Patent Publication Number: US-2007100346-A1

Title: Support for locating instrument guides

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      Cross-reference is made to the following applications: DEP5597USNP titled, “METHOD OF RESECTING BONE” filed concurrently herewith which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      The present invention relates to surgical instruments used to prepare a bone to receive a prosthetic implant, and more particularly, to such an instrument system used in conjunction with computer assisted surgery.  
      When a skeletal joint is damaged, whether as a result of an accident or illness, a prosthetic replacement of the damaged joint may be necessary to relieve pain and to restore normal use to the joint. Typically the entire joint is replaced by means of a surgical procedure that involves removal of the ends of the corresponding damaged bones and replacement of these ends with prosthetic implants. This replacement of a native joint with a prosthetic joint is referred to as a primary total-joint arthroplasty.  
      The surgical preparation of the bones during primary total-joint arthroplasty is a complex procedure. A number of bone cuts are made to effect the appropriate placement and orientation of the prosthetic components on the bones. In total knee arthroplasty, the joint gaps in extension and flexion must also be appropriate.  
      In the case of total knee arthroplasty, cutting guide blocks are used in creating the bone cuts on the proximal tibia and distal femur. The position, alignment and orientation of the cutting blocks are important in ensuring that the bone cuts will result in optimal performance of the prosthetic implant components. Generally, a tibial cutting block is positioned, aligned and oriented so that the cutting guide surface is in the optimal proximal-distal position, posterior slope, and varus-valgus orientation. Depending on the type of prosthetic implant system to be used, one or more cutting blocks are also positioned, aligned and oriented on the distal femur to ensure appropriate positioning of the distal femoral implant component and appropriate joint gaps.  
      A variety of alignment guides and cutting blocks have been provided in the prior art for use in preparing bone surfaces in primary total-knee arthroplasty, including alignment guides and cutting blocks used in preparing the proximal tibia and distal femur.  
      Prior art instrument sets with alignment guides include the Specialist® 2 instruments (DePuy Orthopaedics, Inc., Warsaw, Ind.) for use with DePuy Orthopaedics&#39; P.F.C.® Sigma Knee System. The extramedullary tibial alignment guide for this instrument system includes an ankle clamp, a pair of telescoping alignment rods and a cutting block. The ankle clamp is affixed about the patient&#39;s ankle, without extending through the patient&#39;s soft tissue. Parts of this system are manually adjustable: the proximal-distal position of the cutting block is adjusted by sliding the telescoping rods and then locking the rods in the desired position; posterior slope is set at the ankle by sliding the distal end of the alignment rod in an anterior-posterior direction to thereby pivot the cutting block into the desired orientation; varus-valgus slope is set by pivoting the cutting block so that the alignment guide pivots about a rod at the ankle clamp.  
      U.S. Pat. No. 6,090,114 discloses a tibial plateau resection guide. This system also uses an ankle clamp and extension rods to set the position and orientation of the cutting block. U.S. Pat. No. 5,451,228 also utilizes an ankle clamp but allows for angular orientation in the anterior-posterior plane to predetermined angular orientations using a thumb actuated slide mechanism; the device is however limited to predetermined angular settings. U.S. Pat. Nos. 6,685,711 and 6,595,997 disclose an apparatus and method for resecting bone that provides for aligning a resection guide in three degrees of freedom.  
     SUMMARY OF THE INVENTION  
      The present invention provides a surgical instrument system that can be used to efficiently and accurately set the position, alignment and orientation of cutting blocks and other surgical instruments.  
      In one aspect, the present invention meets these objectives by providing a surgical instrument system for resecting a bone during joint arthroplasty. The system comprises a cutting instrument, an anchoring structure, a guide structure and an articulating linkage. The guide structure guides the path of the cutting instrument. The articulating linkage connects the anchoring structure to the guide structure, and includes a plurality of lockable ball joints arranged in series. Each ball joint provides for freedom of movement about three axes of rotation.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be better understood by reference to the figures of the drawings wherein like numbers denote like parts throughout and wherein:  
       FIG. 1  is a perspective view of a first embodiment of a surgical instrument system embodying the principles of the present invention, shown mounted to a patient&#39;s femur;  
       FIG. 1A  is a plan view of an example of a surgical instrument that may be used with the system illustrated in  FIG. 1 ;  
       FIG. 2  is an end view of an embodiment of an anchoring structure that may be used in the present invention, the anchoring structure being shown mounted to a patient&#39;s femur;  
       FIG. 3  is an elevation, from the lateral side of the bone, of the anchoring structure of  FIG. 2 ;  
       FIG. 4  is a top plan view, from the anterior side of the bone, of the anchoring structure of  FIGS. 2-3 ;  
       FIG. 4A  is an elevation of the pin-clamping half of one of the anchoring clamp assemblies of the anchoring structure;  
       FIG. 4B  is an elevation of the bar-clamping half of one of the anchoring clamp assemblies of the anchoring structure;  
       FIG. 5  is an elevation of the movable clamp assembly and bi-axial articulating assembly of the system of  FIG. 1 , taken from a proximal or distal side;  
       FIG. 6  is an exploded elevational view of the movable clamp assembly and bi-axial articulating assembly of  FIG. 5 ;  
       FIG. 7  is an exploded perspective view of the movable clamp assembly and bi-axial articulating assembly of  FIGS. 5-6 ;  
       FIG. 8  is an elevation of the movable clamp assembly and bi-axial articulating assembly of  FIGS. 5-7 , taken from a medial or lateral side;  
       FIG. 9  is a top plan view of the movable clamp assembly and bi-axial articulating assembly of  FIGS. 5-8 ;  
       FIG. 9A  is an exploded elevational view of an alternative embodiment of a movable clamp assembly and bi-axial articulating assembly that may be used in the instrument system of the present invention;  
       FIG. 9B  is an exploded perspective view of the movable clamp assembly and bi-axial articulating assembly of  FIG. 9A ;  
       FIG. 10  is a top plan view of a housing and articulating ball joints of the articulating linkage of the system of  FIG. 1 ;  
       FIG. 11  is a view similar to  FIG. 10 , with the housing shown in cross-section and with the ball joints shown in one unlocked position;  
       FIG. 12  is a cross-section taken along line  12 - 12  of  FIG. 10 ;  
       FIG. 13  is a view similar to  FIG. 11 , shown with the ball joints in a second unlocked position;  
       FIG. 14  is a view similar to  FIGS. 11 and 13 , shown with the ball joints locked in a selected position;  
       FIG. 15  is an end view of the housing and first ball joint in the locked position of the  FIG. 14 ;  
       FIG. 16  is an elevation of the guide structure of the embodiment of  FIG. 1  shown mounted on a first fully articulatable arm;  
       FIG. 17  is an end view of the guide structure and first fully articulatable arm of  FIG. 16 , taken along line  17 - 17  of  FIG. 16 ;  
       FIG. 18  is a cross-section of the guide structure and first fully articulatable arm of  FIGS. 16-17 , taken along line  18 - 18  of  FIG. 16 , shown with cam in a locked position to fix the position of the guide structure on the first fully articulatable arm;  
       FIG. 19  is a cross-section similar to  FIG. 18 , shown with the cam in a locked position to allow translational movement of the guide structure on the first fully articulatable arm;  
       FIG. 20  is an end view of the first fully articulatable arm;  
       FIG. 21  is an exploded view of the guide structure, cam and first fully articulatable arm of  FIGS. 16-19 ;  
      FIG. 22  is an exploded perspective view of the guide structure of  FIGS. 16-19  and  21 ;  
