FR2885518A1 - Manufacturing procedure for external medical component such as amputated limb cover is made from different materials according to hardness of different zones - Google Patents

Abstract

The external component, designed to make contact with a patient's skin covering part of the body, e.g. following amputation, is made from different materials and based on digital data on the three- dimensional shape of the surface concerned and the hardness or softness of different areas. The data is obtained by means of magnetic nuclear resonance (MNR) or X-ray scans, providing an three-dimensional image of the area to be covered and the relative hardness of different zones, and is used to produce a mould.

Description

The present invention relates to the field of the apparatus of

  the musculoskeletal system, in particular the manufacture of external medical devices intended for fitting a part of the body of a patient, including the upper and lower limbs, as well as the trunk or the neck. She is

  in particular relating to the manufacture of orthoses as well as prosthetic external prostheses for amputation of upper or lower limbs. It also relates to the manufacture of the complete external prosthesis, for example certain aesthetic prostheses of a hand or a finger.

  The external prostheses replace the part of the musculoskeletal system that has been amputated, either for a purely aesthetic purpose or with a functional objective, the prosthesis then having to restore at least part of the lost function (grasping or walking).

  Orthotics are intended to assist a part of the musculoskeletal system. There are different types of orthoses depending on their use. There are thus orthoses intended to prevent or correct a deformation (scoliosis corset, orthosis of postures, etc ...), orthoses intended to help the function of the limb segment (orthosis of opposition of the thumb, orthosis for radial paralysis , croupespédieuse splint with locked knee for paralysis of the quadriceps, etc ....), orthoses for the resting of a joint (orthosis of rest of the wrist and hand in the PR, etc. ..) or orthotics for the immobilization of a limb (fracture, luxation, etc.).

  The external prosthesis sockets and orthoses must be perfectly adapted to the stump or part of the musculoskeletal system on which they act. The constraints between this apparatus and the limb segment or the trunk must be perfectly controlled and oriented to ensure the efficiency of the equipment and its perfect tolerance. These constraints are voluntary in the case of corrective orthoses (corsets, neck brace, orthosis of postures) or related to the pressure function between the stump and the socket, for example during walking. They should be able to be removed if necessary in painful areas or areas with various skin lesions.

  The apparatus must therefore adapt to the geometry of the part of the locomotor apparatus concerned and evolve according to the variations of this geometry (initial edema of the stump, hematoma of a forearm and posture in extension of the elbow, dressing of a limb segment or a stump, etc.). It will be corrected, or redone, as often as necessary. When this geometry is stabilized, the renewal of the apparatus will be more spaced, such renewal of the apparatus being decided because of the aging of the latter, or because of its mismatch caused by the growth of the body part paired or by taking or losing weight of the patient.

  An external medical device of the external prosthesis type for amputation always consists of the following elements: 1. a socket which constitutes the junction between the stump and the prosthesis itself. The socket comprises the contact surface of the external prosthesis which is intended to be in contact with the part of the body to be paired, namely here the skin surface covering the end of the stump. The socket allows, on the one hand, the suspension of the prosthesis and, on the other hand, in particular for amputations of lower limbs, the orientation of the pressures on the stump during walking. Because the stump is not adapted to withstand such stresses of pressures, depressions and shears, the interface between the stump and the socket is the weak point of the amputee equipment; 2. intermediate prosthetic joints, the number of which varies with the level of amputation; 3. a tube reproducing the limb segments.

  4. an alignment adjustment device for lower limb prostheses; and 5. an end effector: foot or prosthetic hand.

  External prostheses therefore constitute a mechanical system that is all the more complex as the level of amputation is proximal, thus multiplying joints that do not have their own internal control. Control of this system is performed by the remaining limb segment through the socket.

  Of the components of an external prosthesis, only the socket is handcrafted by orthoprotésistes. The other elements are manufactured industrially. As indicated above, the socket is the element of the prosthesis, seat of most of the difficulties of fitting, in the manufacture of which many technical problems are encountered.

  Conventionally, the socket is manufactured according to the following steps: 1) realization of a plaster negative of the stump with strips of plaster.

  It is during this phase that the molding is optionally oriented to mark the bearing areas; then 2) realization of a plastered positive by casting plaster in the negative; then 3) manual retouching of the positive plastered by the prosthetist according to the measurements of circumferences of the stump; and finally 4) manufacture of the socket, casting the resin or stamping a thermoformable material on the plastered positive.

  The current techniques of computer-aided design (CAOCFAO) make it possible to eliminate the use of plaster for the realization of the first steps, as is illustrated below: 1. The stump can be digitized by different techniques: - digitization by a stylet to the interior of a plaster negative of the stump, direct digitization of the stump by optical system, digitization of a stump form from the measurement of the circumferences of the stump and a database of stump forms; 2. Retouching of the stump by the prosthetist can be performed using a CAD software (orientation of the support to certain areas, discharge at the sensitive areas, etc. ..).

  3. The retouched positive can be manufactured by a digital milling machine, from the computer file generated by a CAD software, then a resin is then cast on the positive as in the conventional technique, as in conventional manual techniques.

  As can be seen, if the overall shape and the principles of this or that external medical device system, at the level of the supports or the suspension mode, are always the same, the precise shape of the part of the equipment in contact with the part of the paired body, the necessary discharges and the precise orientation of the supports vary from one patient to another according to the specific geometry of the part of the body to be paired.

  For example, when the part of the body to be paired consists of a stump of an upper or lower limb, the precise shape of the part of the apparatus, here called a socket, which is in contact with the part of the paired body, may have a conical, cylindrical, cylindro-conical or bell-shaped shape, depending on the cushioning of the stump, that is to say the amount of soft part around the bones, according to the existence or not of localized pain related to a lesion dermal, neuroma, exostosis, depending on the fragility of the skin at a particular site of the stump related to a defective scar related to the etiology of the amputation (burn, frostbite, purpura fulminans, traumatic, bridging scar in vascular origins, etc ...).

  In terms of evaluation, there are few constraint evaluation techniques at the interface between the contact surface of the medical equipment and the body part. Only the recording of the normal component of the pressure at certain limited locations of said body part, for example of the stump, is currently possible.

  These external medical devices, for maintaining a body part or for total or partial substitution of a limb, are most often made of thermoformable materials (polypropylene, polyethylene or Plexiglas) by stamping on a plastered positive limb. The external joints of these devices are manufactured industrially. The precision of manufacture, the need for support, counter-support and discharge meet those of the contact surfaces with the part of the paired body.

  In any case, to define the final shape of the contact surface geometry of the external medical device, for example an external prosthetic socket, with the part of the body to be paired, the ortho-prosthetist must take into account the need for establishing both support zones, counter-support zones and unsupported contact zones, particularly by respecting the sensitive areas of said body part, for example of the stump. The geometry of this surface is not limited to the faithful reproduction of the external morphology of said body part, for example the stump. Indeed, any part of the body, including an upper or lower limb stump, includes hard parts with the underlying presence of a bone, the remaining portions of the stump consisting of the soft parts. It is from the location of the respectively hard and soft parts of the stump that the final geometrical shape of the surface of the socket is defined by the ortho-prosthetist.

  For example, for the production of external medical devices consisting of contact or ICEROSS type sockets, support zones, counter-support zones and contact zones are defined.

  The bearing areas are located at the anterior part of the stump. These are, in the first place, the patellar tendon, the part underlying the tibial plateau on each side of the anterior tuberosity of the tibia, the anterolateral and antero-external zones of the tibia, on each side of the tibial stop. For the final shape of the socket geometry, lateral stabilization zones must be provided under the internal tibial plateau and, in contrast, in the region between the distal head and the distal end of the fibula, when this is possible.

