System and procedure for planning a surgical intervention

Abstract

System for evaluating the fit of a femoral implant (118A, 188B) to a distal end of a femur (32) in a selected orientation before the femur (32) is resected, the system comprising the following elements: - Means of obtaining predefined form factor information for a variety of femoral implants (118A, 188B); - Means of obtaining information about the shape of the surface of the distal end of the femur (32); - Means for automatically performing a virtual fit assessment of each possible incremental position of a predefined set of incremental positions for each size of an implant to be considered (118A, 188B) before the femur (32) is resected; and - Means for selecting an optimal size and position of an implant (118A, 188B) from the virtual fit assessments, characterized in that the means for selection - Means for calculating a maximum lateral runout of an anterior resection of the femur (32) from an outline (220) of a proximal end of the femoral implant, and / or - Means to calculate a percentage of the outline (220) of the proximal end lying on sectioned anterior cortical bone, and / or - Means of calculating a percentage of the outline (220) of the proximal end that lies on or above uncut anterior cortical bone, and / or - Contains means for calculating a maximum gap between the femoral implant and the uncut anterior cortical bone.

Description

Field of invention

[0001] The present disclosure relates generally to a system and a method for planning a surgical procedure, such as selecting a size and position for an orthopedic prosthetic implant. background

[0002] Computer-assisted surgical systems for orthopedic and / or arthroplasty operations are useful for both planning and performing various operations.

[0003] EP 1 426 023 A1 relates to a method for determining implantation parameters for an orthopedic implant. In this method, bone data of the bone to be treated is calculated based on image data of an implantation site. Furthermore, the method includes a biomechanical analysis of a system consisting of the bone to be treated and the implant. In the biomechanical analysis, physical system parameters are calculated and then compared with stored reference values. This comparison allows for an evaluation of the calculated system. The system data are then available as implantation parameters for further processing.

[0004] Another known system and method are described in US patent application no. 11 / 290,039, filed on November 30, 2005, and published as US patent application no. US 2007 / 0 179 626 A1. Another known system and method are described in US patent application no. 10 / 961,455, filed on October 8, 2004, and published as US patent application no. US 2006 / 0 095 047 A1.

[0005] As schematically in Fig. As shown in Figure 1, the surgical procedure of a total knee arthroplasty involves removing affected portions of the distal end of a femur 10, including the lateral condyle 12 and the medial condyle 14, as well as the opposite proximal end of the tibia 16, and replacing the removed bone segments with prostheses comprising a femoral implant 18 for attachment to the femur and a tibial implant 20, which has a base plate 22 for attachment to the tibia and an articular surface 24. To achieve this, a surgeon resects the condyles at the distal end of the femur so that they have a shape (shown with dashed lines) that is complementary to an inner surface 26 of the femoral implant 18 to accommodate the femoral implant.The surgeon also resects the proximal end of the opposite tibia 16 in a shape (dashed lines indicate hidden edges) that accommodates the complementary baseplate 22. The femoral implant 18 and baseplate 22 are attached to the respective bones 10 and 16, for example, using adhesives or fixatives, and the articular surface 24 is attached to the baseplate facing the femoral implant. After the patella (not shown for clarity) and soft tissue, including tendons and muscles (not shown for clarity), have been correctly repositioned around the knee, the femoral implant 18 is able to flex on the articular surface 24 in a manner similar to natural knee movement.

[0006] A navigation system can be used to collect data during total knee replacement surgery to create an image (or "map") of relevant sections of the patient, such as the femur (10), femoral condyles (12 and 14), tibia (16) and tibial plateau, fibula, and patella, which can then be displayed on a screen, such as a video or computer monitor. One possible imaging system might use a navigation system as disclosed in published patent application US 2001 / 0 034 530 A1, in combination with a tracking device as disclosed in published US patent application US 2005 / 0 199 250 A1, published on September 15, 2005. In other possible systems, the imaging data could be obtained using other known preoperative and / or intraoperative techniques.Using the image, a surgeon can then virtually plan the remaining steps of the procedure, including selecting a specific size and / or shape of replacement prosthesis, and then virtually arrange resections to achieve the desired final fit and position of the prosthesis on the remaining bone. This step can be performed using a database of known prosthesis shapes and / or sizes, which are then compared with the acquired imaging data and displayed side-by-side and / or superimposed on the monitor. Once the operation has been fully planned using the imaging and prosthesis form factor data, the navigation system can be used to guide and monitor the physical steps of the operation, such as performing the various resections, so that the surgeon can proceed with the operation as planned.In other procedures, the steps for carrying out the operational plan can be performed without the aid of a virtual navigation system using other known layout techniques.

[0007] The steps of selecting a specific prosthesis and choosing a preferred arrangement of the prosthesis on the existing bone have, until now, depended entirely or largely on the skill and experience of the person planning the operation, such as the surgeon. For example, in a process of visual selection and matching the prosthesis, the surgeon had to choose a specific size based on their experience in a virtual comparison with an image of the bone, after receiving the image of the relevant bones. Then, after indicating to the computer which prosthesis would be used, the surgeon had to adjust the position of the prosthesis relative to the shape of the corresponding bone (as virtually superimposed on the display screen) by trial and error until a desired position was selected.The surgeon then had to instruct the computer to record the chosen position relative to the image and use this information to guide the remaining steps of the operation. Other techniques can simply select a prosthesis size and position based on a single parameter, such as minimizing or eliminating steps or notches in a resected bone surface that can create local stress concentration points where premature failure is more likely to occur.

[0008] The process of visually selecting and fitting the prosthesis can lead to certain difficulties. One difficulty—selecting the correct prosthesis size—is due to the surgeon's ability to choose the right size solely based on imaging information of the bones. Another difficulty—positioning the prosthesis in the best orientation relative to the bone—is due to both the size of the prosthesis selected by the surgeon and the surgeon's ability to visualize the optimal positioning.One consequence of selecting a suboptimal position and / or size of prosthesis can be the creation of a notch or area where the prosthesis margin and the bone surface do not fit well together, necessitating an undesirably large lateral runout of the resected bone segment beyond one end of the prosthesis, or a large overhang or gap between the end of the prosthesis and uncut portions of the bone. A major limitation on the surgeon's ability to plan the operation most efficiently is that time is a determining factor during surgery, and thus the time the patient is incised must be minimized. Often, planning can only begin and / or be completed after the patient has been incised.

[0009] It would therefore be desirable to have a system and a procedure that can enable more accurate and time-efficient planning of the operation, in order to support the planning of an optimal size and position of the prosthesis, in order to exclude or minimize the creation of notches in the bone and other performance weaknesses and / or less desirable design or concept alternatives. Summary of the invention

[0010] The invention relates to a system for evaluating the fit of a femoral implant according to claim 1, a system for virtually planning the size and position of a femoral implant according to claim 9, a computer-readable medium for automatically calculating an optimal size and position of a femoral implant according to claim 19, a method for virtually planning the size and position of a femoral implant according to claim 23, and a method for evaluating the fit of a femoral implant according to claim 33.

[0011] According to one aspect of the invention, a system for evaluating the fit of a femoral implant to a distal end of a femur in a selected orientation before the femur is resected comprises means for obtaining predefined form factor information for a plurality of femoral implants, means for obtaining information about the shape of the surface of a distal end of the femur, means for automatically performing a virtual fit evaluation of each possible incremental position of a predefined set of incremental positions for each size of implant to be considered before the femur is resected, and means for selecting an optimal size and position of an implant from the virtual fit evaluations.

