Patent Publication Number: US-8114086-B2

Title: Navigated cut guide locator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 10/979,734, filed Nov. 2, 2004, now U.S. Pat. No. 7,993,341 which is a continuation-in-part of U.S. application Ser. No. 10/795,830, filed Mar. 8, 2004 now abandoned. 
    
    
     BACKGROUND 
     The present invention relates to surgical components used in conjunction with a surgical navigation system. In particular, the present invention relates to a navigated instrument for guiding subsequent components during a surgical procedure. 
     Many surgical procedures are now performed with surgical navigation systems in which sensors detect tracking elements attached in known relationship to an object in the surgical suite such as a surgical instrument, implant, or patient body part. The sensor information is fed to a computer that then triangulates the three dimensional position of the tracking elements within the surgical navigation system coordinate system. Thus, the computer can resolve the position and orientation of the object and display the position and orientation for surgeon guidance. For example, the position and orientation can be shown superimposed on an image of the patient&#39;s anatomy obtained via X-ray, CT scan, ultrasound, or other imaging technology. 
     However, most surgical procedures are performed using conventional instruments in which the various components of the surgery are aligned mechanically by the surgeon by visualizing and/or palpating anatomic landmarks. During these procedures, surgical components in the form of instruments to prepare a bone, provisional components to verify sizing, implant components and/or other suitable components are placed in a surgical site. These components often have position and orientation requirements for them to operate properly. For example, a bone cutting guide must be aligned on the bone in the proper orientation to guide a cutter to produce a cut surface in a desire location. 
     SUMMARY 
     The present invention provides a navigated cut guide locator and method for guiding subsequent surgical components. 
     In one aspect of the invention, a navigated guide is provided for use with a surgical navigation system to establish a datum relative to a surgical site to guide placement of a surgical cut guide. The cut guide has a cut slot with a slot thickness, a slot width, and a slot depth. The slot defines a cut plane and is engageable with a cutter to guide the cutter within the cut plane. The navigated guide includes a plate shaped body representative of the cut plane. The body is slidingly engageable with the cut slot. The navigated guide further includes a way for being tracked by the surgical navigation system to position the body at a desired position relative to the surgical site. 
     In another aspect of the invention, a surgical system is provided for use at an orthopaedic surgical site to guide a cutter to cut a bone. The system includes a surgical navigation system, a cut guide, and a navigated guide. The surgical navigation system includes a way for tracking the position of an object during a surgical procedure. The cut guide includes a cut slot for guiding the cutter in a cut plane to form a planar surface on the distal end of the femur. The navigated guide includes a plate shaped body representative of the cut plane. The body is slidingly engageable with the cut slot. The navigated guide further has a way for being tracked by the surgical navigation system to position the navigated guide at a desired position relative to the surgical site. 
     In another aspect of the invention, a method of guiding a cutter at an orthopaedic surgical site to cut a bone includes activating a surgical navigation system to track the position of a navigated guide, the navigated guide comprising a plate shaped body representative of a cut plane; anchoring the navigated guide relative to the surgical site in a desired position as indicated by the surgical navigation system; and engaging a cut guide with the navigated guide by sliding a slot in the cut guide over the plate shaped body of the navigated guide to align the cut slot with the cut plane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various illustrative examples of the present invention will be discussed with reference to the appended drawings. These drawings depict only illustrative examples of the invention and are not to be considered limiting of its scope. 
         FIG. 1  is a perspective view of an illustrative navigated guide according to the present invention in use to establish a datum relative to a bone; 
         FIG. 2  is a perspective view of the bone of  FIG. 1  showing the datum established with the navigated guide of  FIG. 1 ; 
         FIG. 3  is a perspective view showing a surgical component positioned using the datum of  FIG. 2 ; 
         FIG. 4  is a perspective view of an illustrative alternative arrangement for the navigated guide of  FIG. 1 ; 
         FIG. 5  is an exploded perspective view of an illustrative alternative arrangement for the navigated guide of  FIG. 1  having an adjustment mechanism; 
         FIG. 6  is a perspective view of the navigated guide of  FIG. 5  in use to establish a datum relative to a bone; 
         FIG. 7  is a perspective view showing a surgical component positioned using the datum of  FIG. 6 ; 
         FIG. 8  is an exploded perspective view of an illustrative alternative arrangement for the navigated guide of  FIG. 1  having an adjustment mechanism; 
         FIG. 9  is a perspective view of the navigated guide of  FIG. 8  in use to establish a datum relative to a bone; 
         FIG. 10  is a perspective view of the navigated guide of  FIG. 8  in use to establish a datum relative to a bone; 
         FIG. 11  is a cross sectional view taken along line  11 - 11  of  FIG. 10  with the bone omitted for clarity; 
         FIG. 12  is an exploded perspective view of an illustrative alternative arrangement for the navigated guide of  FIG. 1  having an adjustment mechanism; 
         FIG. 13  is a front elevation view of the navigated guide of  FIG. 12 ; 
         FIG. 14  is a top plan view of the navigated guide of  FIG. 12 ; 
         FIG. 15  is a side elevation view of the navigated guide of  FIG. 12 ; 
         FIG. 16  is a perspective view of the navigated guide of  FIG. 12  in use to establish a datum relative to a bone; 
         FIG. 17  is a perspective view showing a surgical component positioned using the datum of  FIG. 16 ; 
         FIG. 18  is a perspective view of an illustrative alternative navigated guide; 
         FIG. 19  is a top plan view of the illustrative navigated guide of  FIG. 18 ; 
         FIG. 20  is a side elevation view of the illustrative navigated guide of  FIG. 18 ; 
         FIG. 21  is a front elevation view of the illustrative navigated guide of  FIG. 18 ; 
         FIG. 22  is a perspective view of the navigated guide of  FIG. 18  in use to establish a datum relative to a bone; and 
         FIG. 23  is a perspective view showing a surgical component positioned using the datum of  FIG. 22 . 