  The counter-support zones are located on the posterior surface of the stump, with a major support in the popliteal hollow substantially at the level of the joint space. To define the counter-support zones, the tendons and hamstrings are avoided as much as possible.

  The contact areas are constituted by the entire surface of the stump, including its end. When making the complete prosthesis or external orthosis, it must be ensured that the distal part of the sleeve conforms exactly to the shape of the stump, ensuring perfect contact with the stump.

  Finally, the sensitive areas are generally located at the level of the head of the fibula and the distal ends of the tibia and fibula. In general, there are sensitive points that are specific to the amputated patient considered.

  As can be seen, the manufacture of an external medical device, for example the manufacture of a socket prosthesis or external orthosis, must take into account many parameters related to mechanical stresses generated by the weight supported by the equipment, whether in static position or during movements, including walking movements.

  There is a need in the state of the art for socket fabrication processes of external prostheses or orthoses which allow a better accuracy in the definition of the geometry of the portion of the socket intended to be in contact with the stump, to further increase comfort for the patient.

  According to the invention, there is provided such a method of manufacturing an external medical device for fitting a body part, for example of the type of external prosthesis socket or orthosis.

  The applicant has endeavored to develop a method of manufacturing prosthesis or external orthosis comprising steps of precise evaluation of the mechanical stresses that will be experienced by the part of the body of the patient to be paired, then stages of refinement the geometry of the contact surface of the future external medical device, from the normal and tangential mechanical stress data that have been previously calculated.

  The method of manufacturing an external medical device, for example an external prosthesis socket or orthosis, which was developed by the applicant comprises a prior step of digitizing the part of the body to be paired, that is to say a step of digitizing the external geometry as well as the geometry of the internal parts of said part of the body, such as the bones and the muscles, then a step of rough determination of the contour of the contact surface said device with said body part. The scanning step is followed by a step of evaluating the mechanical stresses likely to be experienced by the part of the body in contact with the external medical device, especially during static phases and movement. The step of evaluation of the mechanical stresses is followed by a step of correction, partially or totally automated, of the contour of the contact surface of said device initially defined, until complete optimization of the distribution of the normal and tangential mechanical stresses between said body portion and the contact surface of said external medical device.

  According to the invention, the optimization of the constraints comprises one or more of the following operations: adaptation of the stresses to ensure the maintenance of the external medical device, in particular external prosthesis or orthosis, on the part of the paired body; limit over-constraints and sub-constraints, in general; to direct constraints on healthy and adapted areas; distribute stresses evenly by limiting or reducing stress on painful or sensitive areas; consider clinical indications; For example, depending on the type of socket, the stresses are oriented towards the sub-patellar support or, on the contrary, it is sought to distribute the stresses over the entire surface of the socket.

  The invention relates to a method for producing an external medical device for fitting a part of the body of a patient, said external medical device comprising a surface, said contact surface, intended to be in contact with the surface of the skin patient covering at least a region of the part of the body of the patient to be paired, said skin surface, said method comprising the steps of: a) acquiring a first set of digital data representative of the three-dimensional geometry of the part the body on which said external medical device is intended to fit, said set of digital data including information relating to the three geometric dimensions of said body part; b) determining, from the first set of digital data obtained in step a), at least: (i) a first subset of digital data representative of the three-dimensional geometry of the inner soft portions of said body portion; (ii) a second subset of digital data representative of the three-dimensional geometry of the inner hard portions of said body portion; and (iii) a third subset of digital data representative of the three-dimensional geometry of the skin covering said body portion; then generating a second set of digital data representative of the three-dimensional geometry of said body portion, said second set of digital data including data of said first, second and third subsets; c) assigning, to each of the at least three subsets of digital data contained in said second set of digital data, a parameter or a combination of parameters characterizing the elastic law or the viscoelastic law of the behavior of said soft, hard or skin portion vis-à-vis a mechanical stress; d) performing a volumetric discretization, also called a mesh, of the volumes defined in each of the at least three subsets of said second set of digital data obtained in step c) and generating a third set of digital data comprising representative geometric data of said mesh; e) from the third set of digital data obtained in step d), generating a fourth subset of digital data representative of the provisional three-dimensional geometry of the contact surface of said device, and generating a fourth set of digital data comprising said third set and said fourth subset of digital data; f) applying to the fourth set of digital data at least three mechanical stress parameters, respectively: (i) at least one said load case parameter, which is representative of the total force exerted by said body portion on the contact surface said external medical device; (ii) at least one so-called limit condition parameter, which is representative of the conditions by which said fourth set is set upon application of the parameters defined in (i); (iii) at least one so-called contact condition parameter, which is representative of the value of the frictional resistance between the skin surface and the contact surface of said external medical device; then adding the values of the at least three mechanical stress parameters (i), (ii) and (iii) to said fourth set of digital data; g) calculating, from the fourth set of digital data obtained in step f) a normal and / or tangential stress value between said skin surface and said contact surface, at least for each data representative of a point of contact; said skin surface, and generating a fifth set of digital data comprising, for each data representative of a skin surface point, said normal and / or tangential stress value thus calculated; h) comparing, for each data representative of a skin surface point, the normal and / or tangential stress value calculated in step g) with a predetermined limit value, and h1) for each data representative of a point of a skin surface for which there is a difference between the value calculated in step g) and said predetermined limit value greater than a predetermined difference value, varying the value of the location coordinates in the space of said representative datum a point of the three-dimensional geometry of the contact surface of said device until, for said representative data, a difference between the calculated normal and / or tangential stress value and the predetermined limit value is obtained, which is equal to or less than the predetermined difference value; h2) retaining each data representative of a skin surface point for which the difference between the value calculated in step g) and said predetermined limit value is less than the predetermined difference value; and generating a sixth set of digital data representative of the three-dimensional geometry of the contact surface of said device, wherein the data representative of each skin surface point is associated with a normal and / or tangential stress value close to the predetermined threshold value; i) fabricating said external medical device, whose geometry of the surface of contact with said body part consists of the geometry defined by the final digital data set obtained in step h).

  The above method allows the manufacture of prosthesis or external orthosis sockets, which essentially comprises automated steps that do not require the technical intervention of the man, especially when step i) consists of a step of manufacture of the socket according to a rapid prototyping method, wherein the rapid prototyping device directly manufactures the socket, for example by lithography, from the numerical data of the final model of the geometry of the surface of the socket obtained at the end of step h) of said method, according to rapid prototyping techniques known per se.

  To implement the method for manufacturing an external prosthesis or orthosis socket of the invention, a digital data processing system is used, for example of the personal computer type, said system comprising lines allowing the digital data input, and lines allowing the output of digital data. The digital data input line (s) may be connected to digital image acquisition devices as well as to function control devices, for example a keyboard, a pointing device, a graphics palette, etc. The digital data output line or lines may be connected to image display means, in particular computer screens, or to a digital rapid prototyping device.

  In step a) of the method, the first set of digital data representative of the three-dimensional geometry of the part of the body to be paired can be obtained with any known digital image acquisition device, such as a photon-digital apparatus, or else a device for acquiring images by surface scanning, for example an optical scanner device.

  Preferably, in step a), an NMR or scanning X-ray device is used.

  It is advantageous to use an X-ray scanner device comprising an X-ray tube which irradiates the part of the body of the patient to be paired, for example an upper or lower limb stump, as well as a multiplicity of detectors which measure the differences of absorption between the different regions of said part of the body concerned.

  In general, such an X-ray or X-ray scanner device also comprises a computer that makes it possible, for example by using Fourier Transform algorithms, to generate the first set of digital data representative of the three-dimensional geometry of the body part. wherein said external medical device is adapted to fit.

  To acquire the first set of digital data representative of the three-dimensional geometry of the part of the body on which said external medical device is intended to adapt, in step a) of the method, it is thus possible to use a scanning device X-ray (CT or CT scan) or a Nuclear Magnetic Resonance scanning device (NMR scanner).

