Abstract:
A method for performing shoulder arthroplasty or hemiarthroplasty is provided. The method includes generating navigational reference information relating to position and orientation of a body part forming at least a portion of the shoulder joint. The reference information may be stored in a computer. Navigational references are attached to the body part and an object. Information is received regarding the position and orientation of the object with respect to the body part and the object is navigated according to this information. The body part may be modified using the object and the modification may be displayed on a monitor associated with the computer. The navigational references may be used to track a shoulder arthroplasty trial component. Information is received regarding the position and orientation of the trial component with respect to the body part. This information is used to navigate the trial component to the body part.

Description:
RELATED APPLICATION  
       [0001]     The present application claims priority to U.S. Provisional Ser. No. 60/564,162, entitled “Image Guided Surgery for Shoulder Arthroplasty,” filed on Apr. 21, 2004, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to computer-aided surgery, and more particularly relates to methods, systems, and apparatuses for providing computer-aided surgical navigation systems for shoulder arthroplasty.  
       BACKGROUND  
       [0003]     Many surgical procedures require a wide array of instrumentation and other surgical items. Such items may include, but are not limited to: sleeves to serve as entry tools, working channels, drill guides and tissue protectors; scalpels; entry awls; guide pins; reamers; reducers; distractors; guide rods; endoscopes; arthroscopes; saws; drills; screwdrivers; awls; taps; osteotomes, wrenches, trial implants and cutting guides. In many surgical procedures, including orthopedic procedures, it may be desirable to associate some or all of these items with a guide and/or handle incorporating a navigational reference, allowing the instrument to be used with a computer-aided surgical navigation system.  
         [0004]     Several manufacturers currently produce computer-aided surgical navigation systems. The TREON™ and ION™ systems with FLUORONAV™ software manufactured by Medtronic Surgical Navigation Technologies, Inc. are examples of such systems. The BrainLAB VECTORVISION™ system is another example of such a surgical navigation system. Systems and processes for accomplishing computer-aided surgery are also disclosed in U.S. Ser. No. 10/084,012, filed Feb. 27, 2002 and entitled “Total Knee Arthroplasty Systems and Processes”; U.S. Ser. No. 10/084,278, filed Feb. 27, 2002 and entitled “Surgical Navigation Systems and Processes for Unicompartmental Knee Arthroplasty”; U.S. Ser. No. 10/084,291, filed Feb. 27, 2002 and entitled “Surgical Navigation Systems and Processes for High Tibial Osteotomy”; International Application No. US02/05955, filed Feb. 27, 2002 and entitled “Total Knee Arthroplasty Systems and Processes”; International Application No. US02/05956, filed Feb. 27, 2002 and entitled “Surgical Navigation Systems and Processes for Unicompartmental Knee Arthroplasty”; International Application No. US02/05783 entitled “Surgical Navigation Systems and Processes for High Tibial Osteotomy”; U.S. Ser. No. 10/364,859, filed Feb. 11, 2003 and entitled “Image Guided Fracture Reduction,” which claims priority to U.S. Ser. No. 60/355,886, filed Feb. 11, 2002 and entitled “Image Guided Fracture Reduction”; U.S. Ser. No. 60/271,818, filed Feb. 27, 2001 and entitled “Image Guided System for Arthroplasty”; and U.S. Ser. No. 10/229,372, filed Aug. 27, 2002 and entitled “Image Computer Assisted Knee Arthroplasty”, the entire contents of each of which are incorporated herein by reference as are all documents incorporated by reference therein.  
         [0005]     These systems and processes use position and/or orientation tracking sensors such as infrared sensors acting stereoscopically or other sensors acting in conjunction with navigational references to track positions of body parts, surgery-related items such as implements, instrumentation, trial prosthetics, prosthetic components, and virtual constructs or references such as rotational axes which have been calculated and stored based on designation of bone landmarks. Sensors, such as cameras, detectors, and other similar devices, are typically mounted overhead with respect to body parts and surgery-related items to receive, sense, or otherwise detect positions and/or orientations of the body parts and surgery-related items. Processing capability such as any desired form of computer functionality, whether standalone, networked, or otherwise, takes into account the position and orientation information as to various items in the position sensing field (which may correspond generally or specifically to all or portions or more than all of the surgical field) based on sensed position and orientation of their associated navigational references, or based on stored position and/or orientation information. The processing functionality correlates this position and orientation information for each object with stored information, such as a computerized fluoroscopic imaged file, a wire frame data file for rendering a representation of an instrument component, trial prosthesis or actual prosthesis, or a computer generated file relating to a reference, mechanical, rotational or other axis or other virtual construct or reference. The processing functionality then displays position and orientation of these objects on a rendering functionality, such as a screen, monitor, or otherwise, in combination with image information or navigational information such as a reference, mechanical, rotational or other axis or other virtual construct or reference. Thus, these systems or processes, by sensing the position of navigational references, can display or otherwise output useful data relating to predicted or actual position and orientation of surgical instruments, body parts, surgically related items, implants, and virtual constructs for use in navigation, assessment, and otherwise performing surgery or other operations.  
         [0006]     Some of the navigational references used in these systems may emit or reflect infrared light that is then detected by an infrared camera. The references may be sensed actively or passively by infrared, visual, sound, magnetic, electromagnetic, x-ray or any other desired technique. An active reference emits energy, and a passive reference merely reflects energy. Some navigational references may have markers or fiducials that are traced by an infrared sensor to determine the position and orientation of the reference and thus the position and orientation of the associated instrument, item, implant component or other object to which the reference is attached.  
