Method for constructing a femoral component of a total knee prosthesis

Abstract

The invention relates to a method for constructing at least one femoral component (101) comprising at least the preparatory steps of: constructing a three-dimensional model of the femur of a patient from digital medical images; determining a cutting template from morphometric data identified in the three-dimensional model; dividing the three-dimensional model into a plurality of working sections distributed in different planes and defined by a set of geometric points; obtaining, from the plurality of working sections, geometric variables defining a mediolateral width, a medial femorotibial contact surface, a lateral femorotibial contact surface and a patellofemoral contact surface; the construction method then comprising a step of constructing the at least one femoral component from the cutting template and the geometric variables.

Description

[0001] DESCRIPTION

[0002] TITLE: Method of constructing a femoral component of a total knee prosthesis

[0003] [Technical field]

[0004] The invention relates to a method of constructing a femoral component for a total knee prosthesis.

[0005] The invention finds a preferred application in the manufacture of a range of standard femoral components capable of being fitted to a plurality of patients having the same femoral size, as well as in the manufacture of personalized femoral components, specifically adapted to the kinematics of the knee and the morphology of the patients, for the restoration of the mobility of the joint that they replace.

[0006] [State of the art]

[0007] Due to increased life expectancy and the increasing prevalence of obesity, more and more people are suffering from osteoarthritis, a condition that wears down or destroys joint cartilage. This results in pain when walking or even at rest, which lowers quality of life. This is why knee arthroplasty is experiencing a growing boom today, with significant demand. The functional results of this surgical procedure have been improved in recent years thanks to: cutting-edge, more reliable, and less invasive techniques; better postoperative pain management; and the introduction of intense and early physiotherapy.

[0008] As is well known, a total knee replacement aims to remove the worn areas of bone and cartilage from the articular surfaces of the knee (distal part of the femur, proximal part of the tibia, and sometimes the patella) using artificial parts made from materials that are particularly resistant to mechanical and abrasive stresses, and working together to restore the mobility of the knee joints they replace.

[0009] A total knee replacement must also allow the patient to have stable support so that they can regain a good walking perimeter (good ability). Generally, a total knee replacement is only proposed and implemented in cases of serious injuries: advanced osteoarthritis, rheumatoid arthritis, traumatic destruction.

[0010] However, nearly 20% of patients today say they are dissatisfied with total knee replacement surgery, either because post-operative pain and pain persist after the total knee replacement surgery, or because the prosthesis does not meet their expectations in terms of joint mobility. Pain and lack of mobility are generally due to the fact that total knee replacements are offered for standard patient morphologies. While they may be suitable for the majority of patients, in some cases it turns out that their prosthetic size is unsuitable for the patient's morphology, that is to say the morphology, or size, of the distal part of the femur; and / or that of the proximal part of the tibia; and / or that of the patella.

[0011] The femoral component is also the most complex component of the prosthesis to design and manufacture because it must restore the kinematics of the original knee (for example, flexion and steering movements). For example, the mediolateral size of the femoral component must avoid contact with the medial and lateral tendino-ligamentous structures. Inadequate medio-lateral size can lead to abnormal tensioning of the tendino-ligamentous structures and excess pressure on the patellofemoral joint, thus inducing patellofemoral pain.

[0012] It is now known, for example from document US 2014 / 0228860, to design customized or standard femoral components using a purely surface approach, i.e. the femoral component is constructed to fit as closely as possible the external bone surface of the distal part of the femur resected from the patient in the context of a customized femoral component, or from several patients having the same femur size in the context of a standard femoral component. However, this purely surface approach has limitations, because it favors the real and possibly damaged external surface, without taking into account the joint kinematics.

[0013] Document US 20022 / 0087827 proposes to design a femoral component: from a three-dimensional model of a patient's distal femur, which is obtained from digital medical images of the patient's knee to which image processing methods are applied, and taking into account the joint kinematics of a patient's knee. The kinematics of the knee are taken into account by identifying, manually on the three-dimensional model or automatically on the digital medical images, landmarks relating to characteristics of the patient's distal femur, such as the curvatures of the medial and lateral condyles (a method for determining the curvatures of the two condyles of the distal femur is also proposed by document US 2019 / 0175351). However, the identification of the landmarks may not be sufficiently precise.In the case of manual implementation, identification depends on the judgment of a user who will manipulate the mesh of the three-dimensional model of the distal femur, whereas in the case of automated implementation, it depends on the quality of medical digital images and the efficiency of image processing methods.

[0014] [Summary of the invention]

[0015] The invention aims to address the issues set out above by aiming to:

[0016] - to significantly improve the correspondence between the prosthetic size and the initial morphology of the patient's knee,

[0017] - to adapt the articular surfaces of the femoral component of the total knee prosthesis in order to offer the possibility of kinematics as close as possible to the kinematics of the patient's knee physiology.

[0018] Thus, the invention relates to a method of constructing at least one femoral component for a total knee prosthesis, comprising the following preparatory steps:

[0019] - obtaining a set of digital medical images of a patient's femur;

[0020] - construction of a three-dimensional model of the femur from the associated set of digital medical images;

[0021] - determination of morphometric data in the three-dimensional modeling of the femur, said morphometric data characterizing a femoral size;

[0022] - determination of a cutting template in the three-dimensional modeling of the femur, based on morphometric data;

[0023] - sectioning the three-dimensional modeling of the femur into several working sections distributed in different planes, each working section being defined by a set of geometric points, the sectioning being such that the several working sections comprise posterior working sections distributed in different planes around a posterior axis of revolution in a medio-lateral direction, and anterior working sections distributed in different planes around an anterior axis of revolution in a medio-lateral direction and offset by a given center distance with the posterior axis of revolution along a femur axis in a proximo-distal direction;

[0024] - obtaining geometric variables representative of a geometry of the three-dimensional modeling of the femur in the several working sections, said geometric variables comprising first variables representative of a medio-lateral width, second variables representative of a medial femoro-tibial contact surface of a medial condyle, third variables representative of a lateral femoro-tibial contact surface of a lateral condyle, and fourth variables representative of a patellofemoral contact surface of a trochlea; said construction method then comprising a step of constructing at least one femoral component from the cutting template and values ​​of the geometric variables.

[0025] In other words, the construction of a femoral component according to the construction method of the invention is based first of all on the construction of a three-dimensional model of a femur, more precisely the distal part of the femur or distal femur, of a patient (or even of several patients in the context of a construction of a standard femoral component). For this purpose, several digital medical images of a distal femur of a patient are collected, which are taken from different viewing angles in order to ultimately model it in its entirety, to which digital processing is applied, for example a segmentation method.

[0026] Following digital image processing, a three-dimensional model of the distal femur is obtained, which corresponds to a three-dimensional mesh. The three-dimensional model of the distal femur includes three-dimensional models of the medial condyle, the lateral condyle, and the trochlea of ​​the distal femur.

[0027] In the remainder of this description, for convenience, the term "femur" refers to the distal femur.

[0028] From the three-dimensional modeling, morphometric data can be determined, corresponding for example to: precise points on the surface of the femur taken as a reference for surgeons, subsequently designated as remarkable points; and to dimensions of the femur. The remarkable points include in particular the most anterior point of the femur, and the most posterior point of each of the medial and lateral condyles. These three points allow the construction process to calculate / determine as a first approximation the size of the femur, or femoral size, of the patient; which is considered as morphometric data since it characterizes the morphology of the patient's femur.

[0029] From the initially estimated femoral size and other morphometric data (in particular the distal point and the most posterior point of each of the medial and lateral condyles) a cutting template can be determined (more precisely, a three-dimensional modeling of a cutting template). According to a possible embodiment of the invention, from other morphometric data, it is possible to re-evaluate the femoral size so that the value obtained is more precise.