       FIG. 23  is an elevation of alternative embodiment of an intermediate member for use as part of an articulating linkage, shown with the fully articulatable rod in an extended position;  
       FIG. 24  is a view of the alternative intermediate member of  FIG. 23 , shown with the fully articulatable rod in a retracted position;  
       FIG. 25  is a perspective view of the alternative intermediate member of  FIGS. 23-24 ;  
       FIG. 26  is an end view of the alternative intermediate member of  FIGS. 23-25 ;  
       FIG. 27  is a view of the alternative intermediate member of  FIGS. 23-26  with the body of the alternative intermediate member shown in longitudinal cross-section;  
       FIG. 28  is a transverse cross-section of the alternative intermediate member of  FIGS. 23-26 , shown with the handle in an unlocked position;  
       FIG. 29  is a transverse cross-section similar to  FIG. 28 , shown with the handle in a locked position;  
       FIG. 30  is an elevation of a portion of one of the curved interior side walls of the alternative intermediate member of  FIGS. 23-28 ;  
       FIG. 31  is a top plan view of a portion of the fully articulatable arm used in combination with the alternative intermediate member of  FIGS. 23-28 ;  
       FIG. 32  is a side elevation of the fully articulatable arm of  FIG. 31 ;  
       FIG. 33A  is a top plan view of an alternative embodiment of a housing and locking mechanism for the ball joints of the articulating linkage;  
       FIG. 33B  is a cross-section through the housing of the embodiment of  FIG. 33A , with the ball joints shown in an unlocked position;  
       FIG. 34  is an anterior view of a femur and an alternative embodiment of the instrument system of the present invention, shown with a jointed intermediate link in the articulating linkage, and shown with a guide track used as a guide structure to guide the path of an alternative cutting instrument;  
       FIG. 35  is a schematic view of an embodiment of the instrument system of the present invention used to position and orient a distal femoral cutting block;  
       FIG. 36  is a schematic view of an embodiment of the instrument system of the present invention in combination with computer navigation trackers used to position and orient a proximal tibial cutting block;  
       FIG. 37  is a schematic view of the instrument system of  FIG. 36 , shown with a distal femoral cutting block attached to the articulating linkage, illustrating that the instrument system can be used to position and orient a number of cutting blocks during a single procedure without changing the position of the anchoring structure;  
       FIG. 38  is a schematic anterior view of the distal tibia, shown with an embodiment of the instrument system of the present invention used to position and orient a cutting block for use in ankle arthroplasty; and  
       FIG. 39  is a schematic view anterior view of a proximal femur, shown with an embodiment of the instrument system of the present invention used to position and orient a cutting block for use in hip arthroplasty. 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS  
      A first embodiment of an instrument system illustrating the principles of the present invention is illustrated at  10  in  FIGS. 1-22 . The first illustrated instrument system  10  comprises three main parts: an anchoring structure  12  that is mounted to a reference such as a bone shown at  17  in  FIG. 1 ; an articulating linkage  14  that is connected to the anchoring structure  12 ; and a guide structure  16  that is connected to the articulating linkage. With this instrument set, the surgeon can rigidly fix the anchoring structure  12  to one of the patient&#39;s bones, move the guide structure  16  into a desired position and then lock the articulating linkage  14  to hold the guide structure  16  in the desired position. The guide structure  16  may then be fixed to the bone  17  or to a neighboring bone such as tibia  19  with fixation pins or the like if desired. The guide structure  16  may then be used to guide the path of a surgical instrument, such as a reciprocating saw shown at  21  in  FIG. 1A , a milling device, a burr or a drill, for example.  
      As discussed in more detail below, the articulating linkage  14  includes a plurality of lockable ball joints arranged in series. Each ball joint provides for freedom of movement about three axes of rotation. Once the desired orientation of the guide structure is achieved, each ball joint can be locked to set the position, alignment and orientation of the guide structure. The articulating linkage provides for substantial freedom of movement of the guide structure  16  for efficient and accurate placement of the guide structure intraoperatively.  
      As discussed in more detail below, each structure  12 ,  14 ,  16  of the instrument set may comprise assemblies of elements. For example, in the first illustrated embodiment, the anchoring structure  12  comprises an assembly of a plurality of pins  18 ,  20 , an anchoring bar  22 , and a pair of anchoring clamp assemblies  24 ,  26  for fixing the anchoring bar  22  to the pins  18 ,  20  (see  FIGS. 1-4 ). The articulating linkage  14  of the first illustrated instrument system  10  includes a movable clamp assembly  28 , a bi-axial assembly  30  and a multi-axial assembly  32 . The multi-axial assembly  32  comprises a plurality of lockable ball joints  176 ,  217  arranged in series. Each ball joint provides for freedom of movement about at least three axes of rotation. All of the movable elements  28 ,  30 ,  32  of the first illustrated instrument system  10  can be locked to thereby fix the position, alignment and orientation of the guide structure  16 . The guide structure  16  can itself comprise an assembly as well. Each of the illustrated assemblies of elements is described in more detail below.  
      It should be understood that the anchoring structure  12 , articulating linkage  14  and guide structure  16  may comprise fewer or more elements than those described below. In addition, as described in more detail below, some of these structures could be constructed as unitary components, rather than as assemblies of components.  
      First considering the elements of the anchoring structure  12  of the first illustrated instrument system  10 , the pins  18 ,  20  may comprise standard surgical pins or wires used in orthopaedic surgery. The pins  18 ,  20  may be made of any standard surgical grade material such as stainless steel, and should have sufficient size and strength to support the weight of the articulating linkage  14  of the instrument system as well as the guide structure  16  of the instrument set. For example, it is anticipated that stainless steel pins having a diameter of 5 mm. and an overall length of 20 cm. and with pointed ends should be usable with the present invention. It should be understood that these materials and dimensions are provided as examples only; the present invention is not limited to any particular material or dimension unless expressly set forth in the claims.  
      The anchoring bar  22  of the anchoring structure  12  of the first illustrated instrument system  10  comprises a rod of any suitable surgical grade material, such as stainless steel. The bar  22  may be made of a material that can be sterilized by commercially available sterilization techniques without losing its strength. It may be desirable to make the anchoring bar out of a material that is radiolucent or radiotransparent so that radiographs may be taken intraoperatively without interference from the components of the anchoring structure  12 . To decrease the overall weight of the system, it may be desirable to make the anchoring bar  22  out of a hollow tubular material such as stainless steel or out of a lightweight plastic material. For use in knee arthroplasty, the anchoring bar  22  may have a length of about 30 cm. and a diameter of about 18 mm., for example. The illustrated anchoring bar  22  is cylindrical in shape. It should be understood that these materials, dimensions and shape are provided as examples only; the present invention is not limited to any particular material, shape or dimension unless expressly set forth in the claims.  
      The anchoring bar  22  of the anchoring structure  12  of the first illustrated instrument system  10  is connected to the two pins  18 ,  20  through the two anchoring clamp assemblies  24 ,  26 . Each of the illustrated anchoring clamp assemblies  24 ,  26  are the same; one of these clamp assemblies  24  is described below, and it should be understood that the description applies to both illustrated anchoring clamp assemblies  24 ,  26 .  