  In general, the calculator makes it possible to generate the first set of numerical data above by reconstructing the three-dimensional geometry of the body part from a succession of digital data subassemblies, each of these subsets of data. numerals being representative of the two-dimensional geometry of a section or slice of said body part, for example an upper or lower limb stump.

  For example, the computer can generate the first set of digital data when its memory is loaded with a suitable computer program, for example a program of the type S.I.P. (Patran MRI scanner).

  In general, the digital data provided by an X-ray or NMR scanner consists of an image constituted by a matrix of individual elements called pixels. Each pixel is assigned a gray level numerical value, which value is relative to the X-ray absorption power of the three-dimensional geometric entity associated with this pixel. The range of gray level values can generally range from 0 to 4095. However, for carrying out the method of the invention, a range of lower gray level values may be used, such as a range of values. gray level values from 0 to 256, or even a range of gray levels from 0 to 16, which is the maximum number of distinct gray levels perceptible to the human eye.

  Alternatively, when the first set of digital data is acquired using an X-ray or NMR scan type image acquisition apparatus, said first set of digital data also includes densitometric information for every point in the space of the body part of interest. According to this alternative, the soft internal parts, the internal hard parts and the skin are determined according to the densitometric value associated with each numerical data representative of a point of volume of the digitized body part, which can be respectively higher or lower a predetermined threshold value for each of said parts of the part of the body of interest. For this purpose, it is possible for example, from the first set of digital data obtained in step a), to have the system execute instructions corresponding to geometric algorithms such as those implemented by the MIMICS software (Materialize Europe). Ann Arbor, Michigan, USA).

  In step a), it is not necessary for the system to acquire a high resolution digital image. A digital image whose resolution makes it possible to distinguish two points of the part of the scanned body at a distance of 5 mm is satisfactory. Preferably, however, the resolution of the digital image carried out in step a) of the method has a resolution such that it allows the distinction between two points of the surface of the analyzed object distant by at least 2 mm, better d at least 1 mm and most preferably at least 0.5 mm.

  Generally, the first set of digital data comprises a multiplicity of elementary digital data which are in the form of pixels (also called picture elements), or better voxels (also called volume elements). Voxels consist of digital data blocks representative of the volume of each elemental data and are well known to those skilled in the art.

  In step b) of the method, the three subsets of numerical data (i), (ii) and (iii) representative of the three-dimensional geometry of the internal soft parts, the internal hard parts and the skin by discriminating the three types of tissue, for example on the basis of the gray level value of each pixel or voxel data contained in the first set of digital data. For example, for an internal hard part, which is bone and cartilage, which has a high X-ray absorption capacity, the corresponding pixel data will comprise a range of large gray level values, whereas A lower range of gray scale values is associated with the pixel data corresponding to an inner soft portion, which mainly, if not exclusively, includes the muscles, vessels and ligaments, or the pixel data corresponding to the skin.

  According to a first possible alternative of step b), the third subset (iii) of digital data includes a set of numerical data representative of the sleeve which is intended to cover the stump, before nesting of the stub in the socket of the medical device, especially a partial or total prosthesis of a lower or upper limb.

  According to a second possible alternative of step b) of the method, the skin portion is not modeled separately. According to this second alternative, the set of numerical data representative of the skin is included in the first subset (i) of digital data representative of the three-dimensional geometry of the internal soft parts of the portion of the body of interest. According to this second alternative, the third subset (iii) of digital data consists of a set of numerical data representative of the three-dimensional geometry of the sleeve intended to cover the stump and which will be in direct contact with the contact surface of the device. medical interest.

  In the case of a total or partial prosthesis of a lower or upper limb, the sleeve is in direct contact with the contact surface of the socket of the prosthesis.

  In step b) of the method, at least the three subsets of digital data specified above are distinguished within the first set of digital data.

  However, in step b), it is possible to distinguish a larger number of subsets of digital data corresponding to the different types of internal tissues constituting the part of the body to be paired which has been scanned.

  For example, it is possible to discriminate between different internal soft parts of said body part, such as, respectively, the muscle tissue, the vascular tissue, the nerves, the ligaments, which have distinct behaviors with respect to mechanical stress, by example by distinguishing these different tissues, in the first set of numerical data, by ranges of values of restricted gray levels corresponding to each of these tissues. Also, one can distinguish according to different internal hard parts of said body part, for example bone and cartilage, and even within the bone respectively the cortical bone and the cancellous bone.

  In step b), the larger the number of subsets of digital data corresponding to the different tissues distinct from the part of the body of interest, the greater the accuracy of the calculation of the values of normal and / or tangential stress which is realized. in step g) of the process is large.

  However, in practice, the distinction, in step b) of the method, of only the three subsets of previously specified numerical data is satisfactory and sufficient to realize in step g) a computation of the constraints allowing a realistic simulation the behavior of the part of the body to be fitted in response to mechanical stresses, said calculation thus enabling the realization in step i) of an external medical device, for example an external prosthesis or an orthosis, which presents excellent comfort features for the patient.

  From the subsets of numerical data representative of the three-dimensional geometry of the different tissues of the part of the body of interest, ie at least the subsets of numerical data representative of the three-dimensional geometry of the internal hard parts, internal soft parts and skin, generating a second set of digital data representative of the three-dimensional geometry of said body part, said second subset comprising the data contained in each of said subsets.

  In practice, the second subset of digital data is stored in the memory of a computer and its contents can be viewed on a digital printing device or on the screen of a computer, as shown on Figure 2.

  In step c) of the method according to the invention, each of the at least three subsets of digital data contained in the second set of digital data is assigned a parameter characterizing the behavior of the different constituent tissues of each subassembly. against mechanical stress. The parameter is used to simulate the mechanical properties specific to each of the constituent tissue types of the portion of the body of interest that are distinguished in the second set of digital data.

  Preferably, a parameter is used that accounts for linear elastic behavior or viscoelastic behavior of each of the tissue types that are distinguished in the data contained in the second set of digital data.

  Advantageously, said parameter accounts for the linear elastic behavior of each type of distinguished fabric, according to Hooke's law well known to those skilled in the art. According to Hooke's law, the elastic deformation is proportional to the applied stress and the coefficient of proportionality is the Young's modulus (E). The Young's modulus (E) is the coefficient of proportionality between (i) the normal stress in the direction of the external force applied to the object under study, in the direction of the applied force, and (ii) the variation in size. of the object studied in the same direction. The Poisson's ratio (v) is the ratio between the lateral and axial stresses. The Poisson's ratio (v) expresses the ratio between the transverse relative dimension variation and the longitudinal relative dimension variation of the studied object.

  Thus, preferentially, said parameter characterizing the behavior of 1a-said soft, hard or skin parts vis-à-vis a mechanical stress consists of the elasticity constant of said part.

  Preferably, said elastic constant of said soft, hard or skin portion consists of the combination of the Young's modulus (E) and the Poisson's ratio (v) specific to said portion.

  Preferably, for the purposes of setting, for each subset of digital data contained in the second set of digital data, the value of the parameter characterizing the behavior of the corresponding tissue type with respect to a mechanical constraint, the model by an approximation which consists in considering that each of the constituent tissues of the part of the body of interest is isotropic.

  In addition, when certain subsets of digital data contained in the second set of digital data correspond to a plurality of tissue types, as is the case for example the sub-set of digital data representative of the three-dimensional geometry of the internal soft parts. , which includes muscles, vessels and ligaments, the value of the parameter which is fixed reflects the overall mechanical properties of the soft parts, which is an average of the mechanical properties specific to each of the types of tissue contained in said internal soft parts.

