Abstract:
Disclosed is a method and apparatus for repeatably positioning a forearm at a plurality of angular positions for medical analysis. A forearm of a patient is positioned in a support channel within reach of a rotatable handle. The handle can be locked in a number of angular positions, providing a counteractive force as the handle is rotated. The patient rotates and applies a torque force to the handle at selected rotational angles. The forearm and wrist can be scanned in these locked position, and applied torque can be measured to evaluate joint stability.

Description:
[0001]    The present invention is related to positioning devices for medically examining joints, and more particularly to a medical positioning device for positioning the forearm and wrist for DRUJ analysis.  
         BACKGROUND  
         [0002]    Abnormalities of the proximal and distal radioulnar joints (DRUJ) are commonly encountered in clinical practice in association with trauma or dislocation, synovial inflammatory diseases, or congenital abnormalities and may be associated with numerous conditions, including ulnar styloid fracture, Colles fracture, radial diaphyseal fracture, radial head fracture or excision, triangular fibrocartilage complex injury, and disproportionate radioulnar length. The diagnosis of DRUJ abnormalities is difficult, however, since limitations of conventional radiologic imaging procedures make it difficult or impossible to radiographically confirm subluxation or dislocation of the DRUJ. Abnormalities of the DRUJ may, therefore, go undiagnosed.  
           [0003]    Computed Tomography (CT), however, can be used to image the DRUJ. Since CT delineates the cross-sectional anatomy of the DRUJ, this technique can be utilized for the evaluation of the anatomy and mobility of the DRUJ, as well as for suspected joint subluxation. However, a number of problems have also been associated with attempts to diagnose abnormalities of the DRUJ using CT. First, prior art evaluation protocols do not provide a means for positioning the right and left upper extremity in a consistent fashion. Typically, the forearms are simply placed in the CT gantry with the wrists at approximately the same level, and the patient is asked to rotate the forearm into maximum pronation (palm down) and supination (palm up) positions. Thus, the wrists may be at different levels and the forearms may be at different degrees of rotation within the scan. Because the location of the forearms and wrists are not consistent, it is necessary to obtain a large number of images, in order to insure that the same regions of both wrists are imaged. Because of the large number of images acquired, the patients are exposed to a significant degree of radiation. Furthermore, when both forearms are not positioned in the same degree of rotation, it is not possible to compare a left and right wrist or forearm. Additionally, even though most patients complain of their most severe symptoms while actively using their upper extremities, prior art methods do not provide a means for simulating or generating resisted rotation.  
           [0004]    There remains a need, therefore, for a method and apparatus for consistently positioning and rotating a forearm for purposes of imaging and evaluating the forearm joints.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention is a method and apparatus for positioning the forearm of a subject for clinical examination. A support channel and a rotatable handle are coupled to a frame. The support channel is positioned on the frame along a longitudinal access, and is sized and dimensioned to receive the forearm of a subject. The rotatable axis is positioned at a location relative to the support channel such that the subject can grip and rotate the handle. Rotation of the handle is centered substantially around the longitudinal axis.  
           [0006]    Another aspect of the invention comprises providing a counteractive force opposing the rotation of the rotatable handle. The subject is prompted to rotate the rotatable handle against the counteractive force to provide a torque on the handle. A torque cell can be used to measure the applied torque.  
           [0007]    The foregoing and other aspects of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims herein for interpreting the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a perspective view of a forearm positioning device constructed in accordance with the invention.  
         [0009]    [0009]FIG. 2 is a perspective view of the forearm positioning device of FIG. 1, further illustrating the insertion of the device into a computer tomography gantry.  
         [0010]    [0010]FIG. 3 is a rear view of the endplate of the forearm positioning device of FIG. 1, including a partial drawing of the rotation assembly.  
         [0011]    [0011]FIG. 4A is a partial view of the rotational lock assembly of FIG. 1. FIG. 4B is a view of the rotation lock assembly taken above the line  4 B- 4 B of FIG. 4A.  
         [0012]    [0012]FIG. 5 is a perspective view of the forearm positioning device of FIG. 1 illustrating the wrists of the user in a neutral position.  
         [0013]    [0013]FIG. 6 is a perspective view of the forearm positioning device of FIG. 1 illustrating the wrists of the user in a sixty degree supination position.  
         [0014]    [0014]FIG. 7 is a perspective view of the forearm positioning device of FIG. 1 illustrating the wrists of the user in a sixty degree pronation position.  
         [0015]    [0015]FIG. 8 is a perspective view of a second embodiment of a forearm positioning device constructed in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Referring now to the Figures and more particularly to FIG. 1 a forearm positioning device  10  constructed in accordance with the present invention is shown. The forearm positioning device  10  provides a support for maintaining the wrists and forearms of a subject in one or more predefined position for imaging, and is therefore sized and dimensioned for positioning within a scanning or imaging device, and particularly for insertion in a computed tomography (CT) scanner (FIG. 2). The forearm positioning device  10  generally comprises a frame  44  which supports a forearm support assembly  12  and a rotatable handle or grip assembly  14 . Each of these assemblies will be described more fully below.  