[0012] According to another aspect of the invention, a system for virtually planning the size and position of a femoral implant for a patient's femur includes a database containing predefined form factor information for a variety of different implants, a circuit for obtaining information about the shape of the femur's surface, a circuit for defining basic position parameters for an implant's position relative to a virtual representation of the femur based on the surface shape information, a circuit for evaluating a fit calculation for each implant relative to the virtual representation of the femur based on the form factor information and a variety of fit factors at each of a variety of incremental positions relative to the femur, and a circuit for selecting the best-fitting size and position of the implant from all fit calculations.

[0013] According to yet another aspect of the invention, a computer-readable medium for automatically calculating the optimal size and position of a femoral implant for a patient's femur includes a program that comprises a first routine for obtaining predefined form factor information for a multitude of implants of different sizes, a second routine for obtaining information about the shape of the femoral surface, a third routine for defining basic position parameters for the position of an implant with respect to a virtual representation of the bone, and a fourth routine for evaluating a fit calculation for each implant with respect to the virtual representation of the femur based on a multitude of fit criteria at each of the multitude of incremental positions with respect to the femur.and includes a fifth routine for selecting an optimal size and position of the implant from all fit assessments based on a weighted comparison of each fit calculation for each of the multitude of fit criteria.

[0014] According to a further aspect of the invention, a method for virtually planning the size and position of a femoral implant for a patient's femur comprises the steps of obtaining predefined form factor information for a variety of different implants, obtaining information about the shape of the femur's surface, defining basic position parameters for a position of the implant with respect to a virtual representation of the femur, evaluating a fit calculation of each implant with respect to the virtual representation of the femur based on a variety of fit factors at each of a variety of incremental positions with respect to the femur, and selecting a best-fitting implant and a best-fitting position from all fit calculations.

[0015] According to yet another aspect of the invention, a method for evaluating the fit of a femoral implant to a distal end of a femur in a selected orientation before the femur is resected comprises the steps of obtaining predefined information about the form factors of the femoral implant, obtaining information about the shape of the surface of the distal end of the femur, and performing a virtual fit evaluation at each of all possible incremental positions of a predefined set of incremental positions for an implant of each size to be considered before the femur is resected. Brief description of the drawings Fig. Figure 1 is an exploded view of some of the knee bones and prostheses involved in a total knee arthroplasty; Fig. Figure 2 is a schematic view of a patient's knee that has been prepared for surgical knee replacement surgery using components of an embodiment of a surgical navigation system; Fig. 3 is a flowchart of one aspect of the present revelation; Fig. 4 is a flowchart of another aspect of the present revelation; Fig. 4A is a flowchart of another aspect of the present revelation; Fig. 4B is a flowchart of yet another aspect of the present revelation; Fig. 4C is a flowchart of yet another aspect of the present revelation; Fig. 5A-5E are schematic representations of steps that are in Fig. 4A are shown; Fig. 6A-6C are schematic representations of options that are in Fig. 4D are shown; Fig. 7 is a screenshot showing an aspect of a main navigation menu of a system of the present disclosure; Fig. 8 is a screenshot showing one aspect of a function of the system for imaging bones; Fig. 9 is a screenshot showing one aspect of another function of the system for imaging bones; Fig. 10 is a screenshot showing one aspect of a function of the system for positioning the implant; Fig. Figure 11 is a screenshot showing another aspect of the system's function for positioning and sizing the implant; Fig. Figure 12 is a screenshot showing a manual function of the system for manual modification; and Fig. Figure 13 is a screenshot showing another manual function of the system for manual modification. Fig. 14 shows screenshots of additional system functions; Fig. Figure 15 shows screenshots of a function of the system for positioning an implant; Fig. 16A and Fig. 16B shows detailed excerpts of the screenshot from Fig. 15; Fig. Figure 17 is a schematic view of a knee joint showing the rotation and extension gaps; Fig. Figure 18 shows screenshots of a function of the system for capturing a femur; Fig. Figure 19 is another schematic view of a distal end of a femur showing a medial / lateral overhang of the implant; Fig. Figure 20 shows screenshots of a function of the system for resetting the proximal tibia; Fig. Figure 21 shows a screenshot of the implant alignment function and a schematic view of a resected knee joint with a spreader inserted into it; Fig. Figure 22 is a schematic representation of another aspect of the system; Fig. Figure 23 is a schematic representation of an X-ray image of a damaged knee joint; Fig. 24 shows a screenshot of yet another aspect of the system; Fig. Figure 25 is a schematic representation of a distal end of a femur with superimposed biomechanical information; Fig. 26 shows a screenshot of yet another aspect of the system; Fig. Figure 27 is a schematic representation of a knee joint with surgical tools for use during a total knee replacement surgery; Fig. Figure 28 shows screenshots of another aspect of the system; and Fig. 29 shows screenshots of yet another aspect of the system. Detailed description

[0016] As in Fig. As shown schematically in Figure 2, a patient's leg 30 can be prepared for knee replacement surgery by angling the leg 30 so that the patient's thigh or femur 32 is at an angle of approximately 90 degrees to the patient's lower leg or tibia 34. This position of the leg 30 positions the patient's knee 36 for surgery. Two trackers 38, which can communicate with a camera 40 associated with a computer-assisted surgical navigation system 42, are attached to the femur 32 and tibia 34 such that the trackers 38 move with the femur 32 and tibia 34, respectively. This attachment can be achieved by direct attachment to the corresponding bones or by other possible methods.The computer-assisted surgical navigation system 42 is, in one embodiment, one that is well known in the prior art and is not described further here. Suitable surgical navigation systems 42 are described in US Patent Publication No. 2001 / 0034530. A typical navigation system 42 also includes a display device 44, e.g., a computer or video monitor. In addition, most navigation systems 42 also use specialized tools, e.g., a pointer 46, which has been previously calibrated to interact with the navigation system 42. The calibration of the pointer 46 enables the navigation system 42 to determine the precise position of a pointer tip 48 by determining the position of a series of positioning devices 50, e.g., LEDs mounted on the pointer 46. In another embodiment, these positioning devices 50 are of the same type as those used for the tracking devices 38.

[0017] Fig. Figure 3 illustrates an embodiment of a method 70 for performing a surgical prosthesis implantation operation. In one embodiment, the method 70 is configured to be performed using the computer-assisted navigation system 42, which guides both the step-by-step planning and the execution of the surgical operation, as described in detail below. However, the method 70 is not limited to use with any particular execution system and can also be adapted for use and / or execution with other systems capable of performing the steps of the method. For illustrative purposes only, the method and system of the present disclosure are shown in connection with the planning and execution of a total knee arthroplasty or a total surgical knee replacement operation.However, it should be understood that the procedure and the system can be applied to other surgical operations with minor modifications, without deviating from the spirit of the detailed example.