[0030] Three-dimensional modeling of the cutting template is applied to the three-dimensional modeling of the femur in order to remove certain areas. This action relates to the manufacture and use of a cutting template, here a femoral template, which the surgeon applies to the bone surface of the femur to make bone cuts and define support surfaces of the femoral component to facilitate its installation. These cuts of the bone surface can also, for example, participate in removing growths (or osteophytes) that it may possibly present.

[0031] In the remainder of this description, for convenience, the cutting template refers to the three-dimensional modeling of the cutting template.

[0032] By extension, the cutting template has the same shape / curvature as the internal face of the femoral component which is applied and held on the surface of the distal femur. It is thus used to determine a three-dimensional model of a femoral component adapted to the cutting template, and therefore to the three-dimensional modeling of the resected femur.

[0033] It is from this modeling of the femoral component that a femoral component is ultimately constructed / manufactured which will be integrated into the knee prosthesis which will be fitted to the patient. It is understood that the femoral component has the same dimensional characteristics as its representative model.

[0034] In addition to the cutting template, the construction of the three-dimensional model of the femoral component (and therefore, by extension, of the physical femoral component), is based on the determinations:

[0035] - a mediolateral width of the distal femur, corresponding to the width between the most lateral point of the lateral condyle and the most medial point of the medial condyle and allowing to define / construct a medial contour / profile of the medial condyle and a lateral contour / profile of the lateral condyle; and

[0036] - different contact surfaces allowing the definition / construction of joint profiles to restore the kinematics of the knee: a medial femoro-tibial contact surface at the level of the medial condyle, a lateral femoro-tibial contact surface at the level of the lateral condyle, and a femoro-patellar contact surface at the level of the trochlea.

[0037] The mediolateral width and the contact surfaces are determined from geometric variables representative of the geometry of the three-dimensional modeling of the femur. The values ​​that these variables take are deduced from a set of geometric points, also representative of the three-dimensional modeling of the femur, included in sections, called working sections, included in different planes used to segment the three-dimensional modeling of the femur into different ones. In other words, the working sections are fictitious cutting planes of the three-dimensional modeling of the femur that are oriented in different directions and in which the construction process searches for the values ​​of the geometric variables.

[0038] More precisely, the working sections are distributed around two medio-lateral axes of revolution: an anterior axis of revolution and a posterior axis of revolution. The anterior and posterior axes of revolution are used respectively for the segmentation of the anterior part and the posterior part of the three-dimensional modeling of the distal femur. Each of the working sections around the anterior axis of revolution (called anterior working sections) and the posterior axis of revolution (called posterior working sections) is distant from the working sections closest to it anteriorly and posteriorly by an angular distance. This angular distance is for example less than or equal to 5 degrees, and in particular between 1 and 3 degrees.

[0039] In an alternative embodiment of the invention, the anterior, respectively posterior, angular distance separating an anterior, respectively posterior, working section from its close neighbors is the same for all the anterior, respectively posterior working sections. In another alternative embodiment, the anterior angular distance and the posterior angular distance are both less than or equal to 5 degrees, and for example of the order of 2 degrees.

[0040] The two axes of revolution are separated by a given center distance, the value of which depends, as a reminder, on the femoral size. This center distance is coincident in a sagittal plane which extends orthogonally to the anterior and posterior axes of revolution.

[0041] Advantageously, and as will be re-explained later, the construction method is applicable both: in the manufacture of a range of standardized femoral components, for which different femoral components are offered such that each is specifically adapted to a femoral size, and in the manufacture of specific or personalized components which are adapted to particular patient morphologies.

[0042] Another advantage of the construction process is that the three-dimensional modeling of the femoral component is fundamentally based on the search for morphometric, geometric and kinematic data in the three-dimensional modeling of the femur (whether for the construction of the three-dimensional modeling of the cutting box, the determination of the mediolateral width and the contact surfaces that define the joint kinematics). Thus, it is possible from the construction process to construct / manufacture femoral components that fall into the different types available on the market: cruciate retaining component, medial pivot component, posterior-stabilized component, and ultra-congruent component.

[0043] A third advantage of the construction process is to accelerate, whether for standard femoral components or custom femoral components, modeling / development times, and therefore manufacturing times.

[0044] According to a characteristic of the invention, the construction step implements a construction of profiles of the at least one femoral component by interpolation of the values ​​of the geometric variables.

[0045] According to a characteristic of the invention, the construction of profiles comprises constructions of a lateral profile and a medial profile by interpolation of the values ​​of the first variables, of a medial femoro-tibial articulation profile of the medial condyle by interpolation of the values ​​of the second variables, of a lateral femoro-tibial articulation profile of the lateral condyle by interpolation of the values ​​of the third variables, and of a patellofemoral articulation profile of the trochlea by interpolation of the values ​​of the fourth variables.

[0046] According to one embodiment of the invention, the interpolation is a third-order interpolation.

[0047] In other words, the values ​​of the geometric variables, identified in the different working sections segmenting the three-dimensional modeling of the femur, provide indications through which spatially the medial and lateral profiles, and the three articulation profiles, pass. Each of the five profiles is constructed by applying interpolation functions, for example, third-degree interpolation functions, to all the values ​​of the geometric variables through which they pass. The degree of precision of the profiles obtained depends on the number of values ​​to which the interpolation functions are applied, and their spatial proximity. In other words, the more the three-dimensional modeling is segmented into working sections of different orientations but relatively close to each other, the greater the precision of the profiles obtained.

[0048] According to one embodiment of the invention, the set of medical digital images comprises images from a medical scanner, for example in DICOM format. According to one characteristic of the invention, the determination of morphometric data comprises the determination of remarkable points in the three-dimensional modeling of the femur.

[0049] According to a characteristic of the invention, the remarkable points comprise at least one most posterior point of the medial condyle, one most posterior point of the lateral condyle and one most anterior point of a portion of the distal femur.

[0050] According to a characteristic of the invention, the cutting template comprises the placement of several femoral cuts which depend at least on the femoral size.

[0051] According to a characteristic of the invention, the several femoral cuts successively comprise an anterior femoral cut, an anterior chamfer cut, a distal femoral cut, a posterior chamfer cut and a posterior femoral cut.

[0052] In other words, a femoral template is composed of five successive femoral cuts (also called a cut box): an anterior femoral cut, an anterior chamfer cut, a distal femoral cut, a posterior chamfer cut and a posterior femoral cut. Each of these cuts is defined by dimensions: an anteroposterior dimension; an anterior height; and a posterior height which is linked by a linear law to the anterior height. These cuts can also be defined by other parameters, such as inclination angles or coordinates of cutting lines.

[0053] Advantageously, the construction method precisely models the five sections of the femoral template, determining the dimensions and orientations of each of them from, for example, remarkable points included in the morphometric data, and in particular the femoral size.

[0054] According to a characteristic of the invention, the several working sections comprise specific sections which pass through start or end lines of cutting of the femoral cuts of the cutting template, these start or end lines of cutting being in a medio-lateral direction.

[0055] According to a feature of the invention, the specific sections comprise at least one section which passes through a cutting start line of the anterior femoral cut, and one section which passes through a cutting end line of the posterior femoral cut.

[0056] In other words, each of the femoral cuts (or cutting boxes) constituting the cutting template is considered, in terms of representation, as being delimited by a cutting start line and a cutting end line extending mediolaterally; the cutting end line of a femoral cut being merged with the cutting start line of a succeeding femoral cut. The cutting template is then delimited at its ends by two cutting lines corresponding to the cutting start line of the anterior femoral cut, and the cutting end line of the posterior femoral cut.

