FR3143318A1 - Method for constructing a joint component of a total knee prosthesis based on three-dimensional modeling in which osteophytes are removed - Google Patents

Abstract

The invention relates to a method of constructing a joint component for a joint element, firstly comprising a preparatory phase during which a three-dimensional modeling of the joint element is constructed which is then sectioned into several working sections (15) distributed in different planes and each containing a set of geometric points defining a section in the plane of the articulation element. Following this, a phase of osteophyte removal is carried out applied to each working section of the three-dimensional modeling, which consists of determining whether the working section studied contains aberrant zones (Z11, Z12) containing aberrant geometric points representative of osteophytes and if so, to remove these aberrant areas; allowing you to ultimately obtain a cleaned working section. All of the cleaned working sections are finally used to construct the femoral or tibial component. Abstract Figure: Figure 6

Description

Method for constructing an articular component of a total knee prosthesis from a three-dimensional model in which the osteophytes are removed

The invention relates to a method of constructing an articular component of a total knee prosthesis.

It relates more particularly to a method of constructing an articular component of a total knee prosthesis - such as a femoral component and a tibial component - for which said construction is based on three-dimensional modelling of an articulation element - such as the femur and the tibia - on which the articular component is to be placed.

Due to a greater life expectancy or the increase in the prevalence of obesity, more and more people suffer from osteoarthritis, which is a pathology that wears down or destroys articular cartilage. This results in pain when walking or even at rest, which reduces the quality of life. This is why knee arthroplasty is currently experiencing a growing boom, with a significant demand. The functional results of this surgical procedure have been improved in recent years thanks to: cutting-edge techniques that are more reliable and less invasive; better management of post-operative pain; and the introduction of intense and early physiotherapy.

As is 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 that they replace.

A total knee replacement must also allow the patient in whom it is fitted to have stable support so that he or she can regain a good walking perimeter (good capacity). Generally, a total knee replacement is only proposed and fitted in the event of serious injuries: advanced osteoarthritis, rheumatoid arthritis, traumatic destruction.

However, nearly 20% of patients today say they are dissatisfied with the placement of a total knee replacement, either because postoperative pain and pain after the placement of the total knee replacement persist, 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 a majority of them, it turns out in some cases that their prosthetic size is unsuitable for the patient's morphology, that is to say the morphology, or size, of the distal part of their femur; and/or that of the proximal part of their tibia; and/or that of their patella.

The femoral component is also the most complex component of the prosthesis to design and manufacture because it must reproduce the kinematics of the original knee (for example, flexion and extension movements); and the tibial component, although simpler to design, must be adapted to the tibia and the associated femoral component.

It is thus known to design femoral components and tibial components from digital medical images of the femur and tibia, whether to construct standardized models that fit into ranges of components, or to construct personalized models specific to patients.

However, the presence of osteophytes is often observed on the articulation elements, femur and tibia, which are bony growths forming at the ends of a bone in a joint. This is a response of the body to wear, degeneration, or destruction of the articular cartilage, meaning that it no longer fulfills its role as a shock absorber during an effort and that the bone will undergo much more pressure.

Several factors are responsible for the appearance of osteophytes, for example: age, arthritis, excess weight, significant stress on the bones during repeated movements or efforts (as is the case with athletes or people with a mainly manual/physical profession). Osteophytes are particularly common in people suffering from osteoarthritis. This joint disease is becoming more and more widespread with increasing life expectancy and a greater prevalence of obesity.

This is why femoral and tibial components constructed from medical digital images of femurs and tibias with osteophytes may not be suitable for patients. Indeed, these osteophytes constitute forms of aberration that distance from the native articular surfaces, thus tending to construct articular components that are poorly or poorly adapted to these native articular surfaces (before the formation of osteophytes), and very often oversized articular components.

There is therefore a need to improve the construction of such joint components so that they are best suited to conform to the shapes of native joint surfaces.

The invention proposes to address the issues set out above by aiming to very significantly improve the correspondence between the prosthetic size and the initial morphology of the patient's knee. This improvement consists of adapting as precisely as possible an articular component of the knee prosthesis to a native articular surface of a knee joint element on which the articular component is to be placed.

Thus, the invention relates to a method of constructing at least one joint component, of the femoral component or tibial component type, for a total knee prosthesis, said joint component being shaped to be placed on a joint element of the femur or tibia type, in which said construction method comprises a preparatory phase implementing at least the following steps:
- obtaining a set of digital medical images of a patient's joint element;
- construction of a three-dimensional model of the articulation element from the associated set of digital medical images;
- sectioning of the three-dimensional modeling of the articulation element into several working sections distributed in different planes, each working section being defined by a set of geometric points;
wherein the construction method comprises an osteophyte removal phase applied to each of the plurality of working sections to construct a plurality of cleaned working sections, said osteophyte removal phase comprising the following steps:
- determination in the working section of at least one aberrant zone representative of an osteophyte;
- construction of the cleaned working section associated with the working section, said cleaned working section corresponding to the working section in which the at least one aberrant zone is removed;
and wherein the construction method comprises a step of obtaining geometric variables representative of a geometry of the three-dimensional modeling of the articulation element in the several cleaned working sections;
said construction method then comprising a step of constructing the at least one joint component from values of the geometric variables.

In other words, depending on the construction process, the construction of a femoral component (respectively of a tibial component) goes through several successive phases which are:
- the preparatory phase;
- the osteophyte removal phase; and
- finally a three-dimensional modeling phase of the femoral component or the tibial component from which the physical articular component will be manufactured which will be placed on the patient.

The preparatory phase is based firstly on the three-dimensional modelling of the femur (respectively the tibia), more precisely of the distal part of the femur or distal femur (respectively the proximal part of the tibia or proximal tibia), of a patient. For this purpose, several medical digital images of the distal femur (respectively the proximal tibia) of the patient are collected, which are taken from different viewing angles in order to ultimately model it in three dimensions and in its entirety, to which digital processing is applied, for example a segmentation method. The three-dimensional modelling of the articulation element corresponds for example to a point cloud and/or a three-dimensional mesh.

The preparatory phase then comprises a sectioning of the three-dimensional modelling of the articulation element into several sections called working sections which are fictitious cutting planes oriented in different directions. Each of the working sections comprises a set of geometric points corresponding to the points defining the outline of the three-dimensional modelling of the articulation element and which are included in said working section.

Before the method implements image analysis to design the joint component (femoral component or tibial component), this method implements the osteophyte removal phase, which is actually a virtual removal phase of osteophytes in the three-dimensional modeling of the joint element, in order to build a new modeling (or a cleaned modeling) that will be closer to the native joint element (i.e. the joint element before the formation of osteophytes).

Carrying out an image analysis while leaving the osteophytes as they are would in fact lead to taking into account these osteophytes which form aberrations in the joint kinematics and in the dimensions of the articulation elements.

In other words, the construction process includes, before the three-dimensional modeling of the joint component, this phase of removing osteophytes, which therefore amounts to virtually removing any osteophytes from the three-dimensional modeling of the joint element in order to clean it.

The osteophyte removal phase is based on a virtual cleaning of each of the working sections segmenting the three-dimensional modeling of the articular component in order to obtain a plurality of cleaned working sections, and by extension a three-dimensional modeling of the cleaned articular component. The cleaning of the working sections consists in identifying the presence or absence in each of them of a set of points which would be aberrant and which would delimit aberrant zones representative of one or more osteophytes.

Once the osteophyte removal phase is complete, the construction process identifies in the cleaned three-dimensional model of the articulation element geometric variables characteristic of its morphology (without taking into account the aberrations induced by the osteophytes), and from which the construction process will be able to model a suitable joint component, to ultimately be able to ensure its physical manufacture.

According to a characteristic of the invention, each working section is delimited by an articular contour line extended to the right and to the left by respectively a right contour line and a left contour line, the right contour line and the left contour line being arranged on either side of a central axis contained in said working section,
and in which, during the osteophyte removal phase, for each working section, the following steps are implemented:
- determination in the working section of a reference zone framed by a first reference axis and a second reference axis which are parallel and distant from each other;
- determination in the working section of a right reference point and a left reference point, said right reference point corresponding to a point least to the right on the right contour line and contained in the reference zone and said left reference point corresponding to a point least to the left on the left contour line and contained in the reference zone;
- determining a right cutting line and a left cutting line in the working section, said right cutting line passing through the right reference point and said left cutting line passing through the left reference point;
- determination in the working section of at least two aberrant zones comprising a right aberrant zone and a left aberrant zone, the right aberrant zone being located to the right relative to the right cutting line and the left aberrant zone being located to the left relative to the left cutting line.