[0018] In one embodiment, the method 70 begins with the step of creating a patient file, which in one embodiment is in computer-readable form, and entering data for predetermined parameters, such as the patient name, date, surgical operation, etc., using a patient data input routine 72. Subsequently, a navigation system, such as the navigation system 42, is set up, which may include the step of confirming the position of a pointer, such as the pointer 46, using a system setup routine 74.After initial detection, the patient's position is recorded, for example, with the pointer, using a routine 76 for patient detection (or "registration") with the navigation system. In one embodiment, this routine includes a subroutine for defining a verification point, a subroutine 78 for detecting the femur, a subroutine 80 for detecting the tibia to confirm which leg is being operated on, and a subroutine 82 for verifying the detection. During subroutine 78 for femur detection, a detailed measurement of the relevant femoral surfaces is performed. This measurement includes at least the anterior cortex and the most proximal, distal, medial, and lateral points of the lateral and medial condyles using appropriate measuring instruments, as will be further detailed below.Similarly, a measurement of the relevant surfaces of the tibia is performed during subroutine 80, the tibial acquisition procedure. Data regarding other relevant biomechanical properties of the patient, such as the kinematics of the affected joint, can also be collected during patient acquisition procedure 76 through direct observation and / or interpolation. Data from the measurements are then processed by computer to create a virtual image or representation of the measured surfaces for display on the monitor and for use during the remaining steps of surgical procedure 70. After the patient has been acquired with the navigation system, the surgeon can analyze relevant biomechanical properties of the affected area, such as the preoperative alignment of the knee, using routine 84, the original alignment analysis procedure.During Routine 84 for the analysis of the initial alignment, the surgeon may, in one embodiment, record a table, analyze the varus / valgus angles of the knee, and / or plot curves. The information gathered by Routine 76 for patient enrollment and Routine 84 for the initial alignment is used in Routine 86 to determine the size and position of the implant, in order to obtain a final implant size and positioning plan in a novel manner, as detailed below.The final plan for the size and position of the implant can then be used to guide and / or support remaining steps of the surgical operation, such as resection of the bone during a routine 88 for bone resection, placement and analysis of a trial alignment of a trial prosthesis during a routine 90 for trial alignment analysis, placement and analysis of a final placement of a final prosthesis during a routine 92 for final alignment analysis, and creation of a report (or report) of the operation during a routine 94 for display of a report according to well-known surgical navigation techniques and computer-aided data processing techniques.

[0019] Now the Fig. Referring to Figures 4-6C, an embodiment of routine 86 for determining the size and position of the implant is disclosed, during which an optimal implant size and position plan, including an optimal size and position of a specified femoral implant type, is automatically calculated by evaluating a multitude of fit parameters for each possible combination of a range of possible sizes and a range of possible positions based on a set of prioritized parameters by means of an automatic size and position optimization subroutine 100. In one embodiment, the automatic size and position optimization subroutine 100 automatically selects a femoral implant of an optimal size and an application position of the femoral implant at the distal end of the femur in a manner as shown schematically and in more detail in Figure 4-6C. Fig. Figure 4A shows that only rigid bone shapes and femoral implant shape parameters are considered, and does not take into account soft tissue or other anatomical conditions, such as the patient's size and sex, which can also influence a final plan for determining the size and position of the prostheses used by the surgeon to actually attach the implants to the patient. Therefore, the automatically calculated optimal implant size and position plan can subsequently be modified by appropriate input from the surgeon in a routine 102 to reduce the implant size ( Fig. 4B) and / or a routine 104 ( Fig. 4C) to change the implant position manually, as the surgeon deems appropriate, to create one or more agreed-upon implant size and positioning plans. In one embodiment, the agreed-upon plans for determining an implant size and positioning are evaluated by the surgeon with respect to their fit to the bone. The surgeon then selects the final implant size and positioning plan for carrying out the remaining steps from the totality of the previous plans considered in step 108, based on his or her knowledge and experience.

[0020] In one in the Fig. In the embodiment of automatic subroutine 100 for determining size and positioning shown in Figures 4A and 5A-5E, a predetermined set of calculations automatically and sequentially evaluates the fit of the femoral prosthesis of each size—roughly from smallest to largest—with the shape of the bone in each position with two degrees of freedom for four prioritized fit criteria. In one embodiment for fitting a femoral implant to a distal end of the femur, the four prioritized fit criteria include: the maximum lateral offset of the anterior resection from the outline (or contour or area) of the proximal end of the anterior portion of the implant; the percentage of the outline (or contour or area) of the proximal end of the anterior portion of the implant that lies on cut bone; the percentage of the outline (or contour or area) of the proximal end of the anterior portion of the implant that lies on cut bone; and the percentage of the outline (or contour or area) of the proximal end of the anterior portion of the implant that lies on cut bone.the contour or surface) of the end of the anterior portion of the implant that lies on or above uncut anterior cortex, and the maximum gap between the implant and the uncut surface of the anterior cortex. For example, the first criterion may be that the lateral runout must not exceed 12 mm. The second criterion may be that at least 60% of the outline of the proximal end of the inner surface of the anterior portion of the implant lies on cut bone. The third criterion may be that at least 1% of the outline of the proximal end of the anterior portion of the implant lies on or above uncut anterior cortex. The fourth criterion may be that the maximum gap between the proximal outline of the implant and the uncut anterior cortex is preferably less than 1.5 mm.A notch is calculated to be present if either the maximum lateral runout is greater than 12 mm or the entire outline of the proximal end of the anterior portion of the implant lies on resected anterior cortical bone. In one embodiment, the predetermined set of calculations is performed electronically by the computer controlling the navigation system 42, and the calculations are based on the measurement data obtained during routine 76 for patient acquisition, as well as a pre-populated database containing form factor information for a predetermined group of prostheses of one or more types and for each of a multitude of sizes of each type of prosthesis, which can be accessed by the computer, such as an electronic storage system.In other embodiments, the predetermined set of calculations is performed by another electronic computer and / or by other calculating machines and / or with human assistance, and the measurement data are obtained by other methods capable of providing the necessary anatomical information regarding the bones present. In one embodiment, the surgeon selects a prosthesis type based on other factors, and the computer then evaluates the fit for each size and position of the selected type, as described immediately below.

[0021] Before the automatic subroutine 100 is initiated to optimize size and positioning, the surgeon can first define a target reconstruction position based on design or concept parameters to match a selected varus / valgus angle, rotation angle, and / or position on the surfaces of the posterior and distal condyles. As shown schematically in Fig. As shown in Figure 5, the reconstruction position defines a concept baseline 110 for the distal surfaces of the condyles and a concept baseline 112 for the posterior surfaces of the condyles. These are the surfaces that the surgeon initially hopes to maintain constant with the final implant size and positioning plan. After the surfaces of the reconstructed distal and posterior condyles have been determined, in a first step 114 of an embodiment, an implant 118A of a first size, e.g., a smallest size, is selected, and form factor information for it is retrieved from an implant form factor database 116. In a step 118, the first-size implant 118A is positioned on the image or representation of the femur 10, maintaining the distal and posterior positions of the condyles at all times along the reconstructed concept baselines 110 and 112, respectively.Step 118 positions the first-size implant 118A at a predetermined position of 0° flexion and 0.0 mm anterior / posterior displacement (A / P displacement) with respect to a mechanical axis 120 of the femur 10. The fit of the first-size implant 118A is evaluated during step 122 using the four criteria specified above to ensure that at least one notch is present, as shown in 124. Fig. 5A shown, to evaluate. If the A / P displacement is not the maximum A / P displacement for the current flexion angle, the A / P displacement is incremented anteriorly in a step 126, in a Fig. 5B schematically shown embodiment, e.g. by 0.5 mm, and the fit in this new position is evaluated in step 122. This cycle of steps 122 and 126 is repeated until the maximum A / P displacement at a predetermined flexion angle has been evaluated, whereupon the flexion angle is incremented in step 128, as schematically shown in Fig. As shown in Figure 5C, the A / P displacement is reset to the default position in step 130, and the fit of the new flexion angle is evaluated in step 122. Steps 122, 126, 128, and 130 are repeated until the fit has been calculated for each of the positions corresponding to all possible combinations of flexion angle and A / P displacement for the first-size 118A implant. In one embodiment, the evaluated flexion angles are in 1° increments in a range from 0° to a maximum of 5°, and the evaluated A / P displacements move in 0.5 mm increments in a range from 0.0 mm to a first increment calculated to overlap with the increment of the next-size implant and / or until no notch is formed in the anterior cortex of the bone.Preferably, the implant is bent around a single radius to ensure that the reconstructed distal and posterior condyles are held in their corresponding baseline positions. After evaluating the fit at all positions of the first-size implant 118A, the next larger implant 188B is selected in step 132, as shown schematically in Figure 1. Fig. The 5D representation is shown, and steps 122, 126, 128, and 130 are repeated similarly. Steps 122, 126, 128, 130, and 132 are repeated accordingly for each implant of all subsequent incremental sizes in the database until all implant sizes for the selected implant type in every possible incremental position have been fully evaluated for both A / P displacement and flexion degrees of freedom. After the fit of the implants of each size has been fully evaluated, all evaluated fit qualities are compared during step 134 using a weighted algorithm to automatically identify an optimal size and placement plan from all evaluated sizes and positions that eliminates or at least minimizes any bone notching and implant oversizing.In step 136, an image of the femoral implant in the automatic optimal implant size and in the position plan is then superimposed over an image of the femur for use in subsequent steps, as schematically shown in . Fig. 5E is shown. In other embodiments, the steps for iterating through all possible sizes and positions to evaluate fit ratings in every possible position for every possible size may be included in a different order than described herein, preferably as long as a fit rating is used to consider all possible incremental positions for implants of each size.

