WO2015128845A1 - System for measuring laxity of a joint - Google Patents

System for measuring laxity of a joint Download PDF

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Publication number
WO2015128845A1
WO2015128845A1 PCT/IB2015/051464 IB2015051464W WO2015128845A1 WO 2015128845 A1 WO2015128845 A1 WO 2015128845A1 IB 2015051464 W IB2015051464 W IB 2015051464W WO 2015128845 A1 WO2015128845 A1 WO 2015128845A1
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WO
WIPO (PCT)
Prior art keywords
mobile device
respect
sensor
inclination angle
value
Prior art date
Application number
PCT/IB2015/051464
Other languages
French (fr)
Inventor
Luigi VALEO
Andrea Ferretti
Raffaele IORIO
Paolo IORIO
Luca MULIERE
Giovanni GIOVANNETTI
Original Assignee
Valeo Luigi
Andrea Ferretti
Iorio Raffaele
Iorio Paolo
Muliere Luca
Giovannetti Giovanni
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Valeo Luigi, Andrea Ferretti, Iorio Raffaele, Iorio Paolo, Muliere Luca, Giovannetti Giovanni filed Critical Valeo Luigi
Publication of WO2015128845A1 publication Critical patent/WO2015128845A1/en

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
    • A61B5/107—Measuring physical dimensions, e.g. size of the entire body or parts thereof
    • A61B5/1071—Measuring physical dimensions, e.g. size of the entire body or parts thereof measuring angles, e.g. using goniometers
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/45—For evaluating or diagnosing the musculoskeletal system or teeth
    • A61B5/4528—Joints
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/45—For evaluating or diagnosing the musculoskeletal system or teeth
    • A61B5/4533—Ligaments
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/45—For evaluating or diagnosing the musculoskeletal system or teeth
    • A61B5/4538—Evaluating a particular part of the muscoloskeletal system or a particular medical condition
    • A61B5/4571—Evaluating the hip
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/45—For evaluating or diagnosing the musculoskeletal system or teeth
    • A61B5/4538—Evaluating a particular part of the muscoloskeletal system or a particular medical condition
    • A61B5/4585—Evaluating the knee
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/6813—Specially adapted to be attached to a specific body part
    • A61B5/6828—Leg

Definitions

  • the present invention relates to a system for measuring the laxity of a joint, in particular for use in supporting the orthopaedic and physiotherapeutic diagnosis of laxity of the knee as a result of tearing, of internal/external rotation of the hip and of flexion-extension of the knee.
  • Tearing of the anterior cruciate ligament of the knee is one of the most frequent injuries in the field of traumatology and is becoming more common due to the increasing dissemination of sporting activities and road mobility.
  • tearing of the anterior cruciate ligament causes a disability that is directly linked to the degree of articular laxity, which is evaluated by an increased anterior movement of the tibia with respect to the femur.
  • Diagnosis of tearing of the anterior cruciate ligament is currently based on clinical tests that must be carried out by experienced staff and that can sometimes, however, be difficult to evaluate.
  • One example is the Lachman test during which the supine patient keeps the knee flexed at about 25 degrees; the operator holds the femur immediately above the knee and draws the tibia anteriorly; a blockage of movement is typically perceived, said blockage being absent if the anterior cruciate is injured.
  • Evaluation systems for the Lachman test and for the anterior movement of the tibia are currently available on the market, for use in the diagnosis of tearing of the anterior cruciate ligament, based on mere mechanical measurements. Furthermore, these systems are bulky, are expensive and sometimes subject to significant individual variability.
  • One example of the most currently used systems is represented by the KT-1000 arthrometer for which the cut-off point is 3 mm. Disadvantageously, the test is difficult to reproduce if performed by operators who are not particularly expert; this was found in 25% to 50% of cases of non depistage; the maximum accuracy is just 1 mm; it is particularly bulky and expensive. There is therefore a need to produce a system for measuring the laxity of a human joint, which allows to overcome the aforementioned drawbacks.
  • the main aim of the present invention is to produce a system for measuring the laxity of a human joint that it is simple to use and handle, having a bulk and a cost that are significantly lower with respect to known solutions.
  • a further aim of the invention is to provide a system for measuring the laxity of a human joint that allows excellent reproducibility of results to be achieved irrespective of the operator's experience.
  • Another aim of the invention is to provide a method for measuring the laxity of a joint that allows excellent and reproducible results to be very simply achieved.