         [0007]     In addition to navigational references with fixed fiducials, modular fiducials, which may be positioned independent of each other, may be used to reference points in the coordinate system. Modular fiducials may include reflective elements which may be tracked by two, sometimes more, sensors whose output may be processed in concert by associated processing functionality to geometrically calculate the position and orientation of the item to which the modular fiducial is attached. Like fixed fiducial navigational references, modular fiducials and the sensors need not be confined to the infrared spectrum—any electromagnetic, electrostatic, light, sound, radio frequency or other desired technique may be used. Similarly, modular fiducials may “actively” transmit reference information to a tracking system, as opposed to “passively” reflecting infrared or other forms of energy.  
         [0008]     Navigational references useable with the above-identified navigation systems may be secured to any desired structure, including the above-mentioned surgical instruments and other items. The navigational references may be secured directly to the instrument or item to be referenced. However, in many instances it will not be practical or desirable to secure the navigational references to the instrument or other item. Rather, in many circumstances it will be preferred to secure the navigational references to a handle and/or a guide adapted to receive the instrument or other item. For example, drill bits and other rotating instruments cannot be tracked by securing the navigational reference directly to the rotating instrument because the reference would rotate along with the instrument. Rather, a preferred method for tracking a rotating instrument is to associate the navigational reference with the instrument or item&#39;s guide or handle.  
         [0009]     Computer-aided surgical navigation systems have been developed for various surgeries, but currently none exists for shoulder arthroplasty or hemiarthroplasty that includes features according to the present invention.  
         [0010]     One of the leading causes for revision after shoulder arthroplasty is misalignment of the implant. Currently, instrumentation design limits alignment of the humeral resection to average values for inclination and version. While some instrumentation designs allow for adjustability of inclination and offset, assessment is still made qualitatively. Also, surgeons often use visual landmarks, or “rules of thumb,” which can be misleading due to anatomical variability.  
         [0011]     Another problem arising in shoulder arthroplasty is that surgeons cannot resurface the glenoid due to a lack of exposure. Exposure in shoulder arthroplasty is limited due to the extensive amount of soft tissue surrounding the shoulder compartment. Because of this problem, surgeons may be able to perform only a hemiarthroplasty in which only the humeral head is replaced.  
         [0012]     Yet another problem unique to shoulder arthroplasty is the difficulty in determining the thickness of the scapula. Such a determination is necessary to prevent breakthrough during preparation of the glenoid.  
         [0013]     In fracture situations, it is difficult to determine the inferior/superior position of the humeral head due to the absence of landmarks. Malpositioning of the humeral head can lead to instability of the shoulder and even dislocation.  
         [0014]     The surgeon also relies on instrumentation to predict the appropriate size for the humerus and the glenoid instead of the ability to intraoperatively template the appropriate size of the implants for optimal performance.  
         [0015]     Another challenge for surgeons is soft tissue balancing after the implants have been positioned. Releasing some of the soft tissue attachment points can change the balance of the shoulder; however, the multiple options can be confusing for many surgeons. In revision shoulder arthroplasty, many of the visual landmarks are no longer present, making alignment and restoration of the joint line difficult.  
         [0016]     Thus, what is needed are systems and processes that allow a surgeon to use patient-specific measurements to determine proper alignment of implants and appropriate revision in shoulder arthroplasty.  
         [0017]     Also needed are systems and processes that assist in the appropriate placement of shoulder arthroplasty components and in the evaluation of that placement. Systems and methods for performing soft tissue balancing in shoulder arthroplasty are also needed.  
         [0018]     Also needed are systems and methods that address some or all of the problems mentioned above.  
       SUMMARY  
       [0019]     Some embodiments of the invention include a method for performing shoulder arthroplasty or hemiarthroplasty surgical operations on portions of a shoulder joint. The method includes: 
        (a) attaching at least one first navigational reference capable of being tracked by a navigational sensor to a body part forming at least a portion of the shoulder joint,     (b) generating navigational reference information relating to position and orientation of the body part,     (c) storing at least some of the navigational reference information in a computer,     (d) attaching at least one second navigational reference capable of being tracked by a navigational sensor to a surgical instrument,     (e) receiving information from the navigational sensor regarding the position and orientation of the surgical instrument with respect to the body part, and     (f) navigating the surgical instrument relative to the body part according to the position and orientation information.        
 
         [0026]     Other embodiments of the invention include a method for performing shoulder arthroplasty or hemiarthroplasty surgical operations on portions of a shoulder joint. The method includes: 
        (a) attaching at least one first navigational reference capable of being tracked by a navigational sensor to a body part forming at least a portion of the shoulder joint,     (b) generating navigational reference information relating to position and orientation of the body part,     (c) storing at least some of the navigational reference information in a computer,     (d) attaching at least one second navigational reference capable of being tracked by a navigational sensor to a surgical instrument,     (e) receiving information from the second navigational sensor regarding the position and orientation of the surgical instrument with respect to the body part,     (f) navigating the surgical instrument relative to the body part according to the position and orientation information,     (g) modifying the body part using the surgical instrument,     (h) generating and displaying on a monitor associated with the computer information regarding the modification of the body part,     (i) tracking a trial component using at least one of the navigational sensors,     (j) receiving information from at least one of the navigational sensor regarding the position and orientation of the trial component with respect to the body part,     (k) generating and displaying on the monitor associated with the computer a visual image of the trial component properly positioned and oriented relative to the body part, and     (l) navigating the trial component relative to the body part and attaching the trial component to the body part according to the image.        