         [0017]    Referring still to FIG. 1 the forearm support assembly  12  comprises first and second forearm support channels  16 A and  16 B, which are positioned on a mounting plate  18  and aligned in a substantially parallel relationship to each other along parallel longitudinal axes  15 . The forearm support channels  16 A and  16 B are generally U-shaped and are sized and dimensioned to receive the forearms of the subject, and to align and restrain the forearms along their respective axes  15 . Each of the forearm support channels  16 A and  16 B is coupled to the mounting plate  18  by means of mounting posts  20 A and  20 B, the mounting posts of each of the support channels  16 A and  16 B being of the same height in order to maintain the forearms of the user  16 A and  16 B at a substantially equivalent level above a support surface. The mounting posts  20 A and  20 B can be coupled to the forearm support channels  16 A and  16 B and the mounting plate  18  by means of threaded fasteners, adhesives or other fastening devices known to those of skill in the art. A forearm restraint  22  which can comprise, for example, a fastening tape, loop and hook fastener, an elastic band or other restraining or locking device, provides a restraint  22  for maintaining the forearm in a stable and stationary position during the scan. The forearm restraint ensures that torque generated at the wrist is produced from the forearm, and not from upper extremity activity.  
         [0018]    Referring still to FIG. 1, the grip assembly  14  comprises first and second grip handles  26 A and  26 B which are coupled to an end plate  28  through a rotatable axle  30 A and  30 B respectively, each of the grip handles  26 A and  26 B being substantially aligned along a longitudinal axes  15  with a respective forearm support channel  26 A and  26 B. The endplate  28  is fastened to the frame  44 , and oriented in a plane substantially perpendicular to the mounting plate  18  of the forearm support assembly  12 . Each of the axles  30 A and  30 B is mounted to a faceplate  32 A and  32 B, respectively. The faceplates  32 A and B each include rotational indicators which provide an indication of the degree of rotation of the grip handles  26 A and  26 B around the longitudinal axes  15  when aligned with a center indicator  36  on the end plate  28 . Preferably, an indicator  34 A,  34 B, and  34 C is provided at each of three selected rotation points, as described below. When the grip handles  26 A or  26 B are rotated to a predefined rotation point, a grip lock  38 A or B is actuated to lock the axle  30 A,  30 B in place. The grip lock  38  has an extendable post which is inserted into a mating hole in the axle  30 A or  30 B to limit further rotation of the grip handle  26 A or  26 B, as described more fully below.  
         [0019]    Referring now to FIG. 2, in the preferred embodiment the grip handles  26 A and  26 B can be locked at three predefined rotation points around the axes  15 : a neutral position; a position of 60° pronation (i.e. with the wrist up); and of 60° supination (i.e. with the wrist down). The grip handles  26 A and  26 B can be locked in each of these positions by the rotation lock  38 . Preferably, a small amount of “play” is provided in the rotation lock  38  such that, even when locked in place, the grip handles  26 A and  26 B can be rotated within a limited range. Typically, the range of rotation along a lock position is about one degree of rotation around the center point  36 . Therefore, when the grip handles  26 A and  26 B are locked in place, the subject can rotate the hand grips  26 A and  26 B to provide a stress on the forearm and specifically on the DRUJ for analysis. The lock  38  provides a counter-active force opposing rotation. Referring now also to FIG. 1, a torque cell  43  can be coupled to each of the axles  30 A and  30 B to provide a signal indicative of the amount of force, and particularly torque that is applied to the hand grips  26 A and  26 B by the subject, as described below.  
         [0020]    Referring now to FIG. 3, a back view of the end plate  28  is shown. The grip locks  38 A and  38 B each comprise a handle  53  and locking rod  45  which extends into an aperture  47  (FIG. 4B) in a floating block  57  and then into an aperture  49  in the axle  30 A or B. Referring now also to FIGS. 4A and 4B, The floating block  57  is disposed in an aperture  51  formed in the back of the endplate  28 , and above the axle  30 , and is loosely coupled to the endplate  28  by first and second threaded fasteners  59  and  61 . The aperture  51  is sized and dimensioned to allow the floating block  57  to move, wherein rotation of the handle  26  causes the floating block  57  to be driven in the direction of rotation. Preferably, a contact switch  37  is disposed on either side of the floating block  57  wherein, as the hand grips  26 A and  26 B are rotated, the floating block  57  activates one of the contact switches  37 . The contact switches  37  are each electrically coupled to an indicator light, such as a light emitting diode  41 , which provides an indication of the direction of rotation applied to the hand grips  26 A and  26 B. The contact switches  37  and indicator lights  41  are powered by power supply  51  which can be, as shown, a 9 volt dc battery activated by a switch  55 . Other types of switches, indicating devices, and power supplies suitable for use in the present invention will be known to those of skill in the art.  
