Abstract:
A measurement device ( 10 ) for quantitatively measuring stiffness, torque or range of motion (ROM) around the joint axis of the ankle-foot complex of a lower limb in the sagittal and coronal planes, the device ( 10 ) comprising: a plate ( 13, 21 ) for placement of the ankle-foot complex, the plate ( 13, 21 ) operatively connected to an actuator ( 14, 16 ) for manual actuation; an angular measurement device ( 12, 17 ) to measure an angular position of the ankle-foot complex; a torquemeter ( 11 ) to measure resistance torque of the ankle-foot complex; an electromyograph ( 48 ) to monitor muscular activity of muscles of the lower limb; and computer software to record the measured angular position, resistance torque of the ankle-foot complex and EMG of the lower limb muscles.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a measurement device for quantitatively measuring stiffness, torque or range of motion (ROM) of an ankle joint or an ankle-foot orthosis (AFO) in the sagittal and coronal planes of the ankle-foot complex. In particular, the invention assists a prescription of an AFO for persons with a spastic or flaccid ankle joint. 
       BACKGROUND 
       [0002]    AFOs are commonly prescribed as a form of orthotic intervention to improve gait of patients with neuromuscular diseases, such as stroke, cerebral palsy or brain injury. They are primarily designed to provide adequate plantarflexion resistance, to prevent foot-drop and to provide sufficient medio-lateral stability for a pathologic ankle joint. Therefore, quantitative information on stiffness of an ankle joint and an AFO in the sagittal and coronal planes is essential in an AFO prescription. 
         [0003]    An understanding of stiffness properties inherent in the design of an AFO is important because it is the key in preventing an under- or over-prescription and in providing an optimum AFO for a patient. However, the complicated geometry of a thermoplastic AFO and its interaction with the lower limb make it difficult to evaluate the mechanical behavior of an AFO during gait. This has been one of the limitations for the development of a prescription system to provide the most appropriate AFO to patients with various medical conditions. 
         [0004]    Spasticity is one of the most common neurological impairments and occurs after the lesion of the upper motor neuron (UMN) in patients with hemiplegia. It is defined as disordered sensori-motor control resulting from a UMN lesion and presenting as intermittent or sustained involuntary activation of muscles. Some studies indicate that about 36% to 38% of patients with stroke developed spasticity during the first year. Spasticity generally induces an increase in ankle joint stiffness and foot-drop during ambulation. Therefore, patients with a spastic ankle joint are prevalently prescribed with an AFO. 
         [0005]    Joint stiffness is attributed to a reflex stiffness component which is caused by the alternation in the muscular activation level and a non-reflex stiffness component which stems from the mechanical properties of the muscles, joints and tendons. Both reflex and non-reflex changes occur at an ankle joint in patients with hemiplegia. 
         [0006]    A clinician usually evaluates ankle joint stiffness of a patient manually and attempts to reflect its input for decision making in the design of an AFO. However, this protocol heavily relies on the anecdotal or individual clinical experience. In the laboratory setting, a number of sophisticated experimental devices have been introduced to assess resistive torque and stiffness of a spastic ankle joint, such as a device disclosed in U.S. Pat. No. 6,599,255 B2. However, these devices might not be very practical in the clinical setting due to their size, costs and complexity. 
         [0007]    In a clinical environment, a manual device is more practical. They can minimize discomfort and injuries and are considered safer than automated devices and easily applied in a clinical environment. However, they have the disadvantage that the applied force, velocity, and acceleration achieved as well as the point of force application and their orientation are difficult to control. 
         [0008]    Traditionally, it is believed that stiffness of an ankle joint and an AFO should be considered in an AFO prescription. There is no available device to perform this function. Accordingly, there is a need for a manual device which can measure stiffness of both an ankle joint and an AFO quantitatively in order to assist a clinician in an AFO prescription. It would be beneficial for a patient if a clinician is able to prescribe an AFO based on the objective information on stiffness of an ankle joint and an AFO instead of a subjective decision that may be based on their experience. 