      As shown in  FIGS. 1-4 , anchoring clamp assembly  24  comprises a pin-clamping half  34  and a bar-clamping half  36 . As shown in  FIG. 4 , the pin-clamping half  34  of the clamp assembly  24  includes a bridge section  38  with integral spaced legs  40 ,  42 . The bridge section  38  has a reduced thickness in the illustrated embodiment, allowing the spaced legs  40 ,  42  to flex for clamping the pins or wires. The spaced legs  40 ,  42  include parallel semi-cylindrical grooves  44 ,  46  sized and shaped to receive a portion of one of the pins  18 ,  20  longitudinally.  
      As shown in  FIGS. 4 and 4 A, one of the spaced legs  40  in the illustrated pin-clamping half  34  of the anchoring clamp assembly  24  includes a plurality of teeth  48  extending radially outward from a stub  50  with a fastening hole  52  for fastening the pin-clamping half to the bar-clamping half  36 . The pin-clamping half  34  of the anchoring clamp assembly  24  may be fastened to the bar-clamping half  36  with a bolt, such as that shown at  53  in  FIGS. 2-4 .  
      As shown in  FIG. 2 , the bar-clamping half  36  of the illustrated anchoring clamp assembly  24  includes a body  60  with a pair of spaced legs  62 ,  64 . The body  60  has a substantially cylindrical groove  66  sized and shaped to receive a segment of the anchoring bar  22 . The spaced legs  62 ,  64  include co-axial bores to receive a bolt  65  to tighten and loosen the legs  62 ,  64  about the anchoring bar  22 .  
      As shown in  FIGS. 4 and 4 B, one surface of the illustrated body  60  has a fixed circular portion  66 . The fixed circular portion  66  includes a plurality of teeth  68  extending radially outward from a stub  70  with a fastening hole  72  for fastening the bar-clamping half  36  to the pin-clamping half  34 . To fasten the two halves  34 ,  36  together, the stub of one of the halves (such as stub  70  of half  36 ) may be received in the hole of the other half (such as hole  52  in half  34 ); the teeth  48  and  68  will mesh together, and the two halves  34 ,  36  can be locked together with the bolt  53 . The intermeshed teeth  48 ,  68  will prevent relative rotation between the two halves  34 ,  36 .  
      Although the illustrated embodiments of anchoring structures  12  are for mounting directly to the patient&#39;s bone, it should be understood that the articulating linkage  14  and guide structure  16  described below may be used with other types of anchoring structures. For example, the articulating linkage  14  described below could be used with a commercially available ankle clamp, in which case a suitable connection between the ankle clamp and the articulating linkage  14  should be provided, allowing for relative movement between the articulating linkage  14  and the anchoring structure  12 . Anchoring the articulating linkage  14  and guide structure  16  to the patient&#39;s limb (e.g. leg) is advantageous in that if the patient&#39;s limb moves during the procedure, the positions of the articulating linkage  14  and guide structure  16  relative to the limb remain fixed. However, in some applications, other devices or fixtures could be used as the anchoring structure. For example the anchoring structure could comprise a portion of an operating room table or other fixture in the operating room when the system  10  is used in conjunction with computer assisted surgery.  
      Next considering the elements of the articulating linkage  14  of the first illustrated instrument system  10 , the movable clamp assembly  28  is mounted on the anchoring bar  22 . As indicated by arrows  100 ,  102  in  FIG. 1 , the illustrated movable clamp assembly  28  can be moved linearly along the longitudinal axis  103  of the anchoring bar  22  to a desired translational position and then fixed in the desired translational position along the length of the anchoring bar  22 . The illustrated movable clamp assembly  28  can also be rotated about the longitudinal axis  103  of the anchoring bar  22 , as indicated by arrows  104 ,  106  to a desired rotational position along the anchoring bar  22  and then fixed in the desired rotational position. Generally, the illustrated movable clamp assembly  28  can be fixed in the desired translational and rotational positions simultaneously.  
      As shown in  FIGS. 5-7 , the illustrated movable clamp assembly  28  comprises a pair of spaced arms  108 ,  110  joined by a bridge section  112 . The spaced arms  108 ,  110  substantially surround a portion of the anchoring bar  22 . The spaced arms  108 ,  110  can be tightened around the bar  22  to fix the clamp assembly&#39;s linear and rotational positions by tightening bolt  114 .  
      The spaced arms  108 ,  110  of the movable clamp assembly  28  and a portion of the bridge section  112  have a substantially cylindrical cut-out  116  having a diameter substantially the same as the diameter of the anchoring bar  22  for receiving the anchoring bar. The ends of the spaced arms  108 ,  110  have co-axial bores  109 ,  111  (shown in phantom in  FIG. 5 ) to receive the bolt  114  to move the arms  108 ,  110  closer together to lock the arms on the anchoring bar  22 .  
      As shown in  FIGS. 5-9 , the movable clamp assembly  28  is mounted to the bi-axial articulating assembly  30 . The bi-axial articulating assembly  30  includes a ring  118  positioned upon a flat circular surface  119  of the bridge section  112  of the movable clamp assembly  28 . As shown in  FIG. 7 , the ring  118  includes a radial slot  120  and a central longitudinal bore  121 . As shown in  FIG. 6 , the ring  118  also includes a transverse bore  122  intersecting the radial slot  120 .  
      The radial slot  120  of the ring  118  receives a disc-shaped portion  124  of a pivotable arm  126 . The pivotable arm  126  is mounted to the ring  118  through a transverse pin  127  extending through the transverse bore  122  of the ring  118  and through a bore  128  (see  FIG. 6 ) in the center of the disc-shaped portion  124  of the pivotable arm  126 . The pivotable arm  126  can be pivoted or rotated on the pin in the directions shown by arrows  130 ,  132  in  FIG. 6  until a desired position is reached and then locked in the desired position.  
      To lock the pivotable arm  126  in the desired position, the bi-axial articulating assembly  30  includes a locking plate  134 . The locking plate  134  includes a handle portion  136 , a flat surface  138  and an extension  140 . The extension  140  is partially threaded, and extends through co-axial central longitudinal bores  121 ,  123  in the ring  118  and bridge section  112 . The bore  123  of the bridge section is also threaded. When assembled, the extension  140  extends through the central bore  121  of the ring  118  and is received in and threadedly engages the bore  123  in the bridge section  112 . When the locking plate  134  is loose, the ring  118  is free to rotate about the central longitudinal axis of the extension  140 . To lock the movable arm  126  in a desired position, the handle portion  136  of the locking plate  134  is turned so that the flat surface  138  of the locking plate  134  bears against the ring  118  and disc-shaped portion  124  of the pivotable arm  126  to lock them in position.  
      Thus, there are two rotational degrees of freedom of movement of the pivotable arm  126  with respect to the movable clamp  28 : the pivotable arm  126  is rotatable about the transverse pin  127  and rotatable about the extension  140  to a desired position. Once the desired position is reached, the pivotable arm  126  can be locked in position with respect to the movable clamp assembly  28  by turning the locking plate  134 . And since the movable clamp assembly  28  has two degrees of freedom of movement with respect to the stationary bar  22  (one rotational and one translational), the pivotable arm  126  has four degrees of freedom of movement with respect to the stationary bar  22  (and the bone  17  to which the stationary bar is fixed): three rotational and one translational.  
