Patent Publication Number: US-2022211446-A1

Title: Systems and Methods for Intra-Operative Image Analysis

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/594,723 filed Oct. 7, 2019, entitled “Systems and Methods for Intra-Operative Image Analysis,” which is a continuation of U.S. patent application Ser. No. 14/974,225 filed Dec. 18, 2015, now U.S. Pat. No. 10,433,914, which is a continuation-in-part application of U.S. patent application Ser. No. 14/630,300 filed Feb. 24, 2015 (also referred to as “parent application”), now U.S. Pat. No. 10,758,198, which claims priority to U.S. Provisional Application No. 61/944,520 filed Feb. 25, 2014, U.S. Provisional Application No. 61/948,534 filed Mar. 5, 2014, U.S. Provisional Application No. 61/980,659 filed Apr. 17, 2014, U.S. Provisional Application No. 62/016,483 filed Jun. 24, 2014, U.S. Provisional Application No. 62/051,238 filed Sep. 16, 2014, U.S. Provisional Application No. 62/080,953 filed Nov. 17, 2014, and U.S. Provisional Application No. 62/105,183 filed Jan. 19, 2015. All of the above referenced applications are incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to analysis of images of features within a patient and more particularly to accurately analyzing such images during surgery. 
     BACKGROUND OF THE INVENTION 
     Orthopaedic surgeons and other healthcare professionals commonly rely on surgical guidance techniques that can be broadly classified in two categories: pre-operative digital templating or training systems that enable pre-surgical planning, and computer-assisted navigation systems providing intra-operative guidance for placement and movement of surgical instruments within a patient. There are benefits to both of these technologies, but each has respective limitations. 
     Preoperative digital templating techniques enable preoperative surgical planning by utilizing digital or hard copy radiographic images or similar X-ray-type, scaled according to an object of known size. Commonly, a spherical ball marker of known size is placed between the legs or next to the hip of a patient undergoing hip surgery so that it appears in the image; the ball marker is then utilized as a reference feature for image scaling. This preoperative scaling technique has inherent limitations to accuracy because it assumes that the bones within a patient and the surface ball marker will magnify at the same ratio. Commonly, the surgeon will realize during the surgery that this scale factor is inaccurate, due to deviations in magnification ratios, rendering the preoperative template ineffective for intraoperative decision making. For emergency cases such as hip fractures, preoperative digital templating often cannot be utilized, because the X-ray images are taken in a hospital setting without utilizing a ball marker or other scaling device. 
     Surgeons also have the option of utilizing computer-assisted navigation systems which provide intraoperative guidance. The purported benefits of computer navigation include reduction of outliers and adverse outcomes related to intraoperative positioning of surgical hardware. For example, computer navigation is utilized in hip replacement surgery to add precision to implant positioning by providing data on functional parameters such as leg length and offset changes during surgery. 
     Despite obvious clinical benefit, these systems have had limited adoption due to their expense, the learning curve and training requirements for surgeons and, for some systems, the additional procedure and time associated with hardware insertion into the patient. These adoption barriers have limited the use of computer assisted navigation to an extremely small percentage of overall hip arthroplasty surgeries. The surgeons that do not use these systems are limited to traditional techniques that are generally based on visual analysis and surgeon experience. However, these techniques are inconsistent, often leading to outliers in functional parameters which may affect patient satisfaction and implant longevity. 
     Details of one such technique, specifically used in a minimally invasive hip arthroplasty technique referred to as the direct anterior approach, are mentioned in the description of a total hip arthroplasty surgery, by Matta et al. in “Single-incision Anterior Approach for Total hip Arthroplasty on an Orthopaedic Table”, Clinical Ortho. And Related Res. 441, pp. 115-124 (2005). The intra-operative technique described by Matta et al. is time-consuming and has a high risk of inaccuracy due to differences in rotation, magnification and/or scaling of various images. The high risk of inaccurate interpretation using this technique has limited its utility in guiding surgical decision making. 
     What appears to be a software implementation of this technique is described by Penenberg et al. in U.S. Patent Publication No. 2014/0378828, which is a continuation-in-part application of U.S. Pat. No. 8,831,324 by Penenberg. While the use of a computer system may facilitate some aspects of this technique, the underlying challenges to the technique are consistent with the challenges to Matta&#39;s approach, and limit the system&#39;s potential utility. 
     There are various other examples of where intra-operative guidance systems could improve quality of patient care in orthopaedics through the reduction of outliers. One such example is in the treatment of peritrochanteric hip fractures. The selection of the proper implant and associated neck-shaft angle is often incompletely evaluated by the surgeon and implant representative utilizing conventional techniques. Furthermore, variations in placement of screws and other fixation devices and implants can significantly alter patient outcomes in treatment of these fractures. These variations and resulting outcomes are analyzed by Baumgaertner et al. in “The Value of the Tip-Apex Distance in Predicting Failure of Fixation of Peritrochanteric Fractures of the Hip”, J. Bone Joint Surg. 77-A No. 7, pp. 1058-1064 (1995). Other techniques relating to femoral fractures, including measurement of tip apex distance and screw position, are discussed by Bruijin et al. in “Reliability of Predictors for Screw Cutout in Intertrochanteric Hip Fractures”, J. Bone Joint Surg. Am. 94, pp. 1266-72 (2012). 
     Proper reduction of fractures, that is, proper alignment of bones during surgery, often leads to more consistent patient outcomes, and intraoperative analysis of such reductions is incompletely evaluated currently because of the lack of non-invasive technologies that enable intraoperative analysis. One example is in the treatment of distal radius fractures. As referenced by Mann et al, “Radiographic evaluation of the wrist: what does the hand surgeon want to know?” Radiology, 184(1), pp 15-24 (1992), accurate restoration of certain parameters, such as radial inclination, radial length and Palmar Slope or Tilt, during the treatment of distal radius fractures is important. Currently, intraoperative images are utilized by surgeons, but there is no ability to readily analyse these parameters and form comparative analysis to normal anatomy. 
     Given the inherent scaling limitations of preoperative surgical planning and adoption barriers of current intraoperative computer navigation systems, an opportunity exists for a system and method that provides accurate intraoperative guidance and data, but without the barriers to adoption and invasive hardware requirements of traditional computer-assisted navigation. 
     It is therefore desirable to have a system and method to effectively analyze images intra-operatively using comparative anatomical features, to enhance patient quality of care by providing accurate intra-operative guidance and data. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a system and method to accurately and effectively analyze and/or perform calculations on images of anatomical features and/or implants such as prosthetic devices during surgery. 
     Another object of the present invention is to provide image analysis and feedback information to enable more accurate planning, better fracture reduction, and/or optimal implant selection during the surgery. 
     Yet another object of the present invention is to capture and preserve a digital record of patient results for data collection and quality improvements in surgical procedures. 
     A still further object of the present invention is to improve the outcome of bone repositioning, fracture repair, and/or fixation within a patient. 
     This invention results from the realization that offset and length differential of an implant having at least one center of rotation can be accurately estimated during surgery by establishing at least one stationary point on the skeletal bone and at the center of rotation in an intraoperative image, aligning a digital implant representation with the implant, and then copying and positioning the digital representation in at least one reference image including one of (a) a preoperative image of the surgical site and (b) a contralateral image on an opposite side of the patient from the surgical site. Another realization is that changes in offset and length differential can be estimated based on selected alternative changes in at least one dimension of the implant for potential alternative implants. 
     This invention features a system and method that acquire (i) at least one reference image including one of a preoperative image of a surgical site with skeletal and articulating bones and a contralateral image on an opposite side of the patient from the surgical site, and (ii) at least an intraoperative image of the site after an implant has been affixed to the articulating bone. The system and/or method generates at least one reference stationary point on at least the skeletal bone in the reference image and at least one intraoperative stationary point on at least the skeletal bone in the intraoperative image, such as a tear drop, or other feature associated with a pelvic bone of a patient. The location of the implant is identified in the intraoperative image, including the position of first and second centers of rotation, which are co-located in the intraoperative image. At least a first digital implant representation is aligned with the skeletal component and with at least the intraoperative stationary point, and (ii) at least a second digital implant representation is aligned with the articulating bone component and at least one point, such as a landmark point on the greater trochanter of a femur, on the articulating bone. The digital representations are copied and positioned in the reference image in an equivalent location relative to at least the reference stationary point and the articulating bone to determine the position of the first and second centers of rotation relative to each other in the reference image. Any differences between the locations of the first and second centers of rotation in the reference image are utilized to analyze at least one of offset and length differential. 
     In one system embodiment, the system includes a memory, a user interface including a display capable of providing at least visual guidance to a user of the system, and a processor, with the processor executing a program performing at least the steps listed above and described in more detail below. In some embodiments for the system and/or method, analyzing includes generating a vector having its origin at the reference stationary point and its terminal point at the first center of rotation. In certain embodiments, identifying includes determining a longitudinal axis for the second digital implant representation and analyzing includes utilizing a difference in spacing (i) perpendicular to the longitudinal axis to calculate offset and (ii) parallel to the longitudinal axis to calculate length differential. In one embodiment, the pelvis of the patient is selected as the skeletal bone and a femur is selected as the articulating bone, and the skeletal component of the implant is an acetabular cup and the articulating bone component includes a femoral stem having a shoulder, and the reference stationary point and the intraoperative stationary point are generated to have a known location relative to an obturator foramen of the patient, such as the tear drop. In one embodiment, the point on the articulating bone is identified to have a known location relative to the greater trochanter on the femur of the patient. 
     This invention also features a system to analyze images at a surgical site within a patient, the surgical site including at least a first, skeletal bone and a second, articulating bone that articulates with the skeletal bone at a joint, the system including an image selection module capable of acquiring (i) at least a first, reference image including one of a preoperative image of the surgical site and a contralateral image on an opposite side of the patient from the surgical site, and (ii) at least a second, intraoperative image of the site after an implant has been affixed to the articulating bone. The implant has at least a skeletal component with a first center of rotation and an articulating bone component having a second center of rotation, the first and second centers of rotation being co-located in the intraoperative image. The system optionally includes a landmark identification module capable of receiving the reference and intraoperative images and generating at least one reference stationary point on at least the skeletal bone in the reference image and at least one intraoperative stationary point on at least the skeletal bone in the intraoperative image. A templating module is capable of (a) identifying the location of the implant in the intraoperative image, including the position of the first and second centers of rotation, and aligning (i) at least a first digital implant representation with the skeletal component and with at least the intraoperative stationary point, and (ii) at least a second digital implant representation with the articulating bone component and at least one point on the articulating bone, and (b) copying the first and second digital representations and positioning them in the reference image in an equivalent location relative to at least the reference stationary point and the articulating bone to determine the position of the first and second centers of rotation relative to each other in the reference image. An analysis module is capable of utilizing any differences between the locations of the first and second centers of rotation in the reference image to analyze at least one of offset and length differential of at least one of the articulating bone and the implant in the intraoperative image. 
     In some embodiments, the reference and intraoperative images are provided by the image selection module to the data input module in a digitized format. In certain embodiments, the templating module positions the first digital representation in the reference image relative to the reference stationary point according to at least an intraoperative vector calculation utilizing at least the intraoperative stationary point relative to the first center of rotation and a reference vector calculation utilizing at least the reference stationary point relative to the first center of rotation. In one embodiment, the reference vector calculation replicates the intraoperative vector calculation. In a number of embodiments, the landmark identification module further generates at least a reference landmark point on at least one anatomical feature on the articulating bone in the reference image and at least an intraoperative landmark point on at least that anatomical feature on the articulating bone in the intraoperative image and, in one embodiment, at least one of the templating module and the analysis module utilizes the landmark points to assist alignment of the second digital implant representation on the articulating bone in both of the reference and intraoperative images. 
     In certain embodiments, the templating module selects a fixed point on the second digital implant representation and the analysis module is capable of estimating changes in offset and length differential based on selected alternative changes in at least one dimension of the implant for alternative implants, each with a similar fixed point, to be considered by a user of the system as a replacement for the implant in the intraoperative image. In some embodiments, the reference image and the intraoperative image are at least one of rotated, aligned and scaled relative to each other prior to the templating module copying the digital representation and positioning it in the reference image. In one embodiment, the landmark identification module generates at least one other stationary point on the skeletal bone in the reference image to establish a reference stationary base and at least one other stationary point on the skeletal bone in the intraoperative image to establish an intraoperative stationary base, and the analysis module utilizes the reference and intraoperative stationary bases to accomplish at least one of image rotation, image alignment and image scaling. In another embodiment, the analysis module provides at least relative scaling of one of the reference and intraoperative images to match the scaling of the other of the reference and intraoperative images. In yet another embodiment, the analysis module utilizes at least one object of known dimension in at least one of the reference and intraoperative images to provide absolute scaling to at least that image. 
     This invention further features a system analyze images at a surgical site within a patient, the surgical site including at least a first, skeletal bone and a second, articulating bone that articulates with the skeletal bone at a joint, the system including an image selection module capable of acquiring (i) at least one digitized reference image including one of a preoperative image of the surgical site and a contralateral image on an opposite side of the patient from the surgical site, and (ii) at least one digitized intraoperative image of the site after an implant has been affixed to the articulating bone, the implant having at least a skeletal component with a first center of rotation and an articulating bone component having a second center of rotation, the first and second centers of rotation being co-located in the intraoperative image. The system also includes a templating module capable of (a) identifying the location of the implant in the intraoperative image and aligning at least one of (i) at least a first digital implant representation with the skeletal component and with at least one intraoperative stationary point on at least the skeletal bone, and (ii) at least a second digital implant representation with the articulating bone component and at least one point on the articulating bone, and (b) copying at least one of the first and second digital representations and positioning them in the reference image in an equivalent location relative to at least one of (A) a reference stationary point on at least the skeletal bone and (B) the articulating bone, respectively, in the reference image. The system further includes an analysis module capable of utilizing any differences between the locations of at least one of the first and second digital implant representations in the reference image to analyze at least one of offset and length differential of at least one of the articulating bone and the implant in the intraoperative image. The templating module selects a fixed point on the second digital implant representation and the analysis module is capable of estimating changes in offset and length differential based on selected alternative changes in at least one dimension of the implant for alternative implants, each with a similar fixed point, to be considered by a user of the system as a replacement for the implant in the intraoperative image. 
     In one embodiment, the system further includes a landmark identification module capable of receiving the reference and intraoperative images and generating the at least one reference stationary point on at least the skeletal bone in the reference image and the at least one intraoperative stationary point on at least the skeletal bone in the intraoperative image. 
     This invention still further features a method for analyzing images to optimize the restoration of orthopaedic functionality at a surgical site within a patient, the surgical site including at least a first, skeletal bone and a second, articulating bone that articulates with the skeletal bone at a joint, the method including the steps of acquiring (i) at least one digitized reference image including one of a preoperative image of the surgical site and a contralateral image on an opposite side of the patient from the surgical site, and (ii) at least one digitized intraoperative image of the site after an implant has been affixed to the articulating bone, the implant having at least a skeletal component with a first center of rotation and an articulating bone component having a second center of rotation, the first and second centers of rotation being co-located in the intraoperative image. The method includes identifying the location of the implant in the intraoperative image and aligning at least one of (i) at least a first digital implant representation with the skeletal component and with at least one intraoperative stationary point on at least the skeletal bone, and (ii) at least a second digital implant representation with the articulating bone component and at least one point on the articulating bone. At least one of the first and second digital representations are copied and positioned in the reference image in an equivalent location relative to at least one of (A) a reference stationary point on at least the skeletal bone and (B) the articulating bone, respectively, in the reference image. Any differences between the locations of at least one of the first and second centers of rotation in the reference image are utilized to analyze at least one of offset and length differential of at least one of the articulating bone and the implant in the intraoperative image. A fixed point on the second digital implant representation is selected, and changes in offset and length differential are estimated based on selected alternative changes in at least one dimension of the implant for alternative implants, each with a similar fixed point, to be considered by a user of the system as a replacement for the implant in the intraoperative image. 
     In an embodiment, one or more computers perform a method for analyzing images to optimize the restoration of orthopaedic functionality at a surgical site within a patient. The surgical site includes at least a portion of both a skeletal bone and an articulating bone that articulates with respect to the skeletal bone at a joint. The method includes acquiring a preoperative image of the surgical site and acquiring an intraoperative image of the site after an initial implant has been implanted. The initial implant includes a skeletal component and an articulating bone component. The skeletal bone component is secured to the skeletal bone and has a first center of rotation. Likewise, the articulating bone component is secured to the articulating bone and has a second center of rotation. In addition, the first and second centers of rotation are co-located in the intraoperative image. 
     The method further includes generating a first digital landmark on the skeletal bone in both the intraoperative and preoperative images; generating a second digital landmark on the articulating bone in both the intraoperative and preoperative images; identifying the position of the initial implant in the intraoperative image, including the positions of the first and second centers of rotation; positioning the first center of rotation of the skeletal bone component in the preoperative image at an equivalent location relative to the first digital landmark; positioning the second center of rotation of the articulating bone component in the preoperative image at an equivalent location relative to the second digital landmark; determining a difference in the positions of the first and second centers of rotation relative to each other in the preoperative image; and analyzing at least one of offset and length differential of the articulating bone in the intraoperative image with respect to the articulating bone in the preoperative image. 
     In an embodiment the step of positioning the first center of rotation further includes the steps of aligning a first digital implant representation with the stationary bone component in the intraoperative image, wherein the first digital implant representation includes the first center of rotation; determining a location of the first digital implant representation in the intraoperative image with respect to the first digital landmark when the first digital implant representation is aligned with the stationary bone component; and positioning the first digital representation in the preoperative image at an equivalent location relative to the first digital landmark. 
     In an embodiment the step of positioning the second center of rotation further includes aligning a second digital implant representation with the articulating bone component in the intraoperative image, wherein the second digital implant representation includes the second center of rotation; determining a location of the second digital implant representation in the intraoperative image with respect to the second digital landmark when the second digital implant representation is aligned with the articulating bone component; and positioning the second digital representation in the preoperative image at an equivalent location relative to the second digital landmark. 
     An embodiment of the method also includes a step of generating at least one of length and offset differential data for an alternative articulating bone component based on known dimensions of the alternative articulating bone component. To do so, an embodiment performs the steps of selecting a fixed point on the second digital implant representation; selecting an alternative articulating bone component of the implant with known dimensions and selecting a fixed point on the alternative articulating bone component of the implant that corresponds with the fixed point on the second digital implant representation; comparing the relative location of the fixed point on the second digital implant representation with respect to the center of rotation of the second digital implant representation and comparing the relative location of the fixed point on the alternative articulating bone component with respect to a center of rotation of the alternative articulating bone component; and estimating changes in offset and length differential based on a comparison of the relative location of the fixed points with respect to the centers of rotation for each of the second digital implant representation and the alternative articulating bone component. 
     An embodiment further includes automatically providing an alternative articulating bone component based on known dimensions of the alternative articulating bone component to analyze at least one of offset and length differential. 
     An embodiment further includes the step of generating a digital line on the skeletal bone between at least two anatomically identifiable points on both the intraoperative image and the preoperative image. Responsive to a determination that the intraoperative and preoperative images are not orientationally aligned relative to each other, the system orients the intraoperative and preoperative images with respect to each other based on at least the digital line on the skeletal bone. 
     An embodiment also performs the step of scaling the intraoperative and preoperative images with respect to each other in responsive to a determination that the intraoperative and preoperative images are not scaled relative to each other. 
     In an embodiment, a pelvis of the patient is selected as the skeletal bone and a femur is selected as the articulating bone, and the skeletal component of the implant is an acetabular cup and the articulating bone component includes a femoral stem. Moreover, the first digital landmark may be a known location relative to an obturator foramen of the patient. The second digital landmark on the articulating bone may be a known location relative to the greater trochanter on a femur of the patient. 
     In an embodiment, the first center of rotation is measured relative to the first digital landmark in the preoperative image according a vector calculation to determine the location of the first center of rotation in the intraoperative image. In an embodiment a circle is generated around the skeletal bone component of the implant in the intraoperative image to calculate the first center of rotation. 
     An embodiment further includes generating a chart with a plurality of offset and length differentials for an assortment of alternative implant components. 
     In an embodiment, determining offset differential includes generating a first longitudinal axis line along a length of the articulating bone; generating a second longitudinal axis line along a length of the second digital implant representation; comparing the locations of the first and second longitudinal axis lines to calculate offset differential. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In what follows, preferred embodiments of the invention are explained in more detail with reference to the drawings, in which: 
         FIG. 1  is a schematic image of a frontal, X-ray-type view of a pelvic girdle of a patient illustrating various anatomical features; 
         FIG. 1A  is a schematic image viewable on a display screen by a user of an inventive system and method depicting a template image of a prosthesis superimposed over the upper portion of a femur in an X-ray image of the hip region of a patient; 
         FIG. 1B  is an enlargement of the digital template image of  FIG. 1A ; 
         FIG. 2  is an image rendering similar to  FIG. 1A  after the digital template has been removed, illustrating measurement of a portion of the femoral head utilizing a reference line; 
         FIG. 3  is an image similar to  FIG. 1A  after the digital template has been re-scaled; 
         FIG. 4A  is a schematic diagram of an inventive system that interfaces with a user; 
         FIG. 4B  is a schematic diagram illustrating how multiple types of user interfaces can be networked via a cloud-based system with data and/or software located on a remote server; 
         FIG. 4C  is a high-level schematic diagram of an inventive system; 
         FIG. 4D  is a schematic diagram of the Intraoperative Analysis Module in  FIG. 4C ; 
         FIG. 4E  is a schematic diagram of several variations of the Surgical Analysis Module in  FIG. 4D ; 
         FIG. 4F  is a schematic diagram of the Intraoperative Rescaling Module in  FIG. 4C ; 
         FIG. 4G  is a schematic diagram of an alternative Intraoperative Analysis System; 
         FIG. 4H  is a schematic diagram of an AP (Anterior-Posterior) Pelvis Reconstruction System; 
         FIG. 5  is a Flowchart A for the operation of Intraoperative Rescaling in one construction of the inventive system and method; 
         FIG. 6  is a Flowchart B for an Anterior Approach for hip surgery utilizing Flowcharts G and J; 
         FIG. 7  is a Flowchart G showing technique flow for both contralateral and ipsilateral analysis; 
         FIG. 8  is a Flowchart W of several functions performed for hip analysis; 
         FIG. 9  is an image of the right side of a patient&#39;s hip prior to an operation and showing a marker placed on the greater trochanter as a landmark or reference point; 
         FIG. 10  is an image similar to  FIG. 9  showing a reference line, drawn on (i) the pre-operative, ipsilateral femur or (ii) the contra-lateral femur, to represent the longitudinal axis of the femur; 
         FIG. 11  is an image similar to  FIG. 10  with a line drawn across the pelvic bone intersecting selected anatomical features; 