  • the present invention therefore proposes to achieve the above-discussed aims by producing a system for measuring the laxity of a human joint that, in accordance with claim 1 , comprises a support to be fixed to a human limb, and an electronic mobile device fixable to said support and provided with a magnetic sensor, and a gravity sensor and/or an acceleration sensor; wherein said mobile device is configured to measure a displacement of a bone of said human limb with respect to an initial reference position, and wherein said mobile device is provided with a program installed therein and configured to perform the following steps when launched:
  • a second aspect of the present invention provides a method for measuring the laxity of a human joint by means of a software installed in an electronic mobile device that is firmly fixed to a support fixed onto a human limb, the mobile device being provided with a magnetic sensor and with a gravity sensor and/or an acceleration sensor, said method comprising, in accordance with claim 9, the following steps:
  • the present invention allows evaluation, with maximum accuracy for example, of the anterior translation of the tibia with respect to the femur. It is based on an electronic application (mobile app) downloadable onto any electronic mobile device, such as a smartphone, which, once fixed onto a dedicated anatomical support, to be applied to the leg, provides digital data in millimetres in relation to the displacement of the tibia during performance of the Lachman test.
  • mobile app mobile app
  • the present invention also allows evaluation, with maximum accuracy, of the internal/external rotation of the hip and the degrees of flexion-extension of the knee.
  • the software developed, therefore, makes available the tools to perform the following measurements:
  • the software allows evaluation of the displacement of the electronic mobile device with respect to a starting point thereof, in which the electronic mobile device is located at the start of the test.
  • the software allows measurement of the millimetres of anterior displacement of the tibia with respect to the femur.
  • the combination of at least some sensors, provided in the same electronic mobile device allows measurement, thanks to the invention, of the degrees of inclination (angle a of figure 2) of the electronic mobile device with respect to an initial reference position. Knowing the length of the patient's tibia (cathetus of figure 2), it is possible to calculate the displacement, measured in millimetres, of the tibia with respect to the femur (cathetus b of figure 2).
  • the software allows measurement of the degrees of inclination of the tibia with respect to the vertical of the leg considering the patient prone and with the knee inclined at a 90 ° angle (Figure 3).
  • the combination of at least some sensors, provided in the same electronic mobile device, allows measurement, thanks to the invention, of the degrees of inclination of the electronic mobile device with respect to the initial position of the leg in Fig. 2.
  • the current state of the art exploits manual and analogue tools, such as for example the goniometer.
  • the software allows evaluation of the displacement, measured in degrees, of the tibia as shown in figure 4. This functionality allows measurement of the degree of displacement of the tibia with respect to the horizontal plane, which is defined by the natural position of the leg, with the patient prone and with the leg extended (Fig. 4).
  • the combination of at least some sensors, provided in the same electronic mobile device, allows measurement, thanks to the invention, of the degrees of inclination of the electronic mobile device with respect to the initial position of the leg in Fig. 4.
  • the state of the art exploits manual and analogue tools, such as for example the goniometer.
  • the application allows the measurement and digital storage of the results of the clinical evaluation using portable, easily acquired equipment (mobile phones, smartphones, tablets and the like).
  • the algorithm used is the same for the three previously described features.
  • the final result are the millimetres of displacement of the electronic mobile device, while in the case of flexion-extension of the knee and of internal/external rotation of the hip, the displacement is calculated in degrees.
  • low-pass and high-pass filters were applied to dampen the noise generated by the sensors, in order to obtain a stable and accurate measurement.
  • a circular buffer algorithm was also applied in order to stabilise the values in order to standardise the values obtained from the sensors.
  • Figure 1 represents a perspective view of a system, according to the invention, that is fixed to a leg;
  • Figure 2 schematically represents an anterior displacement (b) of the tibia with respect to the femur;
  • Fig. 2a represents a Cartesian reference system that is integral to a mobile device of the system of the invention
  • Figure 3 schematically represents a reference position of a leg for measuring the internal/external rotation of the hip by means of the system of the invention
  • Figure 4 schematically represents an angular displacement of the tibia with respect to a horizontal plane that can be measured by the system of the invention
  • Figure 5 represents a block diagram of the operating logic of the system of the invention.
  • This system comprises:
  • a mobile device 2 fixed to said support 1 and internally provided with some sensors, comprising at least one gravity sensor and one magnetic sensor, and optionally an acceleration sensor or accelerometer.
  • the acceleration sensor measures the acceleration applied to the mobile device 2, including the force of gravity.
  • an acceleration sensor determines the acceleration Ad that is applied to a device measuring the forces applied Fs to the sensor itself using the following relation:
  • Ad - ⁇ Fs / mass
  • the force of gravity constantly influences the measured acceleration.