  By way of illustration, when three subsets of numerical data corresponding respectively to the internal soft parts, to the internal hard parts and to the skin are determined in step b) of the process, step c) is assigned to each of three subsets the parameters corresponding to the following constants of elasticity: for the internal soft part: Young's modulus (E) of the order of 0.1 Gpa; Poisson's ratio (v) of the order of 0.5; for the internal hard part: Young's modulus (E) of the order of 1 Gpa; Poisson's ratio (v) of the order of 0.3; for the skin portion: Young's modulus (E) of the order of 0.4 Gpa; Poisson's ratio (v) of the order of 0.49.

  The value of the parameters given for illustrative purposes above can be easily adapted by those skilled in the art depending on the part of the body of interest, for example depending on the type of bone constituting the internal hard parts of said part of the body. body, using Young's modulus values (E) and Poisson's ratio (v) well known in the state of the art.

  In addition, as already mentioned above, a larger number of parameters can be assigned to step c) of the method, for example when a larger number of subsets of digital data are determined at step b) the process.

  As an illustration, it is possible to determine in step b) of the method a subset of numerical data representative of the three-dimensional geometry of the internal hard part corresponding to the cortical bone and another subset of numerical data representative of the geometry in question. three dimensions of the inner hard part corresponding to the cancellous bone. In step c) of the method, it is possible, for example, to assign each of the subsets of digital data corresponding to each of these distinct internal hard parts the following elastic constants: - cortical bone: Young's modulus (E) 16700 Mpa; Poisson's ratio (v) of 0.3; cancellous bone: Young's modulus (E) of 907 MPa; Poisson's ratio (v) of 0.31; Then, in step d) of the method, a mesh is made of the volumes defined in each of the at least three subsets of said second set of digital data obtained in step c) and a third set of digital data comprising the geometric data representative of said mesh; Preferably, in step d), a discretization of the continuous model of the part of the body of interest by finite element mesh is performed. Meshing by the finite element method makes it possible to determine the mechanical behavior, such as the state of the stresses and deformations, of a previously characterized solid which has been subjected to mechanical stress forces. This finite element method is more faithful to reality than discrete type models, which are often of the spring-mass type, although the latter are of greater algorithmic simplicity.

  In step d), it is possible to use different types of mesh volume, in particular parallelepipedic meshes, tetrahedral meshes, hexahedral meshes or even shell elements, all of which are well known to those skilled in the art.

  For example, the mesh can be made using the PATRAN software, from the digital data contained in the second set of digital data obtained at the end of step c) of the method.

  For the realization of step d) of mesh, it is important to adapt the volume form of the mesh elements in order to respect as much as possible the topology of the structure of the part of the body of interest, by taking into account of its organization, the various elements and structures that constitute it and possible symmetries.

  In step d) of the method, a mesh is preferably produced with unstructured mesh elements of the tetrahedron type, such as those described by Teng and Wong (2000, International Journal of Computational Geometry & Applications, Vol 10 (3): 227-266). The use of mesh elements of the tetrahedron type is particularly well adapted to the mesh of a part of the body of interest comprising structural elements having acute angles, such as certain structures of bone or cartilage. In addition, the mesh elements of the tetrahedron type are geometrically simpler than the hexahedral type mesh elements and consequently require less computation time than when the mesh is made with hexahedron type mesh elements.

  According to an advantageous alternative, the step b) of mesh can be carried out with several mesh elements of distinct geometry, according to the subset of digital data corresponding to a given type of fabric that is considered.

  For example, in order to simplify the finite element mesh computation, the subset of numerical data representative of the three-dimensional geometry of the skin may be meshed using hull element type elements. Indeed, given the simple geometry of the skin tissue, an approximation of the mesh using mesh elements of the 2D shell element type is a satisfactory approximation of the volume geometry of the skin and consequently of its properties. mechanical. In addition, the use in step d) of the method of simple mesh elements of the 2D shell element type makes possible a mesh computation faster than a mesh calculation which would be carried out exclusively with hexahedral 3D mesh elements. , or even exclusively with 3D tetrahedral mesh elements.

  In step d), use is preferably made of a mesh software of the Patran type, which notably contains instructions for implementing algorithms which make it possible to automatically make the connections between the meshes constituting the three-dimensional geometric model of the part. of the body of interest.

  In general, the mesh step d) comprises a preliminary step of detecting the contours of the different types of fabric from the different subsets of numerical data determined in step b), followed by a step creating the geometry of the mesh element which is chosen for each of the subsets of digital data, then finally the step of calculating the mesh itself, this last step comprising the calculation of the connections between the different mesh elements constituting the geometrical model in three dimensions of the body part of interest.

  In general, the step of creating the geometry of the mesh element includes the choice of a type of mesh element, for example tetrahedral, parallelepiped, hexahedral, 2D shell element, then the determination of the dimensions of the mesh. selected mesh element. For 3D mesh elements, such as mesh elements of the tetrahedral type, the dimensions to be fixed are triparametric, according to the three directions of the space x, y and z. For 2D mesh elements, such as shell elements, the dimensions to be fixed are biparametric, according to the two directions of the space x and y, although a third parameter of thickness can also be assigned to these elements.

  Preferably, in step d) of the method, the mesh is made with a ratio between the mesh size and the greatest length of the body part of at least 1/50, the value of said ratio preferably being 1 / 100.

  With a value of the ratio (mesh size) / (greater length) less than 1/50, the degree of geometric precision in three dimensions of the model of the part of the body of interest would be too small to simulate faithfully the deformations of the part of the body in response to mechanical stress. With a value of the ratio (mesh size) / (greater length) greater than 1/100, the accuracy of the model is increased, but the mesh computing time is also considerably increased. By simple routine tests, the person skilled in the art can adapt the value of the ratio (mesh size) / (greater length) according to the dimensions of the part of the body of interest, the complexity of its structural elements, in particular the number of subsets of digital data determined in step b), and the power and speed of the computer that is used. Thus, in general, the mesh calculation can be performed under satisfactory conditions by using, for the definition of the mesh elements, a ratio (mesh size) / (greater length) which varies from 1/75 to 1/1000 better from 1/75 to 1/500 and even better from 1/75 to 1/200.

  At the end of step d), a third set of digital data is generated comprising the geometric data representative of the mesh that has been produced. Said third set of digital data also includes the parameters characterizing the behavior of the different types of tissue that were assigned to the second set of digital data, in step c) of the method. Preferably, the third set of digital data comprises all of the digital data contained in the second set of digital data and the set of digital data generated by the mesh computation performed in step d).

  In practice, the digital data contained in the third set of digital data is stored in the memory of a computer and can be viewed, for example by means of a graphic printing device or with the aid of a computer. computer screen, as shown in Figure 3.

  In step e) of the method, a fourth subset of digital data representative of the provisional three-dimensional geometry of the contact surface of the external medical device that will be made in step i) is generated. The provisional three-dimensional geometry of the contact surface of the external medical device is determined initially with respect to the three-dimensional geometry defined by the digital data representative of the surface of the skin contained in the third set of digital data obtained at the end from step d) of the process.

  In general, in step e), the three-dimensional geometry of the contact surface of the external medical device consists of the representation of a layer of material of the contact surface having a constant thickness.

  According to a first embodiment, the fourth subset of digital data representative of the provisional three-dimensional geometry of the contact surface of the external medical device comprises the digital data representative of the surface of the skin contained in the third data set. obtained at the end of step d) of the method. According to this first embodiment, the temporary contact surface of said external medical device exactly covers the outer surface of the skin of the part of the body of interest.

