This invention relates to a surgical instrument such as a forceps or scissors device. Such devices have been known for many years, US Patent specification 2,111,161 dating from 1937 describing an early example. The present invention attempts to provide a modern improvement to such devices.

Accordingly there is provided a surgical instrument comprising a jaw assembly comprising first and second jaw members pivotally connected one to the other so as to be movable between respective open and closed positions, and first and second handle members connected to the first and second jaw members respectively, the first and second handle members each including a hollow tubular portion at its distal end and having an internal diameter, and the first and second jaw members each including an extension at its proximal end and having an external diameter such that each handle member is connected to the associated jaw member by means of a press-fit connection. The instrument is conveniently an open surgical instrument, that is to say an instrument designed to be used in open surgery. Such an instrument is similar to that described in the US patent specification mentioned above, in that it includes a scissors- like handle with apertures into which the surgeon's fingers can be received. This type of instrument is in contrast to the type used in endoscopic surgery, which typically has actuating elements mounted on a long shaft for insertion into a small aperture in the patient's body.

Typically, the instrument is a forceps instrument, although it is alternatively conceivably a scissors instrument. The instrument is preferably an electrosurgical instrument, with one or more electrodes mounted on the jaw assembly. The press-fit connection is a permanent connection, as opposed to prior art systems such as that described in US Patent specification 6,511,480, which provide removable electrode assemblies. The press-fit connection is sufficiently robust to allow for vigorous use of the surgical instrument, without the concern that the connection may become detached. Thus, the connections of the present invention are "one-time" connections, designed to last for the recommended lifetime of the surgical instrument.

The press-fit connection of the present invention allows for improvements in the cost, weight and component manufacture of the instrument. For example, a single design of handle can be manufactured and connected to different designs of jaw assembly (forceps, scissors etc.), in order to produce a range of instruments. Alternatively, a range of instruments can be provided by means of a single design of jaw assembly, with different designs of handle attached thereto. This may be to accommodate different sizes and shapes for the handles, or merely the preference of one surgeon over another.

According to a preferred arrangement, the hollow tubular portion at the distal end of each handle member is formed of a substantially incompressible material, such as stainless steel. This is in marked contrast to other press-fit connections, which are more generally used with elastomeric materials such as soft plastics and rubber materials. Conveniently, the extension at the proximal end of each jaw member is also formed of a substantially incompressible material, such as stainless steel. The extension at the proximal end of each jaw member preferably has a first end towards the tip thereof, and a second end towards the body of the jaw assembly, and includes one or more externally-facing ribs, the height of each rib increasing from a first height towards the first end of that extension to a second height towards the second end of that extension. For the purposes of this description, the first end of the extension is the end towards the tip of the extension, and the second end of the extension is the end where the extension is connected to the body of the jaw assembly. These terms are used in so that the terms "proximal" and "distal" can be used in an overall sense with regard to the surgical instrument as a whole, as opposed to locally in respect of a particular component such as the extension. Preferably, the extension of each jaw member is provided with a plurality of ribs, extending either longitudinally along that extension or radially around that extension. The ribs allow for a secure press-fit connection to be established between the jaw members and the handle member, even when the tubular portions and the extensions are subject to manufacturing tolerances. The ribs can accommodate small variations in the sizes of the two components, without producing an unduly loose press-fit connection, or one which is unduly difficult to assemble.

Conveniently, the internal diameter of each hollow tubular portion has a first manufacturing tolerance, and the height of the ribs of the associated extension has a

second manufacturing tolerance, the height of the ribs being such that, at the Least Material Condition, the internal diameter of that hollow tubular potion is between the first height and the second height. The Least Material Condition is herein defined as being the situation in which the extension on a jaw member is the minimum diameter allowed under the manufacturing tolerance, and the internal diameter of the associated tubular portion is the maximum diameter allowed under the manufacturing tolerance. Thus the Least Material Condition defines the loosest possible fit permissible under the manufacturing tolerances. Even with this loosest fit, the graduation of the heights of the ribs means that one or more of the ribs forms an interference fit with the internal diameter of the associated tubular portion. Preferably, the height of the ribs of each extension is such that, at the Least Material Condition, the internal diameter of the associated hollow tubular portion is within the middle third of the range between the first height and the second height. For example, if there are nine radially-extending ribs on each extension and a gradual progression in the height of the ribs, the internal diameter of the associated tubular portion will form an interference fit with the fourth to the sixth ribs. Thus, even at Least Material Condition, each tubular portion will form an interference fit with several of the ribs on the associated extension.

Additionally, the height of the ribs of each extension is preferably such that, at the Maximum Material Condition, the internal diameter of the associated hollow tubular portion is greater than or equal to the first height. The Maximum Material Condition is herein defined as being the situation in which the extension on a jaw member is the maximum diameter allowed under the manufacturing tolerance, and the internal diameter of the associated tubular portion is the minimum diameter allowed under the manufacturing tolerance. Thus, the Maximum Material Condition defines the tightest possible fit permissible under the manufacturing tolerances. Even with this tightest fit, the graduation of the heights of the ribs of each extension means that the internal diameter of the associated tubular portion fits over at least one of the ribs to form an interference fit.