  • the acceleration sensor measures the acceleration in m/s 2 that is applied to a device on all three physical axes (x, y, z), including the force of gravity.
  • the gravity sensor provides a three-dimensional vector that indicates the direction and the magnitude of gravity. It can be a physical sensor that is physically present in the mobile device 2 used to perform the measurements, or it can be a virtual sensor, also known as a software sensor.
  • the virtual gravity sensor exploits the combination of the physical sensors available in the mobile device 2 to return the previously mentioned three-dimensional vector.
  • the gravity sensor therefore measures the acceleration of gravity in m/s 2 applied to the mobile device 2 on all three axes (x, y, z). It gives more stable and accurate values than the acceleration sensor, isolating the force of gravity from the measurement of the acceleration imparted on the device.
  • the magnetic sensor instead measures changes in the geomagnetic field.
  • This sensor provides the measurement in ⁇ of the magnetic field for the three axes (x, y, z).
  • This sensor is not used alone, but in combination with the gravity sensor or the acceleration sensor allows the calculation and evaluation of the displacements of the mobile device 2.
  • the support 1 is preferably an anatomical support dedicated to the part of the human limb to which it is to be fixed.
  • the support 1 can be made of composite resin-carbon fibre material or other suitable polymer material.
  • the support 1 is provided with suitable fixing means for solidly fixing the mobile device 2 thereon. These fixing means are not described in detail herein as they are of a known type.
  • the fixing means can comprise a suitably shaped-housing to removably trap the mobile device 2, or comprise a double-sided tape or Velcro-based fixing system with a part of said fixing system provided on the mobile device 2.
  • the mobile device 2 is configured to measure a displacement of a bone of a part of human limb with respect to a predefined reference.
  • the system of the invention in the example of Figure 1 , is applied onto the patient's tibia to measure the anterior displacement of the tibia with respect to the femur.
  • the part of human limb onto which the support 1 is fixed is therefore a leg, while the bone which displacement is measured is the tibia.
  • the system allows in this case the anterior laxity of the knee to be measured, due to tearing of the anterior cruciate ligament, using an information technology application previously downloaded and installed on a mobile device 2.
  • the mobile device 2 is advantageously an electronic device such as a smartphone, a tablet, a mobile phone, a PDA, an MP3 player, a GPS receiver, etc.; it is used as a diagnosis support tool.
  • a software or information technology application is installed on the electronic mobile device 2, which, when launched at the start of the test, performs the following steps:
  • the application is developed according to the specific paradigms of each distribution platform, such as for example Android, Apple iOS, Windows phone, and the like.
  • the software performs the following steps before step a):
  • the acceleration sensor is used when the gravity sensor is not available: this is because the data given by gravity sensor is more stable and accurate.
  • Each new measurement is defined as "examination” and can be linked to a patient: a patient index will therefore be available in which it will be possible to store the examinations and the respective results.
  • the size and the content of the matrices vary depending on the sensor that generated them.
  • the content of the three-dimensional matrix for each type of sensor used is recorded below:
  • acceleration sensor [acceleration (m/s 2 ) on x-axis
  • gravity sensor [gravity (m/s 2 ) on x-axis
  • the output matrix will be populated with the same values as the input matrix. From subsequent invocations, the output matrix will continue to contain the previous values that will be used as described below: for each value contained in the input matrix, the corresponding value in the new output matrix will be equal to the corresponding value of the previous output matrix summed with the multiplication of the alpha multiplication factor (equal to 0.5, for example) times the difference between the value of the input matrix and the value of the previous output matrix.
  • the alpha multiplication factor equal to 0.5, for example
  • the matrices are rotated according to the position of the mobile phone: the reference coordinate system is rotated.
  • the content of the rotated matrix will then be reversed to comply with the new arrangement of the x', y', z' axes.
  • Calculation of the current position of the mobile phone is performed through the use of standard functions that exploit the matrices provided by the sensors (http://developer.android.com/reference/android/hardware/SensorManager.html) and the value defined as "ROLL", i.e. the inclination of the mobile device 2 with respect to the ground, is extracted from this position.
  • the degrees of displacement are expressed in radians.
  • the first ROLL value stored will constitute the initial point (zero angle) of reference for the subsequent evaluations (e.g.: if the initial ROLL value is 30 ° and the second ROLL' value is equal to 32 °, the difference with respect to the initial value will be calculated: i.e. 2 " displacement).
  • the current value (calculated as the difference from the initial value) will be stored for each ROLL' value thus calculated.
