Abstract:
A surgical instrument, for example a cutting block for use in knee surgery, comprises a mounting surface defining at least one opening for receiving a mounting projection. The mounting surface further defines a blind recess which extends linearly from the at least one opening. The blind recess may extend to an edge of the mounting surface. A system including a surgical instrument and one or more mounting projections is also disclosed. The blind recess can be used as a track to guide a projection to an opening, increasing the area of the instrument that can be used to locate the projection in the correct position. The recess acts as a guide for the projection to enter the opening by providing tactile feedback to guide the projection towards the opening. If the recess also extends to the edge of the instrument, the recess may be visible more easily when the surgeon is installing the instrument providing visual as well as tactile feedback.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a National Stage 35 U.S.C. 371 of International Patent Application PCT/GB2010/051279, filed Aug. 3, 2010. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to surgical instruments and in particular to surgical instruments that include openings for engaging projections to hold the surgical instrument in a particular position. 
     Many surgical instruments require fixing in a known position relative to a patient. One example is a cutting block. Cutting blocks are typically affixed to a patient&#39;s bone in a position such that they can guide cutting and resection of the bone surface for receiving an implant. 
     Existing cutting blocks are mounted to a patient&#39;s bone by engaging projections or pins in recesses. In some systems the projections extend from the cutting block and engage holes drilled in the bone. In other systems a fixed reference philosophy is used and the cutting block contains openings or holes that engage projections installed in the bone and which extend from the bone surface. 
     In a fixed reference philosophy, instrumentation is first used to determine the correct position for the projections on the bone. The projections are then inserted into the bone and used to mount the cutting block and hold it in the correct position relative to the bone by engaging the openings on the cutting block. 
     If the cutting block is only intended to be provided in one position relative to the projections then one set of openings is provided, with each opening in the set positioned to receive each projection. Alternatively, the cutting block may be mounted in a number of different positions relative to the projections. For example, the surgeon may need to alter the position of the cut slightly from the measured position without having to reposition the projections. In that case the cutting block may include a number of sets of openings for engaging the projections. 
     Placing the cutting block on the projections is difficult. The projections extend from the bone surface in a direction towards the cutting block. As the surgeon looks at the cutting block and moves it towards the mounting projections, the position of the projections relative to the openings is obscured by the cutting block itself. 
     To overcome this problem, surgeons may attempt to view the bone surface while placing the cutting block on the pins. However, it can be difficult to position the patient such that this view is available, or it can require unacceptable manipulation of the patient. Even if the surgeon can view the projections, surgical lighting is designed for viewing from the direction the cutting block is installed. It can be difficult to identify the projections and openings accurately against the backdrop of the bright surgical lighting. 
     To assist in placement of the projections in the openings it is known to provide chamfers on the edges of the holes. These widen the entrance to the hole slightly, assisting alignment of the pins. However, due to design constraints the chamfer can be very small. For example, the space available between adjacent holes may constrain any chamfer so that it is over a radial distance of less than a millimeter. This limits the usefulness of the chamfer. 
     If the cutting block is placed on more than one projection, for example a pair of projections, it can be difficult to place the cutting block if the projections have not been installed in precisely the correct position. For example, one of the projections may be at a slight angle relative to another of the projections so that they do not align exactly with the openings. 
     Accordingly, the present invention provides a recess or slot which extends linearly from an opening for engaging a projection such as a pin. The recess may extend from the opening to the edge of the instrument. 
     The recess can be used as a track to guide a projection to an opening, increasing the area of the instrument that can be used to locate the projection in the correct position. The recess acts as a guide for the projection to enter the opening by providing tactile feedback to guide the projection towards the opening. If the recess also extends to the edge of the instrument, the recess may be visible more easily when the surgeon is installing the instrument providing visual as well as tactile feedback. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the first aspect of the present invention, there is provided a surgical instrument comprising a mounting surface, wherein the mounting surface defines at least one opening for receiving a mounting projection; and wherein the mounting surface further defines a blind recess which extends linearly from the at least one opening. 
