Abstract:
A medical instrument has a cannula, a seal disposed in said cannula, said seal has an opening for guiding a shaft of another instrument through said seal in a sealed manner. An expansion device serves for expanding said opening in said seal. Said expansion device has an expansion cone comprising a plurality of slats mounted pivotably on an annular body at a first end, a second end of said slots opposite to said first end being connected to said seal in an area of said opening. A flexible casing structure is provided accommodating said seal and said expansion device.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a medical instrument, with a cannula through which shafts of other instruments having different shaft diameters can be guided, with a seal comprising an opening with a variable opening cross section through which the shafts having different shaft diameters can be guided sealingly, with an expansion device for expanding the opening of the seal, which expansion device has an expansion cone with a plurality of slats that are mounted pivotably on an annular body and form an expansion body that narrows from the proximal end to the distal end and that is connected at the distal end to the seal in the area of the opening. 
     A medical instrument of this kind is known from EP 0 696 459 B1. 
     Said medical instrument is a trocar that is used in minimally invasive surgery. The trocar is introduced through a small opening, which is formed by a small incision in the skin for example, through the abdominal wall into the abdominal cavity of the patient by means of a trocar mandrel. After removal of the trocar mandrel, shafts of other instruments used for the surgical intervention are then passed through this trocar. These instruments include, for example, gripping tools, coagulation instruments, endoscopes and the like. These have shafts of different diameters. 
     Since minimally invasive interventions of this kind are often performed during insufflation of the internal cavity in which the operation takes place, all the intervention points must be gas-tight. 
     In the aforementioned EP 0 696 459 B1, this purpose is served by an elastic conical seal that is arranged in the trocar and that narrows from the proximal end to the distal end. To permit a uniform widening of the seal when an instrument of a diameter larger than the opening in the seal is inserted into the trocar, an expansion cone is arranged in the proximal direction from this seal. An instrument inserted into the expansion cone expands the latter radially, which in turn widens the opening in the seal. The expansion cone also prevents damage to the seal during insertion of sharp-edged instruments. 
     Upon insertion of an instrument having a shaft diameter corresponding approximately to that of the cannula of the trocar, the instrument expands the opening to the maximum extent, and the whole circumference of the shaft comes uniformly into contact with the seal. In this way, the trocar system is sealed off at the proximal end. Whenever a shaft of an instrument is inserted into the opening of the seal, said shafts having a diameter of at least the opening or larger. 
     Insertion of an instrument having a slender shaft which is only a little bit larger than the original size of the opening can become offset from the central passage through the opening of the seal. Moreover, particularly in the case of narrower flexible shafts, the shaft may tilt in the trocar. 
     Both of these situations have the effect that the seal does not come uniformly into contact with the shaft about the whole circumference of the latter. This results in undesirable leaks. These lead to an escape of the gas, which has been admitted for the operation, and, consequently, to a loss of the insufflation. 
     The insertion of instruments with narrow shafts can therefore be problematic and may cause difficulties. 
     It is therefore an object of the present invention to develop a medical instrument of this kind in such a way that a lateral offset of an inserted shaft cannot lead to a loss of leaktightness of the trocar. 
     SUMMARY OF THE INVENTION 
     This object is achieved according to the invention by a medical instrument having a cannula, a seal disposed in said cannula, said seal has an opening for guiding a shaft of another instrument through said seal and said cannula in a sealed manner, an expansion device for expanding said opening in said seal for guiding shafts of said other instruments of greater diameter in a sealed manner through said expanded opening, said expansion device having an expansion cone comprising a plurality of slats mounted pivotably on an annular body at a first end, a second end of said slats opposite to said first end, being connected to said seal in an area of said opening, and an flexible casing structure accommodating said and said expansion device. 
