WO2021123424A1

WO2021123424A1 - Surgical instruments

Info

Publication number: WO2021123424A1
Application number: PCT/EP2020/087435
Authority: WO
Inventors: Roger Michael ATKINS
Original assignee: At Ortho Limited
Priority date: 2019-12-20
Filing date: 2020-12-21
Publication date: 2021-06-24
Also published as: GB201918999D0

Abstract

A cannulated surgical knife (100) for providing percutaneous access to a surgical site. The knife has an elongate body defining an axis, a cutter portion at the front end and a handle portion at the rear end. The cutter portion has first and second blades opposed across the axis and each having an outward face. The outward blade faces converge with one another forwardly towards their front tip portions, and have respective oppositely outwardly-directed cutting edges, The blades may have no edge bevel, or a minor edge bevel, on the inward face for closer contact against a guide wire, A mounting portion of the blade, overlying the body, is not more than 40% of the overall blade length. The blade's mounting tang may have an edge bevel around an opening at which it is staked to the handle support portion, to lower the profile of the staking (52). In some embodiments the cutting edge projects out further from the axis on one side than on the other.

Description

SURGICAL INSTRUMENTS

This invention relates to cutting instruments. Particular practical embodiments of the invention include surgical instruments in the form of surgical knives such as scalpels and plunge knives, especially those for use in initiating percutaneous access to a surgical site. However the concepts described may find use for cutting instruments in other fields.

In particular the present application describes developments relative to the disclosure of our earlier application W02020/002365 ("the earlier application"), published on 2 January 2020 after the present priority date. The disclosure of the earlier application is incorporated herein by reference. The present disclosure contemplates that any subject-matter disclosed in the earlier application may be excluded from the ambit of the claims in the present application, in any legal regime where the disclosure of the earlier application constitutes part of the state of the art (prior art).

BACKGROUND

One particular area of use for the present proposals is percutaneous surgery. Particular examples of this are where a primary movement of surgical instruments, implants or devices relative to a surgical site is in or along a single direction. This may be e.g. laparoscopic or thoracoscopic surgery. Another illustrative example is a procedure of intramedullary nailing of a long bone such as the femur, humerus or tibia. A rod must be introduced into the hollow, central medullary canal of the bone from its end, typically in the treatment of a fracture or deformity. The appropriate entry point for the nail must be accurately defined and located, and conventionally this has been done by open surgery involving a long incision in the region of the end of the bone followed by open dissection down onto it so that the site can be visually confirmed and the appropriate entry opened up. A similar initial procedure applies for removing a nail.

More recently it has become preferred to insert a sharpened guide wire (in fact a thin rod with substantial rigidity) through the skin and underlying tissue and into the appropriate entry point. This reduces surgical trauma and scarring. The skin and underlying tissue must be divided with a scalpel to form a space for subsequent passage of other instruments. The cutting with a scalpel is usually done freehand around the guide wire, which is a slow and difficult step if inaccuracy or major scarring is to be avoided: the guide wire marks the location but is no help to the cutting itself. Another relevant area of use is the insertion and removal of orthopaedic screws. Increasingly such screws are inserted and removed percutaneously through a small incision. They may be cannulated screws moved through the incision along a guide wire. The formation of a small "stab" incision for such purposes is a relevant area for the present technology.

In addition to our earlier application mentioned above, there are prior proposals of cannulated scalpels for guided cutting. US6270501B describes a cannulated scalpel with a tubular shaft adapted to slide over a guide wire, with a head having opposed cutting blades projecting to either side in an axial plane, and having leading cutting edges to cut through tissue and narrow trailing edges to facilitate withdrawal. WO2017/133967 describes an instrument similar to that of US6270501B in which the coplanar double blades are detachable from a handle portion. US2011/0087258 is another document describing a cannulated surgical knife.

THE INVENTION

The present invention aims to provide new and useful cutting instruments, such as surgical instruments or scalpels, adapted to make an open incision accurately and conveniently, and able to be guided by a guide wire. In surgical uses, desirable features are that operating time and surgical trauma can be reduced or minimized in making an incision and providing satisfactory access to a surgical site, especially in the context of surgery carried out percutaneously .

The invention relates to a surgical instrument, such as a surgical knife, plunge knife or scalpel, for providing percutaneous (minimally invasive) access to a surgical site.

In general terms the surgical knife has a rear end, a front end and an operating axis extending from the rear end to the front end. It comprises a body, a cutter portion at the front end of the body and a handle portion at the rear end of the body. The body defines a cannulation along the operating axis, to receive a guide wire for guiding movement of the surgical knife in use. The cutter portion comprises a blade, the blade having a tip portion at the front end of the knife, an outward cutting edge directed laterally outwardly relative to the operating axis, and an outward face which is directed laterally outwardly relative to the operating axis, transversely to the outward cutting edge, and which converges forwardly with the operating axis.

Preferably the cutter portion comprises first and second said blades opposed across the operating axis at opposite sides thereof. The first and second outward faces of the two blade portions converge with one another forwardly towards their tip portions. First and second cutting edges (that is to say respective outwardly-directed cutting edges of the first and second blade portions) are generally oppositely outwardly directed.

Alternatively the cutter portion may comprise a single said blade. Preferred constructions for these alternatives are set out later and were also described in the earlier application.

In this application we make the following additional proposals in relation to surgical knives of the kind described.

(1) Blade Edge Form

In the knife, the or each blade has an inward face which, at or towards the tip portion, faces the operating axis. The relation between the blade tip and the guide wire is significant in use.

