Abstract:
The present invention relates to a medical instrument for grasping an object, in particular a surgical needle holder, with two jaw parts arranged at a distal end of a shaft, at least one of the jaw parts being pivotable with respect to the other one of the jaw parts between a grasp state for grasping the object between the jaw parts and a release state for releasing the object, and with a latching mechanism comprising at least one latching element, wherein the latching element has an elongated opening to accommodate a connection pin for connecting the at least one pivotable jaw part with the latching element, and wherein the elongated opening is divided in several sections along its length by periodical projections, such that the at least one pivotable jaw part pivots stepwise from one stable latched position to another stable latched position.

Description:
CLAIM OF PRIORITY 
     The present invention claims priority from European Patent Application No. 11 165 696.3, filed May 11, 2011, of common title and inventorship herewith. 
     FIELD OF THE INVENTION 
     The present invention relates to a medical instrument for grasping an object, in particular a surgical needle holder. 
     BACKGROUND OF THE INVENTION 
     An instrument comprising a latching mechanism is known from EP 1 872 729 A1. 
     In this instrument, a latching element is realized by an arc-shaped lever, which is attached with one end of the arc at the force transmission element and with the other end of the arc attached to the at least one pivotable jaw part. While the location of a connection between the latching element and the transmission element is distal from the location of a connection of the latching element with the at least one pivotable jaw part in the release state, the location of the connection of the latching element with the transmission element is moved in proximal direction by pulling on the transmission element via the at least one operating element. This leads to a pivot of the at least one pivotable jaw part and results in a closing of the jaw parts. The two aforementioned locations connected via the flexible arc-shaped element, i.e. the latching element, are thereby getting closer together, until an end point is reached wherein the location of the connection between arc-shaped element and transmission element lies slightly proximal with respect to the connection location of the arc-shaped element and the pivotable jaw part. In this position, an over-center state is reached, which is possible because of the flexibility of the latching element, i.e. the arc-shaped element. This stable state forms the basis of the latching mechanism. 
     As the instrument is equipped to accommodate objects of different diameter, the aforementioned latching mechanism has to be formed in that way that even with a small object, e.g. a needle of small diameter, the arc-shaped element has to be flexed at least a little in order to provide a working latching mechanism. 
     When accommodating larger objects, such as needles comprising a larger diameter, this results in a much higher flexing of the arc-shaped element and, therefore, in a higher strain for the material. This means that due to the higher and often different stress acting on the latching element, a high amount of strain occurs, which may exceed the elastic limit of the construction material resulting in permanent bending damage. 
     In order to decrease this strain, the aforementioned citation suggests to equip the part of the at least one pivotable jaw part which connects with the latching element with a certain flexibility. However, even here a permanent strain occurs after some time, due to the flexing movements. 
     Further, due to the limitations given by the material properties and the design of such a small mechanical instrument and mechanism, the needle holding force and the maximum jaw opening angle are both sub-optimal. This is also due to the aforementioned needed capability of this instrument to accommodate small as well as larger objects. 
     Further, WO 2005/092216 A1 shows an instrument used for surgical laparoscopy. This instrument is designed such that a pivotable jaw part comprises a pin at the opposite end with respect to the cutting part of the jaws. This pin is slidingly received in a groove of an axially moveable element. The groove may comprise an elevation shift at its bottom. In this elevation shift the aforementioned pin may be temporarily received while the pin moves along this groove due to the axial movement of the element. This results in a temporarily lock of the pin without affecting the linear motion of the jaws relative to the handle actuation. 
     This design comprises only one locked position as well. Also, due to the design with the short pin being slidingly arranged in a groove the locked position is not very stable, especially when stronger forces are applied in order to hold the aforementioned objects, like needles. Also, for the same reasons a twisting of the jaw parts in the direction of the pivot axis may occur due to the strong forces acting on the jaw parts when the aforementioned objects are grasped. 
     It is therefore an object of the present invention to improve the medical instruments of the kind mentioned before, such that the aforementioned drawbacks are avoided, in particular that the instrument is capable to accommodate objects of different sizes safely with the necessary holding force between the two jaw parts while simultaneously the strain in the parts is eliminated or at least reduced. 
     SUMMARY OF THE INVENTION 
     The object is achieved by a medical instrument for grasping an object, in particular a surgical needle holder, comprising:
         an elongated shaft, having a proximal and a distal end,   an axially movable force transmission element running within the shaft,   two jaw parts arranged at the distal end of said shaft, at least one of the jaw parts being pivotable with respect to the other one of the jaw parts,   a connection element for operatively connecting said force transmission element with the at least one pivotable jaw part,   a connection pin,   a handle arranged at the proximal end of the shaft,   the handle having at least one operating element for moving the at least one pivotable jaw part, and   a latching mechanism,   the latching mechanism comprising:
           at least one latching element being at least a part of the connection element, and   at least three latching positions,   
           the latching element comprising an elongated opening to accommodate the connection pin,   the elongated opening comprising:
           two opposing longer walls, and   periodical projections on at least one of the opposing walls along the length of the elongated opening,   
           wherein the at least one pivotable jaw part is pivotable between a grasp state for grasping the object between the jaw parts and a release state for releasing the object by the operating element, and the axially movable force transmission element is operatively connected with the at least one operating element and with the at least one pivotable jaw part via the connection element,   the at least one pivotable jaw part can be immobilized in the grasp state by the latching mechanism,   wherein the latching element is operatively connected to the force transmission element and the at least one pivotable jaw part,   the at least one pivotable jaw part being connected with the latching element via the connection pin, and   wherein the elongated opening is divided in several sections along its length, the sections being formed by the periodical projections, and wherein each of the sections forms one of the latching positions, such that the at least one pivotable jaw part pivots stepwise from one stable latched position to another stable latched position, when the transmission element is moved axially,   wherein the latching mechanism preferably comprises three to eight latching positions, and more preferably comprises three to five latching positions       

     In contrast to the aforementioned instruments, the instrument of the present invention does not comprise only one latching position, it comprises at least three, preferably three to eight and more preferably three to five. By such an arrangement, there are several latched positions of the at least one pivotable jaw part, each of them can be regarded as a stable state. Because of the plurality of the stable states resulting from this arrangement, an object, e.g. a surgical needle, can be accommodated and held by the two jaw parts fixedly in at least one of these stable states. Accordingly, for every object that shall be grasped by the medical instrument of the present invention, a secure position for the at least one pivotable jaw part with respect to the other jaw part exists, in which the object can be held safely with the medical instrument of the present invention, independent of the size of the object to be held, provided the size is within a range capable to be held by the medical instrument of the present invention having itself limits based on the given size of the jaw parts. 
     Providing several stable latched states or latching positions of the jaw parts, rather than having just one latched state for all objects of possible sizes, reduces the strain that occurs to the elements that are part of the latching mechanism. 
     It has been observed that providing at least three, preferably three to eight and more preferably three to five, latching positions as stable positions of the at least one pivotable jaw part with respect to the other jaw part, is sufficient for the instrument of the present invention comprising a common size, in order to accommodate all common objects that shall be grasped. The range from three to eight, preferably three to five, represents that range in which there are enough possible latching positions. At the same time, the amount of latching positions is delimited, in order to maintain a required stability of the elements involved in the latching mechanism. Increasing the amount of latching positions would inevitably result in the usage of smaller mechanical parts. As these are again more easily targets for strain, such designs are counterproductive. 
     The division into sections is easily achieved by even just a small projection on at least one of the opposing longer walls of the elongated opening. Since such an arrangement is easy to be manufactured, the effort and cost for providing an instrument of the present invention is minimized with respect to this feature. In order to achieve the grasp state, the connection pin just needs to move past the projections until it reaches the section that corresponds to the desired grasp state. Once the desired grasp state has been reached the connection pin rests against the previous projection in such a way as to maintain the grasp state. At the same time, a movement of the connection pin to the next section, i.e. by moving past the next projection, is blocked as the at least one pivotable jaw part is unable to pivot further due to the object between the jaw parts. 
     Instead of describing the division into several sections by periodical projections within the elongated opening as mentioned before, this constructive design may be also described by wells or dents being comprised within the elongated opening. This means that one can also regard this separation into several sections being realized by at least one of the opposing walls comprising several wells or dents along the length of the elongated opening. 
     In an embodiment of the present invention, one of the latching position forms the grasp state. 
     The advantage from this is that in the grasp state the jaw parts are arranged in a secured manner with respect to each other, resulting in a safe and strong grasped object. It is further beneficial that any of the latched positions mentioned before is able to form the grasp state. Thereby, the possibility for grasping objects of different sizes in a safe and strong hold is achieved. 
     In another embodiment of the present invention, the latched position forming the grasp state and a latched position forming the release state are achieved by the furthermost movement of the force transmission element in one respective axial direction when interacting with the object to grasp. 
     This measure has the advantage that both necessary states, i.e. the grasp state and the release state, are achieved just by moving the force transmission element in one respective axial direction, i.e. in proximal or distal direction. This is preferably done by using the operating element. Accordingly, a user just needs to push or pull the operating element to one respective end, in order to achieve a grasp state or the release state. This is an easy way of operating the medical instrument of the present invention, as the latched positions responsible for grasping the object are reached automatically. 
     In another embodiment of the present invention, the force transmission element comprises a distal end, and the connection element is arranged at the distal end of said force transmission element in that way that it undergoes the same axial movements as the force transmission element. 
     This arrangement has the advantage that it is very easy to attach the connection element to the force transmission element. This can, for example, simply be done by measures known in the art, e.g. gluing, welding, screwing, or any other fit mechanisms, like latching mechanisms. This contributes to a simple design of the instrument of the present invention, while simultaneously achieving a versatile instrument in which this connection element can be replaced or exchanged, if necessary. 
     In another embodiment of the present invention, the elongated opening is arranged in that way, that a movement of the latching element by an axial movement of the force transmission element results in a pivot of the at least one pivotable jaw part by movement of the connection pin within the elongated opening. 
     This design has the advantage that thereby a transfer of the axial movement of the transmission element and the latching element, which is connected thereto via the connection element, into a rotational movement for the at least one pivotable jaw part, is easily achieved. By such an arrangement, the connection pin for connecting the at least one pivotable jaw part with the latching element is basically just movable within the elongated opening and, accordingly, no flexible parts are needed for this latching mechanism in order to transfer the axial movement into a rotational movement. In contrast to this, the device mentioned at the outset used for this, is the flexible, arc-shaped lever. Here, only strain can occur on the connection pin that moves within the elongated opening along the given way based on the constraints resulting from the walls of the elongated opening. 
     In another embodiment of the present invention, the elongated opening is arc-shaped. 
     The advantage of this design of the elongated opening contributes to a more easily transfer of the axial movement into a rotational movement. The strain of the connection element and, accordingly, latching element, by strains resulting from this transfer, is thereby eliminated. 
     In another embodiment of the present invention, the latching element comprises two opposing faces and the elongated opening passes through the latching element from one of the faces to the other one of the faces, wherein the connection pin preferably passes substantially through the elongated opening. 
     Within the context of the present invention the expression “passes substantially through” is to be understood in such a way that the pin may pass through and protrude from the opening on both sides, as well as that one end of the pin may also be flush with the face of the latching element or even that said end of the pin may also lie within the elongated opening, provided that a contact area between the connection pin and the surface within the elongated opening is such that an adequate force transmission to the at least one pivotable jaw part is possible for grasping the object. 
     The connection pin passing through the elongated opening of the latching element results in a stable arrangement and reliable transmission of force from the force transmission element to the at least one pivotable jaw part. It is thereby particularly preferred if the at least one pivotable jaw part is connected to the two opposing ends of the pin. While the connection pin can be connected to the at least one moveable jaw part at any point along the length of the jaw part, it is preferred if the connection between the pin and the jaw part is arranged at or near the proximal end of the at least one moveable jaw part, as such an arrangement will result in an even distribution of the force transmitted from the force transmission element to the jaws. As a consequence, a twisting of the jaw parts does not occur while grasping an object. 
     In another embodiment of the present invention, the connection pin can move from one of the sections to another one of the sections being latched in each. 
     This way, the latching mechanism according to the present invention is achieved in a simple but effective constructive way. Therefore, the connection pin is the main component that operatively connects the at least one pivotable jaw part to the aforementioned latching element. Keeping the parts of a mechanism at a minimum like this has the further advantage of the whole device being easy to be cleaned. 
     In another embodiment of the present invention, the connection pin comprises a surface having a reduced coefficient of friction. 
     The term “reduced coefficient of friction” refers to the latching element and the elongated opening with its opposing longer walls and shall be understood in comparison to the case wherein the material of the longer walls and the surface of the connection pin are both made of steel. Referring to the surface of the connection pin includes the cases wherein the whole connection pin is manufactured from this material as well as that the connection pin comprises a coating of such a material. 
     Although, the connection pin shall be latched in the aforementioned latching positions, the movement from one latching position to another latching position, that is to say from one section to another section shall preferably be possible without the interference of friction while the connection pin moves within the elongated opening over at least one of the aforementioned opposing longer walls of the latter. This is achieved by the surface of the connection pin having a reduced friction. This low friction surface may be present over the whole connection pin, a part of the connection pin that may be exposed to the outside or at least on that area of the connection pin that gets in contact with the opposing longer walls of the elongated opening. 
     In another embodiment of the present invention, the connection pin comprises a surface of Polytetrafluoroethylene. 
     Such a surface of Polytetrafluoroethylene (e.g. Teflon®) has the advantage that when applied at least to the areas that get in contact with the inside of the elongated opening, the friction may be significantly reduced. Further, Polytetrafluoroethylene is resistant to the harsh conditions used in disinfection of a medical compound, like high temperatures in autoclaves and chemicals. Also, Polytetrafluoroethylene provides a surface that is easy to clean and disinfect. As mentioned before, the surface may be the result of at least partially coating the connection pin or of the connection pin being manufactured from Polytetrafluoroethylene. Also, the reduced friction according to the present invention may also result if both, the surface of the connection pin and the surfaces within the elongated opening are covered with and/or manufactured from Polytetrafluoroethylene. 
     In another embodiment of the present invention, the connection pin comprises a roller, the roller being arranged between the opposing walls and being moveable along the length of the elongated opening. 
     The usage of a roller has the advantage that the aforementioned strain of the connection pin is reduced, due to a certain flexibility of the roller. Further, the roller also shows the desired lower frictional characteristics. This reduction in friction has again the advantage that the movement of the roller within the elongated opening is more easy. 
     In a preferred embodiment of the present invention, each of the sections accommodates the roller via form-fit, and the roller is able to move from one of the sections to another one of the sections. 
     This measure has the advantage that the roller cannot accidentally slide along the elongated opening, thereby leading to an unwanted movement of the at least one pivotable jaw part in either direction. On the other hand, given a suitable design, easy movement of the roller from one section to another section is still possible. For this purpose, the user just has to overcome the barrier given by the form-fit of the roller within the respective section. Thereby a latching mechanism comprising several latching positions is easily achieved. 
     In another embodiment of the present invention, the connection element comprises at least one sliding roller, and the connection element is arranged in the shaft and gets in contact with the shaft via the sliding roller. 
     This measure has the advantage that the connection element itself cannot get directly in contact with the inner wall of the shaft. This results in a highly reduced friction and, accordingly, in an easily movable connection element. The sliding roller itself shows low friction, as it rolls over the inside wall of the shaft. For this, the roller is preferably arranged on the connection element via a pin. 
     In another embodiment of the present invention, the at least one pivotable jaw part comprises a proximal portion being elastically deformable. 
     This measure has the advantage that some strains that may even occur with the device of the present invention can be compensated by this elastically deformable proximal portion. This means that even by the application of a stronger force on the force transmission element, e.g. by a user or an operator, the forces acting on the elements taking part in the latching mechanism are reduced because of this flexibility. 
     This contributes in a positive way to the minimization of damage in the latching mechanism, even in the case of an accidentally improper use of the instrument of the present invention. 
     The aforementioned object is further achieved according to another aspect of the present invention by a medical instrument for grasping an object, in particular a surgical needle holder, comprising:
         an elongated shaft, having a proximal and a distal end,   an axially movable force transmission element running within the shaft,   two jaw parts arranged at the distal end of the shaft, at least one of the jaw parts being pivotable with respect to the other one of the jaw parts,   a connection element for operatively connecting the force transmission element with the at least one pivotable jaw part,   a connection pin,   a handle arranged at the proximal end of the shaft,   the handle having at least one operating element for moving the at least one pivotable jaw part,   a latching mechanism,   the latching mechanism comprising:
           at least one latching element being at least a part of the connection element, and   at least three latching positions,   
           the latching element comprising:
           two opposing faces, and   an elongated opening to accommodate the connection pin, comprising two opposing longer walls, the elongated opening passing through the latching element from one of the faces to the other one of the faces,   
           wherein the at least one pivotable jaw part is pivotable between a grasp state for grasping the object between the jaw parts and a release state for releasing the object, and the axially movable force transmission element is operatively connected with the at least one operating element and with the at least one pivotable jaw part via the connection element,   the at least one pivotable jaw part can be immobilized in the grasp state by the latching mechanism,   wherein the latching element is operatively connected to the transmission element and the at least one pivotable jaw part,   the at least one pivotable jaw part being connected with the latching element via the connection pin, and   wherein the connection pin passes substantially through the elongated opening, and the elongated opening is divided in several sections along its length, and wherein each of the sections forms one of the latching positions, such that the at least one pivotable jaw part pivots stepwise from one stable latched position to another stable latched position, when the transmission element is moved axially.       

     In an embodiment of this aspect of the present invention the elongated opening comprises periodical projections on at least one of the opposing walls along the length of the elongated opening. 
     Further embodiments according to this aspect of the present invention and the according advantages can be obtained by combining this aspect of the present invention with one or several of the features mentioned above in connection with the embodiments of the first aspect. Any such combination is considered part of the scope and disclosure of the present invention. 
     Further features and advantages will become apparent from the following description and the accompanying drawings. 
     It is to be understood that the features mentioned before and those features still to be explained below are not only applicable in the combinations given, but also in other combinations or in isolation, without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described and explained in more detail below with reference to a few exemplary embodiments of the invention in association with the accompanying drawings, in which: 
         FIG. 1  shows an embodiment of the instrument of the present invention in a perspective total view, 
         FIG. 2  shows a distal portion of an instrument according to the present invention shown in a sectional view along its longitudinal axis, 
         FIG. 3  shows an exploded view of the distal portion shown in  FIG. 2 , 
         FIGS. 4   a - 4   d  show schematic representations of a distal portion of an instrument according to the present invention similar to  FIG. 2 , each in another latched position of the at least one pivotable jaw part, 
         FIG. 5  shows a schematic representation of a distal portion of an instrument according to the present invention grasping a larger object, 
         FIG. 6  shows a schematic representation according to  FIG. 5 , wherein the instrument is grasping a smaller object, 
         FIG. 7  shows a further embodiment of a distal portion of an instrument according to the present invention shown in a sectional view along its longitudinal axis as in  FIG. 2 , 
         FIG. 8  shows an exploded view of the distal portion shown in  FIG. 7  as in  FIG. 3 , 
         FIG. 9  shows another embodiment of an instrument according to the present invention similar to  FIG. 7  without a sliding roller, and 
         FIG. 10  shows an exploded view of the distal portion shown in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     An embodiment of a medical instrument according to the present invention is described hereinafter and is shown throughout  FIGS. 1 to 6  in its entirety by the reference numeral  10 . Further embodiments of a medical instrument according to the present invention are also described with reference to  FIGS. 7 to 10  and shown hereinafter by the reference numerals  100  and  150 . 
     The medical instrument  10  comprises a shaft  12  having a distal part  14  and a proximal part  16 . 
     At the proximal part  16 , there is arranged a handle  18  which itself comprises an operating element  20  which will be described later in more detail. 
     At the distal part  14 , the medical instrument  10  comprises two jaw parts  22  and  24 . In this embodiment, one of those jaw parts is a fixed jaw  22 , wherein the other jaw part is a pivotable jaw  24 . The pivotable jaw part  24  pivots around a pivot axis  26 . Within the shown embodiment, the pivot axis  26  runs transversely through a central longitudinal axis  28  of the shaft  12 . 
     Coming now to the representation in  FIG. 2 , the interior of the medical instrument in the distal part  14  can be seen and will be described hereinafter. 
     In order to simplify the shown drawings, the shaft  12  is here just shown with its very distal part. 
     Within shaft  12  runs a force transmission element  30 . This force transmission element  30  comprises a helical section  32 , which is beneficial for the transmission of turning forces along the force transmission element  30  as it is described within EP 1 872 729 A1, as mentioned at the outset. 
     The force transmission element  30 , here only shown in its distal end area, is at its proximal end connected to the aforementioned operating element  20 . 
     By an operation of the operating element  20 , e.g. a push or pull movement, the force transmission element  30  is moved axially along the central longitudinal axis  28  in distal or proximal direction, as it is implied by a double arrow  34 . Apart from this mode of operation, other mechanisms are possible with respect to the operating element  20 , e.g. that a rotation of the operating element  20  leads to an axial movement of the force transmission element  30 . 
     At its distal end, the force transmission element  30  is connected to a connection element  36 . The connection element  36  comprises in its distal end area a latching element  38 , which will be described in more detail hereinafter, and a sliding roller  40 . When reference is made to the distal end of the connection element  36  within the context of the present representations such reference may also be regarded as a reference to the latching element  38  in these embodiments and may be understood as such and vice-versa. 
     The sliding roller  40  is arranged rotatably via a roller pin  42  on the connection element  36 . As it projects from the connection element  36 , the roller  40  prevents the contact of the connection element  36  with the inside wall of the shaft  12 . Thereby, a frictional contact of the connection element  36  with the inner wall of the shaft  12  is avoided. Furthermore, the rotational arrangement of the roller  40  via a roller pin  42  avoids even a frictional interaction of the sliding roller  40  with the wall itself, so that the distal end of the force transmission element  30 , i.e. the connection element  36 , is able to easily slide back and forth with the directly connected force transmission element  30  as described before and as implied by double arrow  34 . 
     In the embodiment described here, the sliding roller  40  is held via the roller pin  42  between two outer faces or sidewalls  44  and  44 ′ of the connection element  36 . This can be seen in more detail in the exploded view of  FIG. 3 . 
     As shown in  FIG. 3  as well, the distal part  14  of the shaft  12  is connected via a connection ring  46  to the remaining part of shaft  12 . Such an arrangement has the advantage that the distal part  14  might be movable with respect to the remaining part of shaft  12  around the central longitudinal axis  28 . For this, the embodiment comprising a helical section  32  of the force transmission element  30  is advantageous, as described earlier. 
     The connection element  36  further comprises an elongated opening  48 . This elongated opening  48  is basically arc-shaped in the present embodiment. It passes through the connection element  36  or latching element  38  from one face  44  to the other, i.e. the opposite face  44 ′, as can been seen in  FIG. 3 . In this special embodiment, a roller  50  is accommodated in this elongated opening  48 . The roller  50  itself is arranged via a connection pin  52  at a proximal end  54  of the at least one pivotable jaw  24 . For this, the proximal end  54  comprises two openings  56  and  56 ′ for receiving the connection pin  52 . This way, the connection pin  52  is connected to the at least one pivotable jaw part  24  with its opposing ends. The proximal end  54  further comprises a recess  58  in order to receive the distal end of the connection element  36 , or, in particular, the latching element  38  in this proximal end  54 . In this embodiment, the connection pin  52  is oriented in that way that it runs transversely to the central longitudinal axis  28 . Also, the connection pin  52  is arranged parallel to the pivot axis  26 . 
     The elongated opening  48  comprises two opposing longer walls  60  and  62 . Herein, the longer wall  60  can be regarded as the distal wall, wherein the longer wall  62  is the proximal wall. 
     The distal longer wall  60  comprises in this embodiment three projections  64 ,  64 ′ and  64 ″. The proximal longer wall  62  comprises two projections  66  and  66 ′. Therefore, these projections  64 ,  64 ′,  64 ″,  66  and  66 ′ are arranged within the elongated opening. 
