WO2017171660A1

WO2017171660A1 - Foot joint health diagnosis system

Info

Publication number: WO2017171660A1
Application number: PCT/SG2017/050189
Authority: WO
Inventors: Chi Chiu Chan; Li Han Chen; Niu LUO; Pui Wah KONG
Original assignee: Nanyang Technological University
Current assignee: Nanyang Technological University
Priority date: 2016-04-01
Filing date: 2017-04-03
Publication date: 2017-10-05
Anticipated expiration: 2018-10-01

Abstract

A foot joint health diagnosis system comprising: a force provider to apply a force onto an application point on a part of a patient's foot, the force provider comprising a load cell to detect the magnitude of the force; and a sensor device comprising a number of fiber Bragg gratings to be attached to the patient's foot in alignment with a corresponding number of toes, wherein movement of the part of the patient's foot consequent to application of the force gives rise to axial strain in the fiber Bragg gratings to determine extent of mobility of the part of the patient's foot consequent to application of the force. Preferably, the fiber Bragg gratings are embedded in an elastic polymer which may be provided in a sock to wear over the foot.

Description

FOOT JOINT HEALTH DIAGNOSIS SYSTEM

FIELD

This invention relates to a foot joint health diagnosis system. BACKGROUND

At present, there is no equipment available for clinicians to accurately and comprehensively assess foot health. Generally, foot joint mobility is an important foot health condition evaluation index, including first metatarsophalangeal joint (MPJ) mobility and first ray (big toe) mobility.

First ray hypermobility has been linked to many abnormal conditions in the foot. Increased first ray mobility has been seen in patients with hallux valgus. Patients with diabetes mellitus are characterized by higher joint stiffness in the first ray than non-diabetic controls. In addition, hypermobility of the first ray may also contribute to laxity in the arch and the development of posterior tibialis tendon dysfunction.

First metatarsal vertical displacement is proportional to the measurement of first ray dorsitlexion. When evaluating a patient's foot, the common practice is to subjectively 'feel' how stiff a joint is and this type of clinical assessment is unreliable. For example, clinical testing of first ray mobility is performed with one hand stabilizing the lateral fourth metatarsals while the other hand applies a displacement force to the first metatarsal head. Although this method is widely used, it allows considerable interobserver error and its reliability and validity are questionable because the direction and the amount of the force applied to the first metatarsal are not controlled.

Existing devices and methods that assess first ray mobility may use a 3D tracking system to record displacement and a bulky load cell to provide force. In practical applications, the clinician often faces great difficulties using these devices. To advance the current practice, a wearable device for clinicians to objectively evaluate the foot health condition, such as joint mobility, is necessary and practical. There therefore exists a need for a wearable device which can evaluate a patient's foot health condition comprehensively for all foot sizes and shapes.

In recent years, wearable physiological monitoring technology has drawn greater attention, becoming a research hotspot in the field of smart textiles. As an important aspect of physiological monitoring, foot health evaluation has also attracted much concern, and l some shoes or insoles within electronic components for stress testing have emerged. Compared with a force plate technology, these devices can measure the plantar pressure distribution in real-time and record the data continuously, out of restriction of testing environments. However, shoes or insoles within electronic components usually have poor electromagnetic or corrosion resistance capabilities.

SUMMARY

According to a first aspect, there is provided a foot joint health diagnosis system comprising: a force provider to apply a force onto an application point on a part of a patient's foot, the force provider comprising a load cell to detect the magnitude of the force; and a sensor device comprising a number of fiber Bragg gratings to be attached to the patient's foot in alignment with a corresponding number of toes, wherein movement of the part of the patient's foot consequent to application of the force gives rise to axial strain in the fiber Bragg gratings to determine extent of mobility of the part of the patient's foot consequent to application of the force.

The force provider may comprise a platform to rest the patient's foot thereon, the load cell provided under the platform to exert an upward force on the part of the patient's foot on the platform.

The load cell may be provided on a moving platform adjustable in orthogonal directions on a horizontal plane.