         FIG. 12  is a schematic screen view of two images, the left-hand image representing a pre-operative view similar to  FIG. 10  and the right-hand image representing an intra-operative view with a circle placed around the acetabular component of an implant to enable rescaling of that image; 
         FIG. 13  is a schematic screen view similar to  FIG. 12  indicating marking of the greater trochanter of the right-hand, intra-operative image as a femoral landmark; 
         FIG. 14  is a schematic screen view similar to  FIG. 13  with a reference line drawn on the intra-operative femur in the right-hand view; 
         FIG. 15  is an image similar to  FIGS. 11 and 14  with a line drawn across the obturator foramen in both pre- and intra-operative views; 
         FIG. 16  is an overlay image showing the right-hand, intra-operative image of  FIG. 15  superimposed and aligned with the left-hand, pre-operative image; 
         FIG. 17  represents a screen viewable by the user during a surgical procedure; 
         FIG. 18  is Flowchart J of AP Pelvis Stitching and Analysis; 
         FIG. 19  represents a screen view with a left-hand image of the contra-lateral, left side of a patient having a line drawn on the pubic symphysis; 
         FIG. 20  is a view similar to  FIG. 19  plus a right-hand, intra-operative image of the right side of the patient, also having a line drawn on the pubic symphysis; 
         FIG. 21  shows the images of  FIG. 20  overlaid and “stitched together” to reconstruct a view of the entire hip region of the patient; 
         FIG. 22  is view similar to  FIG. 21  with one reference line drawn across the acetabular component of the image and another reference line touching the lower portions of the pelvis; 
         FIG. 23  is Flowchart L showing inventive Intraoperative Guidance for Intertrochanteric Reduction and Femoral Neck Fractures, referencing Flowcharts M and N; 
         FIG. 24  is Flowchart M for Intertrochanteric Reduction Guidance, referencing Flowchart P; 
         FIG. 25  is Flowchart P for processing a Contralateral or Ipsilateral Image; 
         FIG. 26  is a representation of a screen view with a left-hand image of the left, contralateral, “normal” side of a patient&#39;s hip region inverted to resemble the right, “fractured” side of the patient and showing marking of the lesser trochanter to serve as a femoral reference point; 
         FIG. 27  is a view similar to  FIG. 26  showing drawing of a line across the obturator foramen for overlay reference; 
         FIG. 28  is a view similar to  FIG. 27  showing measurement of neck shaft angle; 
         FIG. 29  is a screen view with the left-hand image similar to  FIG. 28  and a right-hand image of the fractured side of the patient, showing marking of the lesser trochanter on the fractured side; 
         FIG. 30  is a view similar to  FIG. 29  showing marking of the obturator foramen of the fractured side; 
         FIG. 31  is a view similar to  FIG. 30  showing measurement of neck shaft angle on the fractured side; 
         FIG. 32  is a combined image showing the fractured side image overlaid on the normal, inverted side image; 
         FIG. 33  is Flowchart N showing scaling and measurement as referenced in Flowchart L; 
         FIG. 34  represents a screen view of an image of a screw implanted to treat an inter-trochanteric hip fracture, showing measurement of the screw; 
         FIG. 35  is a view similar to  FIG. 34  showing measurement of Tip-Apex distance in an AP image; 
         FIG. 36  is a view similar to  FIG. 35  plus a lateral view on the right-hand side of the screen, showing measurement of the screw; 
         FIG. 37  is a view similar to  FIG. 36  showing measurement of Tip-Apex distance in the right-hand image; 
         FIG. 38  is a combined “Intertroch” view showing both Tip-Apex Analysis and Neck Shaft Analysis; 
         FIG. 39  is Flowchart Q of Intraoperative Guidance for Distal Radius Fracture Reduction, referencing Flowcharts R and S; 
         FIG. 40  is Flowchart R showing Radial Inclination and Length Reduction Guidance, and referencing Flowchart T; 
         FIG. 41  is Flowchart S showing Palmar Slope Reduction Guidance; 
         FIG. 42  is Flowchart T showing identification of various anatomical features in the wrist and image processing; 
         FIG. 43  represents a screen view of an image of a “normal” wrist of a patient with a line drawn on the radius to indicate its central axis; 
         FIG. 44  is a view similar to  FIG. 43  with marking of selected anatomical points; 
         FIG. 45  is a view similar to  FIG. 44  with a reference line drawn across the carpal bones to provide a stationary base reference; 
         FIG. 46  is a view of an image of the normal wrist rotated to draw Palmar Tilt; 
         FIG. 47  is a screen view with the left-hand image similar to  FIG. 45  and a right-hand image of the fractured side of the patient, showing marking of the central axis of the radius on the fractured side; 
         FIG. 48  is a view similar to  FIG. 47  showing marking of anatomical points on the fractured side; 
         FIG. 49  is a view similar to  FIG. 48  with a reference line drawn across the carpal bones on the fractured side; 
         FIG. 50  is a screen view with the left-hand image similar to  FIG. 46  and a right-hand image of the fractured wrist rotated to draw Palmar Tilt; 
         FIG. 51  is a combined view as an inventive Distal Radius Report; 
         FIG. 52  is an image similar to  FIG. 15  with points marking the lowest point on the ischial tuberosity and points marking the obturator foramen and top of the pubic symphysis in both pre- and intra-operative views; 
         FIG. 53  is an overlay image showing the right-hand, intra-operative image of  FIG. 52  superimposed and aligned with the left-hand, pre-operative image utilizing triangular stable bases; 
         FIG. 54  is a schematic combined block diagram and flow chart of an inventive identification guidance module; 
         FIG. 55  is a schematic block diagram of modules that analyze the orientation of a component such as an acetabular cup to generate abduction angle and anteversion information; 
         FIG. 56  is an image of an acetabular cup positioned in the left acetabulum of a patient with a circle drawn around its hemispherical surface to provide diameter information; 
         FIG. 57  is an image similar to that of  FIG. 56  with a line segment drawn under the cup to calculate abduction angle relative to a neutral axis line; 
         FIG. 58  is an image similar to that of  FIG. 57  with arcs drawn at the bottom of the acetabular cup to assist calculation of anteversion; 
         FIG. 59  is a Flowchart X of abduction angle and anteversion analysis by the modules of  FIG. 55  relative to the images of  FIGS. 56-58   
         FIG. 60  is a schematic screen view of an image of the right side of a patient&#39;s hip prior to an operation and showing a mark placed on the greater trochanter as a landmark or reference point; 
         FIG. 61  represents a screen viewable by the user during an inventive surgical procedure showing two images, the left-hand image representing a pre-operative view similar to  FIG. 60  and the right-hand image representing an intra-operative view with a circle placed around the acetabular component of an implant to enable scaling or rescaling of that image based on an object of known size; 
         FIG. 62  is a schematic screen view similar to  FIG. 61  indicating marking of the lateral shoulder of the prosthesis of the right-hand, intra-operative image, also with the greater trochanter marked in both images as a femoral landmark; 
         FIG. 63  is a schematic screen view similar to  FIG. 62  with a reference box indicating an acetabular template generated on top of the acetabular component of the prosthesis on the intra-operative femur in the right-hand view; 
         FIG. 64  is a schematic screen view similar to  FIG. 63  with the acetabular template now rendered in a precise location across the femoral head in the preoperative view, using intraoperative data gathered during the step represented by  FIG. 63 ; 
         FIG. 65  is a schematic screen view similar to  FIG. 64  showing the acetabular component outline overlaid on the femoral head on the left-hand, preoperative image with an overlay image of the prosthesis superimposed and aligned with the femoral stem of the prosthesis in the right-hand, intra-operative image; 
         FIG. 66  is a schematic screen view similar to  FIG. 65  showing the femoral stem template placed on the pre-operative image, utilizing intraoperative data gathered in the step represented by  FIG. 65 , with intraoperative Offset and Leg Length calculations; 
         FIG. 67  is a schematic diagram of an inventive Intra-operative Analysis Module implementing the Templating Technique generating images as shown above in  FIGS. 60-66 ; 
         FIGS. 68A and 68B  are a Flowchart U showing Intraoperative Templating Flow within the Module of  FIG. 67 ; 
         FIG. 69  is a Flowchart Y showing functions applied to the pre-operative and intraoperative hip images for Intraoperative Templating of Flowchart U; 
         FIG. 70  is an image of a trial implant in a hip with the acetabular component transacted by a stationary base line and with two error analysis triangles. 
         FIGS. 71A and 71B  depict a flowchart RT illustrating an alternative reverse templating technique according to the present invention; 
         FIG. 72  is a schematic block diagram illustrating components of a system according to the present invention that implements Flowchart RT of  FIGS. 71A-B ; 
         FIG. 73  is a schematic screen view of a preoperative image on the left and an intraoperative image on the right with a digital template superimposed on an actual “trial implant” prosthesis; 
         FIG. 74  is a screen view of the intraoperative actual trial implant and femur of  FIG. 73  superimposed on the preoperative image of  FIG. 73 ; 
         FIG. 75  is a screen view of the intraoperative digital template superimposed on the preoperative image on the left and the same digital template and actual trial implant on the right; 
         FIG. 76  is the screen view of  FIG. 75  with both “Details” and “Compare Stems” windows expanded; 
         FIG. 77  is a Flowchart RTC for novel calculation of offset and leg length of alternative implants using known intraoperative data; and 
         FIG. 78  is a schematic block diagram illustrating components of a system according to the present invention that implements Flowchart RTC of  FIG. 77 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention may be accomplished by a system and method that acquire (i) at least one reference image including one of a preoperative image of a surgical site with skeletal and articulating bones and a contralateral image on an opposite side of the patient from the surgical site, and (ii) at least one intraoperative image of the site after an implant has been affixed to the articulating bone. In certain constructions, the system generates at least one reference stationary point on at least the skeletal bone in the reference image and at least one intraoperative stationary point on at least the skeletal bone in the intraoperative image. The location of the implant is identified in the intraoperative image, preferably including the position of first and second centers of rotation which are co-located in the intraoperative image. At least one of (i) a first digital implant representation is aligned with the skeletal component and with at least the intraoperative stationary point, and (ii) a second digital implant representation is aligned with the articulating bone component and at least one point on the articulating bone. One or more of the digital representations are copied and positioned in the reference image in an equivalent location relative to at least one of the reference stationary point and the articulating bone to directly or indirectly determine the position of the first and second centers of rotation relative to each other in the reference image. Any differences between the locations of at least one of the first and second centers of rotation in the reference image are utilized to analyze at least one of offset and length differential. 
     The term “digital representation” or “digital implant representation” as utilized herein includes a digital template or other digital annotation, such as a digital line having at least two points, e.g. a line representing a longitudinal axis or a diameter of an implant or a bone, or a digital circle or other geometric shape which can be aligned with an implant or a bone intraoperatively and then placed in a corresponding location in a preoperative image. 
     Broadly, some inventive techniques, referred to herein as “Image Overlay”, place one image over another image during analysis to generate a combined overlapped image, while certain other techniques according to the present invention, referred to by the present inventors as “Reverse Templating” or “Templating Technique”, obtain information from an intraoperative image and then work with a preoperative image. In some Reverse Templating constructions, the system places a digital template first on a properly-scaled intra-operative image and then on a scaled pre-operative image during analysis. 
     In other constructions according to the present invention, as described in more detail below in relation to  FIGS. 71-78  below, alternative approaches for ‘Reverse Templating’ technique obviate the need for a pelvic reference line having two or more points. In some constructions, these alternatives instead rely upon certain image acquisition techniques, certain known imaging information, direct user manipulation, or the pelvic referencing line technique described in earlier constructions to create consistent scale and rotation between (i) a reference image including at least one of a preop image and an inverted contralateral image and (ii) an intraoperative image. 
     In general, accurate analysis of two images of a patient is directly related not only to how similar the two images are, but also how similarly the images are aligned with respect to scale, rotation, and translation. Using conventional techniques, a user would have to manually adjust the images and/or retake multiple images to achieve this goal, something that would be difficult to do reliably and accurately. As described in the parent application by the present inventors, utilizing two or more points as a stationary base in each image enables accurate analysis of the two images. Furthermore, the inventive Image Overlay technique can analyze how “similar” these images are to give the user feedback as to how accurate the results are, that is, to provide a confidence interval. 
     To obtain useful information, the images (the “intraop” intra-operative image and a “preop” pre-operative image, for example) must be scaled similarly and preferably rotated similarly. If the scale is off, this will lead to error unless re-scaled properly. If the rotation is off, the user is likely to spend significant time “eyeballing” to manually align the digital template on the preop image to match the intraop position during Reverse Templating according to the present invention. Use of one or more landmarks, such as the teardrop of the pelvis and/or the greater trochanter of the femur for hip-related surgery, according to the present invention aids in automated and accurate superimposing of a template onto the preop image to match the intraop position of an implant and superimposed digital template during Reverse Templating. For example, the teardrop helps accurately place the acetabular template and the greater trochanter helps place the femoral template at the right level on each image. As compared to the present Image Overlay technique, the present Reverse Templating technique is less sensitive to how similar the images are, and therefore has a wider breadth of use as images can be taken in different settings, such as comparing a preop image taken in a physician&#39;s office with an intraop image taken during hip surgery involving a posterior approach or other surgical procedure. 
     In some implementations, a system and method according to the parent application analyzes images to provide guidance to optimize the restoration of orthopaedic functionality at a surgical site within a patient, including capturing, selecting or receiving: (i) at least a first, reference image along at least a first viewing angle including one of a preoperative image of the surgical site and a contralateral image on an opposite side of the patient from the surgical site; and (ii) at least a second, results image of the site, preferably also along the first viewing angle, after a surgical procedure has been performed at the site. The system and method according to the parent application further include generating on each of the first and second images at least two points to establish a stationary base on a stable portion of the surgical site and identifying at least one landmark on another portion of the surgical site spaced from the stationary base, and providing at least one of (a) an overlay of the first and second images to enable comparison of at least one of bone and implant alignment within the images, (b) matching of at least one digital template to at least one feature in each of the first and second images, and (b) a numerical analysis of at least one difference between points of interest, such as an analysis of at least one of offset, length differential and orientation of at least one of a bone and an implant within the images. 
     Establishing at least three points for the stationary base, such as described below in relation to  FIG. 70 , is especially useful for determining rotational differences between images. One or more points may be shared with points establishing a scaling line. Preferably, at least one landmark is selected that is spaced from the stationary base points to increase accuracy of overlaying and/or comparing images. 
     In some constructions, scaling, which includes rescaling in some implementations, of at least one of the images is accomplished by measuring an anatomical feature during surgery, and comparing the measured feature to an initial, preoperative image which includes that feature. In other constructions, scaling or rescaling is accomplished by comparing an intraoperative image with at least one known dimension of (i) an implant feature, such as the diameter of an acetabular cup or a screw, or (ii) a temporarily-positioned object such as a ball marker or a tool such as a reamer. Typically, scaling or rescaling is accomplished by establishing two points on a feature, generating a line between the two points, and determining the correct length for the line. 
     In certain constructions utilizing implants, especially prostheses, the combination of accurately scaled templating, together with an innovative approach of combining a software-driven system according to the present invention with intra-operative medical imaging such as digital X-ray images, dramatically improves the accuracy of various surgeries, especially difficult-to-see anterior approach surgery for total hip replacement. The present invention enables a surgeon to compensate for unintended variations such as how a reamer or other tool interacts with a bone during preparation of the surgical site before or during insertion of the implant. In some constructions, the surgeon or other user is able to compare a pre-operative or intra-operative X-ray-type image of a patient&#39;s anatomy with an initial intra-operative X-ray-type image of a trial prosthesis, and deduce changes of offset and/or leg length to help guide surgical decision making. This unique process will greatly improve patient satisfaction by increasing the accuracy of direct anterior surgery and other types of surgeries, and greatly increase surgeon comfort in performing these less-invasive procedures. 
     In some implementations, a system and method according to the present invention includes an inventive alternative “Reverse Templating” methodology for analyzing parameters such as abduction angle, intraoperative leg length and offset changes using a different application of the stationary base or at least one stationary point, intraoperative scaling and anatomical landmark identification techniques. For Reverse Templating implementations, the system and method combines the use of intraoperative data, gathered from intraoperative image analysis, with intraoperative templating on a preoperative ipsilateral image. The method can be applied in a wider range of hip arthroplasty surgeries because it is less sensitive to inconsistencies in preoperative and intraoperative image acquisition, allowing the user to apply this system and method during arthroplasty in the lateral position (i.e. posterior approach). This alternative system and method also enable a user to precisely analyze, intraoperatively, how a potential change in implant selection would affect parameters such as abduction angle, offset and/or leg length. In one novel approach, described below in relation to  FIGS. 60-69 , the user will analyze the preoperative ipsilateral and intraoperative images ‘side by side’, without the need to overlap the images themselves. The system will scale and align these images relative to one another using at least intraoperative data, and then analyze offset and leg length changes by combining intraoperative data with a unique utilization of digital prosthetic templates. 
     For image analysis according to the parent application, preferably at least one stationary base and at least one anatomical landmark are selected. The term “stationary base”, also referred to herein as a “stable base”, means a collection of two or more points, which may be depicted as a line or other geometric shape, drawn on each of two or more images that includes at least one anatomical feature that is present in the two or more images of a region of a patient. For example, different images of a pelvic girdle PG of a patient,  FIG. 1 , typically show one or both obturator foramen OF and a central pubic symphysis PS, which the present inventors have recognized as suitable reference points or features for use as part of a stationary base according to the present invention. Other useful anatomical features, especially to serve as landmarks utilized according to the present invention, include femoral neck FN and lesser trochanter LT, shown on right femur F R , and femoral head FH and greater trochanter GT shown on left femur F L , for example. Femoral head FH engages the left acetabulum of the pelvic girdle PG. Also shown in  FIG. 1  are ischial tuberosities IT at the bottom of the ischium, a “tear drop” TD relating to a bony ridge along the floor of the acetabular fossa, and the anterior superior iliac spine ASIS and the anterior inferior iliac spine AIIS of the ileum. As described below, carpal bones serve as a stationary base in images for radial bone fixation and other wrist-related procedures. In general, having a “non-movable” anatomical feature associated with the trunk of a patient is preferred for a stationary base, rather than a jointed limb that can be positioned differently among two or more images. 
     In general, a longer stationary base is preferred over a shorter stationary base, because the longer base, especially if it is a line, will contain more pixels in images thereof and will increase accuracy of overlays and scaling according to the present invention. However, the further the stationary base is from the area of anatomical interest, the greater the risk of parallax-induced error. For example, if the area of interest is the hip joint, then the ideal stationary base will be near the hip. In some procedures involving hip surgery, for example, a stationary base line begins at the pubic symphysis PS, touches or intersects at least a portion of an obturator foramen OF, and extends to (i) the “tear drop” TD, or (ii) the anterior interior iliac spine AIIS. Of course, only two points are needed to define a line, so only two reliable anatomical features, or two locations on a single anatomical feature, are needed to establish a stationary base utilized according to the present invention. More complex, non-linear stationary bases may utilize additional identifiable points to establish such non-linear bases. 
     Additionally, at least one identifiable anatomic “landmark”, or a set of landmarks, is selected to be separate from the stationary base; the one or more landmarks are utilized in certain constructions to analyze the accuracy of the overlay process. This additional “landmark” preferably is part of the stationary anatomy being anatomically compared. For example, the inferior portion of the ischial tuberosity IT can be identified as an additional landmark. This landmark, in conjunction with the stationary base, will depict any differences or errors in pelvic anatomy or the overlay which will enable the physician to validate, or to have more confidence in, the output of the present system. 
     The term “trial hip prosthetic” is utilized herein to designate an initial implant selected by a surgeon as a first medical device to insert at the surgical site, which is either the right side or the left side of a patient&#39;s hip in this construction. In some techniques, the trial prosthetic is selected based on initial digital templating similar to the procedure described below for  FIGS. 1A-3 , for example. 
     One novel technique according to the parent application is described in relation to  FIGS. 1A-3 , which illustrate successive views or “screenshots” visible to a user of a system and method according to the novel invention utilized for hip surgery.  FIG. 1A  is a schematic representation of a screen view  10  depicting a digital template image  20  of a prosthesis superimposed over the upper portion of a right femur F R . In some techniques a digitized X-ray image of the hip region of a patient along a frontal or anterior-to-posterior viewing angle is utilized for screen view  10  and, in other techniques, a digital photograph “secondary” image of a “primary” X-ray image of the hip region of a patient along a frontal or anterior-to-posterior viewing angle is utilized for screen view  10 . In one construction, screen view  10  is shown on a computer monitor and, in another construction, is shown on the screen or viewing region of a tablet or other mobile computing device, as described in more detail below. Dashed line SK represents skin of the patient and provides an outline of soft tissues for this viewing angle. Pelvic Girdle PG may also be referred to as a pelvis or hip. 
     Ball marker BM represents a spherical metal reference object of known dimension placed between right leg RL and left leg LL, as traditionally utilized to scale many types of medical images including X-ray images. Use of a ball marker or other non-anatomical feature is optional in techniques according to the present invention, as described in more detail below. In particular, the inventive techniques useful for unplanned trauma surgery, where direct measurement of an anatomical feature, such as caliper measurements of an extracted femoral head during emergency hip surgery, can be utilized as described in the parent application to intraoperatively guide such surgery. 
     Template image  20  is shown in greater detail in  FIG. 1B  with a body component  22  including a stem  24 , a fastener recess  26 , and a support  28  with a trunion  29 , and an acetabular component  30  carried by support  28 . Dashed line  32  indicates the longitudinal axis of support  28  and dashed line  34  indicates a longitudinal body axis for template image  20  to be aligned relative to a longitudinal axis of the femur F, as described in more detail below. Also shown are a center of rotation  33  for support  28  of femoral body component  22  and a center of rotation  35  for acetabular component  30 . Offset and leg length differential calculations based on the centers of rotation  33  and  35  are discussed in more detail below in relation to  FIGS. 71A-78 . 
     Additional icons and reference elements are provided in this construction, such as a reference line delete icon  40  for line  41 ,  FIG. 1A , a template body delete icon  42  and an acetabular component delete icon  44  for body component  22  and acetabular component  30 ,  FIG. 1B , respectively. One or more of these “virtual” items can be removed or added to view  10  by a user as desired by highlighting, touching or clicking the “soft keys” or “soft buttons” represented by the icons. In certain embodiments, one or more of the icons  40 ,  42  and/or  44  serves as a toggle to provide “on-off” activation or de-activation of that feature. Characters or other indicia  46 ,  FIG. 1A , can be utilized to designate image number and other identifying information. Other useful information  48  can be shown such as Abduction Angle, Offset Changes and Leg Length Changes, as discussed in more detail below. 
     Screen view  51 ,  FIG. 2 , is similar to view  10  of  FIG. 1A  after the digital template  20  has been removed, illustrating measurement of a portion of the femoral head FH of femur F R  utilizing a reference line  60 . Four indicator squares  52 ,  54 ,  56  and  58 , also referred to as reference squares, navigation handles, or navigation points, are provided in this construction to guide a user to draw the reference line  60  in the viewing plane of screen view  51 . In some constructions, a user touches one of the squares  52 - 58  with a finger or a mouse cursor, and utilizes the square, such as by ‘dragging’ it, to move a marker to a desired location. This enables manipulation without blocking the location of interest. 
     Characters  70  such as “New Femoral Head Width” invite a user to enter a direct measurement into field  72 , such as “50” to represent an actual 50 mm caliper measurement for the dimension represented by line  60 , as described in more detail below. In this example, an initial scaling of image  51  had generated an estimated measurement of “45.6 mm” for line  60 . Other functional “soft buttons” are “Rescale”  74 , “Retemplate”  76 , “Cancel”  78  and “Done”  80 . In other constructions, as described in more detail below, intraoperative rescaling is conducted separately from a hip replacement process, and the direct measurement value, if needed, is utilized for intraoperative rescaling, for adjusting the template size, for comparing drawn lines, and other uses. 
     Direct measurement of the femoral head, such as with calipers, typically is conducted before a trial implant is inserted. The femoral head measurement enables (i) re-scaling of the preoperative template or (ii) accurate scaling for the first time, especially where a preoperative template has not been utilized. During overlay analysis, however, scaling is accomplished in some constructions by measuring or looking up a dimension of an implant, such as the radius or width of the acetabular component of a hip prosthesis, for example. 
       FIG. 3  is an image of a view  90  similar to view  10  of  FIG. 1A , along the same viewing angle, after the digital template  20  has been re-scaled according to the parent application to a revised template  20 ′. In this example, reference line  41  was 13.1 mm in  FIG. 1A , and reference line  41 ′,  FIG. 3 , is now 14.3 mm as calculated by the system after re-scaling based on the direct measurement. Also, for revised information  48 ′, the Offset Changes are re-calculated to be “0.9 mm” and the Leg Length Changes are recalculated to be “4.1 mm”. 
     In one construction, the JointPoint Intraop™ system utilizes an interpolation mapping approach with one or more reference points or “landmarks” to achieve template auto-rescaling. Certain important landmarks on an X-ray image, or on a photograph of an X-ray image, are used to anchor each fragment of a template. This is the basic model: 
     
