Method for generating a kinematic alignment reference system
A computer-based method for generating a kinematic alignment reference system in bone reconstruction addresses the challenge of manual axis identification by using 3D modeling and personalized plane generation, enhancing the efficiency and accuracy of surgical planning.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-08-26
- Publication Date
- 2026-03-19
AI Technical Summary
Existing bone reconstruction methods, particularly in knee arthroplasty, lack the ability to accurately and efficiently identify personalized kinematic alignment reference systems, leading to non-optimal results due to the complexity and expense of manual axis identification.
A computer-executable method for generating a kinematic alignment reference system by acquiring a 3D model of the patient's femur, selecting key points, and generating approximating surfaces and planes to define personalized reference planes for cutting guidance.
Facilitates rapid and effective identification of cutting positions and orientations, optimizing bone reconstruction operations by adapting to individual patient anatomy, reducing complexity and cost.
Smart Images
Figure IB2025058559_19032026_PF_FP_ABST
Abstract
Description
[0001] “METHOD FOR GENERATING A KINEMATIC ALIGNMENT REFERENCE SYSTEM” DESCRIPTION
[0002] The present invention relates to a method, specifically a computerexecutable method, for generating a reference system to be used in a bone reconstruction operation performed following the kinematic alignment approach.
[0003] In the context of a bone reconstruction operation, with particular reference to the application of a prosthesis for the knee, a classic approach involves seeking to obtain a mechanical alignment in which a resection is made in the distal portion of the femoral bone perpendicular to its mechanical axis in order to have a balanced distribution of loads on the prosthesis.
[0004] However, this universal approach has the disadvantage of not taking into account in any way the specificities of the bone and joint structure of the individual patient, entailing the risk of non-optimal final results.
[0005] To overcome this problem, modern medicine is increasingly moving towards personalised solutions that can adapt as much as possible to the characteristics of the patient and in this context a solution of great interest is represented by the kinematic alignment (KA alignment) approach.
[0006] In accordance with this technique, the objective is to reconstruct the specific alignment of the patient's limbs as well as to completely restore his or her biomechanical situation based on the patient's specific kinematic axes.
[0007] By way of example, in the case of a patient suffering from arthritis, an arthroplasty operation of the femur can be performed by resecting the bone along cutting axes specifically selected on the basis of the patient's pre-arthritic kinematic axes.
[0008] However, the operation just illustrated is extremely complex and expensive as the identification of the correct reference axes, as well as then the position and inclination of the cuts to be made for resecting the femoral bone, requires a particularly accurate and precise evaluation. In this context, the need to develop new methods and processes that are able to automate and speed up the identification of a reference system on the basis of which the cuts to be made can be positioned and oriented on the femoral bone is strongly felt.
[0009] In this context, the technical task underlying the present invention is to propose a method that overcomes at least some of the drawbacks of the aforementioned prior art.
[0010] In particular, it is an object of the present invention to make available a method for generating a reference system to be used in a bone reconstruction operation performed according to the kinematic alignment technique that is able to allow the clear, rapid and effective identification of the position and orientation of the cuts to be made and the tools necessary for their realization.
[0011] The technical task mentioned and the objects stated are substantially achieved by a method comprising the technical features set out in one or more of the appended claims.
[0012] According to the present invention, a computer-executable method for generating a reference system for kinematic alignment in a bone reconstruction is shown.
[0013] The method is performed by acquiring a 3D model of a patient's femur at a pre-operative stage.
[0014] 3 points are selected on the anterior cortex of a distal end of the femur.
[0015] A plurality of distal points, preferably 3 points, even more preferably 10 points, are further selected on a distal superficial portion of each condyle.
[0016] A plurality of posterior points, preferably 3 points, even more preferably 10 points, are further selected on a posterior superficial portion of each condyle.
[0017] A provisional coronal plane passing through the 3 reference points, respectively through the reference 10 points, is generated.
[0018] A distal approximating surface is also generated for each condyle.
[0019] Each distal approximating surface is generated as a function of respective distal points.
[0020] A posterior approximating surface is also generated for each condyle.