[0057] Since the three-dimensional modeling of the femur is segmented into a plurality of working sections and the three-dimensional modeling of the cutting template is shaped to be applied thereto, this means that some of the working sections may optionally pass through some of the start and end cutting lines of the femoral cuts (cutting boxes) of the cutting template. These working sections are referred to in the invention as specific sections. According to different embodiments of the invention, one to several working sections may for example be comprised between two specific sections.

[0058] The segmentation of the three-dimensional modeling of the femur into a plurality of working sections may comprise by default two specific sections corresponding to the working sections passing through the start line of the anterior femoral cut, and the end line of the posterior femoral cut; which two specific sections may also be considered as reference sections from which the segmentation of the three-dimensional modeling of the femur is carried out insofar as:

[0059] - these two cutting lines are used to delimit, physically or in modeling, the distal part from the rest of the femur; and

[0060] - that the two cutting lines include the notable points used to determine the femoral size (the most anterior point of the distal femur for the start line of the anterior femoral cut; and the most posterior point of each of the two condyles for the end line of the posterior femoral cut) before segmentation.

[0061] According to a characteristic of the invention, the center distance is a function of the femoral size. For example, the center distance is expressed in the form of an affine function of the femoral size.

[0062] According to a characteristic of the invention, obtaining the first variables representative of the medio-lateral width implements an analysis of the geometric points of a medial contour and a lateral contour of the working section to determine two positions which are a position of a most medial point of the medial condyle and a position of a most lateral point of the lateral condyle on a reference axis of medio-lateral direction, said two positions constituting the first variables associated with the working section.

[0063] According to a characteristic of the invention, the reference axis is determined as being offset by a given spacing in a proximo-distal direction with respect to an extreme line in a medio-lateral direction passing through a most distal point of the lateral condyle or the medial condyle.

[0064] In other words, the mediolateral width of the three-dimensional model of the femur is determined, in each working section, between the most lateral position / point of the lateral condyle and the most medial point of the medial condyle on a reference axis. The two sets of most lateral points of the lateral condyle and most medial points of the medial condyle obtained in each of the working sections form, after application to each of said two sets of an interpolation function, an outer edge / contour of the lateral condyle and an outer edge / contour of the medial condyle which are used to determine the width of the three-dimensional model of the femoral component during its construction.

[0065] The method searches for the two positions on a reference axis which can correspond to a resection axis below which the distal part of the femur is resected (for example by removing osteophytes by image processing) according to the cutting box for the purpose of fitting the femoral component.

[0066] According to a characteristic of the invention, for each working section, obtaining the second variables representative of the medial femorotibial contact surface of the medial condyle implements an analysis of the geometric points of a mediolateral contour of the medial condyle to determine a medial condylar circle defined by coordinates of a medial center and by a medial radius, said coordinates of the medial center and said medial radius constituting the second variables associated with the working section.

[0067] According to a characteristic of the invention, the analysis of the geometric points of the medio-lateral contour of the medial condyle implements a circular regression on the geometric points of the medio-lateral contour of the medial condyle.

[0068] According to a characteristic of the invention, for each working section, obtaining the third variables representative of the lateral femorotibial contact surface of the lateral condyle implements an analysis of the geometric points of a mediolateral contour of the lateral condyle to determine a lateral condylar circle defined by coordinates of a lateral center and by a lateral radius, said coordinates of the lateral center and said lateral radius constituting the third variables associated with the working section.

[0069] According to a characteristic of the invention, the analysis of the geometric points of the medio-lateral contour of the lateral condyle implements a circular regression on the geometric points of the medio-lateral contour of the lateral condyle.

[0070] According to a characteristic of the invention, for each working section, obtaining the fourth variables representative of the femoro-patellar contact surface of the trochlea implements an analysis of the geometric points of a medio-lateral contour of the trochlea to determine a trochlear condylar circle defined by coordinates of a trochlear center and by a trochlear radius, said coordinates of the trochlear center and said trochlear radius constituting the fourth variables associated with the working section.

[0071] According to a characteristic of the invention, the analysis of the geometric points of the medio-lateral contour of the trochlea implements a circular regression on the geometric points of the medio-lateral contour of the trochlea.

[0072] In other words, the lateral femoro-tibial, medial femoro-tibial, and patellofemoral contact surfaces, which serve as previously indicated to restore the kinematics of the knee, are determined respectively from a lateral condylar circle, a medial condylar circle, and a trochlear circle moving respectively on the surface of the lateral condyle, the medial condyle, and the trochlea.

[0073] The geometric variables sought by the construction process in the different working sections (designated as second variables for the medial femoro-tibial contact surface, third variables for the medial femoro-tibial contact surface, and fourth variables for the patellofemoral contact surface) correspond to the coordinates of the center and the radius of each of the three circles.

[0074] In an alternative embodiment of the invention, in each of the working sections, a medio-lateral coordinate and a radial coordinate can be sought for each of the three circles. The medio-lateral coordinate and the radial coordinate are respectively determined for each working section by analyses of medio-lateral and sagittal geometric points included in the medio-lateral and sagittal profiles of each of the three compartments. A linear interpolation can then be applied by the construction method to the medio-lateral and radial coordinates of each of the working sections to determine a sagittal contour / trajectory on which the centers of each of the circles move, between each of the two anterior and posterior ends of the three-dimensional modeling of the femur.

[0075] In each of the working sections, the radii of the medial, lateral and trochlear circles describe respectively a medio-lateral contour of the medial condyle, the lateral condyle and the trochlea. Thus the geometric variables for each of the three radii correspond to geometric points / positions located on the surface of the two condyles and the trochlea, and aligned to form said medio-lateral contour. Obtaining the medio-lateral contours of the condyles and the trochlea are obtained by applying circular regressions on the geometric points identified for each of the three compartments in each of the working sections.

[0076] According to a feature of the invention, the working sections are divided into several series of working sections and, for each series of working sections, the geometric variables obtained in the working sections of said series are averaged to obtain average values ​​of the geometric variables, and the at least one femoral component is constructed from the cutting template and the average values ​​of the geometric variables in the several series, said at least one femoral component being called a customized femoral component.

[0077] As previously indicated, an advantage of the construction method is to allow the construction of a so-called standard femoral component that can be placed on a plurality of patients having the same femoral size, as well as the construction of a personalized femoral component adapted specifically to a given patient.

[0078] By definition, the working sections are divided into different working section series such that each of the working section series segments a part of the surface of the three-dimensional model of the femur, anteriorly or posteriorly. For example, each of the working section series may correspond to a segmental scan in a femoral slice (or in a cutting box) of the cutting template, for a total of five working section series.

[0079] Since the geometric variables are searched through the different work sections, this means that each of the work section series allows us to determine a set of several values ​​that each of the geometric variables can take. There are therefore, for each geometric variable, as many sets of values ​​as there are work section series (i.e., using the previous example, five sets).

[0080] In the case of the construction of a three-dimensional model of a custom femoral component, for each geometric variable: - the values ​​contained in the same set are averaged, making it possible to obtain an average value of the geometric variable in this series of working sections. In the previous example, this amounts to obtaining five average values ​​of the same geometric variable.

[0081] - an interpolation function is then applied to the average values, for the construction of the medio-lateral width and / or of at least one of the three contact surfaces.

[0082] Thus, the three-dimensional modeling of a standardized femoral component is constructed on the basis of the cutting template determined from the morphological data of the three-dimensional modeling of the patient considered, and the average values ​​of each of the geometric variables.

[0083] According to a feature of the invention, the preparatory steps are carried out on the basis of several sets of digital medical images of femurs of several patients characterized by several femoral sizes, thus obtaining for each femoral size a set of statistical data relating to the geometric variables; and the at least one femoral component, associated with one of the several femoral sizes, is constructed from the cutting template associated with this femoral size and statistical values ​​of the geometric variables in the set of statistical data associated with this femoral size, said at least one femoral component being called standard femoral component in this femoral size.

