WO2020165787A1

WO2020165787A1 - Improved surgical aid

Info

Publication number: WO2020165787A1
Application number: PCT/IB2020/051126
Authority: WO
Inventors: Matteo Mantovani; Fabio Catani
Original assignee: Ncs Lab S.R.L.
Priority date: 2019-02-12
Filing date: 2020-02-12
Publication date: 2020-08-20
Also published as: IT201900001987A1; EP3923870A1

Abstract

A surgical aid for joints, comprising: a first plate (10), intended to be positioned in contact with a first bone of a joint; a second plate (20), intended to be positioned in contact with a second bone of the joint; an actuator (50), configured to exert a force that tends to move the first plate (10) and the second plate (20) away from each other. The actuator (50) comprises an inflatable bag (5), interposed between the two plates (10, 20). An elastic casing (4) at least partially encloses the two plates (10, 20) and the inflatable bag (5).

Description

Improved Surgical Aid

DESCRIPTION

The present invention relates to a surgical aid for orthopaedic surgery, in particular for joint prosthesis implant surgery.

In particular, the invention relates to a surgical aid that enables the determination of the orientation and entity of bone resections for the implantation of a unicompartmental, bicompartmental or tricompartmental joint prosthesis so as to maintain the periarticular or intra-articular capsuloligamentous tissues under isometric tension throughout the entire range of joint movement.

The invention is particularly useful in surgery for the implantation of unicompartmental, bicompartmental or tricompartmental knee prostheses. The device quantifies the distance between the femur and tibia medially and/or laterally in an arthrosic knee affected by uni-, bi- or tricompartmental arthrosis throughout the complete arc of motion, while having the capsuloligamentous structures in isometric conditions and the extensor apparatus reduced.

In summary, a total unicompartmental, bi- or tricompartmental prosthesis for the knee joint comprises a femoral element, intended to be applied to the distal end of the femur medially and/or laterally, and a tibial element, intended to be applied to the proximal end of the tibia medially and/or laterally. The femoral and tibial prosthetic components replace the osteo-cartilaginous ends of the femur and tibia in the formation of the new knee joint.

The femoral and tibial prosthetic components are designed by following geometric criteria that are such as to enable the new joint to have stability and mobility without causing pain and allowing the normal locomotor activities of the patient. Recently, the geometry of the prosthetic components and their three-dimensional alignment relative to the femur and tibia have also been defined through computed axial tomography (CAT) or nuclear magnetic resonance (NMR) imaging in order to respect the anatomy of the knee joint.

In order to enable the application of the femoral and tibial prosthetic components, the corresponding ends of the femur and tibia must be resected in such a way that the prosthesis is aligned with the mechanical or anatomical axis of the femur and tibia, respectively.

While a great deal of work has been done on the geometry of joint surfaces, much less has been done in relation to the physiological tension of periarticular or intra-articular capsuloligamentous tissues throughout the whole arc of motion. In particular, the correct positioning of the prosthetic components of the knee during the surgical procedure remains a crucial point in order to restore the joint biomechanics and in particular the stability, kinematics and proprioception of the knee and the entire lower limb. Traditional surgical techniques and innovative ones of the patient specific type have been geared towards changing the anatomy of bone components (aligning them with the mechanical or anatomical axis), thus in actual fact altering the tension of soft tissues and changing the geometry of joint surfaces. Inevitably, the joint kinematics and kinetics are completely altered, as is the tension in capsuloligamentous tissues. Femoral and tibial bone resections are performed to obtain the mechanical axis of the lower limb such that it passes through the centre of the knee. Medial and lateral condylar bone resections are different in thickness due to anatomical variations in patients and because they are aligned with the mechanical axis of the femur and tibia. Asymmetric bone resections and the modification of the geometry of the joint surfaces of the femur and of the polyethylene insert inevitably bring about an altered tension of soft tissues and when the latter are excessively under tension they are often surgically released at the insertion or along the course thereof.

