Abstract:
In order to make an improved securing of the plastic sheath on the holder possible in a surgical tubular-shafted instrument with a shaft, at the distal end of which at least one tool is arranged on a holder which, for its part, is secured in position on the shaft, and with a plastic sheath partially covering the holder, it is suggested that the plastic sheath engage at its edge beneath projections on the holder.

Description:
This application is a continuation of PCT/EP98/05805 filed Sept. 11, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a surgical, tubular-shafted instrument with a shaft, at the distal end of which at least one tool is arranged on a holder which, for its part, is secured in position on the shaft, and with a plastic sheath partially covering the holder. 
     A tubular-shafted instrument of this type is known, for example, from DE 93 18 815 U1. It is possible with such a tubular-shafted instrument, on the one hand, to use very solid metallic materials for the construction of the holder and the shaft and, on the other hand, to electrically insulate the shaft, including the holder, towards the outside as far as the area of the tools, on the one hand by surrounding the shaft itself with an electrically insulating sleeve, on the other hand by the holder having in certain areas a plastic sheath which covers outwardly pointing areas of the metallic holder. If such a tubular-shafted instrument is used as an electrical cutting and coagulation instrument, it is ensured in this way that any voltage applied to the instrument comes into contact with the body tissue only in the area of the actual tool so that cutting or coagulating occurs only in this area. 
     In practice, it has been shown that plastic sheaths of this type lift away from the holder in their edge area during the course of time and in this area cavities are formed which can become soiled and are very difficult to clean. This is due, on the one hand, to the fact that the material of the plastic sheath, which is normally applied by way of spraying on, does not combine with the material of the holder; this material may, for example, be high-quality steel. On the other hand, during the sterilization of these tubular-shafted instruments steam possibly penetrates the gap between the plastic sheath and the holder under increased pressure and increases the size of this gap so that the plastic material of the plastic sheath is removed from its areal contact on the holder. 
     The object of the invention is to design a generic tubular-shafted instrument such that such a lifting of the plastic sheath away from the holder and, in particular, the formation of larger cavities which are difficult to clean are avoided. 
     SUMMARY OF THE INVENTION 
     This object is accomplished in accordance with the invention, in a surgical tubular-shafted instrument of the type described at the outset, in that the plastic sheath engages at its edge beneath projections on the holder. The connection between the plastic sheath, on the one hand, and the holder, on the other hand, is thus designed such that the holder engages over the adjacent plastic sheath in the edge region and thereby prevents any lifting away from the supporting surface of the holder; in this way, a positive securing in position of the plastic sheath is, in practice, obtained in the edge region. 
     In a preferred embodiment it is provided for the projections to be formed by undercuts of a step in the holder which limits a lower-lying area of the holder covered by the plastic sheath. Such a step may, for example, extend over the entire circumference of the holder and results in the plastic sheath being secured in position on the holder in the same way along its entire edge. 
     In this respect, it is advantageous when the backwardly tapering cavity of the undercut is completely filled by the material of the plastic sheath. This results in a complete positive connection and prevents cavities, which can become soiled, being formed at any point. 
     It is particularly advantageous when the undercut is formed by a boundary surface of the step extending at an angle to the height of the step. 
     In accordance with a preferred embodiment, it is provided for the plastic sheath to adjoin non-sheathed, adjacent areas of the holder in a stepless manner so that a continuous outer surface is obtained which extends uniformly over the gap between holder surface and plastic sheath surface. 
     The material of the plastic sheath will preferably be a plastic material which can be sterilized by steam, for example, polyether ether ketone (PEEK) or liquid crystal polymer (LCP). 
     The following description of preferred embodiments of the invention serves to explain the invention in greater detail in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a side view of a tubular-shafted instrument; 
     FIG. 2 a perspective partial view of the area A in FIG. 1 in a tubular-shafted instrument extended in longitudinal direction; 
     FIG. 3 a longitudinal sectional view of the holder of FIG. 2; 
     FIG. 4 a side view of the holder of FIG. 3 in a position turned through 90° with partially cutaway areas and 
     FIG. 5 a sectional view along line  5 — 5  in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The tubular-shafted instrument illustrated in the drawings comprises a tubular shaft  1  which is detachably connected via a coupling member  2  to a handle part  3  at its proximal end. The handle part  3  has two branches  4 ,  5  with finger openings  6  which can be pivoted relative to one another about a pivot axis  7 . The one branch  4  is connected to the shaft  1 , the other branch  5  is articulatedly connected to a rod-shaped actuating element  8  which is arranged in the interior of the shaft  1  and extends as far as its distal end. During the pivoting of the branches  4  and  5  relative to one another, the actuating element  8  is displaced in longitudinal direction in relation to the shaft  1 . 
     At the distal end, a tubular holder  9  engages in the shaft  1  and this holder has at its end facing the shaft  1  an insertion nipple  10 , a cylindrical section  11  adjoining thereto and two longitudinal arms  13  and  14  adjoining thereto, these arms extending parallel to one another and forming a receiving space  12  between them. 
     The insertion nipple  10  can be inserted into the distal end of the shaft  1 ; at its area of transition to the cylindrical section  11  it has a circumferential groove  15 , into which the inwardly projecting ends  16  of the wall sections  17  of the shaft  1  can dip. These wall sections  17  are subdivided by longitudinal cuts  18  into areas which are independent of one another so that these wall sections  17  form spring tongues which can be bent inwards or outwards and which are integrally connected to the shaft  1  consisting of a corresponding elastic material. 