     
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     Embodiments of a navigated guide may be configured to guide a variety of surgical components. For example, a navigated orthopaedic guide may be used to establish a datum relative to a bone such as one or more pins, screws, bars, fins, rails, dovetails, planar surfaces, holes, slots, notches, and/or any other suitable datum in or on a bone. The datum may be used to reference the position and/or orientation of a subsequent surgical component including cutting instruments, reaming instruments, templates, drill guides, provisional implants, implants, and/or other components for any suitable surgical site. Examples of surgical sites include hip joints, knee joints, vertebral joints, shoulder joints, elbow joints, ankle joints, digital joints of the hand and feet, the jaw, the skull, fracture sites, tumor sites, and/or other suitable surgical sites. The navigated guide of the present invention may be used to establish datums that may be referenced by components that are not otherwise usable with a surgical navigation system. Thus, the navigated guide may be used to provide the benefits of three dimensional surgical navigation technology while using existing non-navigated components. The navigated guide may be configured to establish a separate intermediate datum or it may serve as the datum itself to engage and guide a subsequent surgical component directly. A guide that serves directly as the datum may include one or more pins, screws, bars, fins, rails, dovetails, planar surfaces, holes, slots, notches, and/or other feature that directly engages the subsequent component to guide it relative to a surgical site. 
       FIGS. 1-3  depict an illustrative navigated orthopaedic guide  20  configured to guide the placement of datum pins  10  on which a femoral cut guide  50  is positioned to guide the cutting of a femur  2  to receive a femoral component in knee replacement surgery. The guide  20  includes a body  21  having a front surface  22 , a back surface  24  opposite the front surface  22 , and a circumferential side wall  26  extending from the front surface  22  to the back surface  24 . In the illustrative example, the orthopaedic guide  20  includes a tracking element in the form of an electromagnetic coil  28  embedded in the body  21  between the front and back surfaces  22 ,  24  and within the perimeter of the side wall  26 . The coil  28  includes a lead  30  extending from the coil  28  and out of the body  21  to connect to the surgical navigation system for transmitting electrical signals between the surgical navigation system and the coil  28 . When the coil  28  is placed within an electromagnetic field, it generates an electrical charge that is transmitted to the surgical navigation system such that the three dimensional position and orientation of the coil  28 , and thus the orthopaedic guide  20 , can be related to a surgical navigation coordinate system. For example, the surgical navigation system may include multiple sensors at known locations that receive signals from the coil  28  and feed the information to a computer. The computer may then triangulate the three dimensional position of the coil within the surgical navigation coordinate system. The surgical navigation system may then determine the position and orientation of the orthopaedic guide  20  by detecting the position and orientation of the coil  28  and resolving the position and orientation of the orthopaedic guide  20  from the known relationship between the coil  28  and the orthopaedic guide  20 . 
     While the illustrative example depicts an active electromagnetic tracking element, the tracking element may be detectable electromagnetically, acoustically, by imaging, or by other suitable detection means. Furthermore, the tracking element may be active or passive. Examples of active tracking elements may include electromagnetic field emitters in an electromagnetic system (such as the illustrative coil  28 ), light emitting diodes in an imaging system, and ultrasonic emitters in an acoustic system, among others. Examples of passive tracking elements may include elements with reflective surfaces. For example, reflective spheres or discs may be attached to the orthopaedic guide and detected by an imaging system. 
     The orthopaedic guide  20  includes means for establishing a datum on or in a bone to guide subsequent components. In the illustrative guide  20 , holes  32 ,  34 ,  36  extend through the orthopaedic guide  20  from the front surface  22  to the back surface  24 . The holes may guide the placement of pins  10 , screws, or other datums. For example, a drill bit may be guided along one or more of the holes  32 ,  34 ,  36  to create a hole  40  ( FIG. 2 ) in the underlying bone  2 . A pin  10  may then be inserted into the hole in the bone  2 . Alternatively, a self-drilling pin may be used. Alternatively, the pin  10  may be omitted and the hole  40  formed in the bone  2  may itself serve as a datum. Alternatively, the orthopaedic guide  20  may include a notch, slot, guide surface, or other feature to guide forming a notch, slot, or other datum in the bone  2 . Alternatively, the orthopaedic guide  20  may include a slot, notch, guide surface, or other feature to guide placing a bar, rail, or other datum in or on the bone  2 . 
     Once the datum has been positioned on the bone  2 , a surgical component may be referenced to the datum to correctly position the surgical component. For example, in  FIG. 3 , a femoral cut guide  50  includes holes  52 ,  54 , and  56  for receiving datum pins  10  set using the orthopaedic guide  20 . Alternatively, the surgical component may include protrusions for engaging holes  40  formed using the orthopaedic guide  20 , or other features for engaging other types of datums positioned using the orthopaedic guide  20 . The femoral cut guide  50  includes a body  58  having a front surface  60 , a back surface  62 , and a circumferential side wall  63  extending from the front surface  60  to the back surface  62 . The datum receiving holes  52 ,  54 ,  56  extend from the front surface  60  to the back surface  62 . A plurality of slots  64 ,  66 ,  68 ,  70 ,  72  are formed through the cut guide  50  from the front surface  60  to the back surface  62  to guide a cutter to shape the end of the femur  2  to receive a femoral knee implant. For example, a posterior cut slot  70  may guide a saw blade to cut a posterior facet on the femur  2 . A posterior chamfer cut slot  68  may guide a saw blade to cut a posterior chamfer facet on the femur  2 . An anterior cut slot  64  may guide a saw blade to cut an anterior facet on the femur  2 . An anterior chamfer cut slot  66  may guide a saw blade to cut an anterior chamfer facet on the femur  2 . A trochlear recess cut slot  72  may guide a saw blade to cut the base of a trochlear recess on the femur  2 . In addition, drill guide holes  74  may guide a drill bit to form post holes in the femur for receiving a fixation post of a femoral implant. Fixation holes  76  are positioned to receive additional pins, screws, or other fasteners to hold the cut guide  50  in place on the bone  2  while the saw cuts and drill holes are made. 
