Wearable device for measuring the resistance to passive movement of a human subject affected by neuromuscular disorders, and method of use of the results of such measurement

Abstract

Device adapted to be worn by a human subject, particularly a subject affected by neuromuscular disorders, for measuring a resistance to passive movement of said subject, the device comprising: • a proximal unit (102) comprising a first magneto-inertial unit, in turn comprising a three-axis accelerometer, a three-axis gyroscope, a three-axis magnetometer, said proximal unit (102) being adapted to be worn on a limb, upstream of and in proximity to an articulation of said subject; • a distal unit (103) comprising a second magneto-inertial unit, in turn comprising a three-axis accelerometer, a three-axis gyroscope, a three-axis magnetometer, and a load cell (106) for measuring the opposing force exerted by a muscle of said articulation of the subject, said distal unit (103) being adapted to be worn on said limb, downstream of and in proximity to said articulation of said subject; • a processing system (51) adapted to: o receiving measurement data of said three-axis accelerometer, three- axis gyroscope, three-axis magnetometer from said proximal unit (102) and said distal unit (103), when worn, and measurement data of said load cell (106) from said distal unit (103), when worn; o computing said measurement of resistance to passive movement by executing a software application comprising a Sensor Fusion algorithm.

Description

[0001] TITLE

[0002] WEARABLE DEVICE FOR MEASURING THE RESISTANCE TO PASSIVE MOVEMENT OF A HUMAN SUBJECT AFFECTED BY NEUROMUSCULAR DISORDERS, AND METHOD OF USE OF THE RESULTS OF SUCH MEASUREMENT.

[0003] DESCRIPTION

[0004] Field of the invention

[0005] The present invention relates to a device, wearable by a human subject, particularly by a subject, especially a subject affected by neuromuscular disorders, which allows to assess the resistance to passive movement caused, in particular, by spastic hypertonia (spasticity) by means of the biomechanical description of the articulation of interest during the execution of a passive mobilization.

[0006] The present invention also relates to a method for using the results of the measurement performed, in particular of said biomechanical description.

[0007] Description of the prior art

[0008] Systems are known through which a person performing mobilization of a patient’s limb provides a measurement of the perceived resistance by using, typically, semi- quantitative grading scales (e.g., Ashworth scale, modified Ashworth scale, or Tardieu scale). The main problems of such scales are their low reliability, both in kinematic and dynamic terms, due to the subjectivity of the evaluation (performed by a person) and the low sensitivity to changes in the degree of spasticity following a pharmacological or rehabilitative therapy.

[0009] Typically, the involuntary activity of the spastic muscle during the test is monitored by surface electromyography (sEMG). The main problem of this solution is that recording the electromyographic activity only is insufficient to describe the motory pattern of resistance to movement.

[0010] The following will illustrate some of the most relevant prior-art examples based on the above-mentioned principles.

[0011] US 2016 / 0317066A1 describes a single unit that allows measuring the force through the use of a handle positioned on the distal side of the articulation of interest, thus physically separating the operator’s hand from the patient’s body segment. Mobilization is performed on the system, as opposed to directly on the subject, which, in addition to reducing the clinician’s sensitivity when executing the movement, may lead to movement-induced artifacts. Moreover, such a solution cannot provide the relative angle between the two limbs (proximal and distal) when, during mobilization, both limbs move.

[0012] US 2013 / 0303947A1 describes a system for measuring electromyographic activity (EMG), force and range of motion, which is composed of two parts mutually connected by means of a mechanical joint. This system can be used on the ankle, but not on other articulations. Due to its structure, it may generate movement artifacts when performing ankle mobilization. The movement is of the “semi-rigid / semi-constrained” type. Test setup is quite complex (requiring the subject to be prepared during a preliminary experimental session), because the system needs to be adapted to the person’s anthropometric characteristics (e.g., leg length, ankle length, etc.).

[0013] US 8,002,717B2 describes a non-wearable system comprising two parts, one of which is fixed, that are mutually connected by means of a joint. This system permits forcing a rotation of the joint, and hence of the articulation of interest (wrist), at a known speed, and measures the passive force exerted by the limb. This system cannot be worn and can only be used on the wrist, being unsuitable for other articulations like, for example, elbow, knee or ankle, and does not output accelerations and range of motion. In addition, the movement is not performed “directly” by the evaluator.

[0014] “Biomechanical examination of a commonly used measure of spasticity” by A.D. Pandyan, C.I.M. Price, H. Rodgers, M.P. Barnes, and G.R. Johnson (doi: 10.1016 / S0268- 0033(01)00084-5) describes a system including an electrogoniometer and a force sensor which was used for measuring the resistance to passive movement of the elbow articulation of 16 patients affected by ictus. This system is suitable for the elbow, but not for other articulations like, for example, wrist, knee or ankle. Furthermore, mobilization is performed on the system (handle), not on the subject. This, in addition to reducing the clinician’s sensitivity while performing the movement, may lead to movement-induced artifacts.