[0021] Each posterior approximating surface is generated as a function of respective posterior points.
[0022] Each approximating surface approximates a conformation of the respective condyle surface.
[0023] Once the provisional coronal plane and the approximating surfaces have been obtained, it is possible to generate an axial plane and a final coronal plane.
[0024] In particular, the axial plane is generated such that it is perpendicular to the provisional coronal plane, facing the distal superficial portions and tangent to each distal approximating surface.
[0025] The final coronal plane is instead generated in such a way that it is perpendicular to the axial plane, facing the posterior superficial portions and tangent to each posterior approximating surface.
[0026] The axial plane and the final coronal plane define (or contribute to defining) the reference system.
[0027] Advantageously, the method described here allows to obtain in a particularly efficient way a personalised reference system adapted to the specific anatomy of the patient.
[0028] The present invention also relates to a computer program configured to cause the execution of the claimed method as well as an IT system configured to execute the method.
[0029] The dependent claims, incorporated herein by reference, correspond to different embodiments of the invention.
[0030] Further characteristics and advantages of the present invention will become more apparent from the approximate and thus non-limiting description of a preferred, but not exclusive, embodiment of a method for generating a reference system, as illustrated in the accompanying drawings, of which:
[0031] - figures 1A-1 C show some of the stages of the claimed method in which a plurality of points are identified on respective surfaces of a femur, in particular, figure 1A shows a front view of the distal end of the femur, figure 1 B shows a distal view, i.e. from below, of the distal end of the femur and figure 1 C shows a rear view of the distal end of the femur;
[0032] - figures 2A-2B illustrate one of the stages of the method in which a provisional coronal plane is identified;
[0033] - figures 3A-3B illustrate one of the stages of the method in which an axial plane is identified;
[0034] - figures 4A-4B illustrate one of the stages of the method in which a final coronal plane is identified;
[0035] - figure 5 illustrates a reference system obtained by performing the claimed method.
[0036] The method described herein allows obtaining a reference system to be used during a bone reconstruction operation to be performed according to the kinematic alignment technique.
[0037] In particular, the method finds advantageous use in the planning and then subsequent execution of the reconstruction of a knee bone, for example a femur.
[0038] Said method is executable by a computer, i.e. any electronic device comprising one or more processing units, processors, electronic components equipped with computing and manipulation capabilities of the inputs provided for correct execution of the method and presented in the following of the present description.
[0039] In this context the claimed method is performed by acquiring a three- dimensional model of a patient's femur at a pre-operative stage.
[0040] In other words, information is acquired by means of known manners (for example, by means of a tomographic technique or by reconstructing a three-dimensional model from two-dimensional radiographic images), which allows to generate and acquire a three-dimensional representation of the femur on which the bone repair operation must be performed.
[0041] It is then proceeded with the identification of a plurality of points on the surface of the femur, which will be used as starting information for the subsequent operative stages of the method.
[0042] The identification of such points can be performed for example by acquisition of one or more inputs by a user.
[0043] For example, the method may be executed by displaying the three- dimensional representation of the femur on a video terminal and the user may indicate and select specific points on its surface by means of a pointer or by touch in case the video terminal is a touch screen.
[0044] Alternatively, the points can be selected autonomously and automatically by the computer, for example a surface or a surface portion of the femur on which the points are to be selected and by identifying specific structural characteristics (a particular bone conformation, a particular surface area) or by selecting a series of random points within the surface of interest.
[0045] In the event that the points are identified by selecting specific structural characteristics of the femur, these characteristics can for example be identified and provided by a user, or be acquired by a computer by means of a stage of querying a database containing information about specific structural characteristics of interest.
[0046] In the event that the points are acquired randomly, it is possible to impose a constraint regarding their mutual distance or their density within the surface of the femur (for example, by imposing no more than a predetermined number of points per each unit of surface, e.g. per each cm2)
[0047] More in detail, reference points 12, specifically 3 reference points 12, are selected on the anterior cortex 11 C of a distal end 10 of the femur, as illustrated in figure 1 A.
[0048] The term “distal” is intended to mean the end of the femur that contributes to defining the knee joint while, for the sake of completeness, the “proximal” end is usually understood to be the end interfaced with the hip.