       SUMMARY 
       [0009]    In a first aspect, there is provided a measurement device for quantitatively measuring stiffness, torque or range of motion (ROM) around the joint axis of the ankle-foot complex of a lower limb in the sagittal and coronal planes, the device comprising: a plate for placement of the ankle-foot complex, the plate operatively connected to an actuator for manual actuation; an angular measurement device to measure an angular position of the ankle-foot complex; a torquemeter to measure resistance torque of the ankle-foot complex; an electromyograph (EMG) to monitor muscular activity of muscles of the lower limb; and computer software to record the measured angular position, resistance torque of the ankle-foot complex and EMG of the lower limb muscles. 
         [0010]    The plate may be a foot plate or a rotary plate. 
         [0011]    The angular measurement device may be a potentiometer or a protractor. 
         [0012]    The foot plate may have range of motion in the sagittal and coronal planes, and range of motion of the foot plate is adjustable with stoppers positioned under a handle. 
         [0013]    The device may further comprise a base and base frames to support the device, wherein the angular position of the base relative to the base frame is adjustable in the sagittal plane. 
         [0014]    The device may further comprise a metronome to monitor angular velocity of the foot plate. 
         [0015]    The device may further comprise a rotary plate to fix the ankle-foot complex via the foot plate, the foot plate being freely movable on the rotary plate and its height is adjustable to enable correct positioning of the axis of the rotary plate to the estimated rotational center of the ankle-foot complex with reference to the extended axis of the torquemeter and the potentiometer. 
         [0016]    The actuator may be a handle or a steering wheel to manually rotate the rotary plate around the axis of the torquemeter and the potentiometer. 
         [0017]    The EMG may comprise electrodes attached to dorsiflexor and plantarflexor muscles. 
         [0018]    The device may further comprise a hand-held dynamometer and associated software to measure muscle strength of each joint to determine an AFO prescription. 
         [0019]    Optimum stiffness of an AFO (K AFO ) may be determined considering strength of the lower limb joint. 
         [0020]    Range of motion of the ankle joint may be measured by the device to determine an AFO prescription. 
         [0021]    Range of motion of an ankle joint (ROM ANKLE ) and range of motion of an AFO (ROM AFO ), ROM ANKLE ≧ROM AFO  may be satisfied. 
         [0022]    Range of motion of an ankle joint (ROM ANKLE ) or an AFO (ROM AFO ) may be measured using the device in the sagittal and coronal planes. 
         [0023]    Range of motion of an ankle joint may be measured by quantifying the ankle-foot complex angular position that reaches predetermined torque values in both directions in the plane of interest, and range of motion of the ankle is the summation of absolute angular position values in both directions. 
         [0024]    Range of motion of an ankle joint may be measured by stretching the ankle-foot complex to its limit in both directions in the plane of interest and quantify their values, and range of motion of the ankle is the summation of absolute angular position values in both directions. 
         [0025]    In a second aspect, there is provided a method for quantitatively measuring stiffness of an ankle joint and an AFO, the method comprising: using the equation K=ΔT/Δθ; wherein K is stiffness and ΔT is torque increments during a certain amount of ankle-foot complex angular movement (Δθ). 
         [0026]    Stiffness (K ANKLE ) data of an ankle joint and an AFO may be used to determine whether optimum stiffness of a prescribing AFO (K AFO ), and K AFO ≧K ANKLE  may be satisfied. 
         [0027]    Resistance torque (T ANKLE ) data of an ankle joint and an AFO may be used to determine whether optimum resistance torque of a prescribing AFO (T AFO ) at a predetermined ankle-foot complex angular position, and T AFO ≧T ANKLE  may be satisfied. 
