Abstract:
An instrument ( 2 ) for aligning a surgical tool, the instrument ( 2 ) comprising, a body portion ( 4 ) having a tool guide ( 90 ), first and second arms ( 6 ), ( 8 ) operatively connected to the body portion ( 4 ) and adapted to engage a bone, and urging means ( 10 ), acting between the body portion ( 4 ) and the first and second arms ( 6 ), ( 8 ), for urging the first and second arms ( 6 ), ( 8 ) into engagement with a predetermined portion of a bone, thereby clamping the arms ( 6 ), ( 8 ) onto the bone and aligning the tool guide ( 90 ) with the bone.

Description:
This invention relates to a surgical instrument and particularly, but not exclusively, relates to an instrument having a tool guide and a clamping arrangement, the clamping arrangement clamping the instrument to a bone, and at the same time aligning the tool guide with the bone. 
     BACKGROUND 
     During all types of joint replacement surgery, and in many other surgical procedures, it is necessary to make specific cuts or to drill holes into specific areas of bone. Both the point and angle of entry of the cut or drill hole is important. This is particularly so in the case, for example, of femoral head resurfacing, where it is necessary to drill a pilot hole that passes through the centre of the femoral neck at a specific angle with respect both to the epicondylar axis and the femoral shaft axis. Guide tools exist to aid surgeons in the placement of bone cuts and guide holes. Such tools are often difficult and time consuming to operate, and are inaccurate. Many of the tools of the prior art are also bulky, requiring the removal or displacement of large areas of soft tissue in order to be used. 
     Use of conventional tool guides generally involves at least the steps of attaching the guide, referencing the position of the guide from an anatomical feature, and adjusting the position of the guide to correspond to the optimal position indicated in the referencing step. Several iterations of referencing and adjustment may be required to achieve the correct position and orientation of the guide. 
     STATEMENTS OF INVENTION 
     According to a first aspect of the present invention, there is provided an instrument for aligning a surgical tool, the instrument comprising, a body portion having a tool guide, first and second arms operatively connected to the body portion and adapted to engage a bone, and urging means, acting between the body portion and the first and second arms, for urging the first and second arms into engagement with a predetermined portion of a bone, thereby clamping the arms onto the bone and aligning the tool guide with the bone. 
     The first and second arms may terminate in first and second jaws. The first jaw may be curved and the second jaw may be bifurcated and may have at least two distinct jaw elements. As the instrument contacts the bone in at least three distinct points or areas, the instrument is held in a very stable manner relative to the bone. 
     The first and second arms may be pivotally connected to the body portion. Alternatively, the first and second arms may be connected to the body portion by means of a linkage which constrains the arms to translate laterally of the body portion towards and away from one another. The linkage may be a quadrilateral linkage. The advantage of constraining the arms to translate laterally is that the angle of the arms relative to a longitudinal axis of the body portion does not change irrespective of the diameter of the bone to be clamped. This enhances the accuracy of referencing and hence the alignment of the tool guide compared to an instrument having pivoting arms, irrespective of the size of the patient. 
     The first and second arms may be disposed on opposite sides of the body portion. Additional arms may also be provided. For example, three arms may be provided spaced equidistantly around the circumference of the body portion. 
     The urging means may engage the body portion via a threaded connection, and the urging means may be a nut. The nut may comprise a tapering engagement surface, configured to engage the first and second arms directly. 
     The body portion may comprise a post having projecting tabs that extend from the base of the post. The first and second arms may be mounted in opposed recesses formed in the projecting tabs. Each arm may be pivotably connected to one of the tabs by means of a pinned joint. 
     Each arm may be connected to the body portion at an intermediate position along its length. 
     The tool guide may be provided with a plurality of tool guiding openings. At least one of the tool guiding openings may be differently aligned to the or each other tool guiding openings, so that when the first and second arms are clamped to the bone, the said tool guiding opening is aligned with a different part of the bone from the or each other tool guiding opening. 
     The tool guiding openings may comprise bores having longitudinal axes at least some of which converge at a point a predetermined distance proximal of the body portion. The longitudinal axes of some of the bores may converge at a different point from the longitudinal axes of some others of the bores. 
     The provision of a plurality of guide holes or bores enables the surgeon to select an appropriate bore which might compensate for minor misalignment of the instrument. Furthermore, having groups of bores aligned, such that their longitudinal axes intersect at specific points, further increases the options that the surgeon has in selecting an appropriate bore to accommodate minor misalignment or variations in patient anatomy. 