      It should be understood that the design of a suitable bi-axial articulating subassembly and moveable clamp subassembly may vary from that illustrated in  FIGS. 1 and 5 - 9 . For example, an alternative bi-axial articulating subassembly  30 A is shown in  FIGS. 9A-9B  at  30 A. In this example, an additional disc  129  may be inserted between the ring  118  and the flat top surface  119  of the bridge section  112  of the movable clamp assembly  28 . Otherwise, the elements of the embodiment of  FIGS. 9A-9B  are the same as those in  FIGS. 5-9 , as indicated by the use of common reference numbers.  
      The clamp assemblies  24 ,  26 , movable clamp assembly  28  and bi-axial articulating assembly  30  may be made out of any standard surgical grade material. For example, a metal such as stainless steel could be used. If desired, some components of each assembly, or the entire assembly, could be made of other materials, such as a surgical grade plastic or composite material, such as carbon fiber material. They should preferably be made of a material that can be sterilized by conventional sterilization methods and that will retain their stiffness under the weight of the articulating linkage and guide structure during use. It may be desirable to make some or all of the components of the assemblies  24 ,  26 ,  28  out of a material that is radio-transparent or radio-lucent so that the assemblies do not block relevant portions of the patient&#39;s anatomy intra-operatively when radiographs are taken. To reduce the weight of the instrument set, some or all of the components of the assemblies  24 ,  26 ,  28  may be made of a lightweight material such as a carbon fiber-polymer composite.  
      As shown in  FIGS. 5-9 , the pivotable arm  126  of the bi-axial articulating assembly has a bar portion  150  that extends outward from the annular disc portion  124 . In the illustrated embodiment, the bar portion  150  comprises two segments  152 ,  154  meeting at an obtuse angle. It should be understood that the shape of the bar portion  150  is provided by way of example only; the bar portion  150  could be curved or straight or could include addition linear segments meeting at a variety of angles.  
      As shown in  FIGS. 5-6  and  8 , the end of the bar portion  150  of the pivotable arm  126  opposite the annular disc portion  124  extends through a cylindrical sleeve portion  156  of a connector  158  to mount the pivotable arm  126  to the connector  158 . The connector  158  includes an enlarged diameter portion  160  with a cylindrical flange. The cylindrical flange encircles one end of an intermediate link  162  to fix the connector  158  to the intermediate link  162 . Thus, the connector  158  serves to connect one end of the pivotable arm  126  to one end of the intermediate link  162 . This connection is a fixed one in the first illustrated embodiment; there is no relative linear or rotational movement between the pivotable arm  126  and the intermediate link  162  so that rotational and translational movement of the pivotable arm  126  results in rotation and translation of the intermediate link  162  as well.  
      Although the present invention is not limited to any particular size of intermediate link, for use in knee replacement surgery, it may be desirable to use an intermediate link  162  having a length of about 5.5 inches and an outer diameter of about 0.75 inches. The intermediate link  162  of the first illustrated embodiment may comprise a solid bar or a hollow tube, for example. As discussed in more detail below, alternative designs for the intermediate link may be used.  
      The intermediate link  162  and connector  158  may be made of any commercially available surgical grade material, such as metal, plastic or composite material such as a carbon fiber material. They should preferably be made of a material that can be sterilized by conventional sterilization methods and that will retain their stiffness under the weight of the articulating linkage and guide structure during use. It may be desirable to make the intermediate link  162  and connector  158  out of a material that is radio-transparent or radio-lucent so that the intermediate link would not block relevant portions of the patient&#39;s anatomy intra-operatively when radiographs are taken. To reduce the weight of the instrument set, the intermediate link  162  and connector  158  may be made of a lightweight material such as a carbon fiber-polymer composite.  
      The opposite end of the intermediate link  162  is attached to a second connector  164 , similar in structure and material to the first connector  158  described above. The second connector  164  includes a cylindrical sleeve portion  166 . that receives a free end of a first fully articulatable arm  168  to mount the first fully articulatable arm  168  to the second connector  164 . This mounting is a fixed one so that rotational or translational movement of the pivotable arm  126  results in the same rotational or translational movement of the first fully articulatable arm  168 .  
      The illustrated first fully articulatable arm  168  of the first embodiment comprises a bar or tube portion  170  that has two segments meeting at an obtuse angle. It should be understood that the bar or tube portion may have other shapes as well; it may be straight, curved, or may comprise a combination of shapes.  
      Opposite the end received in the connector  164 , the first fully articulatable arm  168  has a spherically-shaped portion  172 . The spherically-shaped portion  172  of the arm  168  is received in a housing  174  to define a first articulating ball joint  176 . The reference to arm  168  as being fully articulatable refers to the fact that the ball joint  176  allows for rotation of the arm  168  about at least three different axes.  
      The housing  174  in the illustrated embodiment includes a body  178  and a first end cap  180 . The illustrated body  178  includes a generally cylindrical outer periphery  182  and an inner longitudinal bore  184 . The bore  184  may be concentric with the outer periphery  182 . The first end cap  180  may have any suitable shape capable of containing the spherically-shaped portion  172  of the first fully articulatable arm  168  while allowing a desired range of relative rotational motion between the housing  174  and the first articulatable arm  168 .  
      As shown in  FIG. 11 , the first end cap  180  includes a concave inner periphery  186  for cooperation with the spherically-shaped portion  172  of the first fully articulatable arm  168 . The first end cap  180  further defines an opening  188  through which a part of the first fully articulatable arm  168  extends. The opening  188  in the illustrated embodiment is circular, with a diameter slightly less than the diameter of the spherically-shaped portion  172  of the first fully articulatable arm  168  so that the first fully articulatable arm  168  is held within the housing  174  while being allowed a substantial range of motion.  
      The illustrated first end cap  180  further includes a body opening  190  for receiving an end  192  of the body  178  of the housing  174 . The first end cap  180  and body  178  may be secured together in any suitable way, for example, by a series of pins, a groove and lip, or, as shown in  FIG. 11 , by internal threads  194  formed on the first end cap  180  adjacent the body opening  190 . The internal threads  194  of the first end cap  180  matingly engage external threads  196  formed on a first hub  198  of the body  178 .  
      In the illustrated embodiment, the housing  174  also includes a second end cap  200 . The second end cap  200  is similar to the first end cap  180  and includes a concave inner periphery  202  for cooperation with a spherically-shaped portion  204  of a second fully articulatable arm  206 . The second cap  200  also has an opening  208  through which a rod or tube portion  210  of the second fully articulatable arm  206  extends. The inner periphery of the illustrated second cap  200  includes internal threads  212  that mate with external threads  214  formed on a second hub  216  of the body  178  of the housing  174 . The spherically-shaped portion  204  of the second fully articulatable arm  206  and the housing  174  define a second multi-axial ball joint  217 .  
      As illustrated in  FIG. 1 , the second fully articulatable arm  206  includes an end  218  opposite the spherically shaped end  204 . As shown in  FIG. 20 , between the two ends  218 ,  204 , the illustrated second fully articulatable arm  206  includes at least one flat surface  220  along a substantial part of its length; in the illustrated embodiment, the end segment  218  of the second fully articulatable arm has three flat surfaces. A portion of the second fully articulatable arm that has such flat surfaces  220  is received in a similarly-shaped bore  224  in the guide structure  16  (see  FIGS. 16-19 ).  