     The at least one opening can delimit a through hole or a blind hole. The opening may have a circular cross-section or another cross-section. For example, in some embodiments the opening may be triangular, square or other shapes for engaging corresponding mounting projections with the same cross-section. (Non-circular cross-sections may be useful when an instrument is mounted on a single mounting projection, but orientation of the instrument in relation to the mounting projection is important). 
     The blind recess is a recess that does not extend through the entire depth of the surgical instrument. 
     A surgical instrument with these features can be installed more easily on the mounting projection without requiring visibility of the mounting projection as it aligns with the opening. The recess extends linearly unlike the radial extension of a chamfer. This allows it to cover more surface area of the mounting surface so the projection can be engaged more easily. The linear nature of the recess then assists in providing tactile feedback to guide the projection towards the opening. The mounting projection can remain in the recess throughout movement of the instrument to align the mounting projection with the opening, so that recess provides tactile feedback to the surgeon as the mounting projection is moved towards the opening. Thus, the surgical instrument according to the present invention can be placed more easily on a mounting projection. 
     The surgical instrument may further comprise a first side surface adjacent the mounting surface and the blind recess may extend to a first edge of the mounting surface such that the recess extends into the first side surface. The surgeon can then generally align the mounting projection with the blind recess while the instrument is tilted slightly, so that the section of the recess which extends to the edge of the mounting surface can be seen. The projection may be aligned with the blind recess visually by the extension of the recess to the side surface and the recess itself then acts as a track or guide, guiding the mounting projection towards the opening. 
     In one embodiment the blind recess has a width which increases in the direction towards the first side surface. For example, this can define a chamfer or funnel shape towards the first side surface. This increases the area of the first side surface in which the mounting projection can be located initially before being guided to the opening, making placement simpler. In embodiments with two or more openings for receiving mounting projections and two or more blind recesses, the increasing width in the direction towards the first side surface can allow the instrument to automatically correct slight differences in the location of the pins. The increasing width will guide all the projections towards the correct position as they move towards the openings. 
     The blind recess may have a depth which increases in the direction towards the first side surface. This increases the visibility of the blind recess when a surgeon is positioning the instrument. It can allow the blind recess to be optimised so that the area available for receiving a projection is maximised towards the edge without compromising the actual depth of opening provided for the projection. This may be important because in order to ensure accurate alignment the opening may have to extend over sufficient depth to hold the instrument in the correct position. 
     It will be noted that the width of the blind recess need not be the same as the width of the opening. For example the blind recess may be slightly narrower than the opening and still guide a projection towards the opening. This may be suitable when design constraints limit the size of the recess that can be formed on the mounting surface. 
     The blind recess may be generally straight and substantially perpendicular to the first edge of the mounting surface. This also assists aligning the instrument with a mounting projection. A surgeon can see the intersection of the blind recess with the first side surface and, if the blind recess is straight and extends perpendicularly the surgeon can then easily determine the direction of movement in order to engage a mounting projection with an opening, in addition to any tactile feedback that may be provided by the blind recess. 
     The blind recess may be intersected by other surface features of the surgical instrument, for example by a slot for guiding a cutting instrument. An intersected recess can still guide a mounting projection. It is desirable that an intersection has a size less than the width of the mounting projection so that the mounting projection can be guided through the recess more smoothly. 
     In one embodiment the mounting surface defines first and second openings for receiving a mounting projection; wherein a first blind recess extends from the first opening and a second blind recess extends from the second opening; wherein both the first and second blind recesses extend to the first edge of the mounting surface such both the first and second blind recesses extend into the first side surface; and wherein the first and second recess are substantially parallel to each other in the plane of the mounting surface. 
     This embodiment provides first and second openings for corresponding mounting projections. This can be useful when the surgical instrument requires mounting on two projections. For example, orientation of the instrument relative to the mounting projections may be important, or a more secure fitting may be required. In this embodiment, it is particularly advantageous if the blind recess has a width which increases in the direction towards the first side surface. As explained above, this can allow slight misalignment of the mounting projections relative to each other to be corrected by the blind recess as the projections are moved towards openings. For example, if one of the projections has been mounted at a slight angle relative to the other projection, the recess may assist in bending the projection slightly so that it is in the correct position relative to the other projection to correctly engage the openings. 
