Abstract:
A device and method is provided whereby application is made to at least part of the sole of a suitably positioned foot for inverting or everting the foot. The device ( 1 ) (FIGS.  1  and  2 ) comprises a member or plate ( 20 ) having a planar surface ( 21 ) for pressure application to the sole by a handle ( 28 ) and in one arrangement is hingedly mounted ( 22, 24, 26 ) about horizontal axes from a leg rest ( 10 ) which lies in use on a seat or couch for the patient. This enables the surface ( 21 ) to be brought against the sole and also tilted for required contact with the latter. The plate ( 20 ) is also shown mounted for angular movement about a vertical axis X for additional tilting of the surface ( 21 ). An electronic unit ( 30 ) on the plate ( 20 ) has an LCD display ( 32 ) for showing angles of tilt. With the surface ( 21 ) in appropriate contact the sole can be manually palpated or manipulated e.g. for contact of the surface ( 21 ) with metatarsal joints or points, and/or the subtalar joint palpated for the neutral condition etc. The required position of the surface ( 21 ) is maintained while moulding material such as plaster of Paris (e.g. as a bandage) is applied to the sole and foot and allowed to set in providing a mould for use in the manufacture of orthoses. Alternatively, the plate may be simply hand held for similar operation. The planar surface may have buttons each for initial contact with a metatarsal point for indicator lamp operation when the metatarsal point lifts away. The handle may operate strain gauge means of the electronic unit to indicate application pressure at the LCD display.

Description:
The present application is a continuation application from U.S. patent application Ser. No. 09/918,582 filed on 31 Jul. 2001 now U.S. Pat. No. 6,782,630. 

   BACKGROUND OF THE INVENTION 
   This invention relates to a device for a foot. 
   Foot orthotics are an essential part of conservative orthopaedic treatment for correction of biomechanical abnormalities, congenital deformities and abnormal positions acquired through accident or disease processes. The taking of accurate plaster of Paris moulds or three-dimensional impressions of feet is a necessary part of the process of manufacture of foot orthotics. 
   At present, the plaster of Paris casts and three-dimensional impressions of feet are taken in the following positions. 
   With a patient sitting with the knee extended, or lying in a prone or supine position, the clinician palpates the subtalar joint to a neutral position with one hand, whilst the remaining hand applies dorsiflexory pressure to the fifth metatarsophalangeal joint or to the plantar surface of the webbing of the fourth and fifth toes. 
   Alternatively, with a patient sitting with the knee flexed, the foot is allowed to semi-weight bear whilst the clinician maintains the subtalar joint in a neutral position with one hand, as the plaster of Paris bandage or three-dimensional moulding material is placed around the foot and hardens. 
   A major problem with conventional methods of making casts and impressions of feet is their inherent lack of reproducibility. This can lead to the production of ill-fitting orthotics which may be uncomfortable and/or detrimental to the user. 
   SUMMARY OF THE INVENTION 
   There has now been devised a device and method for use in the taking of moulds and three-dimensional impressions of feet which overcome, or substantially mitigate, the above-mentioned or other disadvantages. 
   According to a first aspect of the invention, a device for use in the taking of a mould or impression of a foot comprises a generally planar member adapted for abutment with the sole of a patient&#39;s foot, and means by which the device may be held in any desired orientation. 
   According to a second aspect of the invention, a method of taking of a mould or impression of a foot comprises applying to the sole of the foot the planar member of a device as defined above, and holding the device in a desired orientation. 
   According to a third aspect of the invention, a device for use in the taking of a mould or impression of a foot comprises a generally planar member adapted for abutment with the sole of a patient&#39;s foot, and means for detecting angular displacement of the planar member. 
   According to a fourth aspect of the invention, a method of taking of a mould or impression of a foot comprises applying to the sole of the foot the planar member of a device as defined above, and detecting the angular displacement of the planar member. 