       
         
           
             
               
                 
                   
                     
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     By following the model indicated above, each of the template fragments lands in the same position when the size of a template is changed and, therefore, users avoid the need to replace templates every time a rescaling happens. Correct template placement can also be facilitated by storing coordinates of a particular location on the femoral component of a template, such as the midpoint of the top of the trunion  29  shown in  FIG. 1B , for example. 
     In one implementation, a novel system  101 ,  FIG. 4A , has a user interface  103 , a processor  105 , and a communications module  107  that communicates with a remote server and/or other devices via a cloud  109 , which represents a cloud-based computing system. User interface  103  includes a display  111 , a user input module  113  and device input  115  such as (i) a camera, to take a digital photo of a fluoroscopic imaging screen, also referred to as a “fluoro” image, or of a printed or otherwise fixed (i.e., not-alterable and/or non-downloadable) X-ray-type image, or (ii) a connection to a conventional medical imaging system (not shown). Display  111  is a separate computer monitor or screen in some constructions and, in other constructions, is an integrated touch-screen device which facilitates input of data or commands of a user to processor  105 . In some constructions, user input  113  includes a keyboard and a mouse. 
     Processor  105  includes capability to handle input, module  119 , to send and receive data, module  121 , and to render analysis and generate results, module  123 . Two-way arrows  117  and  125  represent wired or integrated communications in some constructions and, in other constructions, are wireless connections. Communications module  107  has a send/upload module  127  and a receive/download module  129  to facilitate communications between processor  105  and cloud  109  via wired or wireless connections  125  and  131 , respectively. 
     In some constructions, the present invention provides the ability to accurately adjust implants and corresponding templates intra-operatively by combining mobile-based templating functionality, utilizing a mobile computing device such as a tablet, a Google Glass™ device, a laptop or a smart phone wirelessly interconnected with a main computing device, and a unique scaling technique translating real life intra-operative findings into selection of an optimally-configured implant for a patient. Preferably, the system includes a mode that does not require connection with a remote server, in the event of loss of internet connectivity or other extended system failure. 
       FIG. 4B  is a schematic diagram of a novel system  141  illustrating how multiple types of user interfaces in mobile computing devices  143 ,  145 ,  147  and  149 , as well as laptop  151  and personal computer  153 , can be networked via a cloud  109  with a remote server  155  connected through web services. Another useful mobile imaging and computing device is the Google Glass wearable device. Data and/or software typically are located on the server  155  and/or storage media  157 . 
     Software to accomplish the techniques described herein is located on a single computing device in some constructions and, in other constructions such as system  141 ,  FIG. 4B , is distributed among a server  155  and one or more user interface devices which are preferably portable or mobile. 
     A novel system  200 ,  FIG. 4C , includes a User Input Module  202  with one or more data items that are provided to a Scaling Module  204 , a Templating Module  206 , an Intraoperative Analysis Module  208 , and a Display  210 . Although Scaling Module  204  is illustrated and described as separate from Intraoperative Module  208  in some constructions, both Modules  204  and  208  can be considered as forms of analysis conducted according to the parent application utilizing a stationary base generated on at least two images. Further, User Input can be considered as a data input module that generates at least two points to establish a stationary base on at least one anatomical feature that is present in the images. In this construction, system  200  also includes a storage media  212  which receives and/or provides data to Modules  204 ,  206 ,  208  and Display  210 . Scaling Module  204  includes Standard Preoperative Scaling unit  214 , Intraoperative Scaling unit  216  and Intraoperative Rescaling unit  218  in this construction and provides data to Templating Module  206  and/or Display  210 . 
     The Intraoperative Analysis Module  208  is illustrated in more detail in  FIG. 4D  with an Image Selection Module  220 , a Stable Base Identification Module  222  which guides the selection of at least one stationary base, and a Landmark Identification Module  224 . Module  222  provides instructions to Overlay Module  226 ; Module  224  provides instructions to the Overlay Module  226  and/or to an optional Longitudinal Axis Identification Module  228 , shown in phantom. When utilized, module  228  communicates with Differential Analysis Module  230  which in turn communicates with Surgical Analysis Module  232 , shown in more detail in  FIG. 4E . Overlay Module  226  communicates with Surgical Analysis Module  232  either directly or via Differential Analysis Module  230 . 
     Also optional and present in some constructions in the Intraoperative Analysis Module  208  is a Stable Base Error Analysis Module  2100  that can provide outputs to Overlay Module  226  and/or Differential Analysis Module  230 . When utilized, the Stable Base Error Analysis Module  2100  compares at least two images selected in Image Selection Module  220 , and analyzes error or differences between the anatomic structures that contain the stationary base points. The module  2100  provides visual and/or quantitative data of image inconsistencies, such as shown in  FIG. 70  below, providing guidance of how much value to place in the output of Intraoperative Analysis Module  208 ,  FIGS. 4C and 4D . Within the module  2100 , the system automatically, or the user manually, identifies one or more anatomic error reference points located within the anatomic structure selected to contain the stationary base. At least one of the error reference points, but preferably all of them, must be separate from the points utilized to establish the stationary base. The two images are scaled, rotated and transformed utilizing the stationary base according to the parent application. Because the error reference points identified in this module  2100  are separate from the stationary base points used to align the images, but are on the same non-movable anatomic structure, differences in error reference point location between the two images allow for the analysis within this module  2100 . If the points seem extremely close, the anatomic structures are likely to be positioned very consistently between the two images being analyzed. If points are further apart, such as shown and described in relation to  FIG. 70  below, then there are likely to be imaging and/or anatomic inconsistencies that may impact the data provided by the Analysis Module  208 . 
       FIG. 4E  is a schematic diagram of several variations of the Surgical Analysis Module  232 ,  FIG. 4D , depending on the surgical procedures to be guided according to the parent application. One or more of the following modules are present in different constructions according to the parent application: Hip Arthroplasty Module  240 , Intertrochanteric Reduction Analysis Module  242 , Femoral Neck Reduction Analysis Module  244  and/or Distal Radius Fracture Reduction Analysis Module  246 . In the illustrated construction, the Hip Arthroplasty Module  240  includes at least one of an Ipsilateral Analysis unit  250   a , a Contralateral Analysis unit  252 , an AP Pelvis Stitching and Analysis unit  254  and an alternative Contralateral Analysis unit  256  which communicates with an Image Flip unit  258  and an AP Pelvis Stitching and Analysis unit  260 . In some constructions, Ipsilateral Analysis module  250   a  optionally provides inputs to a Reverse Templating Module  250   b , shown in phantom. Hip Arthroplasty is described in more detail below in relation to  FIGS. 6-17 , with AP Pelvis Stitching and Analysis described in relation to  FIGS. 18-22  below. 
     Intertrochanteric Reduction Analysis Module  242  includes a Contralateral Analysis Module  270 , a Neck Shaft Analysis unit  272  and a Tip Apex Analysis unit  274  in this construction. Femoral Neck Reduction Analysis Module  244  includes a Contralateral Analysis Module  276  in this construction. Intertrochanteric Reduction Analysis and Femoral Neck Reduction Analysis are described in combination with  FIGS. 23-38  below. 
     Distal Radius Fracture Reduction Analysis Module  246  includes Contralateral Analysis Module  278  in this construction. Distal Radius Fracture Reduction is described in relation to  FIGS. 39-51  below. 
     Three aspects of the parent application are represented by  FIGS. 4F-4H  for intraoperative rescaling, intraoperative analysis, and AP Pelvis reconstruction, respectively.  FIG. 4F  is a schematic diagram of the Intraoperative Rescaling Module  218 ,  FIG. 4C , with Image Input Module  210  which contains Templated Input Module  201   a , Direct Measurement Recording Module  203 , Image Rescaling Module  205 , and Template Object Re-rendering Module  207 . A digital representation of a prosthesis, such as a “template”, is provided to Template Input Module  201  in one construction and, in another construction, is generated by that Module  201 . The digital template is provided to Direct Measurement Recording Module  203 , which also records a direct measurement such as the width of the femoral head in one construction and, in another construction, utilizes a known implant dimension such as the width of a screw or the radius of the acetabular component of a hip prosthesis. The Image Rescaling Module  205  calculates possible adjustments in sizing that may be required. For example, if a first image of a hip depicted a femoral head as having a width of 48 mm, but direct measurement by calipers reveals that the true dimension is 50 mm, then the 2 mm discrepancy represents a four percent difference or deviation, and the first image is rescaled by four percent accordingly. 
     In some constructions, Re-rendering Module  207  includes a Prosthetic Placement Update Module  280  and/or, in certain constructions, an Other Object Placement Update Module  282  to re-render objects other than prostheses. Prosthetic Placement Update Module typically utilizes coordinate information, referred to herein as ‘centroid’ information, that is stored in a database and tells the system what reference point should remain stationary, relative to the image, during the rescaling process. Optionally, Intraoperative Rescaling Module  218  further includes a Stationary Base Identification Module  2110  and a Secondary Image Rescaling Module  2112 , both shown in phantom, which can provide rescaling of the secondary image to Templated Object Re-rendering Module  207 . These phantom modules facilitate the scaling of a second image based on directly observable measurements in the first image, if both images include a stationary base that identify the same anatomic points. More specifically, the first image is scaled directly via the Direct Measurement Recording Module  203 , but this scaling is then applied to the second image by using the length ratios between the stable bases identified in Stationary Base Identification Module  2110 . 
     An alternative Intraoperative Analysis System  208 ′,  FIG. 4G , includes an Image Capture Module  209 , a User Data Input Module  211 , and an Analysis Module  213 . Optional additional capabilities include a Mathematical Correction Input Module  215  and an Error Analysis Module  217  as described in more detail below. Image Capture Module  209  preferably includes at least one of a Camera Picture input  219  for receiving or otherwise acquiring at least one photograph, a Radiographic Image input  221  for accessing a radiographic image from storage media or other location, and an Interface  223  which communicates with a fluoroscope or other medical imaging device to capture, receive or otherwise acquire an image in real time. At least one of inputs  219 ,  221  and/or  223  captures or otherwise acquires (i) at least one preoperative or contralateral reference image and (ii) at least one intraoperative or postoperative results image. The at least two images are provided to User Input Data Module  211  which utilizes a Stable Base Identification Module  225  to guide a user to select at least two stable base points, such as points on a pelvis, to generate a stable base on each image, and a Landmark Identification Module  227  to prompt the user to select a location spaced from and separate from the stable base, such as a location on the greater trochanter, on each image. Optionally, in certain constructions the Image Capture Module  209  also provides the images to the Error Analysis Module  217 , which guides a user to select at least one point on the bony anatomy which contains the stable base points, to be analyzed for anatomical or imaging inconsistencies that could create error in the Analysis Module  213 . An example of the operation of Error Analysis Module  217  is illustrated in  FIG. 70  below, where the difference between two overlaid triangles, representing sets of three points in each image along the bony pelvis, is analyzed for pelvic alignment inconsistencies. These images with selected identifications are provided to the Analysis Module  213  which utilizes at least one of the following modules in this construction: Overlay Module  229  which utilizes visual analysis by the user and/or an image recognition program; Mathematical Analysis Module  231  which performs math calculations; or Other Analysis Module  233  which utilizes different visual change criteria or quantification analysis. 
     If anatomy of the patient being analyzed shifts or otherwise moves between capture of the at least two images, then optional Mathematical Correction Input Module  215  is beneficial to compensate for such movement. Hip Analysis Correction Module  235  is useful for hip surgery, such as by utilizing user identification of the femoral longitudinal axis in each image, while Other Mathematical Correction Modules  237  are utilized as appropriate for other anatomical regions of a patient undergoing surgery or other corrective treatment. 
     An alternative AP Pelvis Reconstruction System  260 ′,  FIG. 4H , utilizes Image Capture  239  to obtain an image of each side of a patient, such as both sides of a hip, both shoulders, or two images of other anatomy for which two locations are substantially symmetrical or otherwise comparable. The at least two images are provided to Image Scaling Module  241  and Image Stitching Location Capture Module  243 , which identifies corresponding locations such as the tip of the pubic symphysis in each image. After scaling and location identification by Modules  241  and  243 , the images updated with that information are provided to Image Stitching Module  245  which generates an overlay as described in more detail below. 
     Optional modules include Contralateral Image Flipping Module  247  which reverses one of the images before it is provided directly to Image Stitching Module  245 , or is provided indirectly via one or both of Image Scaling Module  241  and/or Image Stitching Location Capture Module  243 . The output of a larger, stitched, overlay-type image from Image Stitching Module  245  can be provided directly to an AP Pelvis Analysis Module  251  or via an Image Cropping Module  249  to adjust the viewing area of the stitched image. In this construction, Analysis Module  251  includes one or more of Leg Length Analysis Module  253 , Acetabular Cup Angle Analysis Module  255 , and Other AP Pelvis Analysis Modules. 
     Flowchart A,  FIG. 5 , depicts the operation of Intraoperative Rescaling in one construction of the novel system and method related to hip surgery. The operation is initiated, as represented by “Start” in step  300 , and the femoral head is extracted and measured using calipers, step  302 . The technique proceeds to step  304 , and a line is drawn in software corresponding to femoral head measurement such as illustrated in  FIG. 2  above. The calliper measurement is recorded, step  306 ,  FIG. 5 , and the system calculates intraoperative rescaling from directly measured information, step  308 . The system applies rescaling to the selected image, step  310 , and, in one construction, uses prosthetic centroid information and rescaling data to update location of the prosthesis on the image. More generally, the system utilizes at least one selected point, such as the mid-point of the trunion, that is associated with the prosthetic template to identify where the prosthesis should remain stationary on the rescaled image. The system rescales and redraws all other objects on the image, step  314 , and rescaling is concluded, step  316 . 
     Flowchart B,  FIG. 6 , illustrates an Anterior Approach for hip surgery utilizing Flowcharts G and J. This technique is commenced, step  320 , and the decision whether to conduct ipsilateral analysis is made, step  322 . If yes, Flowchart G is initiated, step  324 ; if no, then a decision is made whether to conduct Contralateral analysis, step  326 . If yes, then Flowchart G is utilized, step  328 , after which it is decided whether to create and analyze stitched AP Pelvis, step  330 . If yes, then Flowchart J is activated. The Anterior Approach is concluded, step  334 . 
     Flowchart G,  FIG. 7 , shows technique flow for both contralateral and ipsilateral analysis. This technique is commenced, step  340 , and either contralateral or ipsilateral analysis is selected, step  342 . For contralateral analysis, the contralateral hip image is captured, step  344 , and the image is flipped, step  346 . For ipsilateral analysis, the preoperative ipsilateral hip image is opened, step  348 . For both types of analysis, Flowchart W is applied, step  350 . 
     Flowchart W,  FIG. 8 , after being activated by step  350 ,  FIG. 7 , guides a user to identify a femoral landmark such as the greater trochanter in step  370 ,  FIG. 8 , and then the femoral axis is identified, step  372 . These steps are illustrated in  FIGS. 9 and 10 , below. A line is then drawn across the bony pelvis, step  374 , as shown in  FIG. 11 . 
     The technique proceeds to capturing an operative hip image, step  352 ,  FIG. 7 , and identifying an acetabular component, step  354 , such as shown in  FIG. 12  below. Acetabular components are also shown in and discussed relative to  FIGS. 52-53  and  FIGS. 55-59  below. The image is scaled by entering the size of the acetabular component, step  356 , and Flowchart W is then applied to the operative hip, step  358 . The operative and comparative hip images are scaled by a stationary base generated by selecting at least two reference points on the bony pelvis, step  360 , such as shown in  FIG. 15 . The scaled images are then overlaid in step  362  using the bony pelvis points, such as the overlaid lines  386  and  412  shown in  FIG. 16 . Differences in offset and leg length are calculated, step  364 , and the technique is terminated, step  366 , returning to step  326 ,  FIG. 6 , for ipsilateral comparison or to step  330  for contralateral comparison. 
     Leg displacement is calculated in the pre-operation and post-operation (intra-operation) to give users a visualization of the operation process. The following steps  1 - 6  with Equations 6-10 are utilized in one construction: 
     1. Draw a landmark, such as a single point or dot to represent a feature such as the greater trochanter, and a “stationary base” generated by selecting at least two points on the bony pelvis in each of the pre-op image and post-op x-ray image.
 