     In another embodiment, a second side surface is adjacent the mounting surface and opposite to the first side surface, and wherein the blind recess extends across the entire mounting surface from the first edge to a second edge such that the blind recess extends into both the first and second side surfaces. 
     In this embodiment the blind recess extends across the entire mounting surface so that it is visible from first and second side surfaces. This embodiment could be used when the surgical instrument could be inserted from different directions, because the blind recess is visible from two different directions by extending into two surfaces. Alternatively, it can also be used when at least two openings are provided in a line. In that case the recess may extend between all the openings allowing a surgeon to align the instrument by sliding it along the projections in the direction of the line formed between the projections. 
     The mounting surface may define at least first and second openings and the blind recess may extend between the first and second openings. 
     Optionally, the mounting surface may define at least one further opening for receiving a mounting projection and wherein no blind recess extends from the at least one further opening This can allow for repositioning the surgical instrument slightly relative to the projections if required. A blind recess is not provided for the further opening. Although this may make it more difficult to locate the projection in the further opening, it avoids confusion between openings and may be more suitable depending on the amount of space available on the mounting surface. 
     The present invention is particularly advantageous when applied to cutting blocks for orthopaedic surgery. For example it may be applied to a cutting block for guiding resection or drilling on the condyles of the knee joint. In that case the cutting block may define slots for bores which pass all the way through the depth of the cutting block for defining anterior and/or posterior chamfers and/or cuts. These slots and bores are not blind recesses because they are formed through the entire depth of the cutting block. However, it will be appreciated that in alternate embodiments the present invention can also be applied to other surgical instruments including, but not limited to: sizing guides, pin pullers, pin inserters, drill towers, notch guides, tibial trials, tibial cutting blocks and femoral cutting blocks. 
     According to another aspect of the present invention, there is provided a system of surgical instruments comprising a mounting projection and a surgical instrument as described above. 
     The mounting projection can be anything suitable for mounting the surgical instrument. For example it may be cylindrical or alternatively may have another cross section such as triangular, square, etc. depending on the particular application. In one embodiment the mounting projection may be adapted for insertion into a bone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which like reference numerals denote like parts and in which: 
         FIG. 1  is an isometric view of a first embodiment of the present invention viewed from the rear; 
         FIG. 2  is an isometric view from the front of the embodiment of  FIG. 1 ; 
         FIG. 3  is a top view of the embodiment of  FIG. 1 ; 
         FIG. 4  is a front view of the embodiment of  FIG. 1 ; 
         FIG. 5  is a view from the right of the embodiment of  FIG. 1 ; 
         FIG. 6  is a view from the rear of the embodiment of  FIG. 1 ; 
         FIG. 7  is a view from the left of the embodiment of  FIG. 1 ; 
         FIG. 8  is a diagrammatic representation of a second embodiment according to the present invention. 
         FIGS. 9   a - 9   d  are a diagrammatic representation depicting the use of the embodiment of  FIG. 1  to engage mounting projections during knee surgery; and 
         FIGS. 10   a - 10   d  are a diagrammatic representation depicting the use of the embodiment of  FIG. 8  to engage mounting projections during knee surgery. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1-7  depict different views of a cutting block  2  according to the first embodiment of the invention. In this embodiment the cutting block is for use in knee surgery. It is a four-in-one cutting block, so called because a single cutting block can define four different cuts by guiding a cutting device through slots  4 ,  6 ,  8  and  10 . In order to allow the cutting block  2  to be positioned on mounting projections or pins (not shown) the cutting block  2  defines a number of openings of through holes. Towards the top of the cutting block  2  three pairs of openings  12 ,  14 ,  16  define through holes. Each of the two openings in each pair,  12 ,  14 ,  16  are positioned the same distance apart but the pairs of openings  12 ,  14 ,  16  are offset slightly from each other. This enables the surgeon to adjust the position of the cutting block relative to the bone slightly in use, without needing to reposition the mounting projections. 