  • the highest value recorded from time to time will also be recorded: if a new value exceeds the maximum recorded value, this then becomes the new maximum reference value.
  • An appropriate function is responsible for calculating the displacement of the tibia in the three above-mentioned types of evaluation: laxity of the cruciate ligament, internal/external rotation of the hip and flexion-extension of the knee.
  • the function performs the following steps to give the required value in the case of laxity of the cruciate ligament ( Figure 2).
  • the function uses the following values as input parameters:
  • cathetus length (a) of the patient's tibia
  • displacement (b) of the tibia with respect to the femur measured in mm.
  • the inputAngle parameter is preferably converted into degrees before calculating the displacement.
  • the displacement (cathetus b) is calculated based on the patient's tibia measurement (cathetus a) and the angle of inclination (angle a).
  • the function performs the following steps to give the required value.
  • the function uses the following values as input parameters:
  • the inputAngle parameter is converted to degrees and the result is given as the displacement variable.

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Abstract

A system for measuring the laxity of a human joint comprising a support (1) to be fixed to a part of a human limb, and a mobile device (2), fixable to said support (1), and provided with a gravity sensor and a magnetic sensor, wherein said mobile device (2) is configured to measure a displacement of a bone of said human limb with respect to a predefined reference. Said mobile device can be an electronic device such as a smartphone, a tablet, a mobile phone, a PDA, an MP3 player, a GPS receiver.

Description

SYSTEM FOR MEASURING LAXITY OF A JOINT
**********
Field of the invention
The present invention relates to a system for measuring the laxity of a joint, in particular for use in supporting the orthopaedic and physiotherapeutic diagnosis of laxity of the knee as a result of tearing, of internal/external rotation of the hip and of flexion-extension of the knee.
Background of the invention
Tearing of the anterior cruciate ligament of the knee is one of the most frequent injuries in the field of traumatology and is becoming more common due to the increasing dissemination of sporting activities and road mobility.
In the majority of cases, tearing of the anterior cruciate ligament causes a disability that is directly linked to the degree of articular laxity, which is evaluated by an increased anterior movement of the tibia with respect to the femur.
Diagnosis of tearing of the anterior cruciate ligament is currently based on clinical tests that must be carried out by experienced staff and that can sometimes, however, be difficult to evaluate. One example is the Lachman test during which the supine patient keeps the knee flexed at about 25 degrees; the operator holds the femur immediately above the knee and draws the tibia anteriorly; a blockage of movement is typically perceived, said blockage being absent if the anterior cruciate is injured.
Evaluation systems for the Lachman test and for the anterior movement of the tibia are currently available on the market, for use in the diagnosis of tearing of the anterior cruciate ligament, based on mere mechanical measurements. Furthermore, these systems are bulky, are expensive and sometimes subject to significant individual variability. One example of the most currently used systems is represented by the KT-1000 arthrometer for which the cut-off point is 3 mm. Disadvantageously, the test is difficult to reproduce if performed by operators who are not particularly expert; this was found in 25% to 50% of cases of non depistage; the maximum accuracy is just 1 mm; it is particularly bulky and expensive. There is therefore a need to produce a system for measuring the laxity of a human joint, which allows to overcome the aforementioned drawbacks.
Summary of the invention
The main aim of the present invention is to produce a system for measuring the laxity of a human joint that it is simple to use and handle, having a bulk and a cost that are significantly lower with respect to known solutions.
A further aim of the invention is to provide a system for measuring the laxity of a human joint that allows excellent reproducibility of results to be achieved irrespective of the operator's experience.
Another aim of the invention is to provide a method for measuring the laxity of a joint that allows excellent and reproducible results to be very simply achieved. The present invention therefore proposes to achieve the above-discussed aims by producing a system for measuring the laxity of a human joint that, in accordance with claim 1 , comprises a support to be fixed to a human limb, and an electronic mobile device fixable to said support and provided with a magnetic sensor, and a gravity sensor and/or an acceleration sensor; wherein said mobile device is configured to measure a displacement of a bone of said human limb with respect to an initial reference position, and wherein said mobile device is provided with a program installed therein and configured to perform the following steps when launched:
a) calculating the inclination angle ROLL of the mobile device with respect to a reference plane by means of said gravity sensor and/or said acceleration sensor and by means of said magnetic sensor, and storing a first value of the inclination angle ROLL calculated, which defines said initial reference position;
b) iterating, at regular time intervals, the calculation of the inclination angle of the mobile device with respect to said reference plane and calculating the difference between the value of the new inclination angle ROLL' calculated and said first value of the inclination angle ROLL;
c) storing the higher value of said difference, which defines the maximum displacement of said bone with respect to the initial reference position.