The force provider may alternatively comprise a hand-held instrument, the hand-held instrument comprising a handle, a connector attached to the handle, the load cell attached to the connector, and a force transmitter attached to the load cell, the force transmitter having a distal end, wherein when the distal end of the force transmitter is in contact with the application point, a force exerted by a user holding the handle is transmitted through the connector and the load cell and applied by the force transmitter onto the application point.

The force transmitter may comprise a transmission rod having a proximal end attached to the load cell. The force transmitter may further comprise a stabiliser comprising an L-shaped bar, a long arm of the L-shaped bar orthogonally attachable to a central portion of the transmission rod, a short arm of the L-shaped bar having a distal end to contact a reference part of the patient's foot.

The fiber Bragg gratings may be embedded in an elastic polymer, the elastic polymer and fiber Bragg gratings provided in a sock to be worn over the foot.

The fiber Bragg gratings may be provided on the sole of the foot when the sock is worn.

Alternatively, the sensor device may comprise one fibre Bragg grating to be adhered to the sole of the patient's foot and along an underside of a toe to be investigated.

The sensor device may comprise a coupler, the fibre Bragg gratings connected to the coupler, an input fiber cable connected to the coupler to connect a light source to the coupler, and an output fiber cable to the coupler to connect the coupler to a data processing module.

BRIEF DESCRIPTION OF FIGURES

In order that the invention may be fully understood and readily put into practical effect there shall now be described by way of non-limitative example only exemplary embodiments of the present invention, the description being with reference to the accompanying illustrative drawings.

Fig. 1 is a schematic illustration of a sensor device of a first embodiment of a foot joint monitoring system.

Fig. 2 is a block diagram of component connections of the sensor device of Fig. 1.

Fig. 3(a) is a schematic illustration of different force application points when using the foot joint monitoring system.

Fig. 3(b) is a schematic illustration of downward pressure applied to immobilize toes that are not being investigated when using the system.

Fig. 3(c) is a schematic illustration of the first embodiment of the foot joint monitoring system.

Fig. 3(d) is a perspective view of a force provider of the first embodiment of the foot joint monitoring system.

Fig. 4 is an illustration of force resolution when a vertical force is applied to measure rotational stiffness of MPJ.

Fig. 5 is a side view illustration of a force provider of the second embodiment of the foot joint monitoring system. Fig. 6 is a photograph of the force provider of Fig. 5.

Fig. 7 is a photograph of a close-up of a connector of the force provider of Fig. 6.

Fig. 8 is a photograph of a perspective view of the force provider of Fig. 6.

Fig. 9 is a photograph of the second embodiment of the foot monitoring system in use to measure first ray mobility.

Fig. 10 is a photograph of a sensor device of the second embodiment of the foot monitoring system applied on a patient and indicating displacement when measuring first ray mobility.

Fig. 1 1 is a photograph of the second embodiment of the foot monitoring system in use to measure rotational stiffness of the MPJ.

Fig. 12 is a photograph of a sensor device of the second embodiment of the foot monitoring system applied on a patient and indicating rotational angle when measuring rotational stiffness of the MPJ.

Fig. 13 is a graph showing Bragg wavelength shift with increase in rotational angle and first ray displacement.

Fig. 14 is a graph showing relationship between rotational angle and FBG wavelength shift.

Fig. 15 is a graph showing relationship between displacement and FBG wavelength shift. DETAILED DESCRIPTION

Exemplary embodiments of the foot joint monitoring system 10 will be described below with reference to Figs. 1 to 15. The same reference numerals are used to denote the same or similar parts in the embodiments shown. In general terms, the system 10 comprises a force provider 100 that exerts a force on a part of a foot such as at the joint of the toes and on the first ray. The force provider 100 may comprise a hand-held instrument 110 or a platform 120 and the force may be exerted manually or automatically with an actuator 122. The force provider 100 incorporates a load cell 102 to detect the magnitude of the exerted force.

The system 10 also comprises a sensor device 200 for measuring ray displacement and angle of bending of the toe. The sensor device 200 comprises a number of FBG sensors 20 arranged in alignment with one or more toes. The three measurements (force, displacement and angle of bend) are obtained and computed to provide a gauge of the toe mobility issues. The measurements may be obtained by wired connections or transmitted wirelessly to a processor. The number of FBG sensors 201 may be incorporated into a wearable device 210 in the form of toe socks or individually attached to the foot.

