WO2024134063A1

WO2024134063A1 - Method for constructing a femoral component of a total knee prosthesis

Info

Publication number: WO2024134063A1
Application number: PCT/FR2023/052005
Authority: WO
Inventors: Laurent Geais; Emilie KEMBERG
Original assignee: Move-Up
Priority date: 2022-12-19
Filing date: 2023-12-14
Publication date: 2024-06-27
Also published as: FR3143319A1

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

DESCRIPTION

TITLE: Method for constructing a femoral component of a total knee prosthesis

[Technical area]

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

The invention finds a preferred application in the manufacture of a range of standard femoral components capable of being placed in 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 to the morphology of the patients, to restore the mobility of the joint they are replacing.

[State of the art]

Due to greater life expectancy or the increase in the prevalence of obesity, more and more people are suffering from osteoarthritis, which is a pathology that wears out or destroys joint cartilage. This results in pain when walking or even when resting, which reduces the quality of life. This is why knee arthroplasty is experiencing growing growth today, with significant demand. The functional results of this surgical procedure have been improved in recent years thanks to: techniques at the cutting edge of the latest technologies, more reliable and less invasive; better management of postoperative pain; and the initiation of intense and early physiotherapy.

In a known manner, a total knee prosthesis aims to remove the areas of worn bone and cartilage from the articular surfaces of the knee (distal part of the femur, proximal part of the tibia, and sometimes patella) by artificial parts made with particularly materials. resistant to mechanical and abrasive stress, and working together to restore the mobility of the knee joints they replace.

The total knee prosthesis must also allow the patient in whom it is placed to have stable support so that he or she regains a good walking perimeter (good capacity). Generally, total knee prosthesis is proposed and implemented only in cases of serious lesions: advanced osteoarthritis, rheumatoid arthritis, destruction of traumatic origin.

However, nearly 20% of patients today say they are dissatisfied with the installation of a total knee prosthesis, either because post-operative pain and after the installation of the total knee prosthesis persist, either 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 prostheses are offered for standard patient morphologies. If they can be suitable for a majority of them, it turns out in certain cases that their prosthetic size is unsuitable for the morphology of the patient, that is to say the morphology, or size, of the distal part of the his femur; and/or that of the proximal part of his tibia; and/or that of his patella.

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

It is now known, for example from document US 2014/0228860, to design personalized or standard femoral components by having a purely surface approach, that is to say that the femoral component is constructed to fit as closely as possible to the external bony surface of the distal part of the patient's resected femur as part of a custom femoral component, or of multiple patients with the same femur size as part of a standard femoral component. However, this purely surface approach has limits, because it favors the real and possibly damaged external surface, without taking into account joint kinematics.

Document US 20022/0087827 proposes to design a femoral component: from a three-dimensional modeling of a distal femur of a patient, which is obtained from digital medical images of the patient's knee to which are applied methods of image processing, and taking into account the joint kinematics of a patient's knee. Knee kinematics are taken into account by identifying, manually on the three-dimensional model or automatically on 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 landmarks may not be sufficiently accurate. 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 medical digital images and the effectiveness of image processing methods.

[Summary of the invention]

The invention aims to respond to the problems set out above by aiming:

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

- to adapt the articular surfaces of the femoral component of the total knee prosthesis in order to offer the possibility of kinematics closest to the kinematics of the physiology of the patient's knee.

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

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

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

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

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

- sectioning of 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 include 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 axis of posterior revolution along an axis of the femur in a proximo-distal direction;

- 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 contact surface medial femorotibial of a medial condyle, third variables representative of a lateral femorotibial 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.

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 modeling of a femur, more precisely the distal part of the femur or distal femur, a patient (or even several patients as part of a construction of a standard femoral component). To do this, several medical digital images of a patient's distal femur are collected, which are taken from different viewing angles in order ultimately to model it in its entirety, to which digital processing is applied, for example a segmentation method.

Following digital image processing, the three-dimensional modeling of the distal femur is obtained, which corresponds to a three-dimensional mesh. Three-dimensional modeling of the distal femur includes three-dimensional modeling of the medial condyle, lateral condyle, and trochlea of the distal femur.

In the remainder of this description, for greater convenience, the term “femur” refers to the distal femur.