A second aspect of the present invention provides a method for measuring the laxity of a human joint by means of a software installed in an electronic mobile device that is firmly fixed to a support fixed onto a human limb, the mobile device being provided with a magnetic sensor and with a gravity sensor and/or an acceleration sensor, said method comprising, in accordance with claim 9, the following steps:
a) calculating the inclination angle ROLL of the mobile device with respect to a reference plane and storing a first value of the inclination angle ROLL calculated, which defines an initial reference position;
b) iterating, at regular time intervals, the calculation of the inclination angle of the mobile device with respect to the reference plane and calculating the difference between the value of the new inclination angle ROLL' detected and said first value of the inclination angle ROLL;
c) storing the higher value of said difference, which defines the maximum displacement of a bone of said human limb with respect to the initial reference position.
In a preferred variant, the following steps are provided before step a):
- activating the gravity sensor and/or the acceleration sensor and activating the magnetic sensor, and consequently generating three-dimensional matrices by means of each activated sensor, the values of said matrices referring to a first Cartesian reference system x, y, z that is integral to the mobile device in question; - standardising the values of said matrices and rotating the matrices so as to express their own values with respect to a second Cartesian reference system x', y', z' rotated through 90 ° with respect to said first Cartesian reference system x, y, z, or vice versa.
The present invention allows evaluation, with maximum accuracy for example, of the anterior translation of the tibia with respect to the femur. It is based on an electronic application (mobile app) downloadable onto any electronic mobile device, such as a smartphone, which, once fixed onto a dedicated anatomical support, to be applied to the leg, provides digital data in millimetres in relation to the displacement of the tibia during performance of the Lachman test.
The present invention also allows evaluation, with maximum accuracy, of the internal/external rotation of the hip and the degrees of flexion-extension of the knee. The software developed, therefore, makes available the tools to perform the following measurements:
- laxity of the knee;
- internal/external rotation of the hip;
- flexion-extension of the knee.
As regards the laxity of the knee, the software allows evaluation of the displacement of the electronic mobile device with respect to a starting point thereof, in which the electronic mobile device is located at the start of the test. In particular, the software allows measurement of the millimetres of anterior displacement of the tibia with respect to the femur.
The combination of at least some sensors, provided in the same electronic mobile device, allows measurement, thanks to the invention, of the degrees of inclination (angle a of figure 2) of the electronic mobile device with respect to an initial reference position. Knowing the length of the patient's tibia (cathetus of figure 2), it is possible to calculate the displacement, measured in millimetres, of the tibia with respect to the femur (cathetus b of figure 2).
On the other hand, the prior art for performing this type of measurement exploits mechanical and analogue equipment that is based on measuring the force needed to perform the displacement in combination with actual measurement of the displacement.
As regards the internal/external rotation of the hip, the software allows measurement of the degrees of inclination of the tibia with respect to the vertical of the leg considering the patient prone and with the knee inclined at a 90 ° angle (Figure 3).
The combination of at least some sensors, provided in the same electronic mobile device, allows measurement, thanks to the invention, of the degrees of inclination of the electronic mobile device with respect to the initial position of the leg in Fig. 2.
In order to perform this type of measurement, the current state of the art, on the other hand, exploits manual and analogue tools, such as for example the goniometer. As regards flexion-extension of the knee, the software allows evaluation of the displacement, measured in degrees, of the tibia as shown in figure 4. This functionality allows measurement of the degree of displacement of the tibia with respect to the horizontal plane, which is defined by the natural position of the leg, with the patient prone and with the leg extended (Fig. 4).
The combination of at least some sensors, provided in the same electronic mobile device, allows measurement, thanks to the invention, of the degrees of inclination of the electronic mobile device with respect to the initial position of the leg in Fig. 4.
In order to perform this type of measurement, the state of the art, on the other hand, exploits manual and analogue tools, such as for example the goniometer. The application allows the measurement and digital storage of the results of the clinical evaluation using portable, easily acquired equipment (mobile phones, smartphones, tablets and the like).
The algorithm used is the same for the three previously described features. In the case of laxity of the knee, the final result are the millimetres of displacement of the electronic mobile device, while in the case of flexion-extension of the knee and of internal/external rotation of the hip, the displacement is calculated in degrees. In addition to the combination of the various sensors, low-pass and high-pass filters were applied to dampen the noise generated by the sensors, in order to obtain a stable and accurate measurement.
A circular buffer algorithm was also applied in order to stabilise the values in order to standardise the values obtained from the sensors.