 
         [0039]     Some embodiments of the invention include a method for performing shoulder arthroplasty or hemiarthroplasty surgical operations on portions of a shoulder joint. The method includes: 
        (a) attaching at least one first navigational reference capable of being tracked by a navigational sensor to a body part forming at least a portion of the shoulder joint,     (b) generating navigational reference information relating to position and orientation of a body part forming at least a portion of the shoulder joint,     (c) storing at least some of the navigational reference information in a computer,     (d) attaching at least one second navigational reference capable of being tracked by a navigational sensor to a surgical instrument,     (e) receiving information from the second navigational sensor regarding the position and orientation of the surgical instrument with respect to the body part,     (f) navigating the surgical instrument relative to the body part according to the position and orientation information,     (g) modifying the body part using the surgical instrument,     (h) generating and displaying on a monitor associated with the computer information regarding the modification of the body part,     (i) tracking a prosthetic component using at least one of the navigational sensors,     (j) receiving information from at least one of the navigational sensor regarding the position and orientation of the prosthetic component with respect to the body part,     (k) generating and displaying on the monitor associated with the computer a visual image of the prosthetic component properly positioned and oriented relative to the body part, and     (l) navigating the prosthetic component relative to the body part and attaching the prosthetic component to the body part according to the image.        
 
         [0052]     Some embodiments of the invention include a method for performing shoulder arthroplasty or hemiarthroplasty surgical operations on portions of a shoulder joint. The method includes: 
        (a) attaching at least one first navigational reference capable of being tracked by a navigational sensor to a humerus forming at least a portion of the shoulder joint,     (b) generating navigational reference information relating to position and orientation of the humerus,     (c) storing at least some of the navigational reference information in a computer,     (d) attaching at least one second navigational reference capable of being tracked by a navigational sensor to a humeral reamer,     (e) receiving information from the navigational sensor regarding the position and orientation of the humeral reamer with respect to the humerus, and     (f) navigating the humeral reamer relative to the humerus according to the position and orientation information.        
 
         [0059]     Other embodiments of the invention include a method for performing shoulder arthroplasty or hemiarthroplasty surgical operations on portions of a shoulder joint; the method includes: 
        (a) attaching at least one first navigational reference capable of being tracked by a navigational sensor to a glenoid fossa forming at least a portion of the shoulder joint,     (b) generating navigational reference information relating to position and orientation of the glenoid fossa,     (c) storing at least some of the navigational reference information in a computer,     (d) attaching at least one second navigational reference capable of being tracked by a navigational sensor to a glenoid reamer,     (e) receiving information from the navigational sensor regarding the position and orientation of the glenoid reamer with respect to the glenoid fossa, and     (f) navigating the glenoid reamer relative to the glenoid fossa according to the position and orientation information.        
 
         [0066]     Some embodiments of the invention include a method for performing shoulder arthroplasty or hemiarthroplasty surgical operations on portions of a shoulder joint. The method includes: 
        (a) attaching at least one first navigational reference capable of being tracked by a navigational sensor to a humerus forming at least a portion of the shoulder joint,     (b) generating navigational reference information relating to position and orientation of the humerus,     (c) storing at least some of the navigational reference information in a computer,     (d) attaching at least one second navigational reference capable of being tracked by a navigational sensor to a humeral reamer,     (e) receiving information from the navigational sensor regarding the position and orientation of the humeral reamer with respect to the humerus,     (f) navigating the humeral reamer relative to the humerus according to the position and orientation information, and     (g) attaching a cutting block to the humeral reamer.        
 
         [0074]     Some embodiments of the invention include a method for performing shoulder arthroplasty or hemiarthroplasty surgical operations on portions of a shoulder joint. The method includes: 
        (a) attaching at least one first navigational reference capable of being tracked by a navigational sensor to a humerus forming at least a portion of the shoulder joint,     (b) generating navigational reference information relating to position and orientation of the humerus,     (c) storing at least some of the navigational reference information in a computer,     (d) attaching at least one second navigational reference capable of being tracked by the navigational sensor to a humeral reamer,     (e) receiving information from the navigational sensor regarding the position and orientation of the humeral reamer with respect to the humerus,     (f) navigating the humeral reamer relative to the humerus according to the position and orientation information,     (g) attaching a cutting block to the humeral reamer,     (h) attaching at least one third navigational reference capable of being tracked by the navigational sensor to the cutting block, and     (i) positioning the cutting block in at least one rotational degree of freedom through a range motion with infinite positions in the range; and at least one translational degree of freedom through a range of motion with infinite positions in the range,     (j) receiving continuous information from the navigational sensor regarding the position and orientation of the cutting block with respect to the humerus or the humeral reamer, wherein the information comprises rotational information in at least one degree of freedom and translational information in at least one degree of freedom.        
 
         [0085]     Some embodiments of the invention include a computer-aided surgical navigation system for performing shoulder arthroplasty or hemiarthroplasty. The system includes: 
        (a) a sensor adapted receive information regarding position and orientation of at least one reference;     (b) a reference adapted to be mounted to a body part forming at least a portion of the shoulder joint;     (c) a reference adapted to be mounted to a surgical instrument for use in performing shoulder arthroplasty or hemiarthroplasty;     (d) a processor adapted to receive and store information from the sensor in order to track a position and orientation of the at least one surgical reference with respect to the body part; and     (e) a monitor adapted to receive information from the processor in order to display at least some of the navigational reference information and the at least one surgical reference.        
 
         [0091]     In some embodiments of the invention, the body part is the humerus. In other embodiments, the body part is the glenoid.  
