Abstract:
A shaft for a medical instrument for a minimally invasive procedure includes a proximal end that is mechanically connectable or connected with an operational device and a distal end that is connectable or connected with a tool, whereby the shaft comprises a bent portion and whereby no plane exists from which the center points of all cross-sections of the shaft are at a lesser distance than one-third of a diameter of the shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority of German patent application No. 10 2010 013 917.3 filed on Apr. 1, 2010, the content of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a medical instrument for a minimally invasive procedure, in particular for a procedure by means of several instruments inserted through a single access opening, and to a shaft for such a medical instrument. 
       BACKGROUND OF THE INVENTION 
       [0003]    Minimally invasive procedures, for example laparoscopic surgical interventions, were originally performed via several small openings. For example, an endoscope was inserted through a central access opening and medical instruments were inserted through one, two, or more lateral access openings. The arrangement of an endoscope centrally and of two instruments from the side is also occasionally referred to as triangulation. Increasingly, however, efforts are made to reduce the number of access openings. For example, in laparoscopic surgery only one central access opening is now used, through which an endoscope and as a rule several instruments are inserted simultaneously. For reasons of space, these instruments cannot be completely straight. With straight instruments whose middle portions are positioned in a small access opening, the comparatively voluminous operational devices at the proximal ends make it difficult or impossible to move the distal ends together. Therefore instruments with a curved shaft have been developed. 
         [0004]    Curved shafts for surgical instruments are described in WO 2006/100658 A2, in EP 2 087 834 A1, and in DE 20 2009 007 592 U1. 
         [0005]    Curved shafts can constitute a marked improvement over straight shafts, in particular in minimally invasive procedures with several instruments in a single access opening. There remains, however, a mutual obstruction among the instruments, in particular concerning the distal ends with the tools, the center portions of the shafts that are positioned in the access opening, and the proximal ends of the instruments with operational devices. Medical staff must constantly keep this potential or actual mutual obstruction in mind in operating the instruments. This means, for one thing, that part of the medical staff&#39;s attention is always directed at careful and anticipatory operation of the medical instruments and, for another thing, that certain movements of the medical instruments must be avoided because of space restrictions or cannot be performed. Neither situation is tolerable for medical staff who need to function with concentration, efficiency, and the avoidance of exhaustion. 
       SUMMARY OF THE INVENTION 
       [0006]    An object of the present invention consists in providing an improved shaft, an improved medical instrument, and improved surgical instruments. 
         [0007]    This object is achieved through the content of the independent claims. 
         [0008]    Refinements are indicated in the dependent claims. 
         [0009]    The present invention is based on the recognition that in many situations, mutual obstruction of several medical instruments is caused by their two-dimensional format. From the viewpoint of production, transport, and storage of medical instruments, it can be advantageous if their shafts are of two-dimensional form. It is also not obvious that two-dimensional configuration of the shafts of medical instruments increases their mutual obstruction or that three-dimensional configuration of the shafts of medical instruments reduces their mutual obstruction. However, a precise and impartial analysis of typical situations arising in practice with several medical instruments in an access opening and empirical investigations with three-dimensionally shaped shafts, surprisingly, resulted in reduced mutual obstruction even when the shafts had only relatively minor deviations from a purely two-dimensional format. Each type of deviation in format from a purely two-dimensional shape—whether in a distal portion of the shaft that is foreseen for positioning in the body, in a center portion that is foreseen for positioning in an access opening, or in a proximal portion foreseen for positioning outside the body being treated—has its specific advantages. 
         [0010]    A shaft for a medical instrument for a minimally invasive procedure includes a proximal end that can be or is mechanically connected with an operational device and a distal end that can be or is connected with a tool, in such a way that no plane exists from which the center points of all cross-sections of the shaft are at a smaller distance than one-third of a diameter of the shaft. 
         [0011]    The shaft is rigid, that is, not flexibly reshapable by the forces and moments that arise in the expected use. The shaft is in particular configured for an exploratory, surgical, therapeutic or other medical procedure through a single access opening. 