     Three more pairs of openings  18 ,  20 ,  22  are defined towards the bottom of the cutting block  2 . As with the three pairs of openings  12 ,  14 ,  16 , the lower pairs of openings  18 ,  20 ,  22  are the same distance apart from each other with each pair offset slightly from an adjacent pair. 
     As can be seen most clearly in  FIGS. 1 and 6  openings  14  towards the top of the cutting block and openings  20  towards the bottom of the cutting block are positioned at the end of a recess formed in a mounting surface  24  of the cutting block  2 . Openings  14  are positioned at the end of recesses  26  and openings  20  are positioned at the end of recesses  28 . The shape of the recesses  26 ,  28  is generally the same in this embodiment. Each recess  26 ,  28  extends from an opening  14 ,  20  to a surface adjacent the mounting surface  24 . The recesses  26 ,  28  define an opening in the surface adjacent the mounting surface  24 . In this embodiment, the cutting block  2  is intended to engage two mounting projections at the same time. Thus, openings  12 ,  14 ,  16  and  18 ,  20 ,  22  are provided in pairs. In order to allow two mounting projections to be guided simultaneously towards the openings, the recesses  26  and  28  follow a generally straight path and are parallel to each other, extending in a perpendicular direction from the respective surface adjacent the mounting surface  24 . 
     Referring again to  FIGS. 1 and 6 , the width of the recesses  26 ,  28  increases towards the surface adjacent the mounting surface  24 . In this embodiment the width increases at a constant rate to define a funnel shaped end  30 ,  32  to each recess  26 ,  28 . 
     As can be seen in  FIGS. 1 and 3 , the depth of the recesses  26  also increases towards the surface adjacent the mounting surface  24 . This is provided by chamfered section  34 . 
     In use, a surgeon can align mounting projections with the pairs of openings  14 ,  20  by using the recesses  26 ,  28 . The process will be described with reference to  FIGS. 9   a - 9   d , which are diagrammatic representations of the installation of the cutting block  2  on mounting projections  50  extending from a condyle of a knee joint. In  FIGS. 9   a - 9   d  the cutting block is depicted in simplified form, showing only those features used to install the cutting block on the mounting projections, other features such as cutting slots are omitted to allow the method to be understood more clearly. 
     The surgeon will typically install the cutting block  2  so that the mounting surface  24  is hidden from view and the surgeon is looking at the cutting block from a position similar to that illustrated in  FIG. 2 . Although the location of the openings on the mounting surface  24  cannot be seen, the recesses  26 ,  28  extend into adjacent surfaces and can be identified by the surgeon. As depicted in  FIG. 9   a , the surgeon can then align the mounting projections with the recesses  26 ,  28 . The cutting block  2  is then tilted slightly and used to locate the mounting projections  50  in the end of the recesses  26 ,  28  ( FIG. 9   b ). Next, the cutting block  2  is slid so that the mounting projections  50  travel along the recesses  26 ,  28  and are guided towards the openings  14 ,  20  ( FIG. 9   c ). 
     The increasing width sections  30 ,  32  and increasing depth section  34  assists the surgeon in aligning the cutting block  2  on the mounting projections if the mounting projections have not been installed at precisely the required distance apart. These features enable the cutting block to align the mounting projections  50  more accurately as they are slid along the recesses  26 ,  28 . 
     Once the mounting projections  50  reach the end of the recesses  26 ,  28  the surgeon can simply push the cutting block  2  onto the mounting projections knowing that they are already partially received within the openings ( FIG. 9   d ). 
     This embodiment illustrates how not all the openings  12 ,  14 ,  16  and  18 ,  20 ,  22  need be provided with recesses to assist insertion of mounting projections. Design constraints may mean that providing a recess for each opening is not possible because it weakens the structure or because the recesses cannot be formed so close together. However, in the embodiment of the present invention the recesses are chosen to be positioned next to the pairs of openings  14 ,  20  which are most often used in surgery. For example, provided that the mounting projections are correctly positioned in a patient, openings  14  and  20  are used in the majority of surgical procedures so the recess assists the surgeon align mounting projections with the most commonly used openings. 