In other words, for each of the working sections of the articulation element, the removal of virtual osteophytes goes through several steps that are partly based on the practices of surgeons in the operating room, with first of all the search in a zone called the reference zone of at least one narrowest width of the bone, whether it is a femur or a tibia. As indicated above, the reference zone is determined as being between a first reference axis and a second reference axis. It is specified later, depending on the type of joint component to be modeled/manufactured, how the construction process identifies/locates these two axes in the three-dimensional models of the articulation elements.

Osteophytes can form on the entire surface of the articulating element, which is not smooth/flat. For example, the medial and lateral condyles of a femur have a rounded shape. Therefore, the cuts made by surgeons to remove osteophytes may be characterized by different orientations/directions imposed by the shape of the articulating element (in the example given, the curvature of the femoral condyles in the case where osteophytes have formed on their anterior and/or posterior part).

Therefore, and as previously indicated, a working section in the three-dimensional modeling of the articulation element (femur or tibia) is a fictitious cutting plane that can be oriented in a given direction (the set of directions basically describing a complete circle of 360 degrees) and which includes a set of geometric points defining an articular contour, or an articular contour line, representative of the articular surface of the articulation element modeled in this cutting plane.

Being contained in a working section/section plane, the contour line has a right side and a left side respectively delimited by a right contour line and a left contour line. Both of the two contour lines are located on either side of a central axis centrally crossing the articular surface. This axis of symmetry corresponds substantially to the extension axis of the articular element, namely the femoral axis or the tibial axis.

Depending on particular orientations, the right and left contour lines of the working section may correspond to a medial contour line and a lateral contour line of the articular surface; or to an anterior contour line and a posterior contour line.

Determination of the at least one narrowest width of the articular surface in the working section consists of a localization in the reference area:
- a right reference point corresponding to a point least to the right on the right contour line (in other words the point on the right contour line which is closest to the central axis), and
- a left reference point corresponding to a point least to the left on the left contour line (in other words the point on the left contour line which is closest to the central axis).

Thus, depending on specific working section orientations the reference points may correspond to the least medial point of the medial surface of the modeled bone and the least lateral point of the lateral surface; or to the least anterior point of the anterior surface of the modeled bone and the least posterior point of the posterior surface.

In the case where the right reference point and the left reference point are aligned along the same axis parallel to the two reference axes, only one narrowest width of the articulation element is considered. Otherwise, two narrowest widths are considered.

After determining the two reference points, a right cutting line and a left cutting line are determined, passing through the right reference point and the left reference point respectively.

Again, these cutting lines may in some working sections correspond to a medial cutting line and a lateral cutting line; or to an anterior cutting line and a posterior cutting line.

The last step implemented in the osteophyte removal phase is the actual removal of the sets of points considered to form aberrant areas representative of osteophytes. This removal consists of:
- determining at least two aberrant areas comprising a right aberrant area and a left aberrant area, the right aberrant area being located to the right relative to the right cutting line and the left aberrant area being located laterally relative to the left cutting line;
- the deletion of all points included in the right aberrant zone and the left aberrant zone.

In the particular orientations, the removal of osteophytes therefore amounts to removing at least one medial aberrant zone and one lateral aberrant zone; or else one anterior aberrant zone and one posterior aberrant zone.

According to one embodiment of the invention, the osteophyte removal phase also comprises a smoothing step during which an interpolation function is applied to the geometric points defining the articular surface of the bone modeled in the working section which were spatially close neighbors of the aberrant points just removed, with the aim of creating/adding new geometric points such that they model the virtually resected parts of the articular surface.

According to a characteristic of the invention, during the osteophyte removal phase, for each working section, the right cutting line and the left cutting line respectively have a right clearance angle and a left clearance angle relative to the central axis, said right clearance angle and said left clearance angle being between 0 and 30 degrees.

In the construction process, in each of the working sections of the three-dimensional modeling of the articulation element, the cutting directions considered according to the shape of the articulation element are spatially and geometrically translated by an inclination of the right and left cutting lines, such that the right cutting line and the left cutting line respectively form a right clearance angle and a left clearance angle relative to the central axis.

Depending on particular orientations of the working section, the right and left clearance angles can correspond either to medial and lateral clearance angles or to anterior and posterior clearance angles.

The areas considered as aberrant in the three-dimensional modeling of the articulation element and which are deleted remain those located respectively to the right of the right cutting line and to the left relative to the left cutting line. The right clearance angle and left clearance angle are defined in the construction method such that they can be between 0 degrees (meaning that the removal of osteophytes is carried out virtually according to the proximo-distal direction) and 30° degrees.

According to a characteristic of the invention, the preparatory phase comprises a determination of morphometric data in the three-dimensional modeling of the articulation element, said morphometric data characterizing a size of the articulation element.

According to a characteristic of the invention, the morphometric data comprises at least remarkable points located in the three-dimensional modeling of the articulation element.

In other words, during the preparatory phase, morphometric data are determined, corresponding for example to: specific points of the articulation element taken as references and/or landmarks by the surgeons, and which are designated as remarkable points; and to its dimensions. The remarkable points allow the construction process in particular to calculate/determine the size of the articulation element (whether it is a femur or a tibia). The size of the articulation element is considered as morphometric data since it characterizes its morphology.

According to a characteristic of the invention, when the articular component is of the femoral component type, the articulation element is of the femur type and the three-dimensional modeling of the articulation element corresponds to a three-dimensional modeling of the femur, such that said three-dimensional modeling of the femur comprises at least a three-dimensional modeling of a lateral condyle, a medial condyle and a trochlea.

According to a characteristic of the invention, when the articular component is of the femoral component type, 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 part of the distal femur.

From these three remarkable points, the construction process can determine the femoral size of the femur of the patient considered, which is considered as morphometric data since it characterizes the morphology of the femur.

According to a characteristic of the invention, when the articular component is of the femoral component type, 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.

In other words, the three-dimensional modeling of the distal femur is segmented into several working sections 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 to segment 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 that are 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.

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.

The two axes of revolution are separated by a center distance whose value depends on the femoral size. For example, this center distance is expressed in the form of an affine function of the femoral size. The center distance is coincident in a sagittal plane which extends orthogonally to the anterior and posterior axes of revolution.

According to a feature of the invention, in each working section, the articular contour line follows a contour of the lateral condyle, the medial condyle and the trochlea, and the right contour line and the left contour line correspond respectively to a medial contour line of the medial condyle and a lateral contour line of the lateral condyle.

In other words, regardless of the direction/orientation of the working section (i.e. whether it is an anterior or posterior working section), the right contour line and the left contour line correspond to the medial border of the medial condyle and the lateral border of the lateral condyle, respectively.

Thus, the steps of the osteophyte removal phase previously described are applied here in the context of the removal of osteophytes that would be present on the medial edge of the medial condyle and/or the lateral edge of the lateral condyle of the articular surface of the femur in the working section considered.

According to a characteristic of the invention, when the articular component is of the femoral component type, the right clearance angle and the left clearance angle correspond respectively to a femoral lateral clearance angle and to a femoral medial clearance angle which are non-zero for each of the working sections.

According to one embodiment of the invention, when the articular component is of the femoral component type, the femoral lateral clearance angle is the same for the posterior working sections and for the anterior working sections.

According to one embodiment of the invention, when the articular component is of the femoral component type, the femoral medial clearance angle is different between the posterior working sections and the anterior working sections.

In a preferred embodiment of the invention, the medial and lateral femoral clearance angles are respectively equal to 25 degrees and 15 degrees when the working section is a posterior working section; and are both equal to 15 degrees when it is an anterior working section.

According to a characteristic of the invention, when the articular component is of the femoral component type, during the osteophyte removal phase, for each working section, an extreme line of medio-lateral direction is determined passing through a most distal point of the lateral condyle or the medial condyle, and the first reference axis is determined as being distant from said extreme line by a first reference distance, the second reference axis is determined as being distant from said first reference axis by a second reference distance.

In other words, the notable points that the construction process identifies during the preparatory phase include the most distal point of the medial condyle and the most distal point of the lateral condyle.

During the osteophyte removal phase, for each working section, the two reference axes are determined from an extreme line of medio-lateral direction and containing either the point that is the most distal among the most distal point of the medial condyle or the most distal point of the lateral condyle. Optionally, both points can both belong to the extreme line if they are spatially aligned.

The two reference axes are both parallel to the end line, with the first reference axis being distant from the end line by a first reference distance which is generally of the order of 8 mm; and the second reference axis being distant from the first reference axis by a second reference distance generally between 6 mm and 10 mm, for example 8 mm.