[0049] The anterior cortex 11 C is thus defined as the anterior surface of the body of the femur in a position thereof proximal to the condyles 11 A, 11 B. In this context, the term “anterior” is intended to identify a portion of the surface of the femur facing frontally with reference to the patient’s body.
[0050] Similarly, the term “posterior” that will be used hereinafter refers to portions and surfaces of the femur positioned, facing, oriented posteriorly with reference to the patient’s body.
[0051] A plurality of points on the condyles 11 A, 11 B of the femur are also identified.
[0052] More in detail for each condyle 11 A, 11 B at least 2 points are selected, preferably at least 3, even more preferably at least 4, in a distal surface thereof (as shown in figure 1 B) and in a posterior surface thereof (as shown in figure 1 C).
[0053] Specifically, a portion of the distal surface of the medial condyle 11 A and a portion of the distal surface of the lateral condyle 11 B are identified and respective groups of points are selected on each of them.
[0054] The term distal surface is intended to mean the inferior surface of the respective condyle 11 A, 11 B, i.e. the surface opposite the proximal end of the femur.
[0055] Similarly, a portion of the posterior surface of the medial condyle 11 A and a portion of the posterior surface of the lateral condyle 11 B are identified and respective groups of points are identified on each of them.
[0056] As discussed, the term posterior is to be understood with reference to the patient's body and therefore the posterior surfaces of the condyles 11 A, 11 B are surfaces facing posteriorly when the knee joint is not flexed, i.e. when the tibial bone is aligned (or substantially aligned) with the femur.
[0057] In general, the selected superficial portions may coincide with and / or be included in the distal and posterior articular surfaces of the condyles 11 A, 11 B.
[0058] The execution of the operations described herein therefore leads to selecting the following groups of points:
[0059] - a first group of points, namely the three distal points 13, selected on the anterior cortex 11 C; - a second group of points, consisting of the distal points 13 selected on the distal superficial portion of the medial condyle 11 A;
[0060] - a third group of points, consisting of the selected distal points 13 on the distal superficial portion of the lateral condyle 11 B;
[0061] - a fourth group of points, consisting of the posterior points 14 selected on the posterior superficial portion of the medial condyle 11 A;
[0062] - a fifth group of points, consisting of the posterior points 14 selected on the posterior superficial portion of the lateral condyle 11 B.
[0063] In particular, the selection of the points can be carried out in such a way as to ignore any osteophyte or similar element that do not contribute to defining the normal articular structure of the femur.
[0064] Therefore, each point of those defined and identified above is selected in a respective osteophyte-free position of the femur.
[0065] To further optimize the process of identifying and selecting the points of interest, with particular reference to the points contributing to defining the groups from the second to the fifth one, each distal superficial portion and each posterior superficial portion is circumscribed in a polygon of predefined dimensions.
[0066] Preferably, each distal superficial portion and each posterior superficial portion has a substantially rectangular shape having a major side comprised between 1 and 55 mm and a minor side comprised between 1 and 30 mm.
[0067] Alternatively, each distal superficial portion and each posterior superficial portion may have any shape having a similar superficial extension.
[0068] This feature allows to circumscribe the zone of selection of the points of interest, facilitating their identification and allowing to define even more clearly, quickly and immediately the zones in which to identify the information of interest for the execution of the method.
[0069] In this context, if the acquisition of the points is carried out autonomously by the computer, it is possible to select the points randomly within the respective selection zones by imposing, for example, constraints such as a minimum distance between the points or a greatest density value of the points.
[0070] Advantageously, the method may further comprise a verification step in which a user modifies and / or validates the position of each point.
[0071] In other words, it is possible to acquire an input from a user (for example medical / healthcare personnel) to validate and optimize the selection of the points, possibly adapting it and verifying it in light of the specific needs of the operation to be performed and / or the needs of the patient.
[0072] In general, as discussed above, the selection of the points can also be performed by the user.
[0073] The groups of points identified so far, and possibly validated by the user, allow to identify / define / calculate respective plans and surfaces that in the manners detailed below will lead to the generation of the reference plan of interest.
