Abstract:
A method of marking a surgical instrument with a symbol formed in or on a smooth surface comprises forming a symbol in or on a smooth surface of the surgical instrument; and forming a plurality of angled surfaces over at least part of the area of the symbol. The angled surfaces define a plurality of parallel ridges and grooves in the symbol. The steps of forming the symbol and forming the plurality of angled surfaces take place substantially simultaneously in a single step.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 13/979,331, which is a national stage 35 U.S.C. 371 application of International Patent Application PCT/GB2012/050004 filed Jan. 4, 2012, the disclosures of which are incorporated by reference herein in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a method of making a surgical instrument which includes a debossed or embossed symbol formed on a surface to give improved contrast with the surface. 
         [0003]    It is usually desired to mark a surgical instrument in some way. Typically, the marking will involve symbols including alphanumeric characters or other typographical symbols, manufacturing designations, logos, and other useful information. 
         [0004]    In order to obtain regulatory approval of a surgical instrument, it is necessary to show that the nature of any marking is biocompatible. This is particularly important when surgical instruments are marked using inks or dyes; the biocompatibility of the inks or dyes must be shown. It also applies to alternative methods such as laser etching. Laser etching may alter the chemical properties of the instrument in the vicinity of the mark and these have to be shown as biocompatible. 
         [0005]    It is known to mark symbols on surgical instruments using debossing or embossing. A debossed symbol is a symbol which is stamped or otherwise formed in the surface of the surgical instrument, so that the debossed symbol defined a recess below the surface of the surgical instrument. An embossed symbol is a symbol is formed on or otherwise raised above the surface of the surgical instrument. 
         [0006]    A debossed or embossed symbol is typically made of the same material as the part of a surgical instrument it is formed in. Therefore any problems with biocompatibility are avoided. However, conventional debossed or embossed symbols can be difficult for a surgeon to read in the operating theatre. The debossed or embossed symbol is formed from the same material as the surface surrounding it and therefore is substantially the same colour and shade as the surrounding surface. This can make it difficult to identify a symbol during a surgical procedure. It is important that symbols imparting information important for the surgical procedure, such as the size of an instrument, can be read clearly by a user. Therefore, the present invention aims to improve the clarity of a symbol on a surgical instrument. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    According to the present invention, a symbol is provided with a plurality of angled surfaces which define ridges and grooves within the symbol. These ridges and grooves create an improved contrast for the symbol relative to the surrounding surface by a combination of different specular reflection of incident light compared to the surrounding surface and shadows formed by the ridges and grooves. 
         [0008]    Although marking systems using ridges and grooves have been proposed in other fields than surgical instruments, these marking systems do not improve contrast of a symbol relative to a smooth surrounding surface. Instead they seek to alter the appearance of the surface depending on the viewing angle. This is not the same as the present invention, where contrast is improved regardless of viewing angle and the symbol retains substantially the same appearance regardless of viewing angle. 
         [0009]    For example, US-A-2007/0291320 (Chen) discusses a wedged surface structure. Some of the ridges may be cut at one or both lengthwise upper edges to produce bevel surfaces at different positions. The bevel surfaces produce at least one engraved pattern and multiple overlapped engraved patterns can be provided on a ridged surface. Which engraved pattern is seen depends on a viewing angle of a user. 
         [0010]    In EP-A-0358495 (Daly) decorative elements are formed with a plurality of elongate surface projections or depressions. Portions of the outer faces of the projections or depressions are formed in different colours so that they appear to have a different colour depending on the viewing angle of the user. 
         [0011]    Neither Chen nor Daly suggest how to improve the contrast of a character from all viewing angles. 
         [0012]    According to the present invention, there is provided a surgical instrument comprising a symbol formed in or on a smooth surface surrounding the symbol, wherein the symbol comprises a plurality of angled surfaces over at least part of the area of the symbol, wherein the facets define a plurality of parallel ridges and grooves in the symbol. 
         [0013]    The grooves are at a greater depth than the ridges. The angled surfaces may be substantially flat or curved. The reference to a “smooth surface” means free of ridges and grooves; some element of roughness may remain. The smooth surface may be substantially flat or non-flat, for the smooth surface may be substantially planar or curved or rounded. The symbol may be any alphanumeric character, typographical character, logo or other graphical item. 
         [0014]    The angled surfaces preferably extend over the entire area of the symbol, although this is not essential to the invention. The angled surfaces are preferably angled relative to the smooth surface. 
