Abstract:
A device and a method for measuring wrist motion is provided. The device allows for direct determination of wrist position in the radial/ulnar and flexion/extension planes, without needing calibration or determination of the center of rotation of the wrist. The goniometer forearm component is adapted to be releasably affixed to a forearm of a user. A hand component is also provided adapted to be releasably affixed to a hand of the user. The displacement measuring devices include cables adapted to be connected to the hand component. The displacement measuring devices are configured to ultimately measure angular displacement of the hand component relative to the forearm component.

Description:
FIELD OF THE INVENTION 
     This application relates to motion measurement devices. More particularly, this application relates to an apparatus for measuring displacement of the wrist, capable of measuring displacement in both the radial/ulnar and flexion/extension planes. 
     BACKGROUND OF THE INVENTION 
     It often is desirable to measure displacement of body parts when in motion. Such measurement may be useful in diagnosing injuries, such as loss of motion, and in studying repetitive motions to determine if such motions cause injury or strain. Knowing the position and displacement of body parts is important to biomechanical analysis. In clinical settings, motion measurement devices may provide information about motion pattern or range of motion. This knowledge may be used to determine the status of the is function of a body part and to guide treatment plans. Also, in the workplace, posture and repetitiveness of tasks may be measured. Some primary factors assessed in the workplace may include posture, force and temporal characteristics. Temporal characteristics may include the number and duration of rests and frequency of the motion. This knowledge may assist in assessing and redesigning tasks that may pose risk of injury. 
     Various systems have been developed for quantification of position and displacement of body parts, including active and passive cinematographic systems and electromagnetic field based systems. These systems are accurate. They tend, however, to be costly, require technical training to use, have certain technical limitations, and are generally not portable. Additionally, portable devices, such as wrist goniometer systems, require calibration for each user. For example, typically joint angular displacement at several points throughout a range are sampled, then linear regression or other techniques are used to estimate the relationship between position and transducer output. A wrist goniometer has been disclosed having two potentiometers with spring loaded cables. Individual calibration, however, is required through sampling multiple points in a range and using linear regression or similar techniques to estimate the relationship between position and transducer output. 
     U.S. Pat. No. 5,012,819 discloses an apparatus for monitoring the motion of components of a spine. The apparatus is mounted on the back of a patient, and includes an exoskeleton of elements which resemble the spinous process and transverse process of the spine. The elements include a central bore for receiving a cable, and three separate openings, each for receiving a wire therethrough. The cable is attached to a potentiometer which measures the twisting motion of the spine. Each of the three wires is attached to a separate potentiometer to measure flexing in the sagittal, transverse and lateral planes. The signals from the potentiometers are processed to provide a measurement of the angular position, angular velocity and angular acceleration of the spine as a function of time, for each of the three planes. 
     SUMMARY OF THE INVENTION 
     A wrist goniometer is provided that allows direct determination of wrist angular displacement in the radial/ulnar and flexion/extension planes without the necessity of extensive calibration or precise alignment relative to bone landmarks of the hand, wrist and forearm. 
     According to one embodiment, a goniometer is disclosed having a forearm component having at least three displacement measuring devices, and adapted to be releasably attached to a forearm of a user. A hand component is adapted to be releasably affixed to a hand of a user, and cables extending from the displacement measuring devices are adapted to be releasably connected to the hand component. The displacement measuring devices are configured to measure angular displacement of the hand component relative to the forearm component. 
     In one embodiment, the displacement measuring devices are configured to measure the angular displacement of the hand component relative to the forearm component on both a radial/ulnar plane and a flexion/extension plane. The cables may be under constant tension when the goniometer is in use. When the goniometer is in use on a hand and forearm of a user and viewed from above at least two cables may be substantially parallel to each other. When the goniometer is in use and on a hand and forearm of a user and viewed the side of the hand at least two cables may be substantially parallel to each other. When the goniometer is in use on a hand and forearm and viewed from the side the cables may be substantially parallel to a volar aspect of the hand and the forearm of the user when the hand and forearm are in a natural flexion position. At least first and second cables extending from the forearm component may be located at substantially the same height from a base of the forearm component. A third cable extending from a third displacement measuring device may be located at a height between the base of the forearm component and the first and second cables. 
     In one embodiment, at least one displacement measuring device is a potentiometer comprising a reel and a cable extending from the reel. At least the first and second cables extending from the first and second potentiometers may be located at substantially the same height from a base of the forearm component. A third cable extending from the third potentiometer may be located at a height between the base of the forearm component and the first and second cables. 
     In one embodiment, the hand component is a unitary piece. The cables may be releasably attached to the hand component allowing for unrestrained rotation. The hand component may include at least two pylons extending from the hand component for locating free ends of the cables. Swivel joints may releasably connect each cable adjacent a top of a pylon. A swivel joint may releasably connect a third cable to a base of a pylon. The hand component may further include a cross-member for locating the pylons on the hand component. The hand component may further include a bar for removably locating the cross-member. The bar may further include slots provided along its length, and the cross-member may include channels such that the cross-member slidably engages the bar. The cross member may be adjustably secured to the bar with at least one screw. 