  According to a second embodiment, the fourth subset of digital data representative of the temporary three-dimensional geometry of the contact surface of the external medical device comprises the digital data representative of a localized surface slightly set back from the outer surface of the external medical device. the skin of the body part of interest. A graphic representation of this second embodiment is illustrated in FIG. 4. According to this second embodiment, the contact surface of the external medical device has a three-dimensional geometry such that the body part will undergo a slight compression when will be in contact with said device. For example, in the case of an external medical device consisting of an external prosthesis of an upper or lower limb, the three-dimensional provisional geometry of the contact surface of the socket defines a volume less than the volume defined by the surface. skin covering the stump. Consequently, during the engagement of the stump in the socket, the stump undergoes a compression, a mechanical stress, which will facilitate its maintenance in place in the socket.

  According to an advantageous alternative of the second embodiment above, the fourth subset of digital data representative of the temporary three-dimensional geometry of the contact surface of the external medical device is generated from the digital data representative of a surface located slightly recessed from the outer surface of the skin of the portion of the body of interest as well as digital data representative of a general geometric shape of a known type of socket. The digital data representative of a general geometric shape of different types of known and predefined external medical devices, for example of different types of predefined sockets, can be stored in the memory of the computer used to carry out step e) of the method. Depending on the type of external medical device to be manufactured according to the method, for example the type of socket to be manufactured, within the set of digital data representative of a general geometric shape of said device, the one which is the more adapted to the patient considered. As an illustration, if the external medical device to be manufactured consists of a socket for external prosthesis of the leg, or for external tibial prosthesis, is selected, within the set of digital data representative of a general geometric shape of medical devices external, the subset of digital data representative of the three-dimensional geometry of the socket best suited to the patient, for example the subset of digital data representative of the three-dimensional geometry of an ICEROSS type socket.

  Preferably, the set of digital data representative of a general geometrical form of external medical devices consists of an ordered collection of subsets of digital data, each subset (set of digital data being representative of the general three-dimensional geometric a known type of external medical device, for example of a known type of socket.

  As an illustration, the general shape of the contour of the temporary contact surface of the external medical device is predefined by selecting, in the set of digital data above, the subset of digital data representative of the three-dimensional geometry of the device best suited to the patient, then the temporary contour of the contact surface is calculated from the digital data representative of the surface of the skin contained in the third set of digital data obtained at the end of step d) of the method In step e) of the method, the fourth subset of digital data representative of the provisional three-dimensional geometry of the contact surface of said device can alternatively be generated manually, semi-automatically or completely automatically.

  In a first aspect, the fourth subset of digital data may be generated manually. According to this first aspect, the computer comprises an interface means enabling the user to generate said fourth subset of digital data manually, directly from the content of the third subset of digital data comprising the three-dimensional geometric data. of the mesh. In general, according to this first aspect, the computer comprises a means for displaying the third set of digital data, for example a computer screen which allows the visualization of the three-dimensional geometry of the part of the body of interest and which comprises the visual representation of the mesh made in step d). The computer further comprises an input means of the digital data representative of the contour of the contact surface of the external medical device to be manufactured. Said digital data input means may be for example any known pointing device, such as a graphic palette provided with a stylus which is connected to the computer or a computer screen provided with a touch surface and a stylus allowing entry of the graphic data into the computer memory or more conventionally a mouse connected to the computer. From a practical point of view, the interface means allows the user to draw the contour of the contact surface of said external medical device, from the visual representation of the part of the body meshed on the screen of the computer. The drawing made by the user, that is to say the path of the stylus on the surface of the interface means, for example a graphic palette or a touch screen, generates the storage in the computer memory of the fourth subset of digital data. representative of the temporary contour of the contact surface of the external medical device to be manufactured.

  In a second aspect, the fourth subset of digital data may be generated semi-automatically. According to this second aspect, the fourth subset of digital data is first generated automatically by the computer, from the digital data representative of the surface of the skin contained in the third set of digital data obtained at the end of the step d) of the method or from the combination of (i) digital data representative of the surface of the skin contained in the third set of digital data obtained at the end of step d) of the method and (ii) data digital representative of a general geometric form of a known type of external medical device, previously stored in the computer memory, and which are selected according to the patient. The data contained in the fourth subset of digital data thus generated can be visually represented on the computer screen in the form of a temporary contour line of the contact surface of the external medical device to be manufactured. The computer includes interface means that allows the operator to manually change the contour line of the contact surface that was first generated automatically. The interface means could consist of any type of pointing means, including a stylus connected to a graphics palette, a stylus actuated on the sensitive surface of a touch screen computer, or a mouse connected to the computer.

  According to a third aspect, the fourth subset of digital data can be generated completely automatically, from the digital data representative of the surface of the skin contained in the third set of digital data obtained at the end of step d ) of the process or from the combination of (i) digital data representative of the surface of the skin contained in the third set of digital data obtained at the end of step d) of the method and (ii) representative digital data a general geometric form of a type of known external medical device, previously stored in the computer memory, and which are selected according to the patient.

  At the end of step e) of the method, a fourth set of digital data is generated comprising (i) the third set of digital data comprising the geometric data representative of the mesh made in step d) and (ii) the fourth a set of digital data representative of the provisional three-dimensional geometry of the contact surface of the external medical device to be manufactured, for example the socket of an external prosthesis for upper limb or for lower limb.

  In step f), parameters are applied to the three-dimensional numerical model generated in the preceding step which will make it possible to calculate, from said numerical model, the various mechanical stresses experienced by the part of the body of interest when the latter will be paired with the external medical device whose temporary contact area was defined in step e).

  The parameters applied in step f) are at least three in number. The first parameter is a so-called load case parameter, which accounts for the overall bearing force of the body part of interest on the contact surface of the external medical device. For example, for making a socket for knee prosthesis, the load case parameter is the overall weight supported by the stump, ie half of the total weight of the patient's body. The second parameter consists of a so-called limit condition parameter which is representative of the zero displacement of one or more surface points of the part of the body of interest. For example, in the case of a socket for knee prosthesis, a limit condition parameter will be set, accounting for the zero displacement of the region of the skin covering the portion of the stump with respect to the contact surface of the knee. socket. The third parameter consists of a so-called contact condition parameter that is representative of the value of the frictional resistance between the part surface of the body of interest, ie the surface of the skin covering the body part of the body. interest, and the contact surface of the external medical device.

  The application of the parameter in case of exchange is visualized by the arrows (1) in Figure (4).

  Thus, in step f) of the method, at least four mechanical stress parameters are applied to the fourth set of digital data obtained at the end of step e), respectively: (i) at least one so-called case parameter of charge, which is representative of the maximum force generated when using the medical device. For example, if the medical device is a leg prosthesis, the value of the maximum force is calculated by multiplying the value of the patient's weight by a factor of 2. This calculated maximum force represents the force value generated by the patient's mass. undergoes acceleration. According to the method of the invention, the maximum force is applied as a pressure value at the proximal end of the portion of the body of interest. (ii) at least one so-called boundary condition parameter, which is representative of the zero displacement of one or more skin surface points, relative to the contact surface of said external medical device. The so-called limit condition parameter is representative of the conditions for maintaining the fourth set, which can be modeled by an instruction to cancel the displacement of one or more data of the fourth set representative of the zero displacement points.

  (iifi) at least one so-called contact condition parameter, which is representative of the value of the frictional resistance between the skin surface and the contact surface of said external medical device; and then adding the values of the at least three mechanical stress parameters (i), (ii) and (iii) to said fourth set of digital data.

  In step f) (i) the load condition parameter, also referred to as the load case, is a static load condition parameter, or it is a dynamic load condition parameter.

  In step g) of the method, from the fourth set of digital data obtained in step f), a normal and / or tangential stress value between said skin surface and said contact surface is calculated, at least for each data representative of a point of said skin surface, and generating a fifth set of digital data comprising, for each data representative of a skin surface point, said normal and / or tangential stress value thus calculated.

  In step g) of the method it is thus possible to calculate the pressure values between said skin surface and said contact surface, which is a combination of normal and / or tangential stress values, in order to generate the fifth set of digital data. .