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 dimensions of the femur. Notable points include 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 patient's femur, or femoral size; which is considered morphometric data since it characterizes the morphology of the patient's femur.

From the initially estimated femoral size and other morphometric data (notably 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 template cutting). According to one 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.

The 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 bony surface of the femur to make bone cuts and define support panels for the femoral component. to facilitate installation. These cuts of the surface of the bone can also, for example, help to remove growths (or osteophytes) that it may possibly present.

In the remainder of this description, for greater practicality, the cutting template refers to the three-dimensional modeling of the cutting template.

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

It is from this modeling of the femoral component that a femoral component is ultimately constructed/fabricated which will be integrated into the knee prosthesis which will be placed in the patient. It is understood that the femoral component has the same dimensional characteristics as its representative model.

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

- a medio-lateral 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 making it possible to define/construct a medial contour/profile of the medial condyle and a lateral contour/profile of the lateral condyle; And

- different contact surfaces allowing joint profiles to be defined/constructed to reproduce the kinematics of the knee: a medial femorotibial contact surface at the level of the medial condyle, a lateral femorotibial contact surface at the level of the lateral condyle , and a patellofemoral contact surface at the level of the trochlea.

The medio-lateral 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 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 which are oriented in different directions and in which the construction process searches for the values of the geometric variables.

More precisely, the working sections are distributed around two axes of revolution in a medio-lateral direction: 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 which are closest to it anteriorly and posteriorly of an angular distance. This angular distance is for example less than or equal to 5 degrees, and in particular between 1 and 3 degrees.

In a variant 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.

The two axes of revolution are spaced apart by a given center distance, the value of which depends, as a reminder, on the femoral size. This center distance coincides in a sagittal plane which extends orthogonally to the anterior and posterior axes of revolution.

Advantageously, and as will be explained again later, the construction process 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, as in the manufacturing of specific or personalized components that are adapted to particular patient morphologies.

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 modeling three-dimensional analysis of the cutting box, the determination of the medio-lateral width and the contact surfaces which define the joint kinematics). Thus, it is possible from the construction process to construct/manufacture femoral components which fall into the different types available on the market: component with preservation of the posterior cruciate ligament (in English: cruciate retaining), component with medial pivot (in English medial pivot), postero-stabilized component, and ultra-congruent component.

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

According to one 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.

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 femorotibial joint profile of the medial condyle by interpolation values of the second variables, a lateral femorotibial joint profile of the lateral condyle by interpolation of the values of the third variables, and a patellofemoral joint profile of the trochlea by interpolation of the values of the fourth variables.

According to one embodiment of the invention, the interpolation is a third order interpolation.

In other words, the values of the geometric variables, identified in the different work sections segmenting the three-dimensional modeling of the femur, provide indications through which the medial and lateral profiles, and the three joint profiles, pass spatially. 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 certainly different orientations but relatively close to each other, the better the precision of the profiles obtained will be.

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.

According to one characteristic of the invention, the remarkable points include at least one most posterior point of the medial condyle, a most posterior point of the lateral condyle and one most anterior point of a part of the distal femur.

According to one characteristic of the invention, the cutting template comprises the implementation of several femoral cuts which depend at least on the femoral size.

According to one 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.

In other words, a femoral template is composed of five successive femoral cuts (also called cutting 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 antero-posterior 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 cutting line coordinates.

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

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

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

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 start line of cut and an end line of cut extending mediolaterally; the end of cut line of a femoral cut being confused with the start of cut line of a femoral cut which succeeds it. The cutting template is then delimited at its ends by two cutting lines corresponding to the start line of cutting of the anterior femoral cut, and the end of cutting line of the posterior femoral cut.

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 cut start and end lines of the femoral cuts (cutting boxes) of the cutting template. These working sections are designated in the invention as specific sections. According to different embodiments of the invention, one or more working sections can for example be included between two specific sections.

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

- these two cutting lines are used to delimit, physically or in modeling, the distal part of the rest of the femur; And

- that the two cutting lines include the remarkable points used to determine the femoral size (the most anterior point of the distal femur for the start line of cutting 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.

According to one characteristic of the invention, the center distance is a function of the femoral size. For example, the center distance is expressed as an affine function of the femoral size.

According to one 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 medial-most point of the medial condyle and a position of a lateral-most point of the lateral condyle on an axis medio-lateral direction reference, said two positions constituting the first variables associated with the working section.