     In one embodiment, the hand component further includes a glove for removably attaching the hand component to a hand of a user. The glove may be a palmless glove. The glove may be a fingerless glove. The hand component may further include a bar secured to the glove. The bar may be secured to the glove such that the bar is adapted for location adjacent a volar surface of a third metacarpal of a hand of a user when the glove is place on the hand of the user. 
     In another embodiment, the forearm component further includes a housing for mounting the displacement measuring devices. A cuff may be provided adjacent the housing and adapted for removable securement to a forearm of a user. The cuff may include at least one hinge adapted for adjustment to the forearm. The cuff may be adapted to adjust to a cross-sectional area enclosed by the cuff. The cuff may be lined with orthotic foam. The foam may be sculpted such that the foam is adapted to fit a radial and ulna of the forearm. The cuff may have a strap adapted to releasably secure the cuff to the forearm. The strap may be removably secured to the cuff with at least hook-and-loop fastener. The cuff may be a band. The band may be elasticized. The band may be a loop. The band may be formed into a loop using hook-and-loop fastener. 
     According to another embodiment, a goniometer is disclosed having a forearm component having at least three potentiometers adapted to be releasably affixed to a forearm of a user. A hand component is adapted to be releasably affixed on a back of a to hand of a user, and the potentiometers are adapted to be connected to the hand component. The potentiometers are configured to measure angular displacement of the hand component relative to the forearm component without calibration. 
     According to another embodiment, a method of determining wrist position in both flexion/extension and radial/ulnar deviation planes of movement is disclosed. The method includes the steps of providing a forearm component for locating three displacement measuring devices above a forearm of a user, providing a hand component on the back of a hand of the user, and connecting a cable from each displacement measuring device to the hand component. The displacement measuring devices are configured to measure angular displacement of the hand component relative to the forearm component in both the radial/ulnar and flexion/extension planes. 
     In one embodiment the method includes connecting the cables to the hand component such that they are under constant tension. The step of connecting may include locating at least a first and second cable at substantially the same height from a base of the forearm component. The step of connecting may include locating a third cable at a height between the base of the forearm component and the first and second cables. The displacement measuring device may be a potentiometer including a reel and a cable extending from the reel. The step of connecting may include connecting the first and second cables from the first and second potentiometers to the hand component such that the cables are located at substantially the same height from a base of the forearm component and are substantially parallel to each other. The step of connecting may include extending a third cable from the third potentiometer to locate the cable at a height between the base of the forearm component and the first and second cables such that the third cable is substantially parallel to at least one of the first and second cables. 
     In one embodiment, the step of providing a hand component includes providing at least two pylons for connecting ends of the cables to the hand component. The step of connecting may include connecting the cables to the pylons with swivel joints. The step of connecting may include attaching the cables to the pylons to allow for unrestrained rotation. The step of connecting may include providing a cross-member for locating the pylons on the hand component. The step of connecting may include removably locating the cross-member on a bar of the hand component. The step of connecting may include removably securing the cross-member to the bar with screws. 
     In one embodiment, the step of providing the hand component includes attaching the hand component onto a glove for removably locating the hand component on the back of a hand of the user. The step of providing the hand component may include locating the hand component such that it is adjacent the volar surface of the third medicarpal on a hand of a user. The step of providing the forearm component may include mounting the displacement measuring devices on a housing of the forearm component. The step of providing the forearm component may include securing the forearm component to a forearm of a user by a cuff. The step of providing the forearm component may include adjusting cross-sectional area enclosed by the cuff. The step of providing the forearm component may include releasably securing the cuff to a forearm of a user with a strap. The step of providing the forearm component may include releasably securing the cuff to a forearm of a user with hook-and-loop fastener. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a goniometer according to an embodiment of the invention; 
     FIG. 2 is a perspective view of the goniometer of FIG. 1; 
     FIG. 3 is a front view of the mounting block and displacement measuring devices of FIG. 1; 
     FIG. 4 is a cross-sectional view of the wrist mount with the mounting block and displacement measuring devices taken along line  4 — 4  of FIG. 2; 
     FIG. 5 is a perspective view of a goniometer according to another embodiment of the invention; 
     FIG. 6 is a cross-sectional view of the wrist mount with the mounting block and displacement measuring devices to taken along line  6 — 6  of FIG. 5; 
     FIG. 7A is a top view of a guide block according to an embodiment of the invention; 
     FIG. 7B is a front view of the guide block of FIG. 7A; 
     FIG. 8A is a top view of the cross member according to an embodiment of the invention; 
     FIG. 8B is a front view of the cross member of FIG. 8A; 
     FIG. 8C is a side view of the cross member of FIG. 8A; 
     FIG. 9 is a front view of an assembled hand component according to an embodiment of the invention; 
     FIG. 10 is a plan view of the right hand displaying the geometry according to an embodiment of the invention; 
     FIG. 11 is a plan view of the medial side of the right hand displaying the geometry according to an embodiment of the invention; and 
     FIG. 12 is a graph of the magnitude of the cosine of the angle σ, as a function of the wrist angle Φ of FIGS.  10  and  111 . 
    