[0074] In detail, the first group of points is used for the generation of a provisional coronal plane CP-CP.
[0075] Specifically, the method is executed by generating a provisional coronal plane CP-CP passing through the 3 reference points 12, as illustrated in figures 2A and 2B.
[0076] As illustrated in figure 3A, the second and third groups of points are instead used to generate respective distal approximating surfaces 15 which approximate a conformation of the distal superficial portion of the respective condyles 11 A, 11 B.
[0077] In a similar and corresponding manner, as visible in figure 4A, the fourth and fifth groups of points are instead used to generate respective posterior approximating surfaces 16 which approximate a conformation of the posterior superficial portion of the respective condyles 11 A, 11 B.
[0078] In other words, for each condyle 11 A, 11 B a distal approximating surface is generated as a function of the respective distal points 13 and a posterior approximating surface as a function of the respective posterior points 14, and as discussed each approximating surface is configured to approximate a superficial conformation of the respective surface to which it is associated.
[0079] Operationally, if only two points have been selected for each group of points, the approximating surface is generated by imposing as limits the passage through these two points and additionally also a further constraint, for example the tangency to a specific area / portion / structural element of the femur.
[0080] This additional constraint can be imposed / provided by the user or be generated a priori by the computer on the basis of predefined rules and, for example, stored in a suitable database that can be queried by the computer.
[0081] If, on the other hand, each group comprises three points, then the approximating surface is identified by generating the plane passing through those three points.
[0082] If, on the other hand, each group of points comprises 4 points, then each approximating surface has a spherical conformation.
[0083] In other words, the profile of the distal and posterior superficial portions of the condyles 11 A, 11 B is approximated with spherical surfaces.
[0084] Advantageously, the use of spherical surfaces represents an optimal balance between the simplicity of computing and surface management and the accuracy and reliability of the result obtained.
[0085] In the event that each group of points comprises a greater number of points, instead, the surface will be a surface modelled by interpolating the selected points.
[0086] For example, to further optimize the quality and actual conformity of the approximating surfaces, the second, third, fourth, and fifth groups of points may each comprise 10 points.
[0087] Thus, for each condyle 11 A, 11 B at least 10 anterior points on a distal superficial portion and at least 10 posterior points 14 on a posterior superficial portion are selected.
[0088] This number also represents in this case an optimal balance between a low use of computational resources for the generation of the approximating surfaces and an optimal conformity with respect to the structure of the surface being approximated.
[0089] It is also highlighted that it is possible that at least one group of points has a number of points different from that of at least another group.
[0090] Therefore, one could have, for example, a first group of points comprising 3 points and generating a flat approximating surface and a second group of points comprising 4 points generating a spherical approximating surface, while the third and fourth group of points could still consist of a different number of points.
[0091] Once the provisional coronal plane CP-CP and the approximating surfaces (two approximating surfaces of respective distal or inferior portions of the condyles 1 1 A, 1 1 B and two approximating surfaces of respective posterior portions of the condyles 1 1 A, 1 1 B) have been obtained, an axial plane A-A can be generated.
[0092] In detail, this axial plane A-A is generated in such a way as to meet the following requirements: the axial plane A-A is perpendicular to the coronal plane, in addition the axial plane A-A also faces the distal superficial portions and finally is also tangent to each distal approximating surface.
[0093] In other words, as can be observed in figure 3B, when observed in the provisional coronal plane CP-CP, the axial plane A-A represents the junction line of the most distal points of the condyles 11 A, 1 1 B, i.e. of the distal approximating surfaces 15.
[0094] By the expression “most distal points” it is intended to mean the points of each condyle that are absolutely the most distant from the proximal end of the femur and therefore the axial plane A-A can also be seen in the provisional coronal plane Cp-Cp as the line passing through these points.
[0095] A final coronal plane C-C is also subsequently generated which in turn meets the following requirements: the final coronal plane C-C is perpendicular to the axial plane A-A, the final coronal plane C-C also faces the posterior superficial portions and is tangent to each posterior approximating surface.
