The invention relates to a method for production of a functional insole to normalise the movement of a person's foot, wherein the method comprises the following steps:

- acquisition of three-dimensional data relating to a morphology of at least one sole-part of the said foot;

- acquisition of foot movement data relating to said foot;

- creation of a model of said morphology on the basis of said three- dimensional data;

- change of said model on the basis of said foot movement data such that said functional insole can be produced on the basis of said modified model;

- production of said insole on the basis of said modified model.

Such a method is known from the prior art, more particularly from the conventional actions of a podiatrist or foot specialist who produces an individually adapted functional insole to correct a person's foot movement. In this action, the podiatrist takes a negative imprint (cast) of a person's foot, with which the podiatrist then creates a positive plaster model or cast that has the same forms and dimensions as the foot. The podiatrist makes changes to this plaster model on the basis of the person's foot movement data.

In relation to the person's foot movement data, it can be assumed that there are in principle three main phases in a person's gait, and each of these phases can require correction. These three phases are the heel contact phase, the mid-stance phase and the propulsion phase or push-off phase. For each of these phases it is known to adapt certain properties in an insole in order thereafter to normalise a person's gait with this insole. In this way negative effects on the person which are a result of the person's deviating gait in relation to a normalised gait can be reduced. In practice such an insole can be made on the basis of a plaster model after the plaster model has been modified.

The plaster model is modified by adding and/or removing plaster on the positive plaster model. So the forefoot platform of the plaster model can be built up, whereby a wedge-shaped structure is formed below the forefoot. This wedge-shaped structure has the effect that the forefoot is no longer flat but stands and functions at an angle to the floor, and due to this angle the movement is controlled and thus normalised. Also a lateral edge of the positive plaster model can be built up, which has the effect that the whole foot is placed at an angle to the ground.

The disadvantage of the known method is that it requires great motor skills and specialist knowledge to produce a plaster model and modify this plaster model by means of building up. Also this is a time- consuming task as the built up plaster takes a certain time to harden. As a result an insole is complex to make, both with regard to the actions and with regard to the timetable to be followed.

The object of the invention is to achieve a simpler method than the conventional method used by the podiatrist or foot specialist.

For this the method according to the invention has the feature that said creation comprises the loading into and processing by computer of said three-dimensional data, and that said modification of said model comprises the following steps:

• definition of:

- a finite line of which a first end point is related to the metatarsal end I or preferably metatarsal end II of said foot, and of which a second end point is related to metatarsal end V or preferably metatarsal end IV of said foot;

- a vector of which a starting point is related to the calcaneus of said foot and which extends in a proximal direction;

- an axis which extends from an proximal part of said foot to a distal part of said foot;

· determination of a direction of rotation and a rotation angle around said axis for at least one of said finite line and said vector, on the basis of said foot movement data; • rotation of said finite line and/or said vector around said axis in said determined rotation direction over said determined rotation angle, to produce said modified model such that a rotation and/or torsion deformation occurs in relation to said morphology.

Because the model of the morphology is a digital model, the model need no longer be constructed with plaster and built up, and therefore much lower motor skills are required to make and modify such a model. In contrast to the known method where the model is a plaster model wherein plaster is built up on modification, according to the invention the digital model must be rotated or twisted. For this an axis is defined on the model, around which the model or at least part thereof can be rotated. Furthermore, related to the model, a finite line and a vector are defined with which the rotation can be controlled. This has the advantage that modifying the model requires lower motor skills and no strict timetable must be followed in order to allow plaster to harden as before.

However performance of the method has a secondary advantage in that whereas before, the relationships between the modifications on the plaster and their effects on the person's gait were very complex, now this is simpler. Namely the vector defined in the model is directly related to the heel part of the foot. By rotating this vector around the axis, the heel contact phase can be controlled. Namely rotation of the vector has the effect that the heel cup in the model, which corresponds to the form of the heel of the foot, is twisted in relation to the forefoot part of the model, whereby a model is produced which shows a torsional deformation in comparison with the foot. If an insole is produced on the basis of this model, the insole will hold the heel cup tilted in relation to the heel of the foot, whereby the foot in the heel contact phase is controlled in the direction of tilt of the heel cup in the insole. Rotation of the vector in the model thus results in a control of the person's foot in the heel contact phase.