In this respect, it is useful to distinguish between

- the operating axis (a hypothetical line of no thickness, extending forwards from the centre of the front opening of the cannulation in the direction of the cannulation at that front opening);

- an actual guide wire in the cannulation;

- the locus of an intended guide wire (which has a thickness/diameter corresponding to that of a guide wire to be used and can be regarded as centered on the operating axis), and

- the projected locus of the cannulation, which like the locus of a guide wire is centered on the operating axis but has the width/diameter of the cannulation or, alternatively stated, of the largest diameter guide wire that the cannulation could take.

To make a clean single cut, generally taking the form of two sideways cuts in opposite directions, and when two opposed blades are used slightly offset from one another but joined at/across the operating axis, it is preferred that in use the tip portion of the blade approaches very closely and preferably contacts positively with the guide wire. The tip of the blade is then positioned very close to the axial centre of the guide wire. Guide wire diameters can vary, provided that they do not exceed the cannulation size. A blade can generally flex to some extent. Accordingly, desirably the blade tip portion overlaps the forward projection locus of the cannulation so that, in use with expected guide wire sizes, it desirably contacts and preferably contacts with some bias against the guide wire. Where first and second opposed blades are present, their blade tip portions correspondingly are desirably contacted or pressed with some bias against opposite sides of the guide wire.

A conventional scalpel blade, such as shown in our earlier application, has a conventional edge grind as seen e.g. in Fig. 4(b). Outward and inward bevel surfaces 42,43 leading from the main surface of each of the outward and inward faces 36,37 are similar in angle and extent, being angled to the main plane at an angle g e.g. between 20° and 30°, so that the cutting edge proper 41 is halfway across the blade thickness t and the widths of the inward and outward bevel as indicated at z, measured in-plane from the cutting edge proper to the inner termination of the bevel surface, are the same. Fig. 5(a) shows that in use, even with the angled blade 3 contacting the guide wire 11 at its tip region (at or near its point) a small gap g still exists between the surface of the wire 11 and the cutting edge proper 41 because of the conventional inward bevel angle.

A proposal here is that, at least at the tip region, the inward face of the blade has no edge bevel, or has an edge bevel angle which is smaller than that of the outward edge bevel, and/or the inward edge bevel accounts for less thickness of the blade than the outward edge bevel, so that the cutting edge proper lies closer to the main inward surface than to the main outward surface. For example the outward bevel may account for at least 70%, at least 80%, at least 90%, or 100% of the thickness of the blade leading to the cutting edge proper.

By thus approximating the cutting edge proper to the guide wire surface in use, we find that knife insertion is smoother and with less possibility of catching tissue between the guide wire and blade, which might cause divergence or interfere with insertion. Having no inward bevel greatly simplifies manufacture. Having some inward bevel, e.g. at an angle approximating to or at least that of the angle of convergence of the blade towards the operating axis, has the advantage of supporting the blade against the guide wire with less point contact force on the cutting edge.

An inward bevel when present is preferably angled at at least 0.5°, preferably at least 1° or at least 1.5°, relative to the main inward surface adjacent the bevel. The angle may be less than 10°, less than 7°, or less than 5° relative to the main inward surface. Preferably in the rest condition of the instrument (without a guide wire present) the inward bevel when present is inclined away from the operating axis in a plane containing the axis by less than 5°, or less than 4°, at its point of closest approach to that axis.

The outward bevel angle may be conventional e.g. greater than 10°, greater than 15° or greater than 20°. A dominant outward bevel helps to ensure cut stability for the convergent blade(s). Preferably the bevel angle of the outward bevel is at least 5 times the bevel angle of any inward bevel. Thus, in preferred embodiments the outward bevel is a conventional grind to provide the cutting edge whereas the inward bevel is absent or is an unconventionally shallow grind whose main function is to improve interaction with the guide wire. The width of any inward bevel, that is, the distance it extends in from the cutting edge proper perpendicular to the line of that edge, measured in the main plane of the blade, may be e.g. from 1 to 6 mm or from 2 to 5 mm. It may be larger than the corresponding width of the outward bevel, e.g. at least twice or at least three times as large.

The above-described inward bevel characteristics are present at least at the blade's tip portion approaching the operating axis, as mentioned, where close approximation to or contact with the guide wire is intended. Desirably for a simple and smooth blade form, inward and outward bevels are substantially co-extensive along the cutting edge e.g. each extends at least 70%, at least 80% or at least 90% of the length of the other.

Where the blade cutting edge has a compound bevel, i.e. more than one bevel angle on one side, the above angle parameters can be applied to the overall bevel region from the onset of the bevel to the cutting edge proper.

Preferably the outward cutting edge (outward in the cut direction) of the or each blade is outwardly convex in form, as discussed below. Preferably it extends rearwardly beyond a position of maximum lateral projection in the cutting direction. Desirably its sharp cutting edge does not extend substantially rearwardly of the position of maximum lateral projection, e.g. not at all, or not more than 10% or not more than 5% of the overall longitudinal length of the cutting edge (measured as a straight line in the longitudinal direction parallel to the operating axis). Thus, a rearwardly-directed outward edge portion of the blade is desirably substantially or entirely non-sharp. This feature is preferred to avoid initiating additional cutting on withdrawal of the knife.

(2) Blade Dimensions and Proportions

Further developments relative to the disclosure of the earlier application concern the general dimensions and proportions of the blade or blades.