In other words, knee prosthesis implant surgery induces an alteration of the physiological conditions of the joint for reasons tied both to the geometry of the prosthetic components and their positioning, with repercussions on the tensioning of capsuloligamentous tissues. All this can determine an unsatisfactory clinical result accompanied by pain and difficulty in carrying out not only normal everyday activities, but also the locomotor activities desired by the patient .

The problems summarised above are substantially resolved by the device described in Italian patent 1429235 and in the publication WO2016/147153, both in the name of the applicant.

Very briefly, the surgical aid described in the documents cited above comprises a first plate, intended to be positioned in contact with a first bone of a joint (in the case of the knee, the distal end of the femur, i.e. the condyles) and a second plate, intended to be positioned in contact with a second bone of the joint (in the case of the knee, the proximal end of the tibia, i.e. the tibial plateau). The first and second plates are movable relative to each other along at least a first direction. The aid further comprises an actuator, configured to exert a force that tends to move the first plate and the second plate away from each other. The actuator is controlled by a processing module which, by measuring the relative displacement between the two plates and the force exerted by the actuator, computes a force/displacement diagram that matches a value of force applied by the actuator with a corresponding displacement value detected by the displacement sensor. As is known, by virtue of the physiological characteristics of the ligaments, the force/displacement diagram changes from a non-linear to a substantially linear trend. The displacement corresponding in the diagram to the section of transition between the two trends just mentioned substantially indicates the height of the prosthesis which is consistent with the physiological characteristics of the ligaments, producing a physiological tension on the latter.

The known surgical aid does not enable a correct identification of the area on which contact is determined between the end of the femur and the upper plate. The identification of this area is important in order to enable the best conformation of the upper part of the prosthesis. The object of the present invention is to improve the surgical aid presently available, so as to enable the identification of the area of contact between the end of the first bone and the corresponding plate of the surgical aid.

One advantage of the invention is that it enables an accurate positioning of the prosthetic elements, thus maintaining the isometry of the periarticular or intra-articular capsuloligamentous structures according to the prosthetic design used.

Another advantage of the invention is that the force leading the two plates to be moved away is exerted directly between the plates themselves, i.e. within the articular space.

A further advantage of the invention is that it offers a compact and, consequently, scarcely invasive instrument, which can be positioned through a minimal incision in one compartment or in both compartments with the extensor apparatus being reduced, without requiring a lengthening of surgery times.

Additional features and advantages of the present invention will become more apparent from the following detailed description of one embodiment of the invention, illustrated by way of non-limiting example in the appended figures in which:

- figure 1 shows a schematic vertical elevation view of the aid according to the present invention;

- figure 2 shows an isometric view of the device of figure 1 ;

- figure 3 shows the device of figure 1 in a partial sectional view, in combination with some functional units;

- figure 4 shows the device according to the present invention in a configuration of use;

- figure 5 shows a setting device for the aid according to the present invention;

- figure 6 shows the aid according to the present invention in a configuration in which it interacts with the setting device of figure 5. With reference to the figures listed above, the surgical aid according to the present invention comprises a first plate (10), intended to be positioned in contact with a first bone of a joint. In the case of a knee prosthesis, the first bone is the femur (F). In particular, the first plate (10) is intended to be positioned in contact with the distal end of the femur. The aid further comprises a second plate (20), intended to be positioned in contact with a second bone of the joint. The second bone, in the case of a knee prosthesis, is the tibia (T). In particular, the second plate (20) is intended to be positioned in contact with the proximal end of the tibia after a minimal tibial resection has been performed.

The first and the second plate (10, 20) are movable relative to each other. An actuator (50) is configured to exert a force that tends to move the first plate (10) and the second plate (20) away from each other.

The actuator (50) is interposed between the first and the second plate (10, 20). Advantageously, the actuator (50) comprises an inflatable bag (5), interposed between the two plates (10, 20). The actuator (50) further comprises an elastic casing (4), which at least partially encloses the two plates (10, 20) and the inflatable bag (5).