[0084] According to a feature of the invention, in the construction method several standard femoral components are constructed in the several femoral sizes from the statistical data sets associated with these several femoral sizes, these several standard femoral components thus forming a range of standard femoral components.

[0085] In the case of a standard femoral component of a given femoral size, the preparatory steps for constructing the three-dimensional model of the femoral component are repeated for several sets of medical digital images associated with several patient distal femurs.

[0086] For each of the three-dimensional models obtained from the digital image sets, the associated femoral size is determined. The three-dimensional femur models are then grouped according to the determined femoral size. For each group of three-dimensional models characterized by a femoral size value, a plurality of geometric variable values ​​are obtained, forming statistical data sets. From these statistical sets, “standard” values ​​of morphometric data and geometric variables can then be deduced / extracted, which allow the construction method to construct standard three-dimensional models of a cutting template and a femoral component applicable to all three-dimensional femur models in the group having the same femoral size.

[0087] According to a feature of the invention, the statistical data sets associated with the several femoral sizes are analyzed to establish mathematical relationships between the values ​​of the geometric variables and the femoral size.

[0088] In other words, in order to advantageously accelerate the construction times of the three-dimensional modeling of a standard femoral component and therefore of the manufacturing of the physical standard femoral component, the statistical sets of geometric variables are analyzed in order to identify evolutionary trends as a function of the femoral size which can be expressed in the form of mathematical relationships.

[0089] Thus, in the case where a three-dimensional modeling of a standard femoral component is to be constructed for a femoral size value not considered until now, it is sufficient to apply the mathematical relationships obtained with said femoral size value to calculate all the standard values ​​of morphological data and geometric variables necessary for the construction of said three-dimensional modeling of the standard femoral component according to this new size. In other words, once these mathematical relationships are established, it is possible to construct standard femoral components for any femoral size, by applying the mathematical relationships.

[0090] In one embodiment of the invention, the mathematical relationships are affine relationships.

[0091] In other words, the relationships linking each of the morphological data and each of the geometric variables to the femoral size are affine functions of the form y = ax + b; where y is the standard value of the morphometric data or geometric variable considered as a function of the femoral size; x is the femoral size; a is a slope coefficient; and b is representative of a difference in value for the morphometric data or geometric variable between the femoral size considered and a lower and / or higher femoral size.

[0092] [Brief description of the figures] Other characteristics and advantages of the present invention will appear on reading the detailed description below, of a non-limiting example of implementation, made with reference to the appended figures in which:

[0093] [Fig 1] is a schematic illustration of a total knee prosthesis, which consists of a femoral component, a tibial component, a patellar component (not shown) and an insert;

[0094] [Fig 2] groups together three-dimensional views of a three-dimensional model of a typical femoral component that can be constructed using the construction method, with two perspective views from the front (a) and back (b), and a profile view (c);

[0095] [Fig 3] illustrates two perspective views of a three-dimensional model of a patient's distal femur in which: the medial and lateral condyles, as well as the trochlea, are visible, with the first view (a) and the second view (b) oriented so that the medial condyle and the lateral condyle respectively face the observer; and morphometric data including notable points are identified;

[0096] [Fig 4] illustrates a perspective view (a) and a profile view (b) of the cutting template determined from the morphometric data, on which are visible all the femoral cuts composing it and each delimited by a start of cut line and an end of cut line; said start of cut and end of cut lines also being reported / represented on a perspective view (c) of the three-dimensional modeling of the femur;

[0097] [Fig 5] illustrates the segmentation of the three-dimensional modeling of the femur, which is represented here in a point cloud, into several anterior and posterior working sections respectively distributed around an anterior axis of revolution and a posterior axis of revolution, the two axes being distant from a center distance in a proximo-distal direction (a); and an example of superposition of three successive working sections articulated around one of the two axes of revolution;

[0098] [Fig 6] is a representation of all the geometric points modeling the distal femur, with its medial and lateral condyle as well as its trochlea, in a working section; on which are visible osteophytes having formed on the bony surface of the femur at the level of the ends of the two condyles and the trochlea / notch;

[0099] [Fig 7] is a representation of the three-dimensional modeling of the femur in the working section considered in Figure 6 after application of an osteophyte removal step; said representation showing that the set of points defining the three-dimensional modeling of the femur in the working section no longer includes the points modeling the osteophytes (or aberrant points);

[0100] [Fig 8] illustrates, for a second working section, the determination in said second working section of the medio-lateral width of the three-dimensional modeling of the femur;

[0101] [Fig 9] illustrates, for the working section of Figure 6, the difference in the medio-lateral width value obtained when the outliers included in the working section are kept or deleted when determining said medio-lateral width value;

[0102] [Fig 10] illustrates, for the working section presented in Figure 8, for all the points modeling the distal femur, the medial femoro-tibial contact surface of the medial condyle, the lateral femoro-tibial contact surface of the lateral condyle, and the patellofemoral contact surface of the trochlea;

[0103] [Fig 11] shows, in connection with Figure 10, the set of geometric variables used to determine the three aforementioned contact surfaces, namely: the coordinates of the center and the radius of the medial circle, the coordinates of the center and the radius of the lateral circle, and the coordinates of the center and the radius of the trochlear circle (or central circle);

[0104] [Fig 12] shows a front view (a) and two perspective views (b and c) of the three-dimensional modeling of the femoral component, for which are visible the medial and lateral profiles of said femoral component, the two femorotibial articulation profiles, the patellofemoral articulation profile, and the junction profiles between the trochlear circle with each of the medial and lateral circles.

[0105] [Detailed description of one or more embodiments of the invention]

[0106] With reference to Figure 1, a total knee prosthesis 100 is at least made up of a femoral component 101, a tibial component 102, and an insert 103 made of plastic (generally polyethylene) inserted between the femoral component 101 and the tibial component 102 to allow interaction between the two components and good sliding of the total knee prosthesis 100 in order to restore the kinematics thereof. Depending on the degree of degradation of the knee cartilage, the total knee prosthesis may also include a patellar component, not shown in Figure 1.

[0107] As previously indicated, the invention relates to a construction method for the construction of a femoral component 101 aiming at:

[0108] - to significantly improve the correspondence between the prosthetic size and the initial morphology of the patient's knee,

[0109] - to adapt the articular surfaces of the femoral component 101 of the total knee prosthesis 100 in order to offer the possibility of kinematics as close as possible to the kinematics of the physiology of the patient's knee.

[0110] In order to respond positively to these two points, the construction process allows the manufacture of:

[0111] - ranges of standardized femoral components 101, for which different femoral components are proposed such that each is specifically adapted to a femoral size; that is to say that the dimensions of a femoral component are a function of a femoral size value. Thus, a femoral component 101 of a given femoral size can be fitted to a plurality of patients having the same femoral size; as well as

[0112] - specific or personalized femoral components which are therefore by definition unique and each specifically adapted to the morphology of a patient's knee.

[0113] The construction process also covers the construction / manufacturing of all femoral component models 101 available on the market: cruciate retaining component, medial pivot component, posterior-stabilized component, and ultra-congruent component.

[0114] The method for constructing a femoral component 101 is based on two main phases. With reference to Figure 2, the first phase consists of a modeling phase resulting in a three-dimensional modeling of the femoral component 101. In one embodiment of the invention, this modeling phase is implemented by means of a 3D femoral component design tool 101 installed on a workstation, for example a desktop computer.

[0115] The second phase consists of the actual manufacturing / construction of the physical femoral component 101 based on sizing information provided by its three-dimensional modeling.

[0116] The modeling phase of a femoral component 101 includes several preparatory steps.

