Patent Publication Number: US-11642155-B2

Title: Stereotactic computer assisted surgery method and system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 12/319,720, filed Jan. 9, 2009, which claims the benefit of the filing date of United States Provisional Patent Application No. 61/010,543 filed Jan. 9, 2008, the disclosures of which are both hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a system and method of computer assisted surgery (CAS) using stereotactic navigation with three-dimensional visualization, and more specifically to a CAS system that is reactive and does not disrupt operating room workflow procedures. 
     A current method of inserting implants (consisting of, for example, a plate and associated screws) is typically accomplished by positioning the plate on the corresponding anatomical location and inserting the screws with the assistance of fluoroscopy. The implantation of plating and nailing systems is often a difficult task because operating room (OR) procedures are generally minimally invasive and thus placement is achieved by trial and error using fluoroscopy such as a C-arm apparatus, i.e., C-arm vision. This generally leads to long operating times. Furthermore, during such a procedure, both the patient and the operator are exposed to significant amounts of radiation. 
     In addition, in some cases it may be impossible to determine the position of implant components (for example, the screws in the bone) with sufficient precision because the fluoroscopic image is only two-dimensional. This may lead to misplacement or insertion of screws of improper length. This, in turn, may cause high revision rates or even injuries (e.g., hip joint injury). In order to ensure that these implant components do not extrude from the bone, it is thus sometimes necessary to position these implant components with an excessively large margin of error away from the edge of the bone. In many instances, the result is that the implant cannot be positioned as intended, and the desired biomechanical stability cannot be achieved. In the case of femoral neck fractures, for example, the use of conventional fluoro-navigation does not result in any significant improvement. 
     Other cutting edge technologies currently being used in operating rooms to assist in surgery include intra-operative three-dimensional (3D) imaging and navigation systems based on tracking technology. However, only a few hospitals are using these technologies. The limited adoption of these technologies is primarily due to their high cost, the effort involved in installing these systems, and the significant resulting changes to OR procedures or workflow. For example, tracking technologies require a line of sight between the tracking device and navigation detection system. This disrupts the normal workflow since the surgeon and other personnel must then remain cognizant of the system&#39;s line of sight requirements. 
     Further, as a general matter, satisfactory positioning of a main implant, like a plate or nail, cannot be defined pre-operatively. For example, during an operation positioning can be done by haptic match on the bone surface or by reaming the bone to make space for an intra-medullary nail. In addition, although the position of sub-implant(s) might be based only on pre-operative images (e.g., fluoroscope or CT images), such position is still relative to the position of the main implant. Thus, a positioning procedure cannot be completely planned pre-operatively, but must be optimized during the operation. In this regard, classical stereotaxis cannot be used due to the fact that the position cannot be predefined. 
     Accordingly, there is a need for a computer assisted surgery (CAS) system that enhances surgical procedures without significantly disrupting the normal OR workflow. More specifically, there is a need for a combined 3D imaging and CAS system which can be easily and readily integrated into the clinical environment. Preferably, such a system would be low cost, easy to set-up and use, and minimize changes to the OR workflow. 
     SUMMARY 
     An aspect of the present invention is a reactive method for stereotactic surgery. The method preferably comprises positioning an implant associated with a reference body on a region of interest of a patient&#39;s anatomy; detecting information associated with the implant using an imaging system; determining, based on the detected information associated with the implant, an action to be taken as part of the surgery; and displaying positional information associated with the implant and the region of interest based on the action to be taken. 
     In accordance with this aspect of the present invention, positioning comprises acquiring two fluoroscope images of the region of interest at two different angles. 
     Further in accordance with this aspect of the present invention, displaying further comprises processing detected information associated with the implant by estimating the contours of the region of interest in at least two dimensions based on the plurality of two-dimensional images. 
     Further still in accordance with this aspect of the present invention, detecting comprises detecting the presence of the reference body based on one or more fiducial markers. 
     In another aspect, the present invention is a method for stereotactic surgery. The method preferably comprises positioning a medical device associated with a reference body proximate a region of interest of a portion of an anatomy of a subject and imaging the region of interest at two or more angles to obtain a plurality of two-dimensional images. In a preferred embodiment, the reference body comprises a plurality of fiducial members, most preferably at least four such markers that are visible to the imaging system. It is further preferred that the fiducial markers comprise spheres that are visible to the imaging system. 
     In accordance with this aspect of the present invention, the plurality of two-dimensional images are processed to produce three dimensional information associated with the region of interest. In addition, the method further preferably includes associating, based on the three dimensional information, a virtual medical device with the region of interest and the reference body and displaying the association as an image showing the virtual medical device superimposed onto the region of interest. 
     Further in accordance with this aspect of the present invention, the virtual medical device comprises a main implant and one or more sub-implants. In addition, the virtual main implant is superimposed over the current location of the actual implant and the virtual sub-implants are generated so as to show its future position. Accordingly, the virtual sub-implants inform the surgeon of where the actual sub-implant will be located before it is placed in the region of interest. 
     In accordance with this aspect of the present invention, imaging preferably comprises acquiring two fluoroscope images of the region of interest at two different angles. In addition, processing further preferably comprises estimating the contours of the region of interest in at least two dimensions based on the plurality of two-dimensional images. 