According to one 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 of medio-lateral direction passing through a point most distal to the lateral condyle or the medial condyle.

In other words, the medio-lateral width of the three-dimensional modeling of the femur is determined, in each working section, between the position/most lateral 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 exterior 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 modeling of the femoral component during its construction.

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) depending on the cutting box for placement of the femoral component.

According to a characteristic of the invention, for each working section, obtaining the second variables representative of the medial femoro-tibial contact surface of the medial condyle implements an analysis of the geometric points of a medio-lateral contour of the condyle medial 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.

According to one 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.

According to a characteristic of the invention, for each working section, obtaining the third variables representative of the lateral femoro-tibial contact surface of the lateral condyle implements an analysis of the geometric points of a medio-lateral contour of the condyle lateral 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.

According to one 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.

According to a characteristic of the invention, for each working section, obtaining the fourth variables representative of the femoropatellar 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 trochlean 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.

According to one 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.

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

The geometric variables sought by the construction process in the different work sections (designated as second variables for the medial femorotibial contact surface, third variables for the medial femorotibial contact surface, and fourth variables for the contact surface patellofemoral) correspond to the coordinates of the center and the radius of each of the three circles.

In a variant embodiment of the invention, in each of the working sections, a medio-lateral coordinate and a radial coordinate for each of the three circles can be searched for. The medio-lateral coordinate and the radial coordinate are respectively determined for each working section by analyzes of medio-lateral and sagittal geometric points included in the medio-lateral and sagittal profiles of each of the three compartments. Linear interpolation can then be applied by the construction process to the medio-lateral and radial coordinates of each of the working sections to determine a sagittal contour/trajectory along which the centers move. of each of the circles, between each of the two anterior and posterior ends of the three-dimensional modeling of the femur.

In each of the working sections, the radii of the medial, lateral and trochlear circles respectively describe a medio-lateral contour of the medial condyle, the lateral condyle and the trochlea. Thus the geometric variables for each of the three rays correspond to geometric points/positions located on the surface of the two condyles and the trochlea, and lined up to form said medio-lateral contour. Obtaining the mediolateral 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 work sections.

According to one characteristic 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 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 personalized femoral component.

As previously indicated, an advantage of the construction method is to allow the construction of a so-called standard femoral component which 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.

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

Given that the geometric variables are sought through the different work sections, this means that each of the series of work sections makes it possible 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 series of work sections (i.e., taking the previous example, five sets).

In the case of constructing a three-dimensional modeling of a personalized 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 work section. In the previous example, this amounts to obtaining five average values of the same geometric variable.

- 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.

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.

According to one characteristic of the invention, the preparatory steps are carried out on the basis of several sets of medical digital images of femurs of several patients characterized by several femoral sizes, thus obtaining for each femoral size a set of statistical data relating to 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 statistical data set associated with this size femoral, said at least one femoral component being called standard femoral component in this femoral size.

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

In the case of a standard femoral component of a given femoral size, the preparatory steps for the construction of the three-dimensional modeling of the femoral component are repeated for several sets of digital medical images associated with several distal femurs of patients.

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 three-dimensional modeling group characterized by a femoral size value, a plurality of values of geometric variables forming sets of statistical data are obtained. From these statistical sets can then be deduced/derived “standard” values of the morphometric data and geometric variables which allow the construction process to construct standard three-dimensional models of a cutting template and of a femoral component applicable to the set of three-dimensional femur models of the group with the same femoral size.

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

In other words, with a view to advantageously accelerating the construction times of the three-dimensional modeling of a standard femoral component and therefore the manufacturing of the physical standard femoral component, the statistical sets of geometric variables are analyzed with a view to identifying evolving trends depending on of the femoral size that can be expressed in the form of mathematical relationships.

Thus, in the case where a three-dimensional modeling of a standard femoral component must 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 values. standards 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.

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

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 = a.x + b; where y is the standard value of the morphometric data or the geometric variable considered as a function of the femoral size; x is the femoral size; has a slope coefficient; and b is representative of a difference in value for the morphometric data or the geometric variable between the femoral size considered and a lower and/or higher femoral size.