[0015] “An Instrumented Glove for Improving Spasticity Assessment” by P. Jonnalagedda, F. Deng, K. Douglas, L. Chukoskie, M. Yip, T. Nga Ng, T. Nguyen, A. Skalsky, and H. Garudadri (doi: 10.1109 / HIC.2016.7797723) describes a system consisting of a glove with foot-sensitive resistors and a magneto-inertial unit which was used to analyze the elbow articulation of 5 patients affected by cerebral paralysis. This system is suitable for the elbow and the wrist, but not for other articulations. Moreover, it cannot output the range of motion of the articulation under analysis.

[0016] “Portable measurement system for the objective evaluation of the spasticity of hemiplegic patients based on the tonic stretch reflex threshold” by K.S. Kim, J.H. Seo, and C.G. Song (doi: 10.1016 / j.medengphy.2010.09.002) describes a system including an electrogoniometer, an EMG sensor, and an algorithm classifying the level of spasticity of the elbow articulation of 15 hemiplegic patients. This solution has been applied to the elbow articulation only, excluding other articulations like, for example, wrist, knee or ankle. In addition, it does not output the resistance to movement exerted by the patient.

[0017] “A simple tool to measure spasticity in spinal cord injury subjects” by A. Arami, N. L. Tagliamonte, F. Tamburella, H. Y. Huang, M. Molinari, and E. Burdet (doi: 10.1109 / ICORR.2017.8009475) describes a device which can only be used for testing the ankle articulation. It includes two bulky handles that reduce the system’s clinical usability and practicality. Adaptation of the handles to the anatomy of the patient’s body segment is achieved by means of a thermoplastic layer that needs to be heated to 80°C. This is time-consuming, and the handles can only be used on a specific segment of the patient. The device does not follow the administration guidelines for manual clinical tests validated for spasticity, and requires the installation of two valves and four Velcro macrostraps, resulting in a longer time taken to prepare the patient for the test. The force sensors are not embedded in the magneto-inertial devices, but mounted externally on the handles, thus making the force measurement more difficult. Functional calibration to align the axes of the proximal and distal units with the anatomical axes requires the operator to perform pure movements about an axis, resulting in limitations in terms of time and intra / inter- operator repeatability.

[0018] “Quantification of spasticity and rigidity for biceps and triceps using the PVRM (position, velocity, and resistance meter)” by S. Y. Song (2019 doctoral thesis) describes a device for testing the elbow articulation only. It has a load cell housed in an external case that considerably increases the overall dimensions of the distal unit, thus reducing clinical usability and practicality. Due to the absence of any magnetometer, orientation cannot be estimated properly, requiring a five-second calibration trial to compute the flexion-extension angle of the elbow. The system calculates the flexion-extension angle through the scalar product of the longitudinal versors of the two IMUs, which is a non- generalizable solution. The orientation estimation algorithm does not allow for parameter tuning, since orientation is obtained directly by the on-board algorithm.

[0019] “Design of a portable position, velocity, and resistance meter (PVRM) for convenient clinical evaluation of spasticity or rigidity” by S. Y. Song, Y. Pei, J. Liang, and E. T. Hsiao-Wecksler (doi: 10.1115 / DMD2017-3503) describes a device which is identical to the previous one in the form of two different publications; therefore, all the objections raised against the previous document also apply. The computation of the angular velocity of the elbow by subtraction of “the lateral gyroscope values” is only valid for a pure flexion / extension movement of the elbow.

[0020] “A clinical measurement to quantify spasticity in children with cerebral palsy by integration of multidimensional signals” by L. Bar-On, E. Aertbelien, H. Wambacq, D. Severijns, K. Lambrecht, B. Dan, C. Huenaerts, H. Bruyninckx, L. Janssens, L. Van Gestel, E. Jaspers, G. Molenaers, and K. Desloovere (doi: 10.1016 / j.gaitpost.2012.11.003) describes a device that only permits testing the lower limb (knee and ankle). All sensors are connected by means of physical cables, resulting in bulkiness and movement hindrance. It has a load cell housed inside an external handheld myometer, which further increases its size. Moreover, the hand-held device is not stabilized; on the contrary, it is free from and not constrained to the region under examination, which may lead to misalignment, slipping and movement-induced artifacts. A preliminary calibration to obtain the ankle angle is carried out by performing a movement from the neutral position to maximum flexion, requiring time and skill and lacking intra / inter-operator repeatability.

[0021] US20070027631 Al describes a device consisting of one IMU which does not allow for arc detection of motion, especially if the proximal segment is moving, and which includes no magnetometers. Integration with surface electromyographic signals is not envisaged. Summary of the invention

[0022] It is the main object of the present invention to provide a device for measuring the resistance to passive movement in subjects affected by neuromuscular disorders, particularly spasticity, and a method of use of the results of such measurement, which can overcome the above-mentioned limitations.