[0096] In other words, as can be observed in figure 4B, when observed in the axial plane A-A, the final coronal plane C-C represents the junction line of the most posterior points of the condyles 1 1 A, 1 1 B, i.e. of the posterior approximating surfaces 16.
[0097] By the expression “most posterior points” it is intended to mean the points that are absolutely the most distant from an anterior face of the condyles 11 A, 11 B and therefore the final coronal plane C-C can also be seen in the axial plane A-A as the line passing through these points.
[0098] Preferably, in order to also take into account the presence and therefore the thickness due to the cartilage associated with the femur (specifically at its distal end 10) the method further comprises a step of distancing the axial plane A-A and the final coronal plane C-C from the approximating anterior and posterior surfaces, respectively by a distance comprised between 1 and 3 millimetres.
[0099] Optionally, this distance can also be selected as a function of the anatomical specificities of the patient (for example as a function of a specific thickness of the cartilage layer at the respective surfaces of the condyles 1 1 A, 11 B).
[0100] This approach is particularly useful in the event that the 3D model of the femur has been obtained by means of a technique capable of visualizing only the bony structure thereof (as happens for example by acquiring information by CT-scan tomography).
[0101] In the event that the 3D model is made using imaging techniques capable of visualizing both the cartilage and the bony structure (or if the 3D model is generated by combining these two pieces of information), it is possible to operate an optimal definition of the reference system by acting upstream of the generation of the planes of interest, thus specifically taking into account the conformation of the cartilaginous structure already in the generation stage of the approximating surfaces 15, 16.
[0102] In particular, in the event that the 3D model is representative of a bony structure of the femur and also of a cartilaginous structure at least of its distal portion, each approximating surface 15, 16 is generated in such a way as to approximate a conformation of the respective surface of the respective condyle as a function also of a thickness of said cartilaginous structure.
[0103] Therefore, each approximating surface 15, 16 can be generated by taking into account the need to approximate also a layer of cartilage being for example enlarged or modified or shaped with respect to the surface that would be obtained by considering only the distal 13 or posterior 14 points, or translates moving away from the surface of the condyle 11 A, 11 B by a distance congruent with the local thickness of the layer of cartilage at the approximated superficial portion.
[0104] Therefore, it is possible to determine a thickness (or an average thickness) of a cartilaginous layer associated with the condyles 11 A, 11 B, generate the approximating surfaces 15, 16 and subsequently modify, for example translate, the approximating surfaces 15, 16 as a function of the determined thickness in such a way that the approximating surfaces 15, 16 identify and are representative of a superficial conformation of the structure defined by the condyles 11 A, 11 B with the respective layers of cartilage associated with them.
[0105] Once the axial plane A-A and the final coronal plane C-C have been identified (by optionally moving them away from the distal end 10 of the femur to take into account the cartilage or generated already with an offset thanks to the use of approximating surfaces 15, 16 that already take into account this cartilage), the definition of the reference system for a kinematic alignment of the bone reconstruction operation is obtained.
[0106] In fact, the axial and final coronal planes are obtained in an extremely personalised way using as reference specific points, surfaces and planes generated and designed as a function of the conformation of the patient's femur.
[0107] It is also possible to identify a sagittal plane S-S by selecting a plane perpendicular to the axial plane A-A and the coronal plane C-C, as well as passing, for example, through the intercondylar fossa of the femur.
[0108] Advantageously, once the optimal reference system has been defined for the specific patient of interest, it is possible to query a database comprising a plurality of cutting guides.
[0109] In other words, it is possible to consult a database within which a plurality of cutting guides with different characteristics (structure, conformation, dimensions,...) are stored.
[0110] It is then possible to select at least one cutting guide based on a conformity between each cutting guide and the reference system.
[0111] Cutting guides are then selected and preferably prepared which, due to their structure and dimensions, once they are implemented, allow the necessary cuts to be made directly along the lines defined by the reference plane without the need for medical personnel to perform further alignment or adaptation operations to the patient's anatomy.