[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:

[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;

[Fig 2] brings together three-dimensional views of a three-dimensional modeling of a typical femoral component that can be constructed using the construction method, with two front (a) and rear (b) perspective views, and one view in profile (c);

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

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

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

[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 osteophytes are visible having formed on the bony surface of the femur at the level of the ends of the two condyles and the trochlea/notch;

[Fig 7] is a representation of the three-dimensional modeling of the femur in the working section considered 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 work section no longer includes the points modeling the osteophytes (or aberrant points);

[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;

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

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

[Fig 11] shows, in connection with Figure 10, all the geometric variables used to determine the three contact surfaces mentioned above, 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);

[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 the medial and lateral profiles of said femoral component are visible, the two femoral joint profiles - tibial, the patellofemoral joint profile, and the junction profiles between the trochlear circle with each of the medial and lateral circles.

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

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 material (generally polyethylene) which is 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.

As previously indicated, the invention relates to a construction method for the construction of a femoral component 101 aimed at:

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

- to adapt the articular surfaces of the femoral component 101 of the total knee prosthesis 100 in order to offer the possibility of kinematics closest to the kinematics of the physiology of the patient's knee.

In order to respond positively to these two points, the construction process makes it possible to manufacture:

- ranges of standardized femoral components 101, for which different femoral components are offered such that each is specifically adapted to a femoral size; that is, 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 placed in a plurality of patients having the same femoral size; as well as

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

The construction process also covers the construction/manufacturing of all femoral component models 101 available on the market: component with preservation of the posterior cruciate ligament (in English: cruciate retaining), component with medial pivot (in English medial pivot), postero-stabilized component, and ultra-congruent component.

The process 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 leading to a three-dimensional modeling of the femoral component 101. In one embodiment of the invention, this modeling phase is implemented by means of a tool 3D design of femoral component 101 installed on a workstation station, for example a desktop computer.

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

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

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

The recovered digital images are then subjected to digital processing, for example a segmentation method, with a view to obtaining a three-dimensional modeling of the femur 1 corresponding, as illustrated in Figure 5, to a cloud of points virtually and spatially forming the entire bony 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 modeling of the femur 1.

In a variant embodiment of the invention, the three-dimensional modeling of the femur 1 can also be modeled using a 3D mesh method. In a second embodiment, the two types of modeling are offered by the 3D design tool. In a third variant, it is possible that the 3D design tool could offer an option for applying textures to the three-dimensional modeling of the femur 1, the shades and colors of which are representative of a physical femur.

From the three-dimensional modeling of femur 1, the construction process goes through several other preparatory stages:

- model a three-dimensional modeling 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 panels for the component femoral 101 to facilitate installation. In the remainder of the description, the term cutting template refers to the three-dimensional modeling of the cutting template.

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

The cutting template 3 and the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, of a femoral component 101 adapted to the three-dimensional modeling of the femur 1.

These several other preparatory stages will be the subject of the following description.

After constructing the three-dimensional modeling of the femur 1, the construction method determines in the modeling morphometric data representative for example of the dimensions, of the thickness of the modeled femur. Morphometric data includes points reference points, referred to as remarkable points, used by surgeons to manufacture femoral components 101.

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 process 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.

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.

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.

Similar to a conventional physical femoral cutting template, the three-dimensional modeling of the cutting template 3 is made up of five successive femoral cuts 31, 32, 33, 34, 35 (or cutting boxes): an anterior femoral cut 31, a cut of anterior chamfer 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 antero-posterior 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 cutting line coordinates, which define their orientation in space.

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

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 face internal of the femoral component which is applied and maintained on the surface of the femur (see Figure 2-c).

With reference to Figure 5, in order to determine the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, several working sections 5 distributed in different plans. In other words, these work sections 5 are virtually comparable to cutting plans. 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 section of femur propagates. work 5. 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.

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

- 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

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

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 work sections. In a variant 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 all equal to 2 degrees. It is also conceivable that the two angular distances could be parameters modifiable by the user in the 3D design tool.

The anterior 501 and posterior 502 axes of revolution are spaced apart 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 depends on the size femoral. In one embodiment of the invention, the center distance is expressed in the form of an affine function of the femoral size.