         [0028]    In a third aspect, there is provided a method for controlling angular velocity of a foot plate and a rotary plate of a measurement device for quantitatively measuring stiffness, torque or range of motion (ROM) around the joint axis of the ankle-foot complex of a lower limb in the sagittal and coronal planes, the method comprising: using the equation Av=(Mt*Rm)/60; wherein Av is angular velocity, Mt is motional tempo, and Rm is range of motion of an ankle joint (ROM ANKLE ) or an AFO (ROM AFO ). 
         [0029]    The angular velocity may be monitored by a metronome. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0030]    An example will now be described with reference to the accompanying drawings, in which: 
           [0031]      FIG. 1  is a front view of the body of a device to measure stiffness, torque or range of motion (ROM) around the joint axis of the ankle-foot complex according to an embodiment of the present invention; 
           [0032]      FIG. 2  is a transverse view of the body of the device of  FIG. 1 ; 
           [0033]      FIG. 3  is a sagittal view of the body of the device of  FIG. 1  from the steering wheel; 
           [0034]      FIG. 4  is a transverse view of the rotary plate and its fixation to the supporter of the device of  FIG. 1 ; 
           [0035]      FIG. 5  is a sagittal view of the rotary plate of  FIG. 4 ; 
           [0036]      FIG. 6  is a front side of the foot plate for sagittal plane measurement of the ankle-foot complex; 
           [0037]      FIG. 7  is a back side of the foot plate for sagittal plane measurement of the ankle-foot complex; 
           [0038]      FIG. 8  is a foot plate attached to a rotary plate for sagittal plane measurement of the ankle-foot complex; 
           [0039]      FIG. 9  is a front side of the foot plate for coronal plane measurement of the ankle-foot complex; 
           [0040]      FIG. 10  is a back side of the foot plate for coronal plane measurement of the ankle-foot complex; 
           [0041]      FIG. 11  is a foot plate attached to a rotary plate for coronal plane measurement of the ankle-foot complex; 
           [0042]      FIG. 12  is a front view of a limb and a device to measure stiffness, torque or range of motion of an ankle joint in the sagittal plane in accordance with an embodiment of the present invention; 
           [0043]      FIG. 13  is a sagittal view of a limb and a device to measure stiffness, torque or range of motion of an ankle joint in the sagittal plane in accordance with an embodiment of the present invention; 
           [0044]      FIG. 14  is a front view of an AFO and a device to measure stiffness, torque or range of motion of an AFO in the sagittal plane in accordance with an embodiment of the present invention; 
           [0045]      FIG. 15  is a sagittal view of an AFO and a device to measure stiffness, torque or range of motion of an AFO in the sagittal plane in accordance with an embodiment of the present invention; 
           [0046]      FIG. 16  is a sagittal view of the device of  FIG. 1  showing a mechanism to alter the angular position of the base relative to the base frame; and 
           [0047]      FIG. 17  is an electronic design diagram of the device of  FIG. 1  with a hand-held dynamometer. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    Referring to  FIGS. 1 to 3 , an ankle-foot orthosis prescription assistive device  10  is provided. The device  10  quantitatively measures stiffness, torque or range of motion (ROM) of an ankle joint or an ankle-foot orthosis (AFO) in the sagittal and coronal planes of the ankle-foot complex. The body of the device  10  generally a torquemeter  11 , a potentiometer  12 , a rotary plate  13 , a steering wheel  14  with a stopper bar  15  and a handle  16 , a protractor  17 , and a urethane stopper  18 . The height position of the urethane stopper  18  is adjustable along a stopper pole  19 . The device  10  is able to measure angular positions with the potentiometer  12  and their corresponding resistance torque with the torquemeter  11  around the rotational center of the ankle joint and the AFO in the sagittal and coronal planes by applying manual force to the steering wheel  14  or the handle  16 , which extends a shaft in a lateral direction to the rotary plate  13 . The full scale of the torquemeter  11  is 50 Nm. Output from the torquemeter  11  and the potentiometer  12  is fed into a computer  27  via an A/D converter  20  for further analysis. Range of motion (ROM) of a foot plate  21  is adjustable with the urethane stoppers  18  positioned under the stopper bar  15  attached to the steering wheel  14 . 