     Further in accordance with this aspect of the present invention, processing may further comprise forming a three dimensional image associated with the region of interest based on the estimation. In a further preferred aspect, the present invention may be applied to a surgical implant procedure wherein the region of interest comprises a femoral head, the plurality of two dimensional images comprise anterior-to-posterior and axial images of the femoral region and estimating comprises forming an outline of the femoral head on the anterior-to-posterior and axial images. In this regard, the method may further comprise forming parts of a three dimensional sphere representing important portions of the femoral head. 
     Further still in accordance with this aspect of the present invention, the medical device preferably comprises an intracapsular plate and the reference body is connected to the plate, and positioning comprises positioning the intracapsular plate on a femur proximate the femoral head. In addition, the virtual medical device preferably comprises a virtual intracapsular plate and displaying comprises showing the virtual intracapsular plate superimposed on the position of the intracapsular plate in relation to the femoral head. 
     In another aspect, the present invention is a computer assisted surgical system, comprising: an apparatus for imaging a region of interest of a portion of an anatomy of a subject; a memory containing executable instructions; and a processor programmed using the instructions to perform a method. In this regard, the processor preferably receives two or more two-dimensional images of the region of interest taken at different angles from the apparatus, processes the two or more two-dimensional images to produce three dimensional information associated with the region of interest, superimpose a virtual reference body onto the region of interest based on the three dimensional information to form an image showing the virtual reference body relative to the region of interest, and generate a display signal associated with the superimposed image. Preferably, the reference body is first detected and superimposed onto an object that models the region of interest, e.g., sphere for a femoral head; and the display signal is then generated. 
     In accordance with this aspect of the present invention, the processor preferably processes the one or more two-dimensional images by outlining the contours of the region of interest in two dimensions and creates a three dimensional object representing the region of interest. The three dimensional object may be derived from a database and based on age and gender of the patient. The three dimensional object may also be determined based on landmarks associated with the region of interest. 
     Further in accordance with this aspect of the present invention, a medical device may comprise a device selected from the group consisting of an intracapsular plate, an artificial joint, a pacemaker and a valve. 
     In another aspect, the present invention is a system and method of computer assisted surgery (CAS) using stereotactic navigation with three-dimensional visualization, wherein an implant or implant system acts as a stereotactic device. The invention provides a reactive CAS system designed for use with mono-axial and poly-axial plates and nails. Based on the principles of stereotactics and 2D-3D matching, a system is provided that virtually suggests or gives indication of the optimal position of an implant by calculating such position. In addition, the system may also calculate screw lengths before drilling. Aided by image processing and virtual 3D visualisation, the system can achieve optimal biomechanics. 
     In addition, unlike existing navigation systems, the CAS system of the present invention is designed to be reactive to reduce any additional effort for the surgeon. In particular, the system may be triggered by use of a reference body, implant K-wires, or screws that are normally used as part of the surgical procedure. In addition, by detecting these devices, the system is able to determine the step in the workflow that&#39;s being performed. More specifically, image processing is used to detect various objects during the workflow and determine which step is being performed by the surgeon and for system adaptation. 
     In another aspect, the system provides necessary 3D information without the need for intra-operative 3D imaging (e.g. 3D C-arms). The system is also low cost, easy to set-up and use, and minimizes changes to the OR workflow. The present system also requires fewer X-ray images and is therefore safer for patients. 
     In another aspect, the invention makes use of an iterative procedure (which for the example of using an ICP to fix a femur neck fracture) includes one or more of the following steps:
         1. positioning an implant in an anatomical region of interest, e.g., based on a satisfying haptic match;   2. fluoroscopic imaging of the anatomical region of interest;   3. virtually checking the future position of the sub-implant(s);   4. virtually realigning the implant according to constraints until a satisfactory virtual position is reached;   5. providing active or passive realignment values for position of the implant to the surgeon (i.e., actively by identifying the best location or passively by allowing the surgeon to decide;   6. actual realignment of the plate by the surgeon based on realignment values and a satisfactory haptic match; and   7. iterate procedure starting at step  2  until operation complete.       

     These and additional aspects and features of the present invention are described in further detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  illustrates a stereotactic computer assisted surgical system in accordance with an aspect of the present invention. 
         FIG.  1 B  depicts a computer that may be used in the system of  FIG.  1    in accordance with an aspect of the present invention. 
         FIG.  2    illustratively depicts how a conventional two-dimensional (2D) image may not accurately show the positions of screws in a region of interest. 
         FIG.  3    illustratively depicts how three-dimensional imagery may be used to depict the positional information that is not apparent with conventional two dimensional images. 
         FIG.  4 A  is a flowchart illustrating a procedure for implanting a medical device in accordance with an aspect of the present invention. 
         FIG.  4 B  is a flowchart illustrating a procedure for positioning an implant in accordance with an aspect of the present invention. 
         FIG.  4 C  is a flowchart illustrating a procedure for generating a virtual image of an implant and a region of interest. 
         FIG.  5    shows the placement of an intracapsular plate implant in accordance with an aspect of the present invention. 