      As shown in  FIG. 1 , the housing  174  also carries an actuator  226  for locking and unlocking the ball joints  176 ,  217 . In the illustrated embodiment, a single actuator  226  is capable of simultaneously locking and unlocking the two ball joints  176 ,  217  through action upon a pair of movable pistons held within the body  178  of the housing  174 .  
      In the first illustrated instrument, the body  178  of the housing  174  includes a transverse opening  228  through which a shaft  230  of the actuator  226  is rotatably fitted. Preferably, to accommodate component tolerances and the resultant tolerance stack of the components of the ball joints  176 ,  217 , the transverse opening  228  may be sized to provide additional clearance between the transverse opening  228  and the shaft  230 . The clearance accommodates the tolerances to that the shaft is not limited in its motion axially to the body.  
      For example, and as shown in  FIG. 10 , the body transverse opening  228  may be oval and defined by an opening length L that is substantially greater than the opening width W. The opening length L is made sufficiently larger than the diameter D of the shaft  230  so that the shaft does not impinge upon the body  178 .  
      The actuator  226  in the first illustrated embodiment further includes a handle  232  and a force-transferring feature. The handle  232  is provided for turning the shaft  230  for locking and releasing the two ball joints  176 ,  217 . The force-transferring feature is provided for translating the turning of the shaft  230  into a force acting to limit movement of the first and second fully articulatable arms  168 ,  206 .  
      As shown in  FIGS. 11 and 13 - 14 , the force-transferring feature in the first illustrated embodiment comprises a cam  234  and a pair of pistons  236 ,  238  held within the housing  174 . The cam  234  controls the movement and position of the two pistons  236 ,  238  within the housing  174 . For example, as shown in  FIGS. 11 and 13 , when the cam  234  is in an unlocked position, the cam  234  does not contact the pistons  236 ,  238 ; the pistons  236 ,  238  are slightly spaced from the spherically-shaped end portions  172 ,  204  of the fully articulatable arms  168 ,  206 , and the arms  168 ,  206  can be rotated about multiple axes to multiple rotational positions, as can be seen, for example, by comparing the positions of the tube portions  170 ,  210  of the fully articulatable arms  168 ,  206 . As the shaft  230  is rotated about its central longitudinal axis, the cam  234  is turned from the position shown in  FIGS. 11 and 13  to the position shown in  FIG. 14 . As the cam  234  turns, it advances the two pistons  236 ,  238  in opposite directions toward the spherically-shaped portions  172 ,  204 . In particular, the first piston  236  advances from a first position (shown in  FIGS. 11 and 13 ) to a second position (shown in  FIG. 14 ). Similarly the second piston  238  advances from a first position (shown in  FIGS. 11 and 13 ) to a second position (shown in  FIG. 14 ).  
      When the first piston  236  and the second piston  238  are in their second positions shown in  FIG. 14 , an outer face of the first piston  236  engages the spherically-shaped portion  204  of the second fully articulatable arm  206  and an outer face of the second piston  238  simultaneously engages the spherically-shaped portion  172  of the first fully articulatable arm  168 , thereby simultaneously locking the first and second fully articulatable arms  168 ,  206  in position. Thus, the first illustrated instrument provides for simultaneous locking of the first fully articulatable arm  168  and second fully articulatable arm  206  with respect to the body  178  by actuation of a single actuator  226 .  
      The outer faces of the pistons  236 ,  238  may have, for example, concave surfaces to mate with the spherically-shaped portions  172 ,  204  of the fully articulatable arms  168 ,  206 . The concave surfaces provide for increased contact and superior locking of the fully articulatable arms.  
      The interior of the housing  174  may include features such as ribs  240  to guide or constrain movement of the pistons  236 ,  238  along desired translational paths.  
      It should be appreciated that the housing  174  may restrain movement of the first and second fully articulatable arms  168 ,  206 . For example, the size and shape of the openings  188 ,  208  in the end caps  180 ,  200  will to some extent define the range of rotational motion for the respective fully articulatable arms. The edges of the end caps defining the openings could also include a plurality of indentations sized and shaped to receive a portion of the fully articutable arm to define a plurality of preset positions for the fully articulatable arm. It should also be appreciated that the ball joints  176 ,  217  may, for simplicity, include restraining features in addition to the housing  174 .  
      It should be understood that instead of a single housing and single actuator for the two articulating ball joints  176 ,  217 , the articulating linkage  14  of the present invention could comprise two separate ball joints with separate actuators for locking the joints in desired positions and for unlocking the ball joints to allow full freedom of motion. Use of a single actuator for two articulating ball joints is advantageous in simplifying the locking procedure for the surgeon during placement of the resection guide.  
      All of the components defining the two ball joints  176 ,  217  may be made of any commercially available surgical grade material, such as metal, plastic or composite material such as a carbon fiber material. They should preferably be made of a material that can be sterilized by conventional sterilization methods and that will retain their stiffness under the weight of the articulating linkage and guide structure during use. It may be desirable to make the components out of a material that is radio-transparent or radio-lucent so that the components would not block relevant portions of the patient&#39;s anatomy intra-operatively when radiographs are taken. To reduce the weight of the instrument set, the components may be made of a lightweight material such as a carbon fiber-polymer composite.  
      Other embodiments of suitable dual-locking ball joints are disclosed in the following United States patent applications, filed concurrently herewith: Docket No. DEP5368USNP entitled “TRAUMA JOINT, EXTERNAL FIXATOR AND ASSOCIATED METHOD”; Docket No. DEP 5558 USNP entitled “ORTHOPAEDIC INSTRUMENT JOINT, INSTRUMENT AND ASSOCIATED METHOD”; and Docket No. DEP5559USNP entitled “ORTHOPAEDIC JOINT, DEVICE AND ASSOCIATED METHOD”. The complete disclosures of these patent applications are incorporated by reference herein.  
      For example, as shown in  FIGS. 33A and 33B , a ratchet and lever mechanism could be used in place of the cam structure  234  of  FIGS. 10-15  to lock the two ball joints. In  FIG. 33 , the ball joints are designated  176 A and  217 A and the actuator mechanism is designated  226 A.  
      In  FIGS. 33A and 33B , parts similar to those of the embodiment of  FIGS. 10-15  are identified with the same reference numbers; except as otherwise noted, the description of these like parts should be considered applicable to both embodiments. In the embodiment of  FIGS. 33A and 33B , the actuator  226 A includes a ratchet  242 , which is connected by first lever  244  to a first piston  246  and by second lever  248  to second piston  250 . A pawl  252  is pivotably connected to body  254  portion of the housing assembly  255 . Teeth  256  formed on the ratchet  242  engage the pawl  252 .  
      As the pawl  252  is advanced the actuator  226  is released, permitting the spherical ends  172 ,  204  of the fully articulatable arms  168 ,  206  to move freely. Extending from the ratchet  242  is a handle  253  that may be rotated to actuate or lock the ball joints  176 A,  217 A. By rotating the handle  253  the ball joints  176 A,  217 A may be locked simultaneously.  
