The application of 4 x 4 matrix method to the correction of the measurements of hip joint rotations.

Abstract The three rotations of the human hip joint can be approximated by using the electrogoniometric technique. Because the measuring device is not directly located at this point, potential errors exist between the recorded and the actual motions. The objective of this paper is to determine the magnitude and the distribution of these errors. The properly attached goniometer linkage and the femur form a 7-link spatial mechanism. The motion of this spatial mechanism is solved by using the 4 × 4 matrix method with three input motions defined from potentiometers attached to the goniometer linkage. From the solution of this mechanism, the corrected rotations of the hip-joint are obtained. The maximum error is less than 5 deg at any point in the walking cycle for a normal subject. The largest corrections occur at maximum internal and external rotations. Measurements of hip motion for several activities of daily living are also corrected, and the errors are magnified, compared to walking, since larger angles of rotation are involved.