         [0092]     In some embodiments, the surgical instrument is a reamer, a resection guide, a cutting block or a probe. In some more particular embodiments, the surgical instrument is a humeral reamer or a glenoid reamer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0093]      FIG. 1  is schematic view showing an environment for using a computer-aided surgical navigation system according to some embodiments of the invention in a shoulder arthroplasty or semiarthroplasty.  
         [0094]      FIG. 2  is view of the shoulder, including a humerus and a scapula to which navigational references according to some embodiments of the invention have been attached.  
         [0095]      FIG. 3  shows navigation and placement of a humeral reamer according to some embodiments of the present invention.  
         [0096]      FIG. 4  shows navigation and placement of a resection guide and a cutting block according to some embodiments of the present invention.  
         [0097]      FIG. 5 . shows the navigation and reaming the glenoid surface in preparation for a prosthetic glenoid component according to some embodiments of the invention.  
         [0098]      FIG. 6  shows navigation and placement of a humeral trial component on a humerus according to some embodiments of the invention.  
         [0099]      FIG. 7  shows navigation and placement of a drill guide on the glenoid surface according to some embodiments of the invention.  
         [0100]      FIG. 8  shows navigation and placement of a glenoid trial component on a glenoid fossa according to some embodiments of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0101]     This invention will now be described more fully with reference to the drawings, showing preferred embodiments of the invention. However, this invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth.  
         [0102]     Systems and processes according to some embodiments of the invention use computing capacity, including stand-alone and/or networked, to determine and/or store data regarding spatial aspects of surgically related items and virtual constructs or references, including body parts, implements, instrumentation, trial components, prosthetic components and anatomical, mechanical and rotational axes of body parts. Any or all of these may be physically or virtually connected to or incorporate any desired form of mark, structure, component, or other fiducial or reference device or technique which allows position and/or orientation of the item to which it is attached to be sensed and tracked, preferably in three dimensions of translations and varying degrees of rotation as well as in time, if desired.  
         [0103]     Systems and processes according to some embodiments of the invention employ computing means to calculate and store references axes of body components such as in shoulder arthroplasty, for example the anatomical axis of the humerus and the retroversion reference axis. From these axes such systems track the position of the instrumentation and osteotomy guides so that bone resections will locate the implant position optimally, usually aligned with the anatomical axis. Furthermore, during trial reduction of the shoulder, the systems provide feedback on the balancing of the soft tissue in a range of motion and under stresses and can suggest or at least provide more accurate information than in the past about which ligaments the surgeon should release in order to obtain correct balancing, alignment and stability. Systems and processes according to some embodiments of the present invention can also suggest modifications to implant size, positioning, and other techniques to achieve optimal kinematics. They can also include databases of information regarding tasks such as ligament balancing, in order to provide suggestions to the surgeon based on performance of test results as automatically calculated by such systems and processes.  
         [0104]      FIG. 1  is a schematic view showing an environment for using a computer-aided surgical navigation system according to some embodiments of the present invention in a surgery on a shoulder, in this case a shoulder arthroplasty. Systems and processes according to some embodiments of the invention can track various body parts such as humerus  101  and scalpula  102  to which navigational sensors  100  may be implanted, attached or associated physically, virtually or otherwise.  
         [0105]     Navigational sensors  100  may be used to determine and track the position of body parts, axes of body parts, implements, instrumentation, trial components and prosthetic components. Navigational sensors  100  may use infrared, electromagnetic, electrostatic, light sound, radio frequency or other desired techniques.  
         [0106]     The navigational sensor  100  may be used to sense the position and orientation of navigational references  104  and therefore items with which they are associated. A navigational reference  104  can include fiducial markers, such as marker elements, capable of being sensed by a navigational sensor in a computer-aided surgical navigation system. The navigational sensor  100  may sense active or passive signals from the navigational references  104 . The signals may be electrical, magnetic, electromagnetic, sound, physical, radio frequency, optical or visual, or other active or passive technique. For example in one embodiment, the navigational sensor  100  can visually detect the presence of a passive-type navigational reference. In an example of another embodiment, the navigational sensor  100  can receive an active signal provided by an active-type navigational reference. The surgical navigation system can store, process and/or output data relating to position and orientation of navigational references  104  and thus, items or body parts, such as  101  and  102  to which they are attached or associated.  
         [0107]     In the embodiment shown in  FIG. 1 , computing functionality  108  such as one or more computer programs can include processing functionality, memory functionality, input/output functionality whether on a standalone or distributed basis, via any desired standard, architecture, interface and/or network topology. In one embodiment, computing functionality  108  can be connected to a monitor  114  on which graphics and data may be presented to a surgeon during surgery. The monitor  114  preferably has a tactile interface so that the surgeon may point and click on monitor  114  for tactile screen input in addition to or instead of, if desired, keyboard and mouse conventional interfaces. Additionally, a foot pedal  110  or other convenient interface may be coupled to computing functionality  108  as can any other wireless or wireline interface to allow the surgeon, nurse or other user to control or direct functionality  108  in order to, among other things, capture position/orientation information when certain components are oriented or aligned properly. Items  112  such as trial components, instrumentation components may be tracked in position and orientation relative to body parts  101  and  102  using one or more navigational references  104 .  