According to a characteristic of the invention, during the osteophyte removal phase, for each working section, the following steps are implemented:
- determination of a medial interior line of the trochlea and a lateral interior line of the trochlea, arranged on either side of the central axis;
- determining in the working section at least two aberrant zones comprising a medial inner aberrant zone and a lateral inner aberrant zone, the medial inner aberrant zone being located laterally with respect to said medial inner line and the lateral inner aberrant zone being located medially by said lateral inner line.

According to a particular embodiment of the invention, the determination of the medial internal aberrant zone and the lateral internal aberrant zone comprises for each working section:
- determining in the working section a medial interior reference point and a lateral interior reference point, said medial interior reference point corresponding to a least medial point on the medial interior line and contained in the reference area, and said lateral interior reference point corresponding to a least lateral point on the lateral interior line and contained in the reference area;
- determining a medial inner cutting line and a lateral inner cutting line in the working section, said medial inner cutting line passing through the medial inner reference point and said lateral inner cutting line passing through the lateral inner reference point

According to a feature of the invention, during the osteophyte removal phase, for each working section, the medial inner cutting line and the lateral inner cutting line respectively have a medial inner clearance angle and a lateral inner clearance angle relative to the central axis, said medial inner clearance angle and said lateral inner clearance angle being between 0 and 30 degrees.

In addition to the medial border of the medial condyle and the lateral border of the lateral condyle, osteophytes can also form at the level of the notch/trochlea of the distal femur; the notch including the lateral border of the medial condyle and the medial border of the lateral condyle. Thus, the steps described above aim at the removal, in the working section considered, of aberrant areas representative of osteophytes that would present the articular surface of the femur at the level of the trochlea.

The procedure for removing osteophytes at the trochlea is similar in principle to the procedure for removing them at the medial edge of the medial condyle and the lateral edge of the lateral condyle.

The medial and lateral borders of the trochlea are considered to be included respectively in a medial interior line and a lateral interior line positioned one on either side of the previously defined central axis.

The steps for removing osteophytes in the trochlea begin with the search, in the reference area previously determined when implementing the steps for removing osteophytes at the level of the two condyles, for the greatest separation distance(s) between the medial edge and the lateral edge of the trochlea. Thus, a medial inner reference point and a lateral inner reference point are sought, such that the medial inner reference point corresponds to the least medial point on the medial inner line and the lateral inner reference point corresponds to the least lateral point on the lateral inner line.

From the medial inner reference point and the lateral inner reference point are respectively determined a medial inner cutting line passing through the medial inner reference point and a lateral inner cutting line passing through the lateral inner reference point, which medial inner and lateral inner cutting lines respectively have a medial inner clearance angle and a lateral inner clearance angle relative to the central axis.

Following this, the construction process removes the aberrant areas present at the trochlea, these aberrant areas corresponding to a medial interior aberrant area and a lateral interior aberrant area such as:
- the medial inner aberrant zone is located lateral to the medial inner cut line, and

- the lateral inner aberrant zone is located medially to the lateral inner section line.

In one embodiment of the invention, the lateral interior clearance angle is the same for the rear working sections and for the front working sections.

In one embodiment of the invention, the medial inner clearance angle is different between the posterior working sections and the anterior working sections.

In other words, in one embodiment of the invention, the values of the medial inside clearance angles and the lateral inside clearance angles may respectively have the same properties as those of the medial clearance angles and the lateral clearance angles.

In a preferred embodiment of the invention:
- the value of the medial inner clearance angle is equal to the value of the lateral clearance angle, i.e. the value of the medial inner clearance angle is equal to 15 degrees regardless of the working section considered (anterior working section or posterior working section); and
- the value of the lateral inner clearance angle is equal to the value of the medial clearance angle, that is, the value of the lateral inner clearance angle is equal to 25 degrees when the working section is a posterior working section, and is equal to 15 degrees when the working section is an anterior working section.

According to a first embodiment variant of the invention, the construction method can implement, as described so far, in the working section, the steps for removing osteophytes that may have formed on the medial edge of the lateral condyle and the lateral edge of the lateral condyle of the articular surface of the femur before proceeding with the removal of osteophytes that may have formed in the trochlea.

In a second embodiment of the invention, the construction method this time implements the steps of removing osteophytes at the trochlea before those of removing osteophytes at the medial edge of the lateral condyle and the lateral edge of the lateral condyle. In this embodiment, this means that the determination of the first and second reference axes delimiting the reference zone is carried out before the step of determining in the working section the medial inner reference point and the lateral inner reference point.

According to a characteristic of the invention, when the articular component is of the femoral component type, the preparatory phase comprises a step of determining a cutting template in the three-dimensional modeling of the femur, based on the morphometric data.

In practice, the cutting template is used by the surgeon, who applies it to the bony surface of the femur, to make bone cuts and define support faces that are used for the placement of the femoral component. The cutting template has the same shape/curvature as the internal face of the femoral component that is applied and held on the surface of the distal femur.

From morphometric data of the three-dimensional model of the cleaned/resected femur, including the distal point and the most posterior point of each of the medial and lateral condyles, the construction method models a three-dimensional model of the cutting template, which will then be used by the construction method for the construction of the three-dimensional model of a femoral component.

Note that the first reference axis physically relates to a mediolateral cutting line in a cutting plane for which any bony portion of the articular surface located distal to this mediolateral cutting line is resected. Thus, the first reference axis corresponds in the three-dimensional modeling of the femur to the support faces of the femoral component.

According to a characteristic of the invention, when the articular component is of the tibial component type, the articulation element is of the tibia type and the three-dimensional modeling of the articulation element corresponds to a three-dimensional modeling of the tibia, such that said three-dimensional modeling of the tibia comprises at least a three-dimensional modeling of a tibial plateau, a medial compartment and a lateral compartment.

According to a characteristic of the invention, when the articular component is of the tibial component type, the remarkable points comprise at least one most anterior point of the medial compartment or one most anterior point of the lateral compartment.

Specifically, the notable points include the most anterior point of the medial compartment or the most anterior point of the lateral compartment depending on the patient's knee deformity. If the knee deformity is genu varum, then the notable points include the most anterior point of the medial compartment. If the knee deformity is genu valgum, then the notable points include the most anterior point of the lateral compartment.

In a first embodiment of the invention, the type of deformation is known from the construction method by being entered by an operator, such as the surgeon, implementing it.

In a second embodiment of the invention, when a tibial component is to be modeled, the preparatory phase comprises an additional step during which the construction method analyzes the morphometric data relating to the three-dimensional modeling of the tibia to determine the type of deformation, and from there identify the remarkable point of interest among the most anterior point of the medial compartment and the most anterior point of the lateral compartment.

According to a characteristic of the invention, when the articular component is of the tibial component type, the preparatory phase comprises the determination of a tibial resection plane which is distant, in a proximo-distal direction of the tibia, either from the most anterior point of the medial compartment by a first given distance, or from the most anterior point of the lateral compartment by a second given distance.

In the case of a genu varum deformity, the tibial resection plane is distant from the most anterior point of the medial compartment by a medial distance generally equal to 6 mm. In the case of a genu varum deformity, the tibial resection plane is distant from the most anterior point of the medial compartment by an external distance generally equal to 10 mm. The medial and lateral distance values are relative to the practices of surgeons in the resection of the proximal part of a tibia and the placement of a tibial component.

Thus, the entire bony part of the tibia located above the tibial resection plane is resected. The articular surface cleaned at the level of the tibial resection plane therefore corresponds to the support surface on which the tibial component will be placed.

In a first embodiment of the invention, the tibial resection plane is a horizontal plane distant by the first distance (respectively the second distance) from the most anterior point of the medial compartment (respectively the lateral compartment).

In a second embodiment of the invention, the tibial resection plane has a non-zero posterior slope of less than or equal to 15 degrees, for example a posterior slope of 3 degrees.

In a third embodiment of the invention, it is possible for the tibial resection plane to have a non-zero varus valgus of less than or equal to 5 degrees, for example a varus valgus of 3 degrees.

According to a characteristic of the invention, when the articular component is of the tibial component type, during the osteophyte removal phase, for each working section, the first reference axis is determined corresponding to the intersection between the working section and the tibial resection plane, and the second reference axis is determined as being distant from said first reference axis by a reference distance along the central axis.

In a preferred embodiment of the invention, the reference distance is equal to 6 mm; meaning that the second reference axis is parallel to the first reference axis of this reference distance.

According to a characteristic of the invention, when the articular component is of the tibial component type, during the osteophyte removal phase, for each working section, the right clearance angle and the left clearance angle are identical for each of the working sections.

In a preferred embodiment of the invention, when the articular component is of the tibial component type, for each working section, the right clearance angle and the left clearance angle are zero.

