track. A work cycle is characterized by the blade carrier being displaced from its retracted protected position to the advanced cutting position, blocked there and, following complete piercing of the body wall, released again by displacement of the protective cap from the work position to the rest position and pushed back into its retracted protected position, so that the assembly again reaches its initial state. 
         [0019]    Provision is made in a particularly preferred embodiment for each cam track to have associated with it two cams which, upon displacement of the blade carrier relative to the switching element, abut one after the other on the cam track. During the displacement of the blade carrier, these cams bring about one after the other a rotation of the switching element. 
         [0020]    The cam track can be formed by the edge of an island-shaped projection along which the cams slide in a work cycle and thereby bring about a rotational movement of the switching element. 
         [0021]    Provision is made in a particularly preferred embodiment for a front cam facing the blade, upon displacement of the blade carrier from the protected position in the direction towards the cutting position, to slide along a first section of the cam track that extends at an incline to the direction of displacement of the blade carrier and to thereby rotate the switching element from an initial position in a first direction, for a rear cam facing away from the blade to enter into abutment with a second section of the cam track that extends in the opposite direction at an incline to the direction of displacement of the blade carrier once the front cam has moved past the first section of the cam track, so that the switching element is rotated in the opposite direction into a blocking position in which, upon subsequent retraction of the blade carrier from an end position located in front of the cutting position, a stop arranged on the blade carrier strikes a stop on the switching element and thereby prevents any further retraction of the blade carrier. In this arrangement the blade carrier is therefore not only advanced out of the retracted protected position into the advanced cutting position, but beyond that. This further displacement beyond the cutting position serves to rotate the switching element into a blocking position, so that upon retraction of the blade carrier in the direction towards the cutting position, a further rearward movement of the blade carrier is blocked by the stops, i.e. the blade remains in an advanced position. 
         [0022]    It is expedient for the stop on the blade carrier to be formed by the front cam. There is then no need for a separate stop, which further simplifies the construction. 
         [0023]    The stop on the switching element can be formed by a third section of the cam track that extends transversely to the longitudinal direction of the tubular housing. This also contributes towards simplification of the construction. 
         [0024]    Furthermore, it may be provided that the cam track and the cams between the switching element and the protective cap are formed by the side flanks of teeth which are arranged on the end faces of the protective cap and the switching element that face one another, and which are in engagement when the protective cap is retracted into the work position. Both the protective cap and the switching element thus carry at their end faces that face one another teeth which are not in engagement so long as the protective cap is in its advanced rest position, but which engage once the protective cap is retracted into the work position. 
         [0025]    The flanks of the teeth can be so arranged and designed that the teeth of the protective cap, upon retraction of the protective cap from the rest position to the work position, rotate the switching element from its blocking position in the first direction until the stop of the blade carrier reaches a fourth section of the cam track of the switching element, which extends at an incline to the longitudinal direction of the tubular housing and adjoins the stop of the switching element. Once the stop of the blade carrier abuts on this fourth section, the blade carrier, under the action of the spring acting upon it, exerts a force on the switching element and attempts to rotate it in the second direction. 
         [0026]    However, in accordance with a further preferred embodiment, such a rotation is prevented by the flanks of the teeth being so designed that a rotation of the switching element in the second direction under the influence of the stop of the blade carrier abutting on the fourth section being limited such that the blade carrier, in relation to its position with the two stops abutting on each other, is retracted only slightly as far as its cutting position. The blade carrier is therefore blocked in a cutting position which is retracted only slightly in relation to the blocked position. In this cutting position, the piercing of the body wall can take place as the blade carrier is prevented by the switching element from retracting in the direction towards the protected position. 
         [0027]    Furthermore, it may be provided that the engagement of the teeth of the blade carrier and the protective cap is released upon displacement of the protective cap into the rest position, so that the limitation of the rotatability of the switching element is eliminated. Once this occurs, the blade carrier can be retracted under the influence of the spring into the protected position, i.e., the displacement of the protective cap to the rest position triggers the rearward movement of the blade carrier. 
         [0028]    It is advantageous for the cam track to have a fifth section which adjoins the inclined fourth section and along which the front cam of the blade carrier slides upon retraction of the blade carrier from the cutting position to the protected position and thereby rotates the switching element in the second direction into the initial position for the next work cycle. 
         [0029]    In accordance with a further preferred embodiment, when the switching element is located in the blocking position and the stop of the blade carrier is in abutment with the fourth section of the cam track, the rear cam of the blade carrier is located opposite a sixth section of the cam track, which prevents a displacement of the blade carrier in the direction from the protected position to the cutting position. In its location in the cutting position, the blade is therefore fixed in both directions, and it is not possible for the blade to be inadvertently advanced beyond the cutting position by actuation of the push rod. 
