Abstract:
A bone measurement device is used to measure the adequacy of the distance between a cavity in the head and neck of a femur and the outer surface of the neck of the proximal femur. A coupling element is fixedly attached to an outer surface of a femoral head. An arm extends from the coupling element and a bone measurement device having an adjustable bone contacting element thereon is coupled to the arm. An adjustable coupler is provided for moving the bone measurement device in a generally proximal-distal direction. The bone contacting element is mounted on the adjustable coupler for movement in a direction transverse to the proximal-distal direction into contact with bone when the coupling element is attached to the femoral head. The adjustable coupler for moving the bone measurement device in a proximal-distal direction and the adjustable bone contacting element are calibrated with distance markings. The markings correspond to sizes of femoral implants for implantation in the cavity.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to apparatus for indicating the bone thickness between the predetermined distal end of a bone cavity located on a proximal/distal axis and the outer surface of a bone. 
         [0002]    When preparing cavities in a bone, for example to receive the insert portion of a prosthetic component, it is necessary to drill into the bone. When fitting a prosthetic component to the proximal end of a femur when carrying out proximal epiphyseal replacement technique surgery, two proximal axially extending holes are drilled, one at an angle to the other. These holes can subsequently be joined by reaming to present a V-shaped cavity. When preparing such a cavity it is essential that one or other of the drill holes does not approach too close, or even break through, the wall of the bone. It is also common to prepare cavities, again, for example, at the end of a femur which are wide and if not accurately dimensioned, for example with regard to the width or the depth, can be too close to the wall of the bone, especially in the neck of the femur. A prosthesis for such cavities is shown in U.S. Pat. No. 6,524,343 the disclosure of which is incorporated herein by reference. 
       SUMMARY OF THE INVENTION 
       [0003]    One aspect of the present invention is to provide an apparatus which will assist in determining the thickness of the bone between the distal end of a bone cavity and the outer surface of the bone. 
         [0004]    According to one aspect of the present invention an apparatus which will assist in determining the thickness of the bone between the distal end of a bone cavity and the outer surface of the bone. 
         [0005]    According to one aspect of the present invention an apparatus is provided for indicating the bone thickness between the predetermined distal end of a bone cavity located on a proximal/distal axis and the outer surface. The apparatus comprises a support member provided with means for location on the bone and having adjustable distance indicating structures which can be adjusted in relation to the support member to contact the outer surface of the bone. 
         [0006]    With this apparatus and knowing the accurate dimensions of the apparatus itself it is possible to measure the bone thickness concerned. 
         [0007]    The apparatus may include a proximal/distal bone axis indicator which can, for example, be in the form of a guide wire. With this in place the guide wire can provide a datum which can be used to set up the apparatus. 
         [0008]    In a preferred form the guide wire is provided by a guide pin which forms part of the location system of the support member on the bone. Thus, the apparatus can be located on this accurately placed pin. 
         [0009]    In an alternative arrangement the location system for the support member on the bone may comprise a collar adapted to fit on the bone at a predetermined location. 
         [0010]    The apparatus can also include an extension which can be adjusted to vary the proximal/distal length of the support member and which in one embodiment may comprise an adjustable carrier on which the adjustable distance indicator is supported. 
         [0011]    In an alternative embodiment the extension may comprise a series of slots provided on the support member and adapted to locate on a co-operating connector carried on the location system on the bone. Use of alternate slots effectively increasing or decreasing the effective proximal/distal length of the support member. 
         [0012]    In a preferred embodiment the adjustable distance indicator includes a sliding pin provided with distance indicating indicia i.e. score marks, which can be adjusted in relation to the support member. 
         [0013]    The invention is not limited to operations relating to a femur and it can be used on any bone in which knowing the distance between an opening of the wall is required. 
         [0014]    Other instruments used in this type of surgery are, for example, U.S. Patent Publication Nos. 2007/0233136 and 2007/0162038 the disclosures of which are incorporated by reference herein. 
         [0015]    Aspects of the invention are provided by a bone measurement device used to measure the distance between a cavity in the head and neck of a femur and the outer surface of the neck of the proximal femur. The device has a coupling element for fixedly attaching it to an outer surface of a femoral head. An arm extends from the coupling element with a bone measurement device having an adjustable bone contacting element thereon coupled to the arm. An adjuster is used for moving the bone measurement device in a generally proximal-distal direction. A bone contacting element is mounted on the adjuster for movement therewith in a direction transverse to the proximal-distal direction into contact with bone when the coupling element is attached to the femoral head. The adjuster for moving the bone measurement device and the adjustable bone contacting element are calibrated with distance markings. The markings correspond to sizes of femoral implants for implantation in the cavity. 