For this purpose we consider the length of a blade as the length projected onto the operating axis (although since the blades are usually flat, proportions are unaffected by this convention) and measured parallel to that axis. The length portion of the blade projects forwardly beyond the front extremity of the blade support portion of the knife body. The length portion of the blade overlying (in contact with) the blade support portion of the body can be regarded as a mounting portion or tang (irrespective of whether there is a cutting edge there). A mounting engagement with the blade support portion may be defined by foremost and rearmost positions where a body projection enters an opening of the blade tang; typically there is a single opening in the blade through which a single projection of the body extends, between the foremost and rearmost positions. This can be termed a securing region. Broadly speaking, it is desired to form the blade so that it can be mounted in a way that provides secure mounting but without interfering with use, e.g. allowing the blade convergence angle to be chosen for effective tissue separation on insertion but without snagging on withdrawal, and without excessively wide blade spacing at the rear end of opposed blades. For these purposes the following features of blade form and proportion are proposed.

The blade length extending forwardly beyond the blade support portion or front extremity of the body is preferably at least 40%, more preferably at least 45%, still more preferably at least 50% of the overall length of the blade. Correspondingly, the blade length from the rear end of the blade to the front extremity of the body is desirably less than 60%, less than 55% or less than 50% of the overall blade length.

The proportion of blade length extending forward of the securing region (foremost position of the mounting engagement) is preferably at least 50%, more preferably at least 55%, still more preferably more than 60%. Correspondingly, the length proportion from the rear end of the blade to the foremost position of the mounting engagement region is preferably less than 50%, less than 45% or less than 40%, and to the rearmost position it is preferably less than 10%.

The proportion of blade length taken up by the securing region (mounting engagement) is preferably less than 45%, more preferably less than 40%, still more preferably less than 35% of the overall blade length.

The overall blade length is preferably between 30 and 50 mm, more preferably between 35 and 45 mm.

The maximum lateral width between the blade cutting edges (especially with two blades) in the cut direction, projected onto the plane of the operating axis, is preferably between 10 and 30 mm and more usually between 15 and 25 mm.

Preferably the blade cutting edge has a position of maximum lateral projection (in the cut direction) at a proportion of the overall blade length between 25 and 50% back from its front extremity.

(3) Blade Mounting

For this proposal the blade is a discrete blade attached against a blade support surface of the body. The blade has a tang portion with an opening, and is held on the body by means of a projection of the body which extends through the opening and has a top enlargement which overlies an edge region of the tang around the opening to retain the blade. This constitutes an interlock joint, a corresponding attachment method commonly being known as staking from the process in which the material at the top of the projection is deformed plastically outwardly to form the enlargement.

In our proposal the tang portion edge extending around the opening has a chamfer, step or other recess formation at the outward side of the blade, recessed relative to the main outward surface thereof, providing an outwardly-directed subsidiary edge surface which is overlain by the top enlargement of the projection. Because of the recess the degree to which the edge of the body projection extends above the level of the blade tang's main outward surface can be reduced or eliminated, so that e.g. the edge of the projection may be substantially flush with the blade surface. This facilitates insertion by making a smoother surface for skin and tissue to pass over in contact.

It is preferable to have an outward step of the body surface immediately behind the rear end of the or each blade, to mask the blade rear end on withdrawal. Or, the body or securing formation may have an extension such as a moulded- over portion covering the rear edge of the blade.

(4) Asymmetric Blades/Offset Cutting

A further proposal herein is a cannulated knife of the general kind described, preferably with the convergent blade feature, in which the lateral projection of blade cutting edge on a first side of the operating axis in a first sense of the cutting direction is greater than the opposite lateral projection of a second side of cutting edge in the opposed sense of the cutting direction. In particular, there may be a greater maximum lateral projection of cutting edge in the one direction than the other (without excluding the possibility that e.g. near a tip portion or at a trailing portion away from the maximum lateral projection, the lateral projections of respective cutting edges or cutting edge portions to either side might be the same, or might indeed differ in the opposite sense to that of the maximum projections).

In practice, the significance of this proposal is that the plunge knife will cut further out in one direction from the operating axis (corresponding to the position of a guide wire in use) than in the other direction.

Preferably the proposal is implemented in a plunge knife having first and second convergent blades, or a single blade converging towards the operating axis, as proposed above and in our earlier application. In the case of a single blade, there may be first and second oppositely- directed cutting edge portions of the blade. In the case of first and second blades, they have respective first and second cutting edges which are oppositely directed as described previously.

Taking the first direction as being that of the greater lateral cutting extent, the maximum lateral projection in that direction is preferably at least 50% greater than the maximum lateral cutting projection in the other direction.

Or, it may be at least 75% greater, or at least twice as large. The difference will depend on intended use, as discussed below. [Since distances involved may apply to plural blades that are non-parallel, as before they should be understood as referring to measurements projected onto a median plane containing the operating axis, in particular for example a plane intercepting the planes of respective blades along a common line.] The maximum lateral projection in the first direction may be e.g. 5-20 mm, more typically 6-15 mm. The maximum lateral projection in the second direction may be e.g. 2-12 mm, more typically 3-8 mm, always subject to being less than that in the first direction.

Preferably the cutting edge blade forms (edge loci) in the first and second directions are convex from a tip or point until they reach a maximum lateral projection, but this is not critical and straight oblique edges may be used. Otherwise the forms of the blade edges in the two directions need not match or correspond at all. Indeed, a single blade might have a cutting edge extending on both sides of the operating axis (in the cutting direction sense) but outwardly (sideways) directed in only one sense of the cut direction. However this is generally less preferred because the blade entry point is then spaced from the guide wire. In other respects, knives embodying this proposal may adopt any of the features disclosed herein and in the earlier application as regards e.g. the type and mounting of the blades, their general dimension, the formation of their cutting edges as regards bevels and so forth.

