Three-dimensional joint range of motion measurements from skeletal coordinate data

Frequently, joint range of motion is reported for a single plane (eg., sagittal, coronal, or transverse). However, the arc of joint motion during functional activities and many clinical tests encompasses motion in all three planes simultaneously. The purposes of this paper are to discuss a method to obtain relative joint three-dimensional angular displacement measurements using coordinates from skeletal landmarks and provide an analytical example of the method using three-dimensional angular displacement of the knee joint as a model. In order to calculate the three-dimensional relative motion, an orthogonal reference frame for each bone needs to be established. To establish the local reference frame, three noncollinear points are used to define unit vectors that are mutually perpendicular. Three-dimensional angles can be determined to describe the magnitude of the moving body rotation angles about the X, Y, and Z axes. These angles indicate the relative motion of body segments for abduction/adduction, flexion/extension, and internal/external rotation. The technique provides a more vigorous biomechanical understanding of joint motion and may have implications for measuring patient progress and evaluating joint mobilization treatment. This technique may also serve as a basis for developing new evaluation and treatment techniques.