As stated above, the height of the ribs of each extension conveniently increases in a steady progression from the first height to the second height, m an alternative arrangement, there can be different groups of ribs, at different heights to other groups of ribs, but with the ribs of each group being all at the same height. In one convenient arrangement, there are one or more additional ribs at the first height towards the first

end of each extension. This ensures that, at the Maximum Material Condition, there are several ribs of each extension of equal height in interference fit with the associated tubular portion. Alternatively, or additionally, there are conveniently one or more additional ribs at the second height towards the second end of each extension. The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which;

Figure 1 is a side view of a forceps instrument constructed in accordance with the present invention;

Figures Ia and Ib are enlarged sectional views of the circled parts of Figure 1; Figure 2 is a side view of a jaw member component of the instrument of Figure 1;

Figure 3 is an enlarged view of a portion of the component of Figure 2, showing the ribs thereon; and

Figure 4 is an enlarged view of a portion of the jaw member component of Figure 2, showing an alternative embodiment of the ribs thereon. Referring to the drawings, Figure 1 shows an open forceps instrument 1, which comprises a jaw assembly 2 comprising a first jaw member 3 and a second jaw member 4, pivotally connected one to the other by means of a pivot pin 5. The jaw member 3 is provided at its proximal end with an extension 6, and the jaw member 4 is provided with a similar extension 7. A first handle member 8 is provided, the first handle member comprising a body portion 9, a tubular portion 10 associated with the body portion, and a gripping portion 11 at the proximal end of that handle member. The body portion 9 of the handle member 8 is over-moulded over the tubular portion 10. The handle member 8 is attached to the jaw member 3 by means of the tubular portion 10 forming a press- fit connection with the extension 6. hi similar fashion, a second handle member 12 is provided, the second handle member comprising a body portion 13, a tubular portion 14 associated with the body portion, and a gripping portion 15 at the proximal end of that handle member. The handle member 12 is attached to the jaw member 4 by means of the tubular portion 14 forming a press-fit connection with the extension 7. Movement of the handle members 8 and 12 causes the jaw members 3 and 4 to open and close relative to one another, so that tissue can be gripped therebetween. A ratchet mechanism 16 is provided on each handle member 8, 12 for locking the handle members when they are moved together into their closed position.

The jaw member 3 is shown in more detail in Figure 2, comprising a central body portion 17, from which depends the extension 6 in one direction and a jaw element 18 in the other direction. The extension 6 is a solid member having a series of ribs 19 provided thereon, the ribs being shown in more detail in Figure 3.

The extension 6 has ten ribs 19a to 19j, extending from a tapered, lead-in portion 20 at a first end 21 of the extension, to the body portion 17 of the jaw member 3 at the second end 22 of the extension. In the example of Figure 3, the ribs 19a to 19j have the following diameters;

All dimensions are in mm (inches) and have a tolerance of ± 0.0254 mm (0.001 inches).

The tubular portion 10 of the handle member 8 has an internal diameter of 4.0894 ±

0.0254 mm (0.161 ± 0.001 inches). It can therefore vary between 4.064 and 4.1148 mm (0.0160 and 0.162 inches). At Least Material Condition, the tubular portion 10 will have an internal diameter of 4.1148 mm (0.162 inches), and the ribs 19a to 19j will be the values given above minus 0.0254 mm (0.001 inches). Thus, the tubular portion 10 will pass over the ribs 19a to 19e and form an interference fit with the ribs 19f to 19j. Depending on the compressibility of the material (stainless steel) and the force used by the machinery to apply the handle member 8 to the jaw member 3, the tubular portion 10 will be engaged with some or all of ribs 19f to 19j. With automated machinery for applying the handle member 8, the tubular portion 10 can be applied over the ribs 19f to 19 j without causing the splitting of the tubular portion. There will, therefore, be five ribs (19f to 19j) securing the extension 6 within the tubular portion

10.

At Maximum Material Condition the tubular portion 10 will have an internal diameter of 4.064 mm (0.160 inches), and the ribs 19a to 19j will be the values given above plus 0.0254 mm (0.001 inches). Thus, the tubular portion 10 will form an interference fit with all of the ribs 19a to 19j. There will, therefore, be ten ribs (19a to 19j) securing the extension 6 within the tubular portion 10. Although not described, it will be appreciated that the handle member 12 is secured to the extension of the jaw member 4 in the same manner.

As will be seen from the above description, the provision of the ribs 19a to 19j allows for a secure press-fit connection between the handle members 8 and 12 and the jaw members 3 and 4, despite the tolerances permitted for the manufactured components. This can allow the components to be manufactured by moulding, with a conventional tolerance of ± 00254 mm (± 0.001 inches), as opposed to being manufactured by precision grinding with a much tighter tolerance. Figure 4 shows an alternative arrangement, in which the ribs 19a to 19j extend longitudinally along the extension 6. The ribs 19a to 19j slope such that they are at a first, relatively shallow height towards the first end 21 of the extension, and are at a second, more pronounced height towards the second end 22 of the extension. The heights of the ribs 19a to 19j are such that, at the Least Material Condition, the internal diameter of the hollow tubular portion 10 is within the middle third of the ribs 19a to 19j. Thus, when the tubular portion 10 is at its loosest, it still engages with a substantial axial length of the longitudinal ribs 19a to 19j. Similarly, the height of the ribs 19a to 19j is sμch that, at the Maximum Material Condition, the internal diameter of the hollow tubular portion 10 is greater than or equal to the first height. Thus, when the tubular portion 10 is at its tightest, it still fits over the shallowest part of the ribs 19a to 19j, so as to be engaged within their longitudinal extent.