     It will be appreciated that the precise design and profile of the recesses may be varied depending on the requirements for a particular surgical instrument. In this embodiment the recess has a width generally equal to the width of an opening. However, the width may also be narrower than the opening, particularly when the mounting projections may have rounded rather than square ends in the direction of the openings. Likewise, it may be desirable to vary the depth of the recess so that it is shallower immediately adjacent the opening. This allows the opening to retain as much depth as possible which can be important for ensuring a secure attachment to the mounting projections. 
     This embodiment also illustrates how the recesses can be intersected by other surface features of the mounting surface  24 . For example, recesses  28  are intersected by cutting slot  6 . 
     In an alternate embodiment (not illustrated), which is the same as the  FIG. 1  embodiment, except as described below, more pairs of openings may be provided with recesses. In this embodiment, for example all of openings  12 ,  14 ,  16  may be provided with a recess extending from them. The recesses for each pair of openings may extend at different angles relative to others of the recesses to assist in differentiating between the opening each recess leads to. It could also enable the recesses to move further apart from each other towards the side surface than adjacent the openings. Optionally, the recesses may be labelled on the side surface to further assist identification. The label may be laser marked on the side surface. 
     Another embodiment of the present invention is depicted in perspective view in  FIG. 8 . In this embodiment a cutting block  36  is provided with two pairs of openings  38 ,  40 . Each pair of openings  38 ,  40  have a respective recess  44 ,  46 . The recesses  44 ,  46  extend across the entirety of the mounting surface  42  so that they are visible from two opposite sides adjacent the mounting surface. Recess  44  extends past both openings  38  and recess  46  extends past both openings  40 . The recesses  44 ,  46  may have a centre line which is offset from the line joining the centres of the openings  38  or openings  46  (as depicted in  FIG. 8 ). Alternatively, in other embodiments, the centre line of the recesses may be coincident with the line joining the centres of the openings. 
     The process of using this embodiment will now be described with reference to  FIGS. 10   a - 10   d , which are diagrammatic representations of the installation of the cutting block  36  on mounting projections  52  extending from a condyle of a knee joint. In  FIGS. 10   a - 10   d  the cutting block is depicted in simplified form, showing only those features used to install the on the mounting projections, other features such as cutting slots are omitted to allow the method to be understood more clearly. In use, the surgeon may place the cutting block  36  so that the projections  52  are against the mounting surface  42  ( FIG. 10   a ). and the cutting block  36  is then moved until both projections  52  engage somewhere along the length of the recess  44  ( FIG. 10   b ). This can be assisted because the surgeon can gauge the position of the recess  44 ,  46  by viewing the side adjacent the mounting surface. Once the mounting projections are engaged with recess  44  or  46  the surgeon can then use the recess to guide the projections into the openings  38  or  40 . The cutting block  36  is slid sideways until the mounting projections  52  engage the openings  38  or  40  ( FIG. 10   c ) and then pushed on the mounting projections  52  ( FIG. 10   d ). 
     The engagement of the openings with the mounting projections can provide tactile feedback to the surgeon. This tactile feedback is enhanced when the openings are offset from the recess and have a chamfered lead-in, as depicted in  FIG. 8 . 
     In an alternate method of use, a surgeon aligns one of the mounting projections with recess  44 ,  46  as appropriate. The mounting projection is then slid along recess  44  or  46  past the first of the openings  38 ,  40  until the second projection is aligned with the recess  44 ,  46 . The surgeon then aligns the second projection with the recess and continues sliding the cutting block  42  until the mounting projections are aligned with the openings  38  or  40 . 
     All of the above described embodiments may be manufactured from any suitable material, for example a medical grade metal or metal alloy. 
     The features of the embodiments may be combined. For example, the pairs of parallel recesses discussed in the embodiments of  FIG. 1  may be combined with the single recess for two openings in the embodiment of  FIG. 8 . Likewise, the present invention can be applied to any number of mounting projections. Although the embodiments described are for aligning a cutting block with a pair of projections, the invention is equally as useful with other surgical instruments or when a surgical instrument is mounted on one, two, three or more mounting projections.