         [0012]    The cross-sections are based on planes of intersection that are cut perpendicularly by the midline formed by the center points. The center point of a cross-section, independently of any hollow spaces in the shaft, is the geometric center point of the simply connected level surface bounded by the outer contour of the cross-section. In particular, all cross-sections of the shaft or at least their outer contours are equal or essentially equal. For example, all cross-sections are circular with the same radius. 
         [0013]    In the case of a cross-section that varies along the shaft, the diameter existing in the particular cross-section is to be taken as the basis with respect to comparing the distance of the center point of the cross-section from a plane with the diameter of the shaft. In a non-circular cross-section, the diameter is taken to be the diameter of the smallest circle that completely surrounds the cross-section. 
         [0014]    In the shaft described here, there exists in particular no plane from which the center points of all cross-sections of the shaft are at a lesser distance than a half-diameter of the shaft. 
         [0015]    In some embodiments the center points of the cross-sections lie in one or more segments of the shaft, in particular also in curved segments of the shaft, in precisely a plane whereby at least one segment of the shaft exists in which the center points of the cross-sections are at a distance of at least one-third or at least one-half of the diameter of the shaft. 
         [0016]    In particular on the basis of the following description of embodiments, it becomes clear that the aforementioned deviation of the shaft from the straight shape markedly reduces or even can avoid the mutual obstruction of the shafts of two medical instruments. Here the deviation of the shaft from the straight form is not necessarily large in many cases. Even a deviation of one-third, one-half, or an entire diameter of the shaft can have the positive effects described here. 
         [0017]    Here the additional production expense incurred for three-dimensional format has proved in a few cases to be lower than previously assumed. Especially at lesser deviations from a straight configuration, the advantages of the straight format can still be largely retained with respect to transport and storage. In any case, slight disadvantages or a moderate additional cost are offset by marked advantages in handling. Mutual obstruction or discomfort or restricted mobility of the shafts of several medical instruments can arise more seldom or with less probability. 
         [0018]    A shaft as described here can comprise a proximal portion, a center portion, and a distal portion, whereby the distal portion and the center portion lie in a plane from which the proximal portion deviates. 
         [0019]    The proximal portion extends to the proximal end of the shaft and is foreseen for positioning outside a body to be treated with the expected application. The distal portion extends to the distal end of the shaft and is foreseen for positioning in the body to be treated with the expected application. The center portion lies between the proximal portion and the distal portion and in particular borders on both. The center portion is especially foreseen for positioning in the access opening or in the area of the access opening. The distal portion and the center portion lie in particular in precisely a plane that is unequivocally defined by the center points of all cross-sections in the distal portion and in the center portion. 
         [0020]    A deviation of the shaft from the straight format in the proximal portion makes possible, for example, a crossing of two shafts in the proximal portion without requiring a lateral displacement of the proximal ends of the shafts or of operational devices positioned on them. If both shafts deviate in the proximal portion from the straight format, a deviation in each case by just a half-diameter can be sufficient. 
         [0021]    A shaft as described here can comprise a proximal portion, a center portion, and a distal portion so that the distal portion and the proximal portion lie in a plane from which the center portion deviates. 
         [0022]    As mentioned, in the foreseen application the center portion of the shaft is positioned in a narrow access opening (for example, a trocar or a trocar sleeve) together with one or more other shafts of an endoscope and/or of other medical instruments. If two shafts in this center portion have a straight format, they can be contiguous with one another either in linear shape or at several locations set apart from one another. In a relative movement of both shafts, this can increase the friction resistance or lead to a discontinuous change of relative rotation points and lever arms. Either of these is undesired, as a rule, because they restrict the sensitivity and precision with which the shafts can be moved in relation to one another. 
         [0023]    If the shape of one or both shafts deviates from a plane in the center portion, the shafts as a rule can be contiguous with one another only at one site. Tipping or sliding of both shafts with respect to one another, in this case, has a minimal friction and has as a consequence no displacement or in any case a continuous displacement of a relative axis of rotation and accordingly no modification or in any case a continuous modification of the lengths of the lever arms. A deviation of the shaft from the straight shape can thus increase sensitivity and precision in handling and in the activities performed by means of the shaft. 
         [0024]    A shaft as described here can comprise a proximal area, a center area, and a distal area, whereby the center area and the proximal area lie in a plane from which the distal area deviates. 