The finite line defined in the model is directly related to the forefoot part of the foot. By rotating the finite line around the axis, the forefoot part in the model is twisted in relation to the heel part in the model, whereby a model is produced which has a torsional deformation in relation to the person's foot. In production of an insole on the basis of this modified model, the insole has a tilt in the forefoot part in comparison with the person's foot. As a result the foot is controlled in the propulsion phase in the direction of tilt of the forefoot part. A rotation of the finite line in the model thus results in a control of the person's foot in the propulsion phase.

By twisting both the finite line and the vector in the same direction over the same angle, the entire model stands in a tilted position. If an insole is produced on the basis of this model, the entire insole will be in a tilted position in relation to the foot. As a result the mid-stance phase of the person's foot will be controlled.

It will be clear that both for the vector and for the finite line independently of each other, a rotation angle and rotation direction can be determined depending on the person's foot movement data in order to obtain a predetermined control of the foot. There is a direct relation between the rotation of the vector and/or finite line around the axis and its effect, after production of an insole, on the person's gait when using the insole. Because the effect of the insole on the person's gait is easier to see in the design phase of the insole, more specifically when modifying the model, fewer errors will be made and therefore the efficiency of the method will be increased in relation to the conventional method.

Preferably said three-dimensional data relate to a morphology of at least one sole-part of a foot which is in a neutral position. The neutral position of a foot is a position well known to the podiatrist in which the ankle joint is balanced and central. More specifically the neutral position is an unambiguous position in which the subtalar joint neither pronates nor supinates. This neutral position is a static position which differs from person to person. This neutral position can also be used as a reference point for describing foot movement data. By taking the neutral position, which is unambiguous, as a reference position when collecting data on the foot, data can be exchanged between podiatrists and/or foot specialists without any ambiguity occurring on the significance of the data. For example consequently a person for whom a functional insole is to be produced can be examined at a first site by a first podiatrist who passes the data concerned to a second podiatrist who performs the method according to the invention.

In the conventional method of production of an insole with predetermined corrective properties, a correction can be applied to the insole after it has been produced on the basis of the model. After production, this insole can be modified by attaching a wedge-shaped element below the insole.

According to the invention said definition preferably further comprises determining a tangent plane on said model, which tangent plane has at least one contact point related to the calcaneus of said morphology and at least two contact points related to metatarsal ends I, II, III, IV and V. Thus a surface is defined on the model which is equivalent to a ground surface when the foot is standing on the ground. The surface in production of the insole can be related to the underside of the insole. By taking this surface into account in modification of the model, corrections which are conventionally only made to the insole after its production can be taken into account in an insole which is produced according to the invention. As a result no extra step is required for attaching a wedge-shaped element below the insole produced.

Preferably said finite line is defined lying in said tangent plane and said axis is defined lying in said tangent plane. An insole has a controlling function on the movement of a foot only if the foot has contact with the ground. Ground reaction forces on the insole and the foot are partly decisive in the function and working of the sole and the foot. On a floating foot, an insole has no movement-correcting effect. Therefore one advantage is if the defined axis and finite line which are related to the foot are in a plane in the model which is equivalent to a ground surface on a foot standing on the ground, namely the insole can then exercise its controlling function. By defining the axis and finite line in this tangent plane, there is a direct link between the rotation of the finite line and/or vector around the axis and the effects on the foot of the insole produced on this basis. As a result, modifying the model is simplified.

The invention will now be described in more detail using the embodiment examples shown in the drawing.

In the drawing:

Figure 1 shows a diagram of a foot sole with relevant areas; and

Figure 2 shows a side view of a lower leg and foot in different phases of the gait.

In the drawing, the same or similar elements have the same reference numeral.