         FIG.  6 A  is a side view of an implant system including a reference body and an implant in accordance with an aspect of the present invention. 
         FIG.  6 B  is perspective view of a reference body and an implant in accordance with an aspect of the present invention. 
         FIG.  6 C  is perspective view of a reference body and an implant in accordance with an aspect of the present invention. 
         FIG.  7    illustrates the placement of an intracapsular plate implant onto a femur. 
         FIG.  8    illustratively depicts the step of taking two fluoroshots from different angles. 
         FIG.  9    illustrates detection of the femur head in the two fluoroshots. 
         FIG.  10    illustrates the visualization of a virtual three dimensional sphere representing the femur head based on conical projections of the two dimensional fluoroshots. 
         FIG.  11    shows the step of displaying a visualization based on a matching of the three dimensional sphere with the two dimensional images. 
         FIG.  12 A  shows a step of automatically adjusting the proposed position of the intracapsular plate in the distal direction. 
         FIG.  12 B  shows a step of automatically adjusting the proposed position of the intracapsular plate in the distal direction. 
         FIG.  13 A  shows a step of automatically adjusting the proposed position of the intracapsular plate by external rotation. 
         FIG.  13 B  shows a step of automatically adjusting the proposed position of the intracapsular plate by external rotation. 
         FIG.  14    shows the re-positioning and fixation of the intracapsular plate based on the proposed position. 
         FIG.  15    shows automatic detection of the insertion of K-wires and detecting movement of the femur head to ensure a reactive behavior. 
         FIGS.  16 A- 16 H  illustrate use of the method of  FIG.  4    in accordance with an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Generally, in one aspect, the system of the present invention is based on the registration of fluoroscopy images with an implant associated with a reference body. For example, the implant (e.g., an angle stable plate) may include the reference body or may be positioned in a predefined location in relation to the reference body, which is detected or recorded in a fluoro image. Thus, the actual spatial dimension and position of the implant can be determined by means of the correct identification and registration of the reference body in the fluoro images. 
     Where multiple related implants are included as part of the procedure, e.g., main implants and sub-implants, after registration of the main implant as described above, the location of any remaining sub-implants may be depicted virtually in the correct spatial position in relation to the fluoro images of the main implant. The sub-implants (e.g., screws of the associated angle stable plate) will be located in a fixed, pre-defined position in relation to the main implant after all implants have been implanted. 
     In order to provide the information necessary for an anatomically correct location of all (main and sub-) implants, important anatomical regions are approximated using three dimensional bodies or objects depicted in the fluoro image in correct relative position. Target values are compared with the values of the location of the remaining implants, which are used in determining the current position of the main implant. 
     During pre-operative planning (for example, using a non-invasive applied reference body), the partial or sub-implants (e.g., screws) can first be placed in an optimum position, independent of the location of the main implant (plate). In a subsequent operation (using an invasive reference body), where the main implant location has been determined by the pre-operative planning (with a position estimate derived by the surgeon), the location of the main implant can be optimized using haptic feedback. After the registration as described above, the resulting location of the partial or sub-implants are depicted virtually; this position is compared to the position of the partial implant in the pre-operative plan, and to the distances to important anatomical (three-dimensional) structures. In a reactive iterative process (adjusting the plate as instructed by the system), it is possible to determine the optimum balance between an ideal main implant location (for example, plate fit) and the ideal partial implant position (for example, screw location). 
     Turning now to  FIG.  1 A , there is illustrated a stereotactic computer assisted surgical (CAS) system  100  in accordance with an aspect of the present invention. As shown, in the preferred embodiment, the system  100  includes an imaging apparatus  110 , such as a C-arm fluoroscope, and a computer device  120  such as laptop computer. In general, the computer device  120  contains a processor  150 , memory  160  and other components typically present in general purpose computers as depicted in  FIG.  1 B . 
     Memory  160  stores information accessible by processor  150 , via bus  162  for example, including instructions  164  for execution by the processor  150  and data  166  which is retrieved, manipulated or stored by the processor  150 . The memory  160  may be of any type capable of storing information accessible by the processor  150 , such as a hard-drive, ROM, RAM, CD-ROM, write-capable, read-only, or the like. The instructions  164  may comprise any set of instructions to be executed directly (such as machine code) or indirectly (such as scripts) by the processor. In that regard, the terms “instructions,” “steps” and “programs” may be used interchangeably herein. The functions, methods and routines of the program in accordance with the present invention are explained in more detail below. 
     Data  166  may be retrieved, stored or modified by processor  150  in accordance with the instructions  164 . The data may be stored as a collection of data. For instance, although the invention is not limited by any particular data structure, the data may be stored in computer registers, in a relational database as a table having a plurality of different fields and records, or as an XML document. The data may also be formatted in any computer readable format such as, but not limited to, binary values, ASCII or EBCDIC (Extended Binary-Coded Decimal Interchange Code). Moreover, any information sufficient to identify the relevant data may be stored along with the data, such as descriptive text, proprietary codes, pointers, or information which is used by a function to calculate the relevant data. 