         [0030]    The following description of preferred embodiments of the invention serves in conjunction with the drawings for further explanation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  a perspective view of a surgical obturator with a tubular housing and a blade with a helical cutting edge; 
           [0032]      FIG. 2  an enlarged detail view of area A in  FIG. 1  with the tubular housing cut in the longitudinal direction; 
           [0033]      FIG. 3  a view, similar to  FIG. 2 , in which, in addition, the protective cap is cut in the longitudinal direction; 
           [0034]      FIG. 4  a view, similar to  FIG. 3 , in which, in addition, the switching element and partially the blade carrier are cut in the longitudinal direction; 
           [0035]      FIG. 5  an exploded representation of the front part of the tubular housing, the blade carrier, the protective cap and the switching element; 
           [0036]      FIG. 6  a longitudinal sectional view of the obturator of  FIG. 1  in the initial position with advanced protective cap and retracted blade carrier; 
           [0037]      FIG. 7  a view, similar to  FIG. 6 , with the blade carrier advanced forwards over the cutting position; 
           [0038]      FIG. 8  a view, similar to  FIG. 7 , with the blade carrier and the switching element in the blocking position; 
           [0039]      FIG. 9  a view, similar to  FIG. 8 , with the blade carrier during the transition from the blocked position to the cutting position; 
           [0040]      FIG. 10  a view, similar to  FIG. 9 , with the blade carrier in the cutting position and the protective cap in the work position; 
           [0041]      FIG. 11  a view, similar to  FIG. 10 , with the protective cap in the rest position and during the retracting movement of the blade carrier; 
           [0042]      FIG. 12  a diagrammatic representation of the cam guide between blade carrier and switching element during the advancing movement of the blade carrier from the protected position in the direction towards the cutting position and up to an end position going beyond the cutting position; 
           [0043]      FIG. 13  a view of the cam guide between switching element and blade carrier and between switching element and protective cap during the displacement of the blade carrier from the end position into a blocking position and subsequently in the direction of the cutting position; and 
           [0044]      FIG. 14  a view, similar to  FIG. 13 , during the displacement of the blade carrier into the cutting position and subsequently from the cutting position back into the protected position and therefore into the initial position of the switching element. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0045]    The surgical obturator  1  shown in the drawings comprises an elongated, tubular housing  2 , at the rear end  3  of which a grip  4  of enlarged diameter is arranged. A pushbutton  5  is mounted in the grip  4  for displacement in the longitudinal direction of the housing  2 . The pushbutton  5  is actuatable from the rear side of the grip  4  and is connected to a push rod  6  which leads in the interior of the tubular housing  2  to the front area A thereof. 
         [0046]    In this front area A, the tubular housing  2  ends in a substantially circular cylindrical end cap  7  forming part of the tubular housing  2  and tapering towards its front end  8 . The end cap  7  is open at its front end  8 . 
         [0047]    The end cap  7  encloses an interior  9  which, starting from the front end  8 , comprises two successive step-shaped widenings  10 ,  11  and then two successive step-shaped narrowings  12 ,  13 , so that ring shoulder-shaped projections  14 ,  15 ,  16 ,  17  are respectively formed at these step-shaped widenings and narrowings ( FIG. 6 ). 
         [0048]    The push rod  6  is fixedly connected to a cylindrical shaft  19  of a blade carrier  20  which extends through the entire interior  9  and at its front end  21  carries a blade  22  protruding over this front end  21  and having a helical cutting edge  23  which extends rearwards from a tip  24  towards two opposite sides of the blade carrier  20  ( FIG. 5 ). The cutting edge  23  engages a corresponding guide  25  in the inner wall of the end cap  7 . This guide  25  is formed by a helical groove in the inner wall of the end cap  7 . When advanced by the push rod  6 , an additional rotational movement about the longitudinal axis of the tubular housing  2  is thereby imparted to the blade carrier  20 . 
         [0049]    In a retracted protected position of the blade carrier  20 , it lies with its rear edge  26  protruding radially over the circumference of the push rod  6  against the projection  17  of the interior  9 , whereby the furthermost retracted position of the blade carrier  20  is defined. Starting from this position, the blade carrier  20  can be pushed forwards by the push rod  6  into a cutting position and beyond that. In all cases, the front area of the blade  22  protrudes over the end cap  7  of the tubular housing  2 . 