For the sake of completeness, we would point out that the terms podiatrist and foot specialist in this text should not be interpreted limitatively but also refer to an assistant to the podiatrist or foot specialist or an engineer or designer who cooperates with the podiatrist or foot specialist to collect the relevant data or perform actions as part of the method for production of a functional insole.

Figure 1 shows a diagrammatic depiction of a bottom view of a person's foot 1. This foot 1 at its proximal end 2 has a heel part 4 and at its distal end 3 a forefoot part 5. In figure 1 , in the forefoot part 5 of the foot, areas are indicated where the metatarsal ends (M1 , M2, M3, M4, and M5) are located in the foot 1. Metatarsal end M1 in the foot 1 is in the proximal direction of and adjacent to the big toe. Metatarsal end M5 in the foot 1 is in a proximal direction of and adjacent to the little toe. Metatarsal ends M2, M3 and M4 in the foot 1 are largely between metatarsal end M1 and metatarsal end M5 and in a proximal direction of and adjacent to a corresponding toe. In figure 1 in the heel part 4 of the foot 1 an area is shown where the heel bone or calcaneus C is present in the foot 1.

Each foot 1 of a person has a neutral position which differs individually. In the neutral position of a foot 1 the ankle joint of the foot 1 is in a predetermined position in which the subtalar joint neither pronates nor supinates. This neutral position is a static position which differs from foot to foot. This neutral position is unambiguous and reproducible and can therefore be used as a reference point for describing further data relating to the foot 1.

Figure 2 shows a side view of the foot 1 in a number of positions, where each position occurs in a phase of a person's gait. Position F1 shows the foot in the floating phase. In this floating phase the foot is not in contact with the ground. Position F2 shows the foot in a phase in which, coming from floating phase F1 , initial contact is made with the ground. The heel touches the ground here, and therefore this phase is called the heel contact phase F2. Position F3 shows the foot in a phase where the whole foot sole is in contact with the ground. This phase is the mid-stance phase F3. Position F4 shows the foot in a phase where only the forefoot is in contact with the ground. In this phase the foot is lifting off the ground to return to the floating phase F1. This phase F4 is called the propulsion phase F4. When a person is walking, the phases described above F1 , F2, F3 and F4 occur for each of the two feet successively and form a cycle.

Morphological variations mean that the lower limbs, in particular the feet, differ. A person's foot therefore in most cases is different from the ideal theoretical model of a foot 1. This difference can be of such a nature that the foot 1 has a different walking pattern caused by certain morphological variations, or a different gait in which other certain morphological variations are compensated. This different gait can be accompanied by secondary pathologies such as degenerative joint deformation in later age. Possible deviations are: hindfoot varus, forefoot varus, forefoot supinatus and forefoot valgus. Such deviations often result in a different gait which is of such a nature that functional insoles are essential to be able to function normally. Also the morphological variations often cause a different gait, wherein the deviation is not sufficiently serious for a functional insole to be necessary in the first instance in order to be able to function normally. However this deviation which is not particularly serious can become serious on repeated loading, whereby use of a functional insole is advisable to normalise the gait.

In a normal gait, in the heel contact phase F2 the rear foot shows a slight inversion. The foot 1 pronates towards the mid-stance phase F3. After this mid-stance phase F3 the foot 1 supinates towards the propulsion phase F4. A different gait is usually characterised by either the wrong direction of movement (supination or pronation) at a particular moment; or by a correct direction of movement but an incorrect extent of movement (too much or too little); or a correct direction and extent of movement but an incorrect speed (too slow or too fast); or incorrect timing; or a combination of the above deviations. Such deviations can result in an abnormal reduction or increase of mobility and can result in overload of muscles and/or joints because these are moved and/or loaded beyond their working limits.

The functional insole normalises the movements and the position of the foot whereby this can again function optimally and must at least compensate for morphological variations. The functional insole influences the movement of the subtalar joint and as a result the complete foot function is optimised. The functional insole ensures that walking, standing and running are more efficient by ensuring an optimum relation between the ground and the foot and between the foot and the proximal segments.