         [0025]    A deviation of the shaft from the straight format in the distal portion can simplify a crossing of the shafts of two medical instruments in the distal portion. As soon as each of the two shafts deviates by a half-diameter from the straight format, a crossing of the two shafts can become possible without a lateral displacement of its distal ends or of tools at their distal ends. The advantages are therefore similar to the aforementioned advantages of a deviation of the shaft from the straight format in the proximal area. 
         [0026]    The advantages of the deviation of the shaft from the straight shape in the distal portion can, however, be still more important because fewer alternatives exist. In the proximal area, that is, in the foreseen application outside the body to be treated, the shafts of medical instruments can be shaped in such a way that a crossing can be avoided in most cases. Crossing in the distal area, however, can be avoided in many cases only at great expense, for example by exchanging both medical instruments. However, exchanging two medical instruments during a procedure costs time, interrupts the operational sequence, demands rethinking by the medical staff, and increases the risk of injury for the patient. These disadvantages can be reduced or avoided by a deviation of the shaft from the straight format in the distal portion. 
         [0027]    In a shaft as described here, at least one portion can be of helical configuration. 
         [0028]    A helix is a spatial curve with constant curvature on a sheath surface of a cylinder. A segment of the shaft is helically configured when the center points of all cross-sections of the shaft lie on a helix. The helically configured segment of the shaft can be the proximal, the center, or the distal portion in the sense of the description above. In addition, the entire shaft or nearly the entire shaft can be of helical configuration. However, in all the embodiments described here, it can be advantageous in view of production if short portions (with a length, for example, of a few millimeters or few centimeters) are straight at the ends of the shaft. 
         [0029]    A helical configuration of the shaft or of a portion of the shaft makes possible, depending on the radius and the pitch of the helix, on the one hand a positioning of the distal ends of several shafts and of tools connected thereto, similarly as in classical triangulation, in which the tools of several medical instruments extend laterally into the field of vision of a central endoscope. At the same time two shafts that are helically configured in the center portion with equal winding direction are contiguous with one another only at one point in the access opening in almost all relative positions. A relative displacement or tipping of two or more spiral-shaped shafts in the access opening is therefore possible with minimal friction and without spasmodic change of effective lever lengths. 
         [0030]    As a rule, it is advantageous to use several shafts with helically configured portions with equal winding direction, equal or similar radii, and equal or similar pitches. Especially positive experience occurs with shafts that form essentially a half-rotation over nearly their entire length, so that the ratio between the radius and the pitch lies between 1:10 and 1:20. 
         [0031]    In a shaft as described here, in a connected portion that includes at least half of the length of the shaft, the derivative of the normed tangential vector of the midline of the shaft along the midline can continuously or discontinuously rotate in one direction or, in straight segments, can be equal to zero. 
         [0032]    As previously mentioned, the midline of the shaft is the quantity of the center points of all cross-sections. An example of a shape of the shaft in which the normed tangential vector rotates continuously in one direction is the aforementioned helical shape. Deviating from a helical shape, the derivative of the normed tangential vector along the midline can change spasmodically or continuously both with respect to its amount and with respect to its direction. For example, a series of several portions that each is curved within a plane can under some circumstances entail a lower production cost than a helical structure or another structure in which the normed tangential vector rotates continuously. 
         [0033]    In a shaft as described here, the proximal end and the distal end can be aligned parallel to one another or can form an angle of at most 10 degrees. 
         [0034]    The direction of an end of a shaft is the direction of the tangential vector of the midline at the end. Parallel or even coaxial alignment of both ends of a shaft encourage particularly intuitive operation by medical staff. Even at the helical configuration of a portion of the shaft as described above, transition areas can be connected on the helical portion so that both ends of the shaft can be aligned parallel or even coaxially, even when the helical portion includes no full rotation. 
         [0035]    A shaft as described here can include a first portion in which the shaft runs parallel to a first plane, and a second portion in which the shaft runs parallel to a second plane, whereby the first plane and the second plane are not parallel to one another. 