In a first embodiment of the system 10, as shown in Fig. 1 , the sensor device 200 comprises a wearable device 210 comprising a five-toe sock 21 1 . The wearable device 210 comprises custom-made FBGs 201-1 to 201-5 for each of the first to fifth rays respectively, and an optical coupler 213 embedded in the five-toe sock 21 1. The sensor device 200 also comprises a light source 202, an input fiber cable 204, an output fiber cable 205, and a data processing module 206. As shown in Fig. 2, the input fiber cable 204 is connected to the light source 202 through or at an input end or terminal 213-1 of the coupler 213. The output fiber cable 205 is connected to data processing module 206 through or at an output end or terminal 213-2 of the coupler 213. A third end or terminal 213-3 of the coupler 213-3 is connected to the optical fiber sensors 201 , transmitting the input light to optical fiber sensors 201 as well as re-transmitting the output light to the data processing module 6. The data processing module 206 comprises a display platform.

As can be seen in Fig. 1 , the optical fiber sensors 201 comprise five fiber Bragg gratings (FBGs) 201. The FBGs 201 and the coupler 213 are embedded in an elastic polymer 215 such as polydimethylsiloxane (PDMS) which is molded into a five-toe shape and packaged with a reusable five-toe sock 21 1 as the wearable device 210. As the sensing sock 210 is made entirely of fabric 21 1 with the PDMS embedded, this makes the wearable device 210 soft without complicated mechanical setups, providing a comfort for patients. The dimensions of the FBG sensors 202 and sock 210 can be made based on conventional sizes of socks for different age groups and gender. Velcro straps may be introduced at the location of each toe and at the sock cuff 216 to cater to abnormal shapes of foot/toe and ensure better fixation of the wearable device 210 for effective signal transduction. In addition, since the fiber sensor 202 is made of silica and no electric current is involved for the transduction, the fiber FBG embedded five-toe sock 210 is washable and sterilizable for hygienic purposes.

It is known that FBG is formed by photo induced periodic refractive index modulation within the fibre core, which results in a series of grating planes along the fibre axis. If the Bragg condition is achieved, light propagating in the core will be reflected at each of the grating planes to form a back reflected signal with a center wavelength commonly known as the Bragg wavelength, A_B. The A_B of a FBG can be described by the equation A_B =2n_eff Λ, where n_eff is the effective refractive index of the fiber core and Λ is the grating period. A variation of axial strain on the FBG has impact on A and n_eff, inducing a shift of A_B. By demodulating the shift of A_B, the applied axial strain can be determined.

Foot joint mobility includes two measurement aspects, which are the rotational stiffness of the metatarsophalangeal joint (MPJ) as well as the stiffness of the first ray (big toe). Fig. 3 shows the first embodiment of the device or system 10 for measuring foot joint mobility in which the force provider 100 comprises a platform 120. The force provider 100 preferably includes a customized immobilizer boot 121 (as shown in Fig. 3(c)) on the platform 120 upon which the patient's foot rests for the patient to maintain a 90° ankle-joint flexion and prevents transverse rotation of the leg. To measure the rotational stiffness of the MPJ, an upward force F from a programmable load cell 102 provided under the platform 120 of the force provider 100 (as shown in Fig. 3(d)) is applied to the big toe (preferably at the proximal phalanx, as indicated by arrow F1 in Fig. 3(a)) while the second to fifth rays are fixed by a screw tightened clamp 130 (as shown in Fig. 3(b) to maintain a downward pressure P. The rotation of the big toe due to the force F will induce a vertical displacement h, and result in length extension of the fiber sensor 201-1 , inducing a strain variation on the big-toe-FBG 201-1. By measuring the Bragg wavelength shift due to strain, the displacement h can be computed by interpolating strain/displacement coefficient of the FBG 201-1. In order to determine angular displacement Θ, the length L from the first MPJ to the force application point will be measured and input to the system.