         [0050]    A protective cap  27  engages over the front area of the blade carrier  20  carrying the blade  22 . The protective cap  27  is arranged between the end cap  7  and the blade carrier  20  and surrounds the latter on all sides. The protective cap  27  is closed at its front end  28  and tapers towards this front end  28 . It has a helical slit  29  whose contour corresponds to the helical cutting edge  23  which extends through this slit  29 . Owing to this slit  29  and the cutting edge  23 , which is guided in the guide  25  of the end cap  7  and projects through the slit  29 , a rotation corresponding to the helical configuration of the cutting edge  23  is also imparted to the protective cap  27  when longitudinally displaced. 
         [0051]    The protective cap  27  carries at its rear end a ring flange-shaped widening  30 , which in the transition to the front, cylindrical area  31  engaging over the blade  22  forms a ring step  32 , and which at its rear edge  33  carries a plurality of teeth  34  uniformly distributed over the circumference and pointing in the direction towards the rear end  3  of the housing  2 . The protective cap  27  is mounted so as to be freely rotatable and displaceable in the longitudinal direction in both its front area  31  and the area of the widening  30  in a ring-shaped intermediate space between the blade carrier  20  and the end cap  7 . It thereby surrounds the blade carrier  20  concentrically. 
         [0052]    In an advanced rest position, the ring step  32  of the protective cap  27  abuts on the projection  14  of the end cap  7 . Starting from this rest position, the protective cap  27  can be pulled back into the end cap  7  up to a retracted work position in which the teeth  34  ending in the rest position in front of the projection  15  project over this projection  15  ( FIGS. 9 and 10 ). This displacement path is short and is limited to a portion of the depth of the teeth  34 . 
         [0053]    Arranged concentrically with the blade carrier  20  and the protective cap  27  in the interior  35  of the blade carrier  20  is a helical spring  36  which is supported, on the one hand, on the end face  37  of the push rod  6  and, on the other hand, on a projection  38 , which is part of the protective cap  27  and projects through a slit-shaped opening  39  in the wall of the blade carrier  20  into its interior  35 . By means of this helical spring  36  the protective cap  27  is displaced into its rest position and the blade carrier  20  into its protected position, i.e., the protective cap  27  abuts with its ring step  32  on the projection  14 , and the blade carrier  20  with its rear edge  26  on the projection  17 . Against the force of the helical spring  36 , the blade carrier  20  can be displaced in the direction towards the cutting position, and a displacement of the protective cap  27  in the direction towards the work position is also possible. 
         [0054]    A sleeve-shaped switching element  40  which concentrically surrounds the shaft  19  is mounted so as to be freely rotatable in a ring-shaped intermediate space between the shaft  19  of the blade carrier  20  and the inner wall of the end cap  7 . The switching element  40  abuts on both the projection  15  and the projection  16  and is thereby mounted immovably in axial direction in the end cap  7 . This switching element  40  carries at its front edge  41  facing the protective cap  27 , opposite the teeth  34  of the protective cap  27 , teeth  42  which are uniformly distributed over the circumference and are formed by indentations  43  extending from the edge  41 . 
         [0055]    Uniformly distributed over the circumference on the inner side of the switching element  40  are a plurality of island-shaped projections  44 , whose outer edge forms a cam track  45  for cams  46 ,  47 , which are arranged on the shaft  19  of the blade carrier  20  and protrude radially outwardly from it. The shaft  19  carries a plurality of front cams  46  distributed uniformly over the circumference and a plurality of rear cams  47  also distributed uniformly over the circumference, which are respectively located in a radial plane ( FIG. 5 ). Upon displacement of the blade carrier  20  in the longitudinal direction, these cams  46  and  47  can rotate the switching element  40  by abutting on the cam tracks  45 . The front and the rear cams successively abut on suitable sections of the cam track  45  and carry out the rotation in accordance with the shape and arrangement of these sections of the cam track  45 . 
         [0056]    In the embodiment shown, the cam track  45 , closed within itself, comprises a first bottom section  48  extending parallel to the longitudinal direction of the housing  2 , a third section  50  adjoining the front side of the island-shaped projection  44  and extending transversely to the longitudinal direction of the housing  2 , adjoined by a fourth section  51  inclined rearwards at approximately 45° to the longitudinal axis of the housing  2 , adjoined by a fifth section  52  inclined to a less pronounced extent in relation to the longitudinal direction of the housing  2 , and a second section  49  inclined from the end of the fifth section  52  in the opposite direction at approximately 45° relative to the longitudinal axis of the housing  2 . Adjoining the rear end of the second section  49  is a sixth section  53  with an upper portion extending forwards at approximately a right angle from the end of the second section  49 , and a bottom portion arranged transversely to the longitudinal direction of the housing  2 , and the bottom end of the sixth section  53  is joined by a seventh section  54  to the rear end of the first section  48 . All sections of the embodiment shown are of straight-lined configuration. 