         [0036]    In particular, the shaft is curved both in the first portion and in the second portion. In mathematical terms, the vector product of the tangential vector and of the derivative of the tangential vector has a first direction in the first portion and a second direction in the second portion, said second direction differing from the first direction. A curvature within a plane can in many cases be realized with minor production costs, so that a series of portions within which the shaft runs in each case parallel to a plane can be produced at reasonable cost. 
         [0037]    The first plane and the second plane in particular form an angle of at least 10 degrees. 
         [0038]    The angle between two planes is the angle between their surface normals. Greater angles of at least 20 degrees or at least 30 degrees or at least 60 degrees can be advantageous. 
         [0039]    A medical instrument includes a shaft as described here and at least either an operational device that is connectable or connected with the proximal end of the shaft, or a tool that is connectable or connected with the distal end of the shaft. 
         [0040]    A surgical utensil includes two medical instruments as described here, whereby, in the shafts of both medical instruments in portions corresponding to one another in terms of the distances from the distal ends of the shafts, the derivatives of the normed tangential vectors of the midlines of the shafts rotate continuously or discontinuously in the same direction along the midline. 
         [0041]    The same-direction rotation of the derivative of the normed tangential vectors reduces the mutual obstruction of two shafts. 
         [0042]    In a surgical utensil as described here, the shafts of both medical instruments, in portions corresponding to one another in terms of the distances from the distal ends of the shafts, are of helical configuration and have the same rotation direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]    Hereinafter, embodiments are explained in greater detail with reference to the appended drawings, which are as follows. 
           [0044]      FIG. 1  shows a schematic depiction of a medical instrument. 
           [0045]      FIG. 2  shows another schematic depiction of the medical instrument from  FIG. 1 . 
           [0046]      FIG. 3  shows another schematic depiction of the medical instrument from  FIGS. 1 and 2 . 
           [0047]      FIG. 4  shows a schematic depiction of an additional medical instrument. 
           [0048]      FIG. 5  shows another schematic depiction of the medical instrument from  FIG. 4 . 
           [0049]      FIG. 6  shows another schematic depiction of the medical instrument from  FIGS. 4 and 5 . 
           [0050]      FIG. 7  shows a schematic depiction of another medical instrument. 
           [0051]      FIG. 8  shows another schematic depiction of the medical instrument from  FIG. 7 . 
           [0052]      FIG. 9  shows another schematic depiction of the medical instrument from  FIGS. 7 and 8 . 
           [0053]      FIG. 10  shows a schematic depiction of another medical instrument. 
           [0054]      FIG. 11  shows another schematic depiction of the medical instrument from  FIG. 10 . 
           [0055]      FIG. 12  shows another schematic depiction of the medical instrument from  FIGS. 10 and 11 . 
           [0056]      FIG. 13  shows a schematic depiction of two medical instruments in the foreseen application. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0057]      FIGS. 1 through 12  show schematic depictions of four different medical instruments. Each three successive drawings show schematic axonometric depictions of a medical instrument from three different perspectives or directions. The planes of projection of the three figures referring in each case to the same medical instrument,  FIGS. 1 through 3  or  4  through  6  or  7  through  9  or  10  through  12 , are perpendicular to each other. The planes of projection of  FIGS. 2 ,  5 ,  8 , and  11  correspond to one another. The planes of projection of  FIGS. 3 ,  6 ,  9 , and  12  correspond to one another. 
         [0058]    Each of the medical instruments  10  illustrated in  FIGS. 1 through 3  or  4  through  6  or  7  through  9  or  10  through  12  includes a shaft  20  with a proximal end  21  and a distal end  25  and with an essentially constant circular cross-section between the proximal end  21  and the distal end  25 . On the proximal end  21  the shaft  20  in each case can comprise a flushing connection  28 . 
         [0059]    An operational device  40  is connected with the proximal end  21 , and a tool  50  is connected with the distal end  25  of the shaft  20 . Both the operational device  40  and the tool  50  can be connected permanently or not detachably without disruption with the shaft  20 . Both the operational device  40  and the tool  50  can alternatively be connected detachably without disruption with the shaft  20 , for example by bayonet and/or catch-lock connections. 