         [0108]     Computing functionality  108  can, but need not, process, store and output on monitor  114  various forms of data that correspond in whole or part to body parts  101  and  202  and other components for item  112 . For example, body parts  101  and  102  can be shown in cross-section or at least various internal aspects of them such as bone canals and surface structure can be shown using fluoroscopic images. These images can be obtained using an imager  113 , such as a C-arm attached to a navigational reference  104 . The body parts, for example, humerus  101  and scapula  102 , can also have navigational references  104  attached. When fluoroscopy images are obtained using the C-arm with a navigational reference  104 , a navigational sensor  100  “sees” and tracks the position of the fluoroscopy head as well as the positions and orientations of the humerus  101  and scapula  102 . The computer stores the fluoroscopic images with this position/orientation information, thus correlating position and orientation of the fluoroscopic image relative to the relevant body part or parts. Thus, when the humerus  101  and corresponding navigational reference  104  move, the computer automatically and correspondingly senses the new position of humerus  101  in space and can correspondingly move implements, instruments, references, trials and/or implants on the monitor  114  relative to the image of humerus  101 . Similarly, the image of the body part can be moved, both the body part and such items may be moved, or the on-screen image otherwise presented to suit the preferences of the surgeon or others and carry out the imaging that is desired. Similarly, when an item  112 , such as a stylus, cutting block, reamer, drill, saw, extramedullary rod, intramedullar rod, or any other type of item or instrument, that is being tracked moves, its image moves on monitor  114  so that the monitor  114  shows the item  112  in proper position and orientation on monitor  114  relative to the humerus  101 . The item  112  can thus appear on the monitor  114  in proper or improper alignment with respect to the mechanical axis and other features of the humerus  101 , as if the surgeon were able to see into the body in order to navigate and position item  112  properly.  
         [0109]     The computing functionality  108  can also store data relating to configuration, size and other properties of items  112  such as joint replacement prostheses, implements, instrumentation, trial components, implant components and other items used in surgery. When those are introduced into the field of position/orientation sensor  100 , computing functionality  108  can generate and display overlain or in combination with the fluoroscopic images of the body parts  101  and  102 , computer generated images of joint replacement prostheses, implements, instrumentation components, trial components, implant components and other items  112  for navigation, positioning, assessment and other uses.  
         [0110]     Instead of or in combination with fluoroscopic, MRI or other actual images of body parts, computing functionality  108  may store and output navigational or virtual construct data based on the sensed position and orientation of items in the surgical field, such as surgical instruments or position and orientation of body parts. For example, monitor  114  can output a resection plane, anatomical axis, mechanical axis, anterior/posterior reference plane, medial/lateral reference plane, rotational axis or any other navigational reference or information that may be useful or desired to conduct surgery. In the case of the reference plane, for example, monitor  114  can output a resection plane that corresponds to the resection plane defined by a cutting guide whose position and orientation is being tracked by navigational sensors  100 . In other embodiments, monitor  114  can output a cutting track based on the sensed position and orientation of a reamer. Other virtual constructs can also be output on monitor  114 , and can be displayed with or without the relevant surgical instrument, based on the sensed position and orientation of any surgical instrument or other item in the surgical field to assist the surgeon or other user to plan some or all of the stages of the surgical procedure.  
         [0111]     In some embodiments of the present invention, computing functionality  108  can output on monitor  114  the projected position and orientation of an implant component or components based on the sensed position and orientation of one or more surgical instruments associated with one or more navigational references  104 . For example, the system may track the position and orientation of a cutting block as it is navigated with respect to a portion of a body part that will be resected. Computing functionality  108  may calculate and output on monitor  114  the projected placement of the implant in the body part based on the sensed position and orientation of the cutting block, in combination with, for example, the mechanical axis of the humerus and/or the shoulder, together with axes showing the anterior/posterior and medial/lateral planes. No fluoroscopic, MRI or other actual image of the body part is displayed in some embodiments, since some hold that such imaging is unnecessary and counterproductive in the context of computer aided surgery if relevant axis and/or other navigational information is displayed. Additionally, some systems use “morphed” images that change shape to fit data points or they use generic graphics or line art images with the data points displayed in a relatively accurate position or not displayed at all. If the surgeon or other user is dissatisfied with the projected placement of the implant, the surgeon may then reposition the cutting block to evaluate the effect on projected implant position and orientation.  
         [0112]     Additionally, computer functionality  108  can track any point in the navigational sensor  100  field such as by using a designator or a probe  116 . The probe also can contain or be attached to a navigational reference  104 . The surgeon, nurse, or other user touches the tip of probe  116  to a point such as a landmark on bone structure and actuates the foot pedal  110  or otherwise instructs the computer  108  to note the landmark position. The navigational sensor  100  “sees” the position and orientation of navigational reference  104  “knows” where the tip of probe  116  is relative to that navigational reference  104  and thus calculates and stores, and can display on monitor  114  whenever desired and in whatever form or fashion or color, the point or other position designated by probe  116  when the foot pedal  110  is hit or other command is given. Thus, probe  116  can be used to designate landmarks on bone structure in order to allow the computer  108  to store and track, relative to movement of the navigational reference  104 , virtual or logical information such as retroversion axis  118 , anatomical axis  120  and mechanical axis  122  of scapula  102 , humerus  101  and other body parts in addition to any other virtual or actual construct or reference.  
         [0113]     Systems and processes according to some embodiments of the present invention can communicate with suitable computer-aided surgical systems and processes such as the BrainLAB VectorVision system, the OrthoSoft Navitrack System, the Stryker Navigation system, the FluoroNav system provided by Medtronic Surgical Navigation Technologies, Inc. and software provided by Medtronic Sofamor Danek Technologies. Such systems or aspects of them are disclosed in U.S. Pat. Nos. 5,383,454; 5,871,445; 6,146,390; 6,165,81; 6,235,038 and 6,236,875, and related (under 35 U.S.C. Section 119 and/or 120) patents, which are all incorporated herein by this reference. Any other desired systems and processes can be used as mentioned above for imaging, storage of data, tracking of body parts and items and for other purposes.  