Fig. 4 shows a rotational force analysis when a vertical force F is applied to determine rotational stiffness of the first MPJ. Once the vertical displacement h is determined, the angular displacement ©can be calculated automatically using trigonometric principles, i.e., Q=arcsin h/L. The torque T applied to cause a rotational displacement Θ can be calculated based on 7 = FcosQ*L. Hence, the rotational stiffness of the first MPJ mobility (Nmm/rad) is computed by Τ/Θ.

In order to facilitate measurements, the load cell 102 is designed and equipped with a mechanical moving platform 123 that is adjustable in the X and Y directions (i.e. in orthogonal directions on a horizontal plane) to allow a clinician to apply the load in the Z direction (i.e. vertically) at the desired location on the patient's foot, as shown in Fig 3(d). For example, as shown in Fig. 3(d) the mechanical moving platform 123 may be mounted to an X-axis linear block 124 and Y-axis linear block 125 that are in turn provided on a base plate to allow for X and Y axis movements. An actuator 122 comprising a motor 126 and up/down slider attachment 127 is provided to exert the force automatically. The slider attachment 127 is connected to the motor 126 via a coupler 131 provided on the moving platform 123. The motor 126 moves the load cell 102 up and down as the load cell 102 is mounted on the up/down slider attachment 127 that is in turn mounted on the moving platform 123. A stopper 128 may be used to prevent movement of the moving platform 123 along each of the X and Y axis once the moving platform 123 is at its desired location. The force provider 120 preferably also includes a load display 109 and a control panel 129.

In an example of the first embodiment, based on stimulation and experimental results, the thickness of the PDMS 215 is adjusted to be 2 mm which offers a maximum bending sensitivity. Considering that an angular displacement of approximately 65° of the first MPJ is normal for the healthy patient, the maximum angular range supplied by the load cell 102 is capped at 120° for safety. According to an previous work, "A novel technique of quantifying first metatarsophalangeal (1st MPJ) joint stiffness, issued on Journal of Foot and Ankle Research, 7(Suppl 1), A32, 2014," the torque T of a flat-foot patient changed from 120 to 180 Nmm when the angular displacement changed from 33° to 45°, so the first MPJ stiffness of that patient was 3.8 Nmm ⁰. Supposing the moment arm or length L of the patient to be 40mm, the applied force F by the load cell 102 should be from 3 to 4.5N. To fulfill the requirements of different applications, the maximum load force that can be provided by the load cell 102 in the present example of the first embodiment was designed to be 100N.

Determining first ray mobility is the same as determining rotational stiffness of the MPJ except that the predefined vertical force F is applied to the first ray at the MPJ (as indicated by arrow F2 in Fig. 3(a)) through the load cell 102. By measuring the Bragg wavelength shift due to strain, the displacement of the first ray can be computed by interpolating strain/displacement coefficient of the FBG. As the device or system 10 provides both predefined load (N) and displacement (mm), hence, the stiffness (N/mm) of the first ray is determined. According to previous work, comparison of two methods used to assess first-ray mobility as published in the issue of "Foot & Ankle International. Vol. 23, No. 3, 2002," the dorsal mobility of the first ray was about 4.2-7.6mm when the corresponding applied force was less than 55N. As a result, the displacement range in the present example of the first embodiment of the system 10 is kept from 0 to 10 mm, and the applied maximum force is up to 100N. In an example of the second embodiment of the system 10, the sensor device 200 comprises one FBG sensor 20 arranged in alignment with a toe that is being investigated (shown as the big toe in the present application). The FBG sensor 20 is adhered to the sole of the patient's foot and along the underside of the toe being investigated, as shown in Figs. 9 to 12.

The force provider 100 in the second embodiment comprises a hand-held instrument 110, as shown in Figs. 5 to 8 and Fig. 10. The instrument 110 is configured to be small and light. Data from the instrument 110 may be output via a USB connection or a wireless connection, e.g. Bluetooth. The instrument 1 10 comprises a handle 1 11 that may be cylindrical or any other appropriate shape. The handle 11 1 is preferably made of a plastics material to reduce weight. The instrument 1 10 also comprises a multidirectional load cell connector 112 that is connected to the handle 11 1 between the handle 11 1 and the load cell 102 of the instrument 1 10. The connector 112 allows the load cell 102 to be attached orthogonally to the handle 11 1 as shown in Figs. 5, 6, 8 and 1 1 , or co-axially with the as shown in Fig. 9.