         [0015]    In some embodiments, the ridges and grooves may be parallel to the smooth surface, if it was extended over the area of the symbol. For example, when the smooth surface is substantially flat or planar, the angled surfaces may be provided by substantially planar facets. Alternatively, when the smooth surface is curved, the angled surfaces may also be curved. 
         [0016]    Unlike the prior art, such as Chen and Daly discussed above, which apply ridges and grooves to an element to present different patterns or colours depending on viewing angle, the present invention enhances contrast compared with the surrounding surface regardless of viewing angle. 
         [0017]    The angled nature of the angled surfaces defining the ridges and grooves means that incident light is reflected differently from the facets than the surrounding surface. In addition, the peaks of the ridges form shadows which further act to increase contrast. Depending on the precise size of the facets the increased contrast may appear as a single, generally uniform shading difference because the eye will blend the different reflection and shadow areas to a single shading. Alternatively, if the facets are relatively large, the contrast may be enhanced by the appearance of different bands of alternate shading within the debossed character arising from the reflection and shadow effects. 
         [0018]    Preferably, adjacent angled surfaces meet at an edge which is sharp. A sharp edge maximises the improved contrast effect. Typically, a sharp edge will have a radius of curvature less than 0.2 mm, more preferably less than or equal to about 0.12 mm. It is generally preferred that the radius of curvature is as small as possible, the actual value that can be achieved is likely to depend on the manufacturing route used. 
         [0019]    Preferably, in a cross-section through the symbol in a plane perpendicular to the ridges and grooves, alternating angled surfaces extend from a trough of a groove to a peak of a ridge and from a peak of a ridge to a trough of a groove respectively. This creates a generally triangular wave pattern. Such a pattern of angled surfaces can be manufactured simply. Other embodiments may have multiple facets between ridges and grooves. 
         [0020]    Preferably, in a cross-section through the symbol in a plane perpendicular to the direction of the peak of the ridges and the trough of the grooves, each pair of adjacent angled surfaces defines two equal sides of an isosceles triangle. Preferably, the angled surfaces are angled at about 90° to each other and about 45° relative to the plane of the debossed symbol. This equalises the contrast effect between reflection and shadow areas within the debossed symbol. In other embodiments adjacent pairs of angled surfaces may define two sides of a triangle other than an isosceles triangle and other angles can be used. 
         [0021]    Preferably, the plurality of angled surfaces have a different surface roughness than the smooth surface. In one embodiment, the plurality of angled surfaces may have a smaller surface roughness than the smooth surface. In another embodiment, the plurality of the angled surfaces may have a greater surface roughness than the smooth surface. For example, in some embodiments the angled surfaces or the smooth surface may be polished to reduce surface roughness. Polishing can be achieved by polishing after formation or during formation. For example, moulds can be used in which the angled surface forming elements of the mould or the smooth surface forming elements of the mould are polished. In such embodiments, the surface roughness of the polished element may have a R a  of less than about 1.8 μm, more preferably between about 1.12 μm and about 1.65 μm. This compares with a typical surface roughness giving an R a  of around 6.3 μm for an unpolished element. 
         [0022]    The debossed symbol may be a typographic symbol and the plurality of ridges may then be substantially parallel to a horizontal element of the typographic symbol. The reference to a horizontal element refers to the horizontal strokes of the typographical symbol, for example a “-” is a horizontal element. 
         [0023]    Preferably, the depth of a trough of a groove from a smooth surface is at least 0.5 mm. This depth provides a sufficient size of facet that the shadow and reflection effects provide a useful enhancement to the contrast of the debossed character. In other embodiments, the groove may extend completely through the surgical instrument. In that case, in embodiments where adjacent angled surfaces define triangles in cross section, there will be a gap between each pair of angled surfaces. 
         [0024]    Preferably, the spacing between peaks of adjacent ridges is between 0.5 mm and 2 mm, more preferably about 1 mm. 
         [0025]    Advantageously, at least three ridges are defined by the plurality of angled surfaces within the area of the debossed symbol. Depending on the size of the symbol, more ridges may be defined. However, it is preferred to have at least three ridges to ensure that the contrast enhancement effect is useful. 
         [0026]    Preferably, the debossed symbol does not comprise any printed markings. More preferably, the entire surgical instrument does not include any printed markings to avoid any difficulty with biocompatibility of marking materials. 
         [0027]    In some embodiments, the symbol may be a debossed symbol formed in the smooth surface. If the symbol is a debossed symbol, the peak of the ridges may be at the same level as the smooth surface, or at a lower level than the smooth surface. In other, less preferred embodiments, the peak of the ridges may extend above the smooth surface. 