         [0021]    Referring now to FIG. 5, it can be seen that the forearm support assembly  12  is moveable in a longitudinal direction along the frame  44  of the forearm positioning device  10 , thereby allowing the distance between the forearm support channels  16 A and  16 B and the corresponding hand grips  26 A and  26 B to be sized and dimensioned to the subject to be examined. One or more grooves  40 A and  40 B are provided in the mounting plate  18 . First and second threaded connectors  42 A and  42 B are coupled to a mounting threaded receptacle in the frame  44  of the forearm positioning device  10  through the slots  40 A and  40 B. When the threaded connections  42 A and  42 B are loosened the mounting plate  18  can be slid along the frame  44  toward the grip handles  24 A and  24 B or away from the grip handles  24 A and  24 B. By repositioning the mounting plate  18  on the frame  44 , a distance between the forearm support assembly  12  and the grip assembly  14  can be established to fit the forearm positioning device  10  to a particular user. When the mounting plate  18  is positioned at an appropriate distance, the threaded connectors  42 A and  42 B are tightened to couple the base  18  to the frame  44  in the selected position.  
         [0022]    In operation, the subject places each of the right and left forearms in a forearm support channel  16 A and  16 B respectively. Thereafter, the distance between the forearm support channels  16 A and  16 B and the hand grips  26 A and  26 B is adjusted for the subject by adjusting the position of the mounting plate  18  in the slots  40 A and  40 B as described above. When an appropriate distance is established, each of the forearms can be restrained or locked in place in the forearm support channels  16 A and  16 B by a restraint  22 . In this position, the wrists and forearms of the subjects are aligned along the longitudinal axes  15  and are maintained in a pre-selected, level position for scanning, as can be verified by a laser guide beam  48  associated with a CT scanner  50  (FIG. 2). When the forearms and wrists are appropriately positioned and restrained in the forearm support channels  16 A and  16 B, the forearm positioning device  10  can be positioned in the gantry  52  of the scanner  50  for scanning or imaging. However, other types of medical examination can also be provided.  
         [0023]    Referring now to FIGS. 5, 6, and  7 , the grip handles  26 A and  26 B are shown as rotated to provide an examination of the forearm and wrists in a plurality of varying rotated and stressed positions. In each of these positions, the forearm positioning device  10  maintains the wrists and forearms in a substantially parallel horizontal plane, and maintains the left and right forearms and wrists in substantially the same rotated position along the longitudinal axes  15  to enable direct comparison of the examination of each wrist. Examination can be provided through CT imaging, wherein the forearm positioning device  19  is positioned in a gantry  52  (FIG. 2) of a CT scanner  50 , but can also be accomplished by an analysis of applied torques or through other medical analysis methods.  
         [0024]    Referring first to FIG. 5 a subject is shown gripping the hand grips  26 A and B as locked in a neutral position  34 B by the grip lock  38 , providing an image of the wrist and forearm in a stable, unstressed position. Referring now to FIG. 4, the grips  26 A and B are shown rotated to the 60° supination position  34 C. Here, the right and left wrists are directed upward and a corresponding stress is applied to each of the right and left forearms. Referring now to FIG. 5, the grip handles  26 A and  26 B are shown locked in the 60° pronation position  34 A, such that the right and left wrists of the subject are pointed substantially downward. By examining the wrist and forearm in each of the positions of FIGS.  5 - 7 , instability in the joints can be determined. As described above, in any of these positions, the subject can additionally rotate the hand grips  26 A and  26 B within a predefined angle of rotation to provide an additional force or torque against the rotation lock  38 . Therefore, a stress can be applied to the forearms and wrists of the subject to provide additional information for analysis. The torque cell  43  and an associated metering device  41 , such as that shown in FIG. 8, can be provided to measure the amount of torque applied by he forearm and wrist. Furthermore, images of the wrist and forearm in each of the defined positions can be provided by a CT scanner  50  (FIG. 2) or other imaging device.  
         [0025]    Referring now to FIG. 8, a forearm positioning device  10  is shown for use in analyzing joint instability based on torque measurement. Here, the forearm positioning device  10  is constructed as described above, including a torque cell  43  and metering device  39 . The torque cell  43  can be any of a number of commercially available products, such as the TRT-200 by Transducer Techniques of Temecula, Calif. The associated metering device  39  is also a commercially available product here the PHM-100 transducer indicator, also sold by Transducer Techniques of Temecula, Calif., is a DC conditioner with peakhold and digital readout. The metering device  39  provide a real-time digital read out of applied torque and also stores a maximum value in memory which can be retrieved to obtain a maximum torque value for a given test. The maximum torque value can be reset, and a new value stored for each test. By rotating the handle as described above, and measuring the applied torque at the neutral, 60° supination, and 60° pronation positions, instability in the joint can be determined. The embodiment of FIG. 8 is preferably portable, and can be used both as a clinical evaluation tool, and as a training device for CT scanning. When used as a training device, the forearm positioning device is preferably used in conjunction with a plurality of indicator lights similar to those encountered in a CT scanner, thereby preparing the patient for testing to be applied in a CT scanner.  
         [0026]    Although preferred embodiments have been shown and described, it will be apparent to one of ordinary skill in the art that a number of modifications could be made to the method and apparatus described without departing from the scope of the invention. It should be understood, therefore, that the methods and apparatuses described above are only illustrative and do not limit the scope of the invention, and that various modifications could be made by those skilled in the art that would fall under the scope of the invention. To apprise the public of the scope of this invention, the following claims are made: