Abstract:
A puncture cannula, particularly for nerve stimulation, comprises a steel cannula ( 10 ) attached to a cannula hub ( 11 ), and a cable ( 19 ) extending through an insertion channel ( 18 ) and having its core ( 21 ) connected to the steel cannula ( 10 ). The hub ( 11 ) of the cannula ( 10 ) comprises a metallic clamping element ( 24 ) formed with a first clamping slot engaging the steel cannula ( 10 ) and with a second clamping slot engaging the core ( 21 ) of the cable ( 19 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims priority from German patent Application No. 201 07 778.7, titled PUNCTURE CANNULA, filed in Germany on May 8, 2001, the entire contents of which is incorporated by reference herein as though set forth in full.  
         FIELD OF THE INVENTION  
         [0002]    The instant invention relates to a puncture cannula, particularly for nerve stimulation, comprising a steel cannula attached to a cannula hub and a cable extending through an insertion channel of the cannula hub and having a core connected to the steel cannula.  
         BACKGROUND OF THE INVENTION  
         [0003]    European Patent 0 102 538 B1 discloses a puncturing and catheterizing device which is suited for the puncturing and catheterizing of nerve strings. This device comprises a steel cannula with a cannula hub provided at the distal end of the cannula. The steel cannula is connected to a cable by which an electric potential can be applied to the steel cannula. When the steel cannula, which has an exposed tip, is brought into a position close to a nerve, electrical pulses, which are applied to the cable by a suitable stimulation device, will cause a nerve stimulation, resulting in corresponding reflexes of the patient. In this manner, it can be verified whether the tip of the cannula has been guided sufficiently close to the selected nerve. Thereafter, an anesthetic agent can be injected either through the cannula or through a catheter which has been set by use of the cannula in order to perform local anesthesia. In the known device, the electrical connection of the core of the cable to the steel cannula is performed by winding the core around the cannula, or by soldering the core to the cannula and subsequently enmolding the connection. Such a connection technique is complicated and overly expensive.  
           [0004]    It is an object of the invention to provide a puncture cannula which is easily manufactured and guarantees a safe contact between the cable and the puncture cannula.  
         SUMMARY OF THE INVENTION  
         [0005]    According to the instant invention, the hub of the cannula comprises a metallic clamping element which is formed with a first clamping slot for engaging the steel cannula and with a second clamping slot for engaging the core of the cable . By insertion of the clamping element into the hub of the cannula, the steel cannula and the core of the cable will be automatically positioned in their respective clamping slot to be tightly surrounded therein. In this manner, these two components are clamped into their desired positions at the same time, while the clamping of one component will not be affected by the other component. The clamping element is provided as a one-piece member, with its clamping slots arranged in such a configuration that the first clamping slot clamps the steel cannula when the second clamping slot clamps the core of the cable. Thus, the clamping slots have the same mutual distance as the steel cannula and the core of the cable and will be activated by displacing the clamping element.  
           [0006]    A considerable advantage of the invention resides in the simple and safe mounting process. By displacement of the clamping member, the steel cannula and the cable are fixed relative to each other and are also fixed relative to the hub of the cannula. It is also possible to perform the clamping prior to the attaching of the steel cannula in the hub of the cannula. In this case, an adhesive is inserted into a recess of the cannula hub after insertion of the clamping element. This adhesive will enter into all gaps to thus fasten the steel cannula in the hub of the cannula. Further, the adhesive serves as a surrounding electrical shielding for the cable and lends further stability the fixation of the cable. Further, the adhesive fulfills the function to cover all metallic parts which exist on or in the hub of the cannula, thus precluding the possibility that a person might inadvertently come into contact with any one of the current-carrying parts.  
           [0007]    According to a preferred embodiments of the invention, it is provided that the second clamping slot is formed with cutting edges adapted to penetrate an insulation of the cable. This obviates the need to first strip the cable and expose the core of the cable. When the clamping element is inserted into the hub of the cannula, the cutting of the cable insulation and the clamping of the core of the cable are performed automatically in the process.  
           [0008]    Preferably, the clamping slots are arranged behind each other in the clamping element, with a converging opening provided between the clamping slots so as to decouple the two clamping slots from each other.  
           [0009]    The puncture cannula of the invention is particularly suited for nerve stimulation. The instant puncture cannula is compatible with different techniques for using a cannula. Thus, for instance, an anesthetic agent can be injected directly through the steel cannula, or the steel cannula can be connected to a short catheter or a capillary tube. It is also possible to set a catheter via the puncture channel generated by the steel cannula, either with or without a guide wire.  
           [0010]    The clamping element can be of a design adapted to various diameters of steel cannulae and/or of cores of cables.  
           [0011]    A preferred embodiment of the invention will be described in greater detail hereunder with reference to the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a longitudinal sectional view of an embodiment of the puncture cannula;  
         [0013]    [0013]FIG. 2 is a cross-sectional view along the line II-II of FIG. 1; and  
         [0014]    [0014]FIG. 3 is a view from the direction of the arrow III in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    The puncture cannula comprises an elongate hollow steel cannula  10  attached to a cannula hub  11  of a plastic material. Steel cannula  10  consists of a tube provided with a nonconductive coating  12 . The tip of the cannula  10  (not shown) is exposed.  
         [0016]    Seated on a tubular connecting piece  13  of cannula hub  11  is a protective hose  9  which surrounds steel cannula  10  and extends beyond the length of cannula  10  to protect users from accidental injuries which might be caused by the tip of the cannula. The protective hose  9  can be withdrawn from the connecting piece  13 .  
         [0017]    The distal portion  10   a  extends through a cavity or a recess  14  of the hub  11  of the cannula and ends in a cavity  15  which is closed by a hose connector  16 . A hose  17 , starting from hose connector  16 , is provided for the administration of an anesthetic agent which will then be injected into the patient&#39;s body through steel cannula  10 .  
         [0018]    An introduction channel  18  is arranged to enter the recess  14  of hub  11  and has a cable  19  extending therethrough. Introduction channel  18  is formed along a part  18   a  of its length as a circumferentially closed bore, while another part  18   b  of the length of channel  18  is formed as an open channel. The channel part  18   b  terminates at an end wall  20  forming a stop face for the end of cable  19 . Cable  19  comprises a cable core  21  made of copper and an insulation  22 . Introduction channel  18  is oriented under an acute angle relative to the longitudinal axis of steel cannula  10 . A guideway  23 , formed for movement of a clamping element  24  therein, is arranged in a transverse direction relative to steel cannula  10  and cable  19 . Clamping element  24  comprises an elastic plate  25  made from spring steel. As illustrated in FIG. 2, this plate is formed with a first clamping slot  26  for steel cannula  10  and with a second clamping slot  27  for the core  21  of cable  19 . Both clamping slots  26 , 27  are arranged behind each other along a common axis and have a widened opening  28  arranged therebetween. Each of the clamping slots  26 , 27  has a tapering shape in the direction of insertion, i.e. from top to bottom in FIG. 2, so that a progressing insertion of the clamping element  24  into the cannula hub  11  will cause an increasingly stronger clamping action on the steel cannula  10  and the cable core  21 , respectively. The edges of second clamping slot  27  are cutting edges provided to cut through the insulation  22  of cable  19 , thus generating a safe electrical contact to the core  21  of cable  19 .  
         [0019]    Clamping slot  26  is delimited by wings  29 , 30  which can be bent about bending regions  31  for adaptation to different diameters of steel cannulae  10 . In FIG. 1, one of these wings,  29 , is shown as bent in outward direction.  
         [0020]    Clamping element  24  comprises a plate which, however, does not necessarily have to be flat. The plate is guided in a linear guideway  23  for displacement between a clamping position and a release position.  
         [0021]    When the steel cannula  10  and the cable  19  are to be mounted, the steel cannula  10  is inserted into the channel of cannula hub  11  which is provided for this purpose, and the cable  19  along with its insulation  22  is introduced into insertion channel  18 . Subsequently, clamping element  24  is inserted into guideway  23  and pushed into the same until reaching the end stop, while the clamping slot  26  exerts a clamping grip on steel cannula  10  and the clamping slot  27  cuts through the insulation  22  into the core  21  of cable  19 . The hub  11  of cannula  10  is then positioned in such an orientation that the recess  14  is facing upwards. In this condition, FIG. 3 represents a plan view from above. Next, a liquid adhesive  33  is filled into recess  14 . This adhesive will occupy the recess  14  completely. The adhesive enters into the annular gap between steel cannula  10  and cannula hub  11  and into the annular gap between introduction channel  18  and the cannula hub  11  and will after hardening also keep the clamping element  24  fixed in position. Thus, a sole adhesion process is sufficient to fix all of the components relative to each other and to close them in a tightly sealed manner. Also the entrance orifice  34  of guideway  23  is closed by adhesive and sealed so that the whole clamping element  24  is embedded in adhesive material. Thus, no electrically conductive components are accessible from the outside.