Given that the three-dimensional modeling of the femur 1 is segmented into a plurality of working sections 5 and that the three-dimensional modeling of the cutting template 3 is shaped to be applied thereto, one or more working sections 5 can possibly pass through some of the start lines 41 and end of cut 42 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 or more working sections 5 can be included between two specific sections.

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

- the start of cut line 43 of the anterior femoral cut 31 and the end of cut line 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

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

The geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2,

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

- second variables XM1, rMl, RI representative of a medial femorotibial contact surface SI at the level of the medial condyle 61;

- third variables XM2, rM2, R2 representative of a lateral femorotibial contact surface S2 at the level of the lateral condyle 62; And - fourth variables XM3, rM3, R3 representative of a patellofemoral contact surface S3 at the level of the trochlea 63.

Prior to determining all of these geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, each of the work sections 5.

By definition, an osteophyte 7 is a bony growth forming at the ends of a bone in a joint. It is a response of the body to wear, degeneration, or destruction of the articular cartilage causing it to no longer perform its role as a shock absorber during exercise and the bone will suffer much more pressure.

In the context of the invention, the medical images used in the construction method to construct the three-dimensional modeling 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 modeling. Osteophytes can form both on the ends of the medial 61 and lateral 62 condyles of the femur and at the level of its notch (that is to say at the level of the trochlea 63).

By definition, osteophytes 7 constitute forms of aberration which move away from the original articular surfaces. In the three-dimensional modeling of femur 1, they are represented by sets of aberrant geometric points.

Depending on their location on the bony surface of the femur, and by extension of its three-dimensional modeling, the osteophyte(s) 7 visible or not in the working sections 5. An example of a working section 5 presenting 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.

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

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

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, the prosthetic size of which will be unsuitable for the patient being treated, causing them to suffer from patellofemoral pain and difficulty moving with their prosthesis.

Figure 7 shows the working section 5 illustrated in Figure 6 after application of 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 which were spatially close neighbors to the groups of aberrant points just removed, in the aim of creating/adding new geometric points such that they model the resected parts of the articular surface, that is to say here the contours of the medial 61 and lateral 62 condyles.

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.

The construction process, after having applied the osteophyte removal step, then determines all of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3.

With reference to Figure 8, which presents 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 process determines the first geometric variables Xmed and work 5 at the abscissa of the most medial point 611 of the medial condyle 61 and the most lateral point 612 of the lateral condyle 62.

Figure 9 takes the example of the set of geometric points defining the three-dimensional modeling of the femur 1 in the working section 5 presented in Figure 6, and illustrates the error made in the estimation of the medio-lateral 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 medio-lateral width MLD is equal to a medio-lateral width MLD1 of 74 mm. When applied, the MLD mediolateral width is equal to a MLD2 mediolateral width of 68.5 mm. Thus, the precision error made in estimating the MLD mediolateral width when osteophytes are not removed is approximately 8%. This precision error may possibly be greater depending on the sizes of the growths on the articular surface of the femur.

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

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 femorotibial contact surfaces SI, lateral femorotibial S2, and patellofemoral S3 in working section 5.

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 to its radius (called medial radius RI).

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).

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, -lateral and sagittal representative of the medial condyle 61, the lateral condyle 62 and the trochlea 63.

To do this, the construction method identifies all of 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 contact surfaces SI, femorotibial lateral tibial S2, and patellofemoral S3), then it applies circular regressions to the identified geometric points; thus allowing it to determine the circumferences and centers of the medial Cl, lateral C2, and trochlear C3 circles and therefore the corresponding variables XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3.

Finally, the construction method determines a plurality of values for all of 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,

As previously indicated, the construction process ultimately makes it possible to manufacture femoral components 101 specifically adapted to the specific morphologies of 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 placed in a plurality of patients having said femoral size.

In the case where the construction method must construct a personalized 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 can be a modifiable parameter in the 3D design tool. In another embodiment of the invention, it may be an imposed number of series.

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 process so that all of the working sections include the specific sections passing through the start of cut line 41 or end of cut 42 of all femoral cuts 31, 32, 33, 34, 35. Thus, all the working sections 5 included between two specific sections are part of a series of working sections 5. In different embodiment variants, the series only includes the specific section corresponding to the start of cut line 41 or the end of cut line 42; or both.

For each geometric variable Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3, the values determined in the work 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.