In other words, in this preferred embodiment of the invention, the right and left cutting lines extend parallel to the central axis.

According to a characteristic of the invention, when the articular component is a tibial component, the several working sections are either:
- sagittal sections parallel to each other and all orthogonal to a medio-lateral direction or an anteroposterior direction; or
- sections distributed in different planes around one or more axes of revolution in a proximo-distal direction.

In other words, during the preparatory phase, in a first embodiment of the invention, the three-dimensional modeling of the tibia is sectioned into a plurality of sagittal sections which are parallel to each other and spaced apart from each other by a separation distance; and all orthogonal to a medio-lateral direction or an anteroposterior direction.

Thus, in this first embodiment of the invention, and as previously explained, depending on the direction with which all the working sections are orthogonal:
- the right and left contour lines of the working section may correspond either to a medial contour line and a lateral contour line of the articular surface of the tibia; or to an anterior contour line and a posterior contour line;
- the right and left reference points can correspond either to the least medial point of the medial surface of the tibia and to the least lateral point of the lateral surface; or to the least anterior point of the anterior surface of the modeled bone and to the least posterior point of the posterior surface;
- the right and left cutting lines can correspond either to a medial cutting line and a lateral cutting line; or to an anterior cutting line and a posterior cutting line;
- and the right and left clearance angles may correspond either to medial and lateral clearance angles, or to anterior and posterior clearance angles; this with the aim of removing either at least one medial aberrant zone and one lateral aberrant zone of the tibial articular surface; or at least one anterior aberrant zone and one posterior aberrant zone.

The sagittal orientation of the working sections is defined according to a line called the Akagi line which connects the medial border of the anterior tibial tuberosity and the insertion of the posterior cruciate ligament.

In a second embodiment, the working sections are distributed around one or more axes of revolution in a medio-lateral direction; for example a medial axis of revolution and a lateral axis of revolution located respectively medially and laterally in the three-dimensional modalization of the tibia.

According to a characteristic of the invention, when the articular component is of the tibial component type, the set of digital medical images comprises images from a medical scanner, for example in DICOM format.

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:

is a schematic illustration of a total knee replacement, which consists of a femoral component, a tibial component, a patellar component (not shown) and an insert;

groups together three-dimensional views of a three-dimensional model of a typical femoral component that can be constructed using the construction method, with a front view (a) and a rear view (b);

illustrates two perspective views of a three-dimensional model of a distal femur of a patient on which the medial and lateral condyles, as well as the trochlea, are visible; with the first view (a), respectively the second view (b), oriented so that the anterior part, respectively the posterior part, of the two condyles are facing the observer; and morphometric data are identified including remarkable points;

illustrates the segmentation of the three-dimensional modeling of the femur, which is here represented 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 proximo-distal direction center distance (a); and an example of superposition of three successive working sections articulated around one of the two axes of revolution;

is a representation of the set of geometric points modeling the outline of 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;

illustrates the principle of the osteophyte removal phase applied to the contour line of the femur of the for the removal of aberrant areas representative of osteophytes that have formed at the medial edge of the medial condyle and at the lateral edge of the lateral condyle of the distal femur;

illustrates the principle of the osteophyte removal phase applied to the contour line of the femur And for the removal of aberrant areas representative of osteophytes that have formed at the level of the notch/trochlea of the distal femur;

is a representation of the contour line of the femur considered in Figures 5 to once cleaned after application of the osteophyte removal phase, and for which the set of points defining it no longer includes the aberrant points;

illustrates the difference in the value of the medio-lateral width determined when the outliers of the contour line of the femur considered in the has ; the mediolateral width being a geometric variable used in the construction of the three-dimensional modeling of the femoral component;

illustrates two three-dimensional models of a proximal part of a tibia in which are identified respectively the most anterior point of the lateral compartment (a), and the most anterior point of the medial compartment (b); and draws the tibial resection plane;

illustrates, by means of a top view of a three-dimensional model of a proximal part of the tibia, the two possibilities of sectioning said three-dimensional model into a plurality of working sections: a sagittal sectioning with sagittal sections parallel to each other and all orthogonal to a medio-lateral direction or an anteroposterior direction (a), a sectioning in different planes around several axes of revolution (b); also shown is the three-dimensional modeling of the tibial component resulting from the construction step.

illustrates on a top view of a tibia the concept of Akagi line from which is defined the sagittal orientation of the working sections according to the sectioning presented -has ;

is a schematic illustration of a contour line of the tibia in a sagittal section to which the osteophyte removal phase is applied;

shows the contour line of the tibia considered in the before and after application of the osteophyte removal method.

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

In reference to the , 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 comprise a patellar component, not shown in the .

The construction method proposed in the invention makes it possible to construct femoral 101 and/or tibial 102 components and aims to:
- to 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 101 and the tibial component 102 to the native surfaces of the distal part of the femur and the proximal part of the tibia of the patient, in order to provide kinematics which are as close as possible to the kinematics of the physiology of the patient's knee.

Regardless of the type of joint component 101; 102 considered, the construction method is based on the succession in particular of two phases which are a preparatory phase and an osteophyte removal phase; followed by a construction step during which the joint component 101; 102 is first modeled three-dimensionally according to at least the actions carried out during the preparatory phase and the osteophyte removal phase; then the physical joint component 101; 102 is manufactured on the basis of its three-dimensional modeling. An example of three-dimensional modeling of a typical femoral component 101 is illustrated .

The two phases and all the steps leading to the construction of the articular component 101; 102 are based on the same principles/foundations whether the articulation element is a femur or a tibia. The remainder of the description is based on a general description of these phases and steps. Then, details are then provided for each of them by considering that the articular component 101; 102 is a femoral component 101; then a tibial component 102.

The preparatory and osteophyte removal phases, and the three-dimensional modeling of the joint components 101; 102 are implemented using a 3D design tool installed on a workstation, for example a desktop computer.

The preparatory phase begins by collecting several medical digital images of a distal femur and/or a proximal tibia of a patient, which are taken from different viewing angles. In the remainder of the description, for greater convenience, the terms femur and tibia alone designate the distal femur and the proximal tibia respectively. In one embodiment of the invention, these medical digital images may come from a medical scanner, and be presented in 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, in order to obtain, depending on the application context, a three-dimensional model of a femur 1 or a tibia 2 corresponding to a point cloud virtually and spatially forming in its entirety the bony surface of the femur or tibia. With reference to the , are notably modeled in the three-dimensional modeling of the femur 1 the medial condyle 61, the lateral condyle 62, and the trochlea 63.

In reference to the , the three-dimensional modeling of the femur 1 includes the three-dimensional models of the medial condyles 161 and lateral condyles 162, and the trochlea 163 (also called notch).

In reference to the , the three-dimensional modeling of the tibia 2 includes the three-dimensional models of the tibial plateau 270, and the medial 271 and lateral 272 compartments.

In an alternative embodiment of the invention, the three-dimensional models of the femur 1 and the tibia 2 can also be modeled using a 3D meshing method. In a second alternative embodiment, both types of modeling are proposed by the 3D design tool. In a third alternative, it is conceivable that the 3D design tool can propose an option for applying textures to the three-dimensional models of the femur 1 and the tibia 2, the shades and colors of which are representative of a physical femur and tibia.

Once the femur or tibia has been modeled three-dimensionally, the preparatory phase includes a determination in both types of modeling of morphometric data. These morphometric data can correspond to: precise points of the articulation element taken as references and/or landmarks by the surgeons, and which are designated as being remarkable points 110, 111, 112, 113, 114; 211, 212; and to dimensions thereof. The remarkable points 110, 111, 112, 113, 114; 211, 212 allow in particular the construction method to calculate/determine the size of the articulation element, which size is also considered as morphometric data since it characterizes the morphology of the articulation element.

When the three-dimensional modeling considered is that of a femur, the remarkable points 110, 111, 112, 113, 114 include for example at least the following points among:
- the most anterior point 110 of the femur, and the most posterior points 111, 112 of the medial 161 and lateral 162 condyles, all three of which are used to determine the size of the femur (or femoral size), as well as:
- the most distal points 113, 114 of the medial 161 and lateral 162 condyles which are determined with a view to implementing the osteophyte removal phase (see below).

When the three-dimensional model considered is that of a tibia, the remarkable points 211, 212 may be a function of a deformation that the patient's knee presents. If the deformation of the knee is of the genu varum type, then the remarkable points include the most anterior point 211 of the medial compartment 271. If the deformation of the knee is of the genu valgum type, then the remarkable points include the most anterior point 272 of the lateral compartment 212. One or the other of the two most anterior points 271, 272 is then used as a landmark when carrying out the osteophyte removal phase (see below).