     The assembly composed of the expansion cone and the seal, made of elastic material, forms a structure that is relatively unstable in the lateral direction. This is particularly so in the configuration in which the expansion cone and the seal extend diametrally away from each other starting from their point of connection to each other. An instrument inserted with a lateral offset or obliquely into the expansion cone would cause a lateral shift or lateral displacement of the assembly. The casing structure surrounding the assembly of seal and expansion cone counteracts this, but provides a certain degree of flexibility. 
     When there is a non-uniform contact between an inserted shaft and the opening of the seal, the flexible casing structure shifts the sealing system in such a way that the shaft extends centrally through the opening of the seal. In this way, the seal once again comes into uniform contact with the shaft about the whole circumference of the latter, as a result of which the desired leaktightness of the trocar system is maintained. The casing structure effects a kind of straightening or aligning of the assembly of seal and expansion cone to the rectilinear orientation. 
     The casing structure thus gives the assembly of expansion cone and seal, an increased stability, which is lacking particularly in the embodiment in which the seal extends in the distal direction away from the distal end of the expansion cone. Since the seal is very movable, the expansion cone is thereby also very movable and, consequently, also the inlet opening into the trocar. This makes inserting a shaft into the trocar difficult and, because of oblique positions of the seal, can also have a negative effect on the sealing properties of the sealing system. This is counteracted by the casing structure, since the latter establishes an additional connection of the proximal end of the expansion cone to the trocar and thus reduces the mobility of the sealing system to a desired degree. 
     If the casing structure is designed as a flexible casing tube a stabilization of the assembly of seal and expansion cone is very proper. 
     In another embodiment of the invention, the flexible casing tube is composed of a substantially parallel series of ring elements, wherein two adjacent ring elements are preferably connected to each other at two radially opposite sites, and, furthermore, the sites connecting a ring element to the distally adjacent ring element are in each case always offset by 90° with respect to the connecting sites to the proximally adjacent ring element. 
     The connecting sites between the ring elements, arranged in a circle shape and alternately offset by 90°, permit a flexibility of the casing tube in all lateral directions since, as a result of the connecting sites being arranged radially opposite one another, the connected ring elements have a tilt axis. 
     By means of this, they can be tilted towards one another, from the mutually parallel arrangement, at sites lying circumferentially between the connecting sites. Within the overall arrangement of the ring elements, the 90° offset from one pair to the next pair of ring elements ensures that certain tilting is possible in two mutually perpendicular directions. That is to say, the casing structure thus formed can be moved at its free proximal end in two independent directions and, therefore, in the plane defined by these directions. In addition to the good mobility, and the associated ability to compensate for an offset of a shaft in the trocar, the connecting sites offset by 90° to each other at the same time provide good axial stability since, in the event of loading, the acting forces are distributed uniformly. 
     A further advantage of using ring elements is that they are fairly uncomplicated structural components, which simplifies production. 
     In one embodiment of the invention, the connections are flexible webs. 
     The advantage of this embodiment is that the narrow and therefore flexible webs are arranged directly on the respective elements without multi-part hinges. In this way, the flexible casing tube thereby formed can be produced as a single workpiece, e.g. from plastic, by an injection moulding technique. Since this does away with subsequent assembling of the ring elements, production is very quick and straightforward. 
     In one embodiment of the invention, the connections are tilting joints. 
     By constructing the flexible casing tube from individual ring elements and connecting these by means of tilting joints, the length of the flexible casing tube can be varied. In the design of a sealing system, this length can therefore be adapted to the length of the expansion cone and to the length of the seal. With one type of ring element, it is therefore possible to construct casing tubes of different lengths, which means that this embodiment affords great variability. 
     In one embodiment of the invention, the ring elements have at the tilting joints at least one tilting-joint socket and at least one tilting-joint insert extending radially from said ring element, said ring elements have a height being higher at the sites of a tilting-joint socket than at those of a tilting-joint insert. 