The actuator (50) is thus substantially free to adapt itself to the conformation of the space comprised in the seat of the prosthesis. Thanks to the deformability of the inflatable bag (5) and of the elastic casing (4), the two plates (10, 20) can be freely oriented relative to each other, taking on an orientation that depends: (i) to a minimal extent on the geometry of the inflatable bag (5) and the elastic casing (4), (ii) to a more considerable extent on the conformation of the space comprised between the seat of the prosthesis on the second bone (tibia) and the first bone (femur) and, in particular, the position of the point of contact between the first plate (10) and the femur (F).

In a preferred embodiment of the actuator (50), the elastic casing (4) comprises an elastic strip or band that wraps around at least a portion of the two plates (10, 20), compressing them in contact with the inflatable bag (5). This conformation of the elastic casing (4) is particularly effective in enabling the plates (10, 20) to be freely oriented, while keeping the actuator (50) assembled.

In a preferable embodiment of the device, actuation is achieved, for example, by means of a volumetric pump and the inflatable bag is filled, for example, with saline solution.

The aid comprises a displacement sensor (30), configured to measure a relative displacement between the first and the second plate (10, 20). In particular, the displacement sensor (30) measures the relative displacement between the first and the second plate (10, 20) with respect to an initial pre-established position, or zero, wherein they are at a known distance. The known initial distance essentially represents the initial reference from which the space between the tibia and femur will be calculated throughout the entire range of motion of the joint. As shown in figure 1 , the displacement sensor (30) is associated with the plates (10, 20). For example, the displacement sensor (30) comprises a magnet associated with the plate (10) and integral therewith, and a sensitive element integral with the plate (20). In the embodiment represented, the displacement sensor (30) is associated with a casing (30a), wherein it is partially housed, which also serves as an element of attachment to the tibia. For this purpose, the casing (30a) is provided with through holes for inserting screws or nails for fastening to the tibia.

The aid further comprises an orientation sensor (31 ), configured to measure the relative orientation between the first and the second plate (10, 20). The measurement of the orientation sensor (31 ) is performed starting from the initial pre-established position, or zero, wherein the plates (10, 20) have a known orientation, for example, wherein the planes in which they lie are parallel to each other. In a possible embodiment, the orientation sensor (31 ) comprises one or more inertial and magnetic sensors such as accelerometers, magnetometers and gyroscopes.

The aid further comprises a force sensor (51 ), only schematically represented, configured to measure the force exerted by the actuator (50). In a possible embodiment of the aid, the force sensor can be a resistor whose resistance varies as a function of the applied force.

The aid likewise comprises a pressure sensor (40), configured to detect the pressure in the inflatable bag (5).

The aid is provided with a processing module (60), connected to the position sensor (30), the orientation sensor (31 ), the force sensor (51 ) and the pressure sensor (40) (if present). The processing module (60) receives as input the measurements read by the sensors (30, 31 , 40, 51 ), to which it is connected, and controls the actuator (50).

The processing module (60) comprises a first calculating unit which is provided with a group of pose (i.e. position and orientation), force and/or pressure data. The processing module (60) makes it possible to correlate the relative orientation between the first and the second plate (10, 20), and the relative displacement between the first and the second plate (10, 20), the force detected at the point of contact and/or the pressure in the inflatable bag (5), measured respectively by the orientation sensor (31 ), the displacement sensor (30), the force sensor (51 ) and the pressure sensor (40), with the position of a point of contact on the first plate (10). Essentially, the processing module (60), knowing: (i) the relative positioning of the plates (10,20) through the measurements read by the orientation sensors (31 ) and the displacement sensors (30), (ii) the force detected at the point of contact through the measurement of the force sensor (51 ) and/or the pressure inside the inflatable bag (5), through the pressure sensor, is capable of identifying the area of contact between the first plate (10) and the femur (F). This applies for any flexion-extension angle between the femur (F) and the tibia (T), i.e. for any joint pose.

The processing module (60) controlling the actuator (50) of the aid and processing the data received from the sensors (30, 31 , 40, 51 ) computes a force-displacement diagram by linking the force detected in the point of contact and the point of contact determined by correlating the measurements of the sensors (30, 31 , 40, 50). The force-displacement diagram is computed in the different joint poses along the whole arc of flexion-extension of the knee.