GENERAL FEATURES

The cutter portion is at the front end of the instrument. In a preferred version the cutter portion comprises first and second blades opposed across the operating axis at opposite sides thereof, each of the first and second blade portions having a tip portion at the front end, an outward cutting edge directed laterally outwardly relative to the operating axis, and an outward face also directed laterally outwardly relative to the operating axis and transversely to the respective outward cutting edge. The first and second outward faces of the two blade portions converge with one another forwardly towards their tip portions. Also, first and second cutting edges (that is to say respective outwardly-directed cutting edges of the first and second blade portions) are generally oppositely outwardly directed.

The tip portions of the first and second blade portions comprise the parts thereof that lie closest to the operating axis and closest to one another. Additionally or alternatively, the tip portions are disposed so that a line between them at the closest approach of the first and second blade portions passes through the operating axis.

Preferably the tip portions have front points; the above statements about the tip portions may also be applicable to the front points.

The angle of forward convergence of the outward faces of the first and second blades is preferably at least 2°, more preferably at least 4°, still more preferably at least 5° or at least 7°. Conversely it is usually not more than 20° or not more than 16° and preferably not more than 12°. This angle can be regarded as the included angle between the blades' outward faces. It may be the included angle in a plane containing the operating axis. Additionally or alternatively it may be the minimum or maximum included angle that they attain, in any direction (e.g. if they are not both flat). Correspondingly, for an individual e.g. single blade the angle made by the outward blade face to the operating axis may be e.g. at least 1°, more preferably at least 2°, still more preferably at least 2.5°. Conversely it is usually not more than 10°, not more than 8° or not more than 6°.

The outward faces of the first and second blade portions may diverge rearwardly such that the width between them across the operating axis at a rear extremity of the blade portions is at least as wide as the body of the instrument at/or immediately behind that axial position.

This can avoid an obstructive step with respect to either forward or rearward movement along the operating axis direction.

The body may have a step formation - an inward step, in the forward direction - positioned adjacent a rear end of the blade portion, especially in the case that the blade portion is a discrete attached component, so that the blade rear end is recessed relative to the adjacent body surface rearwardly of it. This can help to reduce or avoid catching of the rear end of the blade portion on withdrawal of the instrument.

The skilled person will understand that in the 2-blade embodiment the convergent disposition of the first and second blades to either side of the operating axis enables effectively a single incision/cut to be made by advancing the instrument into the substrate to be cut in the forward direction, that is, forward along the operating axis. The cut can be extended laterally up to a controlled width to either side of the guide wire by means of the oppositely- directed outward edges of the blades, which enlarge or lengthen the cut in a cut direction, and can also be opened up in a transverse direction - a separation direction, since the opening corresponds to gaping of the opening rather than extension of the cut line - by the divergence of the blades' outward faces as the cutter portion penetrates deeper. The instrument's body can be formed such that the body/handle of the knife does not catch on material (such as skin/tissue) around the cut and so obstructs neither the cutting movement nor subsequent withdrawal.

Preferably the outward blade face is flat. This enables the use of conventional or readily-manufacturable blades, attached to the body. The blades may be discrete elements and may be fixed against locating or support formations of the body including a forwardly-convergent locating face against which the blade is held to support it in the desired convergent orientation. The locating formations may include securing formations by which the blades are held in place, either removably or permanently. Preferably the blades have openings, e.g. in a shank or tang of the blade, and retaining formations of the body extend through the openings to hold the blade elements. The retaining formations may be heat-formed or moulded-on so that the blade elements cannot be removed. This is suitable e.g. for a single-use type instrument. Alternatively in some embodiments the blades may be over-moulded or bonded onto the body.

The body is typically elongate in form. The body may be a metal unit or of plastics material, for example a one- piece plastics moulding. The handle portion may comprise a laterally- or radially-enlarged grip portion spaced back from the front end, e.g. at or adjacent the rear end. The body may comprise the grip or handle portion, an elongate shaft portion extending in the direction of the operating axis and a blade support portion comprised in the cutter portion of the instrument at the front end.

The preferred cannulation for a guide wire is typically a straight channel, and may extend right through the body from the front end to the rear end thereof. It may have an internal size, typically a circular diameter, of e.g. 1 to 5 mm, more usually 2 to 4 mm. The cannulation is not necessarily fully enclosed by solid material provided that it defines a path that effectively locates and aligns a guide wire relative to the body in use. That is, it may provide a circular capture of the guide wire at points along its length. While a range of cannulation sizes can be provided according to the expected guide wire diameter this is not always necessary; a smaller wire in a larger channel can still give adequate guiding so that e.g. a cannulation between 2 and 3.5 mm in diameter will serve for a wide range of surgical uses. One option is for the front opening of the cannulation to open sideways as well as forwards, directed sideways past or between blade(s). A guide wire end can then be fed in initially from the side rather than directly from the front, making location easier and reducing risk from blade points.

First and second blades may be similarly convergently angled with respect to the operating axis. Indeed the first and second blades in general may be arranged with symmetry, and especially two-fold rotational symmetry, around the operating axis.

The cutting edge form of one or both of the blade portions may be any of various forms - straight, concave or convex - but is preferably convex, i.e. with a belly of the blade edge. This cutting edge, directed out in the cut direction, preferably extends at least from the tip portion of the blade portion to the part of maximum lateral projection thereof. Preferably the blade portion outward edge extends rearwardly beyond this position of maximum lateral projection to a rearward or trailing region thereof. This region may progressively reduce the lateral projection in the rearward direction, i.e. so that the blade narrows rearwardly. This form helps to ensure that the knife is not only easily inserted into the incision, but also easily withdrawn from it.