[0023] The present invention discloses a system comprising two wireless magneto-inertial units to be positioned on the proximal (upstream) and distal (downstream) segments of the articulation involved in the passive mobilization of the limb of interest, and a load cell for measuring the force (embedded into the distal unit).

[0024] The first (upstream) unit is a magneto-inertial unit with three-axis accelerometer, gyroscope and magnetometer, while the second (downstream) unit incorporates a magneto-inertial sensor (with three-axis accelerometer, gyroscope and magnetometer) equipped with a load cell for measuring the opposing force exerted by the spastic muscle(s) during passive movement.

[0025] The system further comprises a system for processing the data thus obtained.

[0026] The system of the invention provides a quantitative description of the resistance to passive movement imposed on a specific articulation by an evaluator directly exerting the force necessary for moving such articulation, without any mechanical parts (e.g., handle) being interposed between the operator’s hand and the patient’s body segment. Furthermore, unlike the devices described in some prior-art documents, wherein the load cell is positioned on the outside of the magneto-inertial unit (as in Arami Arash et al. 2017 and Bar-On et al. 2012), in the system disclosed herein the load cell is built-in. The non- optimal position of the load cell in prior-art systems may hinder the force measurement because the vector of the acceleration measured by the accelerometer does not directly reflect the force value measured by the load cell. In addition, clinical precision and practicality is further reduced when the load cell is positioned in secondary places, as in the systems described in the above-mentioned documents. The system makes it also possible to classify the biomechanical response on a clinical evaluation scale and to solve the problem of subjectivity in spasticity evaluation by collecting quantitative information about resistance (in terms of force opposing movement), range of angular motion of the articulation, and time trends of articular angles and of angular and linear speeds and accelerations.

[0027] The system of the invention does not require the use of any physical parts (e.g., handles) between the person executing the movement and the patient. Therefore, the present solution allows the executor to exert a force directly on the patient, as opposed to indirectly through the interposition of a handle. The executor of the movement places his / her hands directly on the patient, with the system of the invention in between (since the latter is miniaturized, the clinician will make the same type of movement as he / she would in the absence of the system of the invention).

[0028] Because the system of the invention is fully wearable, wireless and much smaller than any prior-art system, the clinician who is imparting the mobilization can grip the patient’s limb while keeping the magneto-inertial unit (equipped with a force sensor) under the palm / fmgers of his / her hand. This implies that:

[0029] • no specific training of the person performing the mobilization is necessary;

[0030] • the conventional clinical test is not affected by any bulky elements or physical interfaces, such as handles, between the evaluator’s hand and the patient’s limb, nor requires stabilization of connecting parts.

[0031] The use of two units (a proximal one and a distal one) makes it possible to measure the relative angle between them (range of motion of the articulation), i.e. not only the angle of the distal unit, as is the case with prior single-unit devices. It is not always true, in fact, that the angle of the articulation is the same as that of the distal unit (this is only true when the proximal limb does not move, otherwise its movement should be added to or subtracted from that of the distal unit).

[0032] The present invention is the only one among the previous patent solutions based on two magneto-inertial units that does not require a specific and preliminary calibration procedure to obtain the articular angle estimate. The main advantage of not having to execute any anatomical calibration procedures to compute the articular angle lies in the device being more practical and easier to use. This approach eliminates the need for making specific movements in order to align the axes of the units with the anatomical axes, resulting in significantly shorter preparation times and improved clinical efficiency. Furthermore, any errors due to variations in the execution of calibration procedures, which can be influenced by intra / inter-operator repeatability, are avoided. Also, such procedures may cause the patient to feel uncomfortable, especially in the presence of spasticity. The integration of the magnetometer into the system offers additional advantages. In some systems lacking a magnetometer, a calibration trial must be carried out to compute the flexion-extension angle, during which the units have to be physically aligned, which leads to reduced clinical usability and practicality. Moreover, in order to obtain the articular angle, some systems require a preliminary calibration movement from the neutral position to maximum flexion. If the zero-degree configuration cannot be reached because of spasticity, it will be necessary to manually use a goniometer, which requires time and skill and is affected by problems of intra / inter-operator repeatability. In the presence of spasticity, imposing a known angular position may cause the patient to suffer discomfort or pain, and such position may not be reached due to pathological limitations.

[0033] The device can be used to quantify the degree of muscular spasticity of the most important articulations of the human body.

[0034] The device can also be used to measure the maximal isometric voluntary muscular force without having to use the bulky elements and physical interfaces that characterize the hand-held dynamometry systems currently known in the art.