     The site of the tilting-joint socket in the ring element must have a certain height in order to be able to receive the complete tilting-joint insert. This height is lower at the other parts of the ring element. In this way, there is an area in which the ring elements can be tilted relative to one another, since the distance between the ring elements is greater at the sites lying circumferentially between the tilting joints. In this way, the greatest possible angle of inclination is achieved, which increases the flexibility of the casing tube. As a result, the sealing system can better adapt to any offset of a shaft in the opening of the seal. 
     In another embodiment of the invention, the flexible casing structure widens conically from the proximal end to the distal end. 
     By means of this widening, the casing structure is adapted to the difference in cross section between the annular body of the expansion cone and the in most cases greater cross section of the distal end of the seal. This ensures, on the one hand, a good hold on the distal end of the seal and the trocar housing on which the latter is arranged and, on the other hand, on the expansion cone. This leads to the desired stability. 
     In another embodiment, the seal is designed as a pot-seal and extends in the distal direction away from the distal end of the expansion cone. 
     The choice of this structural arrangement has the advantage, on the one hand, that joining together the expansion cone and the seal is simple, since both components are connected to each other via easily accessible outer faces. These are the bottom of the pot seal having the opening and the expansion cone connected with its narrower end to the rim of the opening. On the other hand, the resulting arrangement of the seal facilitates the removal of tissue samples, since it in this way has a funnel-like shape that narrows from the distal end to the proximal end. If, for example, such a sample is taken hold of by a gripping tool and is then guided through the trocar sleeve in the proximal direction, it finally reaches the sealing system. There, by virtue of the gradually decreasing diameter of the seal, it is guided to the proximal narrow opening of the seal and, if appropriate, also adapted in shape. This avoids an undesirable situation in which the sample, during its removal, becomes caught because of an abrupt change in diameter. 
     In another embodiment of the invention, the distal end of the slats of the expansion cone is connected with a form fit to a socket at the edge of the opening in the seal. 
     This connection of the distal end of the slats to the opening of the seal prevents the slats from slipping during expansion of the seal. This therefore counters a possibility of the slats becoming wedged and ensures uniform expansion. Moreover, the connection has the effect that, after the removal of a shaft from the trocar, the slats move back to the starting position again together with the sealing opening, on account of the restoring force of the expanded elastic seal. 
     In one embodiment of the invention, the distal end of the slats of the expansion cone is adhesively bonded to the seal. 
     Adhesive bonding between the slats and the opening of the seal ensures a non-releasable and secure contact between the components. Undesired separation of the components is thereby avoided, such that the slats are at all times arranged on the opening of the seal. The adhesive bonding is conceivable as a single measure, but also in combination with the form-fit connection. 
     In another embodiment of the invention, the expansion cone is composed of eight to twelve slats, preferably ten slats. 
     The use of eight to twelve slats, preferably ten slats, permits uniform widening of the opening of the seal, since the number of slats used is such that the gaps arising during widening are as small as possible and, in addition, the distance between two slats in the expanded state is small. Thus, even in the expanded state, a uniform and round shape is still formed by the slats at the opening of the seal. This in particular enhances the leaktightness at the opening of the seal during and after the insertion of a shaft. Moreover, however, these slats also have sufficient stability, since they still have a sufficiently great width. They are therefore not damaged or destroyed by insertion of especially sharp-edged instruments, thereby also providing protection of the seal. 
     In other embodiments of the invention, the expansion cone and the flexible casing structure are made of hard plastic. 
     In the present case, the use of hard plastic for the expansion cone and the flexible casing structure represents a good compromise, since this provides sufficient stability, e.g. during insertion of sharp-edged instruments, but still permits simple production, for example by injection moulding. 
     In another embodiment of the invention, the seal is made of an elastic material. 
     The use of an elastic material for the seal permits suitable widening of the opening of the seal by the expansion cone during insertion of the shaft of an instrument and, at the same time, permits optimal sealing of the shaft of such an instrument, by virtue of the tight contact between elastic material and shaft. This is achieved in particular by the fact that the expanded opening of the seal is pressed against the circumference of the inserted shaft by virtue of the restoring force of the elastic material. 