     The roller  50  connects the pivotable jaw part  24  to the latching element  38  in that way that an axial movement of the connection element  36  and, consequently, of the latching element  38 , which are a result from an axial movement of the force transmission element  30 , results in a movement of the roller  50  within the elongated opening  48 . As the roller  50  fits between the longer walls  60  and  62 , the movement is only possible along the length of the elongated opening  48 . As an axial movement of the latching element  38  results in a movement of the roller  50  that is transverse to the central longitudinal axis  28 , and given the rotational arrangement of the pivotable jaw part  24  via the pivot axis  26 , the result of such an axial movement of the force transmission element  30  and, hence, the latching element  38 , results in a pivot of the pivotable jaw part  24 , as it will be described in more detail hereinafter with reference to  FIGS. 4   a  through  4   d . These explanations of the medical instrument as described in the following are merely described with the roller  50  by way of example. The same explanations are also valid for devices comprising only the connection pin  52  or a connection pin  164  that runs within the elongated opening  48  and that will be described in more detail later on. 
       FIG. 4   a  shows an arrangement wherein the jaw parts  22  and  24  are closed, comparable to the representation of  FIG. 2 . 
     In this state, the force transmission element  30  as well as the connection element  36  and, consequently, the latching element  38  are in their furthermost proximal position. In this position, the roller  50  is arranged within the elongated opening  48  between the distal end of this elongated opening  48  and the first projection  64 ″ of the longer wall  60 . 
     In order to get to the first opening step, as it is shown in  FIG. 4   b , the latching element  38  has to be moved distally. This is done by a distal movement of the connection element  36  via the force transmission element  30 . This movement is implied by arrow  68  of  FIG. 4   a  and can be done by an operator by pushing the operating element  20 , for example. By the force applied on the latching element  38 , the roller  50  is able to overcome the barrier given by the projection  64 ″. Accordingly, the roller  50  reaches a position as shown in  FIG. 4   b . In this position, the roller  50  is arranged between the projections  64 ″ and  64 ′. The roller  50  now lies in a well  70 . This well  70  is formed by the projections  64 ′ and  64 ″. In order to avoid a loose arrangement in this well  70 , the roller  50  is held in this well additionally by the projection  66 ′ of the longer wall  62 . This projection  66 ′ is arranged opposite to the well  70 . As the projections  64 ′,  64 ″ and  66 ′ as well as the well  70  are arranged in that way that they perfectly accommodate the roller  50  in this position, the roller  50  is held or latched in this position via form-fit. Such a form-fit occurs as well in the aforementioned most distal position of the roller  50  in the elongated opening  48  as well as in the following latched positions described in the context of  FIGS. 4   c  and  4   d.    
     Since the roller  50  has undergone a movement transverse to that of the central longitudinal axis  28 , and since it moved in fact closer to the central longitudinal axis  28  compared to the state of  FIG. 4   a , the pivotable jaw part  24  pivoted slightly to a small opening of the jaw parts  24  and  22 . This is the result of the lever-like arrangement of the pivotable jaw part  24  via pivot axis  26 . 
     By a further distal movement of the force transmission element  30 , as implied by arrow  68 ′, the roller  50  is now able to overcome the barrier given by the projection  64 ′. Therefore, a further lateral movement of the roller  50  transverse to the central longitudinal axis  28  occurs, as the roller  50  moves further proximal in the elongated opening  48 . The result of this further movement is shown in  FIG. 4   c.    
     Herein, the roller  50  now is located between projections  64 ′ and  64  in a well  70 ′. The aforementioned form-fit in this position is realized by the projection  66  of the longer wall  62 . This projection  66  is arranged opposite from well  70 ′. The result is an even more enlarged opening of jaw parts  22  and  24  compared to the representation and state of  FIG. 4   b.    
     A further movement of the force transmission element  30  in the distal direction, as implied by arrow  68 ″, leads to the state shown in  FIG. 4   d . Here, the roller  50  overcame the barrier of the projection  64  of longer wall  60 . The roller  50  thereby ends in the most proximal position in the elongated opening  48  of the embodiment of the instrument of the present invention shown here. Accordingly, the pivotable jaw part  24  shows in this state in  FIG. 4   d  the largest possible opening for this embodiment. 
     Each of the shown positions in  FIG. 4   a  through  4   d  forms a latched position according to the present invention. In this embodiment, the medical instrument comprises four such latching positions. However, by equipping the latching element  38  with more or fewer projections  64  and  66 , alternate numbers of latching positions are possible and easy to achieve. 
     Although the mechanism shown throughout  FIGS. 4   a  to  4   d  is described in the context of an opening of the jaw parts  22  and  24 , i.e. a pivot of the pivotable jaw part  24 , the same mechanism works in the opposite direction, meaning for a closing of the jaw parts  22  and  24 . Therefore, the force transmission element  30  has to be moved in the proximal direction. This is indicated by arrow  72  in  FIG. 4   d . This can, for example, be done by an operator by pulling on operating element  20 . 
     The closing procedure works apparently just opposite to the opening procedure, thereby overcoming the aforementioned barriers of the projections  64 ,  64 ′ and  64 ″ basically in the opposite direction. 