[0117] The first of these consists of collecting several medical digital images of a patient's distal femur, which are taken from different viewing angles. In the remainder of the description, for greater convenience, the term femur alone designates the distal femur. In one embodiment of the invention, these medical digital images may come from a medical scanner, and may have a format defined according to the norms and standards in force for data from medical imaging, for example the DICOM standard / format.

[0118] The recovered digital images are then subjected to digital processing, for example a segmentation method, in order to obtain a three-dimensional model of the femur 1 corresponding, as illustrated in Figure 5, to a point cloud virtually and spatially forming in its entirety the bone surface of the femur. With reference to Figure 3, the medial condyle 61, the lateral condyle 62, and the trochlea 63 are modeled in particular in the three-dimensional model of the femur 1.

[0119] In an alternative embodiment of the invention, the three-dimensional modeling of the femur 1 can also be modeled using a 3D meshing method. In a second alternative embodiment, both types of modeling are offered by the 3D design tool. In a third alternative, it is conceivable that the 3D design tool can offer an option for applying textures to the three-dimensional modeling of the femur 1 whose shades and colors are representative of a physical femur.

[0120] From the three-dimensional modeling of the femur 1, the construction process will, during several other preparatory stages:

[0121] - model a three-dimensional model of a cutting template 3, in relation to the femoral cutting templates used by surgeons and which are applied to the bone surface of the femurs to make bone cuts and define support faces of the femoral component 101 to facilitate its installation. In the remainder of the description, the term cutting template refers to the three-dimensional modeling of the cutting template.

[0122] - determine geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 representative of the geometry of the modeled femur.

[0123] The cutting template 3 and the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 are then used by the construction method to construct, during a construction step, a three-dimensional model of a femoral component 101 adapted to the three-dimensional modeling of the femur 1.

[0124] These several other preparatory steps will be the subject of the following description.

[0125] After constructing the three-dimensional model of the femur 1, the construction method determines in the modeling morphometric data representative for example of the dimensions, the thickness of the modeled femur. The morphometric data notably include reference points, designated as remarkable points, used by surgeons to manufacture femoral components 101.

[0126] Among these remarkable points, the construction method can in particular locate the most anterior point 22 of the femur (see Figure 3(b)), the most posterior point 21 of the medial condyle 61 (see Figure 3(a)), and the most posterior point 25 of the lateral condyle 62 which allow the construction method to calculate / determine as a first approximation the femoral size of the modeled femur; which femoral size is also considered as morphometric data since it characterizes the morphology of the femur.

[0127] From other morphometric data (and in particular other remarkable points), it is possible to re-evaluate the femoral size so that the value obtained is more precise.

[0128] With reference to Figure 3 and Figure 4, from the femoral size and other notable points, such as the most distal point 23 of the medial condyle 61 and the most distal point 24 of the lateral condyle 62 (see Figure 3(a)), as well as the aforementioned points 21, 22, 25, the construction method models the cutting template 3.

[0129] Similar to a conventional physical femoral cutting template, the three-dimensional modeling of the cutting template 3 consists of five successive femoral cuts 31, 32, 33, 34, 35 (or cutting boxes): an anterior femoral cut 31, an anterior chamfer cut 32, a distal femoral cut 33, a posterior chamfer cut 34 and a posterior femoral cut 35. Each of these femoral cuts 31, 32, 33, 34, 35 is defined by three dimensions which are a function of the femoral size: an anteroposterior dimension; an anterior height; and a posterior height which is linked by a linear law to the anterior height. They are also defined by other parameters, such as for example inclination angles or coordinates of cutting lines, which define their orientation in space.

[0130] In the three-dimensional modeling of the cutting template 3, the femoral cuts 31, 32, 33, 34, 35 are visually delimited by two mediolateral extension lines, namely a cutting start line 41 and a cutting end line 42. With the exception of the cutting start line 43 of the anterior femoral cut 31 and the cutting end line 44 of the posterior femoral cut 35, the cutting end line 42 of a femoral cut 31, 32, 33, 34, 35 is merged with the cutting start line 41 of the femoral cut 31, 32, 33, 34, 35 which succeeds it.

[0131] Note that the cutting template 3 has the same shape / curvature (due to the orientation of the femoral cuts 31, 32, 33, 34, 35) as the internal face of the femoral component which is applied and held on the surface of the femur (see Figure 2-c).

[0132] With reference to Figure 5, in order to determine the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3, the construction method sections / segments the three-dimensional modeling of the femur 1 into several working sections 5 distributed in different planes. In other words, these working sections 5 are virtually comparable to cutting planes. Thus, each working section 5 contains a set of geometric points representing a contour / a section of the modeled femur (with the two medial 61 and lateral 62 condyles, and the trochlea 63) according to the direction of the plane in which said working section 5 propagates. Figure 3-b illustrates a superposition of three contours / sections of the modeled femur, each of them belonging to a working section of different orientation.

[0133] As illustrated in Figure 5-a, the working sections 5 include anterior working sections 51 and posterior working sections 52:

[0134] - distributed respectively around an anterior axis of revolution 501 and a posterior axis of revolution 502, with the two axes of revolution 501, 502 in a medio-lateral direction; and

[0135] - which respectively segment / section the anterior part and the posterior part of the three-dimensional modeling of the distal femur 1.

[0136] Each of the anterior working sections 51 (respectively posterior 52) is angularly offset from the anterior working sections 51 (respectively posterior 52) which are closest to it anteriorly and posteriorly by an anterior angular distance (respectively by a posterior angular distance); it being noted that an angular distance corresponds to an angle between two consecutive working sections. In an alternative embodiment of the invention, the anterior angular distance and the posterior angular distance are identical. In a second alternative embodiment of the invention, the two angular distances are identical and both less than or equal to 5 degrees, and in particular between 1 and 3 degrees. In a preferred embodiment of the invention, the anterior angular distance and the posterior angular distance are both equal to 2 degrees.It is also conceivable that the two angular distances could be user-modifiable parameters in the 3D design tool.

[0137] The anterior 501 and posterior 502 axes of revolution are distant from each other by a center distance 511 which coincides in a sagittal plane 513 which extends orthogonally to the two axes of revolution 501, 502; and which is a function of the femoral size. In one embodiment of the invention, the center distance is expressed in the form of an affine function of the femoral size.

[0138] Since the three-dimensional modeling of the femur 1 is segmented into a plurality of working sections 5 and the three-dimensional modeling of the cutting template 3 is shaped to be applied thereto, one or more working sections 5 may optionally pass through some of the start 41 and end 42 cutting lines of the femoral cuts 31, 32, 33, 34, 35 of the cutting template 3. These working sections 5 are called specific sections. According to different embodiments of the invention, depending on the value of the anterior and posterior angular distances, one to more working sections 5 may be included between two specific sections.

[0139] In one embodiment of the invention, the sectioning of the three-dimensional modeling of the femur into working sections 5 may comprise by default two specific sections corresponding to an anterior working section 51 and a posterior working section 52 passing respectively through the cutting start line 43 of the anterior femoral section 31, and the cutting end line 44 of the posterior femoral section 35; which two specific sections may also be considered as reference sections from which the sectioning of the three-dimensional modeling of the femur 1 is carried out insofar as:

[0140] - the start line of cut 43 of the anterior femoral cut 31 and the end line of cut 44 of the posterior femoral cut 35 serve to delimit, physically or in modeling, the distal part of the femur from the rest of the bone; and

[0141] - that they contain the remarkable points used to determine the femoral size, namely: the most anterior point 22 of the distal femur for the start line of the anterior femoral cut 43; and the most posterior point of the medial condyle 21 and of the lateral condyle for the end line of the posterior femoral cut 44.