     Although the processor  150  and memory  160  are functionally illustrated in  FIG.  1 B  within the same block, it will be understood by those of ordinary skill in the art that the processor  150  and memory  160  may actually comprise multiple processors and memories that may or may not be stored within the same physical housing. For example, some or all of the instructions  164  and data  166  may be stored on removable CD-ROM and others within a read-only computer chip. In addition, some or all of the instructions  164  and data  166  may be stored in a location physically remote from, yet still accessible by, the processor  150 . Similarly, the processor  150  may actually comprise a collection of processors which may or may not operate in parallel. 
     As shown, computer device  120  may comprise additional components typically found in a computer system such as a display (e.g., an LCD screen), user input (e.g., a keyboard, mouse, game pad, touch-sensitive screen), microphone, modem (e.g., telephone or cable modem), and all of the components used for connecting these elements to one another. 
     As is also shown in  FIG.  1 A , a patient  185  would typically be positioned on an operating table with various restraints such that the area to be operated on is constrained from moving during the surgery. The fluoroscope  110  (or other suitable imaging apparatus) is used to obtain images of the region of interest of the patient&#39;s anatomy, e.g., the region being operated on or area to which the implant will be attached. As is discussed in further detail below, an illustrative region of interest may comprise an area that includes the femoral neck and an intracapsular plate (ICP). The computer  120  (or other suitable image processing and display apparatus) is used to process the images from the fluoroscope, determine positioning for the implant and sub-implants, and provide feedback/instructions to the surgeon. The processing steps performed by the computer are described below. 
     In another aspect, the present invention addresses a problem with the current technique of ICP implantation of accurately positioning the plate using two-dimensional (2D) images. This problem is in part due to the dangerous screw placement needed to avoid cutouts. Specifically, the ends/tips of the screws need to be set as close as possible to the second cortex. However, the 2D images used by the surgeon do not reflect the 3D nature of the problem. 
       FIG.  2    shows common drawbacks of a conventional two-dimensional (2D) image. In particular, a 2D image  200  may not indicate improper positioning of a screw. In this instance, the 2D image  200  makes it appear that the screws are correctly positioned within the bone. However, a 3D illustration could provide additional information showing that a screw may actually have perforated the bone. For example,  FIG.  3    illustrates how 3D imagery may expose a problem with screw positioning that is not apparent with conventional 2D imaging. In  FIG.  3   , neither of the 2D images  300 ,  310  shows a problem with the screw position. However, if the 2D images are combined to create a 3D visualization, it becomes apparent the tip of the screw projects through the bone as illustrated at  320 . Hence, the 2D imagery currently relied upon by a surgeon may not always accurately reflect the location and positioning of medical devices and the like within a region of interest. Thus, in this example, it would be beneficial for a surgeon to have access to 3D imagery. 
     In one aspect, the present invention provides a system and method which generates 3D information from the 2D imagery to allow for more accurate positioning of a medical device, e.g., an implant, and thereby avoiding the above problems. Generally, as used herein, the term medical device includes any biomedical device or structure that is introduced or implanted into the anatomy of a subject. Such devices include those that replace or act as missing biological structures, or that are placed over or within bones or portions of the anatomy. As mentioned above, the present invention is described using the illustrative example of implanting an intracapsular plate (ICP) to repair a femoral neck fracture. Note, however, that the invention may find application in numerous surgeries, including virtually all fields of bone surgery (e.g., trauma, orthopedics, and pediatrics). 
     By way of background, it is generally known that fractures are usually repaired by reduction and fixation of the broken bones. The individual fragments of bone are aligned in their normal anatomical position (i.e., reduced) so that separated parts can grow together again. It is necessary that the parts remain relatively stable with respect to each other over an extended period of time to allow for healing. In some cases, particularly for more complicated fractures, it is necessary to connect the individual broken bone pieces directly to one another. In these cases, the fracture is fixed or reduced via an invasive procedure wherein an implant is installed within the body with screws or nails. 
     Turning now to  FIG.  4 A , there is depicted a high level flowchart  400  of the method steps of implanting an implant in accordance with an aspect of the present invention. As shown, the method begins with positioning of a main implant in a region of interest, at step S 402 . As is explained in further detail below, this initial positioning is preferably done using fluoroshots taken along at least two dimensions or directions. Once the main implant is positioned to the surgeon&#39;s satisfaction, the system  100  generates an image showing the position of a virtual implant and associated virtual sub-implants relative to the region of interest, step S 408 , based on the fluoroshots and the position of a reference body or reference objects within the field of view of the fluoroscope  110 . 
     Using the image of the virtual implants, the surgeon may then affix the implant, using the sub-implants for example, as is depicted at  5424 . Once the sub-implants (e.g., screws) and implants are in the place, the system may perform a quality check, at  5428 , by detecting and displaying the actual location of these implants relative to their desired position. This quality check is desirable given that during implantation, the position of an implant or sub-implant may change from its ideal position due to the mechanical forces during, for example, drilling or screw placement or as a result of movement by the patient. In this regard, quality checks, such as step at S 428 , may also be performed during affixation of implant, at step S 424 . Additionally, quality checks may also be performed post operatively using the system to detect movement in the implant caused by, for example, patient activity. 