         [0057]    The cams  46  and  47  are of such shape that at the sides at which they abut on different sections of the cam track  45 , they have abutment surfaces  55  respectively extending parallel to these sections, i.e., in this way, the outer contour of the cams results, on the one hand, from the orientation of the sections  48  to  54  and, on the other hand, from the abutment or non-abutment of the respective cam on the cam track in the area of corresponding sections. Since front and rear cams are provided, not every cam necessarily abuts on all sections of the cam track, but the abutment is assumed by the front and rear cams one after the other. 
         [0058]    Regarding operation of the described assembly, reference is made hereinbelow, in particular, to the representations of  FIGS. 6 to 14 . Before actuation, the entire assembly is in an initial position shown in  FIG. 6 , in which the protective cap  27  is in its advanced rest position, and the blade carrier  20  is in its retracted protected position. The teeth  34  of the protective cap  27  are disengaged from the teeth  42  of the sleeve-shaped switching element  40 . In that area in which the protective cap  27  protrudes over the end cap  7 , the cutting edge  23  of the blade  22  is completely retracted into the interior of the protective cap  27 , so that the cutting edge  23  outside of the end cap  7  does not protrude over the protective cap  27 . However, the cutting edge  23  in the portion of the protective cap  27  that is arranged in the interior of the end cap  7  still extends through the slit  29  of the protective cap  27  into the guide  25  in the inner wall of the end cap  7 . In this position, the blade carrier  20  and the protective cap  27  are held by the helical spring  36 , which pushes these two parts apart. 
         [0059]    In this initial position, the front cams  46  respectively abut on the rear end of the first section  48  of the cam track  45 , the rear cams  47  are retracted rearwards in relation to the cam tracks  45  and are not in contact with these. 
         [0060]    To use the obturator, it is first necessary to activate the blade. This is done by pressing the pushbutton  5  and, consequently, advancing the push rod  6  and the blade carrier  20  fixedly connected to it. The blade carrier  20  is advanced against the action of the helical spring  36  and owing to the guidance of the helical cutting edge  23  in the guide  25  also slightly rotated. The front cam  46  thereby moves on a path extending at an incline to the longitudinal direction of the housing  2 . In  FIGS. 6 and 14 , this path is indicated by arrow B. During this displacement, the front cams  46  respectively slide along the first section  48  of the cam track  45  and rotate the sleeve-shaped switching element  40  in the direction of arrows C in  FIGS. 7 and 12  in a first direction. The cam track  45  is thus displaced upwards during this rotation in the representation of  FIGS. 7 and 12 . 
         [0061]    During the advancing movement of the blade carrier  20 , the front cams  46  move from the rear end of the first section  48  (solid contour in  FIG. 12 ) to the front end of the first section  48  (dotted contour in  FIG. 12 ), and they are then displaced even further forwards into an end position (dashed contour in  FIG. 12 ). This further displacement takes place without the front cams  46  abutting on the cam track  45 , i.e., the front cams  46  rotate the switching element  40  only during their abutment on the first section  48 . 
         [0062]    The arrangement of the front cams  46  and the rear cams  47  is selected such that the rear cams  47  abut on the second section  49  once the front cams  46  have left the first section  48 . The rear cams  47  are also displaced on a path extending at an incline to the longitudinal axis and also corresponding to the direction of arrows B. Since the second section  49  extends at a steeper incline in relation to the longitudinal direction of the housing  2  than this direction of movement of the rear cams  47 , indicated by arrow B, the rear cams  47  abut on the second section  49  and, upon further displacement of the blade carrier  20 , rotate the switching element  40  in opposition to the first direction in a second direction, which is also indicated by arrow C in  FIG. 12 . 
         [0063]    The advancing movement of the blade carrier  20  is delimited by a stop, not shown in the drawings. For example, this stop may be provided on the pushbutton  5 . When the user releases the pushbutton again, after this foremost point has been reached, the blade carrier  20  is pushed back under the action of the helical spring  36 , more particularly, on the same path indicated by arrow B. The front cams  46  then strike the third section of the cam track  45  as the cam track has been rotated in the second direction by the rear cam  47  and now lies with the third section  50  in the displacement path of the front cams  46  ( FIG. 13 ). The rearward movement of the blade carrier  20  is thus blocked by the abutment of the front cams  46  on the third section  50  of the cam track  45 . In this blocked position, the cutting edge  23  protrudes over the entire area of the slit  29  from the protective cap  27 , as shown in  FIG. 8 . In this blocked position, the obturator is ready to be used to pierce a body wall (solid contour in  FIG. 13 ). 