The isometric tension of soft tissues is identified by the processing module (60) through an evaluation of the force-displacement diagram obtained from the reading of the force sensor (51 ) and/or pressure sensor (40), the displacement sensor (30) and the orientation sensor (31 ) in the various poses of the joint or at different flexion-extension angles of the joint, throughout the entire range of motion thereof. In every pre determined joint pose, the distraction essentially ceases when the force- displacement diagram shows a distinct change in slope indicating the transition through the isometric condition.

During flexion of the knee, the processing module detects the change of slope in the force-displacement diagram for every joint pose or flexion- extension angle imposed on the joint, in order to define, for every pose imposed, the distance between the femur and tibia with the capsuloligamentous tissues in isometric conditions. The number of joint poses or joint flexion-extension angles in which to compute of the force- displacement diagram can be established as desired.

The processing module (60) thus brings about a variation in the force applied by the actuator (50) until the moment when the processing module (60) detects the change of slope in the force-displacement diagram. At that moment, the processing module (60) detects the displacement between the first and the second plate (10, 20) in the determined point of contact between the first plate (10) and the first bone, i.e. the femur (F). In this manner, one obtains the tibial-femoral space along the whole range of motion of the knee. Within that tibial-femoral space the surgeon, possibly with the aid of a computer, will be able to determine the orientation and position of the femoral and tibial prosthetic components. It will therefore be possible to determine the bone resections in terms of entity and relative orientation. The first and the second plate (10, 20) are thus free to move in relation to each other along the first direction (X), whilst the force applied to them by the actuator (50) will vary until the change of slope in the force- displacement diagram.

Throughout the range of motion of the knee, in the various joint poses or flexion-extension angles imposed, the processing module (60) is configured to detect the signal sent by the displacement sensor (30), which corresponds, as said previously, to the displacement along the first direction (X) until the change of slope is reached in the force-displacement diagram. Together with the signal sent by the force sensor (3), the signals of the orientation sensor (60) and the force sensor (51 ) and/or pressure sensor (40) are also detected. The displacement values read are memorised and subsequently processed, by means of a pre-established algorithm, in order to obtain the femoral-tibial space under conditions of isometric tension of the capsuloligamentous tissues, that is, under conditions wherein the capsuloligamentous tissues are not subjected to a tension greater than that in which the change of slope occurs in the force- displacement curve.

The group of pose, force and/or pressure data with which the processing module (60) is provided is obtained by means of a setting device. The setting device comprises a lower abutment (6), intended to enter into contact with the second plate (20). The lower abutment (6) simulates the surfaces of the second bone; if the latter is the tibia, therefore, it preferably has a flattened conformation.

The setting device further comprises an upper abutment (7), configured so as to circumscribe the area of contact with the first plate (10) to a relatively small area and to have a shape representative of the joint surfaces of the first bone, i.e. the femur in the case of the knee joint. The upper abutment is for example in the form of a tapered element, i.e. endowed with a small front area, intended to enter into contact with the first plate (10). The upper abutment (7), for example, has a rounded, convex conformation with the apex or taper turned outwards and towards the first plate (10).

The upper abutment (7) is movable into a plurality of predetermined positions. For this purpose, the setting device comprises an upper body (7a) provided with a plurality of seats (7b) in which the upper abutment (7) can be inserted.

A system of elastic constraints (8) binds the lower abutment (6) and upper abutment (7) together in a manner such as to simulate the presence of a group of ligaments. Essentially, the system of constraints (8) is configured so that the upper abutment (7) and the lower abutment (6) together simulate the joint, in particular the knee joint.

The group of pose, force and/or pressure data configured in the processing module (60) is obtained by arranging the upper abutment (7) successively in the pre-established positions. For each of the pre- established positions of the upper abutment, the plates (10, 20) are inserted between the abutments (6, 7) and the bag (5) is inflated, causing the abutments (6, 7) to be moved progressively away from each other. During the inflation of the bag (5), and for each of the positions of the upper abutment (7), the processing module (60) memorises the displacement and the relative orientation of the plates (10, 20), the force detected by the sensor (51 ) and/or the pressure inside the inflatable bag (5).