2. One procedure for aligning two images utilizing corresponding stationary bases, each base comprised of precisely two points that define a line, is accomplished by the following approach. Based on the positions of zero coordinate in each x-ray image, translate the line segment position into screen coordinate system. P original  is the point&#39;s coordinate on each image&#39;s coordinate plane. Z screen  is the coordinate of zero in each image on the screen coordinate plane.
 
     
       
         
           
             
               
                 
                   
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     3. Find the rotation angle θ between the two line segments and line postop  and line preop  are the line vector of each line segment. 
     
       
         
           
             
               
                 
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     4. Calculate the rotation matrix R and apply it to the landmark in pre-op image. lm preop  is the center point position of landmark, lm′ preop  is the center point position of landmark after rotation. 
     
       
         
           
             
               
                 
                   
                     
                       
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     5. Calculate the length ratio S between the two line segments and scale the pre-op image based on it to get the landmark position after scaling. Use of more than two points for a stationary base benefits from a ‘best fit model’ approach, such as an algorithm that minimizes the distance between respective points in each of the images. 
     
       
         
           
             
               
                 
                   
                     
                       
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     6. Finally, calculate the distance of the two landmarks in both horizontal and vertical direction, visualize the results along with the two overlaid x-ray images. 
     
       
         
           
             
               
                 