         [0114]     These systems may require the use of reference frame type fiducials which have four, and in some cases five elements, tracked by sensors for position/orientation of the fiducials and thus of the body part, implement, instrumentation, trial component, implant component, or other device or structure being tracked. Such systems can also use at least one probe which the surgeon can use to select, designate, register, or otherwise make known to the system a point or points on the anatomy or other locations by placing the probe as appropriate and signaling or commanding the computer to note the location of, for instance, the tip of the probe. These systems also may, but are not required to, track position and orientation of a C-arm used to obtain fluoroscopic images of body parts to which fiducials have been attached for capturing and storage of fluoroscopic images keyed to position/orientation information as tracked by the sensors. Thus, the monitor can render fluoroscopic images of bones in combination with computer generated images of virtual constructs and references together with implements, instrumentation components, trial components, implant components and other items used in connection with surgery for navigation, resection of bone, assessment and other purposes.  
         [0115]      FIGS. 2-7  are various views associated with shoulder arthroplasty surgery processes according to one embodiment of the invention.  FIG. 2  shows a human shoulder, as well as the corresponding the corresponding humerus  101  and scapula  102 , to which navigational references  104  have been rigidly attached in accordance with this embodiment of the invention. Attachment of navigational references  104  preferably is accomplished using structure that withstands vibration of surgical saws and other phenomenon which occur during surgery without allowing any substantial movement of navigational references  104  relative to the body part being tracked by the system.  
         [0116]     Systems and processes according to various embodiments of the invention can be used with cloud of points-type, registration-type, and other surgical location and preparation techniques and methods. For example, in one prosthetic installation procedure, a surgeon can designate a center of rotation of a patient&#39;s humeral head for purposes of establishing the mechanical axis and other relevant constructs relating to the patient&#39;s humerus according to which prosthetic components can ultimately be positioned. Such center of rotation can be established by articulating the humerus  101  within the glenoid  103  or a prosthesis to capture a number of samples of position and orientation information and thus in turn to allow the computer to calculate the average center of rotation. The center of rotation can be established by using a probe  116  associated with a navigational reference  104 , and designating a number of points on the humeral head and thus allowing the computing functionality  108  to calculate the geometrical center or a center that corresponds to the geometry of points collected. Additionally, graphical representations such as controllably sized circles displayed on the monitor can be fitted by the surgeon to the shape of the humeral head on planar images using tactile input on monitor  114  to designate the centers according to that graphic, such as are represented by the computing functionality  108  as intersection of axes of the circles. Other techniques for determining, calculating or establishing points or constructs in space, whether or not corresponding to bone structure, can be used in accordance with the invention.  
         [0117]     In another example, a navigational sensor  100  can be used in designation or registration of items that will be used in surgery. Registration simply means ensuring that the computing functionality  108  knows which body part, item or construct corresponds to which navigational reference or references  104 , and how the position and orientation of the body part, item or construct is related to the position and orientation of its corresponding navigational reference or references  104  attached to an impactor or other component which is in turn attached to an item. Such registration or designation can be done before or after registering bone or body parts. In one instance, a technician can designate with a probe  116  an item such as an instrument or component  112  to which a navigational  104  reference is attached. A navigational sensor associated with a computer-aided surgical navigational system can “see” the  100  position and orientation of the navigational reference  104  attached to the item and also the position and orientation of the navigational reference  104  attached to the probe  116  whose tip is touching a landmark on the item  112 . The technician can designate onscreen or otherwise the identification of the item  112  and then activates the foot pedal  110  or otherwise instructs the computing functionality  108  to correlate the data corresponding to such identification, such as data needed to represent a particular cutting block component for a particular shoulder implant product, with the navigational reference  104  attached to the component. The computer has then stored identification, position and orientation information relating to the navigational reference  104  for the component correlated with the data such as configuration and shape data for the item  112  so that upon registration, when the navigational sensor  100  can track the item  112  and navigational reference  104  in the infrared field, the monitor  114  can show the cutting block component moving and turning, and properly positioned and oriented relative to the body part or navigational information such as axes which are also being tracked.  
         [0118]     Similarly, the mechanical axis and other axes or constructs of body parts can also be “registered” for tracking by the system. Again, the computer-aided surgical navigational system can employ a fluoroscope to obtain images of the patient&#39;s humerus and scapula, including the coracoid process, acromion and glenoid, or other body parts, and/or it can allow generation of navigational information regarding such parts, such as for example, generation of anatomical axis  120  information which can be displayed with the position and orientation of devices, components and other structures connected to navigational references  104 . In the case of obtaining images, the system can correlate such fluoroscopic images with the position and orientation of the C-arm and the patient anatomy in real time as discussed above with the use of one or more navigational references placed on the body parts before image acquisition and which remain in position during the surgical procedure. Using these axes and constructs and/or images and/or the probe, the surgeon can select and register in the computing functionality  108  the center of the humeral head and elbow in orthogonal views, usually anterior/posterior and lateral, on a touch screen. The surgeon can use the probe  116  to select any desired anatomical landmarks or references at the operative site of the shoulder or on the skin or surgical draping over the skin, as on the elbow. These points can be registered in three-dimensional space by the system and can be tracked relative to the navigational references  104  on the patient anatomy which are preferably placed intraoperatively. Although registering points using actual bone structure is one preferred way to establish the axis, a cloud of points approach by which the probe is used to designate multiple points on the surface of the bone structure can be employed, as can moving the body part and tracking movement to establish a center of rotation as discussed above. Once the center of rotation for the humeral head and the epicondylar axis have been registered, the computer can calculate, store, and render, and otherwise use data for, the mechanical axis of the humerus.  