  The normal and / or tangential stress values are calculated using the various parameters added during the various process steps, including the temporary contour data of the contact surface of the external medical device, the elasticity constants of the different types of tissue constituting the part of the body of interest as well as the load case, limit condition and contact condition parameters previously specified in the present description.

  The contents of the fifth digital data set, which comprises the digital data representative of the normal and / or tangential stress values, can be visually represented, for example on a printing device or a computer screen connected to the computer. For example, the value or range of normal and / or tangential stress values can be visually represented by color codes in the graphical representation, as shown in FIG. 5.

  For optimal comfort of the paired patient, prior values of normal and / or tangential stress are defined in each region of the skin surface in contact with the contact surface of the external medical device for the purpose of designing a medical device. external whose contact surface has a spatial geometry respecting, respectively, the support zones, the support zones and the sensitive areas without contact with said device, for example an external prosthesis socket.

  Thus, in step h) of the method, the provisional contour line of the contact surface of the external medical device is corrected until the optimal distribution of the normal and / or tangential stress values is obtained, depending on the result. longed for. Contour line correction is performed according to predefined stress limit values for each region of the contact surface of the external medical device. Thus, for each region of said contact surface, maximum or minimum limit values of normal and / or tangential stress are previously defined, then the stress values calculated in step g) are compared with the predefined limit values, then the provisional contour line of the contact surface of the external medical device generated in step e) is corrected until a corrected contour line is obtained for which the normal and / or tangential stress values are close to the constraint limit values that have been predefined. According to the invention, a calculated normal and / or tangential stress value is close to a predefined limit value if the difference between said calculated value and said limit value is less than a predetermined difference limit value.

  Thus, in step h) of the method, for each datum representative of a skin surface point, the normal and / or tangential stress value calculated in step g) is compared with a predetermined limit value, and h1) for each data representative of a skin surface point for which there is a difference between the value calculated in step g) and said predetermined limit value greater than a predetermined difference value, the value of the values of location coordinates in the space of said datum representative of a point in the three-dimensional geometry of the contact surface of said device until a difference between the normal constraint value is obtained for said representative datum and / or calculated tangential and the predetermined limit value, which is less than the predetermined difference value; h2) each datum representative of a skin surface point for which the difference between the value calculated in step g) and said predetermined limit value is less than the predetermined difference value; and generating a sixth set of digital data representative of the three-dimensional geometry of the contact surface of said device, wherein the representative data of each skin surface point is associated with a normal and / or tangential stress value close to the predetermined threshold value.

  Step h) of the process can be carried out manually, semiautomatically or completely automatically.

  According to a first aspect, in step h), the temporary contour line generated in step e) of the method can be moved manually by the operator, for example with the aid of a pointing device, from a visual representation of said temporary contour line on a computer screen. Then, in a second step, step h) of the method in which one compares (i) the newly calculated normal and / or tangential stress values from the set of digital data representative of the corrected contour line. with (ii) the predefined stress limit values previously specified in the present description. This succession of steps is repeated until the definitive contour line of the contact surface of the external medical device to be manufactured is obtained, for which the newly calculated normal and / or tangential stress values have a difference value with the predefined limit values are lower than the equally predefined difference limit values.

  According to a second aspect, in step h), the temporary contour line generated in step e) of the method can be moved completely automatically, the computer automatically moving the provisional boundary line generated to the step e) and automatically performing step h) of the method until the final contour line is obtained. For example, the memory of the computer may contain a series of instructions for moving, in successive steps, the provisional contour line generated in step e), then possibly intermediate contour lines generated by reiteration of steps of displacement of the line and calculation and comparison of normal and / or tangential stress values. Advantageously, the displacement of a step of a given segment of the contour line corresponds to a displacement of the surface line of the object, in real dimensions, of at most 2 mm, better not more than 1 mm. and most preferably not more than 0.5 mm.

  For the implementation of steps a) to h) of the method of the invention, those skilled in the art will advantageously refer to the use of various known and adapted software such as for example software ABAQUS, IDEAS, NASTRAN, CATIA , SAMCEF and ANSYS. In the examples, essentially ADINA software was used. In step i) the external medical device is made from the set of digital data representative of the three-dimensional geometry of the contact surface of said device, which is generated at the end of step h).

  Depending on the type of external medical device that is concerned, said device is made in one or more manufacturing steps.

  At the beginning of step i), the element of the external medical device which comprises the contact surface of said device with the part of the body of interest is produced in all cases.

  For example, if the external medical device consists of an external prosthesis replacing a part of a lower limb, such as a prosthesis for amputation of the knee, it is realized at the beginning of step i) the main element of the socket which includes the contact surface with the stump. The various other elements of the prosthesis are made separately, the intermediate prosthetic joints, the tube reproducing the segment of the missing limb and the end effector, which is in this case a prosthetic foot.

  With the method according to the invention, an external medical device is manufactured that can be selected from a cervical collar, a functional shoulder stabilization orthosis, an elbow pad, a wrist or thumb stabilization orthosis, a holding orthosis. part of the trunk and a neck support orthosis.

  In step i) of the method for manufacturing an external prosthesis or orthosis of the invention, the final socket is manufactured from the sixth set of numerical data representative of the three-dimensional geometry of the surface. contact of the external medical device which is generated at the end of step h) of the method, according to any known technique.

  In step i), said external device, or at least the portion of said device comprising the contact surface, can be manufactured by boring using a milling machine or by a direct rapid prototyping method, from the data numbers in the sixth set of digital data generated in step h).

  In particular, it is possible to carry out step i) of the method by transmitting the digital data of the three-dimensional geometry of the contact surface of the external medical device to a rapid prototyping apparatus, which, by a process of successive layer lithography, will directly realize the manufacture of the final socket.

  According to another technique, in step i), the element of the external medical device comprising the contact surface, or even the entirety of said medical device, is manufactured according to a process comprising the following steps: element or device, by a milling method using a milling machine or by a rapid prototyping method, from the sixth set of digital data generated at the end of step h); i2) fabricating the element or device by casting the material of said device, for example prosthesis or orthosis, into the mold, for example the socket mold, obtained in step II).

  According to the manufacturing method used in step i) of the process, the contact surface may be made from a single suitable material or may consist of several materials having these appropriate mechanical characteristics.

  From the element of the external medical device comprising the contact surface obtained at the end of step i) of the process of the invention, the final manufacture of said medical device, for example of the external prosthesis or the brace.

  For example, for the final manufacture of an external prosthesis or tibial or femoral orthesis, is fixed, according to known methods, an intermediate tibial segment, at the end of which is added a flexible foot element allowing bending and flexion movements. extension, and possibly laterality.

  The present invention is further illustrated, but not limited thereto, by the following figures and examples.

FIGURES

  Figure 1 is a photographic photograph of the stump to be paired. Figure 2 illustrates the result of an X-ray densimetric analysis of the lower limb stump to be paired. Figure 2D shows the planes A, B and C of the stump shown respectively in Figures 2A, 2B and 2C.

  Figure 3 is a digital representation of the three-dimensional geometry of the stump in which the different parts are distinguished, respectively: (1) the internal hard parts (bone); (2) internal soft parts; and (3) the skin.

  Figure 4 is a numerical representation of the three-dimensional geometry of the stump after application of the parameters of mechanical behavior and mechanical stress parameters. On the upper part, the arrows (1) represent the imposed displacements. Figure 5 is a numerical representation of the three-dimensional geometry of the stub after meshing and calculation of pressure forces and normal and tangential stress forces. A gray scale according to the value of the pressure forces is shown on the right side of the figure. On the left side of the figure, the pressure values are represented by shades of gray, for each unit of surface defined by the mesh, according to the scale of the right part. (1): areas of high pressure values; (2) areas of low pressure values.