   In a preferred embodiment, the device according to the invention is provided with angular measurement means and display means, by which angular displacement of the planar member from a datum position can be determined. In one preferred embodiment, such means may be electronic. In such a case, means for setting the display to zero to provide a datum are preferably provided. This means may be push button actuatable by the clinician, to facilitate measurement of a given angular displacement from the datum position. Alternatively, the angular measurement and display means comprises a Vernier scale arrangement. 
   The angular measurement means may comprise means by which movement in degrees of tilt in the frontal plane of the foot may be measured by mechanical and/or magnetic and/or rotational movement. The angular measurement means may, for instance, include means for detecting a reference and means for determining the position of the vertical plane in relation to that reference. The reference may comprise another part of the foot or leg, or may be an external reference such as magnetic north, a mechanical reference means, or may be provided by means of a gyroscope. A potentiometer may be provided which is rotated when the device is rotated, thereby changing the resistance of the potentiometer. The resultant change in voltage may, after suitable calibration, be converted by digital logic to an output value in degrees which is displayed, e.g. on a liquid crystal display. A separate moving axis may be added to the planar member or built into the planar member to act as a reference point, or a fixed point strapped to the leg or foot or otherwise fixed, e.g. to the patient&#39;s chair, may extend to the planar member. 
   The new device can be used with the patient seated with the knee extended, or with the patient lying in a prone or supine position. 
   The planar member may be hingedly connected to one or more further planar members to allow separate forefoot and rear foot movement and first ray movement of the foot to be detected. 
   The device according to the invention is advantageous primarily in that it facilitates more accurate taking of three dimensional impressions of feet, which is currently carried out manually holding the foot whilst the plaster hardens to form the cast. The accuracy of alignment may be within a single degree or better. The device provides greater stability whilst the mould is being taken and, in preferred embodiments, any movement of the patient&#39;s foot or the clinician&#39;s hand will be visibly seen on the liquid crystal display, enabling the position to be corrected. This is especially important when taking moulds of children&#39;s feet. 
   The device also reduces or eliminates the need for adding estimated amounts of intrinsic posting to the positive cast, which is time consuming and a major source of inaccuracy in the finished orthosis. 
   The device may be used for the manufacture of both foot orthoses and ankle/foot orthoses. The device can be used for a three-dimensional impression of a foot, when using impression materials or impression bagging materials which surround the foot, whilst the clinician can check the angular position of the foot at any time. 
   The device thus improves both the reproducibility and accuracy of three dimensional impressions of feet. 

   
     DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a perspective view of a preferred embodiment of a device according to the invention using electronic means to detect the tilt movement of the handle and plate; 
       FIG. 2  is a schematic elevation of the device of  FIG. 1 ; 
       FIG. 3  shows the electronic circuitry involved in the embodiment of  FIGS. 1 and 2 ; 
       FIG. 4  is a diagram showing how angular measurements are calculated, using the circuitry of  FIG. 3 ; 
       FIG. 5  shows a similar device with a fixed reference point as in  FIG. 1  but using a vernier scale for detection of angular tilt; 
       FIG. 6  is a plan view of a further embodiment of a device according to the invention; 
       FIG. 7  is a side view of the device of  FIG. 6 ; 
       FIG. 8  shows a modified form of the device of  FIGS. 6 and 7 , in use; 
       FIG. 9  is a perspective view of another modified form of the device; 
       FIGS. 10 &amp; 11  are detail perspective views of parts of the device shown in  FIG. 9 ; 
       FIG. 12  is a perspective view of a still further form of the device, and 
       FIG. 13  is a detail cross sectional view on an enlarged scale of one of the micro switch arrangements. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring first to  FIGS. 1 and 2 , a device according to the invention is generally designated at  1 . The device  1  comprises a leg rest  10  which, in use, is placed on the edge of the chair or couch on which a patient sits or lies, the patient&#39;s lower leg being supported by the rest  10  with the ankle and foot projecting beyond it. The front edge of the rest  10  is provided with a soft insert  12 , which acts as a lower leg rest for the patient&#39;s comfort. 
   The rest  10  has a downwardly directed front portion  14  on which a removable tray  16  is received. The front portion  14  is hingedly connected at  15  to the rest  10 , to allow the device to be folded for ease of transport. 