[0022] As schematically in the Fig. As shown in Figures 4B and 6A to 6C, after calculating the optimal implant size and positioning plan, the surgeon can optionally choose to manually adjust the size and position of the implant in routine 102 to make adjustments, for example, to accommodate soft tissue or other anatomical considerations. In step 150, the surgeon selects the next incrementally smaller size of femoral implant than the automatically calculated optimal size. With the new implant size, in step 152, the surgeon selects from three alternative options for maintaining a baseline AP displacement: 1. Maintaining the anterior position of the implant during reduction, schematically shown in Figure 4B. Fig. 6A shown, 2. Maintaining the anterior-posterior center of the implant during reduction, schematically in Fig. 6B shown, and 3. Maintaining the posterior position of the implant during reduction, schematically in Fig. Figure 6C shows that the surgeon also selects a baseline flexion angle to be maintained within a pre-selected range, such as between 0° and 5°, either by choosing to retain the previous flexion angle or by selecting one of the remaining angle options. The fit of the new-size implant is then evaluated in the same manner as described above, and a resulting revised size and placement plan are created. The surgeon may choose to repeat and refine the revised implant size and placement plan in a single step (158) based on their visual inspection, knowledge, and experience until they believe the optimal size and placement have been achieved, taking soft tissue considerations into account.Once a satisfactory modified implant size and a positioning plan have been identified, the identified plan can be saved for future use in step 160.

[0023] In the schematically in Fig. In the subroutine 104 shown in Figure 4C for changing the implant position, the surgeon may optionally choose, in addition to or as an alternative to routine 102 for reducing the implant size, to directly modify all available degrees of freedom set in the automatically optimized implant size and the position plan, and / or the modified implant size and the position plan in one step 170 at his discretion, including the varus / valgus angle, the proximal / distal displacement distance, the rotation angle, the AP displacement distance, the flexion angle and the size of the implant, as the surgeon wishes based on his knowledge and experience in order to make necessary adjustments for soft tissue and / or other anatomical considerations.Such manual adjustments can allow the surgeon to quickly skip obviously unnecessary size and position iterations and / or provide user-controlled operation based, for example, on the surgeon's knowledge and experience. In step 172, the fit of the modified implant size and the positioning plan from step 170 are evaluated, and the surgeon visually analyzes the modified implant size and positioning plan and decides in step 174 whether to accept such a plan, in step 176 whether to attempt further changes, and / or in step 178 whether to accept the previous plan.In one embodiment, the fit in each manually selected position is evaluated for both subroutine 102 for reducing the size of the implant and subroutine 104 for changing the implant position in order to identify whether a particular implant size and position plan creates a notch in the anterior cortex when either the maximum lateral runout is greater than 12 mm or the entire outline of the proximal end of the implant lies on a sectioned surface of the anterior cortical bone, enabling the surgeon to decide to accept or reject each manually selected position based on his or her experience and knowledge.

[0024] At the end of each of subroutines 100, 102, and 104, the surgeon can choose to proceed with subroutine 38 for bone resection after selecting a final implant size and a positioning plan to use to guide the remaining steps of the surgical procedure from all considered plans. After performing the steps described above, the surgeon selects the final implant size and positioning plan, either from the original, automatically calculated, optimal implant size and positioning plan, or from any of the modified implant sizes and positioning plans. Of course, the surgeon can simply choose to omit the manual adjustment and rely on the automatically calculated optimal size and position.

[0025] Fig. 7, Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12 to Fig. Figure 13 shows an embodiment of a computerized system for implementing the method described above. Fig. 3 to 6C in conjunction with the in Fig. 2 hardware shown, to build one in Fig. 1 to perform the total knee replacement shown. The software for implementing the procedure described above controls a computer, e.g., the navigation computer 112, which also has access to the measurement and imaging data of the bones of interest and to the implant form factor database 116. A in Fig. The main menu screen 200 shown in Figure 7 displays a main menu 202 that can help guide the surgeon through the surgical procedure. The main menu 202 contains buttons 204 to initiate each of the following routines described above: Routine 72 for patient data acquisition, the system setup routine 74, routine 76 for patient registration, routine 84 for initial alignment analysis, routine 86 for determining implant size and position, routine 88 for bone resection, routine 90 for trial alignment analysis, routine 92 for final alignment analysis, and routine 94 for displaying a report. A visual cue, such as a check mark 206, is associated with each button to indicate whether the routine has been completed, thus providing a visual signal to help guide the surgeon through the operation.

[0026] As in the Fig. 8 and Fig. As shown in Figure 9, selecting button 204 on the main menu screen 200, which is associated with routine 76 for patient acquisition, displays one of several patient acquisition screens 208A, 208B, which show display subroutine buttons 210 for performing various patient acquisition steps, including a subroutine for capturing hip flexion, a subroutine for capturing hip centering, a subroutine for capturing the medial epicondyle, a subroutine for capturing a lateral epicondyle, a subroutine for capturing the midpoint of a femur, a femoral AP acquisition subroutine, a subroutine for capturing a medial distal condyle, a subroutine for capturing a lateral distal condyle, a subroutine for capturing a medial posterior condyle, and a subroutine for capturing a lateralposterior condyle and a subroutine for acquiring an anterior cortex. In a similar manner to the main menu screen 200, each subroutine button 210 is associated with a visual indicator 206 that shows whether each subroutine has been completed, to help guide the surgeon visually through the various acquiring subroutines. Patient Acquisition screen 208A corresponds to the subroutine for acquiring the medial posterior condyle, during which the most posterior surface of the medial condyle is measured. Patient Acquisition screen 208B corresponds to the subroutine for acquiring the anterior cortex, during which the surface of the anterior cortex of the femur is measured. A visual representation 212 of a general shape of the bone to be resected is also displayed on the screen. The visual representation 212 is selected for each of the subroutine buttons 210.to display the individual bone being captured and imaged. For example, the posterior condyles of a femur are shown on a screen 208A and the femoral anterior cortex on a screen 208B. On each screen 208A and 208B, visual indicators 214, e.g., points showing which survey data points have been obtained and their approximate positions, are superimposed on the bone. In one embodiment, survey data points are obtained using a digitization mechanism, e.g., the pointer 46.