                   
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     A currently preferred implementation of the JointPoint IntraOp™ Anterior system, which provides the basis for intraoperative analysis of the anterior approach to hip surgery, is illustrated in relation to  FIGS. 9-22 .  FIG. 9  is an image  376  of the right side of a patient&#39;s hip prior to an operation and showing a marker  378 , bracketed by reference squares  377  and  379 , placed by a user as guided by the system, or placed automatically via image recognition, on the greater trochanter as a landmark or reference point, such as indicated in box  224 ,  FIG. 4D  and in box  227 ,  FIG. 4G , for the Landmark Identification Module of systems  208  and  208 ′, respectively.  FIG. 10  is an image  376 ′ similar to  FIG. 9  showing a reference line  380 , bracketed by reference squares  381 ,  382 ,  383  and  384 , drawn on (i) the pre-operative, ipsilateral femur or (ii) the contra-lateral femur, to represent the longitudinal axis of the femur.  FIG. 11  is an image  376 ″ similar to  FIG. 10  with a line  386 , defined by two end-points, which is drawn across the pelvic bone intersecting selected anatomical features. 
       FIG. 12  is a schematic screen view of two images, the left-hand image  376 ′ representing a pre-operative view similar to  FIG. 10  and the right-hand image  390  representing an intra-operative view with a circle  392  placed around the acetabular component  394  of an implant  398  to enable rescaling of that image. In some constructions, circle  392  is placed by an image recognition program and then manually adjusted by a user as desired. Reference square  398  designates implant  398  to the user.  FIG. 13  is a schematic screen view similar to  FIG. 12  indicating marking of the greater trochanter of the right-hand, intra-operative image  390 ′ as a femoral landmark  400 , guided by reference squares  402  and  404 .  FIG. 14  is a schematic screen view similar to  FIG. 13  with a reference line  406  drawn on the intra-operative femur in the right-hand view  390 ″, guided by reference squares  407 ,  408 ,  409  and  410 . 
       FIG. 15  is an image similar to  FIGS. 11 and 14  with a line  386 ,  412  drawn across the obturator foremen in both pre- and intra-operative views  376 ″ and  390 ′″, respectively. Reference squares  413 ,  414 ,  415  and  416  guide the user while drawing reference line  412 . 
       FIG. 16  is an overlay image showing the right-hand, intra-operative, PostOp image  390 ′″ of  FIG. 15  superimposed and aligned with the left-hand, pre-operative PreOp image  376 ″. In this construction, soft button icons for selectively changing PreOp image  376 ″ and/or PostOp image  390 ′″ are provided at the lower left-hand portion of the screen. 
     In another construction, more than two points are generated for the stationary base for each image, such as illustrated in  FIG. 52  for a preoperative image  1200  and a postoperative image  1201 , and in  FIG. 53  for a combined overlay image  1298  of the preoperative image  1200  and the postoperative image  1201  of  FIG. 52 . Similar locations on the pelvis in each image are selected to generate the points utilized to establish a stationary base for each image. In image  1200 , for example, a first point  1202  is generated on an upper corner of the obturator foramen or at the pelvic tear drop, a second point  1204  is generated at the top or superior portion of the pubic symphysis, and a third point  1206  is generated at the lowest or inferior point on the ischial tuberosity. Lines  1208 ,  1210  and  1212  are drawn connecting those points to generate a visible stationary base triangle  1216  on image  1200 . Also shown is a point  1214  on the greater trochanter. In postoperative image  1201 , first and second points  1203  and  1205  correspond with first and second points  1202  and  1204  in image  1200 . A third point  1207  is shown in image  1201  between reference squares  1209  and  1211  in the process of a user selecting the lowest point on the ischial tuberosity to correspond with third point  1206  in image  1200 . The user is prompted by “Mark lowest point on Ischial Tuberosity” in the upper portion of image  1201 . Also shown is a circle  1213  around the acetabular component and a point  1215  on the greater trochanter. 
     Establishing at least three points is especially useful for determining rotational differences between images. Overlay image  1298 ,  FIG. 53 , shows the three points  1202 ,  1204  and  1206  of preop image  1200 , forming the visible preop stationary base triangle  1216 , which is positioned relative to the corresponding three points  1203 ,  1205  and  1207  of postop image  1201 , forming a visible postop stationary base triangle  1311  overlaid relative to triangle  1216  in  FIG. 53 . A ‘best fit overlay’ can be created using these points by identifying the centroid of the polygon created by these point, and rotating the set of point relative to one another to minimize the summation of distance between each of the related points. In this construction, scaling of the two images may be performed by these same set of points or, alternatively, a separate set of two or more points may be utilized to scale the two images relative to each other. Clicking on a PreOp soft-button icon  1300  and a PostOp icon  1301  enable a user to alter positioning of images  1200  and  1201 , respectively, within image  1298  in a toggle-switch-type manner to selectively activate or de-activate manipulation of the selected feature. One or more points of a stationary base may be shared with points establishing a scaling line. Preferably, at least one landmark is selected that is spaced from the stationary base points to increase accuracy of overlaying and/or comparing images. 
     Also illustrated in  FIG. 53  are “Offset and Leg Length Changes” with “Leg Length: −0.2 mm”, “Offset: 21.8 mm” and “Confidence Score: 8.1”. A confidence ratio that describes the quality of fit can be created by comparing the overlay area of the two triangles relative to the size of the overall polygon formed by the two triangles, including the non-overlapping areas of each triangle. Abduction angle and anteversion calculations are described below in relation to  FIGS. 55-59 . 
     A screen  420  viewable by a user during a surgical procedure guided by a JointPoint™ IntraOp Anterior™ system according to the parent application is represented by  FIG. 17 . The user selects OVERLAY-IPSILATERAL HIP  422  or OVERLAY-CONTRALATERAL HIP  424  with the option to use an existing overlay. The operative hip side to be “replaced” is selected, via window  426 , to confirm which will be the operative side and the comparative side; the comparative side is the same side as the operative side when a prior ipsilateral image is chosen. Another option for the user is to select AP (Anterior-Posterior) Pelvis simulation, step  425 ; in another construction, AP Pelvis is presented to a user at a later stage within Contralateral Hip overlay creation. 
     Flowchart J,  FIG. 18 , presents one novel technique for AP Pelvis Stitching and Analysis. The technique is commenced, step  500 , and a contralateral image is flipped to its original orientation, step  502 . A stitching line is drawn in the operative image, step  504 , such as a line  516  on the pubic symphysis shown in  FIG. 19  for image  515 , guided by reference squares  517 ,  518 ,  519  and  520 . A similar line is drawn on the contralateral image, step  506 , such as shown by line  522  in  FIG. 20  for image  521 , guided by reference squares  523 ,  524 ,  525  and  526 . The images are stitched, step  508 , to simulate an AP Pelvis image as shown in  FIG. 21  with overlapped stitching lines  516  and  522 , with optional user adjustment by touching movement control icon  527 , also referred to as a “rotation handle”. The images are cropped, step  510 , and the simulated AP Pelvis is utilized for intraoperative analysis, step  512 , such as leg length analysis or acetabular cobb angle. The technique terminates, step  514 , and returns to step  334 ,  FIG. 6 , in one construction. 
       FIG. 22  is view similar to  FIG. 21  with one reference line  530  drawn across the acetabular component of the image  521 ′, as guided by reference squares  531 ,  532 ,  533  and  534 , and another reference line  536 , as guided by reference squares  537 ,  538 ,  539  and  540 , touching the lower portions of the pelvis to enable accurate stitching for intraoperative analysis, including acetabular component cobb angle determination, according to the parent application. Additional analysis of the acetabular component, such as anteversion or other alterations of position, orientation or size, can be utilized as well. 
     Flowchart L,  FIG. 23 , illustrates Intraoperative Guidance for Intertrochanteric Reduction and Femoral Neck Fractures according to another aspect of the parent application, referencing Flowcharts M and N. The technique begins, step  600 , and reduction guidance is considered, step  602 . If selected, then the procedure outlined in Flowchart M is initiated, step  604 . Otherwise, or after the Flowchart M procedure has been completed, the technique proceeds to step  606  where the type of surgical procedure is selected. In this construction, for Femoral Neck Fracture Reduction, the technique proceeds to step  612  to generate a report and store data for future reference. If Intertrochanteric Reduction is selected, then guidance for Apex-Tip calculation is considered. If selected, then the procedure described by Flowchart N is followed, step  610 . Otherwise, or after the Flowchart N procedure has been completed, the technique proceeds to step  612  where a report is generated and data stored as mentioned above. Guidance for those procedures then ends, step  614 . 
     Flowchart M,  FIG. 24 , for Intertrochanteric Reduction Guidance, commences at step  620  when selected and the technique proceeds to step  622  where a contralateral hip image is taken and then flipped, step  624 , to achieve a screen view such as illustrated in  FIG. 26 . The inverted contralateral image is then processed as outlined in Flowchart P as described below. The surgeon then reduces the hip fracture, step  628 , and the user of this Guidance takes an X-ray-type image of the operative hip, indicated in step  630  as “User takes ipsilateral hip fluoro”. That image is then processed by the procedure of Flowchart P, step  632 , and the contralateral and ipsilateral images are overlaid, step  634 , such as shown in  FIG. 32 . 
     The overlay and neck shaft angles are analyzed in step  636 ,  FIG. 24  and, if not acceptable, the procedure returns to step  628  for another round of fracture reduction and analysis. Once acceptable, the procedure of Flowchart M is ended, step  638 , and the technique returns to step  606 ,  FIG. 23  as discussed above. 
     Flowchart P,  FIG. 25 , for processing a Contralateral or Ipsilateral Image, begins at step  640  and then at least one femoral landmark is identified, step  642 , such as marking the lesser trochanter with mark  660  as shown in  FIG. 26  for an inverted image  661  of the normal, un-injured contralateral side of the patient. A stationary base reference, preferably established by at least two points, such as for line  662 , is drawn on the pelvis, step  644 ,  FIG. 25 , as shown in  FIG. 27  for image  661 ′. The neck shaft angle  663  is measured, step  646 , as shown in  FIG. 28  as 138 degrees for image  661 ″. Typically, this step  646 ,  FIG. 25 , includes identifying the longitudinal axis  664  of the femur,  FIG. 28 , because the femoral line  664  serves as one “leg” of the angle  663  to be measured, with the other leg  666  established by the longitudinal axis of the femoral head. In some constructions, the femoral line  664  provides an important reference relative to the stationary base  662  so that the novel system and method can compensate for any difference in leg positions between images. It is not unusual for a leg to shift its orientation by 5 degrees to 15 degrees even when the leg is held in traction. 
     If scaling is desired, step  648 ,  FIG. 25 , then it is considered whether a scaling object is present in the image, step  650 . If yes, then the scaling object is identified, step  652 , and the object size is entered, step  654 . After those steps  652 - 654  are completed, or if no scaling object is found in step  650 , the technique proceeds to the optional step of drawing a femoral line, step  656  shown in phantom, if additional analysis is desired beyond measuring the neck shaft angle in step  646  as described above. In any event, after the procedure of Flowchart P is completed, step  658 , the technique returns to step  628  or step  634 ,  FIG. 24 , in this construction. 
       FIG. 29  is a screen view with the left-hand image  661 ″ similar to  FIG. 28  and a right-hand image  670  of the fractured side of the patient, showing marking of the lesser trochanter on the fractured side with a mark  672 .  FIG. 30  is a view similar to  FIG. 29  showing marking of the obturator foramen of the fractured side with stable base line  674  in image  670 ′.  FIG. 31  is a view similar to  FIG. 30  showing measurement of neck shaft angle of 123 degrees on the fractured side as determined by measuring angle  676  between femoral axis  678  and femoral head axis  679 .  FIG. 32  is a combined image showing the fractured side image  670 ″ overlaid on the normal, inverted side image  661 ″. Stable base lines  662  and  674  are overlapped exactly in this construction. 
     Flowchart N,  FIG. 33 , shows scaling and measurement for APEX TIP calculation as referenced in Flowchart L, step  610 ,  FIG. 23 . The technique begins, step  700 , and a fixation screw is inserted, step  702 . An AP (Anterior-Posterior) X-ray-type photo is taken, step  704 , and the AP image is scaled, step  706 , by measuring the length or width of the screw as shown in  FIG. 34  or by measuring another object of known size. The Tip-Apex distance is measured, step  708 , such as shown in  FIG. 35 . A lateral X-ray-type image is taken, step  710 , and the lateral image is scaled, step  712 , by measuring the screw as shown in the right-hand image of  FIG. 36 ; alternatively, another object of known size is measured in the image and compared to the known measurement. The Tip-Apex distance is measured, step  714 , in the lateral image such as shown in  FIG. 37 . AP and lateral Tip-Apex distances are calculated, step  716 , and the results are displayed such as shown in  FIG. 38 . If the measurement is not satisfactory, step  718 , then the technique returns in one construction to step  704  where replacement x-ray-type photos are taken and reanalyzed. Alternatively, or if re-analysis still does not reveal acceptable measurements, the surgeon repositions the screw as an alternative to step  702 , and then the guidance resumes with step  704 . Once acceptable, the procedure concludes, step  720 , and the technique returns to step  612 ,  FIG. 23 . 
       FIG. 34  represents a screen view  730  of an image of a screw  732  implanted through an implant  734  to treat an intertrochanteric hip fracture, showing measurement of the screw  732  with a longitudinal axis or length line  736 , guided by reference squares  737 ,  738 ,  739  and  740  generated by the novel system in this construction.  FIG. 35  is a view  730 ′ similar to  FIG. 34  showing measurement of Tip-Apex distance  742  of 8.2 mm, guided by reference squares  743 ,  744 ,  745  and  746 .  FIG. 36  is a view  730 ′ similar to  FIG. 35  plus a lateral view  750  on the right-hand side of the screen, showing measurement of the width of the screw  732  with line  752 , guided by reference squares  753 ,  754 ,  755  and  756 .  FIG. 37  is a view similar to  FIG. 36  showing measurement of Tip-Apex distance in the right-hand image  750 ′ with a Tip-Apex line  762  of 3.6 mm, guided by reference squares  763 ,  764 ,  765  and  766 .  FIG. 38  is a combined “Intertroch” view  770  showing both Tip-Apex Analysis and Neck Shaft Analysis. The Lateral Tip Apex measurement of 3.6 mm from view  750 ′ is added to the AP Tip Apex measurement of 8.2 mm from view  730 ′ to calculate a Combined Distance of 11.8 mm in this example. An overlay  780  of normal view  782  and fractured view  784  enables visual comparison, as well as image recognition and analysis, to calculate a Fractured Neck Shaft Angle of 123 degrees and a Normal Neck Shaft Angle of 133 degrees. 
     Guidance according to the parent application and the present invention can be provided for other anatomical regions such as wrists-hands, ankles-feet, and spinal anatomy including shoulders-arms. Flowchart Q,  FIG. 39 , provides Intraoperative Guidance for Distal Radius Fracture Reduction in wrists according to another aspect of the parent application, referencing Flowcharts R and S. This procedure begins, step  800 , and a choice is made whether to use radial inclination and length for reduction guidance, step  802 . If yes, the procedure outlined in Flowchart R is followed, step  804 . Once completed, or if those features are not selected at step  802 , then use of Palmar slope for reduction guidance is considered at step  806 . If selected, the procedure summarized by Flowchart S is followed, step  808 . After completion, or if Palmar slope is not selected at step  806 , then a report is generated and data stored, step  810 . If the radial fracture reduction is not satisfactory, additional reduction is performed on the affected wrist, step  814 , and the technique returns to step  802 . Once satisfactory, the procedure ends, step  816 . 
     Flowchart R,  FIG. 40 , illustrates Radial Inclination and Length Reduction Guidance. An AP (Anterior-Posterior) image of the contralateral wrist is captured, step  822 , and the contralateral image is flipped or inverted, step  824 . The flipped contralateral image is processed utilizing the procedure outlined in Flowchart T, step  826 , and an AP image is captured, step  828 , for the affected wrist on which surgery is to be performed. The affected wrist image is processed utilizing the Flowchart T procedure, step  830 , and the images are scaled and overlaid, step  832 , such as illustrated in  FIG. 51 . The affected and contralateral wrist radial inclination angles are calculated for comparison, step  836 , and a decision whether to scale the images is made, step  838 . If yes, the affected and contralateral wrist radial lengths are calculated for comparison, step  840 . After such calculations, or if not selected, the procedure ends, step  842 , and the technique returns to step  806 ,  FIG. 39 . 
     Flowchart S,  FIG. 41 , depicts Palmar Slope Reduction Guidance. This procedure begins, step  850 , and an image of the contralateral, normal wrist is captured, step  852 . The Palmar slope or tilt is measured, step  854 , such as shown in  FIG. 46 . A lateral image of the affected wrist is captured, step  856 , and the Palmar slope of the affected wrist is measured, step  858 , such as shown in  FIG. 50 . Data and images for the affected and contralateral wrist are displayed, step  860 , such as shown in  FIG. 51 . The procedure ends, step  862 , and the technique returns to step  810 ,  FIG. 39 . 
     Flowchart T,  FIG. 42 , shows identification of various anatomical features in the wrist and image processing. It commences, step  870 , and a radial styloid is identified, step  872 , such as shown in  FIG. 44 . The ulnar styloid is identified, step  874 , and the ulnar articular surface of the radius is identified, step  876 . The longitudinal axis of the radius is identified, step  878 , such as shown in  FIGS. 43 and 47  for the normal and affected images, respectively. 
     A stationary base reference line is drawn across the carpal bones in this construction, step  880 , such as shown in  FIG. 45 . The radial inclination is calculated, step  882 . If the image is to be scaled, step  884 , then at least one scaling object is identified, step  886 , and the object size is entered, step  888 . Intraoperative scaling is applied to the image, step  890 , and radial length is calculated, step  892 . Once completed, or if scaling is not desired, the procedure ends, step  894 , and the technique returns to steps  828  or  832  of  FIG. 40  as appropriate. 
       FIG. 43  represents a screen view of an image  900  of a “normal” wrist of a patient with a line  900  drawn on the radius to indicate its central axis, guided by reference squares  904 ,  906 ,  908  and  910 .  FIG. 44  is a view  900 ′ similar to  FIG. 43  with marking of selected anatomical points: Radial Styloid  912 , guided by reference squares  914  and  916 ; Ulnar Border of Radius  918 , guided by reference squares  920  and  922 ; and Ulnar Styloid  924 , guided by reference squares  926  and  928 .  FIG. 45  is a view  900 ″ similar to  FIG. 44  with a reference line  930  drawn across the carpal bones to provide a stationary base reference, as guided by reference squares  932 ,  934 ,  936  and  938 . 
       FIG. 46  is a view of an image  940  of the normal wrist rotated to draw Palmar Tilt with longitudinal reference line  942 , guided by reference squares  944  and  946 , and lateral reference line  948 , guided by reference squares  950 ,  952 ,  954  and  956 , with a calculated Tilt of 7 degrees in this example. 
       FIG. 47  is a screen view with the left-hand image  900 ″ similar to  FIG. 45  and a right-hand image  960  of the fractured side of the patient, showing marking of the central axis  962  of the radius on the fractured side, guided by reference squares  964 ,  966 ,  968  and  970 .  FIG. 48  includes a screen view image  960 ′ similar to image  960 ,  FIG. 47 , showing marking of anatomical points on the fractured side: Radial Styloid  972 , guided by reference squares  974  and  976 ; Ulnar Border of Radius  982 , guided by squares  984  and  986 ; and Ulnar Styloid  992 , guided by squares  994  and  996 .  FIG. 49  is a view  960 ″ similar to  FIG. 48  with a reference line  1000  drawn across the carpal bones on the fractured side, guided by reference squares  1002 ,  1004 ,  1006  and  1008 . In this constructions, a user touches one of the squares with a finger or a mouse cursor, and utilizes the square, such as by ‘dragging’ it, to move a marker to a desired location. This enables manipulation without blocking the location of interest. 
       FIG. 50  is a screen view with the left-hand image  940 ′ similar to  FIG. 46  and a right-hand image  1010  of the fractured wrist rotated to draw Palmar Tilt with longitudinal reference line  1012 , guided by reference squares  1014  and  1016 , and lateral reference line  1020 , guided by reference squares  1022 ,  1024 ,  1026  and  1028 , with a calculated Tilt of 3 degrees in this example.  FIG. 51  is a combined view as a Distal Radius Report according to the parent application, after the fractured side has been reduced, that is, after a surgical operation has been performed on the fractured side. The “Normal” image is an inverted contralateral image of the opposite wrist-bones of the patient. Although not illustrated, one or more plates or other implants may be utilized before and/or after analysis according to the parent application to reduce fractures as part of the surgical procedures to restore orthopaedic functionality at the surgical site. Upper-left Image  1030  is an AP Overlay of Radial Inclination to analyze radial bone fracture reduction with specific regard to angle in AP orientation. Contralateral or ‘Normal’ Radial Inclination is 2.4 degrees in this example and the Fractured Radial Inclination is 10.5 degrees. Radial inclination reference lines for the normal wrist-bones are shown in dashed lines while reference lines for the fractured wrist-bones are shown in solid lines. Preferably, an overlay line passing through the carpal bones in the each of images is utilized as stationary bases to generate images  1030  and  1050 , although these overlay lines are not shown in images  1030  and  1050 . Lower-left Image  1040  is an AP image of Reduced Fracture, after reduction has been analyzed by the system, to confirm image capture for future reference and digital record-keeping. 
     Upper-right Image  1050  in  FIG. 51  is an AP Overlay of Radial Length to compare analysis of reduced radial bone location, with two sets  1052  and  1054  of substantially parallel lines, also with dashed lines for Normal and solid lines for Fractured wrist-bones. The distance between the two sets  1053 ,  1054  of lines indicates radial length measurement. Radial length lines are drawn using radial styloid and ulnar styloid location information. The quality of the fracture reduction is thereby analyzed; changes in radial length may indicate an orthopaedic problem. Image  1050  enables the user to visually inspect and analyze the quality of the fracture reduction and, therefore, numerical values are not provided in image  1050  in this construction. Lower-right Image  1060  is a Lateral View of Distal Radius Fracture after Reduction to provide Palmar Tilt analysis that compares fractured Palmar Tilt angle of 3 degrees in this example to the contralateral or ‘Normal’ Palmar Tilt angle of 7 degrees, although only the fractured wrist-bones are shown in image  1060  in this construction. 
       FIGS. 52 and 53  are described above. 
     In some constructions, a guidance system is provided to adjust the viewing area of one image on a screen to track actions made by a user to another image on the screen, such as to focus or zoom in on selected landmarks in each image. This feature is also referred to as an automatic ‘centering’ function: as a user moves a cursor to ‘mark’ a feature on one image, such as placing a point for a landmark or a stationary base on an intraoperative image, the other image on the screen is centered by the system to focus on identical points of interest so that both images on the screen are focused on the same anatomical site.  FIG. 54  is a schematic combined block diagram and flow chart of an identification guidance module  1400  utilized in one construction to assist a user to select landmarks when comparing a post- or intra-operative results image, box  1402 , with a reference image, box  1404 . The module is initiated with a Start  1401  and terminates with an End  1418 . When a visual landmark is added to a post-operative image, box  1406 , the module  1400  locates all landmarks “1” on the pre-operative reference image, box  1408 , and calculates the visible area “v” within the pre-operative image in which to scale, such as by using Equation 11: 
     
       
         
           
             
               
                 