         [0016]    The bone measurement device for measuring the distance between a cavity in the head and neck of a femur and the neck outer surface may be mounted on a pin for insertion in a bore in a femoral head. The pin extends along a central axis of a neck of the proximal femur adjacent the femoral head. The arm is mounted on the pin. The arm extends outward of the central neck axis and distally with respect to the proximal femur. A bone measurement device mounted on the arm is moveable in a proximal-distal direction with respect to a medial surface of the femur. A bone contacting element mounted on the bone measurement device is moveable in a direction transverse to the proximal-distal direction into contact with the medial surface of the femur. The bone measurement device and the adjustable bone contacting element are calibrated with distance markings. The markings correspond to sizes of femoral implants for implantation in the cavity. 
         [0017]    A method for determining the distance between a cavity in the neck of the femur and an outer surface of the neck includes mounting a support structure on a head of a femur. A bone measurement device is mounted on the support structure. The bone measurement device has a bone contacting element thereon. The bone measurement device is moved in a proximal distal direction based on the size of a prosthetic component to be implanted in the cavity. The bone contacting element is moved in a direction transverse to the proximal-distal direction into contact with the bone. Calibrations on the bone measurement device and the bone contacting element are read by the surgeon to determine the proper implant. 
         [0018]    As used herein when referring to bones or other parts of the body, the term “proximal” means close to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means toward the head. The term “anterior” means toward the front part or the face and the term “posterior” means toward the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention can be performed in various ways and two embodiments will now be described by way of example and with reference to the accompanying drawings in which: 
           [0020]      FIG. 1  is a diagrammatic side elevation of apparatus for indicating the bone thickness between the predetermined distal end of a bone cavity located on the proximal/distal axis and the outer surface of the bone according to the invention; 
           [0021]      FIG. 2  is a diagrammatic representation of the proximal end of a femur showing how it is prepared to carry out proximal epiphyseal replacement technique surgery; 
           [0022]      FIG. 3  is a diagrammatic cross-sectional representation of a prosthetic component for use in proximal epiphyseal replacement technique surgery and for which a prosthetic stem cavity can be prepared using the apparatus according to the invention; 
           [0023]      FIG. 4  is a diagrammatic cross-sectional view of an alternative form of apparatus according to the invention; 
           [0024]      FIG. 5  is an exploded isometric view of the apparatus shown in  FIG. 4 ; 
           [0025]      FIG. 6  is a side elevation of an alternative construction according to the invention; 
           [0026]      FIG. 7  is an exploded view of parts of the support member; 
           [0027]      FIG. 8  is an isometric view of the construction shown in  FIG. 6 ; and 
           [0028]      FIG. 9  is a cross-sectional plan view on the line IX-IX of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The apparatus according to the invention is particularly, although not exclusively, for use with proximal epiphyseal replacement technique surgery. An example of this type of surgery is explained and shown in U.S. Pat. No. 6,524,343 and includes resecting a femur at a position on the proximal side of its neck to locate a prosthetic femoral component which has a tapered insert portion and a proximal head portion. The insert portion is adapted for location in a prepared socket which, effectively, has inclined side to provide a tapering opening. 
         [0030]    In order to carry out this type of surgery the end of a femur, indicated by reference numeral  1  in  FIGS. 1 and 2 , the femoral head, indicated by reference numeral  2 , is first prepared by machining it with a cylindrical cutter (not shown) to provide a cylindrical portion  3 . In order to accurately locate the cylindrical cutter a proximal/distal opening is drilled in the head to receive a guide wire and this opening is subsequently enlarged to receive a guide pin  5  on which the cylindrical cutter is located. This pin can also be used in the apparatus to be described herein. The neck of the femur is indicated by reference numeral  4 . 
         [0031]      FIG. 3  shows diagrammatically how a typical femoral head component for this type of surgery has a tapered insert portion  11  and a head  12  is fitted into a cavity  13  in the proximal end of the femur  1  which, in this figure, is indicated by broken lines. 
         [0032]    In order to provide the cavity  13  a hole is drilled into the prepared femur on a axis  14  which is substantially co-axial with the proximal/distal axis of the end of the femur. A second opening is also drilled along the line of another proximal/distal axis  15  which is an angle to the line  14  to provide the basis for the tapering socket. Such a surgery is described in a U.S. patent application having the same filing date of this application entitled Apparatus For Preparing A Femur and listing Marie Mondreau, Loic Pinot, Richard Field, and Neil Rushton as inventors claiming priority to Great Britain Patent Application No. 0703691.6. 