[0027] Of particular interest regarding the in Fig. The patient acquisition screen 208B shown during the anterior cortex acquisition subroutine is that a detailed survey of the femoral anterior cortex is performed to obtain an accurate outline of the anterior cortex for use in the calculations performed during routine 86 described above for implant positioning. Generating the outline map generally requires a certain degree of interpolation between observed data points to create an interpolated outline of the surface in question, as is well known in the field of surveying and mapping. The accuracy of the interpolated outline maps is generally directly related to the position and number of data points obtained.For example, it is generally desirable to have data points distributed in a relatively uniform grid and at a target density such that triangles can be formed between adjacent trios of data points, which are equilateral rather than elongated and designed to adequately represent the general topography of the surface in question. To assist the surgeon in obtaining a desired set of data points during the anterior cortex acquisition subroutine, a digitization grid 216 is superimposed on a standardized virtual model 212 of a femoral anterior cortex to help visually guide or assist the surgeon in obtaining a number and location of data points to provide a representation of the anterior cortex outline sufficient to meet specific concept accuracy parameters. A visual indicator 214, e.g.A point is superimposed on the digitization grid 216 and the standardized virtual model 212 of an anterior cortical bone for each acquired data point, provided a minimum number and location of data points have been acquired. A further visual indicator 218, e.g., a change in the grid color, appears on the screen when a minimum number and location of data points have been acquired that meets the designed accuracy parameters. Another visual indicator, such as a proximal outline of the implant 220 displayed in yet another color, is shown on the screen to indicate the general or approximate specific shape projected onto the general area of ​​the inner outline of the prosthetic implant.The proximal outline of implant 220 is derived from the implant form factor information database and determined from the captured positions of the condyles and the mechanical and rotational femoral axes. A further visual indicator, such as a checkmark 222 and a number 224, which indicate which approximate implant sizes can be reasonably calculated from the data points acquired during the anterior cortex acquisition subroutine, is displayed on the screen. Additionally, an error-checking subroutine performs mathematical interpolation to identify potentially erroneous outlier data points acquired during the anterior cortex acquisition subroutine, such as an air point that was not captured on the bone surface.The error-checking subroutine mathematically interpolates all acquired data points from the anterior cortex acquisition subroutine and calculates a smoothed surface using, for example, well-known spline interpolation algorithms. Data points that deviate from the smoothed surface by more than a predetermined distance are identified to the surgeon as potentially erroneous data points. The surgeon can then choose to delete such points or retain them for use in creating the outline mapping based on their understanding of the measured surface.

[0028] A in Fig. The user settings screen 226, shown in Figure 10, prompts the surgeon to select button 228A or 228B to indicate whether the surgeon should be allowed to manually plan the implant position or whether the computer should automatically calculate the implant size and position by automatically executing the automatic subroutine 100 for optimizing size and positioning after the required shape and biomechanical properties of the bone of interest have been obtained. User settings screen 226 also allows the surgeon to set other parameters for the calculations, such as default flexion angles and resection depths.

[0029] Routine 86 for determining the position of the implant is triggered by selecting the associated button 206 of the main menu 202 and then automatically calculates the optimal size of the implant and the optimal positioning plan and displays the results in a graphical representation of the bone and implants and in numerical form in a Fig. The implant positioning screen 230, shown in Figure 11, displays the selected implant positioned on the bone according to the calculations. This allows the surgeon to verify, both visually and by examining the various numerical data displayed, that the automatically calculated size, position, and orientation of the femoral implant are acceptable. The display also shows visual indicators on the graphical representations of the bone and implants to indicate areas of a predefined anterior cortex resection not covered by the femoral implant, any gaps between the implant and uncut areas of the anterior cortex, and the location of a maximum gap between the femoral implant and uncut areas of the anterior cortex. These indicators are identical to those shown on the implant positioning screen.The implant positioning screen 230 displays the actual varus / valgus and flexion alignments of the leg, as determined by the acquisition routines, and the calculated predefined parameters for the femoral implant, including size, flexion, AP displacement, varus / valgus angle, rotation angle, distal resection level, and posterior resection level. The implant positioning screen also displays the implant system and type previously used for automatic size and positioning calculations, as shown in the concept. The implant positioning screen 230 includes a zoom-out button 232, which, when selected, triggers routine 102 to zoom out the implant and switches the display to an implant zoom-out screen 234, which is shown in . Fig. Figure 12 is shown. The implant positioning screen also contains a button 236 for changing the implant position, which, when selected, triggers the subroutine 104 for changing the implant position and changes the display to a position in Fig. The screen shown in section 13 (237) switches to the screen for changing the implant position. A default button (239) can be selected at any time to reset the size and position plan displayed on the screen to the automatically optimized size and position plan.

[0030] Now Fig. Turning towards screen 12, the implant reduction screen displays 234 options for the surgeon to perform the initial manual mode adjustments described above. Specifically, three alternative selection boxes, 238A, 238B, and 238C, are displayed, allowing the surgeon to choose between maintaining the anterior position, the posterior position, or the average position of the concept displayed on the implant positioning screen during routine 102 for implant reduction. Four further alternative selection boxes, 240A, 240B, 240C, and 240D, are displayed, allowing the surgeon to choose between maintaining the flexion angle currently displayed on the implant positioning screen and one of three alternative flexion angles during routine 102 for implant reduction.The selection box 240A, which is associated with maintaining the flexion angle, displays the current angle setting. After the desired selection is made, the surgeon selects a reduction button 242, and the computer updates the calculations based on the selected reference AP displacement, reference flexion angle, and form factor data for the incrementally smaller implant size from the currently designed implant parameters to provide the changed size and position of the implant. The display on the implant positioning screen 230 is automatically updated to reflect the changed implant size and position plan when the reduction button 242 is selected and provides a visual indication of whether the fit assessment calculation indicates that a notch will be produced, as described above.A Cancel button 244 is also displayed, which allows the surgeon to return to the implant positioning screen 230 without saving any changes to the previously displayed implant size and position plan.

[0031] now Fig. On screen 237, the femoral implant 18 and the tibial implant 20 are graphically superimposed on the corresponding bones in accordance with the current implant size and the positioning plan parameters. Screen 237 also displays options for the surgeon to perform the previously described changes in subroutine 104 for changing the implant position. Specifically, the bones are displayed in their actual position and orientation, and the implants are superimposed on the bone in the position of the current setting.The display also shows the same visual indicators as in the implant positioning screen 230 to show areas of a predefined anterior cortex resection that are uncovered by the femoral implant, any gaps between the implant and uncut areas of the anterior cortex, and the position of a maximum gap between the femoral implant and uncut areas of the anterior cortex, identical to the indicators displayed on the implant positioning screen. A pair of zoom-in / zoom-out arrow buttons for each of the six degrees of freedom of the femoral implant are shown for selection by the surgeon, including varus / valgus angle, proximal / distal displacement distance, rotation angle, anterior / posterior displacement distance, flexion angle, and femoral implant size.By using the pair of zoom-in / zoom-out buttons (246), the surgeon can manually modify any predefined parameter as desired. For example, they can modify the automatically calculated optimal implant size and position plan, and / or the modified implant size and position plan obtained from the implant reduction screen (234), to adjust these concepts to account for soft tissue considerations not addressed by the automatic mode for calculating the optimal implant size and position. Similarly, when an OK button (248) is selected, the implant positioning screen (230) is immediately updated to reflect a modified predefined implant position based on the manually changed parameters selected on the implant position modification screen.A default button 250 and a cancel button 252 are also displayed, allowing the surgeon to reset the defaults to the automatically calculated implant defaults or to the implant positioning screen without saving any changes made to them.