   An articulated platform  18  is pivotally mounted at a lower level on the front portion  14  of the rest  10 . Hence, the platform  18  can be rotated about a vertical axis X. The platform  18  carries a planar member in the form of a rigid plate  20  having a planar surface  21  which, in use, is brought into contact with the sole of a patient&#39;s foot, as described in detail below. Hinges  22 ,  24 ,  26  allow movement of the platform  18  about horizontal axes. A handle  28  is fitted to the plate  20  to facilitate manipulation. Mounted on the plate  20 , above the handle  28  is an electronics unit  30  for measuring angular tilt of the plate  20 . The unit  30  has a liquid crystal display  32 , and a zero reset button  34  is incorporated into the handle  28 . The button  34  is positioned so as to be operable by the thumb of a user&#39;s hand which grasps the handle  28 . 
   In this embodiment, electronic means in the form of a potentiometer  36 , positioned at the point of vertical pivotal attachment of the platform  18 , to the front portion  14  is used to detect and measure movement of the platform  18  about the vertical axis X, this movement being indicative of the degree of side tilt of the plate  20  and planar surface  21  about the frontal plane of the foot. A power pack  38  is attached to the underside of the front portion  14 , so as to enable the device to be portably operated. The electronics unit involved, which will be described in more detail later, detects tilt of the plate  20  to 0.1 degree of accuracy, thus enabling the inversion/eversion of the foot to be monitored and closely controlled whilst the mould sets. The degree of correction can therefore be set using the digital readout at  32 , which is indicative of the frontal plane angle of the foot. 
   The method for taking subtalar joint neutral casts using plaster of Paris or three-dimensional moulding materials will now be described. 
   The patient may be in a prone or supine position or sitting up with hip flexed and knee extended as the clinician prefers. 
   A plaster of Paris bandage is applied to the foot in the usual manner in preparation for the casting position and the patient told to relax the foot completely as the bandage application is completed. 
   In order to use the device  1 , the rest  10  is placed on the patient&#39;s chair or couch and the patient&#39;s leg placed in position. The planar surface  21  of the hingedly mounted plate  20  is then brought into contact with the sole of the patient&#39;s foot, which is manipulated, essentially as described below. The tray  16  collects surplus casting material and is easily removed for cleaning (or may be a completely disposable item). 
   The planar surface  21  of the plate  20  (which may be referred to as a casting plate), is held against the plantar surface of the foot by the clinician, and dorsiflexory pressure applied to the handle  28 . The clinician ensures that the plate  20  and the foot are both in line with the leg, then depresses the zero reset button  34  to set a datum position, readable on the display  32 , from which the angle of tilt can be measured. The clinician&#39;s free hand may then simultaneously palpate the subtalar joint position required by inverting and everting the plate  20  by the required amount, as indicated on the display  32 . The subtalar joint position is then held exactly by maintaining dorsiflexory pressure through the plate  20 . The amount of dorsiflexory pressure applied through the handle  28  against the foot may be varied accordingly. The pressure may be applied to both rear foot and forefoot simultaneously or forefoot pressure only to prevent any soft tissue compression of the rear foot. If the forefoot does not become fully plantigrade with dorsiflexory pressure from the plate  20  the other hand can be removed from palpating the talonavicular joint and used to apply a downward force to the dorsum of the metatarsophalangeal joints thereby making the forefoot plantigrade with the planar surface  21  of the plate  20 . The frontal plane angle of the foot is maintained at all times by checking the liquid crystal display. 
   The position is maintained until the plaster of Paris bandage hardens, so that the cast can then be removed without causing deformation of the plaster. If required, the casting procedure is then repeated on the other foot. 