    
     DETAILED DESCRIPTION 
     The invention discloses a goniometer usable to determine wrist position in two orthogonal planes, such as both in a radial/ulnar (hereinafter R/U) plane of movement and in a flexion/extension (hereinafter F/E) plane of movement. The R/U plane of movement is shown in FIG. 10, and is movement within the XY or horizontal plane such as occurs when the hand is moved side-to-side. The F/E plane of movement is shown in FIG. 11, and is movement within the YZ or vertical plane such as occurs when the hand is moved up and down. Wrist angular displacement is tracked based on the differences in length between two parallel sides of a quadrilateral, and these are used to calculate the angle of one adjacent side to the other. A goniometer is disclosed that provides for direct determination of angular displacement on two orthogonal planes, such as the R/U and F/E planes, preferably without the need for calibrating the device and/or without precise alignment relative to bone landmarks of a hand. In one embodiment, a goniometer is provided having a hand component and a forearm component. The forearm component includes three displacement measuring devices with cables removably secured to the hand component. 
     Referring to FIGS. 1 and 2, a goniometer  100  according to the invention is shown on a hand  102  and a forearm  104  of a user. A hand component  106  is removably secured to a back  108  of the hand  102  and a forearm component  110  is removably secured to the forearm  104 . The forearm component  110  includes three displacement measuring devices  112 ,  114  and  116  (FIG.  3 ). Although any displacement measuring device may be used, preferably the displacement measuring devices  112 ,  114  and  116  are spring loaded cable displacement position potentiometers, such as Model  174  manufactured by Space Age Controls, Inc. of Palmdale, Calif. The displacement measuring devices  112 ,  114  and  116  are used to track position of the hand  102  relative to the forearm  104 . Typically, the displacement measuring devices  112 ,  114  and  116  feature reels  118  and cables  120 . 
     As shown in FIGS. 3-4, the displacement measuring devices  112 ,  114  and  116  are provided on a housing  122 . The housing  122  is made of plastic, although it could be made of any suitable material. As shown, the housing  122  has a triangular shape having first, second and third sides  124 ,  126  and  128  between two housing ends  130  and  132  (FIG. 1) with an apex  134  of the triangle being flat. It will be appreciated that the housing  122  may have any suitable size and shape, not just the shape shown in the illustrated embodiments in the drawings. The smaller and lower the profile of the housing and the less it weighs, the less the forearm component will move about the forearm of the user providing more accurate and consistent measurements. The triangular shape shown locates two of the displacement measuring devices  112  and  114  on opposite first and second sides  124  and  126  of the triangular housing  122  angled toward one another, while the third displacement measuring device  116  is provided on the third side  128  of and within the triangular housing  122 . The displacement measuring devices may be attached to the housing by any suitable manner, such as adhesive. 
     The displacement measuring devices  112 ,  114  and  116  are located such that cables  120  exit the devices at particular positions. As illustrated, preferably first and second exit positions  136  and  138  for the first and second displacement measuring devices  112  and  114  are aligned such that the cables will extend within the same horizontal XY plane. A third exit position  140  of the third displacement measuring device  116  is preferably aligned vertically with one of the exit positions  136  and  138  of the first or second displacement measuring device  112  and  114 . As shown, the third exit position  140  is vertically aligned with the second exit position  138  such that the aligned cables will extend through the vertical YZ plane. 