The group of data obtained as described makes it possible, during practical use of the aid, to identify the position of the point of contact between the first plate (10) and the distal end of the femur. Essentially, during practical use of the aid, the two plates (10, 20) are inserted into the articular space, after a seat has been fashioned on the second bone, i.e. the tibial plateau. The bag (5) is then inflated and the two plates (10, 20), during the actuation phase, change their position and reciprocal orientation. The readings are obtained continuously by the two sensors (30, 31 ), together with the force and/or pressure readings obtained continuously by the respective sensors (40, 51 ). The processing module (60) then correlates the pose data obtained by the sensors (30, 31 ), and force and/or pressure data obtained by the sensors (40, 51 ) with the reciprocal data obtained with the setting device. In particular, the processing module (60) estimates the point of contact during practical use of the aid by exploiting the relations between the pose, force and/or pressure measurements and the position of the upper abutment (7) constructed with the setting device. The processing module (60) is preferably endowed with an algorithm for correlating the position/orientation, force and/or pressure data, obtained during practical use of the aid, with a position of the point of contact, based on the data obtained on the setting device. This enables the identification of a point of contact also in the event that the displacement/orientation and force and/or pressure values measured during practical use of the aid do not exactly match any combination of data obtained with the setting device.

The group of pose, force and/or pressure data with which the processing module (60) is provided can also consist of a database populated with data obtained experimentally in vitro and enriched during clinical practice.

In order to be able to position the surgical aid it is necessary to perform an initial resection on the tibia that is sufficient to allow the insertion thereof. Said resection will be modified based on the data related to the femoral-tibial space and the calculation of the orientation and position of the bone resections performed in the course of the above-described procedure.

Furthermore, once the femoral and tibial resections have been performed based on the values of the spaces between the femur and tibia calculated by the module (60), it will be possible to use the aid to verify the isometry of the tissues throughout the whole arc of motion. After the insertion of the trial femoral prosthetic component, which has a surface compatible with the geometry of the final prosthesis, the aid is fixed to the tibia and the plates (10,20) are inserted on the resection of the tibial plateau and, while the knee is moved along the whole range of motion thereof, a reading is taken of the force measured by the force sensor (51 ), and, optionally, of the pressure measured by the sensor (40). Based on the force and/or pressure detected, one can still modify the cuts, the thickness of the insert or the size of the components to try to obtain isometry of the medial and/or lateral capsuloligamentous tissues throughout the whole range of motion of the joint. In the event of use to verify isometry, the aid preferably has, on the surface in contact with the trial femoral prosthetic component, a geometry which is equal to the final geometry of the tibial insert.

The surgical aid according to the invention can be used as described below for the implantation of a medial or lateral unicompartmental prosthesis. The limb is suspended with a grip on the femur to prevent the weight of the thigh from affecting the detection of the force between the femur and tibia.

The method for determining the resection of a first and/or a second bone for the implantation of a joint prosthesis comprises the following steps:

inserting the surgical aid according to one of the preceding claims between the first and the second bone, so that the joint end of the first bone is in contact with the first plate (10) and the joint end of the second bone is in contact with the second plate (20);

in each of the various predetermined joint flexion-extension angles, varying the force exerted by the actuator (50) and reading the displacement measured by the displacement sensor (30), the orientation of the first plate detected by the orientation sensor (31 ), the force detected by the force sensor (51 ) and/or the pressure detected by the respective sensor (40), computing a force-displacement diagram that matches a value of force applied by the actuator (50) with a displacement of the point of contact between the first plate (1 ) and the first bone; at various predetermined joint flexion-extension angles, reading and memorising the displacement values measured by the displacement sensor (30), the orientation of the first plate detected by the orientation sensor (31 ), the force detected by the force sensor (51 ) and/or the pressure detected by the respective sensor (40), determining the area wherein the force-displacement diagram changes from a nonlinear trend to a substantially linear trend, or in any case the area wherein there is a first change of slope in the force/displacement curve;

processing the memorised displacement values according to a predetermined algorithm in order to obtain a set of points approximating a curve, or a portion of surface, at which an isometric tension of the capsuloligamentous structures is produced, i.e. a tension that does not substantially exceed the value of tension corresponding to the change of slope of the force-elongation curve.