     This shall be described in the context of the following  FIGS. 5 and 6 , wherein it is shown and described how objects are grasped by an instrument of the present invention. 
     In  FIG. 5 , a large needle  74  is grasped by the jaw parts  22  and  24 . This is achieved by arranging the needle  74  between the jaw parts  22  and  24  and pulling of the force transmission element  30 , e.g. via the operating element  20 , by an operator. Pulling of the force transmission element  30  results in a proximal movement of the force transmission element  30  and, accordingly, of the connection element  36  comprising the latching element  38 . Thereby, with reference to  FIG. 4   d , the roller  50  is able to overcome the barrier of the projection  64  and, accordingly, moves distal within the elongated opening  48  into well  70 ′, i.e. between projections  64  and  64 ′. In this position of the pivotable jaw part  24  with respect to the jaw part  22 , the needle  74  is held between these jaw parts  22  and  24 . The roller  50  is, as already mentioned, in this state latched in the well  70 ′. Further pulling of the force transmission element  30 , i.e. transmission of force in the proximal direction, results in an exertion of force by the well  70 ′ as well as the projection  64 ′ on the roller  50  in a direction away from the central longitudinal axis  28 . This results in a transferred force as indicated by arrow  76  because of the pivotable arrangement of the jaw part  24  via the pivot axis  26 . In other words, further pulling of the force transmission element  30 , or the operating element  20 , for example, results in a tight grasp of the object, here the needle  74 . 
     A further movement of the roller  50  in the following well  70  in the distal direction is not possible in this example, as this requires a significant larger pivot of the pivotable jaw part  24  which is hindered by the needle  74 . 
     Showing the case wherein a smaller needle  78  shall be grasped by the jaw parts  22  and  24 ,  FIG. 6  shows that in such an example the roller  50  may move within the elongated opening  48  also over the second projection  64 ′, starting from the opening state of  FIG. 4   d . This results in a position of the roller  50  within well  70  and in between of the projections  64 ′ and  64 ″. 
     In this example, with the smaller needle  78 , the roller  50  also stays as well in this latched position. This latching position is, in this case, formed by the well  70  and further by the projections  64 ′ and  64 ″. 
     By further pulling of the force transmission element  30 , as already described before in the context of  FIG. 5 , a force is applied to the roller  50  via the well  70  and projection  64 ″ which is directed in a direction away from the central longitudinal axis  28 . This results in a transferred force at the pivotable jaw part  24  indicated by arrow  76 ′, and, accordingly, to a tight grasp of the small needle  78 . 
     Comparing the examples shown in  FIG. 5  and  FIG. 6 , with a large needle  74  and a smaller needle  78 , it becomes apparent that the forces applied to the parts of the latching mechanism formed by the latching element  38 , are basically of the same amount. Since the necessary closure of the jaw parts  22  and  24  is managed via the latching element  38  comprising the aforementioned latching positions, formed by either the distal or proximal end of the elongated opening  48  or the wells  70  and  70 ′ and the projections  64 ,  64 ′ and  64 ″, the start point for the exertion of a force in order to tightly grasp an object, here the needles  74  and  78 , is the respective latching position. In contrast to this, in EP 1 872 729 A1, mentioned at the outset, there is only one latching position and a flexible latching element  38 , responsible also for the grasp of the respective object, which undergoes different strains and bendings, dependent of the object that shall be grasped. 
     Having the plurality of starting points, i.e. latching positions, and, therefore, almost the same force and strains that act on the parts of the latching element  38 , results in a decrease of stress to the parts of the present medical instrument and, accordingly, to a lower risk of damages and cost-intensive repairs. 
     Further, this grasping force for the objects, here the needles  74  and  78 , which stays nearly the same as already mentioned, allows the grasp of the needles to be optimal, independent of the needles&#39; size. 
     Further, such an arrangement allows a very large jaw opening as shown in  FIG. 4   d , as the elongated opening  48  can be manufactured in that way that its proximal end runs very deep within the latching element  38  of the connection element  36 . 
     In order to achieve a certain flexibility within this latching mechanism, the proximal portion  54  of the pivotable jaw part  24  is equipped with a certain flexibility in one embodiment of the present invention. Thereby, an accidentally and unwanted stronger force applied to the force transmission element  30  is able to be compensated by this flexible proximal part  54  of the jaw part  24 . This avoids the damaging of the parts of the latching mechanism  38 . 
     As mentioned before, medical instruments  100  and  150  shall be described in the following as additional embodiments according to the present invention. 
     The medical instrument  100  is almost identical to the medical instrument  10  as described before. In the following description and the drawings, the parts identical to that parts as described in the context of the medical instrument  10  are designated by the same reference signs. The medical instrument  100  will be described in the following by reference to  FIGS. 7 and 8  showing a distal end  104  of this medical instrument  100 . The parts of the medical instrument  100  not shown in  FIGS. 7 and 8  shall be considered as identical to the respective parts in the medical instrument  10 . 