     Referring to FIG. 4, the housing  122  is shown provided on a cuff  142  for mounting to a forearm  104  of a user. The housing  122  may be removably or permanently mounted to the cuff  142  in any suitable manner, for example with adhesive, rivets, screws, hook-and-loop fastener and/or the like. The cuff  142  may be hinged and may have an adjustable width. As shown in FIG. 4, the cuff  142  may have an outer portion  144  with two hinges  146  and  148 . The hinges  146  and  148  assist in accommodating a forearm and securely mounting the cuff  142  with the forearm component  110  to a forearm  104  of a user. As shown in FIG. 4, the cuff  142  may feature orthotic foam  150  sculpted to fit around a radius and ulna of a forearm. The foam  150  may feature sculpted parts  152  to accommodate the forearm. As shown, the foam  150  is provided on an inside surface  154  of the outer portion  144  of the cuff  142 . The foam  150  may be secured to the outer portion  144  of the cuff  142  using an adhesive preferably, a high strength adhesive. 
     The cuff  142  is secured to a forearm  104  using a strap  156 . The strap  156  may be secured on a first end  158  to a first side  160  of the outer portion  144  using fastening devices  162  (FIG.  2 ), such as rivets, screws, nails, bolts and/or the like. A free end  164  may be removably secured to a second side  166  of the outer portion  144  of the cuff  142 , by a fastening device such as a hook-and-loop fastener, snaps and/or the like. The cuff  142  is placed on the forearm and the free end  164  of the strap  156  is secured to the second side  166  of the outer portion  144  of the cuff  142 . Preferably, an edge  170  (FIG. 1) of the cuff closest to the edge of the forearm near the wrist is 2 or 3 cm from the line between the styloid process and the head of the ulna. 
     Referring to FIGS. 5 and 6, a preferred embodiment of the cuff  142  for use with the invention is illustrated. The housing  122  shown in FIGS. 5 and 6 is substantially the same as that of FIGS. 3 and 4. The cuff  142  features a forearm support  172 , such as an elasticized forearm band  174 . The forearm band  174  may be made at least partially of nylon and/or spandex. The elasticized forearm band  174  may feature stays  176  for additional support provided along the length of the forearm band  174 , particularly where the forearm component  110  is mounted. The stays  176  may be made of any suitable material, such as plastic. The stays  176  may be mounted on the elasticized forearm band  174  on an outer or inner surface  178  or  180  thereof or may be incorporated within the forearm band  174 . The forearm component  110  may be mounted to the forearm band  174  in any suitable manner, such as by adhesive, rivets, screws, hook-and loop fastener and/or the like. The forearm component  110  may be secured directly to the stays  176  and/or to the forearm band  174 . 
     The forearm band  174  is a loop with first and second open ends  182  and  184 . The forearm band  174  may be slipped over the user&#39;s hand and onto the forearm such that the forearm band  174  resides around the forearm. Alternatively, the forearm band  174  is not provided as a loop, but a rectangular shape with two sides  186  and  188  provided between the two ends  182  and  184 . The two sides  186  and  188  (FIG. 6) may be removably mated together, for example with hook-and-loop fastener to form a loop. Thus, the forearm band  174  is removably secured to the forearm by attaching the two sides  186  and  188  of the forearm band  174 . This construction allows the forearm band  174  to fit a wide range of differently sized forearms. The forearm band  174  is preferably provided such that an edge  190  of the band closest to the edge of the forearm near the wrist is approximately 2 cm from the line between the styloid process of the radius and the head of the ulna. 
     Referring now to FIGS. 1,  2  and  5 , the hand component  106  will now be discussed. The hand component  106  is removably secured to the back  108  of the hand  102  by any suitable manner. As illustrated, the hand component  106  is secured to a back  192  of a glove  194 , such that placement of the glove  194  on a hand locates the hand component  106  in the desired position on the back  108  of the hand  102 . Preferably, the glove  194  is a tight fitting glove, such as an elasticized glove. The glove  194  may be made at least partially of nylon and/or spandex. The glove  194  features an open end  196  opposite a finger end  198  of the glove  194  for inserting the hand into the glove  194 . As shown, the open end  196  is provided on the user&#39;s forearm such that a substantial portion of the forearm of the user is covered by the glove  194 . The cuff  142  of the forearm component  110  may be placed over the glove  194  on the forearm for additional stability. It will be understood that the glove  194  may feature an open end  196  that ends adjacent the wrist of the user such that the glove  194  does not fit on a part or all of the forearm of the user. Additionally, the glove  194  may be fingerless and/or palmless to allow the user to more easily perform tasks without the glove obstructing their performance of the tasks. 
