This paper describes a new accurate, reliable, and
cost-effective tool to measure the range of motion of a joint,
specifically the shoulder joint. The system consists of three string
potentiometers which are mounted in a known orientation and
whose ends converge at a point attached to handle. A test consists
of having a patient grabbing and moving the handle through the
desired motion for the specified test time. During the test, a
microcontroller is used to read the potentiometer voltages as the
patient moves the handle. Upon completion of the test, the data is
analyzed to determine the range of motion and also to provide 3-D
plots of the motion. In addition, the changing position of the center
of rotation can be determined for large motions. A number of tests
were performed which showed good results (accuracy within 2°) in
all cases when the system was properly used. The system provides a
simple and intuitive user interface to display, store and recall test
results. Although the system was originally intended for use with
the shoulder joint, it could be used to measure the range of motion
of other joints, such as the elbow and knee, provided a different
attachment is created.
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