EXAMPLES

  Example 1: Acquisition of the digital data set 30 representative of the three-dimensional geometry of a tibial stump This example shows the implementation of steps a) and b) of the method according to the invention.

  In this embodiment of the method of the invention, the part of the body to be paired is a leg stump from the geometry of which is to be made a tibial socket.

  The stump to be paired is represented on the photographic plate of figure 1.

  The images generated by the X-ray scanning tomodensimetry apparatus consist of a series of transverse anatomical sections of the body part. The series of images is performed along the longitudinal axis of the amputated leg. The series of images starts at mid-thigh and ends at the end of the stump. Two successive images are distant from each other, 1 millimeter in the longitudinal axis of the amputated lower limb.

  Each image is transcribed in grayscale. Each gray level value corresponds to a tissue density value, according to the Houndsfield scale. Figure 2 illustrates the result of the densitometric analysis, according to the three main planes of the stump.

  The densest tissue of the stump is the bone. The maximum value of the gray level will be set on the bone and it will appear in white on the images. An image has a resolution of 256 gray levels.

  Segment the image to detect bone, soft tissue and skin.

  This segmentation can be done automatically using the Mimics software by declaring on an image of the series, the zone of the part of the body to be segmented. By contagion of voxel of the same quality, a volume is reconstructed. This operation will be repeated for the desired three planes A, B and C of the body portion, as shown in Figures 2A, 2B and 2C.

  The volumes extracted by this process are considered as solid volumes. The data sets representative of the volumes are stored as files in the memory of a computer.

  The starting files are used to generate other data files in IGES computer format. These last files are then exploited by the execution of the software Solidworks, thanks to which one generates new files in the format parasolid 12.1. The 12.1 parasolid format files can be exploited by the Adina software.

  At the end of this step 3 computer files are generated, which will be named in this example, respectively: - os.x_t, which consists of a file containing all the digital data representative of the three-dimensional geometry of the internal hard parts part of the body; - tissues.x_t, which consists of a file containing the set of numerical data representative of the three-dimensional geometry of the internal soft parts of the body part; and - skin.x_t, which consists of a file containing all the digital data representative of the three-dimensional geometry of the skin covering the body part.

  Example 2 Generation of the Digital Data Set Including the Data Subset Representative of the Contact Surface Contour This example shows the implementation of steps c), d), e) and f) of the process according to the invention. invention, applied in the case of the design of a tibial socket.

  From the digital data representative of the outer surface of the skin, the outline of a socket is generated with the software Solidworks. A layer of constant thickness of 5 millimeters is added outside the previously generated contour. This layer is limited superiorly below the bi-condylar axis of the knee. This layer represents the first socket, which is provisional.

  Figure 3 is a graphical representation of the three-dimensional geometry of the stump to be paired According to the indications of the orthoprosthetic, two geometric modifications will be made digitally. The first is to penetrate the surface of this socket 2 millimeters at the level of the sub-patellar support. The second is to make a homothetic transformation towards the inside of the volume of 10 millimeters to ensure an overpressure of the nest.

  Thus, the 4th subset of digital data is geometrically defined in 3 dimensions and a new computer file is generated. In the example, this digital file has been named embedding.x_t.

  The digital files previously generated in Example 1 are loaded into the computer's memory and run by the Adina software.

  The bone is the body (body) n 1, the stump (soft tissue + skin), the body n 2 and the socket the body n 3. This software performs the analysis of the mechanical behavior of the entire stump according to the parameters defined in Tables 1 to 6 below: For the sake of clarity for those skilled in the art, the main data of Tables 1 to 6 are reproduced as they appear to the user of the Adina software. Some of the terms appear in English for better clarity and reproducibility.

  FIG. 4 illustrates a graphical representation of the three-dimensional structure of the stump, after application of the mechanical behavior parameters and the mechanical stress parameters presented in Tables 1 to 6.

  Before the computation of the mechanical stresses in the static state, an initial penetration calculation is carried out under conditions in which mechanical stresses are applied to the stump so that its three-dimensional external contour matches exactly the three-dimensional contact surface of the stub. socket that was previously defined. This calculation operation corresponds to a mechanical prestressing operation of the stump. To perform this calculation, it is required that the initial volume of the solid "content", in this case the stub, will match the shape of the volume of the solid "containing", in this case the socket. This deformation induces an initial state of stress Example 3: Calculation of the values of the pressures between the stump and the socket, and iterative process of correction of the final contour line.

  This example shows the implementation of steps g) and h).

  From the parameter definitions imposed in example 2, a calculation is made using the Adina software. This calculation generates a set of numerical data representative of all the mechanical quantities involved. The mapping of the pressures on the body n 2 (stump) is visualized in FIG.

  In each point of the surface of the stump are known the value of pressure and the values of normal and tangential stress.

  The next goal is to reduce these three sizes overall. For this purpose, a computer program called processing.m and executed using the Matlab software (Mathworks Inc.), allows to load into memory and read an ASCII file with extension txt containing, for each node value mesh, the pressure value, the normal stress value and the tangential stress value. The sum of the squared values is the validation criterion of good socket.

  By default, the first value can be minimized, since the geometry of the initial socket was purposely designed narrower than the actual outer contour of the stub (10 millimeters thick inwards).

  The operator selects the surface areas for which the pressure values and the normal and tangential stress values are maximum.

  From this selection, the operator will numerically subtract a thickness of 1 millimeter in areas of low pressure value and low value of normal and tangential stresses, using the Solidworks software.

  Then, from this digital subtraction, the operator recreates a new socket (body # 3) in the form of a computer file, which is named in this example emboiturel.x_t. The data in this file is reintroduced to the third subset (stub).

  A new mesh is then made from the new file previously generated, then the same parameters of boundary conditions, load cases and contact are applied to the corrected three-dimensional shape of the socket. An initial penetration calculation is performed again, then the static calculation is made from the data representative of the corrected three-dimensional shape of the socket.

  Once again, the evaluation.m program is executed to check the validation criterion of good socket.

  This process is performed iteratively until the variation of the criterion is less than 10% of the previous value.

  Then the digital data set representative of the last three-dimensional form of the socket, in the form of an extension computer file x_t, is used to generate the stl extension computer file, which will be executed by the rapid prototyping apparatus. .

  In a final step, the extension computer file st1 is loaded into the digital memory of a rapid prototyping apparatus.

  The rapid prototyping apparatus is then implemented for the manufacture of the tibial socket, from the digital data contained in the extension file stl above.

  Table 1: Analysis conditions 1 - Analysis conditions (type of analysis, dof, kinematics, time sampling ...) Type of STATIC analysis Name of the X-BOD-bone-embedding analysis of the X-body translation Ytranslation Z-translation Calculation hypothesis Displacement Deformation a Small Small Time limit of N Time label Value in second simulation 1 0 0 1 1 Time step N Number of steps Time of step in seconds 1, 10 0.1 Method of calculation and Newton-Raphson with search for greater iteration slope 37i Table 2: Limiting conditions 2 - Limiting conditions Definition of rotational and translational locks Applied to ...