[0142] The geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 that determine the construction process in each work section 5 include:

[0143] - first geometric variables Xmed, Xlat representative of a medio-lateral width MLD of the modeled femur;

[0144] - second variables XM1, rMl, RI representative of a medial femoro-tibial contact surface SI at the level of the medial condyle 61;

[0145] - third variables XM2, rM2, R2 representative of a lateral femoro-tibial contact surface S2 at the level of the lateral condyle 62; and - fourth variables XM3, rM3, R3 representative of a femoro-patellar contact surface S3 at the level of the trochlea 63.

[0146] Prior to determining all of these geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3, the construction method can optionally apply an osteophyte removal step 7 to each of the working sections 5.

[0147] By definition, an osteophyte 7 is a bony growth that forms at the ends of a bone in a joint. It is the body's response to wear, degeneration, or destruction of the articular cartilage, which means that it no longer provides its shock-absorbing role during exertion and that the bone will be subjected to much more pressure.

[0148] In the context of the invention, the medical images used in the construction method to construct the three-dimensional model of the femur are taken before any surgical intervention. This therefore means that if the patient's femur has one or more osteophytes 7, this or these will be represented in its three-dimensional model. The osteophytes can form both on the ends of the medial 61 and lateral 62 condyles of the femur and at its notch (i.e. at the trochlea 63).

[0149] By definition, osteophytes 7 are aberrations that deviate from the original articular surfaces. In the three-dimensional modeling of the femur 1, they are represented by sets of aberrant geometric points.

[0150] Depending on their location on the bone surface of the femur, and by extension its three-dimensional modeling, the osteophyte(s) 7 are visible or not in the working sections 5. An example of working section 5 showing several groups of aberrant points representative of the presence of osteophytes on each of the medial 61 and lateral 62 condyles is presented in Figure 6.

[0151] It should be noted subsequently that for each working section 5 illustrated, as in the case of Figure 6, the points modeling the femur in working section 5 are defined by a medio-lateral coordinate (abscissa axis ML of medio-lateral direction) and by a radial coordinate (ordinate axis r of radial direction).

[0152] The osteophyte removal step must necessarily be implemented by the construction method before the determination of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3. Since they constitute outliers among the geometric points contained in the working section 5, they can lead to a bad evaluation / estimation of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3, and therefore of the mediolateral width MLD and the three contact surfaces SI, S2, S3. An example for the mediolateral width MLD is given later.

[0153] A poor estimation of the medio-lateral width MLD and the three contact surfaces SI, S2, S3 can lead to the construction of a model of a femoral component 101, and therefore to the manufacture of a physical femoral component 101, oversized whose prosthetic size will be unsuitable for the patient being treated, thus inducing patellofemoral pain and difficulty moving with the prosthesis.

[0154] Figure 7 shows the working section 5 illustrated in Figure 6 after applying the osteophyte removal step, for which the groups of aberrant geometric points representative of the osteophytes 7 have been removed. The osteophyte removal step also includes a smoothing sub-step during which an interpolation function is applied to the geometric points of the modeled femur that were spatially close neighbors of the groups of aberrant points just removed, in order to create / add new geometric points such that they model the resected parts of the articular surface, i.e. here the contours of the medial 61 and lateral 62 condyles.

[0155] The osteophyte removal step also allows in the working sections 5 to virtually remove one or more osteophytes that may have formed at the level of the trochlea 63.

[0156] The construction process, after applying the osteophyte removal step, then determines the set of geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3.

[0157] With reference to Figure 8, which shows an example of three-dimensional modeling of the femur 1 cleaned in another working section 5, the medio-lateral width MLD in said working section 5 corresponds to the distance separating, on the reference axis XI, the most medial point 61 of the medial condyle 611 and the most lateral point 621 of the lateral condyle 62. From these two points, the construction method determines the first geometric variables Xmed and Xlat which correspond respectively in the working section 5 to the abscissas of the most medial point 611 of the medial condyle 61 and of the most lateral point 612 of the lateral condyle 62.

[0158] Figure 9 takes the example of the set of geometric points defining the three-dimensional modeling of femur 1 in working section 5 presented in Figure 6, and illustrates the error made in the estimation of the mediolateral width MLD by the construction method when the osteophyte removal step is applied (with reference to Figure 7) or not (with reference to Figure 6) to said working section 5. When the osteophyte removal step is not applied, the mediolateral width MLD is equal to a mediolateral width MLD1 of 74 mm. When it is applied, the mediolateral width MLD is equal to a mediolateral width MLD2 of 68.5 mm. Thus, the accuracy error made in the estimation of the mediolateral width MLD when the osteophytes are not removed is approximately 8%. This accuracy error may possibly be greater depending on the sizes of the growths on the articular surface of the femur.

[0159] With reference to Figure 10 and Figure 11, for all working sections 5, the medial femoro-tibial SI, lateral femoro-tibial S2, and patellofemoral S3 contact surfaces are respectively described by a medio-lateral contour of the medial condyle 61, the lateral condyle 62 and the trochlea 63, which contours are formed by successive points delimiting (or defining) these medial femoro-tibial SI, lateral femoro-tibial S2, and patellofemoral S3 contact surfaces in the working section 5 considered.

[0160] The construction method implements a determination of a medial condylar circle Cl, a lateral condylar circle C2, and a trochlear circle C3 respectively and substantially matching the medial femoro-tibial contact surfaces SI, lateral femoro-tibial S2, and patellofemoral S3 in the working section 5.

[0161] Thus, the second variables XM1, rMl, RI determined by the construction method correspond to the coordinates of the center of the medial condylar circle Cl (called medial center Ml) and its radius (called medial radius RI).

[0162] Similarly, the third variables XM2, rM2, R2 correspond to the coordinates of the center of the lateral condylar circle C2 (called lateral center M2) and its radius (called lateral radius R2); and the fourth variables XM3, rM3, R3 correspond to the coordinates of the center of the medial condylar circle Cl (called trochlear center M3) and its radius (called trochlear radius R3).

[0163] For each of the medial center Ml, lateral M2, and trochlear M3, the construction method determines in the working section 5 a medio-lateral coordinate XM1, XM2, XM3 and a radial coordinate rMl, rM2, rM3 by analyzing the medio-lateral and sagittal geometric points representative of the medial condyle 61, the lateral condyle 62 and the trochlea 63.

[0164] To do this, the construction method identifies all the geometric points defining the femur modeled in the working section 5 which are included in the articular surfaces of the medial condyle 61, the medial condyle 62, and the trochlea 63 (in other words the medial femorotibial SI, lateral femorotibial S2, and patellofemoral S3 contact surfaces), then it applies circular regressions to the identified geometric points; thus allowing it to determine the circumferences and centers of the medial circles Cl, lateral C2, and trochlear C3 and therefore the corresponding variables XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3.

[0165] Finally, the construction method determines a plurality of values ​​for all the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3; each of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 taking a given value in each of the working sections 5 segmenting the three-dimensional modeling of the femur 1.

[0166] As previously indicated, the construction method ultimately makes it possible to manufacture femoral components 101 specifically adapted to the specific morphologies of the patients or standard femoral components 101 whose dimensions are a function of the femoral size, meaning that a femoral component 101 associated with a given femoral size can be fitted to a plurality of patients having said femoral size.

[0167] In the case where the construction method is to construct a customized femoral component 101, the working sections 5 (whether anterior working sections 51 or posterior working sections 52) are grouped into working section series. In one embodiment of the invention, the series number may be a modifiable parameter in the 3D design tool. In another embodiment of the invention, it may be a prescribed number of series.