In a first embodiment of the invention, the type of deformation is known from the construction method by being entered by an operator, such as the surgeon, implementing it.

In a second embodiment of the invention, the preparatory phase comprises an additional step during which the construction method analyzes the morphometric data relating to the three-dimensional modeling of the tibia 2 to determine the type of deformation, and from there identify the remarkable point 271, 272 of interest among the most anterior point of the medial compartment 271 and the most anterior point of the lateral compartment 272.

In reference to the And , the preparatory phase then comprises a sectioning of the three-dimensional modelling of the articulation element 1; 2 into several sections called working sections 15; 25 which are virtually comparable to fictitious cutting planes oriented in different directions. Each of the working sections 15; 25 comprises a set of geometric points (see when the articulating element is a femur) corresponding to the points defining the outline of the articulating element (see the illustration diagram for which is represented the outline of the three-dimensional modeling of the tibia 2 in a working section 25 or 251), or articular contour line, modeled according to the direction of the plane in which said working section 15 propagates; 25.

Being contained in a working section, the contour line has a right side and a left side respectively delimited by a right contour line 12; 22 and a left contour line 11; 21. Both of the two contour lines 11, 12; 21, 22 are located on either side of a central axis 10; 20 centrally crossing the articular surface. This axis of symmetry corresponds substantially to the extension axis of the articular element, namely the femoral axis or the tibial axis.

Depending on particular orientations of the working sections 15; 25, the right contour lines 12; 22 and left contour lines 11; 21 of the working section may correspond to a medial contour line and a lateral contour line of the surface of the articular element; or else to an anterior contour line and a posterior contour line; or else to an intermediate contour line between medial and anterior and an intermediate contour line between lateral and posterior.

Following the preparatory phase, the construction process implements the osteophyte removal phase.

By definition, osteophytes 17; 27 are growths forming aberrations in joint kinematics and altering the native dimensions of the articulation elements.

In the context of the invention, the medical images used in the construction method to construct the three-dimensional modeling of the femur 1 and the tibia 2 are taken before any surgical intervention, meaning that if the femur and/or the tibia of a patient has one or more osteophytes 17; 27, this or these will be present in the medical digital images, and are therefore represented in the three-dimensional models of the articulation elements 1; 2 by a set of aberrant geometric points forming aberrant zones Z11, Z12, Z13, Z14; Z21, Z22; in the sense that these zones were not present natively and developed over time, with age. In a femur, the osteophytes can form on the medial and lateral ends of the respective medial 161 and lateral 162 condyles of the femur, as well as at the trochlea 163; In a tibia, osteophytes can form at the tibial plateau 270, on the surfaces and edges of the medial 271 and lateral 272 behaviors.

Since the osteophytes 17; 27 constitute aberrant points in the three-dimensional modeling of the articulation element 1; 2, they can lead to a poor evaluation/estimation of the dimensions of the three-dimensional modeling of the articular component 101; 102 (an example is presented later); and therefore to the manufacture of an oversized physical articular component 101; 102 whose prosthetic bulk will be unsuitable for the patient being treated, thus inducing pain and difficulty in moving with his prosthesis.

This is why this osteophyte removal phase is implemented in the construction process.

The osteophyte removal phase is applied to all of the working sections 15; 25 sectioning the three-dimensional models of the femur 1 and the tibia 2. Depending on the location of the osteophytes 17; 27 on the bone surface of the femur or the tibia, and by extension of their three-dimensional modeling, the working sections 15; 25 may have one or more aberrant zones Z11, Z12, Z13, Z14; Z21, Z22, or none at all. In the case where the analyzed working section 15; 25 does not have any osteophytes 17; 27, it is left as is. In the case where it does, the aberrant zone(s) Z11, Z12, Z13, Z14; Z21, Z22 are virtually removed in order to construct/obtain a working section 15; 25 said cleaned which will be closer to the native articulation element according to the cutting plane in which the working section 15 propagates; 25.

The cleaned working sections 15; 25 are then used in the following steps to model the three-dimensional modeling of the articulation element 1; 2.

Following the osteophyte removal phase, the method implements a step of obtaining geometric variables in the several cleaned working sections 15; 25, which are representative of the morphology of the patient's articulation element before formation of the osteophytes 17; 27.

The determined geometric variables are then used during a construction step to model the three-dimensional modeling of the joint component 101; 102 which is finally physically manufactured from it.

The osteophyte removal phase includes several steps implemented in each working section 15; 25, and fundamentally based on the practices of surgeons in the operating room.

Whether the articulation element considered is a femur or a tibia, the first step of the osteophyte removal phase consists of searching in the analyzed working section 15; 25 for at least one width which is the narrowest of the bone in a zone called reference zone R1; R2 between a first reference axis X11; X21 and a second reference axis X12; X22 which are parallel and distant from each other.

Determining the at least one narrowest width in the working section 15; 25 is equivalent to locating in the reference zone R1; R2:
- a right reference point P12; P22 corresponding to a point least to the right on the right contour line 12; 22 (in other words the point on the right contour line 12; 22 which is closest to the central axis 10; 20), and
- a left reference point P11; P21 corresponding to a point least to the left on the left contour line 11; 21 (in other words the point on the left contour line 11; 21 which is closest to the central axis 10; 20).

In the case where the right reference point P12; P22 and the left reference point P11; P21 are aligned along the same axis parallel to the two reference axes X11, X12; X21; X22; only one narrowest width of the articulation element is considered. Otherwise, two narrowest widths are considered.

Following the determination of the two reference points P11, P12; P21, P22, a right cutting line C12; C22 and a left cutting line C11; C21 are determined, passing respectively through the right reference point P12, P22 and the left reference point P11; P21. More precisely, the cutting lines C11, C12; C21, C22 are geometrically half-lines having respectively as origins the reference points P11, P12; P21, P22.

The last step implemented is the effective deletion of the sets of points considered as forming aberrant zones Z11, Z12, Z13, Z14; Z21, Z22 representative of osteophytes 17; 27 with:
- determining at least two aberrant zones Z11, Z12; Z21, Z22 comprising a right aberrant zone Z12; Z22 and a left aberrant zone Z11; Z21, the right aberrant zone Z12; Z22 being located to the right relative to the right cutting line C12; C22 and the left aberrant zone Z11; Z21 being located to the left relative to the left cutting line C11; C21; and
- the deletion of all points included in the right aberrant zone Z12; Z22 and the left aberrant zone Z11; Z21.

In each of the working sections of the three-dimensional modeling of the articulation element 1; 2, the cutting directions considered as a function of the shape of the articulation element are translated spatially and geometrically by inclinations of the right cutting lines C12; C22 and left cutting lines C11; C21 such that the right cutting line C12; C22 and the left cutting line C11; C21 respectively form a right clearance angle A2; A6 and a left clearance angle A1; A5 relative to the central axis 10; 20.

The aberrant zones Z11, Z12; Z21, Z22 remain those located respectively to the right of the right cutting line C12; C22 and to the left relative to the left cutting line C11; C21. The right clearance angle A2; A6 and left clearance angle A1; A5 are defined as being able to be between 0 degrees (meaning that the removal of osteophytes is carried out virtually in a direction orthogonal to the reference axes) and 30° degrees.

In one embodiment of the invention, the osteophyte removal phase optionally concludes with a smoothing step during which an interpolation function is applied in the working section 15; 25 to the geometric points defining the articular surface of the modeled femur or tibia which were spatially close neighbors of the aberrant points which have just been removed, with the aim of creating/adding new geometric points such that they model the resected parts of the articular surface.

The remainder of the description provides more details on the sectioning of the three-dimensional modeling of the articulation element 1; 2 and the osteophyte removal phase depending on whether the articular component 101; 102 to be constructed is a femoral component 101 or a tibial component 102.

In the case where a femoral component 101 is to be constructed, with reference to the , the working sections 15 sectioning the three-dimensional modeling of the femur 1 are distributed around two axes of revolution 153, 154 in a mediolateral direction: an anterior axis of revolution 154 and a posterior axis of revolution 153. The anterior 154 and posterior 153 axes of revolution are used respectively for sectioning the anterior part and the posterior part of the three-dimensional modeling of the femur 1. Each of the working sections 15 around the anterior axis of revolution 154 (called anterior working sections 152) and the posterior axis of revolution 153 (called posterior working sections 151) is distant from the working sections 15 which are 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.

In an alternative embodiment of the invention, the anterior, respectively posterior, angular distance separating an anterior working section 152, respectively posterior 154, from its close neighbors is the same for all the anterior working sections 152, respectively posterior 151. 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 153, 154 are separated by a center distance 155 whose value depends on the femoral size. For example, this center distance is expressed in the form of an affine function of the femoral size. The center distance 155 coincides in a sagittal plane which extends orthogonally to the anterior 154 and posterior 153 axes of revolution.