      The lever arms  244 ,  248 , pistons  246 ,  250 , and the ratchet  242  are received within a cavity  260  of the body  254  of the housing assembly  255 . The cavity  260  of the body  254  may, for example, have a generally rectangular or square shape. Such a shape makes possible or eases the use of the actuator  226 A that includes the ratchet  242 . The pistons  246 ,  250  can move in the directions of arrows  261 ,  263  constrained by the surfaces defining the cavity  260 . The housing assembly  255  also includes end caps  262 ,  264  mounted to threaded stubs  266 ,  268  at each end of the central body  254 . The end caps  262 ,  264  have openings sized and shaped so that the spherical ends  172 ,  204  of the arms  168 ,  206  are constrained to be held within the housing but are able to articulate about multiple axes.  
      The cavity  260  and pistons  246 ,  250  of the embodiment of  FIGS. 33A and 33B  have generally rectangular shapes. The pistons  246 ,  250  are slidably fitted in the cavity  260 . The ratchet  242  may be positioned in the cavity  260  and may include a portion, which extends beyond the cavity. For example, the pawl  252  may extend outside the body  254  so that the pawl  252  may be actuated or released and so that the handle  253  may be actuated for locking the ball joints  176 A,  217 A.  
      Other variations in the illustrated dual locking ball joint assemblies can be made. For example, instead of the end caps threading onto stubs on the body of the housing assembly, other mechanical locking mechanisms can be used, such as a mating lip and groove.  
      Next considering the elements of the guide structure  16  of the first illustrated instrument system  10 , the guide structure in the first illustrated embodiment comprises a proximal tibial cutting block sized and shaped to be used in resecting the tibial plateau on either the lateral or medial side of the tibia. It should be understood that the present invention is not limited to instruments including proximal tibial cutting blocks; the guide structure  16  could, for example, comprise a distal femoral cutting block. If the instrument is to be used for resecting the bones of other joints, the guide structure could comprise, for example, a proximal femoral cutting guide, a humeral cutting guide or an ankle cutting guide. The guide structure  16  could also comprise a drill or reaming guide for guiding a reamer or drill used to prepare an opening into the intramedullary canal of the bone.  
      As shown in  FIGS. 21-22 , the first illustrated guide structure  16  comprises a body  300  with a through-bore  224 , a cavity  302  and a guide slot  306 ; the body  300  is assembled with a cam lock  304  and a pin  308 . The illustrated through-bore  224  extends in the interior-posterior direction through the body  300 . The illustrated through-bore is defined by flat surfaces, and is sized and shaped to receive a portion of the shaft  210  of the second fully articulatable arm  206 . The cavity  302  is formed in the body  300  adjacent to and in communication with the through-bore  224 .  
      When assembled, the cavity  302  in the body  300  receives the cam portion  307  of the cam lock  304  (see  FIGS. 18-19 ). The cam lock  304  is rotatably mounted to the body  300  through the pin  308 . The cam lock  304  also includes a lever  310  exposed outside of the body  300 .  
      As shown in cross-section in  FIG. 19 , when the cam lock  304  is in an unlocked position, the body  300  of the guide structure  16  can slide along the length of the shaft of the fully articulatable arm  206  in the directions indicated by arrows  312 ,  314  in  FIG. 16 . As shown in cross-section in  FIG. 18 , when the cam lock  304  is rotated to the locked position, the cam  307  bears against the shaft  210  to fix the position of the body  300  on the shaft  210 . Thus, the combination of the shapes of the components  210 ,  300  and the locking mechanism  304  allow for selected translational movement of the guide structure  16  with respect to the second fully articulatable arm  206 , but does not allow for rotational movement. The locking mechanism also allows for the translational position of the guide structure  16  to be fixed on the second fully articulatable arm  206 .  
      In the first illustrated embodiment, the guide structure  16  has a slot  306  sized and shaped to receive a cutting blade (such as the serrated blade of the instrument  21  illustrated in  FIG. 1A ) for resecting the proximal tibia. The illustrated tibial cutting block also includes a plurality of cut-outs  320  to reduce friction between the cutting blade and at least one of the guide surfaces  322  defining the guide slot. It should be understood that a guide slot need not be used; an appropriate tibial cutting block could include a guide surface without any upper constraining surface.  
      Thus, it can be seen that in the first illustrated instrument set, the guide structure  16  has two translational degrees of freedom of movement and at least eight rotational degrees of freedom of movement with respect to the anchoring structure  12 : translational along the anchoring bar  22  and along the shaft  210  of the second fully articulatable arm  206 ; two rotational degrees of freedom about the movable clamp assembly  28 ; at least three rotational degrees of freedom about the first ball joint  176 ; and at least three rotational degrees of freedom about the second ball joint  217 . With such freedom on movement available, the surgeon can position a tibial cutting block in the proximal-distal direction to set the resection level, align the cutting block with a desired reference axis and can orient the cutting block in the medial-lateral and anterior-posterior directions to set the varus-valgus orientation and anterior-posterior slope of the resection.  
      Additional degrees of freedom of movement can be provided in the articulating linkage  14 . For example, an additional translational degree of freedom of movement can be provided by using a telescoping member as the length intermediate link  162  instead of the fixed-length bar of the embodiment of  FIG. 1 . Moreover, an additional rotational degree of freedom of movement can be provided by using a jointed member as the intermediate link  162 .  
      An example of a telescoping member is illustrated in  FIGS. 23-32 . The telescoping member is illustrated at  162 A. It includes a body  324  with a longitudinal through-bore  326  and a slot  328  around part of the periphery of the body  324 . As shown in  FIG. 25 , the illustrated body  324  has a generally cylindrical outer shape, although it should be understood that other shapes may be used. As shown in  FIGS. 25-26 , the through-bore  326  has three flat sides joined by a curved side along part of its length, although other shapes may be used. At the slot,  328 , the through-bore has an expanded volume. The telescoping member  162 A also includes a reciprocable rod  330  and a locking mechanism  338 . The reciprocable rod  330  has a shape corresponding generally with the shape of the longitudinal through-bore  326 , and is capable of being moved in the through-bore  326  along the longitudinal axis of the body  324 . As illustrated by  FIGS. 23-24 , the reciprocable rod  330  can be retracted into or extended out of the body  324 . In the illustrated embodiment, the rod  330  corresponds with the first fully articulable arm  168  of the first embodiment: the exposed end of the rod  330  is connected to a spherically-shaped member  332  corresponding with the portion  172  of the first embodiment. The spherically-shaped member  332  can be received in the housing  174  to define the first ball joint when the telescoping member  162 A of  FIGS. 23-29  is used in place of the intermediate bar  162  of the first embodiment. The opposite end of the body  324  may be connected to a connector  158 A, similar to connector  158  of the first embodiment, to connect the telescoping member  162 A to the bar portion  150  of the pivotable arm  126 .  
      As shown in  FIG. 25 , the rod  330  in the illustrated telescoping member  162 A has a convexly curved upper surface  334  with a plurality of transverse parallel teeth  336  along a substantial part of its length. The remaining four sides of the rod  330  are generally flat, as shown in  FIGS. 26 and 29 - 29 .  
      The illustrated telescoping member  162 A also includes a locking mechanism  338 . The illustrated locking mechanism  338  has a generally cylindrically-shaped outer surface  340 , and it mounted in the slot  328  of the body  324 . The locking mechanism  338  has a through-bore  342  with two flat parallel sides  344 ,  345  joined by two curved sides  346 ,  347 . The curved sides  346 ,  347  have a plurality of parallel teeth  348 .  