The connector 1 12 preferably comprises a generally square block having a threaded hole

1 13 provided in each of its four sides, as shown in Figs. 7 and 8. One end 111-1 of the handle 1 11 is screwed into one of the four holes 113-1 and the load cell 102 is attached to another one of the four holes 1 13-2 using appropriate means such as a set screw. A nut

1 14 may be used to adjust and lock the connection of the load cell 102 with the connector 1 12, as shown in Figs. 5 and 6. Accordingly, the end 1 11-1 of the handle 11 1 (if mainly plastic) may be provided with a steel insert 1 15 to strengthen connection of the handle 1 11 with the connector 112.

The instrument 110 further comprises a force transmitter 140 attached to a distal side of the load cell 10. The force transmitter 140 is configured to contact the patient's foot and to transmit the force F exerted by a person holding the handle 1 11 to the patient's foot, as shown in Fig. 9. As the load cell 102 is provided between the handle 1 11 and the force transmitter 140, the transmitted force F can be determined by the load cell 102.

The force transmitter 140 preferably comprises a transmission rod 141 having a first end 141-1 attached to the load cell 102. For example, the first end 141-1 of the transmission rod 141 may be threaded and a nut 144 may be used to adjust and lock the connection of the load cell 102 with the force transmitter 140. The force transmitter preferably further comprises a contact bar 142 connected transversely to a second end 141-2 of the transmission rod 141. The contact bar 142 comes into contact with the patient's foot and serves to apply the load evenly at the desired application point of the load on the foot. Fig. 9 shows the instrument 1 10 being used to determine stiffness of the first ray by applying the force F onto the MPJ, as indicated by the large single-ended arrow. The displacement (as indicated by the double headed arrow) of the first ray (from the dotted line to the solid line) in Fig. 10 can be computed by measuring the Bragg wavelength shift of the FBG 20, as described above with reference to the arrow F2 in Fig. 3(a).

The force provider 1 10 preferably further comprises a stabiliser 143 provided as an accessory to the force transmitter 140, as shown in Figs. 5, 6, 8 and 11. The stabiliser 143 comprises an L-shaped bar having its long arm 143-1 configured to be orthogonally attached to a central portion of the transmission rod 141 so that a distal end of the short arm of the L-shaped bar contacts a reference part of the patient's foot when the distal end of the transmission rod is in contact with the patient's foot. The short arm 143-2 preferably comprises a reference bar 145 at its distal end that contacts the patient's foot when in use. A distance between the reference bar 145 and the contact bar 142 (i.e. between the distal ends of the transmission rod 141 and the short arm of the stabiliser 143) may be adjusted by varying where along its long arm the L-shaped bar is attached to the transmission rod 141. A screw connection 146 may be used to attach the stabiliser 143 to the transmission rod 141 to allow the length L to be easily adjusted.

As shown in Fig. 1 1 , in use, when the reference bar 145 is applied to the MPJ and the contact bar 142 is applied to the toe (preferably at the first phalanx), the distance between the reference bar 145 and the contact bar 142 defines the length L used to determine rotational stiffness of the MPJ. The length L is measured by clinicians before testing from the first MPJ (contacted by the reference bar 145) to the force application point on the toe (contacted by the contact bar 142). In this embodiment, the applied force F transmitted by the contact bar 142 is always orthogonal to the contact surface on the toe, thus the torque T=F*L.

The force provider 100 in the form of the portable hand-held instrument 110 ensures that the applied force is kept perpendicular to the plane of the sole of the foot. It also allows the mobility of the first ray and the first MPJ to be measured separately according to specific needs of each patient. Components of the hand-held force provider 1 10 may be manually removed and assembled.