[0035] In accordance with claim 1, the present invention relates to a device adapted to be worn by a human subject, particularly a subject affected by neuromuscular disorders, for measuring a resistance to passive movement of said subject, the device comprising:

[0036] • a proximal unit comprising a first magneto-inertial unit, in turn comprising a three-axis accelerometer, a three-axis gyroscope, a three-axis magnetometer, said proximal unit being adapted to be worn on a limb upstream of and in proximity to an articulation of said subject;

[0037] • a distal unit comprising a second magneto-inertial unit, in turn comprising a three-axis accelerometer, a three-axis gyroscope, a three-axis magnetometer, and a load cell for measuring the opposing force exerted by a muscle of said articulation of the subject, said distal unit being adapted to be worn on said limb downstream of and in proximity to said articulation of said subject. The distal unit has the same dimensions as the proximal unit, since the load cell is embedded into a specially designed bay.

[0038] • a processing system adapted to: o receive measurement data of said three-axis accelerometer, three-axis gyroscope, three-axis magnetometer from said proximal unit and said distal unit, when worn, and measurement data of said load cell from said distal unit, when worn; o compute said measurement of resistance to passive movement by executing a software application comprising a Sensor Fusion algorithm for computing the articular angle.

[0039] In accordance with claim 6, the present invention also relates to a method of use of the device for computing said resistance to passive movement of said subject.

[0040] Dependent claims comprise further preferred aspects of the present invention.

[0041] Brief description of the drawings

[0042] The invention will become wholly apparent in the light of the description that follows, provided herein merely by way of non-limiting explanatory example with reference to the annexed drawings, wherein:

[0043] • Figures 1 and 2 show the various parts that make up the system for measuring the resistance to passive movement in subjects affected by neuromuscular disorders according to the invention;

[0044] • Figures 3, 4 and 5 are block diagrams of the system for measuring the resistance to passive movement in subjects affected by neuromuscular disorders according to the invention;

[0045] • Figure 6 schematically shows the process of acquiring and processing the data acquired by the system according to the invention;

[0046] • Figures 7A, 7B, 7C and 7D schematically show some articulations that can be subjected to measurement using the system of the invention;

[0047] • Figures 8 and 9 show two examples of how the “raw” data and the “processed” data can be displayed and compared for one (Figure 8) or two (Figure 9) clinical tests.

[0048] In the drawings, identical reference numerals and letters identify the same or functionally equivalent parts.

[0049] Detailed description

[0050] With reference to Figures 1 to 5, the following will describe an exemplary embodiment of the system for measuring the resistance to passive movement according to the invention.

[0051] The system of the present invention is particularly suited to be worn by a person, since it can be fastened to two portions of the person’s body, in proximity to articulations thereof, and to be used for executing a method of analysis of a mobilization of a person’s limb. Such method will be described in detail later on.

[0052] The system comprises: a proximal unit 102 (Figures 1 and 3), adapted to be fastened to a limb of a human subject, upstream of and in proximity to the articulation of interest, and a distal unit 103 (Figures 2 and 4) adapted to be fastened to the same limb of the human subject, downstream of and in proximity to the articulation of interest (see also Figures 7A-7D, which will be described hereinafter).

[0053] Said proximal unit 102 comprises a magneto-inertial sensor 104 and a data processing unit 105, adapted to process at least the data acquired by said magneto-inertial sensor 104.

[0054] Said distal unit 103 comprises a magneto-inertial sensor 104’, a force sensor 106, and a data processing unit 105’, adapted to process at least the data acquired by said magneto-inertial sensor 104’ and by said force sensor 106. Said distal unit 103 has the same dimensions as the unit 102.

[0055] The structural and operational characteristics of a magneto-inertial sensor, as such, will not be described any further herein unless necessary to illustrate the subject of the present disclosure, since they are known to those skilled in the art.

[0056] Said force sensor 106 is a compression cell that measures the unidirectional thrust or pressure force being applied. Such force is detected by the extensometers of the sensor, which will deform along with the body applying the force, thereby causing a voltage variation. Such a sensor, the functionality of which is known, is connected to the data processing unit 105’ by means of a cable, using one of the two digital VO ports available in the unit 103, and is positioned in a dedicated bay 25 in the upper part of the case 22 of the unit itself (Figure 2).

[0057] The proximal 102 and distal 103 units comprise a power supply device, e.g., a battery, which supplies power to the magneto-inertial and / or to the force sensor and / or to the components comprised therein.

[0058] The proximal 102 and distal 103 units comprise a plurality of interface devices that allow the user to interact, whether directly or indirectly, and whether actively or passively, with them. For example, they comprise USB connectors, analog front-ends, and buttons allowing interaction with the proximal unit 102 and / or with the distal unit 103, e.g., in order to activate one or more functions; lighting devices, e.g., LEDs, to provide visual feedback to the system user, and also a wireless communication system (Wireless module), e.g., using Bluetooth technology, for communicating with, for example, a computer 51 (Figure 5). The proximal 102 and distal 103 units further comprise a memory module (Memory), preferably a non-volatile memory module, adapted to store the data resulting from the measurements taken by the magneto-inertial sensors 104, 104’ and / or by the force sensor 106, or the data processed by said data processing unit 105. The units 102 and 103 further comprise a power management module (Power management) and a crystal oscillator (Crystal).