It is preferred that rearwardly-convergent or rearwardly-directed edges of the blades are - partially or wholly - non-cutting edges, since cutting on withdrawal is usually undesirable and risk of cutting the user's fingers is reduced. The extent of the outward cutting edges in the cut direction away from the operating axis, and the divergent angle between them back from the tip in the cutting plane (defined below), together determine the maximum available width of the cut in the cut direction and the rate of increase of the cut width per given length of blade inserted. Blade types and sizes can be selected accordingly.

Preferably the initial divergence angle between two outward cutting edges - initial in the sense of extending back immediately behind their tips/points from the onset of axial overlap - is at least 70°, more preferably at least 80° or at least 90°, projected onto a median plane between them (cutting plane) in which that angle is maximized: this is usually a plane in the cut direction and containing the operation axis along which the blades are advanced in use. Where one or both edges is convex, the edge divergence angle gradually reduces rearwardly.

First and second blades may have inwardly-directed edges that are cutting edges or non-cutting edges. Generally the preference is to form a single combined incision extending out in two directions from the operating axis, rather than two separate cuts, so that inward cutting edges of the blades may have no significant function and non cutting inward edges are preferred. Indeed, while desirably the first and second blades' outward faces overlap to some extent (i.e. viewed across the operating axis transversely to the directions of their cutting edges, in the separating direction, so that they are mutually opposed) the overlap need not be great provided that the outward faces are sufficient in extent to smoothly separate the opposite sides of the incision and guide the tissues around the body of the instrument. Such oppositely-directed convergent outward faces may indeed be constituted partly by structures integral with the body, and not necessarily entirely by blade element faces.

The body may have an extended or elongate shaft portion which is narrower than the outward extent of the first and second cutting edges, so as easily to be accommodated within the cut opening to an extended depth on further insertion of the instrument into an incision. Optionally in the perpendicular (separation) direction a relatively larger width of the body can be provided to hold the incision open.

The tip portions of the blades desirably intersect or overlap the forwardly projected cannulation locus at the front end of the instrument, so that in use they can contact a guide wire, preferably with positive force or bias. Preferably the closest spacing of the opposed tip portions diametrically across the operating axis is less than the diameter of the cannulation, or less than 90%, less than 80%, less than 70% or less than 60% of the diameter of the cannulation. For a single blade, a corresponding criterion is that the distance of closest approach of the tip portion to the operating axis is less than the radius of the cannulation, or less than 90%, less than 80%, less than 70% or less than 60% of the radius of the cannulation.

When a guide wire is inserted - the size of the wire not being critical - the blade tips can flex slightly away to allow the wire to pass while maintaining a desirably close sliding contact with it.

The foremost extremities (e.g. points) and/or the positions of closest approach of opposed blade tip portions may be diametrically opposed across the operating axis in a direction substantially transverse or perpendicular to the cut direction, e.g. at at least 60°, or at least 70°, or at least 80°, to that direction.

The convergence of the blades stabilises them during the cut, reducing any tendency to separate or wander. It also helps to protect the user's fingers from cutting, and contributes to the formation of essentially a single cut opening even though two spaced blade portions are employed.

In an alternative embodiment as mentioned the cutter portion has only a single blade. In this aspect, any of the above features as regards the one blade's structure and disposition may be as described above for the respective blades of the first embodiment, except insofar as they specifically relate to the relation of two blades as blade portions. With a single blade portion it is preferred although not essential to use a cutting portion which is double-edged, i.e. has outward cutting edges directed laterally in respective opposite senses of the cut direction. For example such a double-edged cutting portion may be symmetrically shaped as regards the opposite cutting edges. The point or tip thereof may be the closest point to the operating axis (or notional prolongation of a guide wire cannulation).

In this aspect it is preferred that the body has an outward separation face axially overlapping with at least part of the blade and directed oppositely outwardly, the body's separation face converging with the outward face of the blade. The convergence angle of the body's separation face may or may not be the same as that of the blade. Thus, the angular relation of the body's separation face and the blade's outward face may be in accordance with options described above for the respective outward faces of the first and second blades of the first aspect. The body's separation face can act in a manner similar to the outward face of the additional blade in the first aspect, acting to open up an incision being made by the cutting action of the blade. It may be straight in cross-section, i.e. converge at a substantially constant angle, and it may be flat. Or, a portion of the body's separation face may have those properties. The body's separation face would of course not reach axially as far forward as the tip of the blade, since it is not a cutter, but desirably there is at least 30% or at least 50% or at least 70% axial length overlap of the convergent separation face with the whole of the blade.

The single-bladed option has an advantage of economy and simplicity, in combination with effects as listed above for the first aspect.

In embodiments which are a surgical instrument such as a scalpel or plunge knife, an optional feature is a conduit incorporated in the surgical instrument for feeding a fluid to the front end thereof during use, especially a liquid, which may be a therapeutic substance or medicament, an anaesthetic, vasoconstrictor or any combination of these, as described in our earlier application, the description of which feature is hereby incorporated by reference.