         [0119]     Any desired axes or other constructs can be created, tracked and displayed, in order to model and generate images and data showing any desired static or kinematic function of the shoulder for any purposes related to shoulder arthroplasty.  
         [0120]     After the mechanical axis and other rotation axes and constructs relating to the humerus and scapula are established, instrumentation can be properly oriented to resect or modify bone in order to fit trial components and implant components properly according to the embodiments shown in  FIGS. 6-7 . Instrumentation such as, for instance, cutting blocks, to which navigational references  104  are mounted, can be employed as shown in  FIG. 4 . The system can then track instrumentation as the surgeon manipulates it for optimum positioning. In other words, the surgeon can “navigate” the instrumentation for optimum positioning using the system and the monitor. In this manner, instrumentation may be positioned according to the system of this embodiment in order to align the osteotomies to the mechanical and rotational axes or reference axes on an extramedullary rod that does not violate the canal, on an intramedullary rod, or on any other type of rod. The monitor  114  can then also display the instrument such as the cutting block and/or the implant relative to the instrument and the rod during this process, in order, among other things, to select the proper size of implant and perhaps implant type. As the instrument moves, the flexion/extension and internal/external rotation of the relative component position can be calculated and shown with respect to the referenced axes; in the preferred embodiment, this can be done at a rate of six cycles per second or faster. The instrument position is then fixed in the computing functionality  108  and physically and the bone resections are made.  
         [0121]     Systems and processes according to embodiments of the invention can be used to track a humeral reamer to create a virtual anatomical axis of the humerus. The anatomical axis can be stored and subsequently used by the computer.  
         [0122]      FIG. 3  shows orientation of an humeral reamer  124  to which a navigational reference  104  is attached. The surgeon views the monitor  114  which has an image of the humeral reamer  124  overlain on or in combination with the humerus  101  fluroroscopic image as the two are actually positioned and oriented relative to one another in space.  
         [0123]     Computer-aided surgical navigation systems according to embodiments of the invention may also be used to determine the degree of humeral head retroversion, if any. The retroversion reference axis may be determined by determining the orientation of the proximal articular surface or the humerus with respect to the epicondylar axis of the elbow. This information may be used to control rotation.  
         [0124]     Once the humeral reamer  124  has been placed, instrumentation can be positioned as tracked in position and orientation by navigational sensor  100  and displayed on monitor  114 . Thus, as shown in  FIG. 4 , a resection guide  128  and a cutting block  126  of the sort used to establish the humeral anterior cut, with its navigational reference  104  attached, is introduced into the field and positioned on the reamer. Because the cutting block  126  corresponds to a particular implant product and can be adjusted and designated on screen to correspond to a particular implant size of that product, the computing functionality  108  can generate and the monitor  114  can display a graphic of the cutting block  126  and a humeral component overlain on the fluoroscopic image. The surgeon can thus navigate and position the cutting block  126  on monitor  114  using not only images of the cutting block  126  on the bone, but also images of a corresponding humeral component which will be ultimately installed. The surgeon can thus adjust the positioning of the physical cutting block  126 , and secure it to the reamer  124  in order to resect the anterior of the humerus  101  in order to optimally fit and position the ultimate humeral component being shown on the monitor  114 . Other cutting blocks and other resections may be positioned and made similarly on the humerus  101 .  
         [0125]     In some embodiments of the invention, the cutting block  126  may be navigated as it moves in six degrees of freedom: three translational and three rotational. For each rotational degree of freedom, the cutting block  126  may be tracked as it moves through a range motion with infinite positions in the range. Likewise, for each translational degree of freedom, the cutting block  126  may be tracked as it moves through a range of motion with infinite positions in the range. In some embodiments, the system receives continuous information from the navigational sensor  100  regarding the position and orientation of the cutting block  126  with respect to the humerus  101  or the humeral reamer  124 , wherein the information comprises rotational information in at least one degree of freedom and translational information in at least one degree of freedom. The information may be displayed on the monitor  114 , allowing the surgeon immediate and detailed information for positioning the cutting block  126 .  
         [0126]     In a similar fashion, instrumentation may be navigated and positioned on the glenoid fossa  103  of the scapula  102  and as tracked by navigational sensor  100  and on monitor  114  by images of the cutting block and the implant component.  
         [0127]     As shown in  FIG. 5  in a total shoulder arthroplasty, a glenoid reamer may be navigated to determine the depth, position and angle of reaming. Subsequently, navigated glenoid instruments are then used to prepare the glenoid to receive a glenoid component trial. Any appropriate glenoid component or component trial may be used, for example, an all-polyethylene glenoid component with three pegs or one keel or with a metal back. Such glenoid components generally have three screw holes on the glenoid base. Depending on the type of glenoid component used, a drill guide  138  or a keel reamer guide may be used to prepare the glenoid for the glenoid component. A navigated drill guide  138  is shown in  FIG. 7 .  
         [0128]     Once resection and modification of bone has been accomplished, implant trials can then be installed and tracked by the system in a manner similar to navigating and positioning the instrumentation, as displayed on the monitor  114 . Thus, a humeral component trial and a glenoid component trial may be placed as navigated on monitor  114  using computing functionality  118  generated overlays corresponding to the trials.  