     According to a second aspect of the present invention, there is provided an instrument for aligning a surgical tool, the instrument comprising a body portion, at least two arms pivotably connected to the body portion and a nut which engages a thread formed on the body portion, the nut engaging the arms as it is threaded onto the body portion in use, thereby forcing the free ends of the arms together to clamp a bone. 
     According to a third aspect of the present invention, there is provided an instrument for aligning a surgical tool, the instrument comprising a body portion, means for clamping the body portion to a bone, and a tool guide having a plurality of tool guide bores, longitudinal axes of some of the bores converging at a different point from longitudinal axes of others of the bores. 
     The instrument my be used in a method of aligning a tool guide, the method comprising the steps of: 
     a placing the arms of the instrument about a predetermined portion of a bone; and 
     b operating the urging means to force the arms to clamp the bone, thereby aligning the tool guide with the bone. 
     The present invention represents a considerable advance over prior art devices, since simply by operating the urging means to force the arms to clamp a predetermined portion of the bone, the tool guide is automatically aligned with the bone. This is achieved because the arms of the instrument reference on a predetermined portion of the bone which has a known orientation relative to the part of the bone which is to be drilled, cut of otherwise worked. The automatic alignment provided by the device means that no additional visual checks of the alignment of the device are required, thereby speeding up the surgical procedure. Furthermore, the level of skill and experience required in the surgeon using the instrument is reduced, whilst the accuracy of the surgery is increased. The instrument is also adaptable to different sizes of bone, so that a single instrument can be used on many patients. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: — 
         FIG. 1  is an exploded perspective view of a surgical instrument, 
         FIG. 2  is a plan view of the instrument of  FIG. 1 , 
         FIG. 3  is a side view of the instrument of  FIG. 1  mounted on a femur, and 
         FIG. 4  is an end view of the instrument illustrated in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , a surgical instrument  2  comprises a body portion  4 , a pair of opposed first and second arms  6 ,  8  pivotally connected to the body portion  4 , and a nut  10  mountable on the body portion  4 . The body portion  4  comprises an annular flange  12  and a post  14  that carries an external thread  15 . 
     In this specification, the terms “distal” and “distally” mean towards the threaded end of the surgical instrument  2 , and the terms “proximal” and “proximally” mean towards the opposite end of the surgical instrument  2 . 
     The post  14  projects substantially perpendicularly from a distal surface  16  of the flange  12 . A first tab  11  projects from a first (or inferior) side of the flange  12  and is bifurcated. A recess  22  is defined between substantially parallel forks  18 ,  20  of the first bifurcated tab  11 . A second bifurcated tab  30  projects from an opposite (or superior) side of the flange  12 . A second recess  24  is defined between substantially parallel forks  26 ,  28  of the second bifurcated tab  30 . 
     The arms  6 ,  8  are mounted on the tabs  11  and  30  for pivotal motion relative to the flange  12  and post  14 . The arm  6  is mounted between the forks  18 ,  20  on a pin  32  which extends through the forks  18 ,  20 , and the arm  8  is mounted between the forks  26 ,  28  on a pin  34  which extends through the forks  26 ,  28 . Each arm  6 ,  8  includes a cylindrical bore (not shown) extending across the width of the arm  6 ,  8 , at an intermediate position along its length, through which the corresponding pin  32 ,  34  passes. 
     Other means of pivotable connections are contemplated, such as replacing the pins  32 ,  34  with set screws, rivets, or nut and bolt arrangements. In an alternative embodiment, not illustrated, the arms  6 ,  8  are connected to the body portion  4  by a quadrilateral linkage so that the arms  6 ,  8  move laterally of the body portion  4 , rather than pivoting about the tabs  11 ,  30 . 
     Each arm  6 ,  8  extends both proximally and distally of its respective bore such that, when mounted in the recesses  22 ,  24 , each arm comprises a referencing portion  40 ,  42 , that extends proximally of the flange  12 , and an engaging portion  36 ,  38 , that extends distally of the flange  12 . Each arm  6 ,  8  is substantially “S” shaped, and is mounted in its corresponding recess  22 ,  24  such that the engaging portion  36 ,  38  is directed away form a central axis  44  of the post  14  and the referencing portion  40 ,  42  is directed towards the central axis  44  of the post  14 . 