     It will be appreciated that the aforementioned features and those still to be explained below can be used not only in the respectively cited combination but also in other combinations or singly, without departing from the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described and explained in more detail below on the basis of a number of selected illustrative embodiments and with reference to the attached drawings, in which: 
         FIG. 1  shows a perspective side view of a medical instrument with a variable seal, 
         FIG. 2  shows a partial cross section along the line II-II in  FIG. 1 , 
         FIG. 3  shows a sealing system of the medical instrument, viewed from the proximal direction, 
         FIG. 4  shows a perspective view of a flexible casing structure of the sealing system, 
         FIG. 5  shows a cross section along the line V-V in  FIG. 3 , 
         FIG. 5   a  shows the cross section after a lateral offset movement, 
         FIG. 6  shows a perspective view of an expansion cone, 
         FIG. 7  shows a perspective view of a seal, 
         FIG. 8  shows a perspective view of a flexible casing tube with tilting joints, 
         FIG. 9  shows a perspective view of an expansion cone with slats that comprise a spherical head, and 
         FIG. 10  shows a perspective view of an individual slat comprising a spherical head. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A medical instrument shown in the figures is designated in its entirety by reference number  10 . 
     The medical instrument  10  shown is a trocar and has at its distal end a trocar sleeve  11 , formed here by a cannula  12 , at its centre a trocar housing  27  and, arranged at the proximal end of the latter, a sealing system  18 .  FIG. 1  also shows a valve  17 , which is arranged on the trocar housing  27  and which can serve, for example, as an admission line for gases. These are used to perform insufflation of the operating site, in order thereby to obtain better access to the organs, vessels, tissues or the like, on which the operation is to be performed. In order to avoid undesired escape of the gases through the trocar in the proximal direction, a self-closing obturator  29  is arranged in the distal direction from the sealing system  18  ( FIG. 2 ). It closes the proximal opening as soon as there is no shaft inserted into the medical instrument  10 . 
     As can be seen from  FIGS. 1 ,  2  and  5 , the sealing system  18  comprises a seal  14 . The seal  14  is designed as a pot-seal. The pot-seal has a peripheral edge designed as a sealing edge. An opening  16  is provided in a bottom area of the pot-seal. The sealing edge  37  of the latter is fastened by a fastening ring  36  to a seal holder  28 , with which the sealing system  18  is mounted on the trocar housing  27 . The seal  14  extends in the proximal direction away from the seal holder  28  and in so doing narrows. At its proximal end, the seal  14  has a socket  30  that surrounds this opening  16  ( FIGS. 5 and 7 ). An expansion cone  20  is secured on the socket  30  and extends in the proximal direction away from the seal  14  ( FIG. 5 ). 
     As can be seen from  FIGS. 5 and 6 , this expansion cone  20  is composed of an annular body  24  on which first ends of slats  22 , oriented in the distal direction, are mounted pivotably by means of film hinges  34  in a ring shape. At the second distal end, these slats  22  have endpieces  32  that are connected with a form fit to the socket  30  of the seal  14 . The expansion cone  20  acquires its conical shape as a result of the difference in cross section between the annular body  24  and the socket  30 . The slats  22  narrow from the proximal end to the distal end in such a way as to provide a uniform and almost closed inner surface of the expansion cone  20  in the unexpanded state. 
     The connection between the slats  22  and the seal  14 , wherein the endpieces  32  are fitted in the socket  30 , means that when a shaft is inserted and impacts on the slats, the slats  22  are initially forced radially outwards, as a result of which the opening  16  of the seal  14  is at the same time expanded, but without being expanded directly by the shaft. 
     The assembly composed of the seal  14  and of the expansion cone  20  is enclosed by a casing structure designed as a casing tube  26 . For this purpose, this casing tube  26  is connected at the distal end to the seal holder  28  and at the proximal end to the annular body  24  ( FIG. 5 ). The casing tube  26  is composed of individual ring elements  38 , which are interconnected via webs  40  lying radially opposite each other ( FIG. 4 ). To obtain a flexibility of the casing tube, the latter is made of a sufficiently elastic material, to ensure a flexibility of the webs  40 , and the webs  40  are in each case also offset by 90° from one to the next pair of ring elements. 