         [0028]    In other embodiment, the symbol may be an embossed symbol formed on the smooth surface. 
         [0029]    In another aspect of the invention, there is provided a method of marking a surgical instrument with a symbol formed in or on a smooth surface. The method comprises forming a symbol in or on a smooth surface of the surgical instrument; and forming a plurality of angled surfaces over at least part of the area of the symbol, wherein the angled surfaces define a plurality of parallel ridges and grooves in the symbol. The symbol may be debossed or embossed. 
         [0030]    If the symbol is formed by moulding, then the steps of forming a symbol and forming a plurality of angled surfaces can take place substantially simultaneously in a single moulding step. For example, the mould may include angled surfaces in the symbol. 
         [0031]    Preferably, the mould is selectively polished or roughened to produces a different surface roughness in the plurality of facets compared to the smooth surface. Either the angled surfaces or the surrounding surface in the mould may be polished, to produce a different surface roughness between the surrounding surface and the angled surfaces. Alternatively, either the surrounding surface or angled surfaces may be roughened in the mould to produce a different surface roughness between the surrounding surface and the angled surfaces. In another embodiment, one of the surrounding surface and the angled surfaces may be roughened in the mould and the other of the surrounding surface and the angled surfaces forming the symbol may be polished in the mould to produce a different surface roughness between the surrounding surface and the angled surfaces. 
         [0032]    If the symbol is formed by machining, then the steps of forming a debossed symbol and forming a plurality of angled surfaces may take place substantially simultaneously in a single machining step. In other words, the machining of the debossed symbol may at the same time machine the angled surfaces into the debossed symbol. The method may further comprise selectively polishing or roughening the plurality of angled surfaces or the smooth surface after formation of the symbol to produce a different surface roughness between the smooth surface compared to the plurality of angled surfaces. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: 
           [0034]      FIG. 1  depicts a top view of a tibial sizing guide according to a first embodiment of the present invention; 
           [0035]      FIG. 2  depicts a bottom view of the tibial sizing guide of  FIG. 1 ; 
           [0036]      FIG. 3  depicts a cross-section through a vertical stroke of a “four” symbol marked on the tibial sizing guide of  FIG. 1 ; 
           [0037]      FIGS. 4A-4G  are a series of photographs of example tibial sizing guides with debossed symbols containing ridges and grooves according to the present invention and prior art plain debossed symbols at a variety of viewing angles; 
           [0038]      FIGS. 5-9  give examples of numeric debossed characters with ridges and grooves formed according to alternative embodiments of the present invention; and 
           [0039]      FIG. 10  depicts a perspective view of a tibial keel punch according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]      FIG. 1  depicts a top view of a tibial sizing guide  2  according to a first embodiment of the present invention.  FIG. 2  depicts the tibial sizing guide of  FIG. 1  from the bottom. The tibial sizing guide  2  comprises six separate tibial sizing guides  4 ,  6 ,  8 ,  10 ,  12 ,  14 . Each tibial sizing guide contains a planar sizing element  16  extending from a shaft  18 . The tibial sizing guides are joined along an axis  20  perpendicular to the plane of the sizing element  16 . In use, the planar sizing element  16  is used to measure the size of a tibia during knee surgery. Each tibial sizing guide,  4 ,  6 ,  8 ,  10 ,  12 ,  14  is marked with a debossed symbol indicating the size it represents. In this case the symbol is a numeric character. 
         [0041]    The debossed symbols are provided with a plurality of ridges and grooves, described in more detail below with reference to  FIG. 3 . For clarity in  FIGS. 1 and 2 , debossed symbols on the tibial sizing guide which include the plurality of ridges and grooves are marked in black. 
         [0042]      FIG. 3  is a diagrammatic representation (not to scale) of a partial cross section through a vertical stroke of a “four” character in the embodiment of  FIGS. 1 and 2 .  FIG. 3  depicts how the debossed symbol contains a plurality of ridges  22  and grooves  24  extending over the area of the debossed symbol. In this embodiment the depth of the trough of the grooves  24  is about 0.6 mm from the smooth surface and the height of the peak of the ridges  22  above the trough of the grooves  24  is about 0.1 mm. The peaks of the ridges  22  in this embodiment are therefore below the level of the surrounding surface  26  in which the debossed symbol is formed. In other embodiments different dimensions may be used as appropriate. 
         [0043]    A single angled surface extends from the peak of each ridge  22  to the trough of each groove  24 . In this embodiment the angled surface is a substantially planar facet  25 . The angle between adjacent facets  25  is about 90°. As can be seen in  FIG. 3 , in this embodiment the debossed symbol, and the trough of the grooves do not extend through the entire depth of the part of the surgical instrument in which they are formed. This means that the debossed characters are invisible from the underside. 