     As shown in FIGS. 1,  2  and  5 , the hand component  106  is secured to the glove  194 . The hand component  106  is mounted to a plate  200  which is secured to the glove  194 . It will be understood that the plate  200  may be secured to the glove  194  in any suitable manner. The plate  200  may include a textile  202  secured to the top of the plate  200 , such as by adhesive. The plate  200  and textile  202  may then be secured to the glove  194  in any suitable manner, for example by adhesive and/or sewing. Edges  204  of the textile  202  may be sewn to the glove  194 . The hand component  106  may be secured directly to the plate  200  and/or to the textile  202 , if present, in any suitable manner such as with adhesive, screws, rivets and/or the like. 
     As shown, the hand component  106  includes a slotted bar  206 . In the illustrated embodiment, a cross-member  208  interfits over the slotted bar  206  and two pylons  210  and  212  rise from the slotted bar  206  which receive the free ends  214  of the cables from the displacement measuring devices  112 ,  114  and  116 . It will be understood that the hand component may be placed in any suitable location on the a back of a hand. Moreover, it will be appreciated that the hand component  106  may be made in any suitable shape and may be a one-piece or multiple-piece unit. The smaller and lower the profile of the hand component and the less it weighs, the less the hand component will move about the hand of the user and the more accurate and consistent the measurements. The hand component  106  may be made in any suitable manner such as by molding and/or machining. 
     Referring to FIGS. 1,  2 ,  5 ,  7 A and  7 B, the slotted bar  206  is shown. The slotted bar  206  is rectangular in shape having two ends  216  and  218  connected by two sides  220  and  222 . It will be appreciated that any suitable shape for the slotted bar  206  may be  523886  used. The sides  220  and  222  of the slotted bar  206  form a longitudinal axis  224  of the slotted bar  206  which is preferably placed along the volar surface of the third metacarpal of the hand of the user. The slotted bar  206  is secured to the plate  200  by any suitable manner. As shown, the slotted bar  206  is secured to the plate by a screw through a hole  228  provided in each comer  230  of the slotted bar  206 . The sides  220  and  222  of the slotted bar  206  each feature a slot  232  running along the length of the sides  220  and  222 . The slotted bar  206  is made of plastic, although any suitable material may be used. 
     Referring to FIGS. 1,  2 ,  5  and  8 A-C, the cross-member  208  is shown. The cross-member  208  is removably secured to the slotted bar  206 . The cross-member  208  fits slidingly onto the slotted bar  206  by engaging the slots  232  of the slotted bar  206 , for example with channels. The cross-member  208  may be located anywhere along the length of the slotted bar  206 . As shown, the cross-member  208  has a shape with a raised middle section  234  between two end sections  236  and  238 . An open area  240  is formed underneath the middle section  234  between the end sections  236  and  238  to accommodate the slotted bar  206 . It will be appreciated, however, that any suitable shape for the cross-member may be used. One side section  236  of the cross-member  208  features at least one cross-hole  242  extending from an end  244  through the end section  236  to the open area  240  of the cross-member  208  for receiving a screw  246  (FIG. 2) to secure the cross-member  208  to the slotted bar  206  at a desired location along the length of the slotted bar  206 . As shown, two cross-holes  242  are provided through the end section  236 . The cross-member  208  may be made of any suitable material, such as plastic. 
     Additionally, a pylon receiving hole  248  is provided on a top surface  250 , of each end section  236  and  238  of the cross-member  208  for receiving a pylon  210  and  212 . As shown the cross-member  208  and pylons  210  and  212 , are made as separate pieces. It will be understood that they could be formed as one piece, for example by machining or molding. Moreover, the pylons  210  and  212  could take on numerous different shapes. For example, instead of two pylons a single block could extend from the cross-member  208 . 