     Significantly, the above method  400  is reactive in that the surgeon is not required to inform the system  100  of which step he/she is performing as part of the OR workflow. In this regard, this system  100  is compatible with the normal OR workflow and is able to determine the step in the OR workflow that is being performed by, for example, detecting the presence of a reference body or object. 
     Turning now to  FIG.  4 B , there is depicted the sub-steps or procedure for positioning or aligning the implant in accordance with step S 402  of  FIG.  4 A . As shown, the procedure begins with insertion and positioning the main implant in the anatomical region of interest at step S 430 . In keeping with the illustrative example, an intracapsular plate (ICP) is used to repair fractures of the femoral neck. Thus, at step S 430 , the ICP would be inserted into the patient and roughly positioned on the bone, in this case the femoral neck. This step may be done, for example, in accordance with the normal OR workflow, such as by allowing the doctor to use haptic feedback to judge an appropriate initial position for the plate. 
     In this regard,  FIG.  5    illustrates the placement of an ICP implant  510  (e.g., the main implant) along with sub-implants (i.e., the screws) to secure a femoral neck fracture. As shown, the ICP  510  is affixed to the femur  520  and screws are inserted through the neck and head of the ICP. Preferably, in accordance with an aspect of the present invention, the screws entering the femoral head are positioned entirely within the head. In an additional aspect of the present invention, as the ICP is contoured to the shape of the femur, the degrees of freedom in positioning the ICP on the bone are limited and are used as part of the alignment procedure  5402 . Specifically, the ICP can only be shifted along (i.e., translation) and/or rotated around the shaft axis of the femur. In addition, the ICP has threaded holes so that the position/angle of the screws relative to the plate is known. 
     In accordance with an aspect of the present invention, prior to insertion of the main implant within the region of interest, the main implant  510  is connected to a reference body or object. The reference body is preferably attached to (or part of) the implant, but may also be attached to an aiming device or instrument (e.g., a drill guide). In this way, the position of the implant may be determined based on the location and position of the reference body. Preferably, each implant is associated with a different reference body that is detectable by the system  100 , in particular the fluoroscope  110 . In a preferred embodiment, the reference body comprises a plurality of spherical fiducial markers inserted on or in the instrument (e.g., aiming device). By arranging the fiducial markers in a predetermined pattern, they may serve as identifiers for different instruments. In addition, the size and shape of the fiducial markers may also serve as identifiers. In this regard, the fiducial markers and instrument may be conveniently referred to as a reference body—though the fiducial markers are what provide the reference. 
     For example,  FIG.  6 A  illustrates a side view of a reference body  604  as part of the implant  610 . Together, the reference body and implant are referred to herein as an implant system  614 . As shown in  FIG.  6 A , the reference body  604  includes a one or more fiducial markers  616  that are detected by the imaging system and used as points of reference or measurement. Preferably, the fiducial markers comprise spheres to make for easier detection in a two-dimensional imaging system such as a fluoroscope. In addition, the arrangement of the fiducial markers within the reference body functions as signature that is used to identify the reference body and the associated implant. Given that the dimensions of the reference body and implant are known and these devices are fixed relative to each other, the location of the implant can be accurately determined by detecting or recording the location of the reference body. As is also shown in  FIG.  6 A , fiducial markers may also be placed on the implant itself, but are not necessary. 
       FIG.  6 B  is a perspective view of the aiming device  604  and implant  610  (which in keeping with the example is an ICP) in a detached condition.  FIG.  6 C  shows these two devices in an attached condition. As is shown, the aiming device  604  is contoured to fit the ICP  610 . In addition, it includes openings that allow access to the screw holes on the ICP  610  that are used to secure the implant  610  as is explained in further detail below. To allow for processing, the reference body must be in the field of view of the image with the implant and the region of interest  640 , which in keeping with this illustrative example includes the femur neck and femoral head. As part of this initial insertion and placement, the surgeon will typically use haptic feedback to determine a starting location for the implant. In addition, in making this initial placement, the surgeon may use either instrument  700  or reference body  604 . In this regard, the instrument  700  may also comprise a reference body by placing the appropriate fiducial markers on or in it. 
     Returning to  FIG.  4 B , once the surgeon determines an initial location for the implant (and accompanying reference body), a fluoroshot is taken of a region of interest along a first dimension or direction, at step  434 . For example, a fluoroshot may be taken along the anterior-posterior dimension or the axial dimension. With reference to  FIG.  1   , the anterior-posterior view is illustrated with the source  190  and detector  192  aligned along the y-axis, while in the axial view the source and detector are aligned along the z-axis As shown in  FIG.  8   , fluoroshots may be taken from any two different dimensions or directions  810 A,  810 B. Preferably, the two images will be taken perpendicular to one another (i.e. close to a 90 degree angle between them), but this is not required and any angle will suffice. 