There illustrates an example of a working section 15 comprising a set of geometric points defining the contour line of the modeled femur in the stroke plane in which the working section 15 propagates, and having several groups of aberrant points representative of osteophytes 17. The contour line of the femur follows the contour of the medial condyle 161, the trochlea 163 and the lateral condyle 162.

Regardless of the working section (anterior working section 152 or posterior working section 151), the right contour line 12 and the left contour line 11 correspond respectively to a medial contour line of the medial condyle 161 and a lateral contour line of the lateral condyle 162 (i.e. lines defining the external contours/curvatures of the two condyles 161, 162). Each geometric point in the working section 15 is defined by a mediolateral coordinate (abscissa axis ML of mediolateral direction) and by a radial coordinate (ordinate axis r of radial direction).

In reference to the , the aberrant right Z12 and left Z11 zones therefore correspond to osteophytes formed on the medial edge of the medial condyle 161 and on the lateral edge of the lateral condyle 162.

When implementing the osteophyte removal phase, the first reference axis X11 and the second reference axis X12 are determined from an extreme line 110 in a mediolateral direction passing through the most distal point 113 of the lateral condyle 161, or the most distal point 114 of the medial condyle 162, or both if they are aligned mediolaterally. The first reference axis X11 is determined to be distant from said extreme line X10 by a first reference distance d11, the second reference axis X12 is determined to be distant from said first reference axis X11 by a second reference distance d12. The first reference distance d11 is generally of the order of 8 mm, and the second reference distance d12 is generally between 6 mm and 10 mm, for example 8 mm.

Then identified in the reference zone R1 between the two reference axes X11, X12 are the right reference point P12 and the left reference point P11 which correspond respectively to the least lateral point of the lateral condyle 162 (i.e. the lateral/right contour line 12) and to the least medial point of the medial condyle 161 (i.e. the medial/left contour line 11); and through which pass a right cutting line C12, i.e. a lateral cutting line, and a left cutting line C11, i.e. a medial cutting line.

The right A2 and left A1 clearance angles formed by the inclination of the right C12 and left C11 cutting lines relative to the central axis 10 correspond to a femoral lateral clearance angle and a femoral medial clearance angle.

As illustrated , the femoral lateral clearance angle A2 is defined such that the right section line C12 (lateral) slopes in a medial direction relative to the central axis 10; and the femoral medial clearance angle A1 is defined such that the left section line C11 (medial) slopes in a lateral direction relative to the central axis 10.

The groups of points forming the aberrant zones Z11, Z12 and which are deleted are located on the contour line of the femur medially to the left section line C11 (medial) and laterally to the right section line C12 (lateral).

As previously stated, the right A2 (i.e. the femoral lateral clearance angle) and left A1 (i.e. the femoral medial clearance angle) clearance angles can both be between 0° and 30°.

In one embodiment of the invention, the femoral lateral clearance angle A2 is the same for the posterior working sections 152 and for the anterior working sections 151.

In one embodiment of the invention, the femoral medial clearance angle A1 is different between the posterior working sections 152 and the anterior working sections 151.

In a preferred embodiment of the invention, the medial A1 and lateral femoral A2 clearance angles are respectively equal to 25 degrees and 15 degrees when the working section 15 is a posterior working section 151; and are both equal to 15 degrees when it is an anterior working section 152.

In the case of constructing a femoral component 101, the osteophyte removal phase also includes steps for removing osteophytes 17 that may have formed in the notch/trochlea 163 of the femur. Referring to Figures 5 and 6, an osteophyte 17 has formed at the lateral edge of the medial condyle 161, i.e. at the medial edge of the trochlea 163.

The steps for removing osteophytes in the trochlea 163 are similar to those performed for removing osteophytes 17 at the medial edge of the medial condyle (left aberrant zone Z11) and at the lateral edge of the lateral condyle (right aberrant zone Z12).

In reference to the , the medial and lateral edges of the trochlea 163 are considered to be included respectively in a medial interior line 13 and a lateral interior line 14 positioned one on either side of the central axis 10 previously defined.

The steps for removing osteophytes in the trochlea 163 begin with the search, in the previously determined reference area R1, for the greatest medio-lateral direction spacing distance(s) between the medial interior line 13 and a lateral interior line 14. Thus, a medial interior reference point P13 and a lateral interior reference point P14 are searched for, such that the medial interior reference point P13 corresponds to the least medial point on the medial interior line 13 and the lateral interior reference point P14 corresponds to the least lateral point on the lateral interior line 14.

From the medial inner reference point P13 and the lateral inner reference point P14 are determined a medial inner cutting line C13 passing through the medial inner reference point P13 and a lateral inner cutting line C14 passing through the lateral inner reference point P14, which medial inner cutting lines C13 and lateral inner cutting lines C14 respectively have a medial inner clearance angle A3 and a lateral inner clearance angle A4 relative to the central axis 10. Like the right cutting lines C12; C22 and left C11; C12, the medial inner cutting lines C13 and lateral inner cutting lines C14 are geometrically half-lines originating from the medial inner reference point P13 and the lateral inner reference point P14.

The medial inside clearance angle A3 is defined such that the medial inside cut line C13 slopes in a medial direction relative to the central axis 10; and the lateral inside clearance angle A4 is defined such that the lateral inside cut line C14 slopes in a lateral direction relative to the central axis 10.

The aberrant zones Z13, Z14 representative of osteophytes 17 having formed in the trochlea 163, and which are deleted, comprise a medial inner aberrant zone Z13 and a lateral inner aberrant zone Z14.

The medial inner aberrant zone Z13 includes all geometric points located lateral to the medial inner section line C13, and the lateral inner aberrant zone Z14 includes all geometric points located medially to the lateral inner section line C14.

The values of the medial inner clearance angles A3 and medial inner clearance angles A4 are both between 0° and 30°.

In one embodiment of the invention, the lateral internal clearance angle A4 is the same for the rear working sections 151 and for the front working sections 152.

In one embodiment of the invention, the medial inner clearance angle A3 is different between the posterior working sections 151 and the anterior working sections 152.

In a preferred embodiment of the invention, the medial inner clearance angles A3 and lateral femoral inner clearance angles A4 are respectively equal to 25 degrees and 15 degrees when the working section 15 is a posterior working section 151; and are both equal to 15 degrees when it is an anterior working section 152. In other words, the medial inner clearance angles A3 and lateral femoral inner clearance angles A4 respectively take the same values as the medial A1 and lateral femoral A2 clearance angles.

In a first variant embodiment of the invention, the construction method carries out in the working section 15 considered the steps for the removal of osteophytes 17 which may have formed on the external edges of the condyles 161, 162 before proceeding with the removal of those which may have formed in the trochlea 163.

In a second variant embodiment of the invention, the construction method this time removes any osteophytes present at the trochlea 163 before those that may have formed at the external edges of the condyles 161, 162. In this variant embodiment, the determination of the first and second reference axes X11, X12 is in fact carried out before the step of determining in the working section 15 the medial internal reference point P13 and the lateral internal reference point P14, and is therefore not repeated as indicated up to now before the step of determining the right reference point P12 and the left reference point P11.

In a third variant embodiment of the invention, following the determination of the first and second reference axes X11, X12, the method simultaneously executes the remaining steps for the removal of osteophytes at the external edges of the condyles 161, 162 and the trochlea 163.

There shows the contour line of the modeled femur in the working section 15 considered in Figures 5 to after application:
- the phase of removing aberrant zones Z11, Z12, Z13, Z14; and
- from the smoothing step previously described.

There shows a comparison, for the working section 15 considered so far, between the contour line of the femur before carrying out the osteophyte removal phase (top figure, with reference to the ) and once it has been cleaned (bottom figure, referring to the ) with all the aberrant zones Z11, Z12, Z13, Z14 removed.

As previously indicated, following the osteophyte removal phase, the method implements a step of obtaining geometric variables consisting of determining in the cleaned working sections 15; 25 geometric variables allowing the construction of the three-dimensional modeling of the articular component 10; 102.

In the case of a femur, the geometric variables sought in the working section 15 include the determination, on the first reference axis X11, of the abscissa of the most medial point of the medial condyle 161 and the abscissa of the most lateral point of the lateral condyle 162. These two abscissas make it possible to determine a medio-lateral width MLD1; MLD2 of the femur.