In the case of the construction of a standard femoral component 101, the preparatory steps are carried out and repeated for several sets of digital medical images associated with several distal femurs of patients. Several three-dimensional models of several femurs are first 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.

For each three-dimensional modeling of femur 1 belonging to a femoral size:

- the cutting template 3 is modeled, and

- the values of the geometric variables of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, three-dimensional femur 1 so that the method is able to analyze several values of a geometric variable Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, different three-dimensional modeling of the femur according to the same plane/same orientation.

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

From these statistical sets, the construction process determines, for each femoral size, standard values of the dimensions of the femoral cuts 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.

In one embodiment of the invention, it is possible 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 cuts 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 possible in one embodiment of the invention that the construction process can identify, for the different standard variables, evolutionary trends that can be expressed under the form of mathematical relationships, then allowing the values of the standard variables to be calculated using these mathematical relationships and knowing the value of the femoral size.

In another embodiment of the invention, the construction method is designed to determine affine functions of the form y = a.x + b from the evolving trends of the standard variables (averaged as indicated above or not), where :

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

- x is the femoral size;

- has a slope coefficient; And

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

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

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

Regardless of the type of femoral component 101 modeled (custom or standard), the preparatory steps end with obtaining the values of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3 (average values or standard values).

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

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

- 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;

- a medial femorotibial 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;

- a lateral femorotibial 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;

- a patellofemoral joint profile T3, by applying a second interpolation function to the values of the fourth geometric variables XM3, rM3, R3.

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

More precisely, the values of the geometric variables Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, where the medial and lateral profiles, and the three joint profiles spatially pass. Each of the five profiles is constructed by applying to all the values of the geometric variables through which they pass interpolation functions Xmed, Xlat, XM1, rMl, RI, XM2, rM2, R2, XM3, rM3, R3.

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 certainly different orientation but relatively close to each other (for example, when the anterior angular distance and the posterior angular distance are both equal to 2 degrees) ;

- in the case of a personalized femoral component 101, 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 cut 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

- 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, plurality of work sections 5.

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

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

Finally, the last step of the construction process consists of manufacturing a physical femoral component 101 based on the three-dimensional model provided by the 3D design tool.

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 medical digital 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 of 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 a anterior axis of revolution (502) in a medio-lateral 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, ), said geometric variables comprising first variables (Xmed, Xlat) representative of a mediolateral width (MLD), second variables (XM1, rMl, RI) representative of a medial femorotibial contact surface (SI) of a medial condyle (61), third variables (XM2, rM2, R2) representative of a lateral femorotibial 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, in which 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, in which 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), d 'a medial femorotibial joint profile (Tl) of the medial condyle (61) by interpolation of the values of the second variables (XM1, rMl, RI), of a lateral femorotibial joint profile (T2) of the condyle lateral (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 medical digital images comprises images from a medical scanner, for example in DICOM format.

6. Construction method according to claim 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. Construction method according to claim 6, in which the remarkable points comprise at least one most posterior point (21) of the medial condyle (61), a most posterior point (25) of the lateral condyle (62) and a point the most anterior (22) of a part of the distal femur.

8. Construction method according to any one of the preceding claims, in which the cutting template (3) comprises the establishment of several femoral cuts (31, 32, 33, 34, 35) which depend at least on the size femoral.

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

11. Construction method according to claims 9 and 10, in which the specific sections comprise at least one section which passes through a start line of cut (41) of the anterior femoral cut (31), and a section which passes through a end of cut 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, in which, 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 medial most 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 mediolateral 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 femorotibial 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 ray (RI), said coordinates of the medial center (Ml) and said medial ray (RI) constituting the second variables (XM1, rMl, RI ) associated with the work section (5).

16. Construction method according to claim 15, in which 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, in which, for each working section (5), obtaining the third variables (XM2, rM2, R2) representative of the lateral femorotibial 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, in which 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, in which, for each working section (5), obtaining the fourth variables (XM3, rM3, R3) representative of the patellofemoral 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 radius trochlear (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, in which 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. Construction method according to any one of claims 1 to 20, in which 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, the at least 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 personalized 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 medical digital images of femurs of several patients characterized by several femoral sizes, thus obtaining for each size femoral a set of statistical data relating to 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, femoral size.

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

24. Construction method according to claim 23, in which the statistical data sets associated with the several 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 femoral size.

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