         [0129]     During the trial installation process, and also during the implant component installation process, instrument positioning process or at any other desired point in surgical or other operations according to the invention, the system can transition or segue from tracking a component according to a first navigational reference to tracking the component according to a second navigational reference. Thus, as shown in  FIG. 6 , the trial humeral component  134  is mounted on an impactor  132  to which is attached a first navigational reference  104 . The trial component  134  is installed and positioned using the impactor  132 . The computing functionality  108  tracks the position and orientation of the trial component  134  relative to the navigational reference  104  on the impactor  132  (such as by prior registration of the component  134  attached to the impactor) so that it can generate and display the image of the humeral trial component  134  on monitor  114  overlaid on the fluoroscopic image of the humerus  101 . At any desired point in time, before, during or after the trial component  134  is properly placed on the humerus  101  to align with anatomical axis and according to proper orientation relative to other axes, the system can be instructed by foot pedal  110  or otherwise to begin tracking the position of the trial component  134  using the second navigational reference  104  attached to the humerus  101  rather than the one attached to the impactor  132 . According to the preferred embodiment, the navigational sensor  100  “sees” at this point in time both the navigational references  104  on the impactor  132  and on the humerus  101  so that it already “knows” the position and orientation of the trial component  134  relative to the first navigational reference  104  on the impactor  132  and is thus able to calculate and store for later use the position and orientation of the trial component  134  relative to the second navigational reference  104  on the humerus  101 . Once this “handoff” happens, the impactor  132  can be removed and the trial component  134  tracked with the navigational reference  104  on the humerus  101  as part of or moving in concert with the humerus  101 . Similar handoff procedures may be used in any other instance as desired in accordance with the present invention.  
         [0130]      FIG. 6  shows the placement of a humeral trial component  134  attached to humerus  101 . The trial component  134  is attached via impactor  132 . As explained above, both the humerus  101  and the impactor  132  have navigational references  104  attached that may be used in tracking and navigating trial component  134 .  
         [0131]     Similarly, as shown in  FIG. 8 , a glenoid trial component  136  can be placed on the glenoid  103  and then registered using a probe. A probe may be used to designate features on the glenoid trial component  136  of known coordinates, such as rotational alignment to the glenoid axis, the flexion/extension angle and the version/retroversion angle. As the probe is placed onto each feature, the system is prompted to save that coordinate position so that the system can match the glenoid trial component&#39;s  136  feature&#39;s coordinates to the saved coordinates. The system then tracks the glenoid trial component  136  relative to the anatomical reference frame.  
         [0132]     The system may also indicate the fit of the glenoid keel or pegs within the glenoid before bone preparation is performed to insure that breakthrough to the posterior aspect of the scapula  102  does not occur.  
         [0133]      FIG. 8  shows the placement of a glenoid trial component  136  attached to a glenoid  103 .  
         [0134]     Once the trial components are installed, the surgeon can assess alignment and stability of the components and the joint. During such assessment, in trial reduction, the computing can display on monitor  114  the relative motion between the trial components to allow the surgeon to make soft tissue releases and changes in order to improve the kinematics of the shoulder. The system can also apply rules and/or intelligence to make suggestions based on the information such as what soft tissue releases to make if the surgeon desires. The system can also display how the soft tissue releases are to be made.  
         [0135]     During this assessment, the surgeon may conduct certain assessment processes such as external/internal rotation, rotary laxity testing, range of motion testing (external rotation, internal rotation and elevation) and stability testing (anterior, posterior and inferior translation). Thus, in the external/internal rotation test, the surgeon can position the humerus at the first location and press the foot pedal. He then positions the humerus at the second location and once again presses the foot pedal so that the computing functionality has registered and stored two locations in order to calculate and display the rotation and whether it is acceptable for the patient and the product involved. If not, the computer can apply rules in order to generate and display suggestions for releasing ligaments or other tissue, or using other component sizes or types. Once the proper tissue releases have been made, if necessary, and alignment and stability are acceptable as noted quantitatively on screen about all axes, the trial components may be removed and actual components navigated, installed, and assessed in performance in a manner similar to that in which the trial components were navigated, installed, and assessed.  
         [0136]     At the end of the case, all alignment information can be saved for the patient file. This is of great assistance to the surgeon due to the fact that the outcome of implant positioning can be seen before any resectioning has been done on the bone.  
         [0137]     The tracking and image information provided by systems and processes according to the present invention facilitate telemedical techniques, because they provide useful images for distribution to distant geographic locations where expert surgical or medical specialists may collaborate during surgery. Thus, systems and processes according to the present invention can be used in connection with computing functionality  108  which is networked or otherwise in communication with computing functionality in other locations, whether by PSTN, information exchange infrastructures such as packet switched networks including the Internet, or as otherwise desire. Such remote imaging may occur on computers, wireless devices, videoconferencing devices or in any other mode or on any other platform which is now or may in the future be capable of rending images or parts of them produced in accordance with the present invention. Parallel communication links such as switched or unswitched telephone call connections may also accompany or form part of such telemedical techniques. Distant databases such as online catalogs of implant suppliers or prosthetics buyers or distributors may form part of or be networked with computing functionality  108  to give the surgeon in real time access to additional options for implants which could be procured and used during the surgical operation.  
         [0138]     The above methods and techniques are provided by way of example only, and other embodiments of the present invention can be used with other surgical location and preparation techniques and methods.  
         [0139]     Changes and modifications, additions and deletions may be made to the structures and methods recited above and shown in the drawings without departing from the scope or spirit of the invention and the following claims.