For this the functional insole must control the foot at least during one of the heel contact phase F2, the mid-stance phase F3 and the propulsion phase F4. For example by rotating the heel cup in the functional insole towards the inside in relation to the heel of the foot, the foot in the heel contact phase F2 is tilted to the inside whereby supination reduces in the heel contact phase F2. Similarly a wedge-shaped element can be placed below the forefoot to influence the propulsion phase F4. To produce a functional insole, data are collected on at least the form of the underside of the foot 1. These data are three-dimensional data which relate to the morphology of at least one sole-part of the foot 1. Preferably the data on the foot 1 are collected when the foot 1 is in the neutral position. The foot can also be in the loaded state, unloaded state or semi- loaded state, where the states are described below.

In the loaded state the foot presses on the largely flat (ground) surface such that the soft tissue around the pressure points of the foot are pressed against the surface. As a result locations in the foot such as the precise position of the calcaneus and the metatarsal ends are less precisely visible in the imprint, namely the soft tissue forms a flat imprint in the vicinity of these areas.

In the unloaded state the foot is suspended so that the soft tissue in the foot 1 is in a rest position. As a result the forms of the foot 1 , and hence locations in the foot such as the precise position of the calcaneus and the metatarsal ends, are most clearly visible. However in the unloaded state the dimensions and forms of the foot are not totally representative of the contact phases of the foot 1 with the ground since, during these contact phases, the soft tissue displaces under pressure and hence the form of the foot changes. For these reasons preferably the imprint of the foot to produce an insole according to the invention is not taken in unloaded state. It will be clear with some corrections, such an imprint can be used to produce such an insole, but this is not preferred.

The semi-loaded state of the foot 1 is a combination of the loaded and unloaded state, wherein the foot 1 presses on a deformable support, exerting an even pressure on the underside of the foot. Here the soft tissue is displaced but also the forms of the foot 1 , in particular the calcaneus and the metatarsal ends, remain clearly visible. Preferably the data on the foot 1 are collected when the foot 1 is in the semi-loaded state.

Three-dimensional data on the form of the underside of the foot or the morphology of at least one sole-part of the foot can be collected in various ways. Conventionally a negative imprint is taken in plaster of the foot 1 , whereby a negative copy of the morphology of the underside of the foot 1 is obtained. According to the invention preferably a digital scan is used of at least one underside of the foot 1. Various methods for performing a digital scan are known from the prior art. Preferably the foot is placed in a cushion which can exert a constant pressure on the underside of the foot, which cushion, after removing the foot, retains its form. Thus a negative imprint of the foot is obtained in the semi-loaded state which then can be converted into a digital model by one or more photos or by a scanner. Preferably when taking the imprint of the foot, the podiatrist or foot specialist places this such that it is in the neutral position. According to the invention one or more photos of the underside of the foot can be taken which are then converted into a digital model. Here the foot is in an unloaded state. Also according to the invention a negative imprint is taken in plaster which can then be read via a digital scanner.

To produce a functional insole, further foot movement data are collected. Foot movement data comprise both static and dynamic data which are related to the movement of the foot. So angles can be measured for maximum pronation and maximum supination of the foot 1. Knowledge of these maximum angles can be used to control the foot in motion such that the foot moves within these limits and no overload occurs.

Foot movement data can also comprise a video analysis of the foot, whereby a video recording of the foot is produced during walking. This video recording preferably shows a rear view of at least the lower limbs of the person while walking, whereby the supination and pronation angles (of the subtalar joint) in each phase of the gait are visible and can be analysed. On the basis of these video analyses a podiatrist or foot specialist can determine in which phase(s) of the gait control is required, in which direction the foot must be controlled and the extent of the control. The three-dimensional data relating to the morphology of at least the sole-part of the foot 1 are loaded into and processed by a computer to produce a digital model of the foot. Preferably this digital model is reproduced on a screen connected with the computer. Preferably the digital model is processed by removing data which is irrelevant for performance of the method according to the invention. Examples of such irrelevant data are the forms of the foot which are recorded in the three- dimensional data but which lie outside the area of the functional insole to be produced, for example the form of the side edge of the forefoot.