It is envisaged that a surgical cutting instrument as proposed may be used in or adapted for a variety of surgical indication where percutaneous surgery is to be done. In addition to the intramedullary nailing of bones as described, such surgical knives may find use in the fixation of bones or ligaments, the fitting, removal or replacing of percutaneous screws, the percutaneous removal of devices from bone - including nails, pins, implants and other items - and use in the percutaneous fusion of joints. They may also be used in all other forms of surgery including but not confined to laparoscopic or thoracoscopic surgery, urological surgery vascular surgery and neurosurgery.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention is now described by way of example, with reference to the accompanying drawings in which:

Fig. 1 is an oblique view of a surgical instrument in the form of a first plunge knife embodying new proposals herein;

Fig. 2 is a side view;

Fig. 3 is a section at A-A of Fig. 2 showing features of blade form;

Figs. 4(a) and 4(b) are fragmentary cross-sectional views showing blade edge grinds, Fig. 4(a) being a newly- proposed form and Fig. 4(b) being a conventional form;

Figs. 5(a) and 5(b) are fragmentary cross-sectional views showing how the respective blade edge grinds of Fig.

4 (a) and 4(b) interact with a guide wire in use;

Fig. 6 is a side view taken at 90° to the Fig. 2 view;

Fig. 7 is an enlarged end view at the front end;

Fig. 8 is an enlarged fragmentary view of the tip portions of the blades, at region B shown in Fig. 6;

Fig. 9 is an enlarged oblique view of the two blades in their operational relative positions but without the body; Fig. 10 is a view from one side of the cutter portion of a second plunge knife embodying the new proposals herein, having asymmetric blades for offset cutting;

Fig. 11 is a view of the second embodiment at 90° from Fig. 10, and

Fig. 12 is a view from the side opposite to Fig. 10.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring firstly to Fig. 1, a surgical instrument embodying our proposals is a plunge knife 100. It consists essentially of a straight elongate body 1 with a handle or grip portion 12 at its rear end, a central shaft portion 13 and a cutter portion 2 at its front end. The cutter portion consists of a blade mounting portion 5 of the body 1 and a pair of blades 3. In this embodiment the body is formed of injection-moulded plastics material and the blades are steel scalpel blades.

The body is penetrated by a longitudinal central cannulation 14, being a straight cylindrical passage extending through the instrument and providing for it to be mounted on a metal guide wire (not shown) so that the instrument can be slid along the guide wire in use. As is well known, guide wires are used to guide the direction, position and orientation of a surgical instrument in relation to a selected surgical site.

At the cutter portion 2, a pair of identical steel scalpel blades 3 are mounted opposed across the operating axis OA defined by the central cannulation 14. Each blade 3 has an outward edge 30 directed generally laterally outwardly relative to the operating axis and leading forward to a blade point 310 adjacent the axis, to lie in contact against a guide wire in use.

At the front end of the body 1 the blade mounting portion 5 (see also Figs. 7-9) has a pair of opposed flat blade support surfaces 51 which are angled towards each other at a convergence angle of 10°, symmetrically to either side of the operating axis. That is to say, the (minimum) angle between each support surface 51 and the operating axis is 5°. The front opening 141 of the central cannulation 14 is through the front extremity of the body.

The following terminology is used to refer to the orientation of the various components. A forward direction (F) and a rearward direction (R) are defined longitudinally as indicated in Fig. 2. Then, with reference to the front end view of Fig. 7, it can be seen that laterally the outward faces 36 of the respective blades 3 are directed oppositely away from each other, and these outward lateral directions are designated the separation direction (S). The edges 30 of the blades including curved cutting edges are directed in respective lateral directions opposite and approximately parallel to one another and also perpendicular to the separation direction S, and these directions are designated the cut direction C.

First, the cutting edges of the blades 3 are described. Each blade is single-edged, with a relatively straight unsharpened rear edge 38 extending all the way from the back end of the blade to the extreme point 310. The outward edge 30 (outward in the lateral cut direction) is generally convex along its length, and has a front belly 33 having a sharpened cutting edge formed by an outward bevel or outer edge grind 42 and an inward bevel or inner edge grind 43, leading to an edge proper 41. See especially Figs. 3 and 9. Each blade is a single flat steel piece. The inward bevel 43 is much shallower and wider than the outward bevel 42. The latter is a conventional edge grind having an angle of e.g. 25° and a border width (z as seen in Fig. 9) e.g. of less than 1 mm (as measured in the blade plane). The inward bevel 43 may have a bevel angle of about 2° (so that the angles and b seen in Fig. 3 are respectively 155° and 178°) and a border width y of e.g. 2-3 mm.

The inward and outward bevels 43,42 continue along the convex edge belly 33 from the extreme point 310 up to a point of maximum lateral width 44. Behind that point, where the lateral projection of the blade in the cut direction gradually tapers away, the inward and outward bevels also taper off in a bevel taper region 45 (Fig. 9) where the cutting edge transitions to a non-cutting, unsharpened edge having the full thickness of the blade plate at its rear or trailing region 34.

Figs. 7 and 8 show in more detail the blade tips and their relation to the forward projection locus of the cannulation 14. The diameter D of the cannulation 40 represents the largest possible guide wire, e.g. from 3 - 4 mm. The positions of closest approach of the blade tip portions to the operating axis - positions actually slightly displaced from the extreme points 310 - are at a spacing x (Fig. 8) which is substantially less than the cannulation diameter, e.g. about half that distance (such as from 1.3 to 2 mm) so that they intrude on the guide wire locus and, when the guide wire is pushed through for use, it pushes the blade tips apart with flexion of the blades. In this position the inward bevels 43 assure satisfactory close contact against the guidewire surface, inhibiting catching and snagging of tissue in use.

Fig. 8 shows how, because of the 2° inward bevels, the angle g between the inward bevels is only 6° as distinct from the angle Q between the blades which is 10°. When the guide wire is pushed through, the inward bevels are brought essentially into alignment with its surface.