     The difference between medical instrument  100  and medical instrument  10  lies in the connection pin  52 . Where in the exemplary embodiment of the medical instrument  10  the connection pin  52  comprises the roller  50  in order to reduce the friction when the connection pin  52  moves through the elongated opening  48  the connection pin  52  is received directly within the elongated opening  48  in the medical instrument  100 . As mentioned before the roller  50  present in the description within the context of  FIGS. 4   a  to  6  was merely used by way of example. Accordingly, all the descriptions and explanations made within the context of  FIGS. 4   a  to  6  demonstrating the functioning of the medical instruments according to the present invention can be used in the same way to describe the functioning of the medical instrument  100  or the medical instrument  150 , which will be described later, just by replacing the wording “roller  50 ” in the explanations mentioned above by “connection pin  52 ” or “connection pin  164 ”, respectively. 
     Accordingly, the connection pin  52  is accommodated within the elongated opening  48  and interacts in the described way with the projections  64 ,  64 ′,  64 ″,  66  and  66 ′. Therefore, the connection pin  52  of this embodiment is designed to be received in an optimal way for the desired sliding function. 
     The usage of just the connection pin  52  allows for an easy cleaning of the whole device. Further, it simplifies the construction. 
     In order to avoid unwanted interferences in the opening or closing procedures of the pivotable jaw part  24  by interactions of the connection pin  52  within the elongated opening  48 , i.e. on the opposing walls  60  or  62  by friction, the connection pin  52  may comprise a surface having a reduced coefficient of friction with the material of the opposing walls  60  or  62 . Such a surface may result from a low friction coating  106 . This low friction coating  106  may cover the whole connection pin  52  as shown here or may just be applied to the areas necessary in order to reduce the friction between the connection pin  52  and the elongated opening  48  with its walls  60  and  62 . 
     An example for a coating that may also act as a low friction coating  106  is Polytetrafluoroethylene (PTFE). PTFE has the advantage that it provides a surface with a reduced coefficient of friction as mentioned before and is also able to be submitted to the generally used sterilizing methods involving autoclaves and chemicals. Further, the in general smooth surface of PTFE makes it harder for dirt and bacteria to get stuck on such a surface and makes it easier to clean. 
     Although the description of the connection pin  52  is made in this context with a low friction coating  106  it goes without mentioning that it is also possible to provide the same medical instruments without such a coating on the connection pin  52 . Further, providing a connection pin  52  that is made of a material providing a reduced coefficient of friction like PTFE lies also within the scope of the present invention. 
     The medical instrument  150  will now be described by reference to  FIGS. 9 and 10 . As the medical instrument  100  this medical instrument  150  is in most parts identical to the medical instrument  10  and only differs in a distal end  154  and the design of the pivotable jaw part  160  which will be described in the following. The parts not shown in  FIGS. 9 and 10  shall be considered as identical to the medical instrument  10 . Further, identical parts with respect to the medical instrument  10  and  100  will be described and designated by the same reference signs. 
     The medical instrument  150  comprises the same latching mechanism as the medical instrument  100 . This means that a connection pin  164  is arranged moveably directly within the elongated opening  48 . Hence, no roller  50  is used in the embodiment of the medical instrument  150 . Accordingly, all the explanations with respect to connection pin  52  made within the context of  FIGS. 7 and 8  describing the function of the latching mechanism are also valid for the medical instrument  150 . However, the medical instrument  150  differs from the aforementioned medical instruments  10  and  100  in the pivotable jaw part  160 . Instead of comprising two openings  56  and  56 ′ at its proximal end  162  the jaw part  160  comprises a connection pin  164  directly attached to it. This connection pin  164  can be designed as the connection pin  52 . This means, that the connection pin  164  may as well comprise a low friction coating  106 . 
     A further difference of the medical instrument  150  to the medical instrument  10  is that the medical instrument  150  does not comprise the sliding roller  40  arranged at a connection element  156 . 
     Aside from using the sliding roller  40  as mentioned before it is also possible to use a connection element  156  that may slide within the shaft  12  of the medical instrument  150  directly. 
     In order to provide a reduced friction of the connection element  156  of the medical instrument  150 , the connection element  156  comprises a low friction coating  158 . Thereby, the coefficient of friction with the inner wall of the shaft  12  is reduced. This provides an alternative to the sliding roller  40  of the medical instruments  10  or  100 . 
     As described before within the context of the connection pin  52  in  FIGS. 7 and 8 , the low friction coating may be realized by a Polytetrafluoroethylene coating. This kind of coating has the same advantages as mentioned before, i.e. that the friction is reduced as desired and that cleaning and sterilizing are possible under the conditions regularly used for medical instruments. 
     Apart from using just a low friction coating  158 , it is also possible that a small element of a low friction material is attached to the connection element  156  replacing the part of the connection element  156  which comprises the low friction coating  158 . Further, the whole connection element  156  may be made out of such a low friction material. In all the mentioned cases, the connection element  156  comprises a surface having a reduced coefficient of friction. The aforementioned low friction materials can also be Polytetrafluoroethylene.