[0059] The proximal unit 102 comprises, as shown in Figure 1, the following elements: a case bottom 11 and a case top 12 adapted to be joined together to enclose, into a single unit, the battery 13 and the electronic board 14. Said electronic board 14 incorporates all the active and passive components required by the device to operate (Figure 3). Preferably, the proximal unit is applied onto the limb under examination in such a way that the case bottom 11 is directly in contact with the limb.

[0060] The distal unit 103 comprises, as shown in Figure 2, the following elements: a case bottom 21 and a case top 22 adapted to be joined together to enclose, into a single unit, the battery 23 and the electronic board 24. Said electronic board 24 incorporates all the active and passive electronic components required by the device to operate (Figure 4). In addition, the case top 22 preferably comprises a special bay 25 adapted to contain the force sensor 106, to which a clip 26 may optionally be applied in order to even out the force being applied by the person performing the mobilization, i.e., in order to enlarge the sensitive area of the force sensor (e.g., 0 = 4 mm) to the whole clip (e.g., 35 mm x 25 mm). The distal unit is applied to the limb under examination in such a way that the force sensor is in contact, whether directly or through the clip, with the limb.

[0061] In one possible, but merely illustrative and non-limiting, embodiment, the proximal 102 and distal 103 units are connected in a known manner to a central processing system 51 (Figure 5), e.g., a computer, for the purpose of transmitting thereto at least the data stored in a memory module comprised in the proximal unit 102 and / or in the distal unit 103. Such data transfer may occur after a phase of analyzing the person’ s movement, once all measurements have been taken, e.g., when the system has been removed from the patient. In one possible embodiment, said system is connected over a radio connection, e.g., a Bluetooth connection or other short-range wireless data transmission technologies equally suitable for such activity, for the purpose of transferring the data processed by the data processing units 105, 105’ of the proximal 102 and distal 103 units.

[0062] The system of the invention allows processing the data coming from the abovedescribed two magneto-inertial sensors 104, 104’ and force sensor 106 to determine the orientation of the person’s body part, e.g., a hand, and the force being exerted on the person’s body part, e.g., a hand, during the execution of the mobilization procedure. The following will describe in detail the process of data acquisition and the method of computing the main outputs, with reference to the blocks of the block diagram shown in Figure 6.

[0063] 61 : START

[0064] 62: positioning the proximal 102 and distal 103 units upstream and downstream, respectively, of the patient’s articulation to be subjected to mobilization.

[0065] A stable positioning can be achieved by applying zip ties 74, 75 around the articulation; the zip ties are inserted through suitable slots 17 and 27 of the case bottoms 11, 21 of the proximal and distal units, and cause the units to closely adhere to the articulations in a non-invasive manner;

[0066] 63 : performing and recording mobilization. In particular, the “raw” data defined below are recorded, which include linear accelerations, angular velocities, local magnetic fields, and force;

[0067] 64: computation of the orientation of the proximal and distal units in the three- dimensional space by means of an advanced signal processing algorithm. Several advanced signal processing algorithms are known, referred to as Sensor Fusion algorithms, for computing orientation in three-dimensional space. An algorithm which is commonly employed due to its simplicity (just one parameter to be fine-tuned) and execution efficiency, and which is used in the present invention, is the one described in publication “Estimation of IMU and MARG orientation using a gradient descent algorithm” by S.O.H. Madgwick, A.J.L. Harrison, and R. Vaidyanathan (doi: 10, 1109 / ICQRR.2011,5975346). A recent study described in publication “Extension of the Rigid-Constraint Method for the Heuristic Suboptimal Parameter Tuning to Ten Sensor Fusion Algorithms Using Inertial and Magnetic Sensing” by M. Caruso, A.M. Sabatini, M. Knaflitz, U. Della Croce, and A. Cereatti (doi: 10, 3390 / s21186307) has demonstrated that no significant difference will be observed in the accuracy of the orientation estimate as long as each algorithm has been appropriately optimized by finetuning its parameters, which must be “adapted” to a specific scenario (i.e., hardware characteristics, movement intensity, etc.). Such fine-tuning involves a first phase of characterizing the sensors 104 and 104’ in order to verify the correctness of the measurements taken by the individual sensors included in 104 and 104’ (accelerometer, gyroscope and magnetometer), and a second phase including one or more acquisition steps during which the mobilization of the articulation of interest is simulated in order to optimize the parameter(s) of the algorithm for a specific movement.