         [0060]    In the illustrated medical instruments, a plug-in connection is provided between the proximal end  21  of the shaft  20  and the operational device  40 , along with rotatability of the shaft in the operational device  40 , so that a detachable catch-lock connection holds the shaft  20  on the operational device  40 . The operational devices  40  of all illustrated medical instruments  10  have mutually corresponding characteristics, which are described in greater detail hereinafter. 
         [0061]    In part, distinctions are made hereinafter between a proximal portion  22 , a center portion  23 , and a distal portion  24  of the shaft  20 . The proximal portion  22  extends as far as or essentially as far as the proximal end  21  of the shaft  20 . The distal portion  24  extends as far as or essentially as far as the distal end  25 . The center portion  23  extends essentially between the proximal portion  22  and the distal portion  24 . In the expected application of the medical instruments  10 , the proximal portion  22  of the shaft  20  is intended to be positioned outside a body that is to be treated; the distal portion  24  is intended to be positioned in a natural or artificial cavity in the body to be treated; the center portion  23  is intended to be positioned in an access opening, for example in a trocar or trocar sleeve. 
         [0062]      FIGS. 1 through 3  show schematic axonometric depictions of a medical instrument  10  whose shaft  20  is straight in the proximal portion  22  and in the center portion  23 . Two curved segments  61 ,  62  and an additional, short straight segment  63  are connected distally to the straight portion. Inside the first curved segment  61  and inside the second curved segment  62 , the shaft has an essentially straight shape. Inside the first curved segment  61 , the center points of all cross-sections lie in a single, first plane; inside the second curved segment  62 , the center points of all cross-sections of the shaft  20  lie in a single, second plane. Both the first plane and the second plane are unequivocally defined on the basis of the curvature of the first curved segment  61  and of the second curved segment  62 . On the basis of the straight form of the shaft  20  proximally from the first curved segment  61  and distally from the second curved segment  62 , the center points of all cross-sections of the first curved segment  61  and proximally from the same lie in the first plane and the center points of all cross-sections of the shaft  20  lie in the second curved segment  62  and distally from the same in the second plane. 
         [0063]    The first plane and the second plane are not parallel to one another. In  FIG. 1  it can be recognized that the first plane is perpendicular to the plane of projection of  FIG. 1 , so that the first curved segment  61  appears straight in  FIG. 1 . It can be recognized in  FIG. 2  that the second plane is perpendicular to the plane of projection of  FIG. 2 , so that the second curved segment  62  appears straight in  FIG. 2 . 
         [0064]    It can be recognized in comparing  FIGS. 1 through 3  that no plane exists in which the center points of all cross-sections of the shaft  20  are found. Instead, the distal portion  24  of the shaft  20  has a suggestion of a screw-like shape. The derivative of the normed tangential vector of the midline of the shaft  20  made up of the center points of all cross-sections lies in the first curved segment  61  in the plane of projection of  FIG. 2  and is perpendicular to the plane of projection of  FIG. 2  at the proximal end of the second curved segment  62 . The derivative of the tangential vector of the midline rotates suddenly by 90 degrees in clockwise direction at the transition between the first curved segment  61  and the second curved segment  62 . 
         [0065]    The shape of the shaft  20  of the medical instrument  10  in  FIGS. 1 through 3  makes possible a collision-free or unhindered crossing of the distal portion  25  of the shaft  20  with the distal portion of a shaft of an additional medical instrument, in particular when the shaft of the second medical instrument is straight or at least is of screw-like or approximately screw-like configuration in the distal portion with the same rotation direction. It can be particularly advantageous to make simultaneous use of two of the same medical instruments  10  that both correspond to the foregoing depictions in  FIGS. 1 through 3 . 
         [0066]      FIGS. 4 through 6  show schematic axonometric depictions of an additional medical instrument  10 , which resembles in some characteristics the medical instrument presented above with reference to  FIGS. 1 through 3 . Contrary to the medical instrument presented above and in  FIGS. 1 through 3 , the shaft  20  of the medical instrument  10  shown in  FIGS. 4 through 6  is straight in the proximal portion  22  and in the distal portion  24  and is curved in the center portion  23 . 