Preferably, in each of the various predetermined joint poses or joint flexion-extension angles, the force exerted by the actuator (50) is progressively increased in order to determine the value at which the relation between the applied force and the displacement changes the slope.

The method for implanting the joint prosthesis comprises the following steps:

performing a resection of first approximation on the second bone;

determining the curve of points that satisfy the isometric condition of the ligamentous tissues;

implanting the trial joint prosthesis on the first bone.

Following the implantation of the joint prosthesis, the following steps are envisaged:

again inserting the surgical aid between the first bone implanted with the prosthesis and the second bone, so that the portion of the prosthesis associated with the first bone is in contact with the first plate (10) and the second bone is in contact with the second plate (20); carrying out the steps described, verifying that the isometric condition is satisfied;

if the new set of points deviates from the previous set of points beyond a predetermined neighbourhood, correcting the pose of the prosthetic component;

implanting the trial prosthesis on the second bone, verifying (possibly with the aid of support tools, such as, for example, surgical navigators) that the points identified with the above-described procedure lie in a neighbourhood of the prosthetic surface.

In other words, before the final resections of the femur and tibia, the aid is inserted between the end of the joint bones with the first and the second plate (10, 20) arranged in contact with the ends of the bones themselves. In order to make this possible, a preliminary resection of the tibia is performed, while the femur is maintained intact (without bone resections).

The joint is then brought from complete extension to complete flexion. In a predetermined number of joint flexion-extension angles, the force applied by the actuator (50) is varied and the first and the second plate (10, 20) move in relation to each other until reaching the point wherein the force-displacement curve computed by the processing module (60) changes from a nonlinear to a linear trend, indicating the value of the isometric tension of the capsuloligamentous tissues.

During the movement, the processing module continuously reads the relative displacement at the point of contact with the first bone between the first and the second plate (10, 20). At the end of the readings, i.e. on reaching complete coverage of the range of motion between the bones, the processing module (60) determines the space between the femur and tibia, based on the previously mentioned algorithm. The optimal space calculated essentially corresponds to the thickness of the final prosthetic tibial component and enables a correct spatial orientation of the prosthetic components to be achieved by means of the above-described procedure. This makes it possible to reconstruct joint kinematics compatible with the isometry of the intra- and extra-articular capsuloligamentous structures. In addition, the determination of the point of contact and the data of the orientation sensor (31 ) enable the positioning (relative to the surface of the second bone (T)) of the planes tangent to the joint surfaces of the first bone (F) to be estimated over the entire arc of flexion-extension covered.

At the end of the resections and insertion of the femoral trial component the aid can be repositioned on the resection of the tibia and it will be possible to verify the isometry of the capsuloligamentous tissues in the medial or lateral compartment. This makes it possible to introduce any necessary modifications in the bone resections or to quantify and modify the tension of the capsuloligamentous tissues.

The definition of the orientation and entity of the femoral and tibial bone resections can be specific for the patient if the data are used with a computer-aided navigation and/or robotics system, in cases where CAT or NMR images of the geometry of the femur and tibia are available. The surgical aid can also be used with the creation of cutting templates for the anatomical positioning of the femoral and tibial components by means of CAT or NMR images in order to be able to optimise and if necessary modify the position of the prosthetic components based on the optimal ligamentous tension.

The same technique can be used to produce unicompartmental prostheses, total bicompartmental prostheses for preservation of the cruciate ligaments, for preservation of the posterior cruciate ligament or replacement of the posterior cruciate ligament using two devices, a medial one and a lateral one.

The surgical aid according to the present invention offers important advantages. It enables the prosthetic elements to be dimensioned and positioned accurately, thus maintaining the isometry of the capsuloligamentous tissues. Moreover, the aid according to the invention is compact and scarcely invasive. A further important advantage is given by the fact that the use of the aid does not require a substantial lengthening of surgery times, since it is sufficient to position it between the ends of the joint bones and carry out a complete joint movement in order to obtain the optimal position and size of the prosthetic components. Furthermore, it can be used as an instrument for verifying the prosthetic implant implanted.

