Loop electrode

Abstract: A medical instrument (3) and a method of making a medical instrument (3) for use in diathermy is described. The medical instrument (3) has a cutting member (5) and a support member (4). Both the support member (4) and the cutting member (5) are electrically conducting and the support member (4) is tubular so that two ends of the cutting member (5) may be received within an end of the support member (4). The two ends of the cutting member (4) are secured to the end of the support member (4) so that there is an electrical connection between the support member (4) and the cutting member (5). The cutting member is preferably a wire which is less than 0.01" thick. Typically, insulation (7,8) is also provided around a portion of the support member (4) and a portion of the cutting member (5). The insulation may include a plastic shrink-fitted sleeve (7) and a plastics material (8) which is moulded around the end of the support member (4) which receives the two ends of the cutting member (5).

Description: This invention relates to a medical instrument for use in diathermy. In medicine, heat can be applied to the human body by high frequency currents in a process known as diathermy. Diathermic surgery involves the use of an electric current passing, for example, through a blade, forceps or thin wire in preference to a knife for cutting through tissue, and has the advantage of sealing the blood vessels at the cut and so reducing bleeding. Diathermy is particularly appropriate for treatment of cervical disease. Iodine is used to stain the tissue of the cervix and the malignant cells show up as white patches. These cells can be excised by carrying out a biopsy using a diathermy loop, in the form of a re-usable hand-held instrument. Figs. 1a and 1b show front and sectional views respectively of a typical diathermal instrument of the prior art. A solid metal rod 1 is welded to a metal tube 2 to form a T-junction. Wire 3 is looped from one end of the tube 2 to the other and the tube ends are stamped down around the wire ends to give the end product. Fig 1b shows a cross-section on line "A-A" of Fig 1a. The instrument has disadvantages in that the wire may break at its connection to the tube and in order to provide sufficient mechanical strength the wire used is generally at least 0.25mm (0.010 inches) thick. However, it would be desirable to use thinner wire as such wire produces a more effective cutting action. Also, the welding point makes the production of the instrument costly. German Patent DE-C-848233 discloses a medical instrument which comprises a tube having a cutting member extending from one end thereof, the cutting member describing a route passing through more than one plane. US-A-3807404 discloses a probe unit having a disposable probe tip comprising a resilient wire which deforms upon insertion into the probe tip to engage with slots in the probe tip. According to the present invention there is provided a method of making a medical instrument for use in diathermy, the method comprising providing a cutting member and a support member, both of the members being electrically conducting, and inserting two ends of the cutting member into one end of the support member, characterised in that when the two ends of the cutting member are inserted into the end of the support member, the end of the support member is deformed to secure the ends of the cutting member and to make an electrical connection between the members, and wherein insulating means covers a portion of the support member and forms a web spanning an area between the two ends of the cutting member. Typically, the support member may be a metal tube which provides a handle for the instrument. Typically, the cutting member is a wire, as it presents the same cutting surface to the tissue, no matter how it is manipulated. Preferably, the cutting member is less than 0.25mm (0.010 inches) thick, to give a more effective cutting action and most preferably is 0.15mm (0.006 inches) thick as this gives the best combination of mechanical strength and cutting action. The insulating means may include sleeves covering the cutting member adjacent the point where it is received by the support member, and may also include a sheath which covers a length of the support member and is shrink-fitted onto the support member The insulating means may be made from plastics material, and may also comprise a plastics (eg nylon) moulding which overlies the sleeves and joins the ends of the sleeves to the sheath. An embodiment of the invention will now be described with reference to the drawings in which: Fig. 2a is a front view of an embodiment of a medical instrument for use in diathermy of the present invention; and Fig. 2b is a cross-section on B-B of Fig. 2. A medical instrument 10 for use in diathermy (Fig. 2) comprises a support member in the form of a metal tube 4 and a cutting member in the form of a wire 5. Both ends of the wire 5 are received by the tube 4 and sections of the wire 5 adjacent the tube 4 are covered in plastic shrink-fitted sleeves 7. A plastic shrink-fitted sheath 6 covers part of the tube 4. The sleeves 7 are in turn enclosed in a nylon moulding 8, which covers the connection between the wire 5 and the tube 4 and completes the insulation so that it is continuous. The instrument 10 has a moulded nylon section 8 which extends along the plastic sleeves 7 of the wire 5 to form a web 9. This instrument is made by taking a stainless steel wire 0.15mm thick, threading a shrink-plastics sleeve on to each end, whilst leaving the ends themselves clear of the sleeve, inserting the ends of the wire into one end of a stainless steel tube 2.4 mm external diameter (13G) x 100mm long and flattening the tube so that the ends of the wire are trapped and an electrical connection is made. A moulding of low density polyethylene is made between the sleeves 7 and around the junction between the wires and tube which contacts the plastics sleeves and so the wire itself does not touch the wall of the mould. The wire loop may have a diameter of 15, 20 or 25mm depending on requirements. In use, the instrument is attached to an electrical source, the wire heats up and is used to cut away tissue as required. The web 9 acts as a guide when using the instrument in that it limits the depth to which the instrument can cut. The construction of the diathermal instrument of the present embodiment confers many advantages upon it. The instrument can be made at a lower cost than a re-usable instrument and is more effective as it has a steel wire almost half the diameter of the wire used in the prior art. The instrument is thus rendered more precise and effective than the conventional instruments. Because the present invention is less expensive it may be provided as a disposable instrument which eliminates the problem of transfer of infection from inadequately-cleaned instruments. Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims: A method of making a medical instrument for use in diathermy, the method comprising providing a cutting member (5) and a support member (4) both of the members (4, 5) being electrically conducting, and inserting two ends of the cutting member (5) into one end of the support member (4), characterised in that when the two ends of the cutting member (5) are inserted into the end of the support member (4), the end of the support member (4) is deformed to secure the ends of the cutting member (5) and to make an electrical connection between the members (4, 5), and wherein insulating means (6, 7, 8) are provided covering a portion of the support member (4) and forming a web (9) spanning an area between the two ends of the cutting member (5). A method as claimed in Claim 1, characterised in that the support member (4) is tubular. A method as claimed in Claim 1 or 2, characterized in that the cutting member (5) is a wire. A method as claimed in Claim 1, 2 or 3 characterised in that the cutting member (5) is less than 0.25mm (0.01 inches) thick. A method as claimed in Claim 4 characterized in that the cutting member (5) is substantially 0.15mm (0.006 inches) thick.

Inventors: BARTLETT JONATHAN EASTON, ROBSON RICHARD, BARTLETT, JONATHAN EASTON, ROBSON, RICHARD
Applicants: ROCKET OF LONDON LTD, ROCKET OF LONDON LIMITED
Application year: 1990
Main classification: A61B17
IPC codes: A61B18