On the digital model according to the invention, a number of elements are defined including an axis 6, a finite line 7, a vector 8 and preferably a tangent plane. The terms axis, finite line and vector are used systematically for clarity but it should be clear that these terms must not be interpreted limitatively. According to the invention the finite line can also be produced as an axis or vector. The digital model represents the person's foot for the design of the insole and thus the elements can be defined on the model in a relation to this foot. The axis 6 is defined from a proximal part 4 to a distal part 5 of the foot 1. Here the axis 6 extends almost along the median of the model.

The finite line 7 is defined in relation to the metatarsal ends. In particular one end of the finite line is related to metatarsal end I or metatarsal end II and the other end of the finite line is related to metatarsal end V or metatarsal end IV. If a loaded imprint of the foot is used as the basis for the digital model, the podiatrist or foot specialist will use several measurements or experience to define the position of the finite line with sufficient accuracy. However in the model obtained on the basis of an unloaded or semi-loaded foot, the positions of the metatarsal ends are perceptible in the form of the model. It is therefore easier to define the finite line 7 in such a model. Preferably the finite line 7 is defined such that the ends of the finite line 7 are adjacent to the metatarsal ends which are perceptible in the form of the model. However according to the invention the finite line 7 can also be defined in relation to said metatarsal ends but with a predetermined offset in a proximal or distal direction. Also the finite line 7 can be defined in relation to said metatarsal ends but with a length which is greater than or smaller than the distance between the metatarsal ends.

The vector 8 is defined in relation to the calcaneus C. In particular the point of contact of the vector 8 is related to the calcaneus and the vector extends in a proximal direction. Considering figure 1 , the vector 8 extends perpendicular to the plane in which the figure is drawn. This plane in which the figure is drawn can be regarded as said tangent plane. Preferably the contact point of the vector 8 lies adjacent to a lowest point of calcaneus C which is perceptible in the form of the model based on an imprint of a foot in unloaded or semi-loaded state. However the contact point of the vector can also be related to the calcaneus C by making contact in the vicinity of the calcaneus. The vector 8 extends in a proximal direction. From the heel part of the foot the vector extends in the direction of the knee. In the model the vector extends largely perpendicular in relation to the model.

The tangent plane is preferably defined touching a lower edge of the model. As a result the tangent plane in relation to the model is comparable to the ground in relation to a foot standing on it. In particular the tangent plane is defined with a contact point related to the calcaneus and with two contact points related to the metatarsal ends. The tangent plane preferably touches the model, but it should be clear that the tangent plane can also be defined at a predetermined distance from the model. In the latter case the tangent plane can be compared with the underside of the functional insole in relation to the foot, where the underside of the insole, due to the thickness of the sole, also lies at a distance from the foot.

Preferably the axis, the finite line and the contact point of the vector are defined in said plane. Furthermore the axis preferably runs through said contact point of the vector on one side and through the centre of the finite line on the other. By defining the elements in relation to each other in this way, the mutual link between the elements is clearly evident and the elements can be determined clearly.

Furthermore in the method according to the invention a direction of rotation and a rotation angle around the axis are determined for at least one of the finite line and the vector. The rotation direction and rotation angle are determined by the podiatrist or foot specialist on the basis of the foot movement data. More specifically the podiatrist or foot specialist establishes in which phase(s) of the heel contact phase, mid- stance phase and propulsion phase control of the foot is desired. The amount and direction of the control are also established by the podiatrist or foot specialist, for example on the basis of foot movement data such as a video recording of the lower limbs of the person during walking. If the direction and amount of the control are known, the rotation direction and rotation angle of the finite line and/or vector can be determined. This determination can take place on the basis of experience of the podiatrist or foot specialist. However the podiatrist or foot specialist can also apply rules which describe the form of the insole and its effect on the foot. These rules can differ depending on whether the functional insole is worn by a child or by an adult. If used for a child to achieve a control of the foot by 4° in one direction in the heel contact phase, the heel cup in the insole is produced with a tilt of around 8° in the same direction. For an adult the same control of the foot of 4° in one direction in the heel contact phase can be achieved by producing an insole with the heel cup having a tilt of around 4° in the same direction.