      The locking mechanism  338  is rotatable within the body  324  about the longitudinal axis of the housing. The locking mechanism  338  includes a handle  350  extending out of the slot  328  and exposed outside of the body  324 . The locking mechanism  338  has an unlocked position shown in  FIG. 28  and a locked position shown in  FIG. 29 . In the unlocked position, the teeth  348  of the locking mechanism  338  are spaced from and do not contact the teeth  336  of the rod  330 . In the locked position, the locking mechanism  338  is rotated 90° with respect to the body  324  so that the teeth  348  of the locking mechanism  338  engage the teeth  336  of the rod  330 . Thus, in the unlocked position, the rod  330  can be moved to a desired translational position and then locked by rotating the locking mechanism  338  from the position shown in  FIG. 28  to that shown in  FIG. 29 . The locking mechanism  338  can be rotated back to the position shown in  FIG. 28  to adjust the length of the telescoping member  162 A if desired. It will be appreciated that the number and size of the teeth  336 ,  348  and distance between the teeth  336 ,  348  can be selected based upon the desired increments for the overall length of the telescoping member  162 A.  
      An example of a jointed member that can be used as the intermediate link  162  is illustrated in  FIG. 34  at  162 B. The intermediate link  162 B is an assembly of two segments  352 ,  354  pivotably joined about a pin or bolt  356 . The intermediate link  162 B may include any suitable locking mechanism, such as a nut to tighten on the bolt, a locking plate such as that shown in the first embodiment at  134 , or a cam locking mechanism or throw so that the two segments  352 ,  354  can be locked in a particular angular orientation and unlocked and repositioned as desired. Thus, with the intermediate link  162  of  FIG. 34 , an additional rotational degree of freedom of movement is available in the articulating linkage.  
       FIG. 34  also illustrates another possible use for the instrument system  10 . In  FIG. 34 , the anchoring structure  12  is again anchored to the femur  17 , but the movable clamp assembly  28  is positioned near the proximal end of the anchoring bar  22  and the articulating linkage  14 B is oriented toward the proximal end of the femur. As in the first embodiment, the articulating linkage  14 B includes two ball joints  176 ,  217 . The guide structure  16 B of the embodiment of  FIG. 34  is different from that in  FIG. 1  in that the guide structure is used to mill, burr or drill into the femur in a proximal-distal direction.  
      The guide structure  16 B of the embodiment of  FIG. 33  includes a guide track  358  fixed to the second fully articulatable arm  206 . The guide track  358  defines a longitudinal path for a follower  360  and includes an elongate slot through which a support arm  362  extends. One end of the support arm  362  is connected to the follower  360  and the opposite end is connected to a mounting bracket  364 . The mounting bracket  364  carries a bone cutting device  366 , which in this case may comprise a high speed mill, drill or burr, for example. The surgeon can use the embodiment of  FIG. 34  to position the guide track  358  parallel to the axis of the bone  17 . The follower  360  can therefore move along the longitudinal path defined by the guide track  358 , parallel to the axis of the bone  17 , and the support arm, mounting bracket and cutter  366  will move along a parallel linear path. Thus, the instrument system of  FIG. 34  also provides freedom of movement along an additional translational path.  
      The principles of the present invention could also be applied to other forms of guide structures  16  for resection of other bones. For example,  FIGS. 35 and 37  illustrate use of the articulating linkage  14  and anchoring structure  12  of the invention to set the position, alignment and orientation of a distal femoral resection guide shown at  419 ; in this case, the guide structure  16  comprises the distal femoral cutting guide  419 .  FIG. 38  illustrates use of the invention in setting the position and orientation of an ankle cutting block  420 , thus illustrating another possible guide structure  16  that may be used with the articulating linkage  14 .  FIG. 39  illustrates use of the invention in setting the position, alignment and orientation of a proximal femoral cutting block  422 .  
      All of the illustrated instrument sets can be used in computer-assisted surgery. As illustrated in  FIGS. 34-37 , a first computer navigation tracker  400 , such as an emitter or reflector array, can be attached to a portion of the anchoring structure  12 , such as one of the pins  18 ,  20  as illustrated in  FIG. 34  or the anchoring bar  22  as illustrated in  FIGS. 35-37 . Suitable fastening mechanisms can be used to secure the arrays  400 : for example, a bore could be provided in one of the components of the anchoring structure, such as anchoring bar  22 , or clamps, clips or other fastening devices could be employed, as shown in  FIGS. 36-37 . The instrument system may also include a computer navigation tracker, for example a second emitter or reflector array, such as that shown at  402  in  FIGS. 36-37 , for mounting to some part of the guide structure  16 : for example, the array  402  could be attached to or integral with a plate  404  that is sized and shaped to be received in a cutting guide slot of the guide structure  16 . It should be understood that other structures could be employed to attach an array to any of the illustrated guide structures  16 . Additional computer navigation trackers, such as those shown at  406  in  FIGS. 36-37 , could be provided for temporary attachment to one or positions on one of the patient&#39;s bones, such as the tibia  19  as shown in  FIGS. 36-37 . The trackers  400 ,  402 ,  406  give the surgeon an image of the position, alignment and orientation of some known part of the guide structure  16 , such as a guide slot, with respect to the position, alignment and orientation of other landmarks, such as some part of the anchoring structure  12  or bone that is also displayed on a computer screen. The computer images can be used by the surgeon to guide the guide structure  16  into a desired position, alignment and orientation while the articulating linkage  14  is unlocked, and freely movable; the surgeon can lock the articulating linkage  14  with the guide structure  16  in the desired position, alignment and orientation and then set the guide structure  16  in this position, alignment and orientation by placing standard pins or the like through bores in the guide structure  16  and into the bone. The surgeon may then perform the bone resections so that the bone may receive the prosthetic implant. An example of an emitter or reflector system potentially usable with the present invention is disclosed in U.S. Pat. No. 6,551,325, which is incorporated by reference herein in its entirety. The system  10  of the present invention is expected to be particularly useful with the Ci tm  computer assisted surgical system available from DePuy Orthopaedics, Inc. of Warsaw, Ind. However, any computer assisted surgery system, with appropriate emitters or sensors and computer with appropriate circuitry and programming could be used with the present invention.  
      The illustrated instrument systems could be used with alternative forms of computer navigation trackers for computer-assisted surgery. For example, instead of an array of emitters or reflectors that is attached to reference points as illustrated in  FIGS. 34-37 , one or more trackers could be embedded in the guide structure  16  and patient&#39;s bone, as well as in the cutting instrument  21 . For example, the computer navigation trackers could comprise electromagnetic sensors, such as one or more coils, transducers and transmitters appropriately housed and sealed, and the instrument system could include electromagnetic field generator coils, receiving antenna and computer with appropriate signal receiver and demodulation circuitry. Such systems are commonly referred to as “emat” (electromagnetic acoustic transducer) systems.  
      Variations from the illustrated embodiments may be made, particularly when the invention is used in with a computer assisted surgical system. For example, the anchoring structure  12  need not be attached to the patient&#39;s bone. Instead, the anchoring structure  12  could comprise a fixture in the operating room, such as a rod or bar fixed to the operating table or a dedicated floor stand.  
      Although the present invention provides advantages in computer-assisted surgery, its use is not limited to computer-assisted surgery. The guide structure  16 , articulating structure  14  and anchoring structure  12  could also be used with standard surgical instruments used to determine position, alignment and orientation, such as a stylus or an extramedullary or intramedullary alignment rod.  FIGS. 36 and 37  illustrate extramedullary alignment rods at  421  and  423 .  