     The referencing portion  42  of the arm  8  mounted in the second recess  24  (the superior arm) terminates at its free end in a jaw  50 . The jaw  50  comprises a single jaw element  52  that extends arcuately so as to define an internal, bone receiving surface  54 . The referencing portion  40  of the arm  6  mounted in the first recess  22  (the inferior arm) terminates at its free end in a jaw  60 . The jaw  60  is bifurcated, comprising two jaw elements  62 ,  64  that each extend arcuately so as to define internal, bone receiving surfaces  66 ,  68 . 
     The engagement portions  36 ,  38  of the arms  6 ,  8  define opposed curved cam surfaces  72 ,  74  that cooperate with an annular engagement surface formed on the nut  10 . 
     The nut  10  comprises a bore  76  having an internal thread  77 . The thread  77  cooperates with the external thread  15  formed on the post  4 . The nut  10  has a frustoconical engagement surface  78  that tapers outwardly from the rim of the bore  76  to a cylindrical gripping surface  80 . Projections  82 ,  84  are integrally formed with the cylindrical gripping surface  80  to facilitate rotation of the nut  10 . Alternatively, the cylindrical gripping surface  80  may be knurled, or otherwise adapted to facilitate turning by hand. In an embodiment not illustrated, the nut may be shaped to facilitate turning using a tool. 
     With reference to  FIG. 2 , the post  14  comprises a series of guide bores  90  extending from a distal surface of the post  14 . The bores  90  are open, allowing communication from a distal to a proximal end of the body portion  4 . The post  14  may be hollow, in which case the flange  12  includes a corresponding opening and the bores  90  extend through the distal end wall of the post  14 . Alternatively, the post  14  may be solid, in which case the bores  90  extend through the length of the post  14  and the thickness of the flange  12 . At least one bore  90  is positioned such that the axis of the bore  90  coincides with the longitudinal axis  44  of the post  14 . The bores  90  are orientated such that the longitudinal axes of the bores  90  converge on predetermined points which are predetermined distances proximal of the body portion  4 . 
     The instrument  2  is particularly suited for use in surgical procedures involving the hip and shoulder. 
     With reference to  FIGS. 3 and 4 , the instrument  2  may be used to guide a femoral alignment pin during a femoral resurfacing procedure. Prior to use, the instrument  2  is prepared by unscrewing the nut  10 , so as to allow free pivoting motion of the arms  6 ,  8 . The instrument is then placed over the femoral head with the inferior arm  6  on the inferior side of the femoral neck and the superior arm  8  on the superior side of the femoral neck. The nut  10  is then screwed onto the post  14 . As the nut  10  progresses proximally down the post  14 , the engagement surface  78  of the nut  10  contacts the cam surfaces  72 ,  74  of the engagement portions  36 ,  38  of the arms  6 ,  8 . Further proximal motion of the nut  10  forces the engagement portions  36 ,  38  of the arms  6 ,  8  apart, thus bringing the jaws  50 ,  60  of the arms  6 ,  8  into contact with the femoral neck. The nut  10  is screwed onto the post  14  until the jaws  50 ,  60  are firmly clamped around the femoral neck. The regions or points of contact provided by the three jaw elements  52 ,  64 ,  66  ensure a stable connection between the instrument and the bone. 
     With the instrument correctly mounted on the bone, the inferior, bifurcated jaw  60  provides a three dimensional reference of the calcar surface of the femoral neck. The superior jaw  50  provides a two dimensional reference of the superior surface of the femoral neck. The position at which the instrument centres itself on the femoral neck is thus determined by the inferior angle of the femoral neck (the calcar angle) and by the diameter of the femoral neck. The curvature of the arms  6 ,  8 , the curvatures of the cam surfaces and engagement surface  72 ,  74 ,  78 , and the orientation of the bores  90  are selected such that, with the instrument clamped in the manner described above, the axes of the bores  90  converge towards the centre of the femoral neck and are aligned at an optimal collodiaphyseal angle (the angle between the femoral neck and shaft) and optimal anteversion to guide the insertion of a femoral alignment pin. The provision of several bores  90 , each having a slightly different orientation, allows a surgeon a certain flexibility, enabling the most appropriate orientation for a particular patient to be selected.