Claims

1) A surgical aid for joints, comprising:

a first plate (10), intended to be positioned in contact with a first bone of a joint;

a second plate (20), intended to be positioned in contact with a second bone of the joint;

an actuator (50), configured to exert a force that tends to move the first plate (10) and the second plate (20) away from each other;

characterised in that:

the actuator (50) comprises an inflatable bag (5), interposed between the two plates (10, 20);

comprises an elastic casing (4), which at least partially encloses the two plates (10, 20) and the inflatable bag (5).

2) The aid according to claim 1 , wherein the elastic casing (4) comprises a strip or band that wraps around at least a portion of the two plates (10, 20), compressing them in contact with the inflatable bag (5).

3) The aid according to claim 1 , comprising:

a displacement sensor (30), configured to measure a relative displacement between the first and the second plate (10, 20);

an orientation sensor (31 ), configured to measure a relative orientation between the first and the second plate (10, 20);

a force sensor, configured to measure a force exerted by the actuator (50) between the first plate (10) and the first bone;

a pressure sensor configured to measure a pressure detected inside the inflatable bag (5);

a processing module (60), containing a group of position/orientation, force and/or pressure data that matches the position of a point of contact on the first plate (10) with the relative orientation between the first and the second plate (10, 20), the relative displacement between the first and the second plate (10, 20) and the force exerted and/or the pressure in the inflatable bag (5), measured respectively by the orientation sensor (31 ) and the displacement sensor (30), by the force sensor (51 ) and/or the pressure sensor (40).

4) The aid according to claim 3, comprising a setting device which comprises: a lower abutment (6), intended to enter into contact with the lower plate (20); an upper abutment (7), endowed with a front surface such as to simulate the anatomical joint surface, movable into a plurality of pre-established positions; a system of elastic constraints (8) which bind the lower abutment (6) and upper abutment (7) together and which simulate the presence of a system of ligaments.

5) The aid according to claim 4, wherein the group of data related to the position/orientation, force exerted and/or pressure in the inflatable bag (5) configured in the processing module (60) is obtained by arranging the upper abutment (7) successively in the pre-established positions and, for each of the pre-established positions, inserting the plates (10, 20) between the abutments (6, 7), inflating the bag (5), and continuously memorising, for each of the pre-established positions, the relative displacement between the plates, the relative orientation between the plates, the force exerted and/or the pressure in the inflatable bag (5).

6) The aid according to claim 5, wherein the processing module (60) is endowed with an algorithm for correlating the position/orientation, force and/or pressure data with a position of the point of contact on the first plate (10).

7) The aid according to claim 3, wherein the processing module (60) is configured to detect the signals of the displacement sensor (30) and force sensor (51 ) and/or pressure sensor (40), and to compute a force/displacement diagram that matches a value of force applied by the actuator (50), obtained from the value detected by the force sensor (51 ), with a corresponding value of displacement in the point of contact between the first plate (10) and the first bone.

8) The aid according to claim 7, wherein the processing module (60) is configured to detect the value of displacement in which the force/displacement diagram shows a change of slope.

9) The aid according to claim 3, wherein the processing module (60) contains a group of position/orientation, force and/or pressure data which matches the position of a point of contact on the first plate (10) with the relative orientation between the first and the second plate (10, 20), the relative displacement between the first and the second plate (10, 20) and the force exerted and/or the pressure in the inflatable bag (5), measured respectively by the orientation sensor (31 ) and the displacement sensor (30), by the force sensor (51 ) and/or the pressure sensor (40), and wherein the group of data is obtained experimentally in vitro.

10) The aid according to claim 3, wherein the processing module (60) contains a group of position/orientation, force and/or pressure data which matches the position of a point of contact on the first plate (10) with the relative orientation between the first and the second plate (10, 20), the relative displacement between the first and the second plate (10, 20) and the force exerted and/or the pressure in the inflatable bag (5), measured respectively by the orientation sensor (31 ) and the displacement sensor (30), by the force sensor (51 ) and/or the pressure sensor (40), and wherein the group of data is populated and enriched by data collected during clinical practice.