      It will be appreciated from a comparison of  FIGS. 36 and 37  that the system of the present invention is advantageous in that the same anchoring structure  12  and articulating linkage  14  can be used to position, alignment and orient cutting blocks for use in all bones of a joint; the surgeon need only change the guide structure  16 . In  FIG. 36 , the guide structure  16  is a proximal tibial cutting block and in  FIG. 37  the guide structure  16  is a distal femoral cutting block. Moreover, as can be seen in  FIGS. 36 and 37 , the surgeon need not change the position of the anchoring structure  12  when using the system for setting multiple cutting blocks. Accordingly, a kit incorporating the system of the present invention may include a single articulating linkage  14  and multiple guide structures  16  for resecting multiple bones of a joint.  
      A method of using the illustrated surgical instrument system  10  in surgery is described below.  
      The patient is placed supine on the operating table and given a satisfactory anesthetic. The leg or other limb is prepped and draped in the usual fashion. The anchoring structure  12  is then set in position. As in  FIGS. 1 and 36 - 37 , the anchoring structure  12  can be set by driving the pins  18 ,  20  into a bone (such as the femur) and fixing the anchoring clamp assemblies  24 ,  26  to the pins  18 ,  20 . The anchoring bar  22 , with the movable clamp assembly  28  and remainder of the articulating linkage  14  mounted on the bar  22 , can then be fixed to the anchoring clamp assemblies  24 ,  26 . At this point, the movable clamp assembly  28  need not be locked in any translational position and the remaining locks  134 ,  226  of the articulating assembly may be in the unlocked state.  
      It will be appreciated that in some environments, the stationary structure need not be attached to the patient. For example, the stationary structure could comprise an operating room fixture, in which case the surgeon would attach the movable clamp assembly  28  to the operating room fixture.  
      The surgeon selects the appropriate guide structure  16  and slides the fully articulatable arm  206  into the cavity  302  of the guide structure  16 . It will be appreciated that a kit including the system  10  may include two or more sizes of each type of guide structure  16  to accommodate the needs of different patients.  
      If the procedure includes the use of a computer to position, align and orient the resection guide  16 , computer navigation tracker  402  can be mounted to the resection guide  16  by sliding the plate  404  into the cutting guide slot (such as slot  306  shown in  FIG. 16 ) of the guide structure  16 ; alternatively, a computer navigation tracker could be embedded within the guide structure  16 . Other computer navigation trackers  400 ,  406  may be affixed to anatomical landmarks (or embedded within the patient&#39;s bone) or to the anchoring structure  12  to serve as references or benchmarks for determining the relative position, alignment and orientation of the guide structure  16 .  
      The surgeon can then move the guide structure  16  into a desired position, alignment and orientation and begin locking the lock mechanisms. For example, once the surgeon is satisfied with the general location of the guide structure  16 , the translational position of the movable clamp assembly  28  on the bar  22  can be fixed by tightening the bolt  114 . The surgeon can then continue to lock the articulating linkage  14 ; for example, the surgeon may next turn the handle  136  of the locking plate  134  to fix the position of the pivotable arm  126  with respect to the anchoring structure  12 . The translational position of the guide structure  16  on the shaft of the second fully articulatable arm  206  may be fixed by pushing on the lever  310  of cam lock  304 . At this point, orientation of the guide structure may still be adjusted since the two ball joints  176 ,  217  can still articulate in three rotational degrees of freedom. The surgeon can set the orientation (varus-valgus angle and the anterior-posterior slope in a knee arthroplasty such as illustrated in  FIGS. 36 and 37 ) and then lock the resection guide  16  in place by turning the actuator  226  so that the pistons  236 ,  238  simultaneously engage the spherical portions  172 ,  204  of the ball joints  176 ,  217 , thus completing the locking process. When the locking process is complete, the articulating linkage  14  is substantially rigid and the guide structure  16  is fixed in position with respect to the anchoring structure  12  . If the surgeon is satisfied with the final fixed position, alignment and orientation and of the guide structure  16 , the surgeon can place pins through receiving holes in the guide structure and into the underlying bone (if the guide structure comprises a resection guide). Throughout this process, the surgeon can monitor the position, alignment and orientation of the guide structure on a monitoring device such as a computer screen. The computer navigation tracker  402  can be removed from the guide structure  16  once the surgeon is satisfied with its location.  
      It will be appreciated that if at any time the surgeon is dissatisfied with the location of the guide structure  16 , one or more of the locking mechanisms  134 ,  226 ,  304  can be unlocked for repositioning of the guide structure  16  followed by locking.  
      In the case of resection guides, it will also be appreciated that if the articulating linkage  14  is obstructing the surgeon in any way, once the resection guide is fixed to the bone with pins, the cam lock  304  can be unlocked and the second fully articulatable arm  206  can be pulled out of the bore  224  and the articulating linkage  14  can be moved out of the way by unlocking one or more of the locks. However, it should not be necessary to remove the articulating linkage  14  from the anchoring structure  12 .  
      The surgeon can then perform bone resections using a cutting instrument such as shown at  19  in  FIG. 1A , for example. Other cutting instruments, such as a rotating burr could also be used. Once the resections of this first bone are complete, the surgeon can select another guide structure  16  (such as a distal femoral resection guide  419  as shown in  FIG. 37 ) designed for resection of the other bone of the joint and mount this guide structure  16  on the second fully articulatable arm  206 . With the locking mechanisms  134 ,  226 ,  304  disengaged, the surgeon can then move the second guide structure  16  into a desired position, alignment and orientation with respect to the second bone of the joint, lock the articulating linkage once the position, alignment and orientation are set, fix the second guide structure to the second bone and make the desired resections. Setting of the position, alignment and orientation of the second guide structure can be computer guided as well. All of the steps involving the first and second resection guides can be performed with a single articulating linkage  14  fixed to a single anchoring structure  12 , and can be performed without moving the anchoring structure  12  and without totally disengaging the articulating linkage  14  from the anchoring structure  12 .  
      It will be appreciated that if the articulating linkage  14  includes features such as the telescoping member  162 A, the surgeon would also adjust and lock the telescoping member at some time during placement of the guide structure  16 . Similarly, if a jointed member  162 B such as that shown in  FIGS. 34 and 38  is used as part of the articulating linkage, then the surgeon would also adjust and lock the jointed member  162 B at some time during placement of the guide structure. If the two ball joints  176 ,  217  do not use a dual-locking mechanism such as that illustrated in FIGS.  11 ,  13 - 14  or  33 , the step of locking the ball joints  176 ,  217  would be a two-step process. It will also be appreciated that although the surgical technique described above relates particularly to knee arthroplasty, the same general steps can be followed for performing other resections at other joints. It will also be appreciated that instead of using computer navigation trackers, the surgical technique could employ standard mechanical alignment devices (such as alignment rods) and standard anchoring structures such as ankle clamps.  
      While only specific embodiments of the invention have been described and shown, it is apparent that various alternatives and modifications can be made thereto. Those skilled in the art will also recognize that certain additions can be made to the illustrative embodiment. It is, therefore, the intention in the appended claims to cover all such alternatives, modifications and additions as may fall within the true scope of the invention.