         [0033]    By careful measurement of the femur and knowing the dimensions of the prosthetic component it is possible to accurately determine the position of the tip  16  of the component in the bone and the present apparatus can be used for indicating the bone thickness between the predetermined distal end of the bone cavity which is located on a proximal/distal axis and the outer surface of the bone, indicated by reference numeral  17 . Reference numeral  18  indicates the calcar which can be used as a reference point. 
         [0034]    The apparatus according to the invention is shown in  FIG. 1  and generally denoted as  100 . The same reference numerals are used for similar parts, as indicated in  FIG. 2 . In  FIG. 1  however apparatus  100  is being employed before the cylindrical cutter (not shown) is used to provide a cylindrical portion  3  and the guide pin  5  is used in connection with the present invention. 
         [0035]    Apparatus  100  according to the invention comprises a support member  20  provided with means for location on the bone in the form of a prepared socket or bore  21  provided in a boss  22  which is dimensioned to be a close but sliding fit on the guide pin  5  which acts as a proximal/distal axis indicator. Thus guide pin  5  which was established on the guide wire provides a datum for setting up the apparatus. The support member  20  has an adjustable distance indicator in the form of a sliding pin  23  which is provided with distance indicating indicia  24 . Sliding pin  23  can be adjusted in relation to support member  20  and carries an operating knob  25  for this purpose. As will be seen from  FIG. 1  the distal end  26  of sliding pin  23  can be pushed into engagement with the medial surface  17  of the bone. 
         [0036]    Apparatus  100  also includes an extension  27  which can be adjusted to vary the effective proximal/distal length of the support member  20 . The extension  27  comprise an adjustable carrier  28  on which the sliding pin  23  is supported in a bore  29 . Carrier  28  is connected to the C-shaped support member  20  by a screw threaded shaft  30 . The proximal end  31  of the screw-threaded shaft  30  is rotatable in a screw-threaded bore  32  and the distal end of the shaft  30  is located in the carrier  28  but is free to rotate. The shaft has an enlarged knurled portion  33  to assist in rotating it. 
         [0037]    Rotation of the shaft  30  causes it to progress through the screw-threaded opening  32  so that the position of the carrier  28  relative to the support member  20  can be adjusted. 
         [0038]    The carrier  28  also has a location strut  36  which is rigidly secured thereto and extends from the carrier through an opening  37  in the support member  20  and can slide within opening  37 . An indicator fin  38  is provided on the support member  20  which aligns with indicia  39  provided on the location strut  36 . With this arrangement therefore the carrier  28  accurately located on the support member  20  so that its proximal/distal position can be adjusted. 
         [0039]    With this arrangement therefore, knowing the precise dimensions of the apparatus, it can be used to measure the distance from the predetermined position of a hole to be drilled in the head to measure the thickness of bone at the predetermined position. 
         [0040]    In most circumstances this apparatus will merely confirm that the thickness of bone is adequate but if it proves to be too small and therefore inadequate, then the surgeon will know that he cannot use the normal surgical technique to drill the holes and it may be necessary to use some different technique for applying the prosthetic insert. Thus the apparatus can prove valuable in overcoming the difficulty of knowing whether a particular technique can be used or not. If, for example, proximal epiphyseal replacement techniques surgery was intended and it was found that there was insufficient bone a different technique could be used whilst the bone was still undrilled. Initial drilling without previously measuring the bone thickness can do considerable damage to the head of the bone which could cause further difficulties if an alternative technique was subsequently to be employed. 
         [0041]      FIGS. 4 and 5  show an alternative construction and in which similar reference numerals are used to indicate similar parts of the bone. This apparatus can conveniently be used on a head which has been prepared as shown in  FIG. 2  but in this case the pin  5  need not be employed because the support member  40  is located on the bone by a collar  41 . The collar can be held in place by pointed screws (not shown) being passed through screw-threaded holes  42 . The collar also has a downwardly projecting pointer  43  which can be used to align collar  41  in the desire position. 
         [0042]    In this construction support member  40  has a series of three slots  45  (as shown in  FIG. 5 ) which are adapted to be a close sliding fit on co-operating connecting elements  46  which are in the form of a projecting lug  47  mounted on collar  41  which fits into the slots  45 . A spring loaded locking pin  48  is provide which can engage an enlarged opening  49  in the lug  47  to rigidly hold the support member  40  in position. As the slots  45  are arranged in a proximal/distal direction alternative use of the slots can effectively extend or contract the length of the support member  40  in relation to the collar  41 . 