     Referring to FIG. 9, the assembled hand component  206  is shown. The pylons  210  and  212  extend substantially perpendicular to the top surfaces  250  of the end sections  236  and  238  of the cross-member  208 . The pylons  210  and  212  are made of steel, although any suitable material may be used. The pylons  210  and  212  feature receiving devices  252  for removably connecting with the free ends  214  of the cables  120 . As shown, each pylon  210  and  212  features a receiving device  252  adjacent a top  254  of the pylon  210  and  212  and one of the pylons  212  includes a third receiving device  252  for the third cable  120  adjacent a base  266  of the pylon  212 . Preferably, the receiving devices  252  are swivel joints and/or allow unrestricted rotation of the cable free ends  214  about the pylons  210  and  212  in both the R/U and F/E planes. The cables  120  are made of steel, although any suitable material may be used. It is preferable the material used have a minimum increase in length over time due to stretching. A light, constant tension may be maintained in the cables  120  by springs intrinsic to the cables of the displacement measuring devices  112 ,  114  and  116 . 
     As shown, the first pylon  210  features a first swivel joint  256  adjacent the top  254  of the first pylon  210  for receiving a first cable  258  (FIGS. 1,  2  and  5 ). When in use, the height H 1E  (FIGS. 4 and 6) of the first exit position  136  of the first cable  258  (FIGS. 1,  2  and  5 ) from the first displacement measuring device  112  is substantially the same as the height H 1J  (FIG. 9) of the first swivel joint  256  on the first pylon  210 . The second pylon  212  features a second swivel joint  260  adjacent the top  254  of the second pylon  212  for receiving a second cable  262  (FIGS. 1,  2  and  5 ). When in use, the height H 2E  (FIGS. 4 and 6) of the second exit position  138  of the second cable  262  (FIGS. 1,  2  and  5 ) from the second displacement measuring device  114  is substantially the same as the height H 2J  (FIG. 9) of the second swivel joint  260  on the second pylon  212 . The second pylon  212  also features a third swivel joint  264  adjacent the base  266  of the second pylon  212  for receiving a third cable  268  (FIGS. 1,  2  and  5 ). When in use, the height H 3 E (FIGS. 4 and 6) of the third exit position  140  of the third cable  268  (FIGS. 1,  2  and  5 ) from the third displacement measuring device  116  is substantially the same as the height H 3j  (FIGS. 9) of the third swivel joint  264  on the second pylon  212 . Thus, the first, second and third cables  258 ,  262  and  268  are substantially parallel to each other when viewed from the side of the goniometer  100  and the second and third cables reside substantially in the same YZ or F/E plane. The first, second and third cables  258 ,  262  and  268  are substantially parallel to each other when viewed from above the top of the goniometer  100  and the first and second cables reside substantially in the same XY or R/U plane. 
     When placing the goniometer  100  on a user&#39;s hand  102  and forearm  104 , typically the user&#39;s hand  102  is first placed in the glove  194  having the hand component  106 , such that the longitudinal axis  224  of the slotted bar  206  of the hand component  106  is placed along the volar surface of the third metacarpal. The cuff  142  having the forearm component  110  is then provided on the user&#39;s forearm  104  over the glove  194 . For convenience, the cables  258 ,  262  and  268  may be kept secured to the swivel joints  256 ,  260  and  264  on the pylons  210  and  212  and thereby to the cross-member  208 . After the glove  194  and cuff  142  have been respectively secured to the user&#39;s hand  102  and forearm  104 , the cross-member  208  may be engaged with the slots  232  in the slotted bar  206 , placed at the desired location along the length of the slotted bar  206 , and screws  246  may be inserted into the cross-holes  242  to secure the cross-member  208  into position on the slotted bar  206 . Thus, the goniometer  100  is ready for use. It will be appreciated that the cross-member may be secured to the slotted bar at anytime and the cables may be secured to the swivel joints of the cross-member any time before or after securement of the cross-member to the slotted bar. 