Tilting the heel cup on an insole is achieved according to the invention by rotating the vector around the axis. Due to rotation of the vector, the part of the model in the direct vicinity of this vector also rotates around the axis. The part of the model which is further away from the vector in the direction of the finite line will rotate less. The finite line will not rotate when the vector is rotated. In this way, on rotation of the vector with the finite line stationary, the model demonstrates a torsional deformation which is evenly divided between the vector and the finite line. If an insole is produced on the basis of this twisted model, the heel cup of the insole in relation to the forefoot will be tilted in comparison with the heel cup in relation to the forefoot on the morphology of the foot.

If control in the propulsion phase is required, the insole will be modified at the forefoot, namely during the propulsion phase the forefoot will be lifted away from the ground. The amount and direction of the desired control can be determined on the basis of the foot movement data by the podiatrist or foot specialist. The desired control is decisive for the direction of rotation and the rotation angle of the finite line in the model. By rotating the finite line, the part of the model in the vicinity of the finite line also rotates. Thus a model is obtained whereby the forefoot part is tilted. An insole produced on the basis of this model will have a tilted forefoot part which controls the foot in the propulsion phase.

In the definition of elements, in particular the axis, vector, finite line and tangent plane in the model, these elements are established according to a specific relation to each other and preferably in an unambiguous position as described above. It will be clear that this relation and unambiguous position of the elements in relation to each other are only applicable on the initial definition of the elements and a model not yet deformed. From the moment that the vector or finite line is rotated about the axis, the relation between the elements changes. Thus the finite line which preferably initially extends in the tangent plane, after rotation around the axis no longer lies in this tangent plane but intersects the tangent plane. Also the vector which initially largely ran perpendicular to the tangent plane, after rotation is at an angle in relation to the tangent plane, which angle is then largely equal to the rotation angle of the vector around the axis.

If the established rotation direction and angle for the finite line and vector are both approximately the same, the model will not show a torsional deformation. However the model will be rotated integrally in relation to the tangent plane. On production of the insole the tangent plane preferably lies parallel to the ground contact surface of the sole. As a result a model which only has a torsion, on production of the insole will stand integrally tilted on the ground, whereby the foot will be controlled in all phases of the gait.

The functional insole is produced on the basis of the modified model. Preferably the insole is produced via a CAD/CAM system whereby production is controlled directly from the computer. The model can then be cut out of a block of material whereby the cutting is controlled by the computer to produce the form of the model. Preferably the underside of the sole which is in contact with the ground is selected parallel to the tangent plane. The lateral edges of the insole are preferably matched to the internal dimensions of the shoes in which they are to be placed. Furthermore the insole can also be produced via a rapid prototyping process. Here a 3D print of the insole is made. The advantage of production of an insole via rapid prototyping is that different materials each with a different hardness can be used arbitrarily in the insole, where on cutting out of a block, the material of the block determines the hardness of the insole. The podiatrist or foot specialist on the basis of experience or measurements can produce strategic areas of the insole from softer or harder material to obtain optimum control and/or optimum comfort.

Furthermore an insole according to the invention can be adapted such that the heel part lies higher in relation to the ground than the forefoot part. This allows a further control of the foot while a person is walking. Furthermore the thickness of the insole can vary by an offset of the ground in relation to the tangent plane, or by defining the tangent plane at a distance from the model. If control of the foot is desired only in the heel contact phase, a functional insole need have only a limited size, wherein only a proximal part of the foot is supported. This has the advantage that in the shoe, the toes have more room as no space is filled by the insole in the forefoot area of the shoe.