         [0064]    During the piercing, the surgeon places the tip  24  of the blade  22  on the body wall and advances the obturator, while at the same time rotating it, in the direction towards the body wall, so that the blade  22  penetrates the body wall along the cutting edge  23 . During this penetration, the front end  28  of the protective cap  27  abuts on the body wall and is pushed by it against the action of the helical spring  36 , while at the same time being rotated by the guidance of the helical cutting edge  23 , into the end cap  7  ( FIGS. 9 and 13 ). The teeth  34  of the protective cap  27  thereby move in between the teeth  42  of the switching element  40  and abut on one another with a very steep flank  56  and  57 , respectively, which is only slightly inclined in relation to the longitudinal direction of the housing  2 . This causes the switching element  40  to be rotated in the second direction, so that the front cams  46  of the blade carrier  20  are thereby advanced beyond the end of the third section  50  (dotted contour in  FIG. 13  and solid contour in  FIG. 14 ). The front cams  46  thus reach the start of the fourth section  51  extending rearwards at an incline. This results in a slight rearward movement of the blade carrier  20  and in a further rotation of the switching element  40  in the second direction (dotted contour in  FIG. 14 ). 
         [0065]    However, both this rearward movement of the blade carrier  20  and the rotation of the switching element  40  are very slight since during the rotation of the switching element  40  the opposite flanks  58  and  59 , respectively, of the teeth  34  and  42  enter into abutment and prevent any further rotational movement of the switching element  40  ( FIGS. 10 and 14 ). In this position, the blade carrier  20  is prevented from being displaced rearwards any further as the front cams  46  are supported on the fourth section  51  of the cam track  45  (dotted position in  FIG. 14 ). This position is referred to as cutting position of the blade carrier  20 . In this cutting position, the cutting edge  23  continues to protrude over the protective cap  27  which, for its part, is in the retracted work position. The surgeon can, therefore, continue with the piercing of the body wall until it has been completely pierced. 
         [0066]    This results, upon advancing the obturator  1  further, in the protective cap  27  also passing with its tapering front end  28  and the adjoining cylindrical area  31  through the opening made in the body wall and now no longer being pushed sufficiently strongly against the action of the helical spring  36  into the end cap  7 . The protective cap  27  can now be displaced forwards again under the action of the helical spring  36  into its rest position until the ring step  32  of the shaft-shaped widening  30  abuts on the projection  14 . The teeth  34  of the protective cap  27  are thereby disengaged from the teeth  42 , i.e., the switching element  40  is released and can now rotate freely again. Therefore, under the action of the helical spring  36 , the blade carrier  20  is now retracted into its protected position as the switching element  40  no longer blocks this rearward movement. The switching element  40  is simultaneously rotated in the second direction as the front cams  46  slide along the fifth section  52  (dashed contour in  FIG. 14 ) until the initial position shown in  FIG. 6  is reached again, in which the blade carrier  20  is completely retracted and in which the cutting edge  23  in the portion lying outside the end cap  7  is completely covered by the protective cap  27 . 
         [0067]    A full work cycle has thus been completed and can be repeated in the same way. 
         [0068]    It will be clear from the representation of  FIG. 14  that the rear cams  47  are located opposite the sixth section  53  of the cam track  45  when the blade carrier  20  moves from the blocked position to the cutting position (dotted contour in  FIG. 13  and solid and dotted contours in  FIG. 14 ). An advancing of the blade carrier  20  in the direction towards the end position, i.e., beyond the blocked or cutting position, is thereby prevented. This is a safeguard in the event that the surgeon should inadvertently actuate the pushbutton  5  during the cutting operation. This actuation does not result in any displacement of the blade carrier  20  as it is secured against axial displacement in both directions, more particularly, by the front cams  46  and rear cams  47  abutting on opposite sides on the cam track  45 . 
         [0069]    The construction of the described assembly is very simple as only three movable parts and a helical spring have to be used in the tubular housing. Assembly is also very simple as it is sufficient to concentrically assemble these parts and then connect the end cap firmly to the adjoining shaft-shaped part of the tubular housing. Separation and then cleaning may also be carried out in the same way. 
         [0070]    The entire assembly can be accommodated in the front part of the tubular housing near the blade without its outer diameter having to be increased and, therefore, with the exception of the pushbutton  5 , no parts of the retracting device need be arranged in the grip area of the obturator  1 .