         [0049]    The protractor  17  is used to provide visual information of the angular positions of the ankle joint or the AFO in the sagittal and coronal planes of the ankle-foot complex to an examiner during assessment. The angular velocity of the foot plate  21  is monitored with a metronome  22 . 
         [0050]    The handle  16  is attached to the steering wheel  14 . The steering wheel  14 , the torquemeter  11  and the potentiometer  12  are held by supporters  23  standing on a base  24  of the device  10 . The torquemeter  11  measures resistance torque, while the potentiometer  12  measures the angular position. The output from the torquemeter  11  and the potentiometer  12  are fed into the computer  27  for further analysis via an A/D converter  20 . Spacers  30  are positioned between the supporters  23  and the rotary plate  13  to reduce friction between them. The base  24  is fixed above base frames  25  of the device  10  using the base holder  52 . A supporting frame holder  55  on the base  24  of the device  10  is used to maintain a supporting frame  46  to fixate a lower limb or an AFO. Manual force is applied to either the handle  16  or the steering wheel  14  to rotate the rotary plate  13  around the axis of the potentiometer  12  and the torquemeter  11 . The height of a rotary plate  13  is adjustable and fixed to a desired location using nut screws  28 . The stopper bar  15  fixed to the steering wheel  14  moves around with it. A urethane stopper  18  whose height is adjustable along a stopper pole  19  is utilized to restrict ROM of the rotary plate  13  and the foot plate for safety reasons and controlling the applied angular velocity using the metronome  22 . The stopper pole  19  is fixed to the base  24  of the device  10  with a stopper pole stand  26 . The protractor  17  is fixed around the rotational axis and it can provide visual information of the rotational angle. This is possible by placing a circular transparent plastic sheet  31  with an arrow, which rotates along with the steering wheel  14  over the fixed protractor  17 . 
         [0051]    Referring to  FIGS. 4 and 5 , the rotary plate  13  comprises two separate plates and has a groove  33  between them. The groove  33  is used to position a foot plate  21  at an appropriate location on the rotary plate  13 . A screw  32  is provided which protrudes from the rotational axis of the torquemeter  11  and the potentiometer  12  to extend a horizontal line, so that it can visually assist in locating the rotational center of an ankle joint and an AFO. Spacers  30  are positioned between the supporter  23  of the device  10  and the rotary plate  13  to reduce friction between them. 
         [0052]      FIG. 6  is a front side of the foot plate  21  and  FIG. 7  is a back side of the foot plate  21  for sagittal plane measurement of an ankle joint. A heel cup  34  is positioned on a metal plate  35 , which allows a convenient replacement of various heel cups  34  according to a foot size. Velcro™ straps  37  are used to fix the ankle-foot complex to the foot plate  21 . The position of one strap  37  is adjustable along a strap holder  36 , while the other strap  37  is fixed. A rubber sheet  38  is sealed on the foot plate  21  as a slip stopper. Three metal frames each with a groove  42  are embedded in a parallel manner at the back of the foot plate  21 . The head of the screw  32  fits in the groove  42  of the metal frames  39  and the screws  32  are used to fix the foot plate  21  to the rotary plate  13 . The head of the screw  32  can move freely along the grooves  42  of the metal frames  39  between the stoppers  53  and their positions are fixed by fly nuts  40  and washers  41  on the rotary plate  13 . 
         [0053]      FIG. 8  illustrates the foot plate  21  attached to the rotary plate  13  for sagittal plane measurement of the ankle joint. The screws  32  extruding from the metal frames  39  at the back of the foot plate  21  are fit into the groove  33  of the rotary plate  13 . Subsequently, the position of the foot plate  21  on the rotary plate  13  is fixed by tightening the fly nuts  40  over the washers  41 . 