     As the implant and reference body are located within the field of view of the imaging device, given their proximity to region of the interest, the fluoroscope  110  detects the presence of the reference body, i.e., the fiducial markers. Computer  120  then uses the image data it receives from the fluoroscope  110  to provide a visualization of the location of the implant relative to the region of interest. In particular, registration of the fluoroscopic images is performed using the reference body. As discussed above, the reference body is typically in a fixed position relative to the implant and bone. Usually, a three dimensional reference is attached to the image intensifier and visible in the X-image to determine the center of the X-ray beam and reduce distortion. As an alternative to using such a three dimensional reference body, a disk with fiducial markers may be used as a reference and may also provide compensation for distortion. In this latter embodiment, determination of the center of x-ray beam may then be provided by the reference body in the implant system. In addition, where digital image intensifiers are used, a disk is not necessary. 
     Determination of the implant relative to anatomical region of interest is done using known image processing techniques based on the variation in the spatial radiation arriving at the detector, including the radiation directed at the region of interest and reference body. Using the spatial variation, the computer is able to construction an image that accurately depicts the spatial relationship between the implant and region of interest (e.g., femur and femoral head) as a two dimensional image. 
     Upon viewing this image, the surgeon may then determine if the implant should be re-positioned, as at step S 438 . For example, the surgeon may decide to adjust the position along the length of the femur closer to the femoral head or other degree of freedom. If the surgeon decides such an adjustment is warranted, he/she repositions the implant as is shown at step S 440  and additional fluoroshots are taken at step S 434 . On the other hand, if the surgeon determines that the no adjustment is needed along in this dimension the procedure continues at step S 442  with stabilization of the implant. In keeping with the example, stabilization could be effected by insertion of a Kirshner wire (K-wire) through one or more openings in the ICP. 
     With the implant fixed as described above, a fluoroshot may then be taken along a different dimension, step S 446 . In particular, if the fluoroshots in step S 434  were taken along the anterior posterior direction, in step S 446  they may be taken along the axial direction or at another angle. In this regard, as part of step S 402 , it may be sufficient to use a single image for this step to optimize position along only one degree of freedom (e.g., a distal shift of the implant) where 3D information is not needed. 
     Upon completion of the fluoroshot at step S 446 , the surgeon may then view an image of the position of the implant. If it is determined that the implant needs to be adjusted at step S 448 , e.g., rotated in the case of an ICP, the procedure returns to step S 446  and additional fluoroshots are taken along this dimension. Once the surgeon is satisfied that the implant is appropriately positioned based on images obtain along this dimension, the procedure continues at step S 450  with additional stabilization of the implant. For example, where the implant or medical device is an ICP, K-wires may be inserted through additional openings in the ICP. As result of the foregoing procedure, the position of the ICP or other implant may be positioned by the surgeon iteratively and in accordance with normal OR workflow procedures. That is, the surgeon may repeat any steps within the procedure until the implant is appropriately positioned. 
     With the implant positioned as described above in relation to step S 402 , the method then continues as shown at step S 408  of  FIG.  4 A  and as will be now described in further detail as shown in  FIG.  4 C . In particular, at step S 454 , the system may then generate 3D information from the two dimensional fluoroshots recorded in step S 402  or additional two dimensional fluoroshots may be taken at different angles as described above. Since the implant is now stabilized relative to the region of interest, additional fluoroshots may be taken with the K-wires acting as a trigger for the system. In addition, as the reference body may also be attached to the implant, it may also serve as a reference object as described above. 
     In accordance with this aspect of the present invention, the resulting 2D images are processed to locate and outline a three dimensional contour, i.e., a sphere, of the femoral head. For example,  FIG.  9    shows an AP view image  910  and an axial view image  920  with superimposed circles  930 ,  940  outlining the contours of the femoral head. The circles  930 ,  940  may be constructed by computer  120  using image processing techniques such as edge detection or computer generated models. Such models may be created pre-operatively using MRI or other non-invasive techniques that can determine the location and size of organs or bones within the region of interest. 
     In addition, using the 2D images, the computer  120  then determines and generates 3D object that is associated with and models the region of interest, step S 456 , in accordance with another aspect of the present invention. In particular,  FIG.  10    illustrates the visualization of a virtual 3D sphere representing the femur head based on conical projections of the 2D images  910 ,  920 . As shown in  FIG.  10   , the virtual 3D sphere is formed by projecting the two dimensional coordinate system onto a three dimensional coordinate system. In this example, as the outline of the femoral head forms circle, the projection onto a three-dimensional coordinate system results in a sphere. Depending on the contours of the region of interest, these projections may be done using a Cartesian and/or spherical coordinate system. In addition, the location of the object in relation to region of interest may be accurately determined based on the position of the implant in relation to the reference body. 
       FIG.  11    shows the step of displaying a visualization of the region of interest, implants and sub-implants based on a matching of the 3D sphere with the 2D images, step S 458 . As shown in  FIG.  11 A , the invention superimposes a virtual ICP  1104  with screws and a spherical outline of the femoral head onto the original 2D axial and AP images. This visualization allows the surgeon to readily see the position of the ICP and screws relative to the femoral head. Notably, the visualization shows the positions of virtual screws, their length and how they will be positioned within the femoral head. In addition, the system can suggest the screw, e.g., particular model, or screw length that would be suitable for affixing the implant. 