In the second embodiment of the system 10, the displacement of the first ray (Figs. 9 and 10) or the rotation of the big toe (Figs. 1 1 and 12) due to the applied force F will induce length extension of the fiber sensor, inducing a strain variation on the FBG 20, due to the sensor 200 being provided at the sole of the foot. By measuring the Bragg wavelength shift due to the strain, the displacement and/or rotational angle can be computed by interpolating strain coefficient of the FBG. With the increase of rotational angle and displacement, the Bragg wavelength will shift to a longer wavelength, as shown in Fig. 13. Furthermore, it was found that the linear relationship between rotational angle and displacement and FBG wavelength shift is good, as can be seen in Figs. 14 and 15 respectively. Thus, before measurements are performed, it is preferably to calibrate each sensor 200 to determine its sensitivity coefficient.

All data collected from the load cell and the FBG sensor can be input directly into a computer for a programmed software to process automatically, which is easy to operate for the clinicians. The system 10 described above is able to accurately measure foot joint mobility which is an important parameter in the evaluation of foot function and disorders. The system can accomplish real-time detection within a simple structure, is easy to produce, has a fast response, is stable, is anti-electromagnetic interference, is corrosion resistant, and can be applied to academic research, medical treatment and industrial products.

Whilst there has been described in the foregoing description exemplary embodiments of the present invention, it will be understood by those skilled in the technology concerned that many variations and combination in details of design, construction and/or operation may be made without departing from the present invention. For example, while Figs. 1 , 3(a) and 3(c) show the FBGs 201 embedded in the elastic polymer 215 being provided at the top of the foot, in alternative configurations, the FBGs 201 embedded in the elastic polymer 215 may be provide at the sole of the foot. It should be noted that the sensor device of the first embodiment may be used with the force provider of the second embodiment and the sensor device of the second embodiment may also be used with the force provider of the first embodiment.

Claims

A foot joint health diagnosis system comprising:

a force provider to apply a force onto an application point on a part of a patient's foot, the force provider comprising a load cell to detect the magnitude of the force; and

a sensor device comprising a number of fiber Bragg gratings to be attached to the patient's foot in alignment with a corresponding number of toes,

wherein movement of the part of the patient's foot consequent to application of the force gives rise to axial strain in the fiber Bragg gratings to determine extent of mobility of the part of the patient's foot consequent to application of the force.

The foot joint health diagnosis system of claim 1 , wherein the force provider comprises a platform to rest the patient's foot thereon, the load cell provided under the platform to exert an upward force on the part of the patient's foot on the platform.

The foot joint health diagnosis system of claim 2, wherein the load cell is provided on a moving platform adjustable in orthogonal directions on a horizontal plane.

The foot joint health diagnosis system of claim 1 , wherein the force provider comprises a hand-held instrument, the hand-held instrument comprising a handle, a connector attached to the handle, the load cell attached to the connector, and a force transmitter attached to the load cell, the force transmitter having a distal end, wherein when the distal end of the force transmitter is in contact with the application point, a force exerted by a user holding the handle is transmitted through the connector and the load cell and applied by the force transmitter onto the application point.

The foot joint health diagnosis system of claim 4, wherein the force transmitter comprises a transmission rod having a proximal end attached to the load cell.

The foot joint health diagnosis system of claim 5, wherein the force transmitter further comprises a stabiliser comprising an L-shaped bar, a long arm of the L-shaped bar orthogonally attachable to a central portion of the transmission rod, a short arm of the L-shaped bar having a distal end to contact a reference part of the patient's foot.

7. The foot joint health diagnosis system of any preceding claim, wherein the fiber Bragg gratings are embedded in an elastic polymer, the elastic polymer and fiber Bragg gratings provided in a sock to be worn over the foot.

. The foot joint health diagnosis system of claim 7, wherein the fiber Bragg gratings are provided on the sole of the foot when the sock is worn.

. The foot joint health diagnosis system of any one of claims 1 to 7, wherein the sensor device comprises one fibre Bragg grating to be adhered to the sole of the patient's foot and along an underside of a toe to be investigated.

0. The foot joint health diagnosis system of any preceding claim, wherein the sensor device comprises a coupler, the fibre Bragg gratings connected to the coupler, an input fiber cable connected to the coupler to connect a light source to the coupler, and an output fiber cable to the coupler to connect the coupler to a data processing module.