         [0067]    In the center portion  23  the shaft  20  comprises four curved segments  71 ,  72 ,  73 ,  74 , within which the center points of all cross-sections of the shaft  20  are each found in a plane. A first plane, in which the center points of all cross-sections of the shaft  20  lie inside the first curved segment  71  and proximally from the same, is perpendicular to the plane of projection of  FIG. 4 . Therefore the first curved segment  71  in  FIG. 4  appears straight. It can be recognized in  FIG. 6  that a second plane, in which the center points of all cross-sections of the shaft  20  lie in the second curved segment  72 , and a fourth plane, in which the center points of all cross-sections of the shaft  20  lie in the fourth curved segment  74 , are each perpendicular to the plane of projection of  FIG. 6 . Therefore both the second curved segment  72  and the fourth curved segment  74  appear straight in  FIG. 6 . 
         [0068]    Upon close observation of  FIGS. 4 through 6  it can be recognized that the shaft  20  has an approximately right-rotating screw-like shape or a helical shape in the center portion  23 . The derivative of the normed tangential vector of the midline of the shaft  20  made up of the center points of all cross-sections rotates discontinuously along this midline in counterclockwise direction. At the transitions between the curved segments  71 ,  72 ,  73 ,  74 , the direction of the derivative of the normed tangential vector rotates spasmodically at angles between 20 and 120 degrees to the right or in clockwise direction. 
         [0069]    The shape of the shaft  20  of the medical instrument  10  presented with reference to  FIGS. 4 through 6  facilitates a low-friction and unimpeded relative movement of the shaft  20  of the illustrated medical instrument  10  and of the shaft or shafts of one or more additional medical instruments that are positioned together in a close access opening. This is true in particular when the shaft or shafts of the one or more medical instruments are straight or similarly curved in the center portion like the shaft  20  of the medical instrument presented with reference to  FIGS. 4 through 6 . In particular, a screw-shaped or helical or approximately screw-shaped or helical configuration with the same rotation direction of all shafts in the center portion can be advantageous. In most or even in most of the relative arrangements of several shafts, this shape makes possible a mutual touching in only one point each or at only one location each. In comparison with a possible mutual touching of two shafts in at least two points at a distance from one another, this results on the one hand in markedly reduced friction. An additional advantage can consist in the fact that, as long as a mutual touching of two shafts occurs in only one point, a sudden displacement of a momentary axis of a relative rotation of two shafts and a sudden change in the lengths of lever arms is not possible. 
         [0070]      FIGS. 7 through 9  show schematic axonometric depictions of a medical instrument  10  that resembles in a few characteristics the medical instrument presented above with reference to  FIGS. 1 through 3  or  4  through  6 . Unlike in the medical instrument presented above with reference to  FIGS. 1 through 3  and  4  through  6 , the shaft  20  of the medical instrument  10  shown in  FIGS. 7 through 9  is curved in the proximal portion  22  and in the center portion  23  and straight in the distal portion  24 . 
         [0071]    In the proximal portion  22  the shaft  20  comprises a short straight segment  81 , a first curved segment  82 , and a second curved segment  83 . In the first curved segment  82  and in the proximally adjoining short straight segment  81  of the shaft  20 , the center points of all cross-sections of the shaft  20  lie in a single, first plane. In the second curved segment  83  and distally from the same, the center points of all cross-sections of the shaft  20  lie in a second plane. In comparing  FIGS. 7 and 8  it is recognizable that the first plane is perpendicular to the plane of projection of  FIG. 7 . Therefore the first curved segment  82  appears straight in  FIG. 7 . It is further recognizable that the second plane is perpendicular to the plane of projection of  FIG. 8 . Therefore the second curved segment  83  appears straight in  FIG. 8 . 
         [0072]    In comparing  FIGS. 7 through 9  it can be recognized that the shaft  20  of the medical instrument  10  shown in  FIGS. 7 through 9  has approximately the shape of a left-threaded screw or helix. The derivative of the normed tangential vector of the midline of the shaft  20  made up of the center points of all cross-sections rotates spasmodically by approximately 90 degrees in counterclockwise direction at the transition between the first curved segment  82  and the second curved segment  83 . 