   In a prone position, where lines have been drawn on the skin to bisect the posterior of the lower leg and to bisect the posterior of the calcaneum, the device  1  may be used to take the cast in either subtalar joint neutral position alone or heel vertical position, or by inverting/everting the planar surface  21  from subtalar joint neutral, the cast may be taken in the degree of varus/valgus correction required. With heel vertical prone casting, a separate 90° heel vertical marker (not shown) is added to the planar surface  21  (e.g. by means of a clip fitting on the plate  20 ) and simply aligned to a bisection line previously marked on the posterior of the calcaneum whilst applying dorsiflexory pressure via the plate  20 . The thumb of the hand holding the handle  28  depresses the zero degree reset button  34  and in a varus foot the free hand applies downward pressure to the dorsum of the first metatarsophalangeal joint bringing it into contact with the planar surface  21 . If the foot is in a plantigrade position against the dorsiflexory pressured planar surface  21  with the heel vertical marker aligned to the posterior bisection of the calcaneum, increased dorsiflexory pressure may be applied at once to both forefoot and rear foot simultaneously, or pressure may be applied to the forefoot only to prevent soft tissue compression to the plantar surface of the calcaneum, whilst the marker still maintains heel vertical position. The position is maintained until the plaster hardens or the three-dimensional moulding material has gone evenly around the foot and sets. 
   When requiring a mould with a degree of correction from subtalar joint neutral, e.g. 4° varus, the subtalar joint neutral position is initially palpated with one hand palpating the talonavicular joint and the other hand inverting and everting the foot with the planar surface  21  applying a constant dorsiflexory force to the plantar surface of the foot until neutral position is palpated. The reset button  34  is then depressed. Then the planar surface  21  is moved in the frontal plane, increasing the height of the arch, to register e.g. 4° on the liquid crystal display  32 . The foot has now been corrected by 4° and the cast will harden in 4° of varus correction. Pressure may then be increased to the forefoot by the planar surface  21  keeping the same frontal plane degree position, as displayed by the liquid crystal display  32 , until the forefoot becomes plantigrade. Alternatively, the hand palpating the talonavicular joint may be removed (without altering the 4° position of the surface  21 ), allowing the apices of the index and third finger of the free hand to apply downward pressure inside the bandage to the dorsum of the first metatarsophalangeal joint, to bring the foot into a plantigrade position with the planar surface  21 . The cast, when removed, will be in 4° of varus correction from subtalar joint neutral. 
     FIG. 3  is a system block diagram of the electronics circuit used in the embodiment of  FIGS. 1 and 2 . The angular displacement of the planar surface  21  ( FIGS. 1 and 2 ) is measured by the potentiometer  36 . The potentiometer  36  is supplied with a reference voltage  38  across its end terminals and a voltage appears at the potentiometer wiper terminal whose value represents the angle to be measured. 
   This voltage is measured by an Analogue to Digital Converter (ADC)  40  which is controlled by a microprocessor  42 . The microprocessor  42  reads the voltage and converts it to an angle using a simple proportional calculation. This reading is the uncorrected angle (represented by the symbol Au in  FIG. 4 ) of the potentiometer  36 . Since the potentiometer  36  has inherent inaccuracies due to its physical characteristics, the microprocessor  42  corrects this reading Au by applying corrections stored in the EEPROM 44 (Electrically Erasable Programmable Read Only Memory). These corrections are calculated during the production calibration phase of the device, by comparing the reading Au against a known accurate reference angle measuring device (not shown). These comparisons are made typically every 5 degrees and the corrections are stored in the EEPROM. EEPROM memory is non-volatile, i.e. its data is retained even when power is removed form the circuit. 
   Referring also to  FIG. 4 , when the microprocessor reads the uncorrected angle Au, it also reads the correction factor for this angle (as described above) and applies it to the reading Au (typically using a linear interpolation algorithm) to create a corrected reading, Ac. 
   This angle Ac represents the absolute angle of the planar surface  21  relative to the body of the device. This angle is not suitable for displaying to the user as it does not represent the angle of the foot in a readily understandable format. To produce a reading that represents the angle of the foot in degrees relative to the line of the leg, the fixture is set so that the planar surface  21  is exactly in line with the leg line. At this point, the user (for example the calibrator, or clinician) presses the zero degree reset button  34 , as indicated in  FIGS. 1 and 2 . At this point the microprocessor notes the angle measured (the ‘absolute null’ denoted by Az, and corrected using the correction data in the EEPROM as before). The relative angle of the planar surface  21  can then be determined by subtracting the corrected angle Ac from the null angle Az. The resulting angle, denoted Af, can therefore be positive or negative and represents the angle of the foot base from the line of the leg. 