[0032] Once the surgeon has selected a final setting from the various settings described above, the remaining routines use the final setting to guide the surgeon through the remaining steps to actually install or implant the prosthesis in the patient in a well-known manner.

[0033] Itself Fig. Figure 14 shows a screenshot of user settings taken from a display screen 270 of a computerized system of the present disclosure. If automatic determination of implant size and positioning is selected, the following functions may be selected optionally or additionally: function to display the flexion / extension gap, function to detect a medial / lateral overhang, function to cut the tibia first and preview the insole, function to estimate the medial condyle for varus knees, function to use a navigation-guided drilling template for AP alignment, and / or function to display the flexion / extension gap. Each function may be selected by means of a corresponding button or a dialog box 272.

[0034] As in Fig. As shown in Figure 15, the flexion / extension gap button provides a preview of the flexion and extension gap size for both the medial and lateral sides before any incisions are made. This allows the surgeon to assess whether the planned resections will provide sufficient space for the planned implants. To obtain an accurate preview of the gaps, it is advisable to ensure that the knee joint is stabilized with some mechanical device, such as a centering device or a spreader ( Fig. 21) is relieved of weight. A correct preview of the flexion gap is given when the knee is unloaded in flexion. The extension gap is shown when the knee is unloaded in extension.

[0035] Now the Fig. 16A and Fig. Turning to 16B, a detailed view of the screenshot associated with the flexion / extension gap display function shows the flexion / extension gap and the tibial resection preview. The gap size preview is based on the calculated distal (and posterior) femoral resection level and the tibial resection level. For the preview, in one embodiment, the tibial resection level is set to 8 mm by default, measured from the most proximal (highest) compartment, as long as the tibia has not been resected and the cut has not been recorded.

[0036] With reference to Fig. 17. The flexion / extension gap is calculated as follows. First, the centroids of the digitized compartments are calculated. These centroids are then projected onto a tibial resection plane 276. The projected centroids are subsequently converted medially / laterally using a factor of 1.53. A line perpendicular to the tibial section plane, passing through the projected and converted centroids and intersecting a femoral section plane 278, is drawn, and a distance “d” between the femoral and tibial section planes along this line is measured.

[0037] now Fig. Referring to Section 18, the function of capturing, e.g., by digitizing the relevant surfaces of the ML overhang, according to one embodiment, includes a step of obtaining the AP position of the relevant medial and lateral overhang region where an overhang of the implant may occur. During digitization, the surgeon can, for example, start at the relevant AP position of the medial / lateral cartilage border and move the pointer tip proximally to describe a line. In the "Position Implant" dialog, the average width of the medial / lateral overhang of the implant or the width of the uncovered bone is displayed as a numerical value. According to one aspect of the disclosure, potential medial / lateral overhang or uncovered bone is not considered in the automatic calculations for determining size and positioning. With reference to Fig. 19 In one embodiment, when the function for detecting an ML overhang involves measuring an overhanging portion of the ML implant or uncovered bone 280 at the AP position of the digitized overhang region, the AP position of the relevant overhang region is determined by the surgeon, and only the average width of the medial / lateral overhang or uncovered bone is numerically displayed. Calculations of the ML overhang are then based on a planned femoral implant 282. In another embodiment (not shown), the potential medial / lateral overhang or uncovered bone is taken into account when determining the optimal size and forms an additional fit criterion.

[0038] Fig. Figure 20 shows screenshots for the "Cut the Tibia First and Preview Insert" function. When the "Cut the Tibia First and Preview Insert" function is selected, the software workflow (dialog box 286) prompts the user to cut the proximal tibia first before a "Position Implant" dialog box 288 is displayed. With the proximal tibial cut performed and recorded, the "Position Implant" dialog box 288 allows a preview of which insert size (thickness) will fit between the actual cut proximal tibia and the planned femoral implant.

[0039] With reference to Fig. 21 During the "Cut the tibia first and preview the insole" function, to obtain an accurate preview of the insole size, the knee joint is preferably unloaded with some type of centering device or spreader 290. The preview of the tibial implant size is provided for the knee in both extension and flexion. The preview and calculation of the tibial implant are based on the recorded cut of the proximal tibia and the calculated / planned distal and posterior resection levels. The software causes a visual indicator to appear on the display screen if the smallest available implant does not fit between the cut proximal tibia and the planned femoral implant in both flexion and extension. Furthermore, with reference to Fig. 22, the calculated tibial implant size shown in box 292 reflects only the average medial / lateral gap size. For an asymmetric knee 294 with a varus / valgus misalignment of more than 3°, the calculated implant size would not fit into the narrower gap. To ensure the calculated implant fits into the gap, the ligaments are preferably centered. With a centered knee 296, the medial and lateral gaps are equal to the average central gap, and the calculated implant size fits. With the asymmetric knee 294, the medial and lateral gap sizes differ from the average central gap size, and the calculated implant size does not fit.

[0040] Now, referring to Fig. 23. One goal of total knee arthroscopy is to reconstruct the original 300° joint line. Using the medial condyle estimation function for a varus knee, the joint line is generally reconstructed with respect to the more prominent medial condyle. However, in the case of varus deformities, the medial condyle can be severely damaged, and referencing a severely damaged medial condyle could lead to excessive femoral resection and proximal displacement of the original joint line. If the medial condyle estimation function for varus knees is enabled, the software warns the user, for example, with a message displayed on the screen. Fig. 24. A visual warning is displayed if the medial condyle is seriously damaged. The software assumes serious damage is present if the digitized lateral condyle protrudes more than the digitized medial one. This warning gives the user the opportunity to either estimate the original medial condyle as a reference for the distal femur resection level or to proceed with the more protruding lateral side as the reference for implant calculation. With regard to Fig. 25 In the function for estimating the medial condyle for varus knees, the angle 302 used to estimate the medial condyle is set to 2.5° in one embodiment of the disclosure. Furthermore, with reference to Fig. 26. The reference level can also be changed within the "Position Implant" dialog using the "Select Reference Level" button after the optimal size and positioning plan have been calculated by the software. When the reference level is changed, the software recalculates the implant size, flexion, and AP position. In one embodiment of the disclosure, any change (e.g., reduction, change in AP displacement, etc.) that may have been previously made is lost and overwritten by the new default position.