In summary, the advantages of the present invention are:
- a greater accuracy, linked to the reduced elasticity of the system with respect to traditional systems;
- a higher reproducibility, due to the fact that the system provides data relating to the three-dimensional starting position during the execution of the test;
- reduced costs;
- reduced performance times;
- smaller dimensions, which also allow the entire system to be carried with ease from one place to another. The dependent claims describe preferred embodiments of the invention.
Brief description of the drawings
Further characteristics and advantages of the invention will become clearer in the light of the detailed description of a preferred but non-exclusive embodiment of a system for measuring the laxity of a human joint, illustrated by way of a non- limiting example, with the assistance of the accompanying drawings, in which: Figure 1 represents a perspective view of a system, according to the invention, that is fixed to a leg;
Figure 2 schematically represents an anterior displacement (b) of the tibia with respect to the femur;
Fig. 2a represents a Cartesian reference system that is integral to a mobile device of the system of the invention;
Figure 3 schematically represents a reference position of a leg for measuring the internal/external rotation of the hip by means of the system of the invention;
Figure 4 schematically represents an angular displacement of the tibia with respect to a horizontal plane that can be measured by the system of the invention; Figure 5 represents a block diagram of the operating logic of the system of the invention.
Detailed description of preferred embodiments of the invention
With reference to Figure 1 , a preferred embodiment of a system for measuring the laxity of a human joint, which is the object of the present invention, is represented. This system comprises:
- a support 1 to be fixed to a part of a human limb,
- a mobile device 2, fixed to said support 1 and internally provided with some sensors, comprising at least one gravity sensor and one magnetic sensor, and optionally an acceleration sensor or accelerometer.
Through the use these sensors, made available by the mobile device 2, it is possible to perform extremely accurate measurements to support diagnosis. Through these sensors it is possible to suitably, and extremely accurately, calculate the displacement of the mobile device 2 and transform the data obtained into results useful for the clinical evaluation (millimetres or degrees where necessary). The acceleration sensor measures the acceleration applied to the mobile device 2, including the force of gravity. Conceptually, an acceleration sensor determines the acceleration Ad that is applied to a device measuring the forces applied Fs to the sensor itself using the following relation:
Ad = -∑Fs / mass
The force of gravity constantly influences the measured acceleration.
Considering a reference system x-y-z, the acceleration sensor measures the acceleration in m/s2 that is applied to a device on all three physical axes (x, y, z), including the force of gravity.
The gravity sensor provides a three-dimensional vector that indicates the direction and the magnitude of gravity. It can be a physical sensor that is physically present in the mobile device 2 used to perform the measurements, or it can be a virtual sensor, also known as a software sensor. The virtual gravity sensor exploits the combination of the physical sensors available in the mobile device 2 to return the previously mentioned three-dimensional vector. The gravity sensor therefore measures the acceleration of gravity in m/s2 applied to the mobile device 2 on all three axes (x, y, z). It gives more stable and accurate values than the acceleration sensor, isolating the force of gravity from the measurement of the acceleration imparted on the device.
References to the gravity and acceleration sensors can, for example, be found for at the following URLs:
http://developer.android.com/guide/topics/sensors/sensors_motion.html
http://developer.android.com/guide/topics/sensors/sensors_overview.html.
The magnetic sensor instead measures changes in the geomagnetic field. This sensor provides the measurement in μΤ of the magnetic field for the three axes (x, y, z). This sensor is not used alone, but in combination with the gravity sensor or the acceleration sensor allows the calculation and evaluation of the displacements of the mobile device 2.
References to the magnetic sensor can be found at the following URL:
http://developer.android.com/guide/topics/sensors/sensors_position.html. The support 1 is preferably an anatomical support dedicated to the part of the human limb to which it is to be fixed. By way of example only, the support 1 can be made of composite resin-carbon fibre material or other suitable polymer material. The support 1 is provided with suitable fixing means for solidly fixing the mobile device 2 thereon. These fixing means are not described in detail herein as they are of a known type. By way of example only, the fixing means can comprise a suitably shaped-housing to removably trap the mobile device 2, or comprise a double-sided tape or Velcro-based fixing system with a part of said fixing system provided on the mobile device 2.
The mobile device 2 is configured to measure a displacement of a bone of a part of human limb with respect to a predefined reference.
The system of the invention, in the example of Figure 1 , is applied onto the patient's tibia to measure the anterior displacement of the tibia with respect to the femur. In this application, the part of human limb onto which the support 1 is fixed is therefore a leg, while the bone which displacement is measured is the tibia. The system allows in this case the anterior laxity of the knee to be measured, due to tearing of the anterior cruciate ligament, using an information technology application previously downloaded and installed on a mobile device 2.