Because the rear portion (shank or tang 32) of the blade 3 has no sharp edge, functioning only to mount the blade, it does not cause any cut on withdrawal of the instrument and is also safe for the user's fingers.

Fig. 9 illustrates novel shape proportions of the blade. A set of length locations A - F are indicated, corresponding to the following positions:

A - front point

B - position of maximum lateral extension in the cut direction

C - position of front extremity of the body 1

D - foremost part of the mounting region (opening 39)

E - rearmost part of the mounting region (opening 39)

F - rear end of the blade The overall length of the blade A-F may be e.g. 35 - 45 mm. Relative to the total length A-F, the blade length A-C forward of the body tip is e.g. from 50%-55% of the total length. The length D-E of the mounting opening is e.g. from 25-35% of the total length. The blade length A-D forward of the mounting slot is e.g. 55-65% of the total length. The blade length A-B back from the point to the widest lateral projection is e.g. from 35-45%.

A shaped stake projection 52 in the form of an elongate rib projects up from each blade support surface 51 and fits a correspondingly-shaped mounting slot 39 of the blade 3 so as to assure its exact longitudinal orientation. The blade 3 is fixed in place by "staking" i.e. heat-deforming the stake elements 52 so that they spread down over the outer faces of the blades; this is a well-known technique.

Fig. 9 shows a refinement of the blade form whereby a chamfer or bevel 391 is formed around the edge 392 of the mounting opening 39 on the outward side. The resulting recess can receive the extremity of the flattened edge of the staked (spread) protrusion 52 of the body so that, as seen in Figs. 6 and 7, the staked projections 52 have a rounded form and their edges are generally flush with the edges of the blade opening 39.

With reference to the use of the instrument, it will be understood that the instrument is advanced forwardly into the skin and underlying tissue along the guide wire, entering at the points 310 of the two blades 3 and thereafter enlarging a cut simultaneously in opposite directions in the cut direction C, while opening up or spreading the sides or walls of the cut away from each other in the separation direction S. This separation is achieved by the advancing of the instrument in combination with the rearward divergence of the outward faces 36 of the blades 3, continuing with a correspondingly divergent region 135 of the body shaft 13 behind the blades. The divergent outward faces progressively separate and open the sides of the incision.

While the separation and cut directions are proposed as orthogonal directions radial of the axis defined by the central cannulation 14 (the operating axis), references to components or motions being directed in the separation direction, cut direction or axial direction are not necessarily intended to require precise alignment with those directions, but general alignment with those directions for functional purposes. They are terms used for ease of explanation and description.

The grip portion 12 is enlarged relative to the shaft 13 by radial grip projections 15 - here in the form of opposed flat lobes but they could take a variety of forms - so that a surgeon can easily control the direction and rotational alignment of the instrument. The central cannulation 14 is open laterally through a series of windows 145, opening alternately to opposite sides of the body 1. These are not in general themselves functional in the instrument, being to facilitate moulding of a component having the desired through-channel for the cannulation. An exception is the foremost side opening 145', which extends to join the front opening 141 of the cannulation, so that effectively the front opening opens not only forwards but also sideways and facing out through the gap between the blades 3. A guide wire end can then be inserted initially from the side rather than directly from the front, reducing risk from the blade tips. Once the wire is fully inserted the length of the cannulation holds it in line and it does not deviate through the side openings.

Figs. 10 to 12 show the cutter portion of a second embodiment of plunge knife, embodying a concept whereby the plunge knife cuts out further from the operating axis in one direction than in the other. This has particular utility in certain surgical situations.

A general aim in modern surgery is to use the smallest practicable access incision. The present plunge knife may be used in situations in which the line of insertion is not necessarily central relative to the expected region of surgical activity. Thus for example in orthopaedic surgery, a first requirement is to find a "safe corridor", that is, a path into the body reaching through to a bone e.g. a fracture site. This safe corridor, along which a guide wire is to be inserted, must avoid sensitive structures such as nerve bundles, tendons etc regardless of the exact nature and position of the object of the surgery. This may mean that the guide wire approaches along a direction (angle) of approach which is not the centre of the working region. An example of this is operating on a trimalleolar fracture of the ankle, making the entry incision from the rear. The most useful preliminary incision will extend out further on one side of the operating axis/guide wire than on the other.

In this embodiment the concept is implemented in a plunge knife with first and second blades 103,203. These are arranged mutually convergent towards the operating axis OA, as in previous embodiments, with their points 310 lying in contact against the guide wire 11 at the same forward position, the respective convergence angles relative to the OA (a¹ and a² seen in Fig. 11) being for example 3.5°.

The distinctive feature is that the first blade 103 differs from the second blade 203, being a larger and wider blade (a No. 22 blade is shown) compared with the second blade which is narrower in its lateral projection (a No. 10 blade is shown). Each blade has an outwardly-directed cutting edge 130,230 as in previous embodiments. The second blade 203 has a cutting edge which reaches its point 244 of maximum lateral projection after only a short convex belly region, whereas the first blade 103 projects out substantially further. The first and second distances of maximum lateral projection are indicated as di and d2 on Figs. 10 and 12, and are as projected onto a median plane: the plane of the drawing in Fig. 10. With the blade types shown the distances di and d2 are about 9 mm and 5 mm respectively. The use of commercially available blades reduces manufacturing costs. The positions of the respective staking projections 152,252 are determined accordingly. Of course the asymmetric cut concept can be implemented with other blades, or with custom blades, or indeed with a single blade. This type of knife is particularly useful with thinner guide wires, such as up to about 2 mm diameter, and the cannulation may be dimensioned accordingly. Notes

In respect of numerical ranges disclosed in the present description it will of course be understood that in the normal way the technical criterion for the upper limit is different from the technical criterion for the lower limit, i.e. the upper and lower limits are intrinsically distinct proposals.