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     The user manipulates one or more visual landmarks in the results image, box  1416 , as desired and/or as appropriate. In some constructions, the user manually ends the guidance activities, box  1418  and, in other constructions, the system automatically discontinues the guidance algorithm. 
     In certain constructions, image recognition capabilities provide “automatic”, system-generated matching and alignment, with a reduced need for user input. Currently utilized image recognition provides automatic detection of selected items including: the spherical ball marker frequently utilized in preoperative digital templating; the acetabular cup in digital templates and in trial prosthetics; and the Cobb Angle line, also referred to as abduction angle. 
     Note that “PostOp” typically indicates post-insertion of a trial prosthesis during the surgical procedure, and is preferably intra-operative. The PostOp image can also be taken, and analysis conducted after a “final” prosthesis is implanted. “PreOp” designates an image preferably taken before any surgical incision is made at the surgical site. In some situations, the image is taken at an earlier time, such as a prior visit to the medical facility and, in other situations, especially in emergency rooms and other critical care situations, the “PreOp” image is taken at the beginning of the surgical procedure. Ball markers BM are shown but are not utilized for alignment because ball markers can move relative to the patient&#39;s anatomy. Further PreOp and PostOp icons are provided to adjust viewing features such as contrast and transparency. Preferably, at least one icon enables rotation in one construction and, in another construction, “swaps” the images so that the underlying image becomes the overlying image. 
     In certain constructions, intraoperative analysis and guidance is also provided to a user for one or more individual components of an implant such as an acetabular cup of a hip implant. System  1500 ,  FIG. 55 , analyzes the orientation, including abduction angle and anteversion, of an acetabular cup in this construction. System  1500  includes Image Selection Module  1502 , Image Recognition Module  1504 , Landmark Identification Module  1506 , Acetabular Cup Bottom Identification Module  1508  and Abduction Angle and Anteversion Calculation Module  1510  in this construction, with system operation and technique described below in relation to  FIGS. 56-59 . 
       FIG. 56  is an image  1520  of an acetabular cup  1522  positioned in the left acetabulum of a patient with a circle  1524  drawn around its outer hemispherical surface to provide diameter information for the component. In some constructions, a user initiates component analysis by touching a finger or a stylus to the “Diameter Information” field  1532 . At any time, as described in relation to  FIG. 59  below, the user preferably is able to return to a previous action such as by touching or clicking another field  1532 , for example “Mark Greater Trochanter”. In one construction, an image recognition algorithm in Image Recognition Module  1504  automatically operates to identify the acetabular cup  1522  in the image  1520  of  FIG. 56  and surround it with the circle  1524 , bracketed by small guide dots  1526 ,  1528 , as indicated by the prompt “Diameter information”  1532  at the top of image  1520 . In some constructions, the guide dots or squares serve as “navigation handles” to enable the user to manipulate one or more features designated by the handles, such as by touching or clicking and dragging the handles to move the designated features. This screen  1520  relates to step  1608  in flowchart X, algorithm  1600 ,  FIG. 59  below. If the initial, auto-generated circle is not acceptable, then the user manually adjusts the position and/or size of circle as appropriate, step  1610 . 
       FIG. 57  is an image  1540  similar to that of  FIG. 56  with two lines  1542  and  1560  drawn to calculate abduction angle. The user accesses screen  1540 , having a heading or prompt  1541  of “Calculate Abduction Angle”, for example, to fit in the abduction angle landmarks for calculation. The terms “abduction” and “abduction angle” are also known as “inclination”. The “User positions neutral axis” step  1612  in flowchart X,  FIG. 59  below relates to screen  1540 ,  FIG. 57 , in which neutral axis line  1560  is placed to touch the two ischial tuberosities of the pelvic girdle. Guide squares  1562 ,  1564 ,  1566  and  1568  enable the user to manipulate the neutral axis line  1560 . Abduction angle line segment  1542  is auto-positioned across circle  1524  using image recognition, step  1614 ,  FIG. 59 , wherein the system automatically detects where the acetabular cup  1522  is positioned,  FIG. 57 , and the system places the line segment  1542  across the abduction angle on the cup as accurately as it can do so. The abduction line segment  1542  preferably is a diameter line of the circle; when segment  1542  is extended virtually by the system to intersect the neutral axis line  1560 , the abduction angle is generated and measured at that intersection. In one construction, the abduction line defaults to about 45 degrees from the neutral line  1560  until more accurate auto recognition occurs. The guide square “handles”  1544 ,  1546 ,  1548  and  1550  around the abduction line segment  1542  enable the user to rotate the abduction line segment  1542 , but the abduction line continues to look like a diameter line so that it remains properly aligned with the actual orientation of the acetabular cup  1522 . 
     During the “User adjusts abduction angle manually if required”, step  1616 ,  FIG. 59 , the user can use the navigation handles  1544 ,  1546 ,  1548  and  1550 ,  FIG. 57 , after the image recognition has run, to make the abduction angle substantially perfect. In “System calculates and displays abduction angle”, step  1618 , the neutral axis  1560  is mathematically compared to the abduction line segment  1542  to determine the angle. In this construction, the abduction angle data of “32°”, for example, is displayed in lower right field  1543  in  FIG. 57 . 
     If the user wants anteversion information, then at step  1620 ,  FIG. 59 , “YES” is selected and arcs  1572 ,  1574 ,  FIG. 58 , are positioned that identify the bottom of the acetabular component  1522  in step  1622 . The system then calculates and displays the anteversion angle, which relates to the z-plane rotation of the acetabular component  1522 . Some users may only want to use abduction angle data and will then skip anteversion at step  1620  and proceed to step  1626  where it is decided whether to modify placement of the acetabular component intraoperatively. If “yes” is selected, then the algorithm proceeds as indicated by path  1628  to reposition the acetabular component, step  1604  et seq. Once the user is satisfied with the placement, then algorithm  1600  terminates, step  1630 , and the system resumes from where step  1602  was initiated. 
       FIG. 58  is an image  1570  similar to that of  FIG. 57  with arcs drawn at the bottom of the acetabular cup  1522  to assist calculation of anteversion in the z-plane. Image  1570  includes a vertically-oriented “slider control”  1580  in this construction, with vertical line  1582  and a movable setting knob  1584 , to enable a user to easily increase or decrease the size of arcs  1572  and  1574 . Vertical slider control  1580  increases or decrease the size of the arcs  1572 ,  1574 . These arc lines  1572 ,  1574  are mirror images of one another relative to the abduction line segment  1542  and are used to identify the location of the bottom of the cup  1522  in the image  1570 . Sliding knob  1584  all the way to ‘0’ will cause the arcs  1572 ,  1574  to overlay the abduction angle line segment  1542 . Sliding all the way to ‘100’ will cause the arcs to overlay the existing circle  1524 . This relates to “Arcs are positioned that identify bottom of acetabular component”, step  1622 ,  FIG. 59 . Guide handles  1569  and  1571 ,  FIG. 58 , are provided for at least one of arcs  1572  and  1574  as described in relation to  FIG. 59  below. 
     During the next step  1624 , “System Calculates and Displays Anteversion”, any updates that are applied to the arcs  1572 ,  1574  via slider  1580  will lead to re-calculation and updated display of anteversion value such as “14°” in field  1594 . Note how the guide handles  1573 ,  1575 ,  1577  and  1579  in  FIG. 58  allow the precise location of the abduction angle to still be updated if required, via manipulation of abduction line segment  1542 , which is especially useful if the user continues positioning the arcs, to more closely achieve actual orientation values. Soft-button icons  1590  and  1592  for “Abduction Angle” and “Anteversion”, respectively illustrated with solid and dashed lines, serve as “toggles” when touched or clicked by a user to selectively activate which screen features may be manipulated by the user. In one construction, the functionality of one or more of guide handles  1573 ,  1575 ,  1577  and/or  1579  is altered according to which of icons  1590  and  1592  is selected, to adjust features relating to abduction and anteversion, respectively. 
       FIG. 59  is a flowchart of anteversion and abduction analysis by the modules of  FIG. 55 . Flowchart X, algorithm  1600 ,  FIG. 59 , is activated when a user selects “Cup Check” icon or text to initiate cup analysis. In some constructions, this prompt will persist somewhere on the navigation screen throughout the workflow. This is a ‘forked’ or loop workflow which will start, step  1602 , from wherever it is initiated and then return to the same place upon finish of the fork. First action of “Position Acetabular Component”, step  1604 , is conducted by a surgeon. The “acetabular component” in this situation of “pre-stem insertion”, can be a number of components: a standard acetabular cup, a reamer, or a trial acetabular cup. The actual component analyzed depends on what the surgeon would like to have analyzed by the novel system. 
     After initial installation of a component, a prompt such as “Take image of acetabular component”, step  1606 , guides the user to take a picture of an AP Pelvis view with implanted cup, such as illustrated in  FIG. 56 . Alternatively, a prompt of “Select from Library” or other guidance can be provided to the user, in a manner similar to other techniques described above. Steps  1608 - 1616  are described above in relation to  FIGS. 56-57  in which a circle is established around the acetabular cup and diameter information of the circle is generated. 
     Initiation of step  1618 ,  FIG. 59 , “System calculates and displays abduction angle”, causes two lines to appear, the pelvic reference line  1560  and abduction angle line segment  1542 ,  FIG. 57 , in a manner that is similar to abduction angle analysis on simulated AP Pelvis described above. Pelvic reference line  1560  is also referred to as the “neutral axis” line, step  1612 . Alternatively, a “T” or other geometric shape appears on the screen when a soft button “toggle” is activated. The pelvic reference line  1560  is a line across image  1540 , placed by default horizontally on image  1540  and approximately 75 percent of the way down the image (in a y-coordinate system). This is similar to the Cobb Angle functionality discussed above. 
     For the abduction angle line, the user draws the line segment  1542  as precisely as possible across the cup  1522 . In some constructions, an image detection/recognition algorithm is provided to assist this process. Abduction angle preferably is calculated in real time and displayed in this step. In one construction, the abduction angle continues to be displayed to the user throughout the additional steps in this process. Determining the abduction angle is a straightforward calculation, calculated as the angle between the neutral axis  1560  and abduction line segment  1542 ,  FIG. 57 , similar to how it works in AP Pelvis reconstruction. When a user such as a surgeon wants to get return to operating on the patient and not continue with anteversion, then the user selects “No” in steps  1620  and  1626 ,  FIG. 59 , the system “saves” the calculated information, and returns to where algorithm  1600  was initiated while the surgeon resumes surgery on the patient. 
     For step  1622 , the user works with two inner arcs to analyze anteversion. The system keeps the acetabular component circle visible from the earlier step, but it is now non-modifiable. The abduction line preferably is removed from the visual display. Preferably the circle appears to be “paper thin” (and even slightly transparent) in this screen. End points  1526  and  1528 ,  FIG. 57 , are added on each side of the circle  1524  where the abduction line  1542  transected the visual circle  1524 . 
     Now the system proceeds to modify the two arcs  1572  and  1574 ,  FIG. 58 , that are contained within the circle  1524 . Each arc is on one of the sides of the abduction line segment  1542 . These arcs are mirror images of one another relative to the abduction line. Each arc should default to a distance of 35% of the circle radius; for example, if the radius is 28 mm (or  28   x  pixels, whatever it may be, as scaling is not needed for this process), the distance of the midpoint of the arc from the abduction line should be approx. 9 mm (or  9   x  pixels). One of the arcs, such as the lower one  1574 , has navigation controls or handles  1569  and  1571  on it, or directly at the center of the arc  1574 . The other arc will move in tandem with this arc in a “captured” manner. Navigation control for this object will be a slider control (similar to a transparency control, but longer and vertical). As described above for one construction, at a setting of 100 percent on the slider, the arc will be directly on the cup, while at 0 percent on the slider, the arc will be directly on the abduction angle line. Preferably an initial default setting of 35 percent is provided. Also, preferably, the slider control  1580  is movable on the screen, and is initially positioned by the system in the middle of the screen. 
     Anteversion is calculated in real-time and displayed as arcs  1572  and  1574  are modified. A larger display is desired for both abduction angle and anteversion. Anteversion is calculated in one construction according to Liaw et al., “A New Tool for Measuring Cup Orientation in Total Hip Arthroplasties from Plain Radiographs”, Clinical Orthopaedics and Related Research No. 451, pp. 134-139 (2006) currently available at: http://www.csie.ntu.edu.tw/˜fuh/personal/ANewToolforMeasuringCupOrientation.pdf. As described on Page 136 of the Liaw et al. article,  FIG. 2 -B shows calculation of ‘true anteversion’ angle: Point F is known, as the midpoint of the diameter line, and Point E can be identified from circle surround the cup. The highest point on the cup is point E, which has the same x-coordinate as Point F and a y-coordinate equal to (y coordinate of Point F+ radius of circle diameter). Point G is a point on the ‘arc’ horizontal from Point F. Angle Beta(t), which represents true anteversion, can be calculated from this data. 
     Finally, the user can Capture/Save this analysis for later review and then ‘Go Back’ to standard workflow. High Level Workflow Functionality Summary: preferably, the system provides the user with the ability to Save, Exit Cup Check, return to previous screen, and view after the final overlay. In some constructions, the system captures anteversion on the reconstructed AP Pelvis as well, in addition to the abduction angle calculation that already exists. A soft button with a designation such as “Calculate Anteversion” is provided for the user to click or touch at the end of ‘abduction angle’ process in simulated AP. If selected, then process continues, else process stops. 
     In some techniques, the Abduction Angle can be altered if user decides to keep a physical handle attached to the acetabular cup. The handle will appear on an x-ray image or fluoro image, and can be used to determine abduction. A perpendicular line to the cup handle line that intersects the Ischial Tub line will produce a very accurate Abduction Angle. Finally, in Flowchart X,  FIG. 59 , is the user satisfied with the results? If not, the user can reposition the acetabular cup, retake a fluoro shot, and begin the process again as shown in the flowchart. Thus, a novel software-controlled solution is achieved, anatomically disconnected from the patient, to provide intraoperative data that improves clinical decision-making during surgery without increasing trauma to the patient. 
     In certain constructions, a system and method according to the present invention includes an inventive alternative methodology for analyzing intraoperative leg length and/or offset changes using a different application of the stationary base, intraoperative scaling and anatomical landmark identification techniques. Referred to herein as ‘Reverse Templating”, the system and method combines the use of intraoperative data, gathered from intraoperative image analysis, with intraoperative templating on a preoperative ipsilateral image. The process begins in some constructions by (1) acquiring preoperative ipsilateral and intraoperative images and (2) scaling and aligning these images by using identifiable features on the pelvis to serve as a stationary base, together with intraoperative data of the acetabular component. The system initially displays the preoperative and intraoperative images next to one another, with the system aligning and scaling the images relative to one another by using the identified stationary bases in each image. The absolute scale, that is, objective scaling according to a measurement system such as in millimeters, at least for the intraoperative image, is determined by visually identifying the prosthetic implant device itself while entering the known metric size for at least one dimension of the device. Both images are scaled in some constructions using their respective stationary bases and, in other constructions, each image is scaled independently, such as by using a ball marker for the preoperative image and the known dimension of the implant for the intraoperative image. 
     In certain preferred implementations of this Reverse Templating method, the user is guided to identify one or more landmark points (i.e. the tear drop anatomical feature of the pelvis) on each image and is then guided by the system to position templates that directly overlay the acetabular component and femoral stem implants visible in the intraoperative image. In other words, a first, acetabular template is superimposed over the acetabular component and a second, femoral template is superimposed over the femoral stem of the implant during certain preferred implementations of the present overlay technique. This template overlay in the intraoperative image does not calculate any offset or leg length data directly, but it provides other intraoperative data (i.e. abduction angle) that enables the system and user to precisely position the acetabular component and femoral stem templates on the preoperative image. The use of intraoperative data in the preoperative image, as gathered from overlaying templates in the intraoperative image, transforms this approach from an “estimation” technique to one that provides extremely precise calculations of intraoperative offset and leg length changes. The technique&#39;s use of templates additionally allows the surgeon to proactively analyse how intraoperative changes to implant selection will affect leg length and offset. 
     One system that implements this intraoperative Reverse Templating technique is shown in Intra-operative Analysis Module  1850  in  FIG. 67 . The method for one construction of the system is depicted in flowchart segments  1870  and  1872 ,  FIGS. 68A and 68B , that comprise a Flowchart U depicting Intraoperative Templating Flow. The system and method that implements this Intraoperative Templating technique generates images such as shown in  FIGS. 60-66 . 
     In one construction, novel intra-operative Analysis Module  1850 ,  FIG. 67 , includes Image Selection Module  1852  which communicates with a Rotation and Scaling Module  1860  that preferably includes an optional Stable Base Identification Module  1854 , shown in phantom. In this construction, Template Input Module  1852  further communicates with an optional Longitudinal Axis Identification Module  1856 , shown in phantom, that provides femoral axis identification in this construction which is particularly useful if the first and second images are not taken in virtually the same position, that is, along the same viewing angle, and a Landmark Identification Module  1858 . All three of modules  1860 ,  1856  and  1858  provide inputs to Intraoperative Template Placement Module  1862 ; in this construction, Stable Base Identification Module  1854  generates a stable base, also referred to as a stationary base formed from two or more points selected on a patient&#39;s anatomy, as part of Rotation and Scaling Module  1860 , whose results are then provided to Intraoperative Template Placement Module  1862 . In one construction, Module  1862  facilitates placement of digital templates of acetabular and femoral components onto a preoperative image using intraoperative data including templating data from the intraoperative image. After templating, information is provided to the Differential Analysis Module  1864  for further calculations and analysis, including offset and leg length calculations in some constructions. One or more of the modules  1852 - 1864  can interface with a display or other interactive communication with a user. Another optional component is an Intraoperative Templating Module  1863 , shown in phantom, which provides further processing of the output of Intraoperative Template Placement Module  1862 , such as performing “what if” planning analysis or to modify one or more of the digital templates, before providing the results to Differential Analysis Module  1864 . 