         [0054]      FIG. 9  is a front side of the foot plate  21  and  FIG. 10  is a back side of the foot plate  21  for coronal plane measurement of an ankle joint. The heel cup  34  is positioned on the metal plate  35 , which allows a convenient replacement of various heel cups  34  according to a foot size. Straps  37  are used to fix the ankle-foot complex to the foot plate  21 . The position of the straps  37  is adjustable along a strap holder  36 . A rubber sheet  43  is sealed on the foot plate  21  as a slip stopper. 
         [0055]    The two metal frames  39  with a groove  42  are embedded at a right angle at the back of the foot plate  21 . The head of the screw  32  fits in the groove  42  of the metal frames  39  to fix the foot plate  21  to the rotary plate  13 . The head of the screws  32  can move freely along the groove  42  of the metal frames  39  between the stoppers  53  and their positions are fixed by the fly nuts  40  and washers  41 .  FIG. 11  depicts the foot plate  21  attached to the rotary plate  13  for coronal plane measurement of the ankle joint. The head of the screws  32  extending from the metal frames  39  of the foot plate  21  are fit into the groove  33  of the rotary plate  13 . Subsequently, the position of the foot plate  21  on the rotary plate  13  is fixed by tightening the fly nuts  40  over the washers  41 . 
         [0056]    Referring to  FIGS. 12 and 13 , a limb and the device  10  to measure stiffness, torque or range of motion of an ankle joint in the sagittal plane is provided. The ankle-foot complex is fastened to the foot plate  21  by straps  37  of the foot plate  21 , while a shank of a lower-limb is fastened by a strap  44  extending from a padding  45 , which is fixed to the supporting frames  46  maintained by the supporting frame holders  55  on the base  24  of the device  10 . The contra-lateral ankle-foot complex is placed on a foot rest  47 . While stretching the ankle joint of interest, ankle joint torque (T ANKLE ), its corresponding angular positions and electromyographic signals from the dorsiflexor and plantarflexor muscles of the lower limb are recorded by an electromyograph (EMG). The EMG signals are collected using electrodes  48  attached to theses muscles. Signals from the torquemeter  11 , the potentiometer  12  and the EMG electrodes  48  are fed into the computer  27  via the A/D converter  20  for further analysis. Angular velocity of the rotation of the foot plate  21  is controlled and monitored using the metronome  22  utilizing the equation Av=(Mt*Rm)/60, wherein Av is angular velocity, Mt is motional tempo, and Rm is ROM of an ankle (ROM ANKLE ) or an AFO (ROM AFO ). ROM of an ankle (ROM ANKLE ) or an AFO (ROM AFO ) in the sagittal and coronal planes may be measured using the device  10 . There are two methods to measure ROM. Firstly, ROM can be measured by quantifying the ankle-foot complex angular position that reaches predetermined torque values in both directions in the plane of interest. For instance, if the predetermined torque value is 5 Nm and its corresponding ankle angular position is 10° in dorsiflexion and 35° in plantarflexion in the sagittal plane, then ROM is their summation 45°. Secondly, ROM can be also measured by stretching the ankle-foot complex to its limit in both directions in the plane of interest and quantifying their values. For instance, if the limit position in the dorsiflexion direction is 15° and in the plantarflexion one is 40° in the sagittal plane, then ROM is their summation 55°. 
         [0057]    Referring to  FIGS. 14 and 15 , an AFO and a device  10  to measure stiffness, torque or range of motion (ROM) of an AFO in the sagittal plane is provided. The AFO is fixed to the rotary plate  13  using a G-clamp  49 . A shank of the AFO was fastened to the device using a dummy limb  50 , which is fixed to the supporting frames  46  maintained by the supporting frame holders  55  on the base  24  of the device  10 . While rotating the rotary plate  13 , AFO torque (T AFO ) and its corresponding angle around the rotational axis are recorded. Signals from the torquemeter  11  and the potentiometer  12  are fed into the computer  27  via the A/D converter  20  for further analysis. Angular velocity of the rotation of the rotary plate  13  is controlled using the metronome  22  and ROM of the AFO (ROM AFO ) is measured as described above. 