     In the illustrative guide  20  of  FIG. 1 , the holes  32 ,  34 ,  36  correspond to holes formed in cut guides  50  provided in a range of sizes. The central hole  32  in the orthopaedic guide  20  corresponds to the central hole  52  in the cut guide  50  and is common to all of the sizes of cut guides  50 . The additional holes  54 ,  56  for receiving the datum pins  10  may vary in location by size of the cut guide  50 . Therefore, the orthopaedic guide  20  includes multiple locations for the corresponding additional orthopaedic guide holes  34 ,  36 . The additional orthopaedic guide holes  34 ,  36  may be labeled to identify the size of the cut guide  50  that is planned to be used. The datum pin  10  is then positioned using the correspondingly labeled orthopaedic guide hole  34 ,  36 . Two pins  10  are sufficient to positively locate the cut guide  50 . 
     The use of the orthopaedic guide  20  will now be described in conjunction with the exemplary femoral cut guide  50  surgical component in a procedure to replace the distal end of the femur  2  during knee joint replacement surgery. The surgeon may preoperatively determine the desired intraoperative size and location of the femoral implant. For example, X-ray images, CT data, MRI data, or other patient data may be digitized to form a computer model of the patient&#39;s anatomy and superimposed with a model of the available knee implants on a computer screen. The surgeon may then pick the appropriate size of implant and virtually maneuver it to a desired location in the computer model. This positioning information may then be used by the surgical navigation system to guide the surgeon to position the central common hole  32  in the orthopaedic guide  20  at the appropriate position to correctly position the chosen cut guide  50 . For example, the surgeon may form the distal cut surface  4  in a conventional manner as is known in the art. The navigated orthopaedic guide  20  may then be positioned on the distal cut surface  4  and maneuvered about until the surgical navigation system indicates that the central hole  32  is in the required position. A datum pin  10  may then be inserted by drilling through the hole  32  into the femur  2  and pressing the datum pin  10  into the drilled hole  40 . The orthopaedic guide  20  is thus fixed in a particular anterior-posterior (A/P) and medial-lateral (M/L) position and may now be rotated about the pin  10  in the central hole  32  until the surgical navigation system indicates that another hole  34 ,  36 , corresponding to the planned implant size, is at the correct rotational position. A datum pin  10  may then be inserted by drilling through the appropriate hole  34 ,  36  into the femur  2  and pressing the datum pin  10  into the drilled hole  40 . The orthopaedic guide  20  may now be removed by lifting it off of the datum pins  10 . The appropriate femoral cut guide  50  may be positioned on the distal cut surface  4  of the femur  2  by sliding the cut guide  50  over the datum pins  10 . The cut guide may be secured to the bone by inserting pins, screws, or other fasteners through one or more of the fixation holes  76  and into the femur  2 . Saw blades and drills may be guided using the slots  64 ,  66 ,  68 ,  70 ,  72  and holes  74  in the cut guide  50  to prepare the femur  2  to receive a particular size of implant in a desired A/P, M/L, and rotational position. 
     Alternatively, the orthopaedic guide  20  may itself serve as a datum for guiding subsequent components. For example, the orthopaedic guide  20  may include a hole, slot, planar surface, and/or other feature for directly engaging and guiding a subsequent component relative to the surgical coordinate system. For example, the guide slots  64 ,  66 ,  68 ,  70 ,  72  and holes  74  of the cut guide  50  may be formed directly in the navigated guide  20 . However, a navigated guide  20  with all of the features of the cut guide  50  may be more expensive and/or more delicate than the cut guide  50 . Since the cut guides  50  are typically provided in a variety of sizes, it may be less costly and/or require less maintenance to provide a single separate navigated guide  20  for establishing a datum as described above. Furthermore, a separate navigated guide may be used to provide the benefits of surgical navigation technology while using existing non-navigated cut guides  50 . This significantly reduces the cost of transition from a non-navigated to a navigated procedure by reducing the number of new instruments required. 
       FIG. 4  illustrates an alternative arrangement for the navigated orthopaedic guide of  FIG. 1 . The orthopaedic guide  120  of  FIG. 4  is approximately one-half the width of the orthopaedic guide  20  of  FIG. 1 . This smaller orthopaedic guide  120  is well suited for use in minimally invasive surgical procedures in which a reduced size incision is made. The guide  120  includes a body  121  and a tracking element in the form of an electromagnetic coil  128  to permit the surgical navigation system to track the position and orientation of the guide  120 . A handle  125  extends from the guide  120  to facilitate insertion of guide into an incision. In a minimally invasive surgical procedure, it may be necessary to slip an edge  123  of the guide  120  under the margins of the incision such that the guide body  121  is largely covered by soft tissue. The handle  125  provides a gripping surface projecting from the incision. The guide body  121  includes a central hole  132  and first and second sets of additional datum guide holes  134 ,  136 . The additional datum guide holes  134 ,  136  are labeled to indicate the corresponding cut guide  50  associated with each hole. In order to better accommodate the datum guide holes  134 ,  136  on a half size instrument, an alternate offset central hole  133  is provided. The alternate central hole  133  is associated with the second set of datum guide holes  136  so that the second set of datum guide holes  136  may be offset from and not overlap the first set of datum guide holes  134 . A visual cue, such as etched lines  137 ,  139  may be provided to associate the corresponding central holes  132 ,  133  and additional datum guide holes  134 ,  136 . 