     All references to “module” in relation to  FIGS. 68A-69  refers to the modules of Intraoperative Analysis Module  1850 ,  FIG. 67 , with “ID” referring to “Identification”. Further, the order in which the preoperative, reference image and the intraoperative, results image are marked or scaled among steps  1876  to  1902  can be interchanged in other implementations. In other alternative constructions, analysis is conducted utilizing a contra-lateral image instead of or in addition to an ipsa-lateral image as described below. 
     The method begins in one construction with initiation, step  1874 ,  FIG. 68A , and a user-selected preoperative ipsilateral hip image is opened for display, step  1876 , by Image Selection Module  1852 . The system guides the user to indicate whether the image is a right or left hip. A screen view  1700 ,  FIG. 60 , depicts the selected image  1702  of the right side of a patient&#39;s hip prior to an operation, with pubic symphysis PS, obturator foramen OF and right femur F R . The image  1702  can be acquired by directly interfacing with an imaging system or otherwise by taking a picture of a radiographic image using an iPhone camera or similar technology. A label  1718  of “PreOp” indicates that it is a pre-operative image. 
     The method continues with the preoperative hip image being processed, step  1878 , by the technique of flowchart  1880 ,  FIG. 69 , which is a Flowchart Y showing functions applied to the pre-operative hip image for Intraoperative Templating of Flowchart U. The specific functions include identification of a ‘stable base’ (sometimes referred to as a ‘stationary base’) according to the parent application, identification of the femoral axis, and identification of the greater trochanter in this construction. 
     At step  1882 ,  FIG. 69 , a reference line is drawn by the Stable Base ID Module  1854  across the bony pelvis, as illustrated by the “stable base” line  1704  in  FIG. 60  which is shown extending from the teardrop TD to the lower portion of the pubic symphysis PS. A femoral axis line  1706 , representing the longitudinal axis of the femur, is then identified in step  1884 ,  FIG. 69 , by the Longitudinal Axis ID Module  1856 . A femoral landmark such as the greater trochanter is identified, step  1886 , by Landmark ID Module  1858 ; in other constructions, one or more alternative femoral landmarks such as the lesser trochanter are identified. As guided by step  1886 , guide squares  1710  and  1712 ,  FIG. 60 , assist the user in placing a marker  1714  on the greater trochanter GT as a landmark or reference point. In some constructions, the “stable base” line  1704 , “femoral axis” line  1706 , and marker  1714  on the greater trochanter (or other femoral landmark) may be automatically placed in appropriate locations by the system&#39;s image recognition capabilities and then may be modified by the user. In other constructions, the user is prompted to place these lines and markers without system intervention. 
     Continuing with step  1890 ,  FIG. 68A , the technique captures the operative hip image, that is, an image is obtained of the patient&#39;s hip during surgery, utilizing the Image Selection Module  1852 . The operative hip image may be captured through various methods, such as through a direct connection with a fluoroscopy machine, a DICOM file upload, or by the user taking a camera picture of the radiographic image using an iPad or other mobile computing device. After capturing the operative hip image, the acetabular component is identified in step  1892  by the Rotation and Scaling Module  1860 , such as shown in  FIG. 61 . The intraoperative image is scaled, step  1894 , by entering the size of the acetabular component into the system, which is processed by Rotation and Scaling Module  1860 . 
       FIG. 61  represents a screen  1720  viewable by the user during a novel surgical procedure guided according to the parent application showing two images in split screen view, the left-hand image  1702 ′ representing a pre-operative view similar to  FIG. 60 , and the right-hand image  1722  representing an intra-operative view with a circle  1724  placed around the acetabular component  1730  of an implant  1732  to enable rescaling of that image. In some constructions, the system attempts to automatically place the circle  1724  around the acetabular component  1730  using image recognition algorithms. In other constructions, the user is prompted to place the circle around the acetabular component without system guidance. The user may use guide squares  1726  and  1728 , if required, to alter the size and position of circle  1724  so that it precisely encircles the acetabular component  1730 . In one construction, the user enters the diameter of circle  1724 , such as “54 mm”, using data entry box  1727 . This enables the system to generate absolute scaling in the intraoperative image by taking the diameter in pixels of the acetabular component and combining that with the known diameter in millimeters. Other prompts to guide the user include the choice of soft-key  1740  for “Use Ball Marker” and soft-key  1742  for “Use Ruler”, to allow the user to accomplish intraoperative scaling using other anatomical features or observable devices if desired. 
     The method continues with step  1896 ,  FIG. 68A , by applying Flowchart Y,  FIG. 69 , to the operative hip, including steps  1882 - 1886  as described above, in order to identify the “stable base”, “femoral axis” and greater trochanter in the operative hip image, as illustrated in  FIG. 62 . The shoulder of the femoral implant is identified, step  1898 , in the intraop image by Landmark ID Module  1858 , which is also illustrated in  FIG. 62 . 
       FIG. 62  is a schematic screen view  1750  similar to  FIG. 61  with pre-operative image  1702 ″ and indicating placement of a mark  1760  of the lateral shoulder  1761  of the prosthesis  1732  of the right-hand, intra-operative image  1722 ′, as guided by guide squares  1762  and  1764 . Also shown is the greater trochanter having mark  1756  as a femoral landmark and a stable base line  1754  connecting the tear drop TD to the lower portion of the pubic symphysis PS. Alternative constructions may use a stable base line  1754  that connects a different set of 2 or more anatomical landmarks across the pelvis, but the landmarks must be placed on consistent points across the preoperative and intraoperative images. Similarly, alternative constructions may replace the greater trochanter with a different femoral landmark (i.e. lesser trochanter) that can be identified in both preoperative and intraoperative images. In some constructions, the system will attempt to auto-generate placement of the mark  1760  at the lateral should  1761  of the prosthesis, the mark  1756  on the greater trochanter, and stable base  1754  across pelvic landmarks, and then allow the user to modify placement. Other constructions will prompt the user to determine placement of this data without automated guidance. 
     The identification of consistent stationary bases in the preoperative image and intraoperative images can be combined with the absolute scaling data in the intraoperative image to apply absolute scaling to the preoperative image. To accomplish this, the method continues in step  1900 ,  FIG. 68A , by scaling the preoperative image in pixels by Rotation and Scaling Module  1860 , which scales the lines across the bony pelvis in both the preoperative and intraoperative images so that they are of identical size in pixels, such as by using stable base line  1704 ,  FIG. 61 , and stable base line  1754 ,  FIG. 62 . 
     Continuing with step  1902 ,  FIG. 68A , absolute scaling is applied to the preoperative image by using the known size of the acetabular component in the intraoperative image. Because both images are scaled according to an identical stationary base, the absolute scale ratio in the intraoperative image, determined by acetabular component diameter, can be applied to the preoperative image. This unique technique provides precise scaling to the preoperative image by using objects of known size in the intraoperative image and applying this scaling to the preoperative image. The result is that a significantly more precise absolute scaling can be determined in the preoperative image, as compared to traditional preoperative image scaling techniques that utilize ball markers or similar techniques. 
     Alternative constructions may alternatively apply absolute scaling to the preoperative and intraoperative images directly in each image, and without the need for a stationary base. For example, each image may be scaled by a ball marker or other scaling device, known magnification ratios of a radiographic device, or direct measurements of anatomical points (such as a direct measurement, via callipers, of the extracted femoral head, which can be used to scale the preoperative image). 
     Alternative constructions may also replace the ‘stationary base’ with various other techniques that could be used to scale and align the preoperative and intraoperative images relative to one another. One example of such a construction would involve overlaying two images and displaying them with some transparency so that they could both be viewed on top of one another. The user would then be prompted to rotate and change their sizing, so that the pelvic anatomy in the two images were overlaid as closely as possible. 
     A “side by side” display is generated by the Rotation and Scaling Module  1860 , step  1904 , which is consistently rotated and scaled based on the stable base line across the bony pelvis. In some constructions, a single image that combines preoperative and intraoperative picture renderings side by side will be displayed. Other constructions will maintain the preoperative and intraoperative images as separate images. All constructions will rotate and scale the images relative to one another using the stationary bases across the pelvis. 
     After aligning the preoperative and intraoperative images, the method continues with step  1906 ,  FIG. 68B , with the user or system drawing an acetabular cup template directly on top of the implant in the intraoperative image, such as shown in  FIG. 63 . The acetabular cup template is placed to match the actual abduction angle by Intraoperative Templating Module  1862 .  FIG. 63  is a schematic screen view  1770  similar to  FIG. 62  with a reference rectangle  1772 , also referred to as a “box” or “frame”, indicating an acetabular component template  1774 , with a central point  1775 , placed directly above the acetabular component of the prosthesis on the intra-operative femur in the right-hand view. In some constructions, the system combines known anatomical data (i.e. the circle  1724  placed around the acetabular component in  FIG. 61 ) and image recognition to generate the initial placement of the acetabular component template on the intraoperative image. In an alternative construction, the acetabular component template is placed at a default abduction angle and modified by the user. In either construction, the user can modify the template abduction angle to match the actual acetabular component abduction angle by using movement control icon  1776 , also referred to as a “rotation handle”, similar to the icon  527  shown in  FIG. 21  above. This assists “touch” or “click and drag” control used to facilitate repositioning and adjustment of the template  1774  relative to the image of the acetabular component  1730  of implant  1732 . In one construction, icon  1777  is clicked or touched to “activate” rectangle  1772 , template  1774  and/or movement control icon  1776  to enable movement thereof by the user. Additional information is provided to the user by fields  1778  such as “Size 54 mm”, “Type Standard”, and “Offset  0 ” as illustrated. Markers  1780  and  1782  have been placed in images  1702 ′″ and  1722 ″, respectively, to designate the location of tear drop TD in each image. In some constructions, the system may automatically generate markers  1780  and  1782  because the teardrop TD has already been identified, for example in a situation when the teardrop is used to create a stationary base and can be readily identified. 
     In step  1908 ,  FIG. 68B , the system positions the acetabular cup template in identical position, relative to the pelvis, in the preoperative image as compared to the placement on the intraoperative image described above. This is illustrated in  FIG. 64  using known teardrop locations in the pre- and intra-operative images. 
       FIG. 64  is a schematic screen view  1790  similar to  FIG. 63  but with the acetabular template  1774 ′, with a central point  1775 ′, now re-positioned on top of the femoral head in the preoperative view  1792 . The acetabular template positioning in the preoperative image, as shown in this figure, is auto-generated by the system using intraoperative image data gathered from the placement of the acetabular template in the intraoperative image. Specifically, the system calculates the x and y distances from the teardrop to the acetabular prosthesis in the intraoperative image display, and auto-generates the acetabular template position in the preoperative image by maintaining the distance from the teardrop to the acetabular template in the preoperative image. The system also maintains the abduction angle obtained by maintaining the acetabular template abduction angle that was analysed in the intraoperative image. This process ensures that the acetabular template is placed in the preoperative image in a position, relative to the pelvis, that precisely matches the acetabular component position in the intraoperative image. The method effectively transforms the templating exercise from one of preoperative estimation and planning to one of precision-guided intraoperative analysis. The acetabular component placement is facilitated by the scaling and alignment of the preoperative and intraoperative images described above. 
     In alternative constructions, a physical device, sensors, calliper measurement of directly observable anatomical landmarks, or some other form of mechanical and electrical hardware may be used to create image scaling as a substitute for scaling based on the acetabular component. One example of an alternative construction (although not as precise) would be to measure the extracted femoral head using callipers, and then to scale the image by marking the femoral head in the preoperative image. In this method, absolute scaling is initially created in the preoperative image, and then propagated to the intraoperative image by scaling and aligning consistent stationary bases. 
     The process continues with step  1909 ,  FIG. 68B , by Intraoperative Templating Module  1862 , with the system or user positioning a femoral stem template directly on top of the femoral stem in the intraoperative image. As with the acetabular component template process described above, this step is used to determine intraoperative data that will be used later in the method.  FIG. 65  is a schematic screen view  1800  similar to  FIG. 64 , demonstrating positioning of the femoral stem template in the intraoperative image. The figure shows the acetabular component outline  1774 ′ overlaid on the femoral head on the left-hand, preoperative image  1801 . The user selects the femoral stem template used in surgery, identified for this implant  1732  as “Depuy Corail AMT Size: Size 9, Offset: COXA VARA, Head: 5”, and the system renders the template for this model on the screen. The user or system overlays the template image  1804 , within rectangle  1802  with a movement control icon  1806 , of the prosthesis  1732 , directly on top of the observed femoral component in the intra-operative image  1803 . Initial calculations of Offset Changes and Leg Length Changes are not yet relevant, but are displayed in one corner of screen  1800  by indicia  1812  including “Offset Changes: −272.0 mm”, and “Leg Length Changes: −12.7 mm”, along with “Abduction Angle: 45.0”. Control icon  1808  for the acetabular cup and an icon  1810  for the femoral stem template  1802  and  1804  are provided in another portion of screen view  1800 . 
     Note dashed  1820  extending from the neck of the implant  1732  over the greater trochanter, and a parallel dashed line  1822  which touches the shoulder of implant  1732 . (The user identified the shoulder of the femoral prosthesis  1732 , also referred to as the superolateral border of the femoral prosthesis, in the intraoperative image illustrated in  FIG. 62  above.) The system draws both lines  1820  and  1822  perpendicular to the femoral axis and is guided by user positioning of markers that identify the greater trochanter and shoulder implant. 
     In step  1910 ,  FIG. 68B , the system identifies the distance between the shoulder of the implant and the greater trochanter along the femoral axis line, as shown in  FIG. 65 . In one construction, this process is supported by dashed reference lines  1820  and  1822  which are generated to be perpendicular to femoral axis line  1752 , identified earlier in the process and displayed in  FIG. 66 . The calculated distance between lines  1820  and  1822 , along the femoral stem axis, is intraoperative data that will be applied to the placement of the femoral stem template in the preoperative image. 
     In step  1912 , the system takes the calculated distance described above and generates a line in the preoperative image that is perpendicular to the femoral axis line and is the same distance away from the greater trochanter, as shown in  FIG. 66 . For step  1914 , the system places the femoral stem template in the preoperative image, using the line generated in step  1912 . 
       FIG. 66  is a schematic screen view  1830  similar to  FIG. 65  showing the femoral stem template  1804 ′, within a rectangle  1802 ′, placed on the pre-operative image  1801 ′ superimposed and aligned with the femur F R . The system automatically repositions the femoral stem template  1804 ′ in preoperative image  1801 ′ by using intraoperative data gathered from the placement of the same template in the intraoperative image. Specifically, the system draws guidance lines and determines the implant position on the femur in the preoperative image through the following steps:
         The system draws dashed line  1832  through the greater trochanter point (as previously identified by a marker) and perpendicular to the femoral axis in the preoperative image (which may be different than the intraoperative femoral axis).   The system takes the calculated distance, along the femoral axis, between the greater trochanter and the shoulder of the implant from the intraoperative image. The system generates dashed line  1834  in the preoperative image below the greater trochanter line  1832 , and perpendicular to the femoral axis, based on the distance calculated in the intraoperative image.   Line  1834  is generated as a visual guide for the user or system to position the femoral stem template by placing the shoulder of the femoral stem template on this line.   The system calculates the difference between the greater trochanter and the shoulder of the prosthesis in the intraoperative image along the femoral axis and perpendicular to the femoral axis. The system then generates the location of the femoral stem template in the preoperative image by replicating the distance relative to the greater trochanter and placing the shoulder of the prosthetic at that location.   Additionally, the femoral stem is automatically rotated so that it maintains consistent angle relative to the femoral axis in both images. For example, if the femoral axis is 15 degrees in the intraoperative image and 10 degrees in the preoperative image, the system will automatically rotate the femoral stem template by 5 degrees when it moves it to the preoperative image. Finally, the femoral stem template may be adjusted, either by the user or automatically by the system, to match the location of the femoral canal (i.e. movement of the femoral stem template perpendicular to the femoral axis).   Having combined intraoperative data with preoperative imaging, the system now precisely calculates, in step  1916  and Differential Analysis Module  1864 , the offset and leg length differences based on the positioning of the femoral stem and acetabular cup templates in the preoperative image.   Finally, the user can now modify, in step  1918 , implant template selections in the system to perform “what if analysis” and to proactively analyze how intraoperative implant changes will affect offset and leg length calculations, allowing intraoperative changes and decision making to be based on calculations made even before inserting a different implant during surgery. The system or user will then place the new implant selection using dashed line  1834  and other guidelines, and will automatically calculate anticipated offset and leg length changes by combining the template technique with the intraoperative data being used.       