[0068] Once the orientations of both units have been estimated, the orientation of the distal unit is expressed in relation to that of the proximal unit to obtain the relative kinematics. For this application, the axes of the units are assumed to be aligned with (parallel to) the anatomical axes on which they are positioned, taking care of ensuring such alignment when preparing the subject. The relative kinematics is then broken up to obtain the articular angle of interest through a specific sequence of Euler angles for each articulation;

[0069] 65: identifying the start and end of movement by processing the data obtained from a magneto-inertial sensor 104;

[0070] 66: computing / identifying the parameters of interest, such as start and end of movement, range of motion (defined as the difference between the maximum value and the minimum value obtained during each test), angular accelerations, and force.

[0071] 67: END The system of the invention can be used for the articulations of the upper limb (shoulder, elbow, wrist) and lower limb (hip, knee, ankle). For example, when the elbow articulation needs to be examined (Figure 7A), the proximal unit 102 is positioned at the level of the fixed segment (arm distal third), while the distal unit 103 is positioned on the free segment (forearm distal third) that will be moved by the operator. This arrangement will make it possible to test either the resistance to passive movement exerted by the flexor muscles of the elbow during extension mobilization, if the distal unit 103 of the free segment is positioned on the palm side (as in Figure 7A), or the resistance exerted by the extensor muscles during flexion mobilization, if the distal unit 103 is positioned on the back (not shown).

[0072] Figure 7B shows how the units must be positioned in order to evaluate the wrist articulation. In particular, the distal unit 103, which is positioned on the palm side, permits testing the palmar flexor muscles of the wrist during dorsal flexion mobilization. Conversely, the dorsal positioning of the distal unit 103 allows testing the dorsal flexor muscles during palmar flexion mobilization (not shown).

[0073] Figures 7C and 7D show the configuration of the system according to the invention for, respectively, the ankle and knee articulations, to which the above considerations still apply.

[0074] More in particular, the following are some non-limiting examples of the abovedescribed phase 62 of positioning the proximal 102 and distal 103 units upstream and downstream, respectively, of the patient’s articulation:

[0075] • elbow articulation: the proximal unit 102 is positioned on the arm with the y-axis of the inertial unit 104 pointing towards the shoulder and the z-axis parallel to the axis of rotation of the elbow; the distal unit 103 is positioned on the forearm, in proximity to the wrist, with the y-axis of the inertial unit 104’ pointing towards the wrist and the x-axis parallel to the transversal axis passing through the radius and the ulna;

[0076] • wrist articulation: the proximal unit 102 is positioned on the forearm, in proximity to the wrist, with the y-axis of the inertial unit 104 pointing towards the elbow and the x-axis parallel to the transversal axis passing through the radius and the ulna; the distal unit 103 is positioned on the hand, with the y-axis of the inertial unit 104’ pointing towards the fingers and the x-axis parallel to the transversal axis passing through the radius and the ulna;

[0077] • ankle articulation: the proximal unit 102 is positioned immediately above the ankle, with the y-axis of the inertial unit 104 pointing towards the knee and the z- axis parallel to the transversal axis passing through the malleoli; the distal unit 103 is positioned on the foot, with the y-axis of the inertial unit 104’ pointing towards the toes and the x-axis parallel to the transversal axis passing through the malleoli;

[0078] • knee articulation: the proximal unit 102 is positioned on the thigh, with the y-axis of the inertial unit 104 pointing towards the hip and the x-axis parallel to the transversal axis of the knee; the distal unit 103 is positioned immediately above the ankle, with the y-axis of the inertial unit 104’ pointing towards the knee and the x-axis parallel to the transversal axis of the knee.

[0079] Once the proximal 102 and distal 103 units have been positioned on the articulation of interest, the operator opens the software application previously installed on the central processing system 51 and establishes a connection (e.g., via Bluetooth or any other wired or wireless communication system) with both units.

[0080] Subsequently, before and after every clinical test, the operator starts and ends the recording of the clinical test by clicking the acquisition start / stop button available in the application. No functional calibration movements are required to obtain an estimate of the articular angle.

[0081] The clinical test conventionally requires a passive mobilization of the limb aimed at stretching the muscle to be tested, and evaluating the response to such stretching action. After a test session, the data acquired by the two units, saved to the local memory of each one of said two units, are transferred (e.g., via Bluetooth or any other wired or wireless communication system) to the central processing system 51, which, by executing a software application comprising the above-described Sensor Fusion algorithm, will automatically process and display the data according to the block diagram shown in Figure 6. At the end of this step, it will be possible to display in graphic form the “raw” data (e.g., linear accelerations, angular velocities, local magnetic fields, and force) directly measured by the sensors 104, 104’ and 106, and also the “processed” data provided by the application software implementing the Sensor Fusion algorithm (e.g., 64: orientation of the proximal and distal units; 65: start and end of movement; and 66: range of motion, and angular accelerations) for each clinical test. Such graphs will then be used by the clinician to evaluate the completed clinical test.