       FIGS. 5-7  depict an illustrative alternative arrangement of the navigated orthopaedic guide of  FIG. 1 . further including an adjustment mechanism. The guide  200  includes a base member  202 , a guide member  280  for establishing a datum, and a connecting link  240  connecting the base member  202  to the guide member  280 . The base member  202  secures the guide  200  within the surgical navigation coordinate system. For example, the base member  202  may be secured to a bone adjacent the surgical site. The narrow elongated shape of the illustrative base member  202  permits it to fit into a narrow incision such as is used in a minimally invasive surgical technique. The illustrative base member  202  includes fixation holes  204  for receiving fixation members to secure the base member  202  to a bone. The fixation holes  204  may be angled to one side, as shown, to permit the fixation members to be inserted at an angle through a small incision and/or through a medially or laterally offset incision. The connecting link  240  permits adjustment of the guide member  280  relative to the base member  202  to permit the guide member  280  to be secured in a desired orientation relative to the bone. This adjustability is provided by adjustment mechanisms connecting the connecting link  240  to the base member  202  and the guide member  280 . 
     The connecting link is connected to the base member  202  through a riser block  206  extending from the base member  202 . A connecting link bolt  208  extends through a saddle washer  210 , through the riser block  206 , and into threaded engagement with a first locking knob  212 . The connecting link bolt  208  includes a head  214  having a transverse bore  216 . The connecting link  240  includes a cylindrical shaft  242  received by the transverse bore  216  for translation along and rotation about the bore  216  axis  217 . As the first locking knob  212  is tightened onto the threads  218  of the connecting link bolt  208 , the connecting link bolt  208  is drawn through the saddle washer  210  and riser block  206 . The cylindrical shaft  242  of the connecting link  240  is drawn into abutment with a notch  220  in the saddle washer  210 . tightening of the first locking knob causes the saddle washer  210  to lock the connecting link  240  relative to the base member  202  and prevent translation and rotation of the connecting link relative to the base member  202 . The connecting link bolt head  214  may be radially enlarged, for example to form a shoulder  222 , so that the connecting link bolt  208  will not inadvertently pass through the saddle washer  210  and riser block  206  if the cylindrical shaft  242  is disengaged from the transverse bore  216 . The connecting link bolt  208  may include a non-circular shaft portion  224  corresponding to non-circular bores  226 ,  228  in the saddle washer  210  and riser block  206  to prevent the connecting link bolt  208  from rotating relative to the base member  202 . By constraining the connecting link bolt  208  against rotation, the only relative motion between the connecting link  240  and the base member  202  is translation along and rotation about the transverse bore axis  217 . Furthermore, constraining the connecting link bolt  208  facilitates tightening the first locking knob  212 . 
     The riser block  206  may include a slit  230  dividing the riser block into two cantilevered spaced apart portions  232 ,  234 . These portions  232 ,  234  act as springs to provide a broader range of tension adjustment in the adjustment mechanism than would be possible without a spring. With the slit  230 , the first locking knob  212  may be easily adjusted to a tension sufficient to hold the cylindrical shaft  242  in a desired position within the transverse bore  216  when acted on by the weight of the guide member  280  yet still allow a user to move the cylindrical shaft  242  in the transverse bore  216  with hand pressure. The first locking knob  212  may then be tightened to lock the cylindrical shaft  242  in the final desired position. 
     The connecting link  240  is connected to the guide member  280  through a tab  244  extending from the connecting link  240 . The tab  244  includes a bore  246  having a bore axis  248  angled relative to the transverse bore axis  217 . The angle between these bore axes  217 ,  248  permits a second degree of rotational adjustment of the guide member  280  relative to the base member  202 . The guide member  280  includes a yoke  282  having first and second spaced apart arms  284 ,  286 . Each arm  284 ,  286  includes an elongated slot  288  that permits a second degree of translation adjustment of the guide member  280  relative to the base member  202 . The tab  244  is received between the arms  284 ,  286  in sliding and pivoting relationship. A guide member bolt  290  extends through one of the arms  284 , through the bore  246  in the tab  244 , through the other arm  286 , and into threaded engagement with a second locking knob  292 . This arrangement constrains the guide member  280  to rotation about the tab bore axis  248  and translation along the elongated slot  288 . The guide member bolt  290  includes a radially enlarged head  294  that abuts one of the yoke arms  284  to prevent the bolt from pulling through the slot  288 . As the second locking knob  292  is tightened onto the threads  296  of the guide member bolt  290 , the yoke arms  284 ,  286  are flexed together to grip the tab  244  of the connecting link  240 . The spring action of the arms  284 ,  286  permits a range of tab  244  gripping tension such that the second locking knob  292  may be easily adjusted to a tension sufficient to hold the tab  244  in a desired position within the yoke  282  when acted on by the weight of the guide member  280  yet still allow a user to rotate the tab  244  within the yoke  282  with hand pressure. The second locking knob  292  may then be tightened to lock the tab  244 , and consequently the guide member  280 , in the final desired position. One or more optional lock washers  250  may be provided between the tab  244  and yoke  282 . The washer may include teeth  252  to increase the grip between the yoke  282  and tab  244 . Furthermore, the guide member bolt head  294  may include a non-circular profile received in a corresponding recess (not shown) adjacent the slot  288  to prevent the bolt  290  from turning when the second locking knob  292  is tightened. For example, the bolt head  294  may have flat sides  295  that fit within a flat sided countersink (not shown) surrounding the slot  288 . 