         [0073]    The shape of the shaft  20  of the medical instrument  10  presented with reference to  FIGS. 7 through 9  can make possible an especially low-obstruction or obstruction-free relative movement of the shafts of several medical instruments that are used simultaneously in an access opening. This is true in particular when the medical instrument  10  presented with reference to  FIGS. 7 through 9  is used together with one or more additional medical instruments whose shafts are configured corresponding to or similar to the shaft  20  of the medical instrument  10  presented with reference to  FIGS. 7 through 9  or straight. In particular, the illustrated shape of the shaft  20  can make possible or facilitate crossing of the proximal portions of two shafts without lateral displacement. 
         [0074]      FIGS. 10 through 12  show schematic axonometric depictions of an additional medical instrument  10 , which is similar in a few characteristics to the medical instruments presented above with reference to  FIGS. 1 through 3  or  4  through  6  or  7  through  9 . Contrary to the medical instruments presented above with reference to  FIGS. 1 through 9 , the shaft  20  of the medical instrument shown in  FIGS. 10 through 12  has an essentially helical shape in a large, center portion of its length. As a result of transitional arcs and straight portions at the proximal end  21  and at the distal end  25 , which are scarcely recognizable in the drawings, the proximal end  21  and the distal end  25  of the shaft  20  have the same orientation or are parallel to one another. 
         [0075]    Advantages of the medical instrument  10  shown in  FIGS. 10 through 12  resemble or correspond largely to the advantages of the medical instruments presented above with reference to  FIGS. 1 through 9  or combinations thereof. In particular, the shafts of two or three medical instruments as presented with reference to  FIGS. 10 through 12  or to  FIGS. 4 through 6  can be positioned in an access opening in such a way that they touch one another only at one point or in one location. This is the case, for example, when two shafts are positioned rotated with respect to one another by 180 degrees or three shafts are positioned rotated with respect to one another by approximately 120 degrees each. On the basis of the illustrated shape of the shafts, the latter cross one another in the access opening at wide angles, so that even with fairly large relative rotations or sliding, a mutual touching of two shafts always occurs only at one point or in one location. 
         [0076]    Simultaneously the illustrated non-straight shape of the shaft of at least one of the simultaneously used medical instruments can make possible a crossing of the distal portions  24  and/or of the proximal portions  22  of the shafts  20  without a relative lateral displacement. 
         [0077]      FIG. 13  shows a schematic depiction of an example of a simultaneous use of two medical instruments as presented for example above with reference to  FIGS. 4 through 6  or  10  through  12 . The medical instruments are used, for example, for an exploratory or surgical minimally invasive procedure in an artificial or natural cavity  91  in the body of a patient. The cavity  91  is bounded by a wall  92  in which there is a natural or artificial access opening  93 . The wall is, for example, the abdominal wall of the patient. 
         [0078]    Shafts  20 ,  120  of two medical instruments are introduced through the access opening  93  into the cavity  91 . In the center portion or in the portion of the access opening  93 , the two shafts  20 ,  120  are positioned wound around one another in the manner of a double helix. With sufficient curvature radii of the shafts  20 ,  120 , the shafts  20 ,  120  touch one another at most at one point. 
         [0079]    If both shafts  20 ,  120  have a flat shape, that is, if the center points of all cross-sections of the shaft  20  lie in a first plane and the center points of all cross-sections of the shaft  120  lie in a second plane, these two planes intersect in the portion of the access opening  93 , but could be non-parallel to one another. The distal ends  25 ,  125  of the shafts  20 ,  120  and the tools  50 ,  150  positioned on them could therefore not be moved together. In most minimally invasive procedures, however, it is required that the tools  50 ,  150  at the distal ends  25 ,  125  of the shafts  20 ,  120  of two or more medical instruments can be approached to one another up to a very small mutual distance. 
         [0080]    In the case of straight shafts  20 ,  120 , contrary to the depiction in  FIG. 13  a parallel positioning of the planes of the shafts  20 ,  120  is conceivable. Then the shafts  20 ,  120  could, however, touch at two points, with the aforementioned disadvantages. 
         [0081]    Only the deviation of at least one of the shafts  20 ,  120  from a straight shape makes possible simultaneously the illustrated arrangement of the two shafts  20 ,  120  at least partly surrounding one another in the access opening and a freedom to approach the distal ends  25 ,  125  of the shafts  20 ,  120  and the tools positioned thereon.