     If a force is applied to the sealing system in the direction of the arrow  63 , for example by the lateral offset of a shaft of smaller cross section, the expansion cone  20  moves along with the shaft in a movable flexible casing tube  26  of this kind ( FIG. 5   a ). By means of the movement of the expansion cone  20  in the direction of the arrow  63 , the proximal end of the casing tube  26  is similarly moved. The resulting offset between the proximal end and distal end of the casing tube  26  is compensated by the flexibility of the latter, such that it has a curved profile. 
     During such a movement of the expansion cone  20 , the connection between the slats  22  and the socket  30  ensures a corresponding deformation of the seal  14 . The result of this is that the shaft, despite the offset, has a central position in the opening  16  of the seal  14  and does not become wedged in the opening  16  and does not cause any loss of leaktightness. By means of the flexible casing tube  26 , the sealing system thus adapts to any offset of a shaft in the medical instrument. 
     A second embodiment of a flexible casing tube is shown in  FIG. 8 . In contrast to the casing tube  26  shown in  FIG. 4 , which can be produced as a single part by means of an injection moulding technique, for example,  FIG. 8  shows a casing tube  73  composed of separate ring elements  74 . These ring elements  74  have two different sides. Whereas one side has two tilting-joint sockets  80 , the other side has two tilting-joint inserts  78  extending away from the ring body. The tilting-joint inserts  78  and the tilting-joint sockets  80  are arranged opposite each other. The tilting-joint socket  80  and the tilting-joint insert  78  on a ring element  74  are arranged in a circle and offset by 90° to each other. 
     As is shown in  FIG. 8 , several ring elements  74  are interconnected by connection of the tilting-joint inserts  78  of one ring to the tilting-joint sockets  80  of another ring. In this way, the casing tube  73  is formed which, with its connections between the tilting-joint inserts  78  and the tilting-joint sockets  80 , resembles the webs  40  between the ring elements  38  of the casing tube  26  ( FIG. 4  and  FIG. 8 ). The tilting-joint insert  78  and the tilting-joint socket  80  thus form a tilting joint  76 , which is responsible for the flexibility of the casing tube  73 . 
     To obtain the greatest possible range of mobility, the height of a ring element  74  is higher at the tilting-joint sockets  80  than at the sites of the tilting-joint inserts  78  ( FIG. 8 ). The ring element  74  can thus be pivoted further about the axis formed by the radially opposite tilting joints  76 . A first ring element  74  can thus be pivoted, at the site of the tilting-joint socket  80 , to a second ring element  74 ′ further than if the latter at the site of the tilting-joint insert  78 ′ were to have the same height as at the site of the tilting joint  76 . 
     In this way, with this illustrative embodiment too, the same effect is achieved, upon a lateral offset of an inserted shaft, as has been explained for the flexible casing tube  26  in connection with  FIG. 5  and  FIG. 5   a.    
     A second embodiment of slats is shown in  FIGS. 9 and 10 . A slat  84  shown there has an endpiece  89  at the distal end and a spherical head  86  at the proximal end. 
     This spherical head  86  serves for movable connection of the slat  84  to an annular body  82 . For this purpose, the annular body  82  has corresponding openings  88  into which the spherical heads  86  can be inserted. It is conceivable for the slats to be inserted in the manner of a catch mechanism and also a simple engagement mechanism. For the latter alternative at least, a cover ring (not shown here) would also be required to prevent the slats  84  from falling out of the annular body  82  ( FIG. 9 ). 
     In this way, an expansion cone  81  is obtained similar to the expansion cone  20  with the film hinges  34  in the previously mentioned illustrative embodiment. Similarly to the latter, the slats  84  also narrow from the proximal end to the distal end.