         [0043]    The distal end of support member  40  carries a sliding pin  50  which is provided with indicia  51  and has an operating knob  52 . This sliding pin  50  operates in a similar manner to the sliding pin  23  in the construction shown in  FIG. 1 . 
         [0044]      FIGS. 6 ,  7 ,  8  and  9  show another alternative construction which can be used in place of that shown in  FIG. 1 . In  FIG. 6  the femur is indicated by broken lines and the same reference numerals are used to indicate similar parts as those shown in  FIG. 1 . The apparatus comprise a support member  60  provided with means for location on the bone in the form of a clamp  62  which is designed to engage and clamp on a guide wire  61 . 
         [0045]    The clamp  62  comprises a cylindrical portion  63  provided on the support member  60  and the distal end of which is provided with a claw-shaped portion  64  which has an inner curved surface  65  shaped to engage the guide wire  61 . The guide wire is held in place by a clamping sleeve  66  which is bifurcated to form a shaped slot  67  at its proximal end and a flat flange  68  at its distal end. 
         [0046]    The bore  69  of the clamping sleeve  66  is dimensioned to be a sliding fit on the cylindrical portion  63 . 
         [0047]    From  FIG. 7  it will be seen that the clamping sleeve  66  is assembled over the cylindrical portion  63  with a compression coil spring  70  which also fits over the cylindrical portion  63  and is located between the flange  68  on the clamping sleeve  66  and the end of an enlarged portion  72  of the support member  60 . In order to retain the clamping sleeve  66  in place a pin  75  is provided which is located in a hole  76  in the cylindrical portion  63 . The pin  75  is long enough to project from one side of the hole  76  and engage at that end in a slot  77  which extends through the wall of the clamping sleeve. As the slot  77  is elongated it acts to hold the sleeve  66  in place but allows sliding movement for the length of the slot between the parts. 
         [0048]      FIG. 9  shows how the shaped slot  67  in the clamping sleeve  66  extends around the claw  62  and, when a guide wire  61  is in place, acts to clamp it against the inner curved surface  65  the claw  62 . To release the wire  61  it is merely necessary to move the clamping sleeve  66  against the action  62  of the spring  70  along the cylindrical portion  63  so that the wire  61  can be withdrawn from the inner curved surface  65  of the claw  64 . Thus the guide wire  61  provides a datum for setting up the apparatus. 
         [0049]    The support member  60  has an adjustable distance indicating means similar to that shown in  FIG. 1  in that it includes a sliding pin  23  which is provided with distance indicating indicea  24 . The sliding pin  23  can be adjusted in relation to the support member  60  and carries an operating knob  25  for this purpose. As will be seen from  FIG. 6  the distal end  26  of the sliding pin  23  can be pushed into engagement with the surface  17  of the bone. 
         [0050]    The adjustable distance indicating means is connected to the support member  60  by extension means  80  which can be adjusted to vary the proximal/distal length of the support member  60 . These extension means comprise an adjustable carrier  81  on which the sliding pin  23  is supported in a bore  82 . The carrier  81  is connected to the support member  60  by passing through a slot  83 , best shown in  FIG. 7 . The carrier means  81  is in the form of a flat bar  81  and is provided with a series of linked openings  84 . The bar  81  can be locked in a number of proximal/distal positions by operation of a locking pin  85  which is assembled in a bore  86  in the enlarged portion  72  of the support member  60 . As will be seen from  FIG. 9  the pin passes through the bore  86  and extends on the far side where it is engaged by an operating button  87 . The button is screw threaded onto the end of the locking pin  85  and a compression spring  88  is located between the operating button  87  and the end of the bore  86  so that the button can be moved towards the bore thus causing the pin  85  to move with it and allow a waisted portion  89  of the pin to be aligned with the slot  72 . The dimensions of the waisted portion  89  of the pin are slightly less than the gaps  99  between the openings  84  in the flat bar  81  and this enables the bar to be moved lengthwise within the slot  72  to vary its operative length. The selected length can be clamped into position by releasing the operating button  86  to allow the locking pin  85  to move into its innermost position, as shown in  FIG. 9 , where an enlarged portion  101  of the locking pin  85  is engaged in one of the openings  84  of the bar  81  and thus holding it in position. 
         [0051]    Suitable indicea  103  is provided on the edge of the extension so that its precise length can be ascertained by the operator. 
         [0052]    The apparatus is operated in the same way as that described with regard to the apparatus shown in  FIG. 1 . 
         [0053]    The apparatus is not exclusively for use when carrying out proximal epiphyseal replacement technique surgery but can be used in many other operations in which a hole has to be drilled into a bone and where it is desirable to know the bone thickness between the end of the hole and the surface of the bone. 
         [0054]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.