The mobile device 2 is advantageously an electronic device such as a smartphone, a tablet, a mobile phone, a PDA, an MP3 player, a GPS receiver, etc.; it is used as a diagnosis support tool.
Advantageously, a software or information technology application is installed on the electronic mobile device 2, which, when launched at the start of the test, performs the following steps:
a) calculating the inclination angle ROLL of the mobile device 2 with respect to a reference plane that is preferably, but not necessarily, horizontal, and storing a first value of the inclination angle ROLL calculated, which defines an initial reference position;
b) iterating, at regular time intervals, preferably in the order of a millisecond, said calculation of the inclination angle of the mobile device 2 with respect to said reference plane and calculating the difference between the value of the new inclination angle ROLL' detected and said first value of the inclination angle ROLL; c) storing the higher value of said difference, which defines the maximum displacement of the tibia with respect to the initial reference position.
The application is developed according to the specific paradigms of each distribution platform, such as for example Android, Apple iOS, Windows phone, and the like.
In a preferred variant, the software performs the following steps before step a):
- activating the gravity sensor and/or the acceleration sensor, and activating the magnetic sensor, and consequently producing three-dimensional matrices by means of each activated sensor, the values of said matrices referring to and being ordered according to a first Cartesian reference system x, y, z that is integral to the mobile device 2 in a preferably, but not necessarily, vertical position;
- standardising the values of said matrices and rotating the matrices so as to express their own values with respect to a second Cartesian reference system x', y', z' rotated through 90 ° with respect to said first Cartesian reference system x, y, z, or vice versa, by first performing the rotation of the matrices and then standardising the values;
The acceleration sensor is used when the gravity sensor is not available: this is because the data given by gravity sensor is more stable and accurate.
Each new measurement is defined as "examination" and can be linked to a patient: a patient index will therefore be available in which it will be possible to store the examinations and the respective results.
The size and the content of the matrices vary depending on the sensor that generated them. The content of the three-dimensional matrix for each type of sensor used is recorded below:
acceleration sensor: [acceleration (m/s2) on x-axis | acceleration (m/s2) on y-axis | acceleration (m/s2) on z-axis]
gravity sensor: [gravity (m/s2) on x-axis | gravity (m/s2) on y-axis | gravity (m/s2) on z-axis]
magnetic sensor: [density (μΤ) on x-axis | density (μΤ) on y-axis | density (μΤ) on z-axis]. Standardisation of the values given by the sensors and contained within the matrices is performed thanks to an exponential algorithm. The algorithm used is described below. The function of the algorithm exploits three variables defined as
- input: matrix produced by the sensor;
- output: matrix resulting from the function;
- alpha: multiplication factor.
If the function is invoked for the first time, the output matrix will be populated with the same values as the input matrix. From subsequent invocations, the output matrix will continue to contain the previous values that will be used as described below: for each value contained in the input matrix, the corresponding value in the new output matrix will be equal to the corresponding value of the previous output matrix summed with the multiplication of the alpha multiplication factor (equal to 0.5, for example) times the difference between the value of the input matrix and the value of the previous output matrix.
The matrices are rotated according to the position of the mobile phone: the reference coordinate system is rotated. The content of the rotated matrix will then be reversed to comply with the new arrangement of the x', y', z' axes.
Calculation of the current position of the mobile phone is performed through the use of standard functions that exploit the matrices provided by the sensors (http://developer.android.com/reference/android/hardware/SensorManager.html) and the value defined as "ROLL", i.e. the inclination of the mobile device 2 with respect to the ground, is extracted from this position. The degrees of displacement are expressed in radians. The first ROLL value stored will constitute the initial point (zero angle) of reference for the subsequent evaluations (e.g.: if the initial ROLL value is 30 ° and the second ROLL' value is equal to 32 °, the difference with respect to the initial value will be calculated: i.e. 2 " displacement).
The current value (calculated as the difference from the initial value) will be stored for each ROLL' value thus calculated. The highest value recorded from time to time will also be recorded: if a new value exceeds the maximum recorded value, this then becomes the new maximum reference value.
An appropriate function is responsible for calculating the displacement of the tibia in the three above-mentioned types of evaluation: laxity of the cruciate ligament, internal/external rotation of the hip and flexion-extension of the knee. The function performs the following steps to give the required value in the case of laxity of the cruciate ligament (Figure 2). The function uses the following values as input parameters:
cathetus: length (a) of the patient's tibia;
inputAngle: displacement angle (a) measured in radians.