[0112] In accordance with a further possible embodiment, the reference system can be generated by a simplified procedure in which instead of the distal points 13 and the posterior points 14 on the surfaces of interest of the condyles 11 A, 11 B individual points are identified in turn used to generate reference lines as a function of which the planes of interest are identified.
[0113] Specifically, starting from the acquisition of the 3D model of a patient's femur at a pre-operative stage, the 3 reference points 12 are still selected on the anterior cortex 11 C in such a way as to be able to generate the provisional coronal plane CP-CP according to the manners presented above.
[0114] At this point, instead of selecting the distal points 13 and the posterior points 14, it is possible to select for each condyle 11 A, 11 B an end point and a rearward point.
[0115] Each end point corresponds to the most inferiorly protruding point of the respective condyle 11 A, 11 B, i.e. the point presenting the greatest distance from a proximal end of the femur or from the anterior cortical portion in which the reference points 12 have been selected.
[0116] Correspondingly, each rearward point corresponds to the most protruding point posteriorly to the respective condyle 11 A, 11 B, i.e. it represents the point presenting the greatest distance from an anterior face of the respective condyle 11 A, 11 B.
[0117] A distal line and a posterior line are thus generated.
[0118] Specifically, the distal line is generated / defined as the line passing through the two end points, while the posterior line is generated / defined as the line passing through the two rearward points.
[0119] In this context, the axial plane A-A is generated perpendicular to the provisional coronal plane CP-CP and passing through the distal line, i.e. the distal line lies in the axial plane A-A.
[0120] Subsequently, the final coronal plane C-C is generated perpendicular to the axial plane A-A and passing through the posterior line, i.e. the posterior line lies in the final coronal plane C-C.
[0121] Also in this case, the reference system is defined on the basis of the axial A-A and final coronal C-C planes thus obtained, with the possible addition of the sagittal plane S-S in the same manner as those set out above.
[0122] Similarly, all the stages and processes described above relating to the selection of points of interest as well as the positioning of the planes A-A, C-C and CP-CP may remain applicable in an identical or corresponding manner, if compatible, even in this embodiment.
[0123] Specifically, it is possible to check and / or verify and / or modify and / or validate the position of the selected points (reference points 12, end points and rearward points) by a user.
[0124] Such points are also preferably selected in this context in an osteophyte- free portion of the femur or in any case ignoring the structure of such osteophytes.
[0125] In addition, both the distal and posterior lines and the planes generated as a function of them can be distanced from the surface of the femur to take into account the possible thickness of the cartilaginous layer associated with the condyles.
[0126] In particular, it is possible to implement a step of moving away from the femur the distal and posterior lines by a distance comprised between 1 and 3 mm or in general by a distance equal to at least a corresponding local thickness of the cartilaginous layer.
[0127] This away-movement can also be carried out by moving the respective end and rearward points away from the condyles 11 A, 11 B by a distance equal to a thickness of the cartilaginous layer at these points and generating distal and posterior lines passing through the points that have already being so distanced.
[0128] In general, the method described herein allows, regardless of its specific manner of execution, to identify the cutting guides that best adapt and are best configured to operate as a function of the specific personalised reference system that has been generated.
[0129] Advantageously, the present invention therefore achieves the proposed objects by overcoming the drawbacks complained of in the prior art by making available to the user a method that allows to facilitate and optimize the identification of a reference system for the execution of a bone reconstruction operation, as well as to identify and select the most suitable tools to execute it.
[0130] The present invention also relates to a computer program comprising instructions configured to cause an IT system (a computer / calculator or a similar electronic device equipped with computing capacity) to execute a method having the characteristics presented above according to one or both of the possible implementable manners described.
[0131] In this way, the user has the possibility to select, also as a function of the computing capacity of the computer used to implement the method, the available information and / or the specific operational needs related to the timing and health status of the patient, the manner that best meets his / her needs.
[0132] Likewise, the present invention also relates to the IT system configured for the execution of the aforementioned computer program and comprising a computing unit configured for the execution of the method described herein according to one or both of the possible implementable manners set forth. Such an IT system may further comprise input / output peripherals (e.g. displays and touch screens) by means of which the user can verify and validate the results obtained.