         [0058]    Stiffness of the ankle-foot complex is calculated using the equation K=ΔT/AO, where K is stiffness and ΔT is torque increments during a certain amount of ankle angular movement (Δθ). Δθ is determined based on ROM of the ankle joint (ROM ANKLE ) or the AFO (ROM AFO ). 
         [0059]    Optimum stiffness of an AFO (K AFO ) is determined based on stiffness of an ankle joint (K ANKLE ). In order to keep the ankle joint at a desired angular position with effective plantarflexion resistance of an AFO, the following equation is satisfied: K AFO ≧K ANKLE . 
         [0060]    Referring to  FIG. 16 , the angular position (Φ) of the base  24  relative to the base frame  25  is adjustable by rotating the base  24  around the base holder  52  and maintain this angular position utilizing the angle adjuster  54 . The ability to adjust and maintain the angular position is advantageous when a measurement of ankle joint stiffness, torque or range of motion is required to be conducted at various knee joint angular positions or postures. 
         [0061]    Referring to  FIG. 17 , an electronic design of the device  10  is illustrated. A power source  160  supplies appropriate voltage to the torquemeter  11 , the potentiometer  12 , the EMG electrode  48 , a hand-held dynamometer  51 , and an amplifier  161 . The output signal from the torquemeter  11  and the EMG electrode  48  is amplified with the amplifier  161  and fed into the computer  27  via the A/D converter  20 . The output signal from the potentiometer  11  and the hand-held dynamometer  51  is directly fed into the computer  27  via the A/D converter  20 . Computer software records the measured angular position, resistance torque of the ankle-foot complex and EMG signals of the lower limb muscles as well as muscle strength of the lower limb joints for further analysis. The hand-held dynamometer  51  is provided to measure muscle strength of the lower limb joints. The hand-held dynamometer  51  can measure strength of plantarflexors and dorsiflexors of ankle joints, and flexors and extensors of knee and hip joints. It is advantageous if muscle strength of each joint is considered in an AFO prescription along with stiffness, torque and range of motion data obtained from the device  10 . It is beneficial to consider muscle strength because an AFO should be designed to compensate weaken lower limb muscle strength of patients with various medical conditions. Therefore, quantified muscle strength data would provide supplemental input for more reliable and evidence-based practice in an AFO prescription. 
         [0062]    In another embodiment, range of motion of the ankle joint is measured by the device  10 . A range of motion measurement is considered in an AFO prescription. Range of motion of the ankle joint should be considered together with stiffness, torque and muscle strength data. ROM ANKLE ≧ROM AFO  is satisfied. It is advantageous to consider ROM for an AFO prescription because stiffness of an AFO (K AFO ) and ROM of an AFO (ROM AFO ) are closely related to each other. Quantitative ROM data also helps a clinician to determine whether an articulated AFO (AAFO) or a non-articulated AFO (NAAFO) should be prescribed. ROM AFO  should be considered in the design of both AAFOs and NAAFOs to optimize their function. Therefore, quantified ROM data would also provide supplemental input for more reliable and evidence-based practice in an AFO prescription. 
         [0063]    Preferably, three components should be considered in the final prescription of an AFO:
       1) Stiffness (K AFO  and K ANKLE ) and/or torque (T AFO ) and T ANKLE ) data by the device  10 ;   2) ROM (ROM AFO  and ROM ANKLE ) data by the device  10 ; and   3) Lower limb joints muscle strength data by the hand-held dynamometer  51 .       
 
         [0067]    It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope or spirit of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects illustrative and not restrictive.