The function gives the following result:
displacement: displacement (b) of the tibia with respect to the femur (measured in mm).
The inputAngle parameter is preferably converted into degrees before calculating the displacement. According to figure 2, the displacement (cathetus b) is calculated based on the patient's tibia measurement (cathetus a) and the angle of inclination (angle a).
In the case of the measuring the internal/external rotation of the hip and of the flexion-extension of the knee, the function performs the following steps to give the required value. The function uses the following values as input parameters:
inputAngle: displacement angle measured in radians.
The inputAngle parameter is converted to degrees and the result is given as the displacement variable.

Claims

1 . A system for measuring the laxity of a human joint, comprising a support (1 ) to be fixed to a human limb,
and a mobile device (2), fixable to said support (1 ), and provided with a magnetic sensor, and with a gravity sensor and/or an acceleration sensor,
wherein said mobile device (2) is configured to measure a displacement of a bone of said human limb with respect to an initial reference position,
wherein said mobile device (2) is provided with a program installed therein and configured to perform the following steps when launched:
a) calculating the inclination angle (ROLL) of the mobile device (2) with respect to a reference plane by means of said gravity sensor and/or said acceleration sensor and by means of said magnetic sensor, and storing a first value of the inclination angle (ROLL) calculated, which defines said initial reference position;
b) iterating, at regular time intervals, the calculation of the inclination angle of the mobile device (2) with respect to said reference plane and calculating the difference between the value of the new inclination angle (ROLL') calculated and said first value of the inclination angle (ROLL);
c) storing the higher value of said difference, which defines the maximum displacement of said bone with respect to the initial reference position.
2. A system according to claim 1 , wherein said mobile device (2) is an electronic device, preferably selected from a smartphone, a tablet, a mobile phone, a PDA, an MP3 player, a GPS receiver.
3. A system according to claim 1 or 2, wherein the following steps are provided before step a):
- activating the gravity sensor and/or the acceleration sensor and activating the magnetic sensor, and consequently generating three-dimensional matrices by means of each activated sensor, the values of said matrices referring to a first Cartesian reference system x, y, z integral to the mobile device (2);
- standardising the values of said matrices and rotating the matrices so as to express said values with respect to a second Cartesian reference system x', y', z' rotated through 90 ° with respect to said first Cartesian reference system x, y, z, or vice versa.
4. A system according to any one of the preceding claims, wherein the support (1 ), preferably anatomical support, is provided with fixing means for fixing the mobile device (2) thereon.
5. Use of a system according to any one of the preceding claims to measure a displacement of the tibia with respect to an initial reference position.
6. Use according to claim 5, wherein said initial reference position is the initial reference position provided in the Lachman test.
7. Use according to claim 5, wherein said initial reference position is the vertical position of the leg considering the patient prone and with the knee at a 90 ° angle with respect to a horizontal plane.
8. Use according to claim 5, wherein said initial reference position is a horizontal plane, defined by the natural position of the leg considering the patient prone and with the leg extended on said horizontal plane.
9. A method for measuring the laxity of a human joint by means of a software installed in a mobile device (2) adapted to be placed on a human limb, the mobile device (2) being provided with a magnetic sensor and with a gravity sensor and/or an acceleration sensor, said method comprising the following steps:
a) calculating the inclination angle (ROLL) of the mobile device (2) with respect to a reference plane, by means of said gravity sensor and/or said acceleration sensor and by means of said magnetic sensor, and storing a first value of the inclination angle (ROLL) calculated, which defines an initial reference position;
b) iterating, at regular time intervals, the calculation of the inclination angle of the mobile device (2) with respect to the reference plane and calculating the difference between the value of the new inclination angle (ROLL') calculated and said first value of the inclination angle (ROLL);
c) storing the higher value of said difference, which defines the maximum displacement of a bone of said human limb with respect to the initial reference position.
10. A method according to claim 9, wherein the following steps are provided before step a):
- activating the gravity sensor and/or the acceleration sensor and activating the magnetic sensor, and consequently generating three-dimensional matrices by means of each activated sensor, the values of said matrices referring to a first Cartesian reference system x, y, z that is integral to the mobile device (2);
- standardising the values of said matrices and rotating the matrices so as to express their own values with respect to a second Cartesian reference system x', y', z' rotated through 90 ° with respect to said first Cartesian reference system x, y, z, or vice versa.
PCT/IB2015/051464 2014-02-27 2015-02-27 System for measuring laxity of a joint WO2015128845A1 (en)

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