     The visualization also allows the surgeon to manually adjust the position of the actual ICP if better alignment is considered necessary. For example,  FIG.  12 A  shows a proposed adjustment of the ICP  510  in the distal direction, as seen from the AP two dimensional image. More specifically, as can be also seen from  FIG.  12 B , the display may also include zones that indicate preferable translational adjustment of the implant relative to its current location. For example, an acceptance zone  1220  (e.g., using colors) may be used to indicate a more preferable location. Thus, if the screws are located outside this area distally, the surgeon may manually adjust the plate at S 55  and view an updated visualization by returning to step S 52 . 
       FIGS.  13 A and  13 B  show how adjustment of the ICP  610  by external rotation  1300  can be achieved. In particular, similar to the case of translational adjustment, if the surgeon believes that the implant is not aligned properly, he/she may adjust arrows  1300  to visualize how the implant is aligned if rotated. As can be also seen from  FIG.  13 B , an acceptance zone  1340  may be used to show how rotation would change the location of the screws from a preferred position. As is also shown in  FIG.  13 B , rotational movement is preferably performed after the location along the femur neck has been satisfactorily determined. In this way, the reference body  604  may fixed to the bone using a pin  1326 . This pin  1326  may then be used with teethed gear mechanism  1330  to more precisely rotate the implant as shown. 
     As discussed above, the present invention is reactive in that the system reacts to the surgeon in lieu of requiring the surgeon to take action or interact with the computer or system. As such, if the surgeon decides that the implant is properly aligned, he/she can then decide to secure the implant and complete the procedure. This minimizes disruptions in current OR workflow and allows the surgeon to use his/her judgment as part of the workflow. In contrast, conventional approaches tend to disrupt the OR workflow by requiring the surgeon to interact with the CAS. This typically lengthens the surgical procedure and requires more in the way of equipment, both of which increase the cost of surgical procedures. 
     Upon completion of the steps outlined above in relation to step S 408 , the procedure continues to step S 424 , where the implant may be affixed to the region of interest. Additional fluoroshots may be taken during or after step S 424  to verify reduction of the fracture and the position of the ICP and K-wires or screws. For example,  FIG.  15    shows the insertion of K-wires  1620 ,  1630  and a detected movement of the femur head  1610 . Ideally, the system will detect such movement and propose a corrective action such as new screw lengths. If necessary, further re-positioning of the implant and reduction of the fracture can be performed as discussed above. 
     As discussed above, Kirshner wires (K-wires) can be inserted through openings in the reference body  604 . More specifically, as shown in  FIG.  15   , a first K-wire ( 1630  may be inserted to fix the plate to the bone. (A second K-wire  1620  may also be inserted through the fracture.) Screws can then be inserted to compress the fracture (S 424 ). The screws may be self-tapping or be inserted through drilled holes. The invention preferably includes image processing software that is based on edge detection to detect any insertion and bending of the screws or K-wires. Such software may comprise a component or routine in a set of instructions that carry out the method described above. The ICP has threaded screw holes so that the screw position/angle relative to the plate is fixed. The K-wires may be removed before or after the screws have been inserted. 
     Alternatively, an aiming apparatus with scaling in combination with an oblong-shaped hole (wherein a K-Wire may be inserted) may be directly attached to the ICP and used to assist in the mounting and any further adjustment deemed necessary by the surgeon.  FIG.  14    shows repositioning using a prior art one-shot apparatus  1400 ; which is preferably replaced by the reference body  604  and other attachments  1326 ,  1330  discussed above. 
     Turning now to  FIGS.  16 A- 16 H , there is shown an alternative use of the methods described above in accordance with a further aspect of the present invention. As will be discussed in detail, these figures show insertion of a locking nail  1654 , which is used as part of a hip fracture repair system. In particular, and with reference  FIG.  16 A , the procedure begins with insertion of the nail  1654  into the femur  1658 . As is also shown, the nail  1654  is attached to an instrument or aiming device  1660 . The aiming device is preferably equipped with a plurality of fiducial markers, e.g., four or more, that act as a reference body that is detectable by the imaging system. In accordance with the methods previously described, at this initial state of the procedure, the surgeon obtains fluoroshots along a first dimension. For example, a fluoroshot may be obtained along the anterior-posterior axis of the patient or at any other angle the surgeon deems suitable. 
     As is shown in  FIG.  16 B , if the shot is taken along the anterior-posterior direction, the computer  120  detects calculates the position of the reference body and instrument  1660 , and displays a virtual nail  1666  in relation to the region of interest  1670 . In addition, the display includes a projection  1674  of the location of a screw that will be used to secure the nail  1654  within the femoral head or region of interest  1670 . As is also depicted in  FIG.  16 B , if the projected path  1674  of the screw is determined by the surgeon to require some adjustment, the surgeon may make a translational adjustment  1678  of the nail within the femur  1658 . After making the translational adjustment  1678 , the surgeon then, preferably, takes an additional fluoroshot to confirm that the adjustment moved the nail  1654  into a more desirable position using they display  1680  similar to that shown. 
     Once the surgeon is satisfied with translational alignment of the nail  1654 , he may then use the system to rotationally align the nail as is shown in  FIG.  16 C . In particular, the surgeon would take a fluoroshot at a different angle, such as along a hip lateral direction to obtain the image  1684  shown in  FIG.  16 C . Using this image, the surgeon may rotate the nail  1654  into a more desirable position and take additional fluoroshots to confirm the adjustment. 