     The Offset and Leg Length change calculations are displayed in one corner of screen  1830  by indicia  1812 ′ including “Abduction Angle: 45.0”, “Offset Changes: 4.2 mm”, and “Leg Length Changes: −0.2 mm”. Also identified is “Pinnacle Acetabular Cup Size: 54 mm” and “Depuy Corail AMT Size: Size 9, Offset: COXA VARA, Head: 5” for implant  1732  in this example. Control icon  1808 ′ for the acetabular cup and an icon  1810 ′ for the femoral stem template  1802 ′ and  1804 ′ are provided in another portion of screen view  1830 . In one construction, dashed reference lines  1832  and  1834  are generated to be perpendicular to femoral axis line  1706 ′. 
     In some constructions, the system will begin with the JointPoint Anterior process and finish with the Reverse Templating system. Most of the data required to do Reverse Templating can be carried over from JointPoint Anterior by the system so that very few steps are required by the system to process the Reverse Templating technique. 
       FIG. 70  is an overlay image  2000  of a preoperative hip image  2001  and an intraoperative hip image  2003  having a trial implant  2002  in a hip with the acetabular component  2004  transacted by stationary base lines  2006  and  2007  extending between a first point  2008  on the obturator foramen OF and a second point  2010  on the anterior inferior iliac spine AIIS of the ileum. Also shown are two error analysis triangles  2020  (solid lines) and  2030  (dashed lines). Circles  2022  and  2032  in this construction represent a landmark point on the greater trochanter in images  2001  and  2003 , respectively. Image  2000  is a representation of preoperative and intraoperative hip images  2001  and  2003  overlaid according to stationary base lines  2006  and  2007 , respectively. Three identical pelvic points  2024 ,  2026 ,  2028  and  2034 ,  2036 ,  2038  in images  2001  and  2003 , respectively, have been identified, with the system  200 ,  FIGS. 4C-4F , generating triangles  2020  and  2030  for each image as represented by  FIG. 70 . The triangles  2020  and  2030  can be visually compared to analyze the error in the anatomic area containing the stationary bases which, in this case, is the pelvis. 
     A numerical confidence score or other normalized numeric error analysis value may also be calculated and displayed in the system by calculating the distance between points, comparing them to the length of the triangle vectors, and then normalizing the data, possibly using a log or other such nonlinear algorithm. The visual display and/or numerical confidence score provides efficacy analysis in the construction. In other words, error analysis and correction is provided in some constructions for at least one image, such as providing a confidence score or other normalized numeric error analysis, and/or a visual representation of at least one error value or error factor, such as relative alignment of one or more geometric shapes, e.g. triangles, or symbols in two or more images. 
     In some constructions of the various alternative systems and techniques according to the present invention, visual and/or audible user instructions are sequentially generated by the system to guide the user such as “Draw line along Pubic Symphysis”. Guidance for surgery utilizing other types of implants, and for other surgical procedures, including partial or total knee or shoulder replacements and foot surgery as well as wrist surgery, will occur to those skilled in the art after reading this disclosure. Also, other types of medical imaging using energy other than visible light, such as ultrasound, may be utilized according to the present invention instead of actual X-rays. Moreover, if a computer interface tool, such as a stylus or light pen, is provided to the user in a sterile condition, then the user can remain within a sterile field of surgery while operating a computing device programmed according to the present invention. 
     Hip- and femur-related constructions of the present system and method will calculate intraoperative changes in offset and leg length, for a selected implant having at least one center of rotation, using a preop and intraop image. To accomplish this, the system requires two consistently scaled images, the generation of at least one stationary point on the stationary anatomic region (such as the pelvis) in both images, and identification of the center of rotation of the prosthetic in the intraop image. The center of rotation in the intraop image can be most simply identified by overlaying an acetabular template, or other digital annotation, that is used to identify the center of rotation. 
     The system and method may make use of additional steps, including identification of the femoral implant using a digital template or other digital annotation, including generation of at least one landmark point on the non-stationary anatomic region (such as the femur) in both images, to generate data about how changing the inserted implant, that is, replacing or modifying the implant in at least one dimension, will affect offset and leg length. This additional data enables a surgeon to understand how changing an implant intraoperatively would affect offset and leg length prior to actually changing the implant. 
     As described in more detail below in relation to  FIGS. 71A-78 , a landmark based Reverse Templating process according to the present invention begins by acquiring (i) at least one of a preoperative ipsilateral or an inverted contralateral image (“preop image”), and (ii) an intraoperative image. The images are scaled and aligned using one of a plurality of techniques and then visually displayed, preferably side by side. The system generates at least one stationary point on the stationary anatomic region in both images (such as identification of the teardrop point on the pelvis in both images), possibly with user guidance in certain constructions. 
     On the intraoperative image, the system generates a digital representation such as a digital template or other digital annotation, such as a digital line having at least two points, e.g. a line representing a longitudinal axis or a diameter of an implant or a bone, or a digital circle, which identifies the actual acetabular component placement and a corresponding center of rotation for that component. Additionally, the system optionally, but preferably, generates a digital template or other representative digital annotation that identifies the actual femoral stem component placement in the intraop image. 
     The femoral stem and acetabular component templates, or representative annotations, generated on the intraoperative image are connected at the center of rotation, replicating the actual positioning of the femoral stem and acetabular components. The system may optionally generate at least one landmark point on the femoral anatomy, consistently identified in both images (such as a point on the greater trochanter). In one construction, the system may use this landmark point to calculate estimated changes to offset and leg length for possible replacement prosthetics if a surgeon were to change femoral stem implant selection. The landmark point may also be used to position (i) a femoral component image, (ii) an “intraop overlay image” including intraop images of at least a portion of the intraop prosthesis and at least a portion of the bone of the patient in which the prosthesis is implanted, as described below in relation to  FIG. 74 , (iii) a femoral template (that is, a digital template of at least the intraop femoral stem, which may also include a digital template of the acetabular cup) or (iv) surrogate digital annotation in the preop image. 
     In one construction, the system calculates the vector in the intraoperative image between the stationary pelvic tear drop point as an “origin” and cup location, as determined by the center of rotation of the acetabular component or representative template, as a terminal point. The term “vector” is utilised herein with the standard meaning of a Euclidean vector having an initial point or “origin” and a terminal point, representing magnitude and direction between the origin and the terminal point. The system then positions an acetabular component template or representative digital annotation, such as a digital line or digital circle, in the preop image by replicating this vector. 
     Some systems and methods according to the present invention can generate a femoral stem template or representative digital annotation in the preop image using information from the generated annotations and templates on the intraop image. In one construction, the system accomplishes this without generating a femoral component template or representative annotation in the intraop image. Instead, the system calculates the vector between the generated landmark point on the femoral anatomy (preferably the greater trochanter) and the center of rotation of the acetabular component template. The system may also analyse positional differences between the preop and intraop femur, relative to the stationary pelvis, and rotate the vector to account for any difference. 
     In  FIG. 62 , femoral axis lines  1761  and  1706  show a representation of how the system or user may identify femoral position. The system can calculate the angle difference between these lines and use this information to transform the vector, referred to herein as a “transformed vector”. The system then places the femoral component template or representative annotation thereof in the preop image by replicating the calculated or transformed vector between the center of rotation and the femoral landmark point in the preop image. In some constructions, the calculated or transformed vector is also rotated if the femur is in different orientations in the preop and intraop images. 
     Preferred system constructions according to the present invention will generate a femoral component template or digital annotation that identifies the femoral stem placement in the intraop image. The system can position the femoral component image, template or representative digital annotation in the preop image by using at least one of a plurality of techniques, such as: (1) calculating the vector between an identified femoral landmark point and a digital femoral template or representative digital annotation thereof in the intraop image, rotating it to account for any differences in femoral positioning between the preop and intraop images, and then positioning the digital femoral template or representative digital annotation according to the transformed vector; and/or (2) overlaying an image of the actual intraop prosthetic femoral stem, preferably with the intraoperative femur image (the intraop femoral stem and femur also referred to as an “intraop overlay image”), directly on top of the preop femur, to replicate in the preop image the actual intraoperative position of the femoral template in the intraop image. The latter may be accomplished by automated system techniques such as image recognition, user placement of the images, or a combination of both. 
     Using actual intraoperative data to create a template on a preoperative image enables a precise intraoperative calculation of offset and leg length that is vastly more accurate than the traditional ‘estimation’ of these parameters previously achieved using standard preoperative templating techniques. 
     Finally, the system may optionally generate a chart that estimates anticipated changes in leg length and offset, such as chart  2520 ,  FIG. 76 , if the surgeon were to replace or otherwise modify the femoral stem prosthetic intraoperatively. As an alternative to a generated chart, the system may generate a recommended femoral stem change based on a user inputting the surgeon&#39;s desired offset and leg length parameters. If the surgeon wants to lengthen the leg by 7 millimeters and not change offset, for example, the system will calculate leg length and offset for all femoral stem options contained in the system, and would present the femoral stem selection to the user that would come closest to accomplishing this. The system generates the results for this chart or recommendation by generating a vector between at least one identifiable point on the femoral anatomy, such as the greater trochanter point identified previously, and an assumed stationary point on the femoral template, such as the femoral stem shoulder, for example as described below in relation to stem shoulder point  2435 ,  FIG. 76 . The data calculated in the chart assumes that if the surgeon implants a different femoral stem, the position of the identified point on the femoral template will not change. The stem shoulder is an ideal point for such an approximation. 
     In one construction, the process begins in the flowchart RT in  FIG. 71A  by acquiring, step  2200 , either a selected preoperative ipsilateral image, or a selected inverted contralateral image. Whichever image is selected is referred to herein as a “first, reference image” or “preop image”. The process continues with acquisition of the intraop hip image, step  2201 . Image acquisition in steps  2201  and  2202  is performed by the Image Capture module  2300 , also referred to as an Image Selection Module, of reverse templating system  2290 ,  FIG. 72 . Acquisition of these images can be performed in a variety of ways, such as a direct connection to a c-arm fluoroscopy unit, image acquisition by taking a picture of a radiographic image, file upload, or other similar techniques. If an inverted contralateral image is used as a ‘preop’ image, the contralateral image may be acquired and then inverted within the software, or otherwise it may be flipped in another system and then input to image capture module  2300 . 
     In step  2202 ,  FIG. 71A , the system determines whether the preop and intraop images have been pre-scaled and aligned according to pelvic anatomy. Consistent scaling and alignment may be previously performed in this construction using a variety of approaches. For example, a software system residing on a digital fluoroscopy system may have been used to align and scale the images prior to image acquisition by this system. Alternatively, the images may already be scaled and aligned because the surgeon took images with the patient and radiographic system in identical position. 
     If the images have not been either scaled or aligned, the system can scale, or align, or scale and align the images in step  2203 . Consistent scale and alignment in this step are accomplished by the optional Image Scaling and Alignment Module  2301 ,  FIG. 72 , shown in dashed lines, which may accomplish these operations in various ways. One method is to use stationary bases (i.e. pelvic reference lines), along with identification and scaling of the acetabular cup in the intraop image, as described in the earlier construction of Reverse Templating and visually illustrated in  FIG. 15 , for example. An alternative approach is to guide the user in overlaying preop and intraop images, with transparency such as described below in relation to  FIG. 74 , so that the user can scale and align the images manually. In common alternative constructions, the input to the system may already have applied consistent alignment or scale to the images, but not both. For example, the absolute scaling of both the preop and intraop images may be determined using known magnification of an imaging system or independent scaling using software, but the images may not be aligned. The system may make use of image recognition to auto-align images, or else provide functionality, such as the use of stationary bases described above, that guides the user or system to align and/or scale the preop and intraop images. 
     The method continues in step  2204  with Landmark Identification Module  2302 ,  FIG. 72 , identifying at least one “stationary” point on the pelvis in both the preop and intraop images. In a preferred construction, a point in each image will be placed on the pelvic teardrop, a particularly useful pelvic reference point because it is easily identifiable and near the implanted acetabular cup, which helps to reduce the propagation of any scaling error within the system. In various constructions, the user is either prompted to identify the point on the teardrop, or otherwise the system auto-identifies the point location using image recognition or other technology and then allows the user to modify the point placement. 
     In step  2205 ,  FIG. 71A , the templating Module  2303 ,  FIG. 72 , identifies the center of rotation by identifying the acetabular cup in the intraop image using a digital template or alternative digital annotation. This can be implemented in a variety of ways. In a preferred approach, the system auto-recognizes the acetabular cup in the intraop image and places a digital template directly on top of it, with the user able to adjust the placement of the template. The digital template may be selected based on the known size of the inserted cup. Alternative constructions may instead make use of digital annotations to identify the center of rotation. The digital circle annotation  392  in  FIG. 12  represents how a digital circle may be positioned by the user or system to encircle the acetabular component, with the midpoint of this circle identifying the center of rotation. 
     Alternative constructions may similarly make use of a semicircle or digital line, such as line  530  in  FIG. 22 , which can be drawn by the system or user to identify the base of the acetabular cup. In this construction, the center of rotation corresponds to the midpoint of the digital line. As an alternative to auto-identification of the cup, the system may simply direct the user to place the template or surrogate annotation directly on top of the acetabular implant. Placement of a template or alternative digital annotation in this manner enables the system to generate the vector between the acetabular cup and the pelvic reference point (e.g. teardrop  2470 ,  FIG. 73 ) identified in step  2204 . 
     In step  2206 , Templating Module  2303 ,  FIG. 72 , identifies the location of the prosthetic femoral stem in the intraop image using a digital template or representative annotation. In a preferred implementation, the user will select the known manufacturer, model, and size of the femoral implant, and will then position the template directly over the actual implant in the intraop image. Some implementations of the system may also auto-recognize the femoral stem and attempt to auto-position the template. In a preferred construction, the femoral and acetabular templates will be locked together along their center of rotation, so that offset and leg length readouts on the intraop image are both set to 0.0 mm, matching known data about interlocking femoral and acetabular implants. 
     In Step  2207 , the Landmark Identification Module  2302 ,  FIG. 72 , is used to identify at least one consistent femoral landmark point in both the preop and intraop images. In a preferred construction, a single identifiable point will reside on the greater trochanter, such as landmark points  2417  and  2472  in  FIG. 73 . 
       FIG. 73  is a schematic screen view  2400  of a preoperative image  2410  on the left, with a pelvis  2412 , obturator foramen  2414  and a femur  2416 , and an intraoperative image  2420  on the right with a digital template  2422 , also referred to as a femoral template  2422 , superimposed on an actual “trial implant” prosthesis  2424  inserted within the femur  2417 , which is the same bone as femur  2416 , left-hand preop image  2410 , after the femoral head has been removed intraoperatively. Stationary tear drop point  2415 , identified in step  2204 , is marked above obturator foramen  2414  in the preop image  2410  and stationary tear drop point  2470 , also identified in step  2204 , is marked above obturator foramen  2425  in the intraop image  2420 . Landmark point  2417 , identified in step  2207 , is placed on the greater trochanter of femur  2416 , image  2410 , and landmark point  2472 , also identified in step  2207 , is placed on the greater trochanter of femur  2427 , image  2420 . Digital template  2422  lies within a frame  2426  moveable by a user via movement control icon  2428  in one construction, and includes a digital acetabular cup template  2430  placed over an acetabular component  2431  and a femoral stem template  2432  positioned over a femoral component  2433 , connected at a center of rotation  2434 . Acetabular cup template  2430  was positioned on acetabular component  2431  in step  2205 , and femoral stem template  2432  was positioned over femoral component  2433  in step  2206 . 
     Acetabular cup control icon  2440  permits a user to activate the digital cup  2430 , if desired, so that the user may improve its alignment with the actual implant in the image. Control icon  2442  indicates that digital box  2426  containing the femoral template  2422  is activated and responsive to user manipulation. Selecting the “x” within the activated control icon  2442  will delete the femoral template  2422 . Details window  2450  is expanded to show selected parameters such as Abduction Angle, Leg Length Changes, and Offset Changes for the specified trial implant. Compare Stems window  2452  is closed in this view. 
     In Step  2208 ,  FIG. 71B , the Analysis Module  2304 ,  FIG. 72 , calculates the vector between the acetabular template, or other surrogate annotation, and the pelvic point (e.g. teardrop) in the intraop image. The Templating Module  2303  uses this information to generate placement of the acetabular cup template in the preop image by replicating the intraop vector in the preop image. This process ensures that the vector between the teardrop (or other pelvic points) and the acetabular cup is consistent in both the preop and intraop images. Effectively, this process uses intraoperative placement data to precisely position the acetabular template in the preop image. In one construction, Templating Module  2303  overlays a femoral template on femoral implant image  2424   i ,  FIG. 74 . Like the earlier construction of Reverse Templating, the general process is using intraoperative data to place templates on a preoperative image, transforming an estimation process to one that precisely analyzes intraoperative offset and leg length data. 
     In Step  2209 ,  FIG. 71B , the Analysis Module  2304 ,  FIG. 72 , takes the femoral template (or representative digital annotation) from the intraop image and propagates its position, relative to femoral anatomy, to the preop image. In this particular construction, a ‘cutout’ (exact copy) of the femur from the intraop image is moved to the preop image and overlaid digitally as an intraop overlay image. The system does this by connecting the preop image and the intraop ‘cutout’ of the femur using the femoral landmark identified on the greater trochanter. The system provides the user with the ability to rotate the femoral overlay image around the greater trochanter point. This enables the system to precisely align the preop and intraop femurs, even when they are positioned differently relative to the pelvic anatomy. 
     Various implementations may provide different functionality to position the intraop image of the femur on top of the preop image. For example, the system may auto-identify points on the femoral anatomy in each image and attempt to overlay femoral anatomy automatically in the preop image. 
     Once the intraop image has been positioned, the system generates the femoral template, positioned on the intraop image in step  2206 , so that its position relative to the intraop cutout is consistent with how the template was positioned relative to the intraop image. The system then removes the intraop ‘cutout’ and leaves the generated template on the preop image. 
     One construction of the system also provides ‘+’ and ‘−’ buttons, such as buttons  2464  and  2466 ,  FIG. 74 , that allow the user to manipulate the size of the intraop overlay image, so that it can precisely match the preop femur. Use of this scaling functionality is generally not required because the images have already been scaled consistently, but the technique preferably accounts for any alignment and scaling differences between the preop and intraop femurs relative to the pelvis. Alignment differences in particular may exist between the preop and intraop image, because the system has aligned the images according to the pelvis but the femoral axis in each image may change. Addressing any differences in this step ensures that offset and leg length are calculated correctly. 
       FIG. 74  shows the described construction that implements step  2209 . A screen view  2400   a  of images of the intraoperative actual trial implant  2424  and femur  2427  of  FIG. 73  superimposed in  FIG. 74  as an “intraop overlay image” on the preoperative image  2410  of FIG.  73  to form a combined image  2410   a  in  FIG. 74 . The intraop overlay image, with femoral prosthesis image  2424   i  including cup  2431   i  and femoral stem component  2433   i , and femur image  2427   i , lies within a frame  2460  controlled by movement control icon  2462 . Although center of rotation  2434   i  is illustrated in  FIG. 74 , it is not needed at this stage in the procedure. Plus symbol  2464  and minus symbol  2466  enable a user to increase or decrease magnification, allowing the user to manipulate the size of the intraop overlay image, so that it can be made to precisely overlay and align with the preop femur  2416 , even when there are scaling inconsistencies between the preop and intraop images. Image  2410   a  includes the stationary pelvic tear point  2415  above obturator foramen  2414  and a landmark point  2472   i  on the greater trochanter of intraop femur  2427   i , which matches landmark point  2417  of femur  2416 . 
     Screen  2400   a  includes acetabular cup control icon  2440   a  and femoral template control icon  2442   a  plus an overlay control icon  2480 . The control icon  2480  indicates that the intraop overlay image is activated on top of the preop image. Selecting the “x” in overlay control icon  2480  enables the user to stop and re-initiate the overlay process. Selecting control icon  24440   a  or  2442   a  enables the user to return to the previous steps of positioning the acetabular cup template or femoral template on the intraop image. Windows  2450   a  and  2452   a  are shown in a “collapsed” or closed condition. A transparency adjustment control  2500  includes a button  2502  movable by a user between contrast positions  2504  (lighter) and  2506  (darker) to lighten or darken the intraop overlay image within frame  2460 . 
     Once the femoral template and acetabular template, or equivalent digital annotations, have been placed on the preop image such shown in  FIGS. 75 and 76 , the system continues to step  2210  in which Analysis Module  2304 ,  FIG. 72 , calculates offset and leg length changes using the digital templates in the preop image. To do this, the system analyses the difference between the acetabular cup template center of rotation and the femoral stem template center of rotation. Leg length is calculated as the distance between these points along the axis of the femur, which is identifiable by the straight line running through the center of the femoral template. Offset is calculated as the distance between these points along the axis perpendicular to the femur. The use of intraoperative data to guide template placement in the preoperative image enables offset and leg length calculations that are vastly more accurate than the traditional preoperative ‘estimation’ of these parameters. 
       FIG. 75  is a screen view  2400   b  of the intraoperative digital template  2422  superimposed on the preoperative image  2410   b  on the left and the same digital template  2422  and actual trial implant  2424  on the right in the intraop image  2420   b .  FIG. 76  shows screen view  2400   c , which is the screen view  2400   b  of  FIG. 75  with both “Details” and “Compare Stems” windows expanded in  FIG. 76 . 
     Also shown in both  FIGS. 75 and 76  is the center of rotation  2434   ii  of acetabular cup template  2430   ii  on the left, PreOp images  2410   b ,  2410   c , and superimposed cup center of rotation  2434  on the right, PostOp images  2420   b ,  2420   c . Femoral stem center of rotation  2435   ii  of femoral template  2432   ii  is shown in the left, preop images  2410   b  and  2410   c  as slightly mis-aligned or offset from the cup center of rotation  2434   ii ; of course, the actual femoral stem center of rotation is the same as the cup center of rotation  2434  in intraop images  2420   b  and  2420   c . A femoral stem shoulder point  2510  is shown in preop images  2410   b ,  2410   c  with a shoulder line  2512 . 
     Finally, in Step  2211 ,  FIG. 71B , the Analysis Module  2304 ,  FIG. 72 , generates a chart or other user-perceptible information that estimates how leg length and offset will change if the surgeon changes the currently inserted femoral stem. For example, image  2400   c ,  FIG. 76 , shows a chart  2520  with selected parameters for the current, actual implant  2424  highlighted as the third entry “5.8 mm, 0.8 mm” in the left, “Standard Collared” column, indicating that current Standard Collared implant  2424  adds 5.8 mm to the patient&#39;s natural, preop leg length and an offset of 0.8 mm. Estimated offset and leg length calculations are calculated for alternative femoral stem implants using known intraoperative data, and displayed in chart  2520 . 
     One or more of modules  2300 ,  2302 ,  2303  and  2304  of  FIG. 72  can be combined in certain constructions, such as indicated by dashed line  2306  showing a combined operation module for Templating Module  2303  and Analysis Module  2304 . Also illustrated in phantom is a Display  2308 . Other modules and components shown and described elsewhere in this application can also be combined or rearranged with this system  2290  or other illustrated systems as will be readily apparent, after reviewing this application, to those of ordinary skill in coding and programming. For example, module  2306  can include system  2616 ,  FIG. 78 . 
     The process of calculating offset and leg length of alternative implants using known intraoperative data, but prior to their insertion, is a unique system and method according to the present invention, such as described by flowchart RTC,  FIG. 77 , which is implemented by system  2616 ,  FIG. 78 . The method begins in step  2600  with identification of an implant “fixed” point on the femoral stem template that is assumed to remain fixed (i.e. reproducible, repeatedly re-locatable, and/or shared in common) if an alternative prosthetic were to be inserted. Shoulder point  2510  in  FIG. 76  illustrates the identification of a suitable implant fixed point in this construction. 
     To implement step  2600 ,  FIG. 77 , Database Retrieval Module  2622 ,  FIG. 78 , retrieves the coordinate of the fixed point relative to the template, and Calculation Module  2620  calculates its position relative to the preoperative image based on the placement of the femoral stem template. In one construction, initial input to Calculation Module  2620  is received from Image Scaling and Alignment Module  2301 , Landmark Identification Module  2302 , and Templating Module  2303 ,  FIG. 72 , so that the images and digital implant representations are at least scaled relative to each other; image alignment is not necessary for the process illustrated by Flowchart RTC. 
     In step  2602 ,  FIG. 77 , Calculation Module  2620 ,  FIG. 78 , calculates the vector between the identified fixed point on the femoral template and the previously identified greater trochanter femoral landmark in the preop image, such as by using shoulder point  2510 , shoulder line  2512  and greater trochanter point  2417  illustrated in preop images  2410   b ,  2410   c  in  FIGS. 75, 76 . 
     In Step  2604 , Database Retrieval Module  2622  retrieves the alternative femoral stem templates from the database along with the fixed-point coordinates, which in this construction will be the equivalent fixed shoulder point in each template. The database may be located on either a server, the local device on which the software runs, or both. 
     The process continues in step  2606  with the Calculation Module  2620  replicating, for each alternative femoral stem template, the calculated vector for the existing template between the shoulder point on the femoral template and greater trochanter landmark. 
     In step  2208 , Templating Module  2624  uses the data calculated in step  2606  to simulate the position for each alternative femoral stem template. The simulated position for each alternative implant template, also referred to herein as a virtual alternative template position, assumes that the fixed point location for each alternative femoral stem template does not change relative to the greater trochanter, and also assumes that the angle of each alternative prosthetic, relative to the femur, will not change. 
     In step  2210 , Analysis Module  2626  uses the simulated positioning of each alternative femoral stem template to generate offset and leg length data for each alternative template. It generates this data by analysing the vector between the acetabular template center of rotation and each alternative femoral stem center of rotation. 
     Finally, in step  2212 , Output Module  2628  generates the chart or other user-perceptible information, as shown in chart  2520 ,  FIG. 76 , that estimates how leg length and offset will change if the surgeon changes the currently inserted femoral stem. In an alternative construction, the system may provide a recommended femoral stem change based on the surgeon&#39;s desired offset and leg length parameters instead of a general chart, effectively “dialling in” a “best fit” recommendation for the desired change, thereby enabling the surgeon to optimize implant selection. 
     Although specific features of the present invention are shown in some drawings and not in others, this is for convenience only, as each feature may be combined with any or all of the other features in accordance with the invention. While there have been shown, described, and pointed out fundamental novel features of the invention as applied to one or more preferred embodiments thereof, it will be understood that various omissions, substitutions, and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the invention. For example, it is expressly intended that all combinations of those elements and/or steps that perform substantially the same function, in substantially the same way, to achieve the same results be within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. 
     It is also to be understood that the drawings are not necessarily drawn to scale, but that they are merely conceptual in nature. Other embodiments will occur to those skilled in the art and are within the scope of the present disclosure.