In the considered working section 15, when the osteophyte removal phase is not applied, the mediolateral width MLD1; MLD2 is equal to a mediolateral width MLD1 of 74 mm. When it is applied, the mediolateral width MLD1; MLD2 is equal to a mediolateral width MLD2 of 68.5 mm. Thus, the precision error made in the estimation of the mediolateral width MLD1; MLD2 when the osteophytes are not removed is approximately 8%. This precision error may possibly be larger depending on the dimensions of the aberrant zones Z11, Z12, Z13, Z14. Thus, this example demonstrates that keeping the zones Z11, Z12, Z13, Z14 on the contour line of the modeled femur in all the working sections can lead to more or less significant errors in the determination of the geometric variables and the estimation of the dimensions of the three-dimensional modeling of the femoral component 101.

Note that in addition to the geometric variables, a three-dimensional modeling of a femoral cutting template can also be used in order to three-dimensionally model the femoral component 101. This femoral cutting template is modeled during an additional step of the preparatory phase from the remarkable points 110, 111, 112, 113, 114 identified on the three-dimensional modeling of the femur 1, in particular the most posterior points 111, 112 and the most distal points of the medial 161 and lateral 162 condyles.

In practice, the femoral cutting template is used by the surgeon, who applies it to the bony surface of the femur, to make bone cuts and define support faces which are used for the placement of the femoral component 101. The femoral cutting template has the same shape/curvature as the internal face of the femoral component 101 which is applied and held on the surface of the patient's distal femur.

Note that the first reference axis X11 physically relates to a mediolateral cutting line in a cutting plane for which any bony part of the articular surface located distal to this mediolateral cutting line is resected. Thus, the first reference axis X11 corresponds in the three-dimensional modeling of the femur to the support faces of the femoral component

The following description provides more details on the preparatory and osteophyte removal phases in the construction of a tibial component 102.

During the preparatory phase, a tibial resection plane RP is determined from the three-dimensional modeling of the femur, which is distant, in a proximo-distal direction of the tibia, either from the most anterior point 211 of the medial compartment 271 by a first given distance d211 if the patient's knee has a genu varum type deformation, or from the most anterior point 212 of the lateral compartment 272 by a second given distance d212 if the knee has a genu valgum type deformation.

In a preferred embodiment of the invention, the first distance d211 is equal to 6 mm, and the second distance d212 is equal to 10 mm. These two values are consistent with the practices of surgeons in the resection of the proximal portion of a tibia and the placement of a tibial component 102.

According to different embodiments of the invention:
- the RP tibial resection plane is a horizontal plane, or
- is a plane with a non-zero posterior slope less than or equal to 15 degrees, for example a posterior slope of 3 degrees; and/or a non-zero varus valgus less than or equal to 5 degrees, for example a varus valgus of 3 degrees.

The invention proposes for the step of three-dimensional modeling of the tibia 2 in a plurality of working sections 25 two sectioning methods. In different embodiments of the invention, the 3D design tool can propose one or the other of these two methods, or propose both to the user.

In reference to the -a, The first sectioning method consists in sectioning the three-dimensional modeling of the tibia 2 into a plurality of working sections 25 formed of sagittal sections 251 which are: parallel to each other and distant from each other by a predetermined separation distance; and all orthogonal either to a medio-lateral direction or to an anteroposterior direction.

In reference to the , the orientation of the sagittal sections 251 is defined according to a line called the Akagi line AL which is perpendicular to the projection of the femoral transepicondylar axis TEAP, which connects the medial edge of the anterior tibial tuberosity 7 and the insertion of the posterior cruciate ligament 8.

In one embodiment of the invention, the medial edge of the anterior tibial tuberosity 7 is determined by the construction method during the preparatory phase by determining:
- the height of the anterior tibial tuberosity 7, which is obtained by searching in the three-dimensional modeling of the tibia 2 for its most anterior point between 20 mm and 50 mm below the tibial sulci,
- the most anterior point of the anterior tibial tuberosity 7 at the height previously determined, and
- the most medial point to the thickness of the anterior tibial tuberosity 7.

The second sectioning method consists in sectioning the three-dimensional modeling of the femur 2 into a plurality of working sections 25 formed of sections 252 distributed around one or more axes of revolution AX0, AX1, AX2 in a proximo-distal direction. With reference to the -b, the working sections 252 are distributed around a central axis AX0, a medial axis of revolution AX1 and a lateral axis of revolution AX2 located respectively medially and laterally in the three-dimensional modalization of the tibia 2. Consequently, the working sections 252 have a plurality of directions. In particular directions, the working sections 252 propagate mediolaterally or anteroposteriorly.

In the osteophyte removal phase, for the first sectioning method, according to the direction with which all sagittal sections 251 are orthogonal:
- the right contour lines 22 and left contour lines 21 may correspond either to a medial contour line and a lateral contour line of the articular surface of the tibia; or else to an anterior contour line and a posterior contour line; - the right reference points P22 and left P21 may correspond, in the reference zone R2, either to the least medial point of the medial surface of the tibia and at least the least lateral of the lateral surface; or else to the least anterior point of the anterior surface of the modeled bone and to the least posterior point of the posterior surface;
- the right C22 and left C21 cutting lines can correspond either to a medial cutting line and a lateral cutting line; or to an anterior cutting line and a posterior cutting line;
- and the right clearance angles A6 and left clearance angles A5 can correspond either to medial and lateral clearance angles or to anterior and posterior clearance angles;
this in order to remove at least one right aberrant zone Z22 and/or one left aberrant zone Z21 which correspond respectively either to a medial aberrant zone and a lateral aberrant zone of the tibial articular surface; or else to an anterior aberrant zone and a posterior aberrant zone.

These correspondences are also found in the second sectioning method provided that the working sections 252 considered propagate in the particular directions.

A schematic example of a sagittal section 251 orthogonal to the anteroposterior direction of the tibia is illustrated . For sagittal sections 251 orthogonal to this direction, the right side and the left side of the contour line of the modeled tibia therefore represent respectively its lateral side and its medial side of it is illustrated .

The first reference axis X21 is determined as being the intersection between the working section 25 and the tibial resection plane RP. In the case of a sagittal section orthogonal to the anteroposterior direction of the tibia, the first reference axis coincides with the tibial resection plane RP. The second reference axis X22 is determined as being parallel and distant by a reference distance d22 from the first reference axis X21 along the central axis 20. In the preferred embodiment of the invention, the reference distance d22 is equal to 6 mm.

The right clearance angels A6 and left clearance angels A5 are defined as being between zero degrees and 30 degrees and such that in the working section 25, relative to the central axis 20:
- the left cutting line C21 is inclined to the right of the left clearance angle, and
- the straight cutting line C22 is inclined to the left of the right clearance angle A6.

In a first embodiment of the invention, the right clearance angle A6 and the left clearance angle A5 are identical for each of the working sections.

In the preferred embodiment of the invention, the two clearance angles A5, A6 are equal and zero; meaning that the right cutting lines C22 and left cutting lines C21 extend parallel to the central axis 20.

There schematically illustrates the contour line of the femur considered in the sagittal section 251 of the after application of the osteophyte removal phase for zero clearance angles A5, A6.

Once all the working sections 25 have been cleaned, geometric variables are identified in each of them to three-dimensionally model the tibial component 102.

Note that in practice, the entire bony portion that is proximal to the RP resection plane is resected by the surgeon. The bony surface of the tibia then presents at the level of the RP resection plane a substantially horizontal tibial plateau 270 on which the tibial component 102 will be placed.

Claims (26)