[0168] In the remainder of the description, it is considered that the working sections 5 are distributed / grouped into five series, each of the series being associated with a femoral cut 31, 32, 33, 34, 35 of the cutting template 3. This means that in this specific embodiment, the three-dimensional modeling of the femur 1 is segmented by the construction method so that the set of working sections comprises the specific sections passing through the start of cut line 41 or the end of cut line 42 of all the femoral cuts 31, 32, 33, 34, 35. Thus, all the working sections 5 comprised between two specific sections are part of a series of working sections 5. In different embodiment variants, the series comprises only the specific section corresponding to the start of cut line 41 or the end of cut line 42; or both.

[0169] For each geometric variable Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3, the values ​​determined in the working sections included in a series are averaged. In the example given above, this implies that the construction method calculates five average values ​​(one per series) for each geometric variable Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3.

[0170] In the case of the construction of a standard 101 femoral component, the preparatory steps are performed and repeated for several sets of medical digital images associated with several distal femurs of patients. First, several three-dimensional models of several femurs are obtained for which the femoral size is determined. The three-dimensional models of femur 1 are then classified / grouped according to the determined femoral size.

[0171] For each three-dimensional model of femur 1 belonging to a femoral size:

[0172] - the cutting template 3 is modeled, and

[0173] - the values ​​of the geometric variables of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 are determined in a plurality of working sections 5, the sectioning being the same for all the three-dimensional models of femur 1 so that the method is capable of analyzing several values ​​of a geometric variable Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 of a working section sectioning different three-dimensional models of the femur according to the same plane / the same orientation.

[0174] For a femoral size, sets of statistical data are then obtained relating to the morphometric data, to the dimensions of the femoral sections 31, 32, 33, 34, 35 of the cutting template 3 and to the values ​​that the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 can take.

[0175] From these statistical sets, the construction method determines, for each femoral size, standard values ​​of the dimensions of the femoral sections 31, 32, 33, 34, 35 of the cutting template 3 and the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3. All of these “standard” values ​​will be used to model a three-dimensional model of a femoral component 101 and construct a standard femoral component 101 adapted to a femoral size value.

[0176] In one embodiment of the invention, it is conceivable that the values ​​of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 included in the statistical sets are average values ​​(i.e. standard average values) calculated according to the method used when constructing a personalized femoral component 101, with the aim of reducing the size of the statistical data set.Knowing that the standard variables associated with the morphometric data, the dimensions of the femoral sections 31, 32, 33, 34, 35 of the cutting template 3 and the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 can take different values ​​depending on the femoral size, it is conceivable in one embodiment of the invention that the construction method can identify, for the different standard variables, evolutionary trends that can be expressed in the form of mathematical relationships, then making it possible to calculate the values ​​of the standard variables using these mathematical relationships and knowing the value of the femoral size.

[0177] In another embodiment of the invention, the construction method is configured to determine affine functions of the form y = ax + b from the evolutionary trends of the standard variables (averaged as indicated above or not), where:

[0178] - y is the standard value, depending on the femoral size, of the morphometric data; of the dimension of the femoral section 31, 32, 33, 34, 35 considered; or of the geometric variable Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 considered;

[0179] - x is the femoral size;

[0180] - has a slope coefficient; and

[0181] - b is representative of a difference in value between the femoral size considered and a lower and / or higher femoral size.

[0182] In one embodiment of the invention, upon launching the 3D design tool, the user has the choice between modeling a customized or standard femoral component 101. If the user chooses to design a standard femoral component 101, then the 3D design tool offers the user two options: either to three-dimensionally model the standard femoral component 101 by carrying out all of the preparatory steps; or to three-dimensionally model the standard cutting template 3 and the standard femoral component 101 from all of the mathematical relationships.

[0183] As explained before, the advantage of mathematical relationships is to make possible the three-dimensional modeling of a standard 3 cutting template and a standard 101 femoral component for a femoral size for which the user would not have a set of medical images of patients presenting it.

[0184] Regardless of the type of femoral component 101 modeled (custom or standard), the preparatory steps are completed with obtaining the values ​​of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 (mean values ​​or standard values).

[0185] Following the preparatory steps, the construction method comprises a step of modeling / construction of the femoral component 101, implemented in the embodiment described by the 3D design tool.

[0186] Referring to Figure 12, the 3D design tool models / builds:

[0187] - a medial profile PI and a lateral profile P2 corresponding respectively to the medial contour of the medial condyle 61 and to the lateral contour of the lateral condyle 62, by applying a first interpolation function to the values ​​(averaged or standard depending on the type of femoral component 101) of the first geometric variables Xmed, Xlat;

[0188] - a medial femoro-tibial joint profile Tl of the medial condyle 61, by applying a second interpolation function to the values ​​of the second geometric variables XM1, rMl, RI;

[0189] - a lateral femoro-tibial joint profile T2 of the medial condyle 62, by applying a second interpolation function to the values ​​of the third geometric variables XM2, rM2, R2;

[0190] - a T3 femoro-patellar joint profile, by applying a second interpolation function to the values ​​of the fourth geometric variables XM3, rM3, R3.

[0191] The articulation profiles Tl, T2, T3 correspond to trajectories on which the contact points on the circles Cl, C2, C3 move respectively, which are aligned with the respective centers Ml, M2, M3 according to the radial direction in each working section 5, as visible in Figure 11.

[0192] More precisely, the values ​​of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3, identified in the different work sections 5 segmenting the three-dimensional modeling of the femur 1, provide indications through which spatially the medial and lateral profiles, and the three articulation profiles, pass. Each of the five profiles is constructed by applying interpolation functions Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 to all the values ​​of the geometric variables through which they pass.

[0193] In one embodiment of the invention, the interpolation functions are third-degree functions. The degree of precision of the profiles obtained depends on the number of values ​​obtained for each geometric variable Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 and to which the interpolation functions are applied. The degree of precision also depends for each geometric variable Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 on the spatial proximity of the different values. This therefore means that the precision will be high if: - the three-dimensional modeling of the femur 1 is segmented into a large number of working sections 5 of different orientations but relatively close to each other (for example, when the anterior angular distance and the posterior angular distance are both equal to 2 degrees);

[0194] - in the case of a customized 101 femoral component, the number of average values ​​for each geometric variable Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 is important. In the previous example, an average value associated with a femoral section 31, 32, 33, 34, 35 (i.e. five average values) offers a good degree of precision in the construction of the different profiles Pl, P2, Tl, T2, T3, T13, T23; or

[0195] - in the case of a standard femoral component, the 3D design tool has a standard value for each geometric variable Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 in a plurality of working sections 5.

[0196] Note that a first T13 junction profile and a second T23 junction profile are also constructed, which correspond respectively to two contact / junction trajectories between the circumferences of the medial C1 and trochlear C3 circles; and between the circumferences of the lateral C2 and trochlear C3 circles.

[0197] From the three-dimensional modeling of the cutting template 3 and the different articulation profiles, the 3D design tool three-dimensionally models the femoral component 101 as illustrated in an example in Figure 2 and Figure 12.

[0198] Finally, the last step of the construction process is to manufacture a physical femoral component 101 based on the three-dimensional model provided by the 3D design tool.

Claims

CLAIMS 1. Method for constructing at least one femoral component (101) for a total knee prosthesis (100), comprising the following preparatory steps: - obtaining a set of digital medical images of a patient's femur; - construction of a three-dimensional model of the femur (1) from the associated set of digital medical images; - determination of morphometric data (21, 22, 23, 24, 25) in the three-dimensional modeling of the femur (1), said morphometric data (21, 22, 23, 24, 25) characterizing a femoral size; - determination of a cutting template (3) in the three-dimensional modeling of the femur (1), based on the morphometric data (21, 22, 23, 24, 25); - sectioning the three-dimensional modeling of the femur (1) into several working sections (5) distributed in different planes, each working section (5) being defined by a set of geometric points, the sectioning being such that the several working sections (5) comprise posterior working sections (51) distributed in different planes around a posterior axis of revolution (501) in a mediolateral direction, and anterior working sections (52) distributed in different planes around an anterior axis of revolution (502) in a mediolateral direction and offset by a given center distance (512) with the posterior axis of revolution along a femur axis (513) in a proximo-distal direction; - obtaining geometric variables (Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3) representative of a geometry of the three-dimensional modeling of the femur (1) in the several working sections (5), said geometric variables comprising first variables (Xmed, Xlat) representative of a mediolateral width (MLD), second variables (XM1, rMl, RI) representative of a medial femoro-tibial contact surface (SI) of a medial condyle (61), third variables (XM2, rM2, R2) representative of a lateral femoro-tibial contact surface (S2) of a lateral condyle (62), and fourth variables (XM3, rM3, R3) representative of a patellofemoral contact surface (S3) of a trochlea (63); said construction method then comprising a step of constructing the at least one femoral component (101) from the cutting template (3) and values ​​of the geometric variables.