[0082] The operations described in the previous paragraph are carried out in a per se known manner, particularly those executed by the Sensor Fusion algorithm.

[0083] • Figures 8 and 9 show two examples of how the “raw” data and the “processed” data can be displayed and compared for one (Figure 8) or two (Figure 9) clinical tests. Such data may be: o “raw” data:

[0084] ■ proximal unit: linear accelerations (x, y and z components), angular velocities (x, y and z components), and local magnetic fields (x, y and z components);

[0085] ■ distal unit: linear accelerations (x, y and z components), angular velocities (x, y and z components), local magnetic fields (x, y and z components), and force; o “processed” data:

[0086] ■ proximal unit: orientation (x, y and z components);

[0087] ■ distal unit: orientation (x, y and z components);

[0088] ■ start and end of movement, range of motion, and angular accelerations (x, y and z components).

[0089] For example, in Figure 8 the curves 83 and 84 refer to “processed” data, whereas the curves 85 and 86 show “raw” data.

[0090] Likewise, in Figure 9 the curves 902, 903, 907 and 908 show “processed” data, whereas the curves 904, 905, 909 and 910 show “raw” data.

[0091] Similar considerations also apply to other data that can be displayed, e.g., orientation, etc.

[0092] More in particular, Figure 8 shows one possible screen displaying a subset of 4 possible outputs (83: range of motion; 84: angular accelerations of the distal unit in its three x, y and z components; 85: force; and 86: angular velocities of the distal unit in its three x, y and z components) for a clinical test selected from the list of completed tests 81. Additional functions assisting the clinician, the person performing the mobilization, or the person using the application software in interpreting the data are available in 82 (e.g., selection of a particular time instant, zoom in / out, etc.).

[0093] Figure 9 shows one possible screen displaying a subset of 4 possible outputs (902: range of motion; 903: angular accelerations of the distal unit in its three x, y and z components; 904: force; 905: angular velocities of the distal unit in its three x, y and z components; 907: range of motion; 908: angular accelerations of the distal unit in its three x, y and z components; 909: force; and 910: angular velocities of the distal unit in its three x, y and z components) for two different clinical tests selected from the lists of completed tests 901, 906. Additional functions assisting the clinician, the person performing the mobilization, or the person using the application software in interpreting the data are available in 901, 906 (e.g., selection of a particular time instant, zoom in / out, etc.).

[0094] The software application executed by the central processing system 51 comprises a program that makes it possible to do the following:

[0095] • computing the orientation in three-dimensional space of the proximal 102 and distal 103 units by applying a Sensor Fusion algorithm, e.g., the one described in 64, to the “raw” data (linear accelerations, angular accelerations, and local magnetic field);

[0096] • computing the start and end of movement, the range of motion, and the angular accelerations (x, y and z components), e.g., as described in 64, 65 and 66;

[0097] • displaying the “raw” data and the “processed” data for one or more clinical tests (Figures 8 and 9).

[0098] It can therefore be inferred that the method of the present invention is a method adapted for use of the above-described device for measuring said resistance to passive movement of a subject, the method comprising the following phases:

[0099] • phase of characterizing said first and second magneto-inertial units, adapted to verify that the results of the operations executed by said three-axis accelerometer, three-axis gyroscope and three-axis magnetometer are consistent with the specifications provided in the respective datasheets. This phase is executed only once; • phase of optimizing, or fine-tuning, parameters of said Sensor Fusion algorithm, by recording at least one acquisition of data concerning a simulation of said mobilization of said articulation. This phase is executed only once;

[0100] • phase of computing, by means of said Sensor Fusion algorithm, the orientation in three-dimensional space of said proximal and distal units;

[0101] • phase of expressing the orientation of said distal unit relative to the orientation of said proximal unit to obtain a relative kinematics of said units;

[0102] • phase of breaking up said relative kinematics to obtain an articular angle of interest through a specific sequence of Euler angles for each articulation;

[0103] • phase of identifying the start and end of movement by processing data obtained from said magneto-inertial unit of said distal unit (103), applying thresholds to a signal recorded by a gyroscope;

[0104] • phase of computing and identifying parameters of interest comprising said start and end of movement, range of motion, defined as the difference between the maximum value and the minimum value of said movement, angular accelerations, and force;

[0105] • phase of displaying in graphic form said received data comprising linear accelerations, angular velocities, local magnetic fields, and force, as directly measured by said first and second magneto-inertial units (104, 104’) and by said load cell (106), and said computed data comprising the orientation of said proximal and distal units (102, 103), said start and end of movement, said range of motion, and said angular accelerations.

[0106] Preferably, during said phase of expressing the orientation, the axes of said proximal unit and of said distal unit are assumed to be aligned with, in particular parallel to, the anatomical axes on which they are positioned. Combined with specially developed biomechanical models, this assumption avoids the need for any functional calibration movements.