     The guide member  280  includes means for establishing a datum in the surgical navigation system coordinate system. In the illustrative orthopaedic guide of  FIG. 5 , the guide member  280  includes guide holes  298  for guiding pins to establish a datum. The guide member  280  includes a tracking element, such as an electromagnetic coil  300 , to permit the surgical navigation system to track the position and orientation of the guide member  280 . 
     In use, the base member  202  is secured within the surgical navigation coordinate system by mounting it to an object known to the system. For example, the base member  202  may be mounted on a femur  299  as shown in  FIG. 6 . The narrow elongated shape of the illustrative base member  202  permits it to fit into a small incision. For example, the base member  202  may be inserted through a narrow medial or lateral incision adjacent to a knee joint. Furthermore, the fixation holes  204  may be angled, as shown, to permit fixation members to be inserted through such a medial or lateral incision. The first and second locking knobs  212 ,  292  are loosened to permit the guide member  280  to be moved relative to the base member  202 . With the base member  202  positioned on the femur  299  as depicted in  FIG. 6 , the first locking knob  212  locks the medial-lateral position and the flexion angle of the guide member  280 . The second locking knob  292  locks the varus-valgus position and resection depth of the guide member  280 . The mechanism is manipulated until the surgical navigation system indicates that the guide member  280  is located in a desired position. The first and second locking knobs  212 ,  292  are then tightened to lock the guide member  280  in place relative to the base member  202 . The guide member  280  may then be used to establish a datum for guiding a subsequent surgical component. For example, pins  302  may be inserted through guide holes  298  and into the femur  299 . The navigated orthopaedic guide  200  may then be removed. 
       FIG. 7  illustrates a distal femoral cut block  304  mounted on the pins  302 . The distal femoral cut block  304  includes holes  306 ,  308 ,  310  to receive the pins  302  and a cutter guide  312  for guiding a cutter to form a surface on the bone. The holes  306 ,  308 ,  310  may be provided as a plurality of rows of holes. Each row may provide a different level of resection. For example, one row of holes  308  may correspond to a predetermined nominal resection level. Additional rows  306 ,  310  may provide for cutting more or less bone should surgeon preference or the condition of the bone require it. By providing more holes in each row than the number of pins  302  used, the distal femoral cut block  304  may be adjusted anteriorly and posteriorly by lifting it off of the pins  302  and repositioning it on adjacent holes in the same row. With the cut block  304  positioned at the desired resection level and anterior-posterior position, additional fixation members may be inserted through some of the holes  306 ,  308 ,  310  to hold the cut block  304  in position while a cutter is guided to cut the bone  299 . 
     The adjustable navigated orthopaedic guide  200  of  FIGS. 5-7  has been shown configured to position a datum on the distal portion of a femur  299  to position a distal femoral cut guide  304 . However, this adjustable guide may also be used to establish datums for other surgical components including cut guides such as a femoral finishing guide and/or a tibial cut guide. Also, as with the navigated orthopaedic guides of  FIGS. 1-3  and  4 , the guide of  FIGS. 5-7  may itself serve as a datum to directly guide a subsequent surgical component. 
       FIGS. 8-11  depict another illustrative alternative arrangement for the orthopaedic guide of  FIG. 1  further including an adjustment mechanism. The guide  400  includes a base member  402 , a guide member  480 , and a connecting linkage  440  for adjustably connecting the base member  402  and the guide member  480 . The base member  402  includes a receiver block  404  for receiving the connecting linkage  440  and an anchor portion  406  for securing the guide within the surgical navigation coordinate system. The illustrative anchor portion  406  includes a primary mounting post  408  that may be driven into a bone. The primary mounting post  408  may include fins  410  to resist rotation of the base member  402  relative to the bone. A supplemental mounting post  411  may also be included to resist rotation of the base member  402 . The supplemental mounting post  411  may be spaced radially from the primary mounting post  408  to create a larger moment arm to resist rotation. The base member  402  may include means for gripping the base member  402  to remove it from the bone. The illustrative anchor portion  406  extends above the base member  402  and includes an annular groove  412  that may be engaged by a pin puller, slap hammer, and/or other suitable instrument to extract the base member  402 . 
     The connecting linkage  440  permits adjustment of the guide member  480  relative to the base member  402  to permit the guide member  480  to be secured in a desired orientation relative to the bone. This adjustability is provided by adjustment mechanisms connecting the connecting linkage  440  to the base member  402  and the guide member  480 . 
     The connecting linkage  440  is connected to the base member  402  by way of a rotating support  442 . In the illustrative example, the rotating support  442  includes a plate-like body  444  having a top surface  443 , a bottom surface  445 , and a trunnion  446  projecting from one end. The trunnion  446  is received in a bore  414  formed in the receiver block  404  for rotation about the bore  414  axis  416 . A set screw  418  is threaded into the receiver block  404  to lock the rotating support  442  in place. The trunnion  446  may include an annular groove  448  to receive the tip  420  of the set screw  418 . With the set screw  418  loosely engaging the groove  448 , the rotating support  442  may rotate about the bore axis  416  but it is prevented from translating along the bore axis  416 . tightening the set screw  418  locks the rotating support  442  in its rotated position. 