2. Construction method according to claim 1, wherein the construction step implements a construction of profiles of the at least one component femoral (101) by interpolation of the values ​​of the geometric variables (Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3).

3. Construction method according to claim 2, wherein the construction of profiles comprises constructions of a lateral profile (P2) and a medial profile (PI) by interpolation of the values ​​of the first variables (Xmed, Xlat), of a medial femoro-tibial joint profile (Tl) of the medial condyle (61) by interpolation of the values ​​of the second variables (XM1, rM1, RI), of a lateral femoro-tibial joint profile (T2) of the lateral condyle (62) by interpolation of the values ​​of the third variables (XM2, rM2, R2), and of a patellofemoral joint profile (T3) of the trochlea (63) by interpolation of the values ​​of the fourth variables (XM3, rM3, R3).

4. Construction method according to claim 2 or 3, in which the interpolation is a third order interpolation.

5. Construction method according to any one of the preceding claims, in which the set of digital medical images comprises images from a medical scanner, for example in DICOM format.

6. A construction method according to any one of the preceding claims, wherein the determination of morphometric data (21, 22, 23, 24, 25) comprises the determination of remarkable points in the three-dimensional modeling of the femur (1).

7. A construction method according to claim 6, wherein the notable points comprise at least a most posterior point (21) of the medial condyle (61), a most posterior point (25) of the lateral condyle (62) and a most anterior point (22) of a distal femur portion.

8. A construction method according to any one of the preceding claims, wherein the cutting template (3) comprises placing a plurality of femoral cuts (31, 32, 33, 34, 35) which depend at least on the femoral size.

9. Construction method according to claim 8, wherein the several femoral cuts (31, 32, 33, 34, 35) successively comprise an anterior femoral cut (31), an anterior chamfer cut (32), a femoral cut distal (33), a posterior chamfer cut (34) and a posterior femoral cut (35).

10. Construction method according to claim 8 or 9, wherein the several working sections (5) comprise specific sections which pass through cutting start lines (41; 43) or cutting end lines (42; 44) of the femoral cuts (31, 32, 33, 34, 35) of the cutting template (3), these cutting start lines (41; 43) or cutting end lines (42; 44) being in a medio-lateral direction.

11. A construction method according to claims 9 and 10, wherein the specific sections comprise at least one section which passes through a cutting start line (41) of the anterior femoral cut (31), and one section which passes through a cutting end line (44) of the posterior femoral cut (35).

12. Construction method according to any one of the preceding claims, in which the center distance (512) is a function of the femoral size.

13. Construction method according to any one of the preceding claims, wherein, for each working section (5), obtaining the first variables (Xmed, Xlat) representative of the medio-lateral width (MLD) implements an analysis of the geometric points of a medial contour and a lateral contour of the working section (5) to determine two positions which are a position of a most medial point (611) of the medial condyle (61) and a position of a most lateral point (621) of the lateral condyle (62) on a reference axis (XI) of medio-lateral direction, said two positions constituting the first variables (Xmed, Xlat) associated with the working section (5).

14. Construction method according to claim 13, in which the reference axis (XI) is determined as being offset by a given spacing (dl) in a proximo-distal direction with respect to an extreme line (X0) in a medio-lateral direction passing through a most distal point of the lateral condyle (23) or the medial condyle (24).

15. Construction method according to any one of the preceding claims, in which, for each working section (5), obtaining the second variables (XM1, rMl, RI) representative of the medial femoro-tibial contact surface (SI) of the medial condyle (61) implements an analysis of the geometric points of a medio-lateral contour of the medial condyle (61) to determine a condylar circle medial (Cl) defined by coordinates of a medial center (Ml) and by a medial radius (RI), said coordinates of the medial center (Ml) and said medial radius (RI) constituting the second variables (XM1, rMl, RI) associated with the working section (5).

16. Construction method according to claim 15, wherein the analysis of the geometric points of the medio-lateral contour of the medial condyle (61) implements a circular regression on the geometric points of the medio-lateral contour of the medial condyle (61).

17. Construction method according to any one of the preceding claims, wherein, for each working section (5), obtaining the third variables (XM2, rM2, R2) representative of the lateral femoro-tibial contact surface (S2) of the lateral condyle (62) implements an analysis of the geometric points of a medio-lateral contour of the lateral condyle (62) to determine a lateral condylar circle (C2) defined by coordinates of a lateral center (M2) and by a lateral radius (R2), said coordinates of the lateral center (M2) and said lateral radius (R2) constituting the third variables (XM2, rM2, R2) associated with the working section (5).

18. Construction method according to claim 17, wherein the analysis of the geometric points of the medio-lateral contour of the lateral condyle (62) implements a circular regression on the geometric points of the medio-lateral contour of the lateral condyle (62).

19. Construction method according to any one of the preceding claims, wherein, for each working section (5), obtaining the fourth variables (XM3, rM3, R3) representative of the femoro-patellar contact surface of the trochlea (S3) implements an analysis of the geometric points of a medio-lateral contour of the trochlea (63) to determine a trochlear condylar circle (C3) defined by coordinates of a trochlear center (M3) and by a trochlear radius (R3), said coordinates of the trochlear center (M3) and said trochlear radius (R3) constituting the fourth variables (XM3, rM3, R3) associated with the working section (5).

20. Construction method according to claim 19, wherein the analysis of the geometric points of the medio-lateral contour of the trochlea (63) implements a circular regression on the geometric points of the medio-lateral contour of the trochlea (63).

21. A construction method according to any one of claims 1 to 20, wherein the working sections (5) are divided into several series of working sections (5) and, for each series of working sections (5), the geometric variables (Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3) obtained in the working sections (5) of said series are averaged to obtain average values ​​of the geometric variables, and the at least one femoral component (101) is constructed from the cutting template (3) and the average values ​​of the geometric variables in the several series, said at least one femoral component (101) being called a custom femoral component.

22. Construction method according to any one of claims 1 to 20, in which the preparatory steps are carried out on the basis of several sets of digital medical images of femurs of several patients characterized by several femoral sizes, thus obtaining for each femoral size a set of statistical data relating to the geometric variables (Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3); and the at least one femoral component (101), associated with one of the several femoral sizes, is constructed from the cutting template (3) associated with this femoral size and statistical values ​​of the geometric variables (Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3) in the statistical data set associated with this femoral size, said at least one femoral component (101) being called standard femoral component (101) in this femoral size.

23. A construction method according to claim 22, wherein a plurality of standard femoral components (101) in the plurality of femoral sizes are constructed from the statistical data sets associated with these plurality of femoral sizes, these plurality of standard femoral components (101) thus forming a range of standard femoral components (101).

24. The construction method of claim 23, wherein the statistical data sets associated with the multiple femoral sizes are analyzed to establish mathematical relationships between the values ​​of the geometric variables (Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3) and the femoral size.

25. Construction method according to claim 24, in which the mathematical relationships are affine relationships.

Images