[0107] The method of the present invention can advantageously be implemented by means of a computer program, also referred to as software application, comprising program coding means for executing one or more steps of the method, when such program is run on a computer. It will therefore be appreciated that the protection scope of the invention extends to such a computer program and also to a computer-readable medium containing a recorded message, said computer-readable medium comprising program coding means for executing one or more steps of the method, when such program is run on a computer.

[0108] The elements and features described in the various preferred embodiments may be mutually combined without departing from the scope of the invention.

[0109] No other construction details will be described herein, in that those skilled in the art will be able to implement the invention on the basis of the teachings provided in the present description. In particular, those skilled in the art may be one or more of the inventors or authors previously mentioned in the discussion on the prior art.

Claims

CLAIMS1. Device adapted to be worn by a human subject, particularly a subject affected by neuromuscular disorders, for measuring a resistance to passive movement of said subject, the device comprising:• a proximal unit (102) comprising a first magneto-inertial unit, in turn comprising a three-axis accelerometer, a three-axis gyroscope, a three-axis magnetometer, said proximal unit (102) being adapted to be worn on a limb, upstream of and in proximity to an articulation of said subject;• a distal unit (103) comprising a second magneto-inertial unit, in turn comprising a three-axis accelerometer, a three-axis gyroscope, a three-axis magnetometer, and a load cell (106) for measuring the opposing force exerted by a muscle of said articulation of the subject, said distal unit (103) being adapted to be worn on said limb, downstream of and in proximity to said articulation of said subject;• a processing system (51) adapted to: o receiving measurement data of said three-axis accelerometer, three- axis gyroscope, three-axis magnetometer from said proximal unit (102) and said distal unit (103), when worn, and measurement data of said load cell (106) from said distal unit (103), when worn; o computing said measurement of resistance to passive movement by executing a software application comprising a Sensor Fusion algorithm.

2. Device according to claim 1, wherein said processing system comprises a program adapted to execute the following operations:• computing an orientation in three-dimensional space of said proximal unit (102) and said distal unit (103) by applying said Sensor Fusion algorithm to the data received from said proximal unit (102) and said distal unit (103);• computing the start and end of said movement, the range of motion, and the angular accelerations of said movement;• displaying said received data and / or said computed data.

3. Device according to claim 1 or 2, wherein said proximal unit (102) furthercomprises:• a first case bottom (11) and a first case top (12) adapted to be joined together to contain said first magneto-inertial unit;• first positioning means (74) connected to said first case bottom (11) and adapted to hold said proximal unit (102) in a fixed position on said limb.

4. Device according to claim 1 or 2 or 3, wherein said distal unit (103) further comprises:• a second case bottom (21) and a second case top (22) adapted to be joined together to contain said second magneto-inertial unit;• second positioning means (75) connected to said second case bottom (21) and adapted to hold said distal unit (103) in a fixed position on said limb.

5. Device according to claim 4, further comprising:• on said second case top (22), a bay (25) adapted to contain said load cell (106);• on said load cell (106), a clip (26) adapted to enlarge a sensitive area of said load cell (106) when applied on said limb.

6. Method suitable for using the device according to any one of claims 1 to 5, for computing said resistance to passive movement of said subject, said method comprising the following phases:• phase of characterizing said first and second magneto-inertial units, said phase being adapted to verify that the results of the operations executed by said three-axis accelerometer, three-axis gyroscope and three-axis magnetometer are consistent with the specifications provided in the respective datasheets;• phase of optimizing, or fine-tuning, parameters of said Sensor Fusion algorithm, by recording at least one acquisition of data concerning a simulation of said mobilization of said articulation;• phase of computing, by means of said Sensor Fusion algorithm, the orientation in three-dimensional space of said proximal and distal units;• phase of expressing the orientation of said distal unit relative to the orientation of said proximal unit to obtain a relative kinematics of saidunits;• phase of breaking up said relative kinematics to obtain an articular angle of interest through a specific sequence of Euler angles for each articulation;• phase of identifying the start and end of movement by processing data obtained from said magneto-inertial unit of said distal unit (103), applying thresholds to a signal recorded by a gyroscope;• phase of computing and identifying parameters of interest comprising said start and end of movement, range of motion, defined as the difference between the maximum value and the minimum value of said movement, angular accelerations, and force;• phase of displaying in graphical form said received data comprising linear accelerations, angular velocities, local magnetic fields, and force, as directly measured by said first and second magneto-inertial units (104, 104’) and by said load cell (106), and said computed data comprising the orientation of said proximal and distal units (102, 103), said start and end of movement, said range of motion, and said angular accelerations.

7. Method according to claim 6, wherein, during said phase of expressing the orientation, the axes of said proximal unit and of said distal unit are assumed to be aligned with, in particular parallel to, the anatomical axes on which they are positioned.

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