All Face 1 of the Body 1

Table 3

  Parameters of mechanical behavior of the distinct parts of the abutment 3 Materials N Type Characteristics 1 Elastic and Isotropic E = 15000106 Pa v = 0.3 (Socket) 2 Elastic and Isotropic E = 400106 Pa v = 0. 4997 (Skin) 3 Elastic and Isotropic E = 1,109 Pa v = 0.3 (Soft Parts)

Table 4: Meshing

  4 Mesh Group N Type Specificity of elements 1 3DSolid Material 1 2 3DSolid Material 2 3 Shell Material 3 (Reference table 3) e Part N type Coefficient of Sub Geometry or Element Size division zs body l: os Face 1, 2 of Body 1 CSD = 50 Contour 1,2,4,5 of Body 1 CSD = 10 ô Body 2: Body 2 TE = 0.005 m tu) abutment Face 4,6 of Body 2 TE = 0.01 me coprs3: Face 1, 2,3,4,5 TE TE = 0.008 m EMB 3 Mesh Type of Element N of Specificity Geometry Group N Geometry Body 1 1 Body 2 2 Face 3 1,2,3,4,5 of Body Set of N Node Specifics Nodes 1 1438 to 1462 1464 to 1472 2865 to 2872 2874 to 2888 4880 to 4906 4908 to 4922 4927 to 4976 Table 5: Load Case Parameters - Load Cases Type Definition Applied to Displacement Xtranslation = 0.03 m Set 1 of nodes Y-translation = 0 (See Table 4) Z-translation = 0 288551 8 Table 6: Parameters of contact conditions Contact N Type Specificity 1 3Dc contact Bone-to-bone contact Group Initial penetration: Eliminated contact Time to eliminate the initial penetration = 1 second o Contact N Geometry ADINA-M Specificity Surface 1 Face 1,2,3 of the Body 1 Defined on the ADINA-M 2 face geometry 1,9,10 of the Body Defined on the ADINA-M geometry o Pair of N Target surface Surface Coefficient of contact Contactor Coulomb friction 1 2 1 0,5 N Type Specificity Group 2 3Dcontact Contact stub-socket N contact Initial penetration : Eliminated Time to eliminate the initial penetration = 1 second o Contact N Geometry ADINA-M Specificity c = Surface 1 Face 2,3,4,7,8 of the Defined on the geometry of ADINA-M o &.

  Body 2 2 Face 1,2,3,4,5 of Defined on the geometry of ADINA-M o Body 3

U

  Pair of N Target area Surface Coefficient of contact Contactor Friction of Coulomb 1 2 1 0,5

Claims (11)

  A method for making an external medical device for fitting a body part of a patient, said external medical device comprising a surface, said contact surface, intended to be in contact with the surface of the skin of the patient covering at least a region of the part of the patient's body to be paired, said skin surface, said method comprising the steps of: a) acquiring a first set of digital data representative of the three-dimensional geometry of the part of the body on which said external medical device is adapted to adapt, said set of digital data comprising the information relating to the three geometric dimensions of said body part; b) determining, from the first set of digital data obtained in step a), at least: (i) a first subset of digital data representative of the three-dimensional geometry of the inner soft parts of said body part, ( ii) a second subset of digital data representative of the three-dimensional geometry of the internal hard parts of said body part; and (iii) a third subset of digital data representative of the three-dimensional geometry of the skin covering said body portion; then generating a second set of digital data representative of the three-dimensional geometry of said body portion, said second set of digital data including data of said first, second and third subsets; c) assigning, to each of the at least three subsets of digital data contained in said second set of digital data, a parameter or combination of parameters characterizing the elastic law or the viscoelastic law of the behavior of said soft, hard or skin portion vis-à-vis a mechanical stress; d) performing a volumetric discretization, or mesh, of the volumes defined in each of the at least three subsets of said second set of digital data obtained in step c) and generating a third set of digital data comprising the geometric data representative of said mesh ; e) from the third set of digital data obtained in step d), generating a fourth subset of digital data representative of the provisional three-dimensional geometry of the contact surface of said device, and generating a fourth set of digital data comprising said third set and said fourth subset of digital data; f) applying to the fourth set of digital data at least three mechanical stress parameters, respectively: (i) at least one said load case parameter, which is representative of the total force exerted by said body portion on the contact surface said external medical device; (ii) at least one so-called limit condition parameter, which is representative of the conditions by which said fourth set is set upon application of the parameters defined in (i); (iii) at least one so-called contact condition parameter, which is representative of the value of the frictional resistance between the skin surface and the contact surface of said external medical device; then adding the values of the at least three mechanical stress parameters (i), (ii) and (iii) to said fourth set of digital data; g) calculating, from the fourth set of digital data obtained in step f) a normal and / or tangential stress value between said skin surface and said contact surface, at least for each data representative of a point of contact; said skin surface, and generating a fifth set of digital data comprising, for each data representative of a skin surface point, said normal and / or tangential stress value thus calculated; h) comparing, for each data representative of a skin surface point, the normal and / or tangential stress value calculated in step g) with a predetermined limit value, and h1) for each data representative of a point of a skin surface for which there is a difference between the value calculated in step g) and said predetermined limit value greater than a predetermined difference value, varying the value of the location coordinates in the space of said representative datum a point of the three-dimensional geometry of the contact surface of said device until, for said representative data, a difference between the calculated normal and / or tangential stress value and the predetermined limit value is obtained, which is equal to or less than the predetermined difference value; h2) retaining each data representative of a skin surface point for which the difference between the value calculated in step g) and said predetermined limit value is less than the predetermined difference value; and generating a sixth set of digital data representative of the three-dimensional geometry of the contact surface of said device, wherein the data representative of each skin surface point is associated with a normal and / or tangential stress value close to the predetermined threshold value; i) fabricating said external medical device, whose geometry of the surface of contact with said body part consists of the geometry defined by the final digital data set obtained in step h).   2. Method according to claim 1, characterized in that in step a), the acquisition of the first set of digital data representative of the three-dimensional geometry of the part of the body on which said external medical device is intended to adapting is performed using an NMR or scanning X-ray device.   3. Method according to one of claims 1 and 2, characterized in that in step c), the parameter characterizing the behavior of said internal soft part, internal hard or skin vis-à-vis a mechanical stress consists of the elasticity constant of said part.   4. Method according to claim 3, characterized in that the elasticity constant of said soft, hard or skin portion consists of the combination of the Young's modulus (E) and the Poisson's ratio (v) specific to said part.   5. Method according to claim 4, characterized in that the elasticity constant is fixed, respectively: - for the soft part: Young's modulus (E) of 0.1 Gpa; Poisson's ratio (v) of 0.5; - for the hard part: Young's modulus (E) of 1 Gpa; Poisson's ratio (v) of 0.3; for the skin portion: Young's modulus (E) of 0.4 Gpa; Poisson's ratio (v) of 0.49.   6. Method according to one of claims 1 to 5, characterized in that in step d), the mesh is made with a ratio between the mesh size and the greatest length of the body part of the less than 1/50, the value of said ratio being preferably 1/100.   7. Method according to one of claims 1 to 6, characterized in that the fourth subset of digital data representative of the provisional three-dimensional geometry of the contact surface of said device comprises the data representative of the three-dimensional geometry of the surface of the skin.   8. Method according to one of claims 1 to 7, characterized in that said external medical device is selected from an external prosthesis or orthosis for upper limb, for lower limb, for the trunk or for the neck.   9. Method according to one of claims 1 to 9, characterized in that said external medical device is selected from a cervical collar, a shoulder stabilization functional orthosis, a elbow guard, a wrist or thumb stabilization orthosis and a brace for maintaining part of the trunk.   10. Method according to one of claims 1 to 9, characterized in that in step i), said external medical device, or at least the portion of said device comprising the contact surface, is manufactured by boring with the using a milling machine or a rapid prototyping method directly, from the digital data contained in the sixth set of digital data generated in step h).   11. Method according to one of claims 1 to 9, characterized in that in step i), said external medical device, or at least the portion of said device comprising the contact surface, is manufactured according to a process comprising the next steps: il) fabricating a mold of said device, or part of said device comprising the contact surface, by a milling method using a milling machine or by a rapid prototyping method, from the data numerals contained in the sixth set of digital data generated in step h); i2) manufacturing said device, or the part of said device comprising the contact surface, by casting the material constituting said device or said part in the mold obtained in step ii).