[0041] As in Fig. As shown in Figure 27, navigation-guided drilling templates (such as those available from Stryker Navigation in Freiburg, Germany) can be used for AP alignment to prepare a four-in-one cutting block for navigation and rotational alignment and AP positioning. The navigation-guided drilling templates can replace a conventional AP sizer. Unlike a conventional AP sizer, the navigation-guided drilling templates can be both easy to use and offer greater flexibility with respect to AP displacements without requiring modifications to the instrument. In one embodiment of the disclosure, navigation-guided drilling templates can be selected in a system section of the user settings if automatic size determination is enabled. With navigation-guided drilling templates, as most clearly shown in Figure 27, the user can select the appropriate templates for AP alignment. Fig. As shown in Figure 28, the software facilitates navigation in two degrees of freedom: rotational orientation and AP position. In one embodiment, the rotational orientation is calculated with respect to the mean axis of rotation, the femoral AP axis, and the transepicondylar line. The reference point for the AP position is the calculated implant and the virtual fixation holes, which are displayed on the screen. The deviation of the virtual fixation holes from the template is also displayed on the screen. Additionally, a frontal view of the anterior cortex is displayed, providing a preview of the position and size of the uncovered bone resection against the given flexion / extension of the distal femoral section and the AP implant position. In one embodiment, the medial lateral position cannot be navigated.

[0042] now Fig. 29. In one embodiment, if any femoral landmarks are redigitized after the optimal implant size and positioning plan have been calculated, the software repeats the implant calculation and prompts the user to check the changed implant parameters. For this purpose, the Fig. 16. The “Check implant position” dialog shown is open, with the changed parameters displayed in yellow.

[0043] Although the above detailed description is directed toward a total knee replacement operation using a navigation system, the method and system disclosed herein can be readily adapted for use in at least other surgical operations where a prosthetic device must be selected from a variety of different sizes and / or shapes and then positioned to meet user-specified constraints. The method and system can also be readily adapted for use in other surgical operations, and it is understood that the scope of this disclosure is not limited to the specific surgical operations described in detail herein. Furthermore, the specific method of collecting anatomical data, such as measurement data of the bone to be resected, is not limited to direct digitization during the operation.The anatomical data can be collected using any preoperative procedure capable of acquiring the necessary anatomical shape data, such as an X-ray scan, an MRI scan, a CT scan, an ultrasound scan, and other preoperative procedures; other intraoperative procedures such as indirect digitization, a guided probe with a stylus, the use of visual, mechanical, or similar localizers, the use of distance measuring devices such as lasers or moiré patterns, and / or other data acquisition techniques. Furthermore, the execution of the final size and placement plan for implant placement is not limited to the use of the navigation techniques described herein. Rather, the implant can be placed according to the final determination of the implant size and placement plan using any procedure capable of satisfactorily executing the final plan. Commercial applicability

[0044] In one embodiment, the technology of the present disclosure allows a surgeon to use a computer to rapidly calculate an optimal prosthesis concept based on patient information collected, for example, during the surgical procedure. This concept is calculated to optimize several parameters, such as avoiding notching and achieving improved mutual fit between the anterior implant outline and the anterior cortex of the femur, during a total knee replacement arthroplasty operation. The technology of the present disclosure can also be used to allow the surgeon to manually modify the automatically calculated optimal implant concept to make adjustments that he deems necessary, for example, to address soft tissue concerns based on his knowledge and experience.The technology of the present disclosure may in some cases help to avoid common problems such as the unnecessary oversizing of an implant, the failure to cover an unnecessarily large amount of anterior bone resection, or the presence of an unnecessarily large anterior overhang or gap between the anterior surface of the implant and uncut areas of the anterior cortex, which are attributable to earlier methods, such as simply selecting an implant concept based on the surgeon's visual inspection.

[0045] Numerous modifications to the present disclosure are apparent to a person skilled in the art from the preceding description. Accordingly, this description is to be construed merely as an example and is presented for the purpose of enabling skilled persons to manufacture and use the disclosure and to teach the best way to carry it out. The exclusive rights to all modifications falling within the scope of the attached claims are reserved.