     An adjustment screw housing  450  is supported at an opposite end of the rotating support  442 . The housing  450  includes a body  452  with a transverse opening  454  defined by opposed fulcrums  456 . The rotating support is  442  is received in the opening  454  with its top and bottom surfaces  443 ,  445  in close fitting relationship to the vertices  458  of the opposed fulcrums  456 . The fulcrums  456  permit the housing  450  to rock relative to the rotating support  442 . A pair of angle adjustment screws  460  is threaded into the adjustment screw housing  450  transverse to and in communication with the opening  454  such that the screws  460  may engage the top surface  433  of the rotating support  442 . The screws  460  are positioned in the housing  450  so that they are on opposite sides of the fulcrum vertices  458 . By loosening one of the angle adjustment screws  460  and tightening the other, the housing  450  will pivot on the fulcrum vertices  458  to allow adjustment of the angle of the housing  450  relative to the support  442 . 
     The connecting linkage  440  is connected to the guide member  480  by means of a portion of the guide member  480  connecting to the housing  450 . In the illustrative example, a threaded rod  482  projects from the guide member  480  and extends through the housing, through the vertices  458  of the opposed fulcrums  456 , through an elongated slot  462  formed in the rotating support  442 , and into threaded engagement with an adjustment nut  464 . A spring  466  is interposed between the guide member  480  and housing  450  to bias them apart. Tightening the adjustment nut  464  draws the threaded rod  482  into the housing  450  and thereby moves the guide member  480  toward the housing  450  and compresses the spring  466 . Loosening the adjustment nut  464  allows the guide member  480  to move away from the housing  450 . 
     The guide member  480  includes means for establishing a datum in the surgical navigation system coordinate system. In the illustrative orthopaedic guide of  FIG. 8 , the guide member  480  includes a guide member body  483  having a front face  484  and a back face  486 . Guide holes  487  for guiding pins to establish a datum extend from the front face  484  to the back face  486 . The guide member  480  includes a tracking element in the form of an electromagnetic coil  488  to permit the surgical navigation system to track the position and orientation of the guide member  480 . 
     The guide member  480  may optionally include a datum surface to directly guide a subsequent surgical component. The illustrative orthopaedic guide of  FIGS. 8-11  includes a datum surface in the form of an elongated cutter guide slot  490  extending from the front face  484  to the back face  486  to directly guide a subsequent surgical component. If the optional direct guiding datum surface is provided, the holes  487  may receive fixation members to hold the guide member  480  in place while the guide member  480  directly guides a subsequent surgical component. Unlike femoral cut guides, which typically must be provided in a range of sizes, a single tibial cut guide is often able to be used to cut a wide variety of tibial sizes. Therefore, it may be advantageous to provide a single, direct guiding, orthopaedic guide configured for tibial use as shown. However, the orthopaedic guide of  FIGS. 8-11  may also be used to establish datums for a separate surgical component such as a tibial cut guide, femoral cut guide, implant, and/or other surgical component. It may also advantageously be used to establish datums for existing tibial cut guides to provide the benefits of surgical navigation technology with existing non-navigated components. 
     In use, the mounting post  408  is inserted into a bone to secure the guide  400  adjacent the bone, as shown in  FIGS. 9 and 10 . For use on a tibia  500 , the mounting post  408  may be inserted through the proximal tibial surface  502  to position the guide member  480  adjacent the anterior tibial cortex  504 . With both of the angle adjustment screws  460  loosened, the housing  450  and guide member  480  may be slid along the rotating support  442  to a desired position relative to the anterior tibial cortex  504 . With the set screw  418  loosened, the rotating support  442 , housing  450 , and guide member  480  may be rotated to adjust the varus-valgus orientation of the guide member  480 . By differentially tightening the angle adjustment screws  460 , the housing  450  and guide member  480  may be angled about the fulcrum vertices  458  relative to the rotating support  442 , as best seen in  FIG. 11 . This angle adjusts the posterior slope orientation of the guide member  480 . Finally, by tightening or loosening the adjustment nut  464 , the height of the guide member  480  may be varied to establish the resection depth position of the guide member  480 . All of these adjustments may be made while the surgical navigation system is used to track the guide member  480 . When the surgical navigation system indicates that the guide member  480  is in a desired position, the adjustment screws may be tightened to lock the position. The guide member  480  may now be used to establish a datum on the tibia  500 , such as by inserting datum pins  506  through the holes  487  in the guide member  480  and into the anterior tibial cortex  504 . The guide  400  may then be removed and the datum pins  506  may be engaged by a subsequent surgical component. For example, a cut block for guiding a cutter to resect the proximal tibial surface  502  may be engaged with the datum pins  506 . Alternatively, the guide member  480  may directly establish a datum, such as with the guide slot  490 , to guide a subsequent surgical component. For example, a cutter may be inserted in the guide slot  490  to guide the cutter to resect the proximal tibial surface  502 . 
     The illustrative orthopaedic guide  400  of  FIGS. 8-11  has been shown configured to directly guide a cutter to form a cut surface on the proximal tibia during a knee replacement surgical procedure. However, this orthopaedic guide  400  may also be used to directly guide or to establish datums for other surgical components and/or other surgical locations. For example, the orthopaedic guide  400  may be used to directly guide, or establish datums to guide, instruments or implants into a desired position relative to the tibia or femur of the knee joint, the femur or pelvis of a hip joint, and/or other components and locations. 