Method for constructing at least one joint component (101; 102), of the femoral component (101) or tibial component (102) type, for a total knee prosthesis (100), said joint component (101; 102) being shaped to be placed on a joint element of the femur or tibia type, in which said construction method comprises a preparatory phase implementing at least the following steps:
- obtaining a set of digital medical images of a patient's joint element;
- construction of a three-dimensional model of the articulation element (1; 2) from the associated set of digital medical images;
- sectioning of the three-dimensional modeling of the articulation element (1; 2) into several working sections (15; 25) distributed in different planes, each working section (15; 25) being defined by a set of geometric points;
wherein the construction method comprises an osteophyte removal phase applied to each working section (15; 25) among the plurality of working sections (15; 25) in order to construct a plurality of cleaned working sections (15; 25), said osteophyte removal phase comprising the following steps:
- determination in the working section (15; 25) of at least one aberrant zone (Z11, Z12; Z21, Z22) representative of an osteophyte (17; 27);
- construction of the cleaned working section (15; 25) associated with the working section (15; 25), said cleaned working section (15; 25) corresponding to the working section (15; 25) in which the at least one aberrant zone (Z11, Z12; Z21, Z22) is removed;
and wherein the construction method comprises a step of obtaining geometric variables representative of a geometry of the three-dimensional modeling of the articulation element (1; 2) in the several cleaned working sections (15; 25);
said construction method then comprising a step of constructing the at least one joint component (101; 102) from values of the geometric variables. Construction method according to claim 1, in which each working section (15; 25) is delimited by an articular contour line extended to the right and left by respectively a right contour line (12; 22) and a left contour line (11; 21), the right contour line (12; 22) and the left contour line (11; 21) being arranged on either side of a central axis (10; 20) contained in said working section (15; 25),
and in which, during the osteophyte removal phase, for each working section (15; 25), the following steps are implemented:
- determination in the working section (15; 25) of a reference zone (R1; R2) framed by a first reference axis (X11; X21) and a second reference axis (X12; X22) which are parallel and distant from each other;
- determining in the working section (15; 25) a right reference point (P12; P22) and a left reference point (P11; P21), said right reference point (P12; P22) corresponding to a point least to the right on the right contour line (12; 22) and contained in the reference zone (R1; R2) and said left reference point (P11; P21) corresponding to a point least to the left on the left contour line (11; 21) and contained in the reference zone (R1; R2);
- determining a right cutting line (C12; C22) and a left cutting line (C11; C21) in the working section (15; 25), said right cutting line (C12; C22) passing through the right reference point (P12; P22) and said left cutting line (C11; C21) passing through the left reference point (P11; P21);
- determining in the working section (15; 25) at least two aberrant zones (Z11, Z12; Z21, Z22) comprising a right aberrant zone (Z12; Z22) and a left aberrant zone (Z11; Z21), the right aberrant zone (Z12; Z22) being located to the right relative to the right cutting line (C12; C22) and the left aberrant zone (Z11; Z21) being located to the left relative to the left cutting line (C11; C21). Construction method according to claim 2, wherein, during the osteophyte removal phase, for each working section (15; 25), the right cutting line (C12; C22) and the left cutting line (C11; C21) respectively have a right clearance angle (A2; A6) and a left clearance angle (A1; A5) relative to the central axis (10; 20), said right clearance angle (A2; A6) and said left clearance angle (A1; A5) being between 0 and 30 degrees. Construction method according to any one of claims 1 to 3, in which the preparatory phase comprises a determination of morphometric data in the three-dimensional modeling of the articulation element (1; 2), said morphometric data characterizing a size of the articulation element. Construction method according to claim 4, in which the morphometric data comprise at least remarkable points (110, 111, 112, 113, 114; 211, 212) located in the three-dimensional modeling of the articulation element (1; 2). Construction method according to any one of claims 1 to 5, in which the articular component (101; 102) is of the femoral component type (101), the articulation element is of the femur type and the three-dimensional modeling of the articulation element (1; 2) corresponds to a three-dimensional modeling of the femur (1), such that said three-dimensional modeling of the femur (1) comprises at least a three-dimensional modeling of a lateral condyle (162), a medial condyle (161) and a trochlea (163). A method of construction according to claims 5 and 6, wherein the remarkable points (110, 111, 112, 113, 114; 211, 212) comprise at least a most posterior point (111) of the medial condyle (161), a most posterior point (112) of the lateral condyle (162) and a most anterior point (110) of a distal femur portion. Construction method according to claim 6 or 7, in which the several working sections (15) comprise posterior working sections (151) distributed in different planes around a posterior axis of revolution (153) of medio-lateral direction, and anterior working sections (152) distributed in different planes around an anterior axis of revolution (154) of medio-lateral direction and offset by a given center distance (155) with the posterior axis of revolution (153) along a femur axis (156) of proximo-distal direction. A method of construction according to claims 2 and 8, wherein in each working section the articular contour line follows a contour of the lateral condyle (162), the medial condyle (161) and the trochlea (163), and the right contour line (12; 22) and the left contour line (11; 21) correspond respectively to a medial contour line (11) of the medial condyle (161) and a lateral contour line (12) of the lateral condyle (162). Construction method according to claims 3 and 9, in which the right clearance angle (A2; A6) and the left clearance angle (A1; A5) correspond respectively to a femoral lateral clearance angle (A2) and to a femoral medial clearance angle (A1) which are non-zero for each of the working sections (15). A method of construction according to claim 10 wherein the femoral lateral clearance angle (A2) is the same for the posterior working sections (151) and for the anterior working sections (152). A method of construction according to claim 10 or 11, wherein the femoral medial clearance angle (A1) is different between the posterior working sections (151) and the anterior working sections (152). Construction method according to any one of claims 9 to 12, wherein, during the osteophyte removal phase, for each working section (15), an extreme line (X10) of medio-lateral direction passing through a most distal point (113, 114) of the lateral condyle (162) or of the medial condyle (161) is determined, and the first reference axis (X11) is determined as being distant from said extreme line (X10) by a first reference distance (d11), the second reference axis (X12) is determined as being distant from said first reference axis (X11) by a second reference distance (d12). Construction method according to any one of claims 9 to 13, in which, during the osteophyte removal phase, for each working section (15), the following steps are implemented:
- determination of a medial interior line (13) of the trochlea (163) and a lateral interior line (14) of the trochlea (163), arranged on either side of the central axis (10);
- determining in the working section (15) at least two aberrant zones (Z13, Z14) comprising a medial inner aberrant zone (Z13) and a lateral inner aberrant zone (Z14), the medial inner aberrant zone (Z13) being located laterally with respect to said medial inner line (13) and the lateral inner aberrant zone (Z14) being located medially with respect to the lateral inner line (14). Construction method according to claim 14, wherein the determination of the medial inner aberrant zone (Z13) and the lateral inner aberrant zone (Z14) comprises for each working section (15):
- determining in the working section (15) a medial inner reference point (P13) and a lateral inner reference point (P14), said medial inner reference point (P13) corresponding to a least medial point on the medial inner line (13) and contained in the reference area (R1), and said lateral inner reference point (P14) corresponding to a least lateral point on the lateral inner line (14) and contained in the reference area (R1);
- determining a medial inner cutting line (C13) and a lateral inner cutting line (C14) in the working section (15), said medial inner cutting line (C13) passing through the medial inner reference point (P13) and said lateral inner cutting line (C14) passing through the lateral inner reference point (P14). A construction method according to claim 15, wherein, during the osteophyte removal phase, for each working section (15), the medial inner cutting line (C13) and the lateral inner cutting line (C14) respectively have a medial inner clearance angle (A3) and a lateral inner clearance angle (A4) relative to the central axis (10), said medial inner clearance angle (A3) and said lateral inner clearance angle (A4) being between 0 and 30 degrees. A construction method according to claim 16, wherein the lateral interior clearance angle (A4) is the same for the rear working sections (151) and for the front working sections (152). A method of construction according to claim 16 or 17, wherein the medial interior clearance angle (A3) is different between the posterior working sections (151) and the anterior working sections (152). Construction method according to any one of claims 1 to 5, in which the articular component (101; 102) is of the tibial component type (102), the articulation element is of the tibia type and the three-dimensional modeling of the articulation element (1; 2) corresponds to a three-dimensional modeling of the tibia (2), such that said three-dimensional modeling of the tibia (2) comprises at least a three-dimensional modeling of a tibial plateau (270), a medial compartment (271) and a lateral compartment (272). A method of construction according to claims 5 and 19, wherein the remarkable points (110, 111, 112; 211, 212) comprise at least one most anterior point (211) of the medial compartment (271) or one most anterior point (212) of the lateral compartment (272). Construction method according to claim 20, in which the preparatory phase comprises determining a tibial resection plane (RP) which is distant, in a proximo-distal direction of the tibia, either from the most anterior point (211) of the medial compartment (271) by a first given distance (d211), or from the most anterior point (212) of the lateral compartment (272) by a second given distance (d212). Construction method according to claims 2 and 21, wherein, during the osteophyte removal phase, for each working section (25), the first reference axis (X21) is determined as corresponding to the intersection between the working section (25) and the tibial resection plane (RP), and the second reference axis (X22) is determined as being distant from said first reference axis (X21) by a reference distance (d22) along the central axis (20). Construction method according to claims 3 and 22, wherein, during the osteophyte removal phase, for each working section (25), the right clearance angle (A6) and the left clearance angle (A5) are identical for each of the working sections. Construction method according to claim 23, in which for each working section (25), the right clearance angle (A6) and the left clearance angle (A5) are zero. A construction method according to any one of claims 19 to 24, wherein the plurality of working sections (25) are either:
- sagittal sections (251) parallel to each other and all orthogonal to a medio-lateral direction or an anteroposterior direction; or
- sections (252) distributed in different planes around one or more axes of revolution (AX0, AX1, AX2) in a proximo-distal direction. A method of construction according to any preceding claim, wherein the set of medical digital images comprises images from a medical scanner, for example in DICOM format.