   The user may also want to be able to set a ‘local null’, Al, at some position other than the ‘absolute null’, Az. When the planar surface  21  is at the required position, the user re-presses the reset button  34  to obtain a ‘local null’ reading. Alternatively, a second switch may be provided for this ‘local null’ reading function. The local angle, denoted by As, is then displayed on the liquid crystal display  32 , as indicated in  FIGS. 1 and 2 , relative to the ‘local null’ by subtracting Ac from the local null Al. The angle of the planar surface  21  relative to the leg line ‘absolute null’ Af is also displayed to the user. To ensure that the system retains its settings when the unit is powered down, the local null and absolute null values are stored in the EEPROM  44 . 
   The device may be provided with a communication link to an external computer, to allow transfer of data and/or parameters, for example patient information, patient treatment history, historical data or calibration curves. This link may take the form of a parallel or serial data port. Measurements may then be stored in or transferred from a patient database, for example to be compared with measurements from previous treatment sessions. 
   Turning now to  FIG. 5 , a device according to this embodiment of the invention is generally designated  50 . The device  50  comprises a leg rest  51  which, in use, is placed on the edge of the chair or couch on which the patient sits or lies, the patient&#39;s lower leg being supported by the rest  51  with the ankle and foot projecting beyond it. The rest  51  is padded for the patient&#39;s comfort. 
   The rest  51  has a downwardly directed end portion  52  on which a removable tray  53  is received. An articulated platform  54  is pivotally mounted beneath the end portion  52 , such that the platform  54  can be rotated about a vertical axis. The platform  54  includes a planar member or casting plate  55 , having a planar surface  55   a  which, in use, is brought into contact with the sole of a patient&#39;s foot, generally as described in detail above with reference to  FIGS. 1  to  4 . Hinges  56 ,  57 ,  58  allow movement of the platform  54  about horizontal axes. A handle  59  is fitted to the plate  55  to facilitate manipulation. 
   Angular movement of the platform  54  about the vertical axis is monitored by means of a Vernier scale on adjustment knobs  60 ,  61 . 
   The device  50  is used in a broadly similar manner to the embodiment described above. The rest  51  is placed on the patient&#39;s chair or couch and the patient&#39;s leg placed in position on the rest. The plate  55  and the patient&#39;s foot are then manipulated, essentially as described above, the degree of correction being set using the Vernier at  60 ,  61 . The tray  53  collects surplus casting material and is easily removed for cleaning (or may be a completely disposable item). 
   Referring now to  FIGS. 6 and 7 , a hand-held device according to this embodiment of the invention is generally designated  62  and comprises a planar member or casting plate  63  with a handle  64 . The plate  63  is a rigid plate of approximate thickness  3 mm having a planar surface  65 , and may be formed integrally with the handle  64  e.g. by moulding in plastics material. Two spring-loaded clips  66  are provided laterally of the handle  64 , for retaining the edges of a paper towel wrapped around the surface  65  of the plate  63 . 
   Mounted on the plate  63  and (as viewed in  FIG. 6 ) above the handle  64 , is an electronics unit  67  which incorporates a means for measuring angular tilt of the plate  63  and surface  65 . The unit  67  has a liquid crystal display  68 , and a zero reset button  69  is incorporated into the handle  64 . The button  69  is operable by the thumb of the user&#39;s hand which grasps the handle  64 . 
   The electronics unit  67  includes means for detecting an external reference from which the degree of tilt of the planar surface  65  can be calculated. For example, the electronics unit  68  may include means for detecting magnetic north, and/or a rotational potentiometer which is rotated when the plate  63  is rotated, thereby changing the resistance of the potentiometer. The resultant change in voltage is converted by digital logic circuitry to an output value in degrees which is displayed on the liquid crystal display  68 . Alternative means for detecting the tilt of the plate  63  may be provided by a mechanical reference means or by means of a gyroscope. 