For the avoidance of doubt it is confirmed that in the general description above, in the usual way the proposal of general preferences and options in respect of different features of the surgical instrument constitutes the proposal of general combinations of those general preferences and options for the different features, insofar as they are combinable and compatible and are put forward in the same context.

Claims

1. A surgical knife for providing percutaneous access to a surgical site, the surgical knife having a rear end, a front end and an operating axis extending from the rear end to the front end, and comprising a body, a cutter portion at the front end of the body and a handle portion at the rear end of the body, and wherein the body defines a cannulation along the operating axis, to receive a guide wire for guiding movement of the surgical knife in use, the body also having a blade support portion and a front extremity; the cutter portion comprises a blade, a portion of the blade projecting forwardly beyond the front extremity of the body, the blade having a tip portion at the front end of the knife, an outward cutting edge directed laterally outwardly relative to the operating axis, and an outward face which is directed laterally outwardly relative to the operating axis, transversely to the outward cutting edge, and which converges forwardly with the operating axis, and the knife additionally has any one or more or all of the following characteristics (i) - (iv)

(i) at least at a tip region, an inward face of the blade has no edge bevel, or has an edge bevel angle which is smaller than an edge bevel on the outward face, and/or an inward edge bevel accounts for less thickness of the blade than the outward edge bevel, so that the cutting edge lies closer to the main inward surface than to the main outward surface;

(ii) the blade length extending forwardly beyond the blade support portion or front extremity of the body is at least 40% of the overall length of the blade;

(iii) the blade has a tang portion with an opening, and is held on the body by means of a projection of the body which extends through the opening and has a top enlargement which overlies an edge region of the tang portion around the opening to retain the blade, and in which the tang portion edge extending around the opening has a chamfer, step or other recess formation at the outward side of the blade, recessed relative to the outward surface thereof, providing an outwardly-directed subsidiary edge surface which is overlain by said top enlargement of the projection of the body;

(iv) the cutter portion has first and second cutting edges generally oppositely outwardly laterally directed in respective opposite cutting directions, and the lateral projection of the first cutting edge on a first side of the operating axis in one cutting direction is greater than the opposite lateral projection of the second cutting edge in the other cutting direction.

2. Surgical knife of claim 1, having any one or more or all of said characteristics (i) - (iv), in which the cutter portion comprises first and second said blades opposed across the operating axis at opposite sides thereof and each having an outward face, the respective outward faces of the two blade portions converging with one another forwardly towards their tip portions, and first and second cutting edges, being respective outwardly-directed cutting edges of the first and second blade portions, are generally oppositely outwardly directed.

3. Surgical knife of claim 2 in which the first and second blades make the same convergent angle with respect to the operating axis, and/or in which the angle of forward convergence of the outward faces of the first and second blades is at least 4° and not more than 16°.

4. Surgical knife of claim 2 or 3 in which the first and second blades have inwardly-directed edges that are non cutting edges at the tip portion.

5. Surgical knife of any one of the preceding claims having said characteristic (i), in which the or each blade tip portion overlaps a forward projection locus of the cannulation, and an outward bevel of the or each blade accounts for at least 80%, at least 90%, or 100% of the thickness of the blade leading to the cutting edge proper.

6. Surgical knife of any one of the preceding claims having said characteristic (ii), in which said blade length extending forwardly beyond the blade support portion or front extremity of the body is at least 50% of the overall length of the blade.

7. Surgical knife of any one of the preceding claims in which the cutter portion has first and second cutting edges generally oppositely outwardly laterally directed in respective opposite cutting directions and in which the maximum lateral width between the oppositely-directed cutting edges, projected onto the plane of the operating axis, is between 10 and 30 mm.

8. Surgical knife of any one of the preceding claims in which the or each blade cutting edge has a longitudinal position of the maximum lateral projection in the cutting direction which is between 25 and 50% back from its front extremity, as a proportion of the overall blade length.

9. Surgical knife of any one of the preceding claims in which the or each blade has a rear end and the body has an outward step of the body surface immediately behind the rear end, to mask the blade's rear end on withdrawal of the surgical knife in use.

10. Surgical knife of any one of the preceding claims in which the or each outward blade face is flat, disregarding any edge bevel.

11. Surgical knife of any one of the preceding claims in which the cutting edge of the or each blade is convex in form, at least in a region which extends from the tip portion of the blade to a part of maximum lateral projection thereof.

12. Surgical knife of any one of the preceding claims having said characteristic (iv) in which the maximum lateral projection of the first cutting edge in said one cutting direction is at least 50% greater than the maximum lateral projection of the second cutting edge in the other cutting direction.

13. Surgical knife of any one of the preceding claims having said characteristic (iv) in which the maximum lateral projection in said one cutting direction is 6-15 mm and the maximum lateral projection in said other cutting direction is less and is from 3-8 mm.

14. Surgical knife of any one of the preceding claims in which the body has an elongate shaft portion behind the cutter portion which is narrower than the outward lateral extents of first and second oppositely-directed cutting edges of the cutter portion.

15. Use of a surgical knife of any one of claims 1 to 14 to provide percutaneous access to a surgical site, optionally including advancing the knife along a guide wire extending through said cannulation of the body of the knife.