         [0044]    The facets  25  forming the ridges  22  and the grooves  24  are preferably polished. 
         [0045]    In use, the angling of the facets  25  relative to the surrounding surface  26  creates a combination of different specular reflection and shadows caused by incident light. In an operating theatre, incident light is generally from above, designed to illuminate the operating area evenly. This gives surgical lighting a directional quality that improves the enhanced contrast of the present invention under surgical lighting conditions. In use, the facets  25  create a pattern of reflection and shadow which alters the perceived shade of the debossed symbol relative to the surrounding surface. 
         [0046]      FIGS. 4A-4G  are a series of photos showing the improved contrast of a debossed symbol with ridges and grooves according to the present invention compared with a prior art plain debossed symbols. On the instrument on the right hand side of the photos a debossed symbol with ridges and grooves of the invention is depicted. On the left hand side, a conventional surgical instrument without the ridges and grooves in its debossed symbols is depicted. It can be seen how the debossed symbol of the invention on the right hand side instrument, including ridges and grooves, has improved contrast versus the prior art symbol at virtually all angles relative to an onlooker. 
         [0047]    Although this embodiment has been described in terms of a tibial sizing guide, it will be appreciated that the improved contrast of the present invention is advantageous when applied to any surgical instrument, not just tibial sizing guides. 
         [0048]      FIGS. 5-9  depict examples of debossed numerical characters according to further embodiments of the invention. To understand the effect of extending the debossed character through the entire depth of the component to be marked,  FIGS. 5-9  depict numerical symbols debossed on a side visible to an onlooker at the bottom. At the top, debossed symbols formed on the opposite to the onlooker are depicted. 
         [0049]    In  FIG. 5  the grooves of the facets formed within the debossed numerical characters  28  do not extend through the entire depth of the material. Therefore, no evidence of the corresponding debossed characters marked on the underside of the example surface in  FIG. 5  can be seen. 
         [0050]    In the embodiments of  FIGS. 6-9  the grooves extend through the entire depth of the component in which the debossed numerical characters are marked. The spacing between alternating pairs of facets either side of a groove which extends through the entire depth of the substrate is increased in the embodiment of  FIG. 7  compared with  FIG. 6 , further increased in the embodiment of  FIG. 8  compared with  FIG. 7  and still further increased in the embodiment of  FIG. 9  compared with  FIG. 9 . 
         [0051]      FIGS. 6-9  show how, even when the troughs of the groove extend through the entire depth of the component and occupy a significant area of the numerical character, there is a low risk of confusing a character marked on the opposite surface with a character marked on the surface viewed by an onlooker. 
         [0052]    In the embodiments of  FIGS. 5-9 , the details of the surgical instrument to which the debossed symbols are applied has not been shown. For example, the numerical characters depicted in these embodiments could be applied to the numerical markings on the tibial sizing guide of  FIGS. 1 and 2 , as well as any other surgical instrument. It will also be appreciated that the concepts of  FIGS. 5-9  can be applied to any symbol and is not limited to numerical characters. 
         [0053]    The present invention is preferably manufactured from injection moulded plastics material. In that case, the debossed characters and facets can be defined in a single injection moulding step. Other moulding processes may also be used. Alternatively, the debossed characters may be formed by machining. This can be useful when the surgical instrument is manufactured of other materials than plastics materials, for example, metal alloys. The invention can also be applied to ceramic materials. Other production processes may also be used, including casting, metal injection moulding, stamping or embossing. 
         [0054]    A further embodiment of the invention is depicted in  FIG. 10 . This depicts a tibial keel punch having debossed symbols  30  provided on a curved surface  32 . The construction of this embodiment is the same as described above, apart from the debossed symbols  30  are provided on a curved surface rather than a flat surface. The ridges and grooves defined by the angled surfaces  34  of the debossed symbols  30  are also curved, generally following the shape of the curved surface  32  if it were extended over the debossed symbol. The ridges and grooves defined by the angled surfaces remain parallel to each other. 
         [0055]    To improve the contrast effect of the present invention it is preferred to use a lighter rather than a darker material so that the shadows and highlights produced by the facets create a greater difference in contrast. However, the invention still has an effect with all colours and shades. 
         [0056]    While the above described embodiments have discussed debossed symbols, it will be appreciated that the construction and techniques discussed can equally be applied to embossed symbols, and will improve the contrast of an embossed symbol relative to a surrounding surface.