Claims
CLAIMS1. Computer-executable method for generating a reference system for kinematic alignment in a bone reconstruction, said method comprising the stages of:- acquiring a 3D model of a patient's femur at a pre-operative stage;- selecting 3 reference points (12) on an anterior cortex (11 C) of a distal end (10) of the femur;- for each condyle (11 A, 11 B), selecting at least 3 distal points (13) on a distal superficial portion of said condyle (11 A, 11 B) and at least 3 posterior points (14) on a posterior superficial portion of said condyle (11A, 11 B);- generating a provisional coronal plane (CP-CP) passing through the 3 reference points (12);- for each condyle (11 A, 11 B), generating a distal approximating surface (15) as a function of the respective distal points (13) and a posterior approximating surface (16) as a function of the respective posterior points (14), each approximating surface being adapted to approximate a conformation of the respective surface of said condyle (11 A, 11 B).- generating an axial plane (A-A) perpendicular to the provisional coronal plane (CP-CP), facing the distal superficial portions and tangent to each distal approximating surface (15);- generating a final coronal plane (C-C) perpendicular to the axial plane (A- A), facing the posterior superficial portions and tangent to each posterior approximating surface (16), said reference system being defined by the axial plane (A-A) and the final coronal plane (C-C).
2. Method according to claim 1 , wherein for each condyle (11 A, 11 B) at least 10 anterior points are selected on a distal superficial portion of said condyle (11 A, 11 B) and at least 10 posterior points (14) on a posterior superficial portion of said condyle (11 A, 11 B)3. Method according to claim 1 or 2, wherein each point is selected in arespective osteophyte-free position of the femur.
4. Method according to any one of the preceding claims, wherein each distal superficial portion and each posterior superficial portion has a substantially rectangular shape having a major side comprised between 1 and 55 mm and a minor side comprised between 1 and 30 mm5. Method according to any one of the preceding claims, comprising a verification step in which a user modifies or validates the position of each point.
6. Method according to any one of the preceding claims, wherein at least 4 distal points (13) and at least 4 posterior points (14) are selected for each condyle (11 A, 11 B) and wherein each approximating surface (15, 16) has a spherical conformation.
7. Method according to any one of the preceding claims, comprising a step of distancing the axial plane (A-A) and / or the final coronal plane (C-C) from the anterior and posterior approximating surfaces, respectively, by a distance comprised between 1 and 3 mm.
8. Method according to any one of the preceding claims 1 to 6, wherein said 3D model is representative of a bony structure of the femur and a cartilaginous structure of at least the distal portion of said femur, each approximating surface being adapted to approximate a conformation of the respective surface of the respective condyle (11 A, 11 B) as a function also of a thickness of said cartilaginous structure.
9. Method according to any one of the preceding claims, further comprising the stages of:- querying a database comprising a plurality of cutting guides;- selecting at least one cutting guide based on a conformity between each cutting guide and the reference system.
10. Computer-executable method for generating a reference system for kinematic alignment in a bone reconstruction, said method comprising the stages of:- acquiring a 3D model of a patient's femur at a pre-operative stage;- selecting 3 reference points (12) on an anterior cortex (11 C) of a distal end (10) of the femur;- for each condyle (11 A, 11 B), selecting an end point presenting the greatest distance from a proximal end of the femur and at least one rearward point presenting the greatest distance from an anterior face of the respective condyle (11 A, 11 B);- generating a provisional coronal plane (CP-CP) passing through the 3 reference points (12);- generating a distal line passing through the extreme points and a posterior line passing through the rearward points;- generating an axial plane (A-A) perpendicular to the provisional coronal plane (C -C ) and passing through the distal line;- generating a final coronal plane (C-C) perpendicular to the axial plane (A- A) and passing through the posterior line, said reference system being defined by the axial plane (A-A) and the final coronal plane (C-C).11 . Computer program comprising instructions configured to cause an IT system to execute a method for generating a reference system for kinematic alignment in a bone reconstruction according to any one of the preceding claims.
12. IT system configured to execute a computer program according to claim 11 , said system comprising a computing unit configured to execute a method according to any one of the preceding claims 1 -10.