     Wires  270  to the displacement measuring devices  112 ,  114  and  116  extend from the displacement measuring devices  112 ,  114  and  116  out the second end  132  of the housing  122  and may be connected to an A/D converter, sampled at 100 Hz, and the output data may be stored in a computer file to be analyzed later. The output data of the displacement measuring devices  112 ,  114  and  116  may be used to determine the angular displacements in the R/U and F/E planes. Output data from the displacement measuring devices  112 ,  114  and  116  may also be collected in a computerized spreadsheet program. An IBM PC compatible computer may be used to acquire data, but the analog output from the displacement measuring devices could be passed to any suitable microprocessor based device with processing analog to digital conversion capability. A palm sized computer may also be used and may be capable of displaying real-time angular displacement data, providing a very compact system important in some field applications. The method described below may be used to determine the angular displacement in the R/U and F/E planes based on the output data from the displacement measuring devices  112 ,  114  and  116 . 
     Referring to FIGS. 10 and 11, a discussion of a method of determining the angular displacement of the hand component  106  relative to the forearm component  110  in both R/U and F/E planes will be discussed. The difference in cable length of co-planar displacement measuring devices  112 ,  114  and  116  can be used to directly calculate a trigonometric solution of the angular displacement of the hand component  106  relative to the forearm component  110  in both the R/U and F/E planes. It will be appreciated that although a preferred method is described below, any suitable manner for calculating the angular displacement of the hand component relative to the forearm component may be used. 
     FIG. 10 presents a view of the volar aspect of a right hand deviating radially by φ degrees about the joint center X from a starting position to an end position in the R/U plane. The relative differences in length of the first cable  258  and the second cable  262  are used to calculate the trigonometric solution for angular displacement in the R/U plane. The points S 1  and S 2  represent the cable origins at the first and second exit positions  136  and  138  from the forearm component  110  at the starting position. The points S 3  and S 4  represent the starting position of the cable free ends  214  at the pylons  210  and  212  located on the hand component  106 . Points E 3  and E 4  represent the end position of the cable free ends  214  at the pylons  210  and  212  located on the hand component  106  after movement of the hand. The lengths of the line segments {overscore (S 1 S 2 )}, {overscore (S 3 S 4 )}, and {overscore (E 3 E 4 )} are of fixed and preferably substantially equal length z. The center of rotation of the wrist X is assumed to be located between line segment {overscore (S 1 S 2 )} on the forearm component  110 , and line segment {overscore (S 3 S 4 )} on the hand component  106 . As shown, the location of the center of the rotation of the wrist X is not constrained to below line segment {overscore (S 2 S 4 )} or above line segment {overscore (S 1 S 3 )}. 
     Line  1  is constructed substantially parallel to line segments {overscore (S 1 S 2 )} and {overscore (S 3 S 4 )}, and passes through the center of rotation X. Lines  2  and  3 , are constructed substantially parallel to line segment {overscore (E 3 E 4 )} and pass through the center of the rotation of the wrist X and the point S 2 , respectively. The angle φ is provided between Line  1  and Line  2 , and between Line  3  and line segment {overscore (S 1 S 2 )}. Line segments {overscore (E 3 S 1 )} and {overscore (E 4 S 2  )}represent the first and second cables  258  and  262  of the first and second displacement measuring devices  112  and  114  having lengths C 1  and C 2 , respectively. Line  4  is constructed substantially parallel to line segment {overscore (E 4 S 2 )} and passes through point E 3 , and intersects Line  3  at point P. A parallelogram is formed by line segment {overscore (E 4 S 2 )}, line segment {overscore (E 3 E 4 )}, Line  4 , and the line segment {overscore (PS 2 )}, which lies along Line  3 . The line segment {overscore (PS 2 )} is substantially equal to line segment {overscore (E 3 E 4 )}, and both have a length z. An angle σ is provided between Line  4  and line segment {overscore (E 3 S 1 )}. Additionally, line segment {overscore (PS 1 )} lies along Line  5 . 
     For triangles ΔP E 3  S 1 , and ΔP S 2 S 1 , the law of cosines (c 2 =a 2 +b 2− 2 ab  cos C) can be applied to create the following two equations: 
     