       FIGS. 12-17  depict another illustrative alternative arrangement of the navigated orthopaedic guide of  FIG. 1  further including an adjustment mechanism. The guide  600  includes a base member  602 , a guide member  680  for establishing a datum, and a connecting link  640  connecting the base member  602  to the guide member  680 . The base member  602  secures the guide  600  within the surgical navigation coordinate system. For example, the base member  602  may be secured to a bone adjacent the surgical site. Alternatively, the base member  602  may be secured to another surgical component as shown in  FIG. 16  in which the illustrative base member  602  is secured to the distal femoral cut guide  304  of  FIG. 7 . The illustrative base member  602  includes a clamping nut  604  engageable with the distal femoral cut guide  304 . The clamping nut  604  includes an axial threaded bore  606  and an undercut slot  608  transverse to the bore  606 . A screw  610  includes a threaded shank  612  engageable with the axial bore  606  of the nut  604  and a knob  614 . The shank  612  passes through a base clamp hole  616  in the base  602  and engages the nut  604 . A pair of side wings  616  project downwardly from the base  604  to prevent the nut  602  from turning when the screw  610  is rotated. The clamping nut  604  permits clamping of the base  602  onto the distal femoral cut guide  304  in a selected relative position. 
     The connecting link  640  permits adjustment of the guide member  680  relative to the base member  602 . This adjustability is provided by adjustment mechanisms connecting the connecting link  640  to the base member  602  and the guide member  680 . The connecting link  640  includes an arm  642  at one end that slidingly engages an arm receiving opening  618  in the base  602  transverse to the undercut slot  608  such that the base  602  position can be adjusted relative to the distal femoral cut guide  304  in a first direction and the connecting link  640  can be adjusted relative to the base  602  in a second direction transverse to the first direction. In the illustrative example of  FIGS. 12-17 , the first and second directions are normal to one another. The base  602  includes a threaded hole  620  communicating with the arm receiving opening  618 . A locking knob  622  includes a shank  624  that threads into the hole  620  such that the tip  626  of the shank  624  may be engaged with the arm  642  and tightened to lock the arm  642  relative to the base  602 . The connecting link  640  includes a saddle  644  opposite the arm  642 . The saddle  644  includes spaced apart sides  646 ,  648  which in turn include coaxially aligned bores  650 ,  652 . The bores  650 ,  652  receive a clamping bolt  654  and a clamping knob  656  threads onto the bolt  654 . One of the bores  652  may be non-cylindrical to receive a non-cylindrical head  658  of the bolt  654  to prevent the bolt  654  from turning when the knob  656  is turned. 
     The guide member  680  includes means for establishing a datum in the surgical navigation system coordinate system. In the illustrative orthopaedic guide of  FIGS. 12-17 , the guide member  680  includes guide holes  682  for guiding pins to establish a datum. The guide member  680  includes a tracking element, such as an electromagnetic coil  684 , to permit the surgical navigation system to track the position and orientation of the guide member  680 . The guide member  680  includes a tab  686  that engages the saddle  644 . A through hole  688  in the tab  686  aligns with bores  650 ,  652  in the saddle such that the clamping bolt  654  may pass through one saddle bore  652 , through the hole  688  in the tab  686 , through the other saddle bore  650 , and engage the clamping knob  656 . The saddle  644  and tab  686  arrangement forms a hinge that permits the guide member  680  to be pivoted about the clamping bolt axis and locked in a desired angular position by tightening the clamping knob  656 . 
     In use, the base member  602  is secured at the surgical site. For example, the base member  602  may be mounted on the bone. Alternatively, as shown in  FIG. 16 , the base member  602  may be mounted on the distal femoral cut guide  304 . This provides a convenient mounting arrangement that facilitates the logical and rapid progression of the surgical procedure. The undercut slot  608  of the base clamping nut  604  engages a rail  305  and slot  307  formed along the top  309  of the distal femoral cut guide  304 . The base  602  is slid along the distal femoral cut guide  304  to adjust the anterior/posterior position of the guide member  680  relative to the surgical site. The anterior/posterior position is locked by tightening the screw  610 . The connecting link arm  642  is slid within the arm receiving opening  618  to adjust the medial/lateral position of the guide member  680  relative to the surgical site. The medial/lateral position is locked by tightening the knob  622 . The guide member  680  is pivoted in the saddle  644  to adjust the interior/exterior rotation angle of the guide member  680  relative to the surgical site. The interior/exterior rotation angle is locked by tightening the knob  656 . The mechanism is manipulated until the surgical navigation system indicates that the guide member  680  is located in a desired position. The locking knobs  614 ,  622 ,  656  are then tightened to secure the position. The guide member  680  may then be used to establish a datum for guiding a subsequent surgical component. For example, pins  303  may be inserted through guide holes  682  and into the femur  299 . The navigated orthopaedic guide  600  and distal femoral cut guide  304  may then be removed. 
       FIG. 17  illustrates an anterior rough cut guide block  700  mounted on the pins  303 . The anterior rough cut guide block  700  includes holes  702  to receive the pins  303  and a cutter guide  704  for guiding a cutter to form a surface on the bone. With the anterior rough cut guide block  700  at the desired position as established by the pins  303 , additional fixation members may be inserted through some of the holes  702  to secure the anterior rough cut guide block  700  while a cutter is guided to cut the bone  299 . With the distal and anterior surfaces of the femur  299  cut, the proximal/distal, anterior/posterior, and internal/external rotation of a femoral implant are established. A finishing guide may be referenced to the distal and anterior cut surfaces of the femur  299  and placed in a desired medial/lateral position. The finishing cuts may then be made and the femoral implant inserted. The navigated orthopaedic guide of  FIGS. 12-17  has been shown in use to position an anterior rough cut guide  700 . However, it may also be used to position a posterior rough cut guide or other suitable surgical components. 