Claims

[1] System for evaluating the fit of a femoral implant (118A, 188B) to a distal end of a femur (32) in a selected orientation prior to resection of the femur (32), the system comprising the following elements: - Means of obtaining predefined form factor information for a variety of femoral implants (118A, 188B); - Means of obtaining information about the shape of the surface of the distal end of the femur (32); - Means for automatically performing a virtual fit assessment of each possible incremental position of a predefined set of incremental positions for each size of an implant to be considered (118A, 188B) before the femur (32) is resected; and - Means of selecting an optimal size and position of an implant (118A, 188B) from the virtual fit assessments, characterized by that the means of selection - Means for calculating a maximum lateral runout of an anterior resection of the femur (32) from an outline (220) of a proximal end of the femoral implant, and / or - Means to calculate a percentage of the outline (220) of the proximal end lying on sectioned anterior cortical bone, and / or - Means of calculating a percentage of the outline (220) of the proximal end that lies on or above uncut anterior cortical bone, and / or - Contains means for calculating a maximum gap between the femoral implant and the uncut anterior cortical bone. [2] System according to claim 1, wherein a desired reconstruction position is defined on the basis of concept parameters to correspond with a selected varus or valgus angle, a rotation angle and a surface position of the posterior condyle and distal condyle of the femur (32). [3] System according to claim 1, wherein the selection means includes means for comparing each evaluated fit with a weighted algorithm to identify an optimal size and position of the implant (118A) that minimizes bone indentation and implant oversizing (118A, 188B). [4] System according to claim 1, further comprising means for previewing the size of a flexion and extension gap for a medial and lateral side. [5] System according to claim 1, further comprising means for determining a medial / lateral overhang. [6] System according to claim 1, further comprising means for cutting a proximal tibia (16) and for previewing an insert. [7] System of claim 1, further comprising means for estimating medial condyles (14) for a varus knee. [8] System of claim 1, further comprising means for using a navigation-guided drilling template for an anterior-posterior alignment. [9] System for virtual planning of the size and position of a femoral implant (118A, 188B) for a patient's femur (32), the system comprising: - a database (116) containing predefined form factor information for a variety of different implants (118A, 188B); - a surveying system for obtaining information about the shape of the surface of the femur (32); - a circuit for defining basic position parameters for the position of an implant (118A, 188B) with respect to a virtual representation of the femur (32) based on information about the shape of the surface; - a circuit for evaluating a fit calculation for each implant (118A, 188B) with respect to the virtual representation of the femur (32) based on the form factor information and a variety of fit factors at each of a variety of incremental positions with respect to the femur (32); and - a circuit for selecting the most suitable size and position of the implant (118A, 188B) from all fitting calculations, characterized by , that The circuit for evaluation contains one or more circuits for calculating parameters for - a maximum lateral deviation of an anterior resection of an outline (220) of a proximal end of an anterior section of the implant (118A, 188B), and / or - a percentage of the outline (220) of the proximal end of the anterior portion of the implant (118A, 188B) that lies on resected bone, and / or - a percentage of the outline (220) of the proximal end that lies on or above uncut surface of an anterior cortex, and / or - a maximum gap between the implant (118A, 188B) and the uncut surface of the anterior cortex. [10] System according to claim 9, wherein the measurement system includes a digitizer and an additional circuit for performing a measurement of a surface of the femur (32). [11] System according to claim 9, wherein the evaluation and selection circuits are activated before a femur resection system (32) is activated. [12] System according to claim 11, further comprising a circuit for manually adjusting the most suitable size and position of the implant (118A, 188B). [13] System according to claim 11, wherein the selection circuit includes one or more systems for evaluating a plurality of pass parameters. [14] System according to claim 13, wherein the plurality of fitting parameters includes parameters about rigid bone shapes and implant shapes. [15] System according to claim 9, wherein the selection circuit includes a circuit for processing the evaluated parameters with a weighted algorithm for identifying an optimal size and position. [16] System according to claim 9, further comprising a circuit for determining a resection level of the femur (32) that corresponds to the best-fitting size and position of the implant (118A, 188B). [17] System according to claim 9, wherein the circuit for defining the basic position parameters includes a circuit for calculating a maximum gap between the implant (118A, 188B) and the uncut surface of an anterior cortex of the femur (32). [18] System according to claim 9, wherein the circuit for evaluating a pass calculation optionally includes at least one of the following circuits: - a circuit for previewing the size of flexion and extension gaps for a medial / lateral side of the femur (32), - a circuit for detecting medial and lateral overhang, - a circuit for cutting a proximal tibia (16) and for previewing an insertion, - a circuit for estimating medial condyles (14) for a varus knee and - a circuit for using a navigation-guided drilling template for anterior-posterior alignment. [19] Computer-readable medium for automatically virtual calculation of an optimal size and position of a femoral implant (118A, 188B) for a patient's femur (32), wherein the computer-readable medium contains a program comprising: - an initial routine for obtaining predefined form factor information for a variety of implants (118A, 188B) of different sizes; - a second routine to obtain information about the shape of the femur surface; - a third routine for defining basic position parameters for the position of an implant (118A, 188B) with respect to a virtual representation of the femur (32); - a fourth routine for evaluating a fit calculation for each implant (118A, 188B) with respect to the virtual representation of the femur (32) based on a multitude of fit criteria at each of the multitude of incremental positions with respect to the femur (32); and - a fifth routine for selecting an optimal size and position of the implant (118A, 188B) from all fit assessments based on a weighted comparison of each fit calculation for each of the multitude of fit criteria, characterized by , that the routine for evaluating a passport calculation also includes routines for calculating passport criteria, which - a maximum lateral deviation of an anterior resection of an outline (220) of a proximal end of an anterior section of the implant (118A, 188B), and / or - a percentage of the outline (220) of the proximal end of the anterior portion of the implant (118A, 188B) that lies on resected bone, and / or - a percentage of the outline (220) of the proximal end that lies on or above uncut surface of an anterior cortex, and / or - contain a maximum gap between the implant (118A, 188B) and the uncut sections of the anterior cortex. [20] Computer-readable medium according to claim 19, wherein the routine for obtaining information about the shape of the surface includes a routine for obtaining survey data points of the femur (32) by means of a pointer and a routine for assisting a user to obtain a desired set of data points to provide an image of the outline of the shape of the surface of the femur (32) sufficient to satisfy predetermined concept accuracy parameters. [21] Computer-readable medium according to claim 20, wherein the routine for defining basic position parameters further includes a routine for matching a selected varus-valgus angle, a rotation angle and a surface position of a posterior condyle and a distal condyle of an implant. [22] Computer-readable medium according to claim 20, wherein the routine for selecting the optimal size and position of the implant (118A, 188B) further includes a routine for comparing each fit calculation with a weighted algorithm for each fit criterion to determine the optimal size and position of the implant (118A, 188B) from all evaluated sizes and positions of implants (118A, 188B), wherein the optimal implant size at least minimizes notching and oversizing of the implant (118A, 188B). [23] Method for virtually planning the size and position of a femoral implant (118A, 188B) for a patient's femur (32), the method comprising the following steps: - Obtaining predetermined form factor information for a variety of different implants (118A, 188B); - Obtaining information about the shape of the surface of the femur (32); - Defining basic position parameters for a position of the implant (118A, 188B) with respect to a virtual representation of the femur (32); - Evaluating a fit calculation of each implant (118A, 188B) with respect to the virtual representation of the femur (32) based on a multitude of fit factors at each of a multitude of incremental positions with respect to the femur (32); and - Selecting the best-fitting implant (118A, 188B) and the best-fitting position from all the fit calculations, characterized by , that the step of evaluating a passport calculation includes an evaluation of the implant (118A, 188B) based on - of a maximum lateral angle of an anterior resection of an outline (220) of a proximal end of an anterior section of the implant (118A, 188B), and / or - a percentage of the outline (220) of the proximal end of the anterior portion of the implant (118A, 188B) that rests on resected bone, and / or - a percentage of the proximal outline (220) of the end that lies on or over an uncut portion of an anterior cortex, and / or - the maximum gap between the implant (118A, 188B) and the uncut surface of the anterior cortex. [24] Method according to claim 23, wherein the step of obtaining the surface shape of the femur (32) includes a step of performing a measurement of the femur surface. [25] Method according to claim 23, wherein the steps of measuring and selecting are carried out prior to a step of resecting the femur (32). [26] Method according to claim 25, further comprising the step of manually adjusting the calculated optimal size and position. [27] Method according to claim 25, wherein the calculation step includes the step of evaluating a plurality of fit parameters. [28] Method according to claim 27, wherein the plurality of fitting parameters includes parameters about rigid bone shapes and parameters about the shape of implants (118A, 188B). [29] Method according to claim 23, wherein the step of selecting the best-fitting implant (118A, 188B) and the best-fitting position includes the step of comparing the evaluated fit accuracies with a weighted algorithm to identify an optimal size and position. [30] Method according to claim 23, further comprising the step of determining a resection level for the femur (32). [31] Method according to claim 23, wherein the base position parameters are used to calculate a maximum gap between the implant (118A, 188B) and the uncut surface of an anterior cortical bone. [32] Method according to claim 23, wherein the step of evaluating a fit calculation optionally includes steps of previewing a size of a flexion and a strain gap for a medial and lateral side, capturing medial / lateral overhangs, cutting a proximal tibia (16) and previewing an insert, estimating a medial condyle (14) for a varus knee and using a navigation-guided drilling template for anterior-posterior alignment. [33] Method for evaluating the fit of a femoral implant (118A, 188B) to a distal end of a femur (32) in a selected orientation prior to resection of the femur (32), the method comprising the following steps: - Obtaining predefined information about the shape factors of the femoral implant (118A, 188B); - Obtaining information about the shape of the surface of the distal end of the femur (32); and - Performing a virtual fit assessment at each of all possible incremental positions of a predefined set of incremental positions for an implant (118A, 188B) of each size to be considered, prior to resecting the femur (32), characterized by that the step of carrying out a passport assessment - the step of calculating a maximum lateral runout of an anterior resection of the femur from an outline (220) of the proximal end of the femoral implant (118A, 188B), and / or - the step of calculating a percentage of that outline (220) of a proximal end that lies on sectioned anterior cortical bone, and / or - includes the step of calculating a percentage of the outline (220) of a proximal end that lies on or above uncut anterior cortical bone, and / or - includes the step of calculating a maximum gap between the femoral implant (118A, 188B) and the uncut anterior cortical bone. [34] Method according to claim 33, wherein a desired reconstruction position is defined on the basis of concept parameters for matching a selected varus or valgus angle, a rotation angle and a surface position of the posterior condyle and distal condyle of the femur (32). [35] Method according to claim 33, wherein the step of performing a fit assessment includes the step of comparing the assessed fit accuracies with a weighted algorithm to identify an optimal size and position. [36] Method according to claim 33, wherein the step of performing a fit assessment optionally includes steps of previewing a size of a flexion and extension gap for a medial and lateral side, determining medial / lateral overhang, cutting a proximal tibia (16) and previewing an insert, estimating the medial condyle (14) for a varus knee and using a navigation-guided drilling template for anterior-posterior alignment.

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