     Once the surgeon determines that the nail  1654  is suitably aligned, he may then insert a K-wire  1687  as is shown in  FIG.  16 D . With the K-wire inserted, two or more two-dimensional images may be obtained with the fluoroscope, as described above. Using these two or more images, the system is then able to determine the appropriate screw lengths, as is shown in  FIG.  16 E . In particular, the two-dimensional images are used to create an object that models the region of interest, in this case, the femoral head. More specifically, where the region of interest is the femoral head, the computer  120  uses these two-dimensional images to create a sphere  1689  and superimposes within the sphere the location and lengths of screws that may be used to attach the nail  1654 . As is shown in  FIG.  16 E , the display includes a virtual screw  1691  along with tick marks  1693  that indicate the length of the screw just within the sphere  1689  and out through an opening in the nail  1654 . 
     Based on the tick marks  1693  shown in  FIG.  16 E , the surgeon may then select an appropriate screw of desirable length to affix the nail  1654 . Once the screw is selected, it is then inserted as is shown in  FIGS.  16 F and  16 G . As is also described above, once a screw is in place, additional images may be taken to verify that the length of the screw secure the device without protruding outside the region of interest as a result of the forces that were applied during the affixation procedure, as is illustrated in  FIG.  16 H . 
     The image processing performed by the invention includes: anatomic feature detection and segmentation; position detection of the reference body; generation of 3D information from 2D images; registration, rendering and display of 3D information on 2D images; and calculation of the optimal position of the implant. In addition, in another aspect, the system may propose an appropriate length for each screw. 
     As discussed above, at least two 2D images containing the reference body are required by the invention to provide 3D information. These images should be taken at different angles (preferably near a 90 degree angle). Additional 2D images can also be used to provide information. The images can be registered to one another by detecting distinctive anatomic features in the images and/or by using the reference body. The reference body (which occurs in each image) can be used to precisely register the images in three dimensions. The reference body can also be helpful in automatically detecting these anatomic structures for segmentation (e.g. detecting feature borders). The relative position of specific anatomical structures to the position of the reference body may also be estimated based on general bone shape statistics and on patient data (e.g. size, gender, age). This relative position may be used as a starting point for the segmentation algorithms Once the anatomic structures have been segmented, the image processing software can correlate the structures from different images to generate 3D information. 
     Various three-dimensional reconstruction algorithms can be used to generate this information. Typically, the algorithms will approximate the segmented anatomic features with geometric shapes (e.g., a circle). The geometric shapes are then matched/registered to their known relative positions in the 2D images. These shapes are then projected into 3D space to form, for example, a sphere or cylinder. The invention may initially select a typical 3D Shape for an anatomic region from a database and match it with the image by zooming, rotating, and/or translating the shape. The shape may also be altered, such as with a morphing algorithm, for a better match. In fact, pre-operative images may be taken of the same anatomic region to better determine the actual shape of various features. 
     Because the reference body is located within each image and is attached to an anatomic region (e.g. a bone), movement of the patient during surgery is not a problem in accordance with an aspect of the present invention. This is because the system can use the location of the reference body to register different fluoroscope images (independent of the image content) and generate a low artifact real 3D image using 3D reconstruction algorithms. This aspect of the invention to precisely register the images significantly reduces artifacts due to patient movement during surgery. 
     Preoperative planning may be performed by taking pre-operative images similar to the intra-operative images. This pre-operative planning can be used to determine the optimal sub-implant positioning which may then be checked against the intra-operative positioning. Such pre-operative images could be processed using different algorithms which are too time consuming to use during surgery or could be segmented and matched manually. 
     As discussed above, the invention may also provide a reactive workflow by automatically detecting the status of an operation and thus knowing the next operative steps to be performed. In this manner, the invention might provide suggestions to the surgeon. For example, the invention may suggest a specific type, size, or shape of a best-fit implant based on the detected geometry of a fracture. Moreover, the invention could modify a previous suggestion based on additional information determined during the surgery. 
     Additional distinctive aspects of the invention include that the stereo-tactic device is implanted in the body. In addition, the invention uses 2D images (e.g. fluoroscopic x-rays) to generate 3D information. The reference plate (ICP) is contoured to match the surface contour of the bone to restrict the degrees of freedom for adjustments. The reference plate (ICP) is also threaded so relative screw position is known. The invention calculates and proposes reference plate position, sphere position, screw position and lengths. 
     Advantages of the invention include that it reduces the surgery time for insertion of an implant, requires almost no interaction between the surgeon and the system, provides three-dimensional information on important regions, requires little change to operating room procedures, and is cheaper than current tracking based navigation. 
     Additional features of the invention include that it takes into account any bending of Kirshner wires (K-wires) through automatic detection, calculates and displays any dislocation of the femur head during implantation, and calculates the screw lengths. 
     Although the invention herein has been described with reference to an ICP procedure, it is to be understood that this embodiment is merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiment and that other arrangements may be devised without departing from the spirit and scope of the present invention.