     In the vicinity of their free end the longitudinal arms  13  and  14  have openings  19  which extend transversely to the longitudinal direction of the holder  9  and into which a bearing shaft of tools  20 , which is not illustrated in the drawings, can be inserted so that the tools  20  are held in the receiving space  12  so as to be pivotable about the axis formed by the bearing shaft and protrude in a distal direction out of this space. These tools can, for example, be scissor blades, clamping jaws or the like. These tools  20  are pivoted via gear means  21  via the actuating element  8  when this is displaced in longitudinal direction in relation to the shaft  1 . In this case, techniques known per se can be used and so these gear means  21  are not explained in further detail. 
     An outer sleeve  22  is mounted on the shaft  1  for displacement in longitudinal direction and this sleeve consists of an electrically insulating material. In the advanced state it covers the flexible wall sections  17  of the shaft  1  and thus holds their inwardly projecting ends  16  in the circumferential groove  15  of the insertion nipple  10 ; as a result, the holder  9  is held in the shaft  1  so as to be non-displaceable in axial direction. To release this connection it is sufficient for the outer sleeve  22  to be pushed back so that the wall sections  17  can spring outwards; their ends  16  thereby exit from the circumferential groove  15  and the holder can then be withdrawn from the shaft  1 . 
     As a result of the use of an electrically insulating material, the outer sleeve  22  covers, in addition, the entire shaft  1  and the cylindrical section  11  of the holder  9  when the holder is inserted. 
     A broad circumferential groove  23  is formed in the insertion nipple  10  and this groove is limited laterally by respective steps  24 . The step is designed in cross section to be undercut by a boundary surface  25  extending at an angle. In addition, a narrow circumferential groove  27  with an essentially triangular cross-sectional surface area is worked into the base  26  of the circumferential groove  23 . 
     The circumferential groove  23  accommodates a plastic sheath  28  which fills it completely and supports longitudinal ribs  29  protruding radially beyond the outer surface of the insertion nipple  10 . During the insertion of the insertion nipple  10  into the shaft  1 , these longitudinal ribs slide into the longitudinal cuts  18  between the wall sections  17  and form a means for securing the holder  9  against rotation. In the area located between the longitudinal ribs  29 , the plastic sheath  28  adjoins the circumferential surface of the insertion nipple  10  in the areas located next to the circumferential groove  23  in a stepless manner. 
     The plastic sheath  28  can, for example, be applied by spraying around the holder in the area of the circumferential groove  23 . The plastic material applied in this way engages beneath the step  24  forming an undercut so that in the area of the edge of the plastic sheath  28  a positive connection is formed between plastic sheath  28 , on the one hand, and insertion nipple  10 , on the other hand, and this connection prevents the plastic sheath  28  from being able to lift away from the base  26  of the circumferential groove  23  in a radial direction. As a result of the material of the plastic sheath  28  engaging in the circumferential groove  27 , an axial securing is achieved, in addition. 
     A circumferential groove  30 , which extends approximately from the center of the cylindrical section  11  as far as the start of the longitudinal arms  13 ,  14 , is likewise located in the cylindrical section  11 . This circumferential groove  30  is limited at its distal end by a step  31  which is likewise undercut and has an inclined boundary surface  32 . A further groove  33  extending in circumferential direction is let into this circumferential groove  30  over part of the circumference and this groove  33  forms a recess in the base of the circumferential groove  30  and is likewise limited by an undercut step  34  with an inclined boundary surface  35  (FIG.  3 ). 
     The circumferential groove  30  and the groove  33  are completely filled by an additional plastic sheath  36  which merges in the area of the step  31  in a stepless manner into the circumferential surface of the cylindrical section  11 . In the area of transition between the cylindrical section  11  and the longitudinal arms  13 ,  14 , this plastic sheath  36  forms a step  37  which projects radially outwards and forms a stop for the outer sleeve  22 . 
     The plastic sheath  36  continues on the outer side of the longitudinal arms  13  and  14  and surrounds these on the upper side, on the outer side and on the underside as well as at the end side and at the distal end of the inner side. 
     In the area of the openings  19 , the longitudinal arms  13  and  14  have cylindrical recesses  38 , the outer edge of which forms an undercut step  39  with an inclined boundary surface  40 . The plastic sheath  36  engages in this recess  38  but leaves the central area of the recess  38  free so that the opening  19  remains accessible from the outside. 
     The edge  41  of the plastic sheath  36  located on the inner side of the longitudinal arms engages beneath a likewise undercut step  42  with an inclined boundary surface  43  which extends between the distal end of the longitudinal arms  13 ,  14 , on the one hand, and the opening  19 , on the other hand, transversely to the longitudinal direction of the longitudinal arms  13 ,  14 . 
     It is ensured in this way that the plastic sheath is held positively on the holder  9  in the area of the steps  31 ,  34  as well as  39  and  42  and is secured against any separation. 
     A similar securing results on the upper side and on the underside of the longitudinal arms  13  and  14 ; these have towards their inner side longitudinal grooves  44 , which extend parallel to the longitudinal direction of the longitudinal arms  13 ,  14 , are open towards the inner side and the side walls  45  of which are undercut, namely by an inclined design of the boundary surfaces  45 . These longitudinal grooves  44  with the undercut boundary surfaces  45  are also filled by the material of the plastic sheath  36  and thereby positively secured against any separation. 
     The plastic sheath  36  has a completely closed design in the area adjacent to the cylindrical section  11 , as illustrated in FIG.  5 . This applies for the area of the longitudinal arms  13  and  14 , into which the receiving space  12  does not extend. In the area of the receiving space  12 , on the other hand, this remains laterally recessed in the plastic sheath  36  so that tools dipping into the receiving space  12  can be pivoted sidewards out of the receiving space  12 .