       FIGS. 18-23  depict another illustrative embodiment of a navigated orthopaedic guide for establishing a datum to guide the placement of a surgical cut guide  900  ( FIG. 22 ). The navigated guide  800  includes a body  802  having a top surface  804 , a bottom surface  806 , a leading edge  808 , a trailing edge  810 , and a peripheral sidewall  812 . The top and bottom surfaces  804 ,  806  are relatively closely spaced such that the body  802  is in the form of a relatively thin plate shaped body. A centerplane  805  bisects the body  802  between the top and bottom surfaces  804 ,  806 . The body  802  thickness is sized as a slip fit within a cut slot  902  in the cut guide  900 . Thus, the body  802  is a solid representation of the cut plane established by the cut slot  902  and the body  802  serves as the datum to guide the cut guide  900 . The centerplane  805  of the body corresponds to the center of the cut slot  902 . The body  802  optionally tapers toward the centerplane  805  in the direction of the the trailing edge  810  to ease insertion of the trailing edge  810  into the cut slot  902 . The guide  800  includes fasteners for attaching the body to a bone. In the illustrative embodiment, the fasteners are in the form of a plurality of spikes  814  formed integrally with the body  802  and projecting outwardly from the leading edge  808  parallel to the centerplane  805 . Each spike  814  defines a rectangular pyramid tapering from the leading edge  808  to a sharp point  816  for penetrating bone. Alternatively, the fasteners may be cylindrical, conical, spiral, and/or any other suitable shape. The fasteners may be formed integrally with the body  802  as shown or they may optionally be provided separately from the body  802 . If they are provided separately, the body may include suitable holes, grooves, channels, and/or other structures to permit the fasteners to hold the body  802  onto a bone. 
     The body  802  further includes a tracking element  818  to permit the surgical navigation system to track the position and orientation of the body  802 . The tracking element  818  may be an electromagnetic coil, as shown. Alternatively, as with the other embodiments disclosed, the tracking element  818  may be in a form suitable for acoustic, visual, radio frequency, and/or other suitable surgical tracking system. The tracking element  818  may be embedded in the body  802  as shown. Alternatively, the tracking element  818  may be placed on the surface of the body  802  or placed on a support extending from the body  802 . For example, the tracking element  818  may include an array of tracking elements in a tracking array removably mounted to the body  802  as is known in the art. Once the body  802  has been navigated to a desired position and secured, the array may optionally be removed. It is preferable to have a tracking element that does not extend beyond the surface of the body  802  or that is removable in order to improve visualization, ease insertion of the body into a cut slot, and/or otherwise streamline the body  802 . 
     The illustrative cut guide  900  for use with the navigated guide includes a body  904  having a front surface  906 , a back surface  908 , a top surface  909 , a bottom surface  910 , and a peripheral side wall  911 . A slot  902  extends through the body  904  from the front surface  906  to the back surface  908 . The slot  902  has a slot thickness from top to bottom, a slot width from side to side, and a slot depth from front to back defining a plane to guide a cutter (not shown) within a plane to form a planar surface on a bone. The cutter may include a saw blade, a rotary burr, a side cutting mill, and/or other suitable cutter. The slot  902  is a close slip fit over the body  802  of the navigated guide  800 . The cut guide  900  further includes fixation holes  912  for receiving fasteners (not shown) to hold the cut guide  900  in position on a bone while the bone is cut. The fasteners may include pins, screws, and/or other suitable fasteners. 
     In use, the surgical navigation system is activated and used to manipulate the navigated guide  800  into a desired position relative to a bone ( FIG. 22 ). For example, if it is desired to cut the distal femur  850  in knee replacement surgery, the guide  800  is navigated so that it lies in a plane corresponding to the desired plane of the distal femoral cut. The surgical navigation system may display the cut plane location relative to the bone for surgeon reference. The surgical navigation system may also provide visual, auditory, alpha numeric, and/or other position adjustment cues to the surgeon to indicate when the navigated guide  800  is in a desired position. The shape of the guide  800  further permits the surgeon to visually and tactilely verify the location of the cut plane. By visualizing the plate-like body  802  the surgeon can see where the cut plane intersects the surgical site. The rectangular plan form of the illustrative navigated guide  800  facilitates mentally extrapolating the cut plane through the surgical site. Similarly, the relatively broad, flat top and bottom surfaces  804 ,  806  and narrow leading and trailing edges  808 ,  810  facilitate the surgeon feeling the cut plane. By placing his fingers on the surfaces and edges, the surgeon can tactilely determine the cut guide position and orientation. When the cut plane is properly established, the navigated guide  800  is attached to the bone by driving the fasteners ( FIG. 22 ). In the illustrative embodiment, the surgeon can strike the trailing edge  810  to force the spikes  814  into the bone. With the navigated guide  800  attached to the bone, the cut guide  900  is positioned by sliding the cut guide  900  slot over the body  802  and seating the cut guide  900  against the bone ( FIG. 23 ). Fasteners may then be used to anchor the cut guide  900  relative to the bone. The navigated guide  800  is then pulled away from the bone through the slot  902  and the cut guide  900  is used to guide a cutter to cut the bone. The navigated guide  800  can be similarly used to establish a cut plane at any desired anatomic location for any surgical purpose. 
     Although examples of a navigated orthopaedic guide and its use have been described and illustrated in detail, it is to be understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. The invention has been illustrated with orthopaedic guides setting pins, guiding cutters, and establishing cut planes in specific locations related to knee replacement surgery. However, the orthopaedic guide may be configured to position other types of datums, for use with other types of surgical components, and at other locations within a patient&#39;s body. Accordingly, variations in and modifications to the orthopaedic guide and its use will be apparent to those of ordinary skill in the art, and the following claims are intended to cover all such modifications and equivalents.