       
         {overscore ( PS   1 )} 2   ={overscore (E 3   S   1 )}   2   +{overscore (PE 3 )}   2 −2· {overscore (E 3   S   1 )}·{overscore (PE   3 )}·cos σ  (1) 
       
     
     
       
         and; 
       
     
     
       
         {overscore ( PS   1 )} 2   ={overscore (PS 2 )}   2   +{overscore (S 1   S   2 )}   2 −2 ·{overscore (PS 2 )}·{overscore (S   1   S   2 )}·cos φ  (2) 
       
     
     Substituting (2) in to (1); 
     
       
         {overscore ( E   3   S   1 )} 2   +{overscore (E 4   S   2 )}   2 −2 ·{overscore (E 3   S   1 )}   3   ·{overscore (PE 3 )}·cos σ={overscore (   PS   2 )} 2   +{overscore (S 1   S   2 )}   2   −{overscore (PS 2 )}·{overscore (S   1   S   2 )}·cos φ  (3) 
       
     
     The following values are known: 
     {overscore (S 1 S 2 )}=z (fixed by hardware), 
     {overscore (PS 2 )}=z (by definition), 
     {overscore (E 3 S 1 )}=C 1  (is the length of the first cable  258  of the first displacement measuring device  112 ), 
     {overscore (E 4 S 2 )}=C 2  (is the length of the second cable  262  of the second displacement measuring device  114 ), 
     {overscore (PE 3 )}=C 2  (by definition), 
     substituting the above values into (3) yields the following: 
     
       
           C   1   2   +C   2   2 −2 ·C   1   ·C   2 ·cos σ= z   2   +z   2 −2 ·z·z  cos φ, or 
       
     
     
       
         cos φ=1−( C   1   2   +C   2   2 −2 ·C   1   ·C   2 ·cos σ)/2 z   2   (4) 
       
     
     Rearranging the terms yields: 
     
       
         cos φ=1−(( C   1   2   +C   2 ) 2 +2 ·C   1   ·C   2 −2 ·C   1   C   2 ·cos σ)/2 z   2   
       
     
     The equation can be rewritten as: 
     
       
         cos φ=[1−(Δ C   2 /2 z   2 )]−[2 ·C   1   ·C   2 ·(1−cos σ)/2 z   2 ]  (5) 
       
     
     The difference in length between C 1  and C 2  is ΔC. For cable lengths C 1  and C 2  typical for the proposed goniometer  100 , a change in φ of ±50° results in a change in σ of ˜±3°. FIG. 12 is a graph of the cos σ as a function of φ, for the goniometer  100  as described and shown. For values of σ of this magnitude, cos σ→1, and the second term of the equation →0. The equation can thus be simplified to: 
     
       
         φ=cos −1 (1 −ΔC   2 /2 z   2 ).  (6) 
       
     
     Based on this mathematic simplification, angular displacement of the hand  102  relative to the forearm  104  in the R/U plane can be determined from differences in the cable lengths of the first and second cables  258  and  262  of the first and second displacement measuring devices  112  and  114 . It will be understood that the trigonometric solution for angular displacement in the F/E plane can be calculated independently, in similar fashion, utilizing the relative differences in length of the second cable  262  and the third cable  268 , as seen in FIG.  11 . The length C 3  of the third cable  268  is simply substituted for C 1  in the above described equations. 
     The goniometer  100  may be easily applied to people with wrist anthropometry representative of the general population. Application of the goniometer  100  is simplified by the fact that determination of angular displacement is not dependent on location and alignment with the joint center of rotation X. This also may effectively improve accuracy considering that the wrist center of rotation X is dynamic, changing with wrist position, particularly in the F/E plane. The goniometer  100  could potentially be used to track the instantaneous center of rotation of the wrist X in either plane by rearranging the trigonometric solution. 
     Following application of the goniometer  100  to a person, angular displacement calculations can be used directly. However, as with any approach to joint goniometry, a brief data collection at a neutral position is recommended to allow correction for individual differences in fit and alignment. Referencing a neutral position also permits more appropriate comparison between people and on repeated measures within the same person. 
     Further improvement in system accuracy is possible through refinement of the hardware and/or enhancement of the trigonometric solution. The main assumption made in the algorithm development is that the angle σ is small, and therefore cos σ−1 approaches zero, allowing simplification of equation (5) to equation (6). The addition of an “error term” accounting for the angle σ could be introduced, but minimal improvement in accuracy would be expected, even at the extremes of range, based on the relationship presented in FIG.  12 . Hardware refinement focusing on further improvement of fixation of the hand and forearm components  106  and  110 , as well as efforts to improve comfort, optimization of system weight, durability, and displacement measuring device cable tension, should help to further improve usability and accuracy of the system. Accuracy could also be improved by increasing the distance between the hand and forearm components  106  and  110 , effectively reducing the angle σ. Sensitivity could also be increased by increasing the distance between the cable ends z in either or both planes. However, increases in cable length or the distance between the cable ends require the tradeoff of increasing the size and inertia of the device. 
     From the foregoing description those skilled in the art will appreciate that numerous modifications may be made of this invention without departing from its spirit. For example, the cross-member and pylons of the hand component may be made as a single-piece unit. Moreover, the pylons could be replaced with one solid wall for attaching the free ends of the cables. The wall could have any suitable height or thickness and be made separate from the cross-member or as part of the cross-member. Therefore, the breath of the invention is not to be limited to the specific embodiments illustrated and/or described. Numerous modifications will occur to those skilled in the art, and therefore, the scope of the invention is to be determined by the appended claims and their equivalents.