   In order to use the device  60 , a clean paper towel is placed against the planar surface  65  of the plate  63  and folded back and inserted under the raised clips  66 . A plaster of Paris bandage is applied to the foot in the usual manner, in preparation for the casting position, and the patient told to relax the foot completely as the bandage application is completed. 
   The planar surface  65  of the plate  63  is then brought into contact with the sole of the patient&#39;s foot and the method for taking subtalar joint neutral casts is then carried out, substantially as described above. 
   The device of  FIG. 8  (generally designated  70 ) is similar to that described with reference to  FIGS. 6 and 7 , in that it comprises a casting plate  71  having a planar surface  72 , and a handle  73 . An electronics unit  74  with an LCD display (not visible) is mounted on the plate  71  above the handle  73 , and a reset button  75  is provided to zero the display. 
   The device  70  differs from that of  FIGS. 6 and 7  in that it is provided with a reference arm  76  which is pivotally connected to the plate  71 . The free end of the arm  76  bears against the patient&#39;s lower leg. The point at which the arm  76  is pivotally connected to the planar surface  72  of the plate  71  includes means (not shown in detail) which is operably linked to the electronics unit  74 , by which the angle of the arm  76  relative to the surface  72  can be measured. The arm  76  provides a fixed point relative to which the angle of tilt of the surface  72  can be measured. 
   Another form of the device is shown at  80  in  FIGS. 9  to  11  in which the planar member or casting plate  81  has a handle  83  secured at one end  83   b  to the plate  81  whilst the other free end  83   a  extends towards a lower part of the electronics unit  84 . On the manual application of pressure to the handle  83  it yields so that the end  83   a  contacts a resiliently flexible extension  85   a  of a printed circuit board  85  in the electronics unit  84 . The extension  85   a  carries a number of strain gauges  86  ( FIG. 10 ) thereon which, on deflection of the extension  85   a  by the handle  83 , produce a signal which is representative of the force applied. This is indicated in the LCD display  87  of the unit  84 . 
   The action of the strain gauges  86  is such that it allows substantially exact repeatability of pressure on the planar surface of the plate  81  against the sole of the foot especially whilst a plaster of Paris bandage or other moulding material sets. 
   Referring to  FIGS. 12 and 13  a further form of the device is shown at  90  in  FIG. 12  where the planar surface  92  of the casting plate  91  is provided with a triangular shaped guide line  95 , which assists the clinician in positioning the planar surface  92  against the sole of a foot at the fore foot. The plate  91  has two buttons  96   a  and  96   b  bounded by the guide line  95  and located in respective holes  97  through the plate  91  (FIG.  13 ). Each button  96   a ,  96   b  is located in its hole  97  by a compression spring  98  and a cranked peripheral flange  96   c  of the button which bears against the back of the plate  91  about the hole  97 . Each button  96   a ,  96   b  has a central adjustment screw  99  which contacts a micro-switch  100  on contact of the button with the sole of the foot. 
   One button  96   a  is for use with a right foot (as shown in  FIG. 12 ) and the other button  96   b  is for use with a left foot. On initial contact of the first metatarsal joint or head of the forefoot sole area with a corresponding button  96   a , the latter is depressed into operating contact with the switch  100 . When the first metatarsal lifts away from the planar surface  92  the button  96   a  and its screw  99  will move away from the switch  100  causing a light (not shown) or other indication to be operated to draw the attention of the clinician to the fact that the metatarsal lifting has taken place. Such light may be conveniently situated at the LCD of an electronics unit (not shown) provided on the plate  91  in the manner already described. 
   This arrangement enables the maximum range of motion of how far the foot inrolls to be measured before the head of the first metatarsal lifts away from the planar surface  92 . Thus by placing the planar surface  92  of the plate  91  against the forefoot sole area and putting pressure predominantly on the outer metatarsal heads, the whole forefoot moves out of contact and so measures the angle of pronation. 
   At the maximum range of motion the head of the first metatarsal will lift away from